B. MARTINIS, G.C. PAREA, T. PESCATORE, A. RIZZINI, F.C ... 6/GR_6_345_420_Angelucci et al.pdfof Mollusca, Corals, macrophoraminifers, etc. (DAI NELLI 1912, FABIANI 1915). Also microfauna

A. ANGELUCCI, E. DE ROSA, G. FIERRO, M. GNACCOLINI, G.B. LA MONICA, B. MARTINIS, G.C. PAREA, T. PESCATORE, A. RIZZINI, F.C. WEZEL

Gruppo di Ricerca per la Geologia dei Sedimenti del Consùzlio Nazionale delle Ricerche

SEDIMENTOLOGICAL CHARACTERISTICS OF SOME ITALIAN TURBIDITES

On account of the great development, also practical, of Sedimentology, in these last years, the Committee for the Geologica[ and Mining Sciences, of the National Research Council, created in 1965 the Gruppo di Ricerca per la Geologia del Sedimenti. This Group, led by prof. B. Martinis of University of Milan, consists of young researchers from severa! Italian Universities. The present work represents the first positive contribution of the Group, and is the result of a long and co-ordinated activity from all the researchers. The subject concerned with, is one of particular interest as the turbidite deposits are widely diffused in Italy. It has been carried out in severa[ regions, so that it includes sediments which are different on account of their geographical location, characteristics, age. This work, for the numerous data collected, which have been elaborated by modern methods, will surely be a sensible contribution to the knowledge of Italian turbidites. We wish that this Team-activity, which has already shown its outcomes, and is therefore praiseworthy, will continue in the future. Finally, the close collaboration between researchers, is increasingly more indispensable in order to solve problems of genera! interest.

INTRODUCTION

Friuli and Venezia Giulia Flysch

Bellunese Flysch . . . .

Prealpi Flysch near Bergamo

« Siate Formation >> in the Ligurian Apennines

<< Flysch ad Elmintoidi >> in the Western Alps

Langhe Turbidites in Piemonte

« Arenarie superiori >> (Apennines of Eastern Liguria)

Bismantova Sandstones (Emilian Apennines)

<<Macigno>> (Middle-Northern Apennines)

<< Pietraforte >> (Middle-Northern Apennines)

<< Marnoso-Arenacea >> (Romagna Apennines)

IN DEX

<< Argilloso-Arenacea Formation >> in Lazio-Abruzzi Apennines

Calcarenitic Turbidites in Molise Apennines

Miocenic Turbidites of Sorrento Peninsula

Western Cilento Flysch . . . . . . . .

Numidian Flysch (Mt. Madonie and Mt. Nebrodi)

<< Reitano Flysch >> (North-Eastern Sicily)

Final remarks .

Riassunto

References

Appendix (numerica! tables)

Giambattista Dal Piaz

345

Pag.

346 346 353

356

362

363 365

368

371

373

375

377

383

388

391

393

396

400 403 404 405 409

E. DE RosA M. GNACCOLINI, B. MARTINIS, A. RrzzrNI: Istituto di Geologia dell'Università di Milano - G. FIERRO: Istituto 'di Geologia dell'Università di Genova - G.C. PAREA: Istituto di Paleontologia dell'Università di Modena - A. ANGELUCCI G.B. LA MoNICA: Istituto di Geologia dell'Università di Roma - T. PESCATORE: Istituto di Geologia dell'Università di Napoli - F.C. WEZEL: Istituto di Geologia dell'Università di Catania.

GEOL. ROM., VI, 1967, pp. 345-420, 65 fìgg., 4 tab., 97 logs.

346 A. ANGELUCCI, E. DE ROSA, G. FIERRO, M. GNACCOLINI, G.B. LA MONICA, ecc.

INTRODUCTION

This paper is the result of a study carried out by all the researchers belonging to the Gruppo di Ricerca per la Geologia dei Sedimenti (National Research Council of Italy). The aim of the study is to examine some of thc sedimentary characteristics o{ turbidites in Italy. A number of exposures were studied regardless of the age and including as many formations as possible; in particular, the thickness of the layers and their grain size were measured, and the presence of shale nodules and of sole and internai structures, and the frequency distribution of intervals were noted.

Particular care was taken in analizing the c interval of BouMA which was divided into five levels: cross lamination (Fig. 64 ), deformed cross lamination (Fig. 14), wavy lamination (Fig. 5), convolute lamination (Fig. 11) and corrugateci convolute lamination (Fig. 10).

The graphical logs surveyed are scattered over an area extending from the Eastern Alps to Sicily, including the whole of the Apennines. In this area 97 graphical logs were surveyed with a total number of l ,888 layers an d a thickness of 602 m; their l.ocation is shown in Fig. l.

The 97 graphical logs were surveyed in the following formations:

- Friuli and Venezia Giulia Flysch (Paleogene)

- Bellunese Flysch (Paleogene)

- Prealpi Flysch near Bergamo (Cretaceous): includes Pontida Flysch, Sarnico Sandstones and Bergamo Flysch

- << Siate Formation >> in the Ligurian Apennines (Lower Cretaceous)

- << Flysch ad Elmintoidi >> in the Western Alps (Upper Cretaceous)

- Langhe Turbidites in Piemonte (Miocene): includes Cassinasco Formation an d Cortemilia Formation

- << Arenarie superiori >> in the Apennines of Eastern Liguria (Upper Cretaceous - Palcocene)

- Bismantova Sandstones m the Emilian Apennines (Miocene)

- <<Macigno>> in the Middle-Northern Apennines (Oligocene ?)

- << Pietraforte >> in Middle-Northern Apennines (U pper Cretaceous)

- << Marnoso-Arenacea >> in Romagna Apennines (Miocene)

- <<Argilloso-Arenacea Formation >> in LazioAbruzzi Apennines (Miocene)

Calcarenitic Turbidites in Molise Apennines (Middle Miocene)

Turbidites of Sorrento Peninsula (Miocene)

- Western Cilento Flysch (Cretaceo-Miocene ?)

- Numidian Flysch in Madonie and Nebrodi Mts. (Oligocene-Middle Miocene)

- <<Reitano Flysch >> in North-Eastern Sicily ( Oligocene-Miocene)

Only macroscopically clear structures were considered and no special techniques were u:>ed. The descriptive terms << layer >> and « bed >> are according to 8TANLEY and BOUMA (1964, p. 36) and the term << interval >> according to BouMA (1962, p. 48).

Grain size was measured mainly in the field with the aid of comparison samples and severa! samples were studied in the laboratory using a ro-tap for the coarser fraction and a pipette for the finer one, after disaggregation in HCI. Samples for the mechanical analyses were collected essentially from a, b and c intervals. All data obtained from the field survey of the sections are represented in graphical logs according to BouMA (1962, p. 2).

Owing to the abundance of data and in order

to gain a better understanding of their significance the Authors decided to use a computer (I.B.M. 7040), analizing the data with a linear regression program.

FRIULI AND VENEZIA GIULIA FL YSCH

by Bruno Martinis

In north-eastern Italy (Veneto, Friuli-Venezia Giulia) the term << Flysch >> is generically used to indicate a Paleogenic mainly arenaceous-marly formation. This formation is widespread in the concerned region and has rather uniform generai characteristics, even though locally i t shows considerable variations. It crops out mainly in the middle-eastern area of Friuli-Venezia Giulia and in particular between Tagliamento and Isonzo rivers where it forms the entire strip of foot hills. Beyond Isonzo nver, Flysch is also present

SEDIMENTOLOGICAL CHARACTERISTICS OF SOME !TAL/AN TURBIDITES

o 100 200 Km

o 'f,

3\:,

',,,ANCONA ~

\

347

N

BARI

FIG. 1 - Location of the graphicallogs surveyed by thc Authors in the different formations: log 1-6 Friuli and Venezia Giulia Flysch; 7-11 Bellunese Flysch; 12-13,34-37 Prealpi Flysch; 14-19 << Slate Formation>>; 20-26 << Flysch ad Elmintoidi >>; 27-33 Langhe Turbidites; 38-46 <<Arenarie Superiori>>; 47 Bismantova Sandstones; 48-53 <<Macigno>>; 54-57 << Pietraforte >>; 58-65 << Marnoso-Arenacea >> in Romagna Apennines; 66-80, <<Argilloso-Arenacea Formation >> in Lazio-Abruzzi Apennines; 81-86 Calcarenitic Turbidites; 87-88 Turbidites of Sorrento Peninsula; 89-92 Western

Cilento Flysch; 93-95 Numidian Flysch; 96-97 <<Reitano Flysch ».

- Ubicazione dei logs grafici campionati dagli Autori nelle diverse formazioni: log 1-6 Flysch del Friuli-Venezia Giulia; 7-11 Flysch del Bellunese; 12-13, 34-37 Flysch delle Prealpi; 14-19 <<Formazione delle Ardesie>>; 20-26 << Flysch ad Elmintoidi >>; 27-33 Torbiditi delle Langhe; 38-46 «Arenarie Superiori>>; 47 Arenarie di Bismantova; 48-53 <<Macigno»; 54-57 << Pietraforte >>; 58-65 << Marnoso-Arenacea » nell'Appennino romagnolo; 66-80 <<Formazione Argilloso-Arenacea» nell'Appennino laziale-abruzzese; 81-86 Torbiditi calcarenitiche; 87-88 Torbidi ti della Penisola sorrentina;

89-92 Flysch del Cilento occidentale; 93-95 Flysch Numidico; 96-97 << Flysch di Reitano>>.


along the Adriatic coast as far as the Jugoslavia

border. West of Tagliamento river Flysch outcrops are

discontinuuos and limited to small outcrops located in correspondence to the core of synclines; the most important outcrops are those of Vito d'Asi o, Meduno-Frisanco, Andreis-Barcis, Claut, T. Vajont

etc. This formation has, in generai, evident turbiditic

characteristics; sometimes, however, i t is believed that areas of normal sedimentation are locally present. This can be found, for instance, in Rocca Bernarda area (Udine) where shallow water deposits are present; they sedimented not far from the coast (MARTINIS 1955) in particular at Rosazzo and Noax where the normal sedimentation is partially of delta type also (CASTELLARIN and ZuccHI 1963).

Friuli-Venezia Giulia Flysch consists of a more or Iess regular sequence of sandstone and interbedded mari. Sometimes, however, one of the two lithotypes clearly predominates so that the formation shows an essentially marly facies, as happens between Cormòns and Lucinico (Gorizia), or an arenaceous facies as it can be found near Gorizia (between Mt. Calvario and Vallone dell'Acqua) and Trieste.

Coarser sediments are locally present in the formation. They are fine-grained breccias with essentially calcareous fragments, cropping out in lenses or isolated layers (Cormòns); in Natisone Valley this facies becomes prevalent with << pietra piasentina >>, a fine calcareous breccia abundantly cropping out at the base of the formation. In the Tarcento surroundings (Udine) this fine breccia crops out in continuous layers wich are spread over several kilometres; breccias are often graded and they change upward to arenaceous limestone, then to marly limestone and ultimately to marl (FERUGLIO 1954).

Thin conglomerate is also present even if not very frequent. At Cormòns, for instance, it overlies sandstone, and the transition between the two lithotypes occurs by means of a fine breccia with calcareous cement and with mainly siliceous elements having a diameter of 1-1.5 mm. Elements diameter increases from bottom to top where the conglomerate consists of siliceous and calcareous cobbles (10 cm diameter) with calcareous cement and sometimes marly matrix.

More to the West, and essentially in the Natisone Valley, conglomerate is frequently interbedded in the lower part of the formation: i t is << pseudo-

cretaceous conglomerate >> with calcareous elements, whose size is sometimes outstanding, belonging to Cretaceous rocks.

Sandstone present in the formation crops out in beds generally 3-40 cm thick. Their colour is grey tending to bluish and more exceptionally to violet; weathering colour is yellowish or brown.

Clastics mainly consist of quartz; feldspars too are frequent and sometimes they equa! or are even more frequent than quartz itself. According to the research carried out by MALARODA (1947) in the surroundings of Trieste, feldspars are plagioclasic and always more or less altered. Beside these elements, mica is frequently found, mainly biotite and less frequently muscovite, together with glauconite, tourmaline, zircon, rutile, etc. Feldspathic quartz sandstone has a CaC03 content generally varying between 4 and 30%.

In some outcrops sandstone contains abundant calcareous elements, even of organic origin, and consequently CaC03 content results considerably higher and the rock is a typical calcarenite. In Andreis outcrop, for instance, CaC03 reaches values of 74%.

Sandstone cement is always calcareous; sometimes a clayey marly matrix is present. The transition from sandstones to pelite is generally abrupt downward and graduai upward where it occurs through siltstone.

Pelite is generally represented by marl, clayey marl and marly clay. These sediments are dark grey or bluish-grey coloured, they are often laminated, less frequently compact. Pelite, when washed, leaves a scanty residue, mainly formed by quartz grains and also by calcareous elements and rare mica laminae. Limonite concretions and pyrite crystals are rather frequent; the latter are sometimes so frequent that they constitute nearly all the washing residue.

Fossils aren't generally frequent in the formation, even though in the region there are some classic localities which, in the past, supplied rich faunae of Mollusca, Corals, macrophoraminifers, etc. (DAINELLI 1912, FABIANI 1915). Also microfauna so far found and mainly constituted by planktonic specimens, is not abundant (MARTINIS 1962).

In arenaceous beds carbonized fragments are rather frequent, in particular along lamination surfaces. Sometimes carbonized remains are very abundant and form lignite lenses, as it occurs near Cormòns.

In the centrai area of the region, Flysch unconformably overlies Cretaceous deposits. Elsewhere

SEDIMENTOLOGICAL CHARACTERISTICS OF SOME ITALIAN TVRBIDITES 349

it can be found in sedimentary continuity, as for instance at the border of Gorizia Carso, where Flysch overlies Tertiary << San Michele Mt. Limestones >> or in the Vajont Valley where it gradually changes to Senonian << scaglia >>.

Only west of Tagliamento river, Flysch is covered by marine Oligocenic or, more commonly, Miocenic deposits which lie in unconformity.

Flysch thickness is considerably changeable: i t goes from some hundred metres in isolated outcrops west of Tagliamento, to more than 2300 m near Gorizia (MARTINIS 1962) and probabily to more than 3000 m in the Natisone Valley, including the coarsest facies, such as << pietra piasentina >>,

which is more frequent towards the formation base (FERUGLIO 1925).

Friuli-Venezia Giulia Flysch has been generally ascribed to Eocene (DAINELLI 1912, FABIANI 1915, FERUGLIO 1925 and 1954, D'AMBROSI 1955, MARTINIS 1962) and mainly to Middle Eocene. On the basis of new paleontological studies during the last few years, in the nearby Flysch of !stria (PicCOLI and PROTO DECIMA 1962) the presence of Upper Eocene was ascertained - FERUGLIO (1925) only assumed its presence in the region under consideration - together with the presence of Cuisian in the area of Rosazzo and Noax (CASTELLARIN and ZuccHI, 1963). Some research, presently under way on the outcrops of centrai and western Friuli, makes us think that in some instances Paleocene as well is present in the formation.

The outcrops under consideration are located in different areas of Friuli-Venezia Giulia and show some of the most typical characteristics of the formation. The logs surveyed, from East to W est, are the following: log l Trieste, NE side of the Trieste-Opicina (Poggioreale del Carso) road about l 00 m before Km 4.5 by the main front of an abandoned sandstone quarry (Sheet 40A Gorizia, Tav. II SW); log 2 Trieste, NE side of the Trieste-Opicina (Poggioreale del Carso) road about 100m before Km 4.5, by an abandoned sandstone quarry, 50 m SE of the preceding log (Sheet 40A Gorizia, Tav. II SW); log 3 Caste/monte, northern sidc of the Cividale del Friuli-Santuario di Castelmonte road (Udine), about 20 m past the cross-road for Purgessimo, 700 m east of Subit Mt. (Sheet 26 Tolmino, Tav. III NW); log 4 Attimis, NW side of the Attimis-Nimis road (Udine) about 100 m SW of Rio Croce and 300 m SSW of Nongruelle Mt. (Sheet 25 Udine, Tav. I SW);

log 5 Attimis, NW side of the Attimis-Nimis road (Udine), about 100 m SW of Rio Croce and 300 m SSW of Nongruelle Mt., some metres up the preceding log (Sheet 25 Udine, Tav. I SW); log 6 Andreis, western bank of Rio Ledròn, about 500 m north of Andreis (Udine) and some 10 m downcurrent from the bridge of the mule-track leading to Case Parnans (Sheet 24 Maniago, Tav. IV SE).

Trieste logs were surveyed in outcrops mainly consisting of hard sandstone (locally called << masegno >>) in beds with a thickness ranging from 11 to 58 cm in log l (Fig. 2); thickness is much more

~···

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o •• o

----

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.--...

. -

)"-) . . ....---.------. .~-,

___!___~ . . D O .------..--.--~---.

~ ' ~:~.

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l~.~ -':.

l l l :.-tl" l

l ~

'l

CASTS

IL_

l/

n 1

: l ! l ;

l l l

i c l

!

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FIG. 2 - Friuli - Venezia G ulia Flysch (Eocene); log no. 1 Trieste. Scale 1 : 20.

- Flysch del Friuli-Venezia Giulia (Eocene); log n. 1 Trieste. Scala 1 : 20.


variable m log 2. In the latter, in fact, beside beds of sandstone 40-42 cm thick, there are also some short layers where the arenaccous bed is only 1 cm thick. CaC03 content of this beds is generally 4-30%.

Clastics maximum size, on the lower bedding p lane of graded layers, falls within class 2 <D; the contact with underlying pelite is always clearly

latter is rather frequently found elsewhere also, while other internai structures were not noticed.

Organic and inorganic casts are sometimes present o n the lower bedding p lane of layers: they are bo un ce an d groove casts; the former are deformed and in layer 2 of log 1 only it is really possible to determine a direction (N 66° E - S 24° W); the latter, more frequent, generally show

FIG. 3 - Friuli - Venezia Giulia Flysch, near Trieste (Eocene). Hard sandstone, locally cal!ed << _masegno •>, in beds with a thickness ranging from 11 to

58 cm; m th1s sequence we have surveyed log no. 1 Trieste.

- Flysc):l del Friuli - Venezia Giulia, presso Trieste (Eocene). Arenarie compatte, chiamate localmente << masegno •>, in strati di spessore variabile fra 11 e 58 cm.

In questa sequenza è stato campionato il log n. 1 Trieste.

marked; the upper contact too is generally clearly visible. In layer 19 of log 1 there are day pebbles 1 cm long and 2 mm wide.

Nearly all beds are graded except some beds of log 1, among which n° 2 (48 cm thick, Fig. 2) and beds belonging to some layers where the arenaceous bed, 1-2 cm thick and very finely grained, lacks internai structures or sometimes shows only traces of parallel lamination. The

three directions (Fig. 2) and have variable height and length.

Caste/monte log was surveyed in the typical facies of Friuli Flysch (Fig. 3). Layers have a thickness generally varying between 4 and 39 cm where the arenaceous bed is prevalent. The lower contact between sandstone and pelite is always visible, whereas the upper one 1s often not clear because sandstone

SEDIMENTOLOGICAL CHARACTERISTICS OF SOME ITALIAN TURBIDITES 351

~· ~ ~ S ~: d

1 o UTHOLOGY ~ CASTS

~ LAMINATIONS GRAIN S.ZE ~

& . Il . ~ ~ ~ 8 ' ...-_ ~ ....._ ~ -~--·

~ :.'~+1_5 #t.4·.·~A:IV\.~-4_ 1-2_o,2 1 4;6 s, .

, 1=o1 . · 'D' . i l '

; i l l ' '

111 ~o ."""': ........... --:- ~

~~ l __ ,,-~-----

1-) \-h .. · _ __:.=:_

o l b ' d

D'

·.~ ' l

l '

' l i

o l =

o'

D. =

D -._D.

n

D i

' ' !

D

D D

D

FIG. 4 - Friuli - Venezia Giulia Flysch (Eocene); log no. 3 Castelmonte. Scale 1 : 20.

- Flysch del Friuli-Venezia Giulia (Eocene); \og n. 3 Castelmonte. Scala 1 : 20.

FIG. 5 - Friuli - Venezia Giulia Flysch >> (Eocene). Layer 15 of log no. 3 Castelmonte; parallel lamination passing to wavy and convolute lamination.

- Flysch del Friuli - Venezia Giulia (Eocene). Sequenza 15 del log n. 3 Castelmonte; laminazione parallela passante a laminazione ondulata e con-

voluta.

gradually changes to siltstone and then to mari. In layer 15 a marly calcilutite bed was found m

the mari. CaC03 content m sandstone vanes from 10 to

30%. Clastics maximum size in the lower bedding plane of graded layers falls within class 2<1>. Among internai structures, parallel lamination is particularly frequent; i t often prevails almost all along the layer thickness, as it happens in layer 21 (Fig. 4).

Besides these structures, there are cross laminations and most of all wavy and convolute ones. Wavy lamination shows a maximum wave lenght of 22-23 cm and a height of 2-3 mm. Convolute ones are less frequent and they are limited, in the log, to the layers 15 (Fig. 5) and 21.

Beside trace fossils, flute casts and grove casts are present in Castelmonte log. The former were found on the lower bedding plane of layer 21, where probable direction is S 50° E; the latter on the lower bedding plane of layer 15 where they have a N 50° W - S 40° E direction.

Attimis logs too were surveyed in typical Flysch outcrops where layers have a considerably variable thickness: 5-40 cm.

In thick layers of log 4 the arenaceous bed prevails, in thin sequences the pelite one is prevalent. In the latter cases sandstone is only 2-3 cm thick and it is difficult to establish whether such reduction is due to a residue of turbidite having a norma! thickness, or to a scanty supply of materia! when sedimentation occurred.

352 A. ANGELUCCI, E. DE ROSA. G. FIERRO, M. GNACCOLINI, G.B. LA MONICA, ecc.

l

;---·~·--·i-'_:_'-~ ~

l .....L.___!__ ...L ~ ~

:l~ .!.l'l' ·-:-:;:.-~~---~-::- -·

"--"---"-

~---l l l '~' . :___. . .

I ,; 'i

~ 1 ) ;

1---'- ........ _._j

-:-.-:-.-:-.---

LAMINATIONS

D

D: D

D. =

o D

D

D

.·~l ' ' l

FIG. 6 Friuli - Venezia Giulia Flysch (Eocene); log no. 5 Attimis. Scale l : 20.

Flysch del Friuli-Venezia Giulia (Eocene); log n. 5 Attimis. Scala l : 20.

In Iog 5 (Fig. 6) sandstonejpeiite ratio is more steady; in Iayers 2,3,5 and 7 pelite predominates, in other Iayers it is Iess frequent.

Transition from sandstone to peiite is clear downward an d rather confuse upward; often sandstone changes to more and more marly siltstone, as it is particuiarly evident in Iayer 8. Sometimes the graded bed does not show peiite a t its top; it changes to a subsequent graded bed, as m layers 27,28, and 29 of log 4.

CaC03 content in sandstone is 29-30%. Ciastics maximum size in the Iower bedding piane of graded Iayers falls within class 4 <l> in Iog 4 and class l <l> in log 5.

Not ali layers are graded; grading is Iacking mainly in thiner sequences where sandstone is very fìnely grained and with parallel Iamination. Beside this internai structure, only exceptionally wavy laminations are present with maximum wave length of 23-45 mm and a heigth of 1-3 mm.

Fossi! tracks on Iower bedding planes are Iacking and casts are rare. Only on the bedding piane of Iayer 27 in log 4 one prod cast showing a W 34° S direction was found.

Andreis log (Fig. 7) was surveyed in an outcrop with variable characteristics, as it is sometimes characterized by thin arenaceous-marly Iayers and sometimes by mainiy arenaceous thick layers. Layers havc therefore unsteady thickness, ranging from 5 to 73.3 cm; sandstonejpelite ratio is aiso extremely changeabie. Pelite in fact is sometimes prevalcnt, as in the interval showed in Fig. 7; sometimes, on the contrary, it is just a few centimetres thick. For instance, out of 73.3 cm (thickness of Iayer 36) 73 cm consist of sandstone and only 0.3 cm of mari.

Contact between sandstone and pelite may be clear or rather indistinct downward whiie upward it 1s generally not very clear, even if sometimes it 1s evident.

l~~~

! ~~l I__L_ ...._ --'--1

:è~ èli 1~~~~~1

...:.._· _:_-:....._·---

1 ~'""'":"~·"'

i

"--1

LAMINATIONS GRAIN S.ZE ~

i l ~ :.:.:..:.:._+15~ /~4_-=-;A,fV\.:4.) _o.-;. 4.6 s.

:oj . ! l

-l l i

i=lq ,_ l

l ' ' . l

·=

' l '

. ID •D: ! ~ :

1-! l

i l p l i l !

i l '

; l

,o o

i i

FIG. 7 - Friuli - Venezia Giulia Flysch (Eocene); log no. 6 Andreis. Scale l : 20.

Flysch del Friuli-Venezia Giulia (Eocene); log n. 6 Andreis. Scala l : 20.


FIG. 8 - Friuli - Venezia Giulia Flysch (Eocene); log no. 6 Andreis. Convolute lamination of the type es (corrugateci convolute lamination).

(x 1).

« Flysch del Friuli - Venezia Giulia,, (Eocene); log n. 6 Andreis. Laminazioni convolute del tipo c, (\aminazioni con-

volute ribaltate). (x 1).

FIG. 9 - Friuli - Venezia Giulia Flysch (Eocene); log no. 6 Andreis. Convolute lamination of the type es (corrugateci convolute lammatwn). (x 1 ).

Flysch del Friuli - Venezia Giulia (Eocene); log n. 6 Andreis. Laminazioni convolute del tipo es (laminazioni convolute ribaltate). (x 1 ).

CaC03 content in sandstone is high and reaches values of 72-73% and therefore clastics mainly consist of limestone and the rock becomes calcaremt!c. Clastics maximum size in graded layers falls within class 2 <D. Grading is however exceptional an d occurs only in some layers; elsewhere clastics are uniformly grained in all the arenaceous bed. Parallel lamination is frequent and it sometimes affects the whole clastic bed as it can be seen, for instance, in layers 36 and 37 which are essentially calcarenite. In layer 36 carbonized fragments are frequent.

In Andreis log there are also other internai structures: cross, wavy an d convolute lamination (Fig. 8,9). Waves in wavy lamination are 15-35 mm long and 3-5 high.

Trace fossils are present on the lower bedding piane of some layers while casts are rarer and limited, in the surveyed log, to the bedding piane of layer 2. They are groove casts of variable size, in both height and length, having mainly a E 10° N -W 100 S direction and of prod casts having an E-W direction.

BELLUNESE FLYSCH

by M aria Gnaccolini

Bellunese Flysch is widespread in most of the southern half of Sheet Belluno of the Geologica! Map of Italy. In the Alpago area (East of Belluno, on the left side of Piave River) Flysch is made up by a thick (about 1000 m) succession of layers whose main characteristic is the regular presence of the pelitic interval, generally thicker than the arenaceous bed. The arenaceous beds are made up by grey, yellow brown if weathered, sandstone and siltstone with calcareous cement. Clastics are mainly calcareous grains (sometimes fossils ), an d subordinately quartz an d chert; accessori es are muscovite, feldspars, and fragments of crystalline schists. The percentage of calcareous grains is generally high: in almost 80% of examined samples i t exceds 50% (l).

(1) Grain size analyses have been carried out only for samples having a calcite percentage lower than 45%. Samples analyzed have also been_ exll:mined in thin section: size of the calcareous clastrcs rs usually as large as clastics of different materia!.

354 A. ANGELVCCI, E. DE ROSA, G. FIERRO, M. GNACCOLINI, G.B. LA MONICA, ecc.

FIG. lO - Bellunese Flysch (Eocene); log no. 4, layer no. l. Convolute laminati o n of the type es (corrugateci convolute lamination); in the lower levels of the layer a gentle cross lamination is present. (x . 7).

Flvsch del Bellunese (Eocene); log n. 4, strato n. l. Laminazioni convolute del tipo c5 (laminazioni convolute n-. balta te); nella parte inferiore dello strato è osservabile una blanda laminazione obliqua. (x O, 7).

FIG. 11 - Bellunese Flysch (Eocene); log no. 4, layer no. l. Convolute lamination of the type c~ (convolute lamination), towards the bottom becomes a gentle cross lamination. (x . 7).

Flysch del Bellunese (Eocene); log n. 4, strato n. l. Laminazioni con volute del tipo c4 (!ami nazioni con volute), passante verso il basso a laminazione obliqua (x O, 7).

SEDIMENTOLOGICAL CHARACTERISTICS OF SOME !TAL/AN TVRBIDITES

------ -~, -- ------

1 ~ g 1 LAMINA TIONS •

1

~ ;,

1

·

: LITHOLOGY, g CASTS ~ : 1

ti J 1

l ; 0 : ~ =·15 ,4 4<=1AAA;_,, 0_"[•1_ 6,

1

,

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' -:-::;_-.:..:..-----·, -,-,--- -.-t---- t~ t--r t t-j,. t - ~ ·, ! l : l i l l l l l

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l

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' l l l l=

i l i

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FIG. 12 Bellunese Flysch (Eocene); Lavina Valley. Scale 1 : 50.

log. no. 7

- Flysch del Bellunese (Eocene); log n. 7 Valle Lavina. Scala 1 : 50.

FIG. 13 - Bellunese Flysch (Eocene); log no. 9 Lavina Valley. Scale 1 : 50.

- Flysch del Bellunese (Eocene); log n. 9 Valle Lavina. Scala l : 50.

27

l~~~~~,

Il!/\' l--'-...._~......_~ L

! l ....... _._

!)l\.'

-vl

~--+-,----,---t----; .]. ~ lù0

' l '

' l

i!

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o ,o o lo '0' 0: • '

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i l

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loh=l l l l

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FIG. 13

355

l D'


The pelitic intervals are composed of grey mari, grey clayey mari or grey calcareous mari.

Alpago Flysch lies on reddish mari (<< Scaglia )) type) and marly Iimestone. It is unconformably overlaid by a thick succession of Miocenic sands and sanstones, glauconitic in the Iower part.

Studied outcrops belong to the southern sidc of <<Al pago syncline )) (sheet 23 Belluno, tav. II NE). Localities of log survey (5 Iogs, for a total of 223

layers) are as follows: log 7 Lavina Valley, 700 m north-west of Tambre; log 8 Turcan Valley, 350 m south-west of C.se

Fachin; log 9 Lavina Valley, 600 m south-south-west of

Borsoi; log 10 right side of Roccalana Stream, 500 m northeast of the bridge on the road Schiucaz-Puos

d'Alpago; log 11 right side of Tesa Stream, 350 m west-southwest of the above mentioned bridge.

The above mentioned outcrops are made up by succcssion of layers from one centimeter to a maximum of 7 m thick. Layers, whose sandstone bed is usually 12-15 to about 80 cm thick (with a maximum thickness of almost 2 m), are fairly regularly interbedded with a succession of layers whose arenaceous bed thickness varies between Iess than l cm and about 6-7 cm. These successions of thin layers are a few centimeters to about 2 m thick. The pelitic interval, which is nearly always present, is normally thicker than the arenaceous bed of the layer; i t is l cm to 1.5 m thick (with a maximum thickness of about 5 m).

Ali the surveyed Iogs show rather uniform charactenstics. The observed sequence of internai structures are the following (in decreasing frequcncy or der): l) pelitic interval; para Il cl lamination ( sometimes Iacking); current ripple lamination (more rarely convolute lamination); parallel lamination; graded interval - 2) peli tic interval; parallel lamination (sometimes lacking); cmrent ripple lamination (more rarely convolute lamination) - 3) peli tic interval; parallel Iamination; graded interval - 4) peli tic interval; parallel lamination ( often lacking); current ri p p le laminati an (sometimes convolute lamination); parallel lamination. It is interesting to notice that somctimes in the sequences type l, 2 and 4 there is a rhythmic repetition of interwds of current ripple lamination and parallel lamination.

In layers whose arenaceous bed is very thin, parallel or current ripple lamination generally prevails; however graded bedding is also frequent.

Often no particular structure can be observed in

these layers. Size of clastics, at the base of layers, does not

exceed generally class 0-2 <D. Markings on Iower bedding pian es are not frequent: flute casts, groove casts (both at the base of layers starting with the graded interval), prod casts, bounce casts (at the base of a layer starting with the interval of parallel lamination), load casts and worm tracks and burrows were observed.

PREALPI FLYSCH NEAR BERGAMO

by Eugenio De Rosa - Antonio Rizzini

The stratigraphic series of Lombardy, which from Trias to Cretaceous includes almost exclusively carbonatic formations, shows after the dose of this period a clear change in the type of sedimentation (VENZO, 1954). << Maiolica )) (Titonic-Neocomian), composed of pelagic-type micrites and biomicrites, begins the Cretaceous series and shows very uniform features throughout. The Black Schist Formation (Barremian-Lower Albian) follows; this consists of dull black or reddish bituminous pelagic-type claystone. Thin laminated siltstone beds begin to be found in this formation · they mark the first terrigenous clastic supplies t~ the basin in which, up to this point, the carbonatic series had prevailed. The << Sass della Luna >>

(Albian) indicates a new period of stasis in clastic supply, which gradually recommences with siltstone and sandy beds in Cenomanian << scaglia rossa )) and then becomes exclusive in the turbidites of the Pontida Flysch (Turonian) (DE RosA, 1965). Turbidites of Pontida become more and more frequent and coarser whilst pelites decrease so that a new formation is distinguishable: Sarnico Sandstone (Santonian), also characterized by conglomerate an d coarse sand (FERNANDEZ, 1963 ). The clastic supply becomes finer in the successive formation (Bergamo Flysch) which, together with the overlying << scaglia rossa >>, ends the Cretaceous se n es.

Pontida Flysch - This formation is composed of calcareous cemented sandstones alternating with more or less calcareous mari and sometimes with claystone. The sandstones are grey, brown by weathering, from fine to medium grain. The detrital part is composed of clastic fragments derived from the underlying formations which, being mainly carbonatic, influence its composition. The


siliceous fraction mainly consists of quartz, chert and porphyry fragment grains. The carbonatic part is composed not only of fragments of underiying formations, but also of microfossils which sometimes constitute almost the whole of the detrital part.

The cementing materia! is cleariy recrystallized and consists mainly of carbonates and partially of clay minerals. Mari is usually more calcareous in the western Bergamo area and more clayey m the eastern one.

Tb_e toxmation is composed of a succession of turbidites whose layers are sufficiently uniform from Lake Iseo to Western Brianza. It outcrops discontinuously for 60 km from the western side of the Adrara Valley (W est of Lake Iseo) to centrai Brianza. On the northern side the formation is limited by the straightening of underiying forma-

Frc. 14 - Prealpi Flysch near Bergamo: Pontida Formation (Turonian); log Gallavesa, layer 27. Ripple lamination of

the type Ct. x 1/z. - Flysch delle Prealpi bergamasche: << Formazione di Pontida>> (Turoniano); log Gallavesa, strato 27. Ripple la-

mination di tipo c,. x 1/z.

tions and on the southern it is covered by the valley alluvium materia!. The average width of the outcrops here is about 5 Km.

The formation lies on Cenomanian <• scaglia rossa >> which mainly consists of distai turbidites; its lower part is composed of 10-15 cm thick sequences, with a sand/shaie ratio approximately e qual to l, characterized by pelites which are frequently red. Further up, the formation becomes more and more mariy and calcareous and at the same time the thickness of the sequences increases (from 20 cm to 2 m), whilst 6-8 m thick layers of a calcareous mari, conglomeratic at the base (elements whose maximum size is l cm), are often interbedded.

Locally, mainly in the centrai-western part of the outcrop there are lenses of conglomerate, interbedded with arenaceous turbidites; these aiso present a very abundant clayey matrix in which there are fragments of folded arenaceous Iayers. The genesis of these conglomerates is due to mud flowing. Current directions, estabiished on the

basis of markings on the bedding piane, show that the transport mainly occurred from the quadrant between NE and SE. The Brianza area is especially characterized by extremely fine sandstone. Prevailing internai structures are rippie laminations (fig. 14), wavy laminations and, in Brianza only, con volute laminations (fig. 15); parallei Iaminations are found more rareiy.

Current structures consist aimost exclusiveiv of flute casts. Two Iogs were surveyed in this -formation: o ne aiong the Galla v esa torrent (Bergamo) and the other near Aizzurro (Lecco).

log 36 Calolziocorte (Bergamo), not far from Lecco, in the Gallavesa Valley at the bend immediately south of Cascina Besena.

The outcrop lies in the middle-upper part of the formation; a tilloide has been found l km

east in a similar stratigraphic posrtwn. The outcrop is composed of beds whose average thickness is 20-30 cm with infrequent intervals in which the single sequences are 6-10 cm thick. Layers have a very costant thickness, with parallel bedding planes, sometimes irregular because of organic marks and flute casts not always well formed. T a-e type sequcnces an d sometimes abundant clay fragments, some centimeters wide, are found.

log 37 Aizzurro, is located on the right side of the River Adda, in the Province of Como, near Lecco, on the Airuno-Aizzurro road, immediately after the bend at 375 m above sea-level (fig. 16).

The outcrop is in the middle of the formation which is here characterized by considerable vertical

uniformity. The outcrop is located in the westernmost part of the area in which the formation crops out; this area is characterized by a considerable

decrease in the average size of clastic. It is to be noted that, according to the direction of the flow markings, this area shouid be the most distai


of this formation; i t is in any case downcurrent with respect to the Gallavesa outcrop. The outcrop consists of layers whose thickness varies betwecn l O an d 100 cm with an average of 20-30 cm.

The sandstone, which is considerably calcareous, is fine grained and nearly always shows convolutions (fig. 15) always related to ripple laminations. Sometimes, we found micrite layers, intcrbcdded with arenaceous turbidites, lacking inner laminations. Current marks are almost absent while Fucoids are plentiful especially within the layers.

Sarnico Sandstone. l t is composed of thick layers of sandstone or conglomerate interbedded with less abundant marl. The sandstone has a strongly recrystallized calcareous cement, and the detrital fraction is composed of a carbonatic and a siliceous part. The calcareous part consists of considerably recrystallized limestone fragments, mainly micrites and dolomites; the siliceous part is composed of quartz, microcrystalline chert, metamorphic rocks, muscovite, chlorite, and rare glauconite grains. Quartz shows clear solution features and is replaced by crystalline calcite.

Calcareous (<< Maiolica >>, << Sass della luna>> et al.), dolomite, black chert pebblcs an d fragments of crystalline rocks are found in the conglomerate. The marl is calcareous, very compact and light grey coloured; i t is particularly frequent in the lower part of the formation (Colle di Bergamo). The eastern part of the formation, cropping out near Lake Iseo (dose to Capriolo) is built up of thick layers of coarse sandstone or conglomerate; pelitic intervals are almost lacking. In this area graded intervals and, more rarely, parallel laminations prevail. As far as markings on the bedding piane are concerned, erosional channels and groove casts clearly prevail. In the western part, graded

intervals are prevalent but parallel and wavy laminations are also developped. Convolute laminations, on the contrary, are almost completely lacking. The laminations, in coarser parts, are characterized by association of larger grains which are mainly composed of carbonatic materia!.

In the finer parts, on the other hand, the laminations are emphasized by carbonized plant remains. Sole markings are more varied than in Pontida Flysch; whilst erosi o n channels disappear, scour marks and tool marks become more frequent.

FrG. 15 - Prealpi Flysch near Bergamo: Pontida Flysch (Turonian); log no. 37 Aizzurro (Lecco). Convolute laminations

of type c2.

Flysch delle Prealpi bergamasche: Flysch di Pontida (Turoniano); log n. 37 Aizzurro (Lecco). Laminazioni convolute

del tipo cz.

From East to West the carbonate content increases whilst the average size of clastics decreases. The area in which the formation crops out lies between Iseo and centrai Brianza. Eastwards the formation

= D

D

D D

Fig. 16 - ~realpi Flysch nea~ Bergamo: Pontida Flysch (Turoman); log no. 37 Arzzurro. Scale 1 : 50.

Flysch delle Prealpi bergamasche: Flysch di Pontida (Turoniano); log n. 37 Aizzurro. Scala 1 : 50.


is heteropic with << Scaglia Rossa >>. On the southern side the outcrop is covered by the alluvional plain, on the north side i t is interrupted by the outcropping of underlying carbonatic formations.

Two logs were surveyed: o ne a t Pedrazzoli Quarry and one near Castagneta.

log 34 Pedrazzoli Quarry, is located on the Palaz

zolo-Sarnico road, west of Capriolo-Paratico road in Pedrazzolo Quarry. The log was surveyed in

the lower part of the Sarnico Sandstone and represents the character of the most eastern part of the

formation, except the conglomeratic part, quite

well. The latter, on the other hand, is present

only in the upper part of Sarnico Sandstone. The

current, it becomes undistinguishable from the overlying bed (fig. 17). This is of type a an d its upper surface is plane-parallel.

Upstream, the third and thicker sequence gegerally lacks structures and contains, in the upper part, large parallel laminations which change to mega-ripples. A few metres downstream, the abrupt disappearance of the pelitic bed between the second and the third sequence can be noticed. Its piace is taken by an alignment of day fragments which soon disappears. In the third sequence mega-ripples become more evident with clearly asymmetric shapes whose the steepest side lies upstrczm. Going on downstream an increase in the thickness of the lower sequence may be ob-

w:·:::·.·.·.·..-·.· ... ·_ .... · . .. .. . . ."·.· ........ ·, . .. . . . . · .. : .·. :-:: .. · .. ·.·: ·.: ·.·.·.· .': .. :.:_.·>" .~: ·.::: .: : ... : :_::. -: .. :·.: .. ·: · ... :_ :_ : ........ :: : . . :: · .. ·.. . . .... .

. . . . . . . ... : .. : . : . . . . . . . .. . . . ..... : ..... : .... :. . . . . . ·: ... . · .... ·. : .. ·: ·.'. . . . : . . ~ . ·. . . . . . • • • • • • • • • • • • • • • •• ·-:.: ..... : • • • • •• :_.: •• _:... • •• •• ... :··.··: • •• :·: ••• :····: :. • • • ' • o : : : •• ••• : • • •• •

; .. ..• ~N.·~·····.· .•.... · :7 ~f.<'·••·••·••ii;: .. ds <·~ C\.. :;;;:;/:<~-"--- ; ;: \ UI / .: ... . --:.:.:.::·:·:··:··.·:.- . : ·:.:-.· .. .. ··. ·.-.·.· ... · . -:- .. · .. -:::~~-:-:.::: .. -· . .. · ......... ~·:·.·_· . .-:·:::··.:·~---... -

. . . . . . . . . . . . . .. :: ·_·.·.~: ... =·:··: .... : ·:· :: ·. : ..... : ·. . . . . . . . . . . . . .. . . . . . . . :. :. ~.: . .

' •. •.•.·······•·.············· i·• .• ···•·••i···i; <i;<i9-,•.-.z -~Lf.->•··t.~;§F:)W-1••/•••/• Frc. 17 - Prealpi Flysch near Bergamo: Sarnico Sandstone (Santonian); log no. 34 Pedrazzoli Quarry (Brescia).

Sketch of a particular of the outcrop. A detailed description of it is given in the text.

Flysch delle Prealpi bergamasche: Arenaria di Sarnico (Santoniano ). Log. n. 34 Cava Pedrazzoli. Disegno di un particolare dell'affioramento. Una descrizione dettagliata è riportata nel testo.

log undoubtly represents a very proximal facies of the formation even if it does not contain very coarse clastic elements. The outcrop surveyed consists of thick layers (up to 5-6 m thick) of soft, grey-brown sandstone interbedded with sandy pelite (a fèw centimeter thick) very rich in carbonized plant remains.

Layer thickness is variable; this is due both to lenticular layers and to the lack of pelitic intervals which makes single adjacent layers undistinguishable. The layers are mainly a intervals, but graded bcdding is not so evident. A more detailed description of a section of the outcrop with particularly interesting sedimentary structures, now follows. This section has a thickness of 6 m and is composed of three truncated sequences and the lower sequence (a-type) is limited upwards by an alignment of clay fragments which follows the generai trend of pelitic intervals existing among the sandy layers. Its upper surface is wavy and, a few meters up-

served togethcr with the disappearance of the middle one and the presence of a new sequence in the upper part of the third one (IV, in fig. 17).

The features of this outcrop do not permit it to be considered as undoubtedly due to turbidity currents. On thc other hand, the outcrop in question can certainly be related, from the chronostratigraphic point of view, to turbidites towards which it changes westwards. It should also be taken into account that since the Sarnico Sandstone overlies a pelagic-type formation (<<Scaglia Rossa>>) at least at the base, it must have deposited in a

sufficiently deep-sea environment.

log 35 Castagneta, is located about l km N-W of Bergamo Alta, W of the Bergamo Alta-Pontesecco road, immediately lies in the middle of the Sarnico Sandstone Formation and in the centrai part of the whole outcrop area.

The lower part of the sampled series is composed


of very thick, arenaceous Iayers interbedded with thin, very calcareous, hard marls. The uppermiddie part of the outcrop is composed of a quite reguiar alternation of sandstone and marly Iayers. The sandstone is very hard, due to the high percentage of calcitic cement. Fragments of Iimestones are aJso abundant in the detritai part and are strongiy recrystallized.

Quartz and chert grains are the Iargest among the detritai grains and therefore, even if the detritai carbonatic part is very abundant, the maximum diameters obtained by grain size anaiysis after acid treatment, are sufficiently representative.

The composition of this sandstone is very constant throughout the outcrop.

Bergamo Flysch - This formation is built up of alternations of sandstone and mari, differing greatly between the Iower and upper parts of the formation. The Iower is separated from the upper part by a calcareous marly intervai (average thickness: 40 m).

The Iower part is characterized by the prevaience of thin sequences whose carbonate content is very high.

The sandstone contains abundant calcareous cement; carbonates aiso prevaii in the detritai part, and therefore it sometimes actually becomes calcarenite. Colour variations within calcarenite layers are frequent and emphasize the structures. The detritai part is similar to the o ne of the formation previously described. Both marl and sandstone are light brown coioured, yeliow through weathering.

The calcareous marly interval is a single thick Iayer, the lower part of which is sandy and in it a great number of plant remains and some slumping features are met with, whilst the middle-upper part consists of compact and rather uniform mari. Immediately above the thick calcareous marly layer, begins a new succession of turbidites composed of scarcely cemented sandstone layers, rich in carbonized plant remains, interbedded with sandy pelite. Here too the sandstone clastic part has a high carbonatic content which is much coarser than the siliceous part.

The formation occupies the area from Lake Iseo (where it is known as <<pietra di Credaro)>) to Carvico and Mt Giglio (Western Bergamo area).

In the Iower part it is characterized by calcareousmarly turbidites ( clastics whose size is that of medium-fine sand) interbedded with calcareous mari.

In spite of the fact that the average thickness of sequences is about 20 cm they generaliy include ali the intervals. The thinner ones show cross laminations only.

Markings on the bedding piane consist almost exlusively of tra ce fossils; load casts, groove casts and scour marks are also present. The base of the upper part of this formation, directly overlying the thick calcareous Iayer, has different features: detritai elements are coarser and layers are frequently lenticular.

Graded (a) intervals and paraliel lamination (b) are the most frequent; peiite is rare and has a considerable sandstone component. The upper part of this formation is not weli known because it generaliy lies beneath the piain. A few outcrops, directly underlying the so calied Maastrichtian << scaglia cinerea )), show turbidites made up of thin alternations, scarcely cemented and rather finegrained.

Aiso in Bergamo Flysch two logs have been surveyed: Bastia and Carvico.

log 13 Bastia, is Iocated on the top of the hili which lies between Bergamo Alta and Sombreno, about 500 N-W of Bastia. The outcrop is characterized by the presence of thin calcarenite layers interbedded with thin mari. The calcarenites, according to Folk's classification, could be defined as calclitite. The clastic carbonatic part is strongly recrystaliized and it is therefore very difficult to distinguish the different components.

Micrites, microdetrital limestone and dolomite fragments were found. Dolomites are also present as isolated rhombohedra often covered by a film of iron oxides. Among detrital elements there are also quartz, chert, mica and, very rarely, plagioclases.

Almost ali the quartz grains have straight extinction an d are very angular. V ery often, they ha ve sinuous crenulate boundaries because they have been greatly corroded by the calcitic cement. Chert is found as microcrystaliine or, more rarely, fibrous quartz. It also shows evident corrosion due to calcite. The cementing part consists of crystalline calcite containing day and iron oxide. The arrangement of flat or elongate elements 1s paraliel to bedding planes.

The grain size of the limestone fragments is up to l mm and is clearly less than that of chert grains which are the largest in the whole detrital part and which sometimes reach 2 mm. Fossils are


very rare, but when they do occur are often well preserved and stili intact.

Muscovite flakes are sometimes folded or broken because of the load of overlying sediments. This mainly occurs when a rather large quartz grain lies on the center of a flake, which deforms and bends downwards, testifying to the extent of the load sustained. In sequence 31 (sample 75) one may notice, in the middle part of the layer, a zone of materia!, finer (200-300 microns average) than the one composing the bulk of the layer (500-600 microns ), which is sinuous an d is inclined a t 20-30° to the base of the layer. The materia! of the finer zone, which may be the result of an internai erosion, is lithologically similar to that of the rest of the layer.

The upper contact of this zone with the rest of the layer is marked by a microstilolite, accentuated by the existence of iron oxides concentrated along an area of considerable corrosion which involves both quartz and chert grains and limestonc fragments. In sequence 37 an anomalous succession of intervals is to be observed: the layer starts with an interval ( 4 cm thick) of parallel lamination followed by a graded interval (about 12 cm thick) which changes upwards dircctly to

FIG. 18 - Prealpi Flysch near Bergamo: Bergamo Flysch (Eocene); log no. 13 Bastia, layer 31. Laminae are determinateci by a change from coarse (lower part of the figure) to fine grains (upper part). The coarser grains are carbonate fragments which show some cor-

roswn.

- Flysch delle Prealpi bergamasche: Flysch di Bergamo (Eocene); log n. 13 Bastia, strato 31. Le lamine sono determinate dal cambiamento dei granuli da grossolani (parte bassa della figura) a fini (parte alta). I granuli più grossolani sono frammenti di carbonati che

mostrano fenomeni di corrosione.

:._-';"_;_-:-...:~ j' . _,_ . ...........__, . . . . -

:::::.<l . ,, •• • ..... 1

'ol l l l l

D' l

' l 'd

l

FIG. 19 - Prealpi Flysch near Bergamo: Bergamo Flysch (Coniacian); log n. 12 Carvico. Scale 1 : 50.

Flysch delle Prealpi vicino Bergamo: Flysch di Bergamo (Coniaciano); log n. 12 Carvico. Scala 1 :50.

an interval of cross laminations. This layer is probably composed of two sequences: o ne of parallel lamination on the lower part and the other consisting of the two overlying intervals.

log 12 Carvico, was surveyed along the road which climbs from Carvico along Grandone stream to the quarry near Predazzi, 500 m N of Carvico, immediately over the thick mari layer, 40 mm thick, which separates the lower part of the formation from the upper.

From a lithological point of view the sandstone is poorly cemented by a clayey calcareous cement. In the detrital part, as far as size is concerned, the carbonatic component prevails.

Coarser grains are well rounded. Detrital quartz is present only within medium-fine sand and silt.

Layer thickness is not constant, even though, the outcrop being so limited, no actual lenticular feature 1s visible. Variations in thickness of


15-20 cm were noticed over distances of less than 4 m in some thick sandstone layers.

Scour marks are completely absent; a few flute casts only were found; these are very irregular both in direction and m shape and are partially deformed by Joad.

The bedding piane is nearly always perfectly plane-parallel. The outcrop is characterized by the presence of carbonized materia! which is comnwn both in sandstone beds and in pelites.

In generai the pelitic intervals contain sand and silt laminae, appearing as a thinly laminated layer (fig. 19).

The outcrop, from the litological point of view, is a typical proximal facies.

<< SLATE FORMATION >> IN THE LIGURIAN APENNINES

by Giuliano Fierro

The <<Siate Formation >> (Ardesie) extends NWSE along Lavagna Valley in two strip-shaped outcrops, with a maximum length of 25 Km, some outcrops are in Bisagno Valley, in the upper part of Recco Valley, and in Capenardo Mt. near Lavagna Mt. This formation shows generally a succession of layers consisting of sandstone or calcarenite changing to marly shale (siate) or shale (fig. 20). Thickness is variable in the different areas but does not seem to exceed 600 m. The most recent papers on this subject are by REUTTER (1961), BONI (1961-62), ELTER (1962), CONTI (1963), CASELLA e TERRANOVA (1963), TERRANOVA ( 1966). EL TER an d REUTTER refer t o this formation as << Scisti della Val Lavagna>>.

Siate lacking microfacies have been ascribed to Albian-Cenomanian by CASELLA and TERRANOVA (1963) on account of their stratigraphic position; they overlie in fact Aptian-Aibian shale and Iie under the Antola calcareous formation with El.minthoids whose base is Turonian in age. Shale, varying in coiour, which normally occurs at the base of the above mentioned formation, is Iacking along Lavagna Valley where it is replaced by the upper part of siate formation. TERRANOVA (1966) ascertained heteropy between Lavagna siate and the Iower part of Ramaceto Mt. sandstone. In Vara Valley, GHELARDONI, PIERI, and PIRINI (1966) have ascertained a similar stratigraphic position for facies that these AA. had referred to << Siate Formation >>.

In younger Ieveis of << Siate Formation >> siate Iithotypes were found more frequentiy, while shale is present with an aimost constant frequency. Logs were surveyed in Lavagna Valley and they include the whoie formation; convoiute laminations were found in the arenaceous bed of Iayers. The calcareous cement of sandstone prevails in upper layers and mainiy on the right siope of Lavagna Valley where siate is sometimes repiaced by a limestone with siate characteristics. The presence of such a lithotype stresses that a marly sedimentation occurred in this area of the basin. Such sed;mentation preceded the deposition of the overlying Antola mariy limestone. The northern area of the basin consists of siate cropping out on the Ieft side of Lavagna Valley.

The levels on both sides of the valley, stratigraphically corresponding, can be considered as brought closer by tectonics. In layers of the Ieft side, calcarenite is considerabiy less frequent than sandstone. On the same side massive siate Iithofacies with poor fissiiity are less frequent.

For this formation we have surveyed 6 Iogs numbered as 19, 18, 17, for those stratigraphically located (from bottom upward) on the Ieft side of Lavagna Valley. The Iogs Iocated in a corresponding position on the other side have been indicated as nos. 1+, 15, 16 and they referto siate of the right side. Logs Iocation in the sheet 83, Rapallo, from W to E, is the following: log 18 Verzi, 500 m downcurrent the Church; coordinates 32 TNQ 19881920 (Tav. II NW);

log 16 Passo della Crocetta, along the road running from Coreglia Ligure to Passo della Crocetta; coordinates 32 TNQ from 20081+75 to 20041472 (Tav. II SW);

log 14 Pian dei Manzi, WNW S. Bartolomeo; coordinates 32 TNQ 21+01545 (Tav. II SW);

log 15 Coreglia, aiong the road Pian dei ManziCoreglia Ligure; coordinates 32 TNQ from 21+31525 to 21+31536 (Tav. II SW);

log 17 Orero, road Pianmegorino-Orero, about l Km SW Pianmegorino bridges; coordinates 32 TNQ 22351806 (Tav. II SW);

log 19 Ruota, along the road Caivari-Romaggi, about 200 m past Ruoto; coordinates 32 TNQ 24551+95 (Tav. II SW).

The quartz-micaceous sandstone with clayey siliceous cement shows a high maturity in d ex: in fact sandstone is well sorted and shows rather rounded grains. Quartz is metamorphic with wavy extinction.


Macroscopically slate appears as a marly shale characterized by a high fissility index, black-grey coloured, whitish if weathered. Sometimes it contains pyrite nodules. Microscopically the rock is a micrite with scattered detrital quartz grains (about 10% using SHEVESTov's visual method). Sometimes grains are arranged in sub-parallel laminae. Through several chemical analyses of slate coming from different quarries, the following minimum and maximum percentage values for some oxides were obtained: CaO (27.5 - 37.9); Si.G~ \1'1 .4 - 31.2); Ah03 (6.2 - 8.9).

Current casts on lower bedding planes are more frequent in northern facies of Lavagna Valley. while in the southern one only rare organic casts can be found.

From logs surveyed in the layers of siate formation showing convolutes, the following frequency distribution was obtained: T (c-e) 50%, T (b-e) 32% T (a-e) 9%; sequences T (d-e) and T (b-e) showed equal percentage values (4.5%).

As it can be noticed, the most frequent layers are those in which the interval a is lacking: in sandstone there are present intervals b, c, e, whereas in siate and shale intervals d and e are present. Even though type a is often lacking the layer appears, even on field survey, finely graded along its whole thickness. Sand/day ratio for convolute intervals is 1.07.

On the basis of such observations << Siate Formation )) can be defined as a succession of sandstoneslate layers, where slate can be replaced by shale. At the top of the formation, especially in the southern facies, sandstone is often replaced by a calcarenite, and slate by marly limestone.

Frc. 20 - Upper leve! of the << Siate Formation •>; log no. 16. The convolute laminations are located into the colcarenitic part of the layer. At the bottom of the fi-

gure appears the siate lithofacies.

- Livello superiore della << Formazione delle Ardesie >>; \og n. 16. Le convolute laminations sono localizzate nella porzione calcarenitica del ritmo. Nella parte inferiore

della figura si osserva la litofacies ardesiaca.

Some grain size analyses have been carried out for << Siate Formation >>, after disaggregation in hydrocloric acid, on samples collected in the different intervals of logs 14 and 17. By comparing cumulative curves with those of the corresponding terms of logs 14-17 and 43 of << Arenarie superiori>> (see page 368) it is possible to notice in slate a finer grain size composition for Te and a coarser one for Te and Tb.

<< FLYSCH AD ELMINTOIDI )) IN THE WESTERN ALPS

by Giuliano Fierro

In western Liguria, the << Helminthoid Flysch >> lies in a wide area, nearly triangular in shape, whose boundaries run from Albenga to Bordighera and Mont Bertrand. This Flysch was first attributed to Upper Priabonian, and later to Cretaceous on the basis of microfauna occurrence (LANTEAUME, 1956). This formation has recently been studied by BONI and VANOSSI (1960), and RICHTER (1961).

On the basis of a stratigraphical syntesis by LANTEAUME (1961) i t is possible to recognize this Flysch as belonging to the facies of San RemoMonte Saccarello, Moglio-Testico, Alassio-Borghetto d'Arroscia. According to LANTEAUME i t is possible to subdivide, the Helminthoid Flysch, in different séries

Complexe de base Série à dominante gréseuse Série à dominante calcaire Série à dominante marneuse

These séries are ali included between Turonian

and Maastrichtian.

The complexe de base consists of two levels the lower, very sandy, becomes psammitic at its top with inclusions of green and red shales. The upper level, mainly calcareous, corresponds to the LANTEAUME's Flysch finement lité à dominante calcaire. A different explanation of the complexe de base has bee n offered by BoNI an d V AN OSSI (1960) w ho interprete d this complexe as two levels: one prevalently clayey-arenaceous, and the upper one mainly calcareous-clayey.

The série à dominante greseuse is characterized by detrital sandstone sediments, sometimes breccialike or conglomerate-like, having been deposited by turbidity currents. Graded bedding and se-


dimentary structures that are typical of this kind of sedimentation, have been found there very frequently. The pelitic interval e is sometimes lacking and the lower ones often show erosion marks.

The série à dominante calcaire is characterized by remarkable variations in three facies, it differs from the preceding one for the prevailing presence of calcareous and marly- limestone levels. About th.e facies variations occurring in the Helminthoid Flysch it may be remarked that the western facies of San Remo and the eastern one of Alassio-Borghetto d'Arroscia are comparable because of the abundant pelagic sedimentation following the sandy one. On the contrary, the two facies differ for their lithological and mineralogica! components which have been synthetically described by LANTEAUME an d HA C CARD ( 1961) as follows: Western facies of San Remo: arkosic sandstones, eruptive and methamorphic lithoclasts. Eastern facies AlassioBorghetto d'Arroscia : detrital quartz with a high roundness index, lower percentage of feldspars and plagioclase, gneissic and sedimentary lithoclasts. It is possible, therefore, to suggest that there is a different direction of supply of detrital grains far the two basins, and a higher index of maturity for the eastern facies. Convolute laminations are not easily found, with exception far the northern area of the facies Maglio-Testico: far this reason no graphical log was surveyed.

Other Authors have investigated the Helmithoid Flysch considering its different sedimenthological aspects. In 1957 KuENEN and his co-workers pointed aut the directions of supply of the clastic grains; in 1965 PLESSMAN studi ed mainly the sedimentary structures. In the same year V ANOSSI carried aut a complete sedimenthological study covering the sedimentary structures present in the layers and the distribution of heavy and light minerals. The layers have been investigated both by LANTEAUME and VANOSSI.

LANTEAUME has represented and called them sequences, considering as a sequence that thickness of sediment included between the two inferior surfaces of contiguous layers. The Author has the convincement that each sequence is due to a contiguos period of sedimentation. From the observation of various series of sequences in the whole Flysch formation, LANTEAUME has guessed that the peculiar characteristic of Helminthoid Flysch facies may be represented by a pelagic sedimentation in situ, disturbed by accidents caused by detrital deposition.

The << Helminthoid Flysch )) formation would be made up by a succession of pelagic and detrital lithofacies; however, pelagic sedimentation would continue during the detrital deposition. Because of the great occurrence of very fine sole markings and the rare presence of erosion structures, LANTEAUME believes that the mechanism of this detrital deposition has a calme course, even if instantaneous and compares it to that of a chemical precipitation owing to its fast sedimentation. Nevertheless, the Author thinks that the transportation of clastic material has been carried out especially by turbidity currents at least far the série à dominante greseuse, in the San Remo area.

VANOSSI investigated the layers in the Valle Argentina, and used the graphical log method. The Author has been able to confirm the presence of the sequence Ta-e and of base cut-out or truncated sequences. VANOSSI has become aware, moreover, that in the complexe à dominante greseuse the intermediate intervals b and c are very often lacking. According to the Author the occurrence of overlapping layers such as: T a, Te-e an d T a-b, Td-e should be excluded, and therefore he proposes to set up two new sequences, respectively A and B.

The graphical logs given here are located in the series of San Remo (logs nos. 20-21-22-23-24) and in that of Alassio-Borghetto d'Arroscia (logs nos. 25-26).

The logs location is the following: log 20 Andora Marina, Km 634,134 of State Main Road no. l, << Aurelia )) (Sheet l 03 - Tav. IV NE); log 21 Pontedassio (Oneglia), Km 136, State Main Road no. 28 (Sheet 103 - Tav. IV SW); log 22 San Romolo, Main Road San Romolo-Baiardo, west side of bridge on the Valle di San Romolo (Sheet 102 - Tav. I SW); log 23 Monte Bignone, Main Road from San Romolo to Baiardo, 500 m besides the cross road to M t. Bignone (Sheet 102 - Tav. I SW); log 24 Vignai, quarry at the 3rd Km on the way from Baiardo to Case Vignai (Sheet 102 - Tav. I SW); log 25 Caso, on the road between Caso and the cross road to Madonna della Guardia; SW from Caso (Sheet 92 - Tav. III SE); log 26 Madonna della Guardia, at 200 m from cross road on the Alassio-Madonna della Guardia road (Sheet 92 - Tav. III SE);

Our logs of the complexe de base confirm the VANossr's results concerning the occurrence of the sequences Ta-e (log no. 24) and the high percentage of base cut-out sequences (log no. 22).

The more frequent sequences of the complexe

SEDIMENTOLOG!CAL CHARACTERISTICS OF SOME ITALIAN TURBIDITES 365

à dominante gréseuse is the truncated type with the a interval very thick (log no. 23). The sequences Tb-e (log no. 20, layers 3 and 12) is more common in the complexe cale aire; however, the sequence Ta-e is also present there. The logs concerning the Flysch with convolute laminations show the following or der of presence in percent: Tb-e (46,5); Ta-e (26,5); Te-e (13,3); Td-e (6,5).

Fucoids and Helminthoids appear in the interval e of the sequence Ta-e. In the present logs the thickness of the intervals had been classified in t.b_e <>ame way as those carried out for the << Maci-

characteristic is the almost constant presence of the pelitic interval, whose thickness is often quite the same than that of the arenaceous part of the layer. In the western area of the region, Cortemilia Formation changes upward to a unit consisting of a thick series of layers, sometimes remarkably thick, in which the pelitic interval is generally thinner than the arenaceous bed, and sometimes is even absent (Cassinasco Formation) (3). In the eastern part of the region Cortemilia Formation, on the contrary, gradually changes to an essentially marly unit, whose sediments are only partially deposite.d

FIG. 21 - Langhe Turbidites in Piemonte (Lower-Middle Miocene). Cross lamination which, towards the bottom of the layer, becomes parallel lamination (log 27, layer no. 4 - x 1.1).

- Torbiditi delle Langhe in Piemonte (Miocene medio-inferiore). Laminazione obliqua passante verso il basso a laminazione parallela (log 27, strato n. 4 - x 1,1 ).

gno )) an d << Arenarie Superiori )) formations (l). The thickness of sequences presents a maximum percentage in the 4-8 cm class. The a interval, generally rare, is most frequently found in the 32-64 cm class, if present. Interval b shows a maximum value of frequency in the 1-2 cm class, interval d, which is most frequently found after interval c, presents a maximum of frequency in the 1-2 cm class. The sand-clay ratio has a value of 0.35.

LANGHE TURBIDITES IN PIEMONTE

by Mario Gnaccolini

It is possible to distinguish three main lithostratigraphic units in the Lower and Middle Miocene of north-eastern Langhe. The lower unit (Cortemilia Formation) (2) is made up, in this area, by a thick succession of layers whose most evident

by turbidity currents, prevailing the normal pelagic sedimentation (Cessole Marls (4) which are heteropic partially with Cortemilia Formation and mainly with Cassinasco Formation).

The outcrops here described belong to Cortemilia and Cassinasco Formations. In the layers of these two units the arenaceous bed consists of grey-light brown to yellow-brown sand (or sandstone) an d siltstone, mainly compose d of quartz, fragments of metamorphic rocks, muscovite and feldspars, with calcareous cement. The pelitic interval is sometimes lacking; when present i t consists of grey clayey mari or grey marly clay.

(1) The frequency classes are the same used in the ''Arenarie Superiori formation >), by G. FIERRO and G.C. PAREA, and ''Macigno formation >) by G. FIERRO and G. C. P AREA, and ''Siate formation >) by G. FIERRO.

(2) Name recently adopted by the geologists of the Italian Geologica! Survey (Sheet Ceva).

(3) and (4) Names introduced by C.C. VERVLOET (1966) and adopted by the geologists of the Italian Geologica! Survey (Sheet Ceva).


l)

14 i i l 2llù • •

l 1----i-----,-,~· ~-=-·-:;:~=-· -,.=<'1---1 ~'-+--'-o----,------:-1· •.

13tt0 ~ l 1---+--t'''---"--' _ _._. -'_:.T---1 rl l I J) --L._._ _._....L._._

~l'' -.-.-.··

\ - ':: -~: 11

340 ~-~·; i 1·-·-· • i

l \ •••

l ~ ~ l l~-1~10 220 l:~:~ ...

l r.-.-.-. ;Jq) ~ l -..._·.· ..

! l ~ ~-1! ltoO ~-l l - -~ ..•.

r 91

1230 -

l -~·1 . . .

85 -":..,_-~~

l 7 120 l~'f.i i " ., - _, ::i l " -- ~

! is 115 -.~ •• 1

l ' 1111) 1.~~.--.-. ! 114 ! ~.~.l~ U tHo ·~·-·~· l '1

jjj Iso ~~ ._:_ .. ~~u~ l J Ilù .--'-;--"-;--'-. i

bO ~- _, .

60

20 .-.---.--. . .

l i !

' l l

' l

! l

' '

Frc. 22 - Langhe Turbidites in Piemonte (LowerMiddle Miocene); log no. 27 Cortemilia-Gorzegno road.

Scale 1 : 25.

- Torbiditi delle Langhe in Piemonte (Miocene medio-inferiore); log n. 27 strada Cortemilia-Gorzegno.

Scala 1 : 25.

The strata of the concerned outcrops form a slightly inclined monocline which gently clip towards the Piemontese plain.

Localities of log survey (7 logs for a total of 95 layers) are the following: log 27 Cortemilia-Gorzegno road, km 29 (sheet 81 Ceva, tav. IV SE); log 28 Vesime-Cessole road, 150 m east of Vesime (sheet 81 Ceva, tav. I NO);

log 29 Bubbio-Cassinasco road, by C. Albesano, 500 m south of Cassinasco (sheet 69 Asti, tav. II SO); log 30 Bubbio-Cassinasco road, about 150m downstream of log 3 (sheet 69 Asti, tav. II SO); log 31 Cravanzana- Torre Bormida road, by km 4 (sheet 81 Ceva, tav. IV SE); log 32 Cravanzana-Torre Bormida road, by C. Biula (sheet 81 Ceva, tav. IV SE); log 33 Arguello (sheet 81 Ceva, tav. IV SE).

The above mentioned outcrops are characterized by a series of layers in which the pelitic interval is sometimes lacking or is just a few cm thick; it may also be almost as thick as the arenaceous bed. The layer thickness varies between a few cm and about 2 m; the arenaceous bed thickness is similarly varying; peli tic intervals are generally from zero to less than 30 cm thick.

In log 27 the pelitic interval is always present, it is 4.5 to 23 cm thick. Layer thickness ranges from 7 to about 45 cm, and the arenaceous bed one from 2.5 to 34 cm. The prevailing sequence of internai structures are the following: l) peli tic interval; parallel lamination; graded interval, 2) peli tic interval; graded interval. The sequence: pelitic interval; parallel lamination; current ripple lamination; parallel lamination; graded interval is rare. The size of clastics, at the base of the layers, belong at most to the class -2 ;O <D. Groove casts and tracks and burrows can be found.

The series, by which log 31 has been surveyed, shows characteristics alike those of log 27. Here too the pelitic interval is always present, its thickness varies between l and 20 cm. The thickness of arenaceous beds varies between 8 and 58 cm. Total thickness of layers ranges from 9 to 61 cm. The prevailing sequence of internai structures, unlike the preceeding outcrop, is the following: peli tic interval; gn:ded interval. In graded layers clay pebbles (size up to about 20 cm) might sometimes be found. Size of clastics, at the base of layers, belongs a t most to the class -2 ;O <D. Flute casts and crescent casts are present.

Logs 28, 32 and 33 have ali rather similar charactenstrcs. In fact, they are ali characterized by successions of irregularly thick layers in which the pelitic interval is quite frequently absent. Layer thickness is greatly varying (between 4 and 70 cm); the arenaceous beds are l to 70 cm thick and the pelitic intervals are zero to 30 cm thick. Sequences may either be complete or truncated at the top, prevailing o n es are: l) peli tic interval; graded interval, 2) graded interval. The following ones


.... . -·--·1 l'' -170 >~<-:

: : ' 130

:~ 4 2)0 i=--=-= ! l l •••••••

!l 1·~·1 1

: 3 \ISO f: ·: · ~ ·1 , l ' r ... ' '. . .. ·l

~'l : i,:·· .. :_- :_-1

l j. "-:-'~:~:; ' 211750 ~ ~.·:-.1 l

l • • • i

l ·~l l l 1·~1 i l :• •••

l

·.~·1, ... •! •..... :

FIG. 23 - Langhe Turbidites in Piemonte (LowerMiddle Miocene); log no. 30 Bubbio-Cassinasco road.

Scale 1 : 50.

- Torbiditi delle Langhe in Piemonte (Miocene medio-inferiore); log n. 30 strada Bubbio-Cassinasco.

Scala 1 :50.

FIG. 24 - Langhe Turbidites in Piemonte (LowerMiddle Miocene); log no. 33 Arguello. Scale l : 25.

- Torbiditi delle Langhe in Piemonte (Miocene medio-inferiore); log n. 33 Arguello. Scala 1 : 25.

t- ~ f t--

l -'--~--. 2] 230 ,, .

. . . . ~-·

.Jtl: ....... .

.____..____. ---~·~ T .....

l

li 1-J.)

.------.-. ... ~ ~· ... ·.~

CASTS ~ : LAMINA TIONS , GRAIN S>ZE ~

l ~ l ' ' i -l

ri '.:....:..:..:. 15 # 4!~A~-4-'2 o 2 "6·8 'l u t l ... ,, •••.

. l

ro o:nl

u ',H l

u n Il

u

o


are more rare: 1) peli tic interval; parallellamination: current ripple lamination; parallel lamination; graded interval, 2) current ripple lamination; parallel lamination; graded interval, 3) pelitic interval; parallel laminati o n; graded interval. In arenaceous layers clay pebbles (size up to 40 cm) are occasionaly found. The size of clastics, at the base of layers, exceed sometimes -2<1>. Flute casts, groove casts, load casts, tracks and burrows are observed; erosi o n channels are sometimes present. Finally, in log 29 and 30 the pelitic interval is only discontinuously present. Layer thickness varies between 4 and 175 cm; the pelitic interval, if present, is at most a few centimeters thick.

The only visible sequences are the following: l) graded interval (truncated at the top), 2) peli tic interval; gradcd interval. These series are characterized by the presence, in some laycrs, of many clay pebbles whose size somctimes exceeds 30-40 cm and numerous erosion channels. At the base of layers only one groove cast has been observed. Size of clastics, at the base of laycrs, exceed somctimes -2 <t>. Flute casts, groove casts and crescent casts obscrved in the investigated series are all at the base of layers st2rting with the graded int-:rval.

<<ARENARIE SUPERIORI ))

by Giuliano Fierro - Gian Clemente Parea

The <<Arenarie Superiori)) Formation (also called << Mt. Gottero Sandstone )) or << Mt. Ramaceto Sandstone )>) outcrops essentially in eastern Liguria. Thin layers of marly or siliceous limestone are also present but rare. Total thickness of <<Arenarie Superiori >> is about 750 m at Mt. Zatta while it exceeds 1500 m in the area of Mt. Gottero according to GHELARDONI, PIERI and PIRINI (1965).

According to P AREA (1965) <<Arenarie Superiori)) represent the first turbidity deposit in the Apennine eugeosyncline. This Author ascribes to this Formation other arenaceous Flysch slabs (Monghidoro and Macinaggio in Corsica) and also the lower part Imperia Flysch.

TEN HAAF (1959), considering <<Arenarie Superiori )) as allochthonous slabs of Macigno, reported some current direction coming from N.W. and only a few from S. P AREA ( 1964 an d 1965) stressed that the actual provenance of turbidity currents

(1) This work deals, in the chapter of <<Siate Formation )), with the geologica! and lithological features of this Formation.

is from S. Only a single provenance from N.W. was found among 241 measurements and a northwesterly supply is no longer maintainable.

<< Arenarie Superiori )) grades downwards to a marly and shaly formation with very thin arenaceous layers interbedded. These are clearly visible on the southern side of Mt. Zatta. In some areas of Val Lavagna (left si de) an d by Sestri Levante (Mandrella Coast) <<Arenarie Superiori )) changes downwards to blackish calcareous-marly Formation of Ardesie, known in literature as << Scisti della Val Lavagna)) (1). Upwards the Formation changes to vati-coloured shale of Cichero (REUTTER, 1961; FIERRO and TERRANOVA, 1963).

FIG. 25 - << Arenarie Superiori >> Formation. Side of a deep erosion channel cutting through a dozen or more anterior layers. Ligurian coast south of Mt. Vè, bet-

ween Levanto and Monterosso.

- Formazione delle <<Arenarie Superiori )). Fianco di un profondo canale di erosione che attraversa una dozzina o più di strati precedenti. Costa ligure a Sud di

Monte Vè, fra Levanto e Monterosso.

Lateral facies transitions are difficult to determine. An arenaceous formation, outcropping at E (Ostia Sandstone) can, however, be considered as a distai facies of this formation.

The age of this formation is Albian-Cenomanian according to REUTTER (1961 ), Albian-Turonian according to FIERRO and TERRANOVA (1963), proparte Maastrichtian according to ELTER and RAGGI (1965) while PASSERINI and PIRINI (1965) state that its top in Mt. Zatta is not older than Paleocene.

Facies heteropy with the calcareous Flysch with Elminthoids (Mt. Antola Formation) suggested by FIERRO, CONTI, LANTEAUME (1960) must therefore be limited only to a part of <<Arenarie Superiori >>.

The contrast between the light grey superficial colour of the arenaceous bed and the blackish one

SEDIMENTOLOGICAL CHARACTERISTICS OF SOME !TAL/AN TURBIDITES 369

FIG. 26 - <<Arenarie Superiori>> Formation. Prad casts in which the pebbles responsible for the structure are trapped. Ligurian coast, near Baffe Point between

Riva Trigoso and Moneglia.

- Formazione delle << Arenarie Superiori >>. Si notano dei prod casts in cui sono ancora conservati i ciottoli che hanno causato le impronte stesse. Costa ligure,

presso Punta Baffe tra Riva Trigoso e Moneglia.

of the pelitic one is typical of this Formation. Weathering makes the two materials lighter; however, they can also become brownish because of iron component oxidation.

The upper part of each layer (when it has not been removed by the erosion of thc subsequent turbi dite) consists of silty peli te often affected by a fissure network with two main directions transverse to the stratification plane. These fissures divide the rock into prisma tic elements; << argilloscisti a coltellini >> (CASELLA and TERRANOVA, 1963).

In << Arenarie Superiori >> small carbonized plant remains are rather frequent.

From a mineralogica! point of view sandstone is composed of quartz and feldspars with a fair quantity of rock fragments; mica is rare an d calcareous cement is almost lacking. MALESANI (1966), according to Folk classification, has recently defined <<Arenarie Superiori >> as feldspathic greywackes. He also recognized that quartz has mainly a metamorphic origin. Because of the absence of potassic feldspar in the sandstone of Mt. Ramaceto and of Mt. Zatta, this Author considered this sandstone separately, mineralogically speaking, from that of M t. Gottero; among the outcrops of the Ligurian coast he ascribed the sandstone of Deiva Marina to Mt. Gottero sandstone.

In his work on heavy minerals GAzzr (1965) stressed the existence of strong differences between the sandstone of Mt. Ramaceto and Mt. Zatta and that of Mt. Gottero and Mt. Molinatico. The

Author emphasized, moreover, the very high degree of mineralogica! maturity of the former type, << the highest found, up to now, in Apennines sandstone (starting from Cretaceous) >>; GAZZI found in fact in this sandstone a high percentage of very stable minerals (zircon, tourmaline, rutile) and a very low percentage of garnet.

Going from W towards E in the <<Arenarie Superiori>> Formation, the following logs have been surveyed (l): log 44 Romaggi (G.F.), 200 m from the church o n the road leading to Passo di Romaggi; coordinatcs 32 TNQ 25001555 (Sheet 83 - Tav. II SW); log 41 Montemoggio (G.F.), along the road Montemoggio-Passo del Bocco; coordinates 32 TNQ from 32651825 to 34981830 (Sheet 83 - Tav. II SE); log 43 Passo del Bocca (G.F.), along the road Passo del Bocco-Sopralacroce; coordinates 32 TNQ from 35462045 to 35462055 (Sheet 83 - Tav. II NE); log 42 Mt. Zatta (G.F.), left side of Valle della Malanotte; coordinates 32 TNQ 37501810 (Sheet 84 - Tav. III SW); log 39 Lemeglio (G.F.), 300 m SE of Lemeglio, 50 m above sea level, coordinates 32 TNP 39909750 (Sheet 95 - Tav. IV SW); log 40 Deiva (G.F.), locality <<Cava di Pietra;>, western side; coordinates 32 TNP 41799572 (Sheet 95 - Tav. IV SW); log 45 Riva Trigoso (G.C.P.), along the beach

FrG. 27 - << Arenarie Superiori >> Formation. Frondescent cast on the sole of a layer from the same outcrop in which the Riva Trigoso log (no. 45) was surveyed.

- Formazione delle <<Arenarie Superiori>>. Frondescent cast sulla superficie inferiore di uno strato dell'affioramento su cui è stato campionato il log Riva Trigoso

(n. 45).

(1) The piace name is followed by the initials of one of the two Authors who carried out the field survey.


outside the first tunnel, formerly a railway tunnel, which one meets going from Riva Trigoso to Moneglia, by a promontory which is the most advanced point which can be reached on foot from the southern opening of the above-mentioned tunnel (Sheet 94 - Tav. I NE);

log 46 Madonna del Carmine (G.C.P.), on the slope above the road Sòrbolo-Tavegna (about 7 Km N of La Spezia), 50 m beforc the bridge on the stream flowing S of Tivegna (Sheet 95 -Tav. I SE).

In the logs surveyed by G. FIERRO, 68 sequr.:nces showed convolute laminations. The following frequency arder was observed: T c-e 38%; T a-e

FIG. 28 - <<Arenarie Superiori>> Formation. Dendritic ridge casts on the sole of layer no. 7 from Riva Trigoso

log (no. 45). Current from right to left.

- Formazione delle << Arenarie Superiori >>. Dendritic ridge casts sulla superficie inferiore dello strato n. 7 del log Riva Trigoso (n. 45). La direzione della corrente è

da destra verso sinistra.

32%; T b-e 14%; T d-e 10%; T c and T b-e sequences have percentage values lower than 3%. The above mentioned frequences must be referred only to << Arenarie Superiori >> levels which show, among structures occurring within layers, con volute laminations; simple shaped o n es are prevalent. A statistica! investigation on thickness of sequences for the frequency classes 0-2-4-10-20-40 cm indicated that the more frequent sequence is 10-20 cm thick. The same investigation concerning the thickness of each interval (following the geometrie progression at the rate of 2: 1,2,4,8 ... ) showed that c-interval is most often 2-8 cm thick; d-interval, which after c occurs most frequently is most often 4-8 cm thick.

FIG. 29 - <<Arenarie Superiori >> Formation. Moulds of armoured shale inclusions in the coarse-grained sandy part of a thick layer containing smaller shale and sandstone fragments as well. The pebbles which armoured the shale are identica! in size and composition to those forming the lowermost part of the layer. The same outcrop in which the Riva Trigoso log (no. 45)

was surveyed.

- Formazione delle << Arenarie Superiori >>. Impronte di armoured pebbles nei livelli grossolani sabbiosi di un potente strato contenente piccoli frammenti di argilla ed arenaria. I ciottoli che circondano le inclusioni argillose sono identici, in dimensioni e composizione, a quelli che costituiscono i livelli basali dello strato. La fotografia è stata eseguita sullo stesso affioramento in cui

è stato campionato il log Riva Trigoso (n. 45).

In different areas of this formation great differences are found in maximum grain sizes near the base of the layers in their thickness and in the ratio between arenaceous and pelitic bed thickness

Frc. 30 - <<Arenarie Superiori >> Formation. Shale inclusions of widely differing sizes sometimes deformed in the upper part of the a interval of layer no. 7 of Riva

Trigoso log (no. 45).

- Formazione delle <<Arenarie Superiori >>. Si notano inclusioni argillose, di dimensioni molto variabili ed a volte deformate, localizzate nei livelli superiori dell'intervallo a dello strato n. 7 dellog di Riva Trigoso (n. 45).

SEDIMENTOLOGICAL CHARACTERISTICS OF SOME /TAL/AN TURBIDITES 371

of the layers. In << Arenarie Superiori >> casts of burrows on the sole of the layers are very frequent and many kinds of current and toolmarks are also quite frequent. It is possible to observe good examples of rather rare or unusual structures especially in the outcrops along the coast where large parts of bedding plane are frequently exposed. Among structures due to the dragging of objects on the bottom an interesting example is supplied by slide casts with a sinuous trend which can be observed for about 15 m Sestri Levante promontory. Prod casts embedding the small pebble which caused them (Fig. 26) are also quite interesting. Among structurcs connected with the erosion of the turbidity currents on the sca bottom, a deep erosion channel visible on the stecp coast of Mt. Vè promontory, near Levanto, is a good Example. (a photograph of one side of the channel is shown in figure 25). Also connected with the erosional activity are the inclusions of shale fragmcnts in the arenaceous bed of the layer shown in Fig. 30. Sometimes some shale fragments are armoured by small pebbles, the same which lay ::.t the base of the turbidite which eroded and transported them. Moulds of such armoured shale fragments are visible in Fig. 29. In <<Arenarie Superiori >>

dendritic ridge casts and frondescent casts (Fig. 27 and 28) are also encountered.

BISMANTOVA SANDSTONES

by Gian Clemente Parea

It is only recently that Bismantova Sandstone formation has been described (PIERI 1961 ). Lithologically and sedimentologically it includes very heterogeneous rock all Middle to Lower Miocene m age. The Formation extends from the Asti basin almost to Bologna. Downwards Bismantova Sandstone grades to Antognola Marls and it is covered by Tortonian mari an d day (P IERI 1961) where it is possible to observe the transition. So far the paleogeographic situation of Bismantova Sandstone in not clear; we only know that i t li es in regular deposition over the allocthonous calcareous flysch of the eugeosyncline.

This paper deals with the thick slab of Vetto d'Enza belonging to the said formation. In this outcrop the facies is clearly turbiditic and shows some interesting features. Graded layers, varying in thickness from two centimetres to severa! metres, are grey coloured and become considerably lighter

by weathering. The lower part of each layer is a sandy calcarenitc and the top a marly-silt or silty pelite. The noncarbonatic part is micaceous quartz-fddspar and carbonates havc both an inorganic and an orgamc ongm.

; 1- - ~ r ~ l ~ 1 < l LITHOCOGY Z .

1 ~ l 8

CASTS

l • l L) l 1/ù

l i

~l!

i l

! .••• l· ... l"· .. ·.-. r .. . l ... .

. .

Il • 1/ .

. . .... 1 il ~·~..L ...L..

1- ·.· _·. l

l_,_.__._ • ..!..

Il·:~:. ·_J_·!..J....~· .... ...... . . l-'- ...1... _..L

i •••••

Il·~·~"'-. . l. • •

l • • ~ ~-'-

••• • •

l l ........

l '----+-+----+---1 i 1 11' 100 ~.~

18' lhO

18 90 : i' .·.·.· 19 90 ~~ ;, w 19 100 il ·········--

l~ l . l

\ l !

:o:

l l

FIG. 31 - Bismantova Sandstones; detail of log no. 47 Vetto, surveyed in a risedimented member (Langhian in age). The difference in sedimentary features between risedimented layers and normally sedimented

pelagic ones is clear.

- Arenarie di Bismantova; dettaglio del log n. 47 Vetto campionato in un membro risedimentato di età langhiana. Risulta evidente la differenza delle caratteristiche sedimentologiche fra gli strati risedimentati e

quelli di normale sedimentazione pelagica.


FIG. 32 - Bismantova Sandstones. Grain-size frequency distribution of 10 samples from Vetto log (no. 47). Samples 1 and 2 were collected from layer no. 1, sample 3 from layer no. 5, samples 5 to 8 from layer no. 14 an d sample 1 O from layer no. 18. Samples 4 and 9 were collected from pelagic beds. Size-frequency distributions of samples 1, 2, 3, 6, 7, 8, 10 from a, b, c, d intervals of layers occupy the same narrow strip of the diagram. This is probably due to the pre-analysis acid treatment which dissolved all calcareous grains of the samples. The frequency distribution of sample 5 (e interval) is very dose t o tha t of samples 4 and 9 (pelagic sediments) and together are distinct from ali the others.

-----Ta

-- Tbcd

················· Te _. -·- _ pelagico

80

50

20

5

%

- Arenarie di Bismantova. Nel diagramma sono riportate le distribuzioni di frequenza granulometrica di 10 campioni prelevati dall'affioramento in cui è stato campionato il log Vetto (n. 47). I campioni 1 e 2 sono stati prelevati dallo strato n. 1, il campione 3 dallo strato n. 5, i campioni dal 5 all'8 dallo strato n. 14 ed il campione 10 dallo strato n. 18. La distribuzione di frequenza granulometrica dei campioni 1, 2, 3, 6, 7, 8, 10 prelevati dagli intervalli a, b, c, d, di diversi strati, è caratterizzata da curve concentrate in una ristretta fascia del diagramma. Questo è probabilmente dovuto al trattamento con acido cloridrico, cui è stato sottoposto il campione prima dell'analisi, che ha dissolto tutti i granuli di origine carbonatica. La distribuzione di frequenza del campione 5 (intervallo e) è molto vicina a quella dei campioni 4 e 9 (sedi-

menti pelagici) e si distingue nettamente dalle distribuzioni di frequenza di tutti gli altri.

On the whole, the carbonate content, which doesn't considerably decrease from hottom to top, ranges from 30% to 50%. Near the surveyed log an d in other outcrops of the V etto slab, ftute casts prove a supply of sediments from W-NW. In the slab of Bismantova Sandstone concerncd thc following log has been surveyed: log 47 Vetto, on the Southern side of the spur carrying the bridge over the Enza, NW of Vetto. On the right bank, above a cart track going from the head of the bridge to the nver bed (Sheet 85 -II NE).

In the outcrop studied and in other nearby outcrops casts of organic burrows were frequently encountered on layer sole as well as some groove and ftute casts mainly in rather thick layers.

Fig. 31 is a detailed representation of a portion of the surveyed section. The most interesting feature peculiar to Vetto turbidites is the presence of calcareous pelitic layers rich in Pteropoda and fairly rich in pelagic Gasteropoda alternating with turbiditic graded layers. These layers were also examined and discussed during a field survey with Prof. L.M.J.U. van Straaten who, comparing them to analogous layers observed in cores sampled from the Adriatic sea-ftoor, considers them to be due to normal pelagic deposition. This interpretation is also supported by the sharp difference of lithofacies, between these beds of Pteropoda marls and the pelitic interval of the underlying

Frc. 33 - Bismantova Sandstones. Burrows traversing severa! layers as straight cylinders of nearly 1 cm diameter. Normally sedimented pelagic beds are marked by P and the numbers correspond to turbidite layers ofVetto log (no. 47). The longest burrow traverses at least two pelagic beds and two interbedded turbidite layers and cannot therefore be interpreted as an << escaping burrow >).

- Arenarie di Bismantova in cui sono visibili tane di vermi; le tane, cilindriche e del diametro di 1 cm circa, sono rettilinee ed attraversano più strati. Gli strati dovuti a normale sedimentazione pelagica sono contrassegnati con una P ed i numeri corrispondono agli strati per torbida del log Vetto (n. 47). La tana più lunga attraversa al minimo due livelli pelagici e due strati torbiditici; quindi non può essere interpretata come una escaping burrozv.


turbidite. Moreover, the thickness of these pelagic layers, which in the surveyed log ranges between 2.5 and 17 cm, changes quite independently of the thickness of the contiguous turbidity layers, while inside these layers the thickness of the pelitic bed is always roughly proportional to that of the arenaceous one. Even grain-size analysis of the insoluble residue shows that in the pelagic layers grains are finer than in the pelitic interval of the turbidity ones (Fig. 32).

Vetto Flysch is, up to now, the sole turbidite formation in the Northern Apennines where marly beds of normal pelagic deposition interbedded between resedimented layers are clearly recognizable. In the outcrop concerned burrows are present crossing the layers in ali directions. Sometimes it is possible to follow the same burrow through three or more layers, for a considerable sediment thickness, as shown in Fig. 33. In Fig. 32 the grain-size frequency distributions concerning a, b, c and d intervals do not group in distinct areas. This can be easily explained if one takes into account that in Vetto Turbidites the coarsest grains are essentially calcareous and that they are not present in the grain-size analyses having been destroyed by the acid attack. Only the e interval grain-size frequency distribution stands out from the others and this can be easily explained if we consider that in the finer parts limestone is more rare or is present in grains having the same size as the silty ones. It is worthy of note that pelagic pelite is finer grained than the e interval of turbiditic origin and their grain stze frequency distributions are very similar.

<<MACIGNO))

by Giuliano Fierro - Gian Clemente Parea

<< Macigno )) is a thick arenaceous turbidite formation very widespread in the Apennine Chain. It outcrops essentially along the highest part of the chain, but also in some areas west of the Apennine watershed and along the Tyrrhenian coast. Eastward <<Macigno)) grades into pelagic multicoloured shales while the materia! to which it grades along the other edges is not known. The age of this Formation, mainly based on macroforaminifera, is essentially Oligocene. Downwards << Macigno )) changes to pelagic shales with big lenses of calcareous turbidites: << Scisti policromi )) interbedded. Upwards <<Macigno)) grades to a

similar turbi dite formation of Lower Miocene age: Mt. Cervarola Sandstone.

<< Macigno )) is usually grey coloured with brownish or reddish shades only where it is deeply weathered. << Macigno )) in the first stage of the thick turbidite arenaceous filling up of the Apennines miogeosyncline above the discontinuous calcareous turbidites of << Nummulitico )) interbedded with << Scisti Policromi )) shales. Thick layers of coarse-grained sandstones outcrop along the Tyrrhenian coast; they are either graded only in the upper part or lack any grading at ali. It must be assumed that these layers were originally caused by fluxoturbidites and by submarine slidings more than by actual turbidites. Often these thick layers are interbedded with successions of layers usually less than 20 cm thick, fine-grained also at the base. Fine-grained layers of this type often occur in the upper levels of <<Macigno)), which were defined by GHELARDONI, PIERI and PIRINI (1965) as the << Macigno siltoso-arenaceo )) unit to distinguish it from the more purely arenaceous unit of <<Macigno propriamente detto )). For the latter the above mentioned Authors indicate a very high sand/ clay ratio, aro un d the value: 8. Two of the surveyed logs can be ascribed to << Macigno siltosoarenaceo )): Punta Ala log (no. 52) (Field survey by G.C. Parea) and Riomaggiore log (no. 50) (Field survey by G. FIERRO). In the latter locality two holistostroms with calcareous fragments have been found. Similar holistostroms can be observed in the whole << Macigno )) formation and, according to GHELARDONI, PIERI and PIRINI (1965), there is a leve! of these materials at the transition between the two above-mentioned << Macigno )) units. The sand-day ratio in Riomaggiore is 3.5. In << Macigno)) carbonized plant fragments scattered on lamination palnes are rather frequent. Turbidity currents which supplied the sediments to this Formation carne from NW (TEN HAAF, 1959).

The lower part of each layer consists of a quartzfeldspathic micaceous sandstone nearly lacking calcareous clastics and rich in silty-clayey matrix which cements it. According to CIPRIANI (1964) quartz in this formation has mainly a metamorphic ongm and plagioclases are very acid. Among heavy minerals (GAZZI, 1961; MEZZADRI, 1964) garnet is prevalent; epidote, titanite, rutile, tourmaline, zircon are also rather frequent. The top part of each layer, when it has not been eroded by the subsequent turbidite, consists of silty pelite. Carbonate content is usually very low (lower than 10%) but in some zones (as for instance on Mt.


Zuccone or W and NW of La Spezia) carbonates can reach 20-30% (MALESANI, 1966).

From E towards W the following logs have been surveyed in << Macigno >> (l): log 53 Valle delle Tagliole (G.C.P.), along the road that climbs from Pievepelago along the Valley of the Tagliole, at the point at which it crosses the 1000 m contour line. (Sheet 97 - Tav. IV SE); log 51 Populonia (G.C.P.), on a small slope above the parking area at the entrance of Populonia village, SW of the castle tower. (Sheet 127 -Tav. IV NW)

log 49 (layers 13-18) Mulattiera Vernazza-Corniglia (G.F.); over Vernazza beach, coordinates 32 TPN 54878724. (Sheet 95 - Tav. III NE); log. 49 (layers 19-26) Molo di Vernazza (G.F.), coordinates 32 TPN 54628728 (Sheet 95 - Tav. III NE); log 48 Vernazza (G.F.), on the subway under the road bordering the coast, coordinates 32 TPN 54698825 and 56508896. (Sheet 95 - Tav. II NW).

From the logs surveyed by G. C. PAREA the prevalent sequence is seen to be T (c-e); T (b-e) is sometimes found in thicker layers; T (d-e) and

95

FIG. 34 - << Macigno >> Formation. Size-frequency distribution of eleven samples collected from the layers surveyed in log no. 53. Samples 11, 12, 13 were collected from layer no. 2; sample 14 from .;"' .- · --·:::-

~§~ 1f!tt~~j~J~~ ///:;;Jj[~!:;~~;::,o••···· 80

50

come from a interval; samples 1 1- 1 1 .-;:· 12, 13, 14, 17, 18, 19, 20 come l/ l 1 l .. ;:·

from c interval and samples 1 11 11/1/ .··.· .... :::/ 11,16 from e interval. Grain- 1 size frequency distribution of 1 l l 1 l Il 1 1

T o

20

samples from each interval tend 20/ l l 1 11 /,/ . d" . f /; 11 ,/,:

--- -- Te

-------·----------- T e 5 to group m Istmct areas o uv l 11 1; i/ the diagram. The partial over- 21 l 1 l . l . f h d" "b . f 19 l /J17 ,/.:' appmg o t e tstn utwn o / samples from a and c intervals 15 14/ J n/:' % should be due to the presence ,_ __ ,__ ___ ,___...:.13:::...1.__:11:.:_2 -~:'--,:16:____---+--------+--------+-------+------+------' 0,4 of a large quantity of fine 95 3 5 6 7 a 9 10

matrix in the a interval. - Distribuzione di frequenza granulometrica di 11 campioni della Formazione del <<Macigno>> (log 53). I campioni 11, 12,13 sono stati prelevati dallo strato n. 2; il14 dal n. 4; il15 dal n. 5; il16 e 17 dal n. 6; il18 dal n. 9; il19dal n. 10; il 20 dal n. 13. I campioni 15 e 21 provengono da intervalli di tipo a; 12, 13, 14, 17, 18, 19, 20 da intervalli di tipo c; 11 e 16 da intervalli di tipo e. Le distribuzioni di frequenza di campioni da ciascun intervallo tendono a raggrupparsi in fasce ben definite del diagramma ed il parziale sovrapporsi delle curve che si riferiscono agli intervalli a e c potrebbe es-

sere dovuto ad una notevole percentuale di matrice fine negli intervalli gradati.

log 52 Punta Ala (G.C.P.); on the small rocky wall immediately below the end of the path running towards the tip of Punta Ala towards the reefs called << Porchetti >> (Sheet 127 - Tav. II NW); log 50 (layers 1-8) Spiaggia di Riomaggiore (G.F.), coordinates 32 TNP 59128327. (Sheet 95 - Tav. II NW). log 50 (layers 9-25) Riomaggiore (G.F.), Strada dell'Amore, coordinates 32 TPN from 58928350 to 58808350. (Sheet 95 - Tav. II NW); 54698825 and 56508896. (Sheet 95 - Tav. II NW). log 49 (layers 1-12) Spiaggia di Vernazza (G.F.), coordinates 32 TPN 54778720. (Sheet 95 - Tav. III NE);

(1) The piace name is followed by the initials of one of the two Authors who carried out the field survey.

T (a-e) are rarer. The Vernazza and Riomaggiore logs (in layers which can be related to << Macigno siltoso-arenaceo >> of GHELARDONI, PrERI and PrRINI (1965) show that out of 152 layers showing convolute laminations T (c-e) was present in 67%, T (b-e) in 15%, T (a-e) in 6% and T (e) in 4% while T (d-e), T (b-e) and T (a-c) were present in percentage values lower than 3%.

A statistica! investigation on sequence thickness for the frequency classes 0-2-4-10-20-40 cm indicated that the more frequent sequence thickness is between 1 O an d 20 cm. A similar investigation carried out on the thickness of the single intervals (following the geometrie progression at the rate of 2: 1,2,4,8, ... ) showed that c-interval is most often 2-8 cm thick; d-interval, which after c occurs most frequently, is most often 4-8 cm thick. Cur-


rent marks on the sole of thin layers are, on the whole, not very frequent. Casts of burrows are more frequent.

Grain-size analyses have been carried out on some samples of macigno collected in the Tagliole log (no. 53). By examining Fig. 34 it is evident that the grain-size frequency distributions concerning intervals a, c and e tend to group in distinct areas. The areas of a an c intervals partially overlap each other for the fraction finer than 6 <l> and this is clearly due to the presence of fine matrix in a interval. The largest grain in the c is less than 2<1>; this agrees with what is stated in literature.

<< PIETRAFORTE >>

by Gian Clemente Parea

<< Pietraforte >> is a turbidite formation of which only scattered slabs are known, outcropping mainly in Tuscany and partly in the surrounding regions. Outside the peninsula the arenaceous flysch of the Isle of Elba (P AREA 1964) can be considered part of this formation. Since it normally appears in isolated outcrops, it is impossible to observe in the field the lateral transition to coeval formations. On account of sedimentological and paleogeographic data (PAREA 1965) it can be assumed that the << Flysch a Helminthoidi >> deposited East of << Pietraforte >>. Along its Western edge this formation should grade to pelagic shales, rich in thin resedimented layers to a greater or lesser extent. Such shales are known to form a part of the allochthonous cover. The formation to which << Pietraforte >>

grades Northwards and Southwards are unknown.

Upwards this formation grades (BoRTOLOTTI 1962) to red pelagic silty shales and downwards to silty shales locally rich in arenaceous and calcareous sedimented layers. This formation is Upper Cretaceous in age (BORTOLOTTI 1962). <<Pietraforte >> is dark grey coloured changing to brown when weathered. Sandstone is formed by rock fragments, quartz, feldspar and calcareous clastics of both organic and inorganic origin. Mica is very poorly represented. Carbonates, on the whole, are about a third of the total clastics and about half of them consist of dolomite (CIPRIANI an d MALESANI, 1966). Carbonate percentage is considerably lower in the pelitic intervals. Among quartz grains those of metamorphic origin prevail and among feldspars acid plagioclases are prevalent (CIPRIANI and MALESANI 1966).

<< Pietraforte >> deposited in the Western part of eugeosyncline of the Apennines (PAREA 1965) and at present it outcrops discontinuously inside the allochthonous cover which covered the myogeosyncline deposits.

Turbidity currents which supplied sandstone strated from the Western edge of the through from an area which should be roughly located between present Sardinia and Corsica (PAREA 1965).

In << Pietraforte >> the follo"'ing logs were surveyed: log 56 Barrigazzo, rocky slope above the State Road of Abetone and Brennero, at Km 115.400 (Sheet 97 - Tav. IV NE);

log 54 Castel di Casio, slope above the Limentra Valley road which runs from Savignano to Suviana a t Km 5.800 (Sheet 98 - Tav. III NW);

log 55 S. Felice a Ema, front of a small disused quarry above Villa Cremoncini East of S. Felice a Ema village (South of Florence). G. Silvani Street no.s 153-157 (Sheet 106 - Tav. II SW); log 57 Rio Fiume, front of a quarry above the road running from the coast to the village of Tolfa along the valley of Rio Fiume, where the road crosses the 50 m contour line (Sheet 142 - Tav. II SE).

From the logs surveyed and from observations carried out on most of the outcrop area of this formation a considerable uniformity of grain size was observed in the arenaceous bed of layers. It is mainly a question of fine and very fine Sandstone with a smaUer number of layers with a mediumgrained sandy base. A certain number of clearly conglomeratic layers (the finest varieties are called Cicerchina), caused by turbidite and fluxoturbidite deposits, are typical of this formation. Another feature differentiating this formation from the other arenaceous Flysch of the Northern Apennines are the exceedingly fine grains at the top (often consisting of day) of graded layers. In particular, only in the Barigazzo log is the upper most part of each layer formed by silty pelite while in the other 3 logs layers with a clayey top are frequent or prevailing.

Such clayey levels could even represent the normal pelagic deposition in the interval between two turbidites. So far no evidence has been found in favour of such a hypothesis whereas various points of view suggest that these clays are of turbiditic origin (PAREA 1965).

In ali the surveyed logs there are layers one or two centimetres thick, interbedded with other thick or very thick layers.


In Pietraforte casts of organic marks on the sole of layers are very frequent and casts of inorganic marks are also rather frequent.

In outcrops where S. Felice a Ema and Rio Fiume logs were surveyed one can see the very clear latera] transition from single arenaceous

FIG. 35- << Pietraforte >>Formation, layers fmm 2 to 15 of Rio Fiume log (no. 57). A single thick layer on the right side of the photograph takes the piace of layers 7, 8, 9 and 10 which are distinctly visible on the left side (only layers 7 and 1 O are actually visible because of the perspective). The single thick layer shows a fairly visible repeated grading (indicated by the dotted line) and it is clearly due to a !oca! deep erosion of the turbidite which deposited layer

no. 7.

ceous material of the underlying turbidite is only a local phenomenon due to the erosion exerted by the overlying turbidite before it stoppcd (Fig. 35). In the disused quarry of S. Felice a Ema there are other strange structures as well: groove casts as thick as the total thickness of the arena-

- Formazione della << Pietraforte>>, strati dal n. 2 al n. 15 del log Rio Fiume (n. 57). Sulla destra della fotografia un unico potente strato rimpiazza gli strati 7, 8, 9 e 1 O; di questi sono visibili a sinistra sulla foto soltanto il 7 e il 1 O a causa della prospettiva. Nel banco più potente si ha gradazione ripetuta (linea punteggiata) dovuta ad erosione da parte della torbida che ha deposto

lo strato n. 7.

layers with repeated grading to couples of normally graded layers. In such examples it is evident that the coarse-grained arenaceous bed overlying the finer-grained arenaceous one (within what can firstly appear as a single layer) is nothing but the lowermost bed of a layer deposited by another turbidite. The lack of pelitic or very thin arena-

FIG. 36 - << Pietraforte >> Formation, layer surveyed in log no. 55 S. Felice a Ema. Two layers show unusually deep groove casts in respect to the thickness of the layer itself. A possible explanation is that the grooving were made by a big turbidity current only the tail of which was responsi-

ble for the casting.

- Formazione della << Pietraforte >>, log n. 55 S. Felice a Ema. Due strati mostrano groove casts molto profondi in relazione allo spessore totale dello strato. Una possibile spiegazione può essere che le impronte furono scavate da una corrente di torbida di notevoli dimensioni e di cui si è sedimentata, in quel punto, soltanto la coda.

ceous bed of the layer in which they occur and even more(figg. 36 and 37). It is quite clear that tool marks 9-10 cm thick must have been caused by objects too big to have been transported by turbidity currents so limited in thickness as to deposit sand beds 2-11 cm thick, as can be seen in the outcrop under consideration.

SEDIMENTOLOGICAL CHARACTERISTICS OF SOME !TAL/AN TVRBIDITES 377

FIG. 37 - Detail of ;fig. 36. The two deep groove casts supporting the hammer belong to a thin layer, the a interval of which is better visible on the left of the

photograph.

- Dettaglio della fig. 36 in cui si notano due profondi groove casts alla base di uno strato notevolmente sottile. L'intervallo a di questo strato è visibile sulla sinistra della

fotografia.

different grain-size intervals. Besides the medians, whole grain-size frequency distribution develops in distinct areas of thc diagram, the coarsest tail excepted. But the overlapping of the coarsest classes of the different samples is only apparent since we must consider that in << Pietraforte >> the coarsest clastics are mainly calcareous and therefore were destroycd by thc acid attack which was used to disintegrate the rock before grain -size analysis.

In figure 38, thercfore, the grain size frequency distributions which ref!ect the actual sedimeRt closest are those concerning the e interval while the others should have a coarse tail more to the left. It is evident that parallel tansverse and convolute laminations are found together in sediments belonging to the grain-size classes of fine sand and silt in accordance with what was observed in all pre-oligocene Flysch of Central-Northern Apennines (P AREA 1961 an d 1961 b).

FIG. 38 - << Pietraforte >> Formation. Grain-size frequency distribution of 9 samples from Barigazzo log (no. 56). Samples 22, 23, 24 were collected from layer no. 2, 4, 6, respectively; samples 25,26 from layer no. 9 and samples 27, 28, 29, 30 from layer no. 14. The grainsize frequency distribution of samples from c, d and e intervals tends to develop in distinct areas of the diagram. The partial overlapping of the << coarse tail >> of the grain distribution of ali samples is clearly due to the pre-analysis acid treatment which dissolved ali calcareous grains (which represent a part of the coarsest fraction in these samples).

r-----------------------------------------------,95 -----;:;~-::::::--- --_....::::= -- ~~~-- ,.-?---- / .;::::"~~-- /

-~- ....... ....- / ~~..-::::--- ,........,...-_,_~ -------- / ....-~:;;.-- ........... _........ /

/ --;j§:::/ / / -- :·:<---//i'/ / / ,·'/

/~;~> ></; // ;;f;' --'

l l l l //' / 24/ l~ 1·'/ (---

1 l ... f l l /1 --;· l l; //

- Distribuzione di frequenza 30/ 1ft :l l granulometrica di 9 campioni l 'Jf2s//h.81 prelevati dalla stessa serie in 29/i/ :'27 46

----Tcd

---------------Te

80

50

20

5

% cui è stato campionato il log //'22 Barigazzo (n. 56 - Formazione '-::----'2=3=-+--(---+----+----+-----+-----+-----+----~0,4 della << Pietraforte >>). I campioni J25 3 4 5 6 7 8 9 10 22, 23, 24 derivano, rispetti-vamente, dagli strati n. 2, 4, 6; i campioni 27, 28, 29, 30, dallo strato n. 14. Le curve relative ai campioni derivanti dagli intervalli c, d ed e tendono ad occupare zone diverse del diagramma e la parziale sovrapposizione delle code grossolane delle curve è dovuta, probabilmente, alla disgregazione del campione in acido. Questo tipo di attacco ha ovvia-

mente distrutto i granuli di origine carbonatica che costituiscono una parte della frazione grossolana.

This fact can be explained assuming that each thin layer with the big groove casts is only the « tail >> of a large turbidity current. The nose of such a current should therefore be able to transport objects whose size was sufficient to produce thick tool marks, which the << tail >> of the turbidite itself would then have covered with a thin layer of sediment. From Fig. 38 it can clearly be seen that the medians of grain-size frequency distribution of the samples of c, d and e intervals occur in three

<< MARNOSO-ARENACEA >>

by Gian Clemente Parea - Antonio Rizzini

The << Marnoso-Arenacea >> Formation consists of a succession of arenaceous turbidites up to 3,000 m thick (RrzziNI and PASSEGA, 1964). It outcrops on the eastern side of the Apennine Chain from round about Santerno Valley up to Marche (MERLA 1951, SELLI 1954). The Formation, along the


eastern border of its outcrop area, gradually changes to Schlier facies (marly formation with thin calcareous-silty alternations) or i t disappears, dipping under younger formations. Its southern border is not well known; N orthwards an d W estwards << Marnoso-Arenacea >> is limited by faults and overthrustings. Dating of this Formation, based on scarce and badly-preserved fossils found in the pdùic intervals of layers, is essentially Helvetian. The base of the Formation, in the few spots where it outcrops, lies on day whose age ranges between Oligocene and Lower Miocene. Upwards << Marnoso-Arenacea >> changes to scarcely cemented sandstone, with few, if any, pelitic alternations, and then to day and to Messinian gypsum.

The << Marnoso-Arenacea >> Formation is the last stage of the filling up of the Apennine miogeosyndine due to turbidite and presently belongs to the autochthonous backbone of the Chain itself.

The following logs have been surveyed in << Marnoso-Arenacea >> (l): log 64 Santa Margherita (G.C.P.), on the northern slope of the short road-cutting near S. Margherita church (altitude 420 m) in which the road runs from Fontanelice (Val Santerno) to Casola val Senio (Sheet 99 - Tav. IV SW); log 63 Passo della Sambuca (G.C.P.), along the rocky wall overhanging the road which climbs from Palazzuolo sul Senio to Passo della Sambuca a t Km 6.450 (Sheet 99 - Tav. III SW); log 62 Casaglia (G.C.P.), on the edge of the slope overhanging Casaglia cemetery, west of the junction of the mule track dimbing from Casaglia to the ridge of Mt. La Faggeta with the northbound mule track, or, as it is later, path, to Le Fogare (Sheet 99 - Tav. III SW); log 65 Passo dei Mandria/i (G.C.P.), about 100 m away from the Mandrioli Pass along the rocky slope above the road that runs down from the pass towards Bagno di Romagna (Sheet 107 -Tav. II NE); log 59 Bargi (A.R.), in a country road joining the Bargi-Castiglion dei Pepoli road 500 m from Bargi, a t the foot of the hill where the church is located; log 60 Firenzuola (A.R.), along the Santerno Valley, on the road Imola-Firenzuola, at Km 30; log 58 Castel del Rio (A.R.), along the Santerno Valiey, on the road Imola-Firenzuola, l Km west of Castel del Rio; log 61 S. Angelo in Vado (A.R.), along the Me-

(1) The piace name is followed by the initials of one of two Authors who carried out the field survey.

tauro river-bed, 500 m west of S. Angelo in Vado viliage, up to the Forestry Commission seeding nursery.

The sedimentological homogeneity of the Formation is evident from ali surveyed logs and from field observations carried out on ali the formation outcrop area.

The colour of the Formation is generally grey, lighter when weathered. The lower part of each single layer consists of a quartz-feldspar micaceous sandstone and of a smalier quantity of calcareous dastics either of organic origin or not. This sandstone contains a fair percentage of marly matrix which cements it. According to CIPRIANI and MALESANI (1963) quartz in this Formation is mainly of magmatic origin, plagioclases are acid and among carbonates dolomite is present. Among heavy minerals garnet, epidote, staurolite, tourmaline an d rutile ( G AZZI 1961) are frequent.

The top of each single layer ( except when i t has been eroded by subsequent turbidite) is composed of silty marly pelite.

Carbonate content is quite high (about 20-30%) both in the coarse and in the fine parts of the layers. In << Marnoso-Arenacea >> carbonized plant fragments scattered on lamination planes are very frequent. Sometimes one can find flattened fragments of lignite whose length may reach and even exceed 10 cm.

Turbidity currents which form << Marnoso-Arenacea >> run along the basin from N-W towards S-E (TEN HAAF 1959). The supply probably carne from N-W as weli as from W; anyway, a smali part of turbidites also carne from S-E (PAREA 1967 h). The materials from S-E can also be identified by the almost complete lack of mica and because they are rich in microfossils and calcareous clastics. << Marnoso-Arenacea >> is one of the more classic turbidite series (SIGNORINI 1943, TEN HAAF 1959). Only by taking into account the whole region it is possible to observe a northward and westward increase of the thickness of sandstone beds and, to some extent, of the grain size of sediments. Towards South-East it is mainly built up of mari interbedded either with very thin silt layers or with fine-grained sandstone. This agrees with the direction of turbidity currents which originated the deposit. In this Formation casts of both inorganic and organic marks are frequent at the sole of layers. Inside the layers burrows of animals are rather frequent.

In generai, in << Marnoso-Arenacea >>, as in ali turbidite formations, the outcrops have a typical


FIG. 39 - A typical outcropping of layers in the upper part of « Marnoso-Arenacea >> Formation. Black lines indicate layer limits. The lower parts of severallayers are very poorly cemented and do not protrude at ali. Layers 3 to 14 from S. Margherita log (no. 64).

- Affioramento tipico della parte alta della <c Marnoso-Arenacea ». Le linee nere indicano ;, limi.ti fra i diversi strati. Molti di essi sono caratterizzati da una scarsa cementazione dei livelli inferiori e generalmente non presentano impronte di carico sulla superficie inferiore di strato. La fotografia rappresenta gli strati dal n. 3 al n. 14 del log S. Margherita

(n. 64).

saw-edged section due to the fact that the sandy bed of each layer projects outwards in respect to the shaly one which is more easily weathered. This, however, does not occur in the outcrops along the eastern border of the outcrop area of << MarnosoArenacea >> where the top of the formation outcrops. A clear example of this way of outcropping is the S. Margherita log (Fig. 39). In this outcrop the finer arenaceous beds are often better cemented than the coarser one so that the greater projection can occur in the middle or even in the higher part of each single layer, which, nevertheless, can always be very well distinguished by means of grading.

In almost all logs studied is a certain number of very thin layers, 1-4 cm thick, which can be easily identified and which have a lower bed of

fine or very fine-grained sandstone and a top bed generally of silty pelite. Up to now it has been impossible to ascertain whether they are the extreme border of a normally thick turbidite or very thin turbidites originated by the sliding of small quantlttes of sediment. Recently P AREA

(1967 a) stressed the existence of a kind of raw lamination within the bedding plane of medium -to coarse-grained layers (Fig. 40).

In this structure (which P AREA, 1967 a, suggested calling << pseudolamination >>) single laminae do not differ in grain size like true laminae of the Tb-d sequence but are separated by very thin muscovite veneers and can be distinguished only under the microscope or on deeply weathered surfaces.

This << pseudolamination >> may be parallel, crossed or convoluted like the normal lamination in

FIG. 40 - <c Pseudo-lamination >> in the a interval of layer no. 7 from Casaglia log (no. 62), <c Marnoso-Arenacea >> Formation. The thickness of the '' pseudo-laminae >> is rather irregular and they are clearly seen on the cross-sections of thc b=d, h~cause of the weathering of thin veneer of mica

between them.

- Pseudolaminazione nello strato n. 7, intervallo a, del log Casaglia (n. 62 - <c MarnosoArenacea >>). Le pseudolamine sono irregolari e risultano evidenti a causa dell'erosione che ha asportato i livelletti micacei interstratificati fra le lamine.

380 A. ANGELUCCI, E. DE ROSA, G. P/ERRO, M. GNACCOLINI, G.B. LA MONICA, ecc.

T b-d types of T a-e sequence defined by BouMA (1962). Thus in the coarse lower part of some layers a sequence can develop of a1 az a3 a4 intervals of which only a1 actually lacks structures while az a3 a4 correspond to b, c and d of the normal sequence.

Although the two sequences of structures are normally found in the same layer they cannot be consiàered a repetition of the same sequence because the normal laminae differ greatly from the << pseudolaminae >> in thickness and in the grain size of the sediments in which they occur.

Bargi outcrop is built up by big sandstone layers (up to 4-5 m thick) interbedded with very thin pelitic layers which are sometimes reduced only to stratification (Fig. 41 ).

j /o l <>40:~~~ 1 1

= l i ----'- _._

l

~y. l•~l

l l i

'l l

l-'--......_ ...J...._

; _.____.___ _:- __.___ ~ c;çJ

i.~~~~---, ....

••• l

l

... l ... •' ... , .... ( ...

l• •••

l

l ' l l

l '

l

l !

' l l

l l

i

i l • ' l i

FIG. 41 - Log Bargi, an example of proximal facies sedimentation in the > Formation.

- Log Bargi. Esempio di facies prossimale della >.

m

2

l l l

l

'i l iJ l

f5 l : l 5 l

l l

l l • l

l l l l

• l

o 2

100 90 80

r l l l l l l l

l

•

l l l l • 3

70

• l

>-:"i u l

•

l l •

DIAMETER IN 0 7 8 9 10

0~ OF CLAY 40 30 20 10 o FIG. 42 - > Formation, log Bargi; grain size variation along the thickness of the sandy

bed of layer no. 2.

- Formazione >, log Bargi. Variazioni granulometriche all'interno del banco arenaceo

della sequenza n. 2.

The grain size of a interval of the layers is very uniform and grading is hardly visible. For instance, three grain size analyses carried out on layer no. 2 show that, on 240 cm (thickness of that arenaceous layer) the median decreases from 2.9 to 3.5 <l> and that the day increases very slightly; however in the middle of the layer these variations are barely observable and day is not at ali increased (Fig. 42).

It was noted that the grain size of these thick sandstone layers (which moreover show evident erosional structures o n the sole) does not exceed l mm. This fact should perhaps be related to the probable lack of coarse materia! in the sediments which contributed to turbidite deposition. It seems in fact quite improbable that turbidites such as these able to erode such a considerable channels in cohesive day and able to deposit, with one single turbidite, more than 4 or 5 m of sand, could not transport grains larger than l mm. Also the filling materia! of channels is not coarser than the one of the overlying bed as it normally occurs when the grain size exceeds 2-3 mm or pebbles are present.

Erosion channels seem to lack load deformations and are isooriented and parallel to groove casts present in layer l. Erosion channel width is rather variable ranging from a few centimeters


(layer 5) up to 50-60 cm (layer 2); their depth varies accordingly and may reach 30 cm. Erosion is not limited to thicker layers, also thinner ones show sometimes remarkable erosion features.

In Firenzuola log, sandstone is very cemented and in thicker layers vertical grading is not clearly distinct. In layer 19 (Fig. 43) this grading is very poor in the middle-lower part of the layer: the sample taken at the base is considerably less coarse - as mean - and clayey as the sample taken in the middle of the layer. The sample taken at the base, however, contains coarser grains as it has 0.02% of materia! exceeding l mm which was absent in the upper sample. Grading is distinct in the upper part of the layer. In thinner layers grading is more marked and regular (Fig. 44).

m r--------------------------------------.

4

i 3

i-

i l ()

Il l Q l ~ o l

l l

l

2 •

l

l l l l l

l l l l

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100 90 80

l

l

i

. l

l

z 51 IJJ ::; l

l

l \ \ \ \

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3 DIAMETER IN

70 '\, OF CLAY

0 7 8

30 20

9

. l l

• >- l d l

l l •

10

10

o

FIG. 43 - <1 Marnoso-Arenacea >> Formation, log Firenzuola; grain size variation along the thickness of the

sandy bed of layer no. 19.

-- Formazione <1 Marnoso-Arenacea >>, log Firenzuola. Variazioni granulometriche all'interno del banco arenaceo


m -;r-· ----y--------------,

/. ' . / / l

l l \ l

l 2 l

l

l l l ....

z l "' IJJ

"' fil IJJ z IJJ

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o 2 3 DIAMETER IN 9.1 7 8 9 10

1Q0 90 80 70 0 0 OF CLAY 40 30 20 10 o FIG. 44 - « Marnoso-Arenacea >> Formation, log Firenzuola, grain size variation along the thickness of the

sandy bed of layer no. 1.

- Formazione <1 Marnoso-Arenacea >>, log Firenzuola. Variazioni granulometriche all'interno del banco arenaceo


The thickness of sandstone layers is regular but, in sequence n. 17, within the pelite, thick sandstone lenses aligned to make a discontinuous layer (Fig. 45) can be observed. The discontinuity of this layer does not seem to be due to slumpings or to erosion. It rather seems that this layer was already originally a lenticular one, made of big isolated ripples. Inner cross laminations, is in agreement with ripple structure.

In the sampled outcrop, carbonized plant remains were found especially in finer parts of layers.

In Castel del Rio log, the transition between the graded interval and the laminated one of layer 23 is marked by current ripples very wide towards the base which become then much smaller (Fig. 46). Downwards trough laminae are about 30-40 cm wide, in the upper bed they are just a few cm wide while keeping the trough shape. These laminations do not show strong deformations but they seem to lie in their originai depositional position. This would imply that current ripples should have occurred as a consequence of erosion which should have irregularly eroded the upper part of the graded interval and might also have completely removed the interval of parallel lamination which lacks in the sequence.

Convolute laminations present in this outcrop are sufficiently developed but never show very


complicate convolutions. On the contrary, they often change to current laminations and in fact it is often difficult to establish wether they are current or convolute laminations.

Grading of arenaceous layers is very distinct. Grain size analyses (layer no 23) confirmed it. Here too, however, the mean of the sample taken at the base is smaller than the one taken in the middle of the layer. The sample taken at the base, however, contains the largest grains in the whole layer.

S. Angelo in Vado sequence is built up by a marly succession interbedded with thin very hard and compact siltstone (Fig. 47). In this outcrop laminae, rich in mica flakes, which allow an easy lamination of siltstone, are very frequent. Siltstone

Frc. 46 - Santerno River valley, in a quarry in the << Marnoso - Arenacea>> Formation, about 3 km far from Firenzuola. The photograph shows a fragment of coal sometimes found in these sediments.

- Valle del Santerno. Cava nella << Marnoso-Arenacea >> a 3 Km da Firenzuola. Frammento di carbone nella arenaria.

FIG. 45 - << Marnoso-Arenacea •> Formation, log Firenzuola, layer no. 17. The lenticular shape of a layer characterized by cross lamination is clear.

Formazione << Marnoso-Arenacea •>, log Firenzuola. Sequenza n. 17. Strato lenti colare

a stratificazione obliqua.

is made of quartz grains and of very angular carbonate fragments cemented by abundant carbonatic clayey cement. The matrix recrystallization is rather strong and it is therefore difficult to distinguish the actual size of carbonatic fragments as compared to quartz grains.

The thickness of sandstone layers is very regular and reaches at most 40 cm.

Siltstone alternations show very uniform features and almost completely lack markings on bedding piane. Layer surfaces are nearly always wavy because of the existence of current ripples on ali the layer thickness.

Current ripples are always well marked and often show deformations which stress the lenticular


l iu) 2300

i l

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~ i 'l l il l ~~~~~l i l 7 ,16)0 ~~~~!

l ....1......-'- l

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..u1 l_'-~'__,' _·_.__· ._·_' ---'--, <J_· _IY_'\-'-"L...A-, ~1 •• ~--~-l. _ _,_ __ Q

FIG. 47 - Log S. Angelo in Vado, an example of distal facies sedimentation in the << Marnoso-Arenacea » Forma

tion. - Log S. Angelo in Vado. Esempio di facies distale

della « Marnoso-Arenacea >>.

trend of laminae, and therefore very often change to convolute laminations.

The uniformity in structure types and the thickness of sandstone layers appears also in grain size composrtwn. Ali layers lack grains with a diameter exceeding 125 micron and also the thinner layers differ very little, from the grain size point of view, from thicker ones as they always have grains whose size exceeds 60 micron.

The arenaceous part of the layer no. l shows inner structures lying in a disordered arrangement; at the base and at the top parallel laminations are present while the middle part lack structures. This arrangement could be regarded as due to two turbidites lying o ne o n the other; the grain size analysis however stresses a vertical regular graded bedding and therefore we do not think it

necessary to divide the layer in two separate sequences. It is perhaps more logical to think that the middle part is related to an interval where parallel laminations are not clearly visible or that this interval is a lamina of anomalous thickness.

<<ARGILLOSO-ARENACEA FORMATION 1> IN THE LAZIO-ABRUZZI APENNINES

by Antonello Angelucci - Giovanni Battista La Monica

Two flyschioidal formations, Middle and MiddleUpper Miocene in age, wère studied in centrai Italy: l) << Argilloso-Arenacea Formation 1> (Tortonian) which represents the southern part of the formation described by RIZZINI and PAREA, 2) Calcarenitic turbidites (Langhian-Helvetian). The former, widespread in centrai Italy (AccoRDI, DEVOTO, LA MoNICA, SIRNA and ZALAFFI, 1967), were studied in detail in three areas: Carseolani Mts., Aterno River Valley and Frentani Mts. The latter formation, which crops out in a more limited area, has been studied by G. B. LA MoNICA in Frentani Mts. (pag. 388).

<<Argilloso-Arenacea Formation 1> overlies m

generai, a clayey-marly sequence, Helvetian in age, under which a Langhian-Helvetian organogenous limestone is found. In Frentani Mts. area, on the contrary, <<Argilloso-Arenacea>> overlies calcarenite, described in the following chapter.

In generai, the top of the formation lacks throughout centrai Italy. There are some areas in which flyschioidal series are covered by other sediments, either arenaceous (Torrice - LA MoNICA 1967), or clayey-arenaceous (Monte S. Giovanni Campano - CoMPAGNONI 1964, AccORDI 1964) or conglomeratic (Broccostella near Frosinone).

It is very difficult to date these sediments and therefore it is hard to establish when the sedimentary cycle ended. It is to be noticed, moreover, that towards the Thyrrenian sea gravitative landslides with the slumping characteristics of <<argille caotiche 1> were found interbedded or sometimes overlying the flyschioidal formation; microfauna therein contained may lead to ascribe them to Upper Miocene-Lower Pliocene (ANGELUCCI, DEVOTO and FARINACCI 1963).

<<Argilloso-Arenacea Formation >> in central Italy is made up by sandstone and interbedd'::'d marly shale mainly sedimented by turbididity currents. Formation thickness seems to decrease from NW towards SE while the sandy beds are thicker and


coarser on the Thyrrenian side than on the Adriatic one. The direction of currents was, in generai, from NW towards SE (ANGELUCCI 1966) even if different directions were ascertained in some areas.

Structural relations and tectonics of this formation have been recently dealt with by many papers on a regional level (AccORDI 1966, PIERI 1966). It resulted, also on the basis of deep drillings carried out by AGIP, that Cenozoic formations, together with Mesozoic calcareous sediments on which they generally lie by means of the wellknown Cretaceous-Miocene transgressive overlapping, were pushed by tectonics in such a way to give large submarine landslides during Lower Pliocene.

In Aterno River Valley, two logs (nos. 66 and 67) have been surveyed by ANGELUCCI; they are respectively 540 cm and 1,647 cm thick. Probably log 66 represents the lower part of the outcropping series. In the sheet 146 (tav. I SE) the location of the two logs is the following:

log 66 Valle il Fossato, 42° 14' 02" lat. N, 13° 52' 12" long. E;

log 67 C.le Viduno, 42° 13' 49" lat. N, 13° 52' 38" long. E (fig. 48).

It was possible to ascertain that these series consist of marly sandstone and interbedded clayey marl. Sediments are generally poorly sorted but they are graded; the calcareous cement percentage is largely variable in the different layers. Grain size frequency curves are very skewed towards finer fractions. In log 67 it is possible to notice that clayey marl beds in the lower part are thicker than marly sandstones, while in the upper part (uppermost 5 m) the latter are thicker than the former. In log 66 the prevailing thickness of clayey marl beds is even more marked. No grain larger than zero <D was found.

Micropaleontological study allowed to recognize abundant planktonic microfauna in the clayey beds of log 66 and in the lower beds of log 67 while the upper beds (uppermost 5 m) of log 67 are very poor in fossils. Log 66 and the lower beds of log 67 (first 8 m) should correspond to << cenozona >>

with Globorotalia menardii (n'ORBIGNY) according t o CRESCENTI ( 1966).

In the upper layers of log 67 fossils are very rare; among them Globigerina euapertura JENKIS and G. regularis D'ORBIGNY were found. Anyhow it is mainly the sudden change in thanatocenosis and the abrupt decrease in microfauna which

~~~:~

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~ l !". · ....

Il l· • • • Il 1 1----. ;:!)1 1·-· ..

i l l •••

l' llùhù •••.

n1o l l

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l l l l

l i l

o P -v-? "-l l

IO'Oo .....,... l l

l

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.... , ..-------. l

:l l i·~~ l ••• l l • • • '

'~ l lJO ---- -

l 12411]0 -~·:1 123 l 70 .... -:-:. -----

1 ! l l ---

l l l

l

22 1310 ·-·. j ... ..

l -- l - --- -

FrG. 48 - Log no. 67 Pescosansonesco, surveyed in <<Argilloso-Arenacea Formation >> of Lazio-Abruzzi Apennines (Upper-Middle Miocene). The log, 16.50 m thick, consists of 51 layers. In this sketch only the layers from 20 to 27 are represented, where interval c is always lacking. This is an example of incomplete sequence in which intermediate intervals lack.

Flute casts are not frequent.

- Log n. 67 Pescosansonesco, campionato nella << Formazione Argilloso-Arenacea>> dell'Appennino lazialeabruzzese (Miocene medio-superiore). Questo log, potente circa 16,50 m, è formato da 51 strati dei quali sono rappresentati soltanto quelli compresi fra il 20 ed il 27. In questa parte mancano del tutto gli intervalli del tipo c e quindi essa costituisce un esempio di sequenza incompleta nella parte centrale. Nella serie sono presenti solo

rari jlute casts.


Fra. 49 - The photograph shows the sequence in the <• Argilloso-Arenacea Formation l) where log no. 71 was surveyed. The log is 4 m thick and consists of just 5 layers made up by a sandstone bed underlying a shaly one. Sometimes the layers begin with the graded interval a, but sometimes the lower sandy levels do not show any structure. In the picture it is possible to see the lower layer characterized by the interval a followed by a well developed interval b (32 cm). In this sequence sole marks are always abundant and ftute casts pointed out a current direction from NW. The arrow

at the lower right side indicates the point where fig. SO was taken. (Photograph by A. Ciancarelli).

- La fotografia mostra la serie della<< Formazione Argilloso-Arenacea l) in cui è stato campionato illog n. 71, che ha uno spessore totale di circa 4 m dovuto a 5 strati. Si tratta di alternanze regolari di arenarie ed argille; non sempre lo strato arenaceo inizia con l'intervallo gradato a, ma a volte si ha un intervallo privo di qualsiasi struttura. Nella foto lo strato basale mostra, sopra l'intervallo a, un bellissimo esempio di intervallo b (cm 32). Questa serie è ricca di impronte basali fra le quali i flute casts hanno permesso di determinare una direzione delle correnti da NW. La freccia in basso a destra

indica il punto cui si riferisce la fig. 50. (Foto A. Ciancarelli).

allow to relate these layers to the ones ascribed by CRESCENTI (1966) to Messinian.

In both series studied in Aterno River Valley, sole markings are rare and the complete Ta-e sequence (according to BouMA 1962) is completely lacking. Load casts and worm tracks are very frequent in log 67 while flute casts can only be found in the lower layers. In log 66 load casts are very rare. Current direction, based on few flute casts, is from S 35 E to N 55 W. Grading is always present and generally clearly visible in the lower interval (a). Only in the lower part of layer 7 of log 66 grading is absent. Lamination is also very abundant in almost all layers of the two logs, the other types of internai structures

are rare or absent. In log 66 c and d intervals are completely lacking while e is very thick and it is difficult to determin the part of it which is due to normal pelagic sedimentation. In log 67 c and d intervals also are sometimes present; in particular, c consists of cross lamination and, only in the lower layer, of wavy lamination.

In Carseolani Mts. area ANGELUCCI surveyed 6 logs (68 to 73). They are all located in Sheet 145 III NE along the road Pietrasecca-Tagliacozzo:

log 68 Prato/ungo, coordinates 42° 07' 31" lat. N, 13° 09' 09" long. E;

log 69 Luppa West, coordinates 42° 07' 22" lat. N, 13° 09' 25" long. E;


log 70 Luppa East, coordinates 42° 07' 19" lat. N, 13° 09' 44" long. E; log 71 Bracane, coordinates 42° 07' 22" lat. N, 13o lO' 23" long. E (fig. 49, 50); log 72 Meschino, coordinates 42° 07' 20" lat. N, 13° 10' 48" long. E; log 73 Mandrea, coordinates 42° 07' 20" lat. N, 13° 11' 07" long. E.

Field and laboratory analyses aliowed to determin lithologic and grain size characteristics which are

very different from the ones described for Aterno River Valiey series. Layers lacking grading are very frequent in this area and especialiy log 69 is characterized by beds 2-3 m thick without any grading and overlaid directly by d interval.

Thickness of this interval does not exceed 40 cm, and sometimes is limited to 4-5 cm. Also in the other logs there are levels without any grading and, generaliy, very thick; only rarely they are overlaid by d interval through the b one.

Often the a interval is characterized by the presence of large more cemented sandy nodules which are very evident for the differential action of weathering (fig. 51).

The complete sequence Ta-e is never present. Convolute laminations, both symmetric and asymmetric, are very rare; cross laminations are almost lacking. Both types of laminated intervals are very thin (from few cm to some decimeter). Sole marks were found in ali logs. Flute casts are prevalent and they indicate an average direction from N 35 W; they can also be found a t the base of layers lacking grading. Lithologically, marly sandstone, marly-clayey sandstone and mari are

FrG. 50 A detail of fig. 49. In the photograph it is clear the transition from interval b to interval c (type es) and then to interval e, lacking interval d. The wave height of the convolutions is about 8 cm. Darker levels in the parallel lamination interval are characterized by very small carbonaceous fragments. (Pho-

tograph by A. Ciancarelli)

- Particolare della figura precedente: è visibile l'intervallo laminato b, sormontato da quello convoluto di tipo es che passa direttamente all'intervallo e senza che sia riconoscibile il d. L'altezza d'onda delle convoluzioni è di circa 8 cm. I livelli più scuri delle laminazioni parallele sono dovuti a minutissime inclusioni di frammenti carboniosi. (Foto A. Ciancarelli)

present. Maximum grain size is l <1>. Modal class in sandstone is between 2 and 4 <P while in finer grained beds the modal class is between 5 and 6 <P. Ali frequency curves are asymmetric and very skewed towards the finer fractions and seem to be formed by two or more grain size populations.

Six logs surveyed in Carseolani Mts. belong to the lower series of << Argilloso-Arenacea Formation )) in opposition to the ones surveyed in Aterno River Valiey. These logs belong to the first flyschioidal beds sedimented after the grey shales, underlaid by marly limestones and organogenous limestones with Bryozoa and Lithothamnia (ANGELUCCI, CHI-


MENTI, PASQUINI 1959). In some pelitic beds of the examined logs scarce and badly preserved microfauna was found: Globorotalia scitula (BRADY), Globigerina bulloides (n'oRBIGNY), Orbulina universa n'oRBIGNY and few Globigerinoides trilobus (REuss). This fauna} assemblage is related to the << cenozona >>

with Orbulina universa ascribed to Helvetian by CRESCENTI (1966).

In Frentani Mts. area LA MoNICA studied seven series belonging to the <<Argilloso-Arenacea Formation >>. The series, in the Sheet 153 of the Geologica} Map of Italy are located as follows:

FIG. 51 - The interval a of a layer surveyed in the log no. 72. Some large nodules crop out from the erosion surface of the bed and this differential weathering is due to the fact that they are harder than the sandstone of the bed. CaC03 in the nodules is about 60%, while the CaC03 content of the sandstone is about 40%. Lithologically the nodules also are sandstone and they show a concentric structure. These sandstone nodules are widespread in the Carseolani Mts.

area.

- Intervallo a di uno strato appartenente al log n. 72. Sono visibili alcuni grossi noduli che l'erosione selettiva ha messo in evidenza sulla testata degli strati. I noduli sono costituiti da arenaria e si differenziano dal resto dell'intervallo solo per

Castiglione Messer Marino (Sheet 153 - Tav. II NE).

In this area the Bouma layers are always very thin and only in few series we have layers l m thick; a an d b layers are widespread; con volute laminations are common and cross laminations very rare. Generally e levellacks. In ali the logs, and essentially in logs 77 and 78, many sandy levels without any grading are present. In log 77 is very peculiar a bed which has at the base a graded level 15 cm thick (2-4 ) and underlying another level 225 cm thick lacking any grading (grainsize is

una più elevata percentuale del CaC03 (60%) che in questi strati di norma non supera il 40%. I noduli, che presentano una struttura concentrica, sono molto diffusi in tutta l'area dei M.ti Carseolani.

log 74 Pennadomo I, along the road from Pennadomo to Villa Santa Maria Villages, about 5 km far from Pennadomo (Sheet 153 - Tav. I NE); log 75 Pennadomo II, about 300 m from the previous log, towards Villa Santa Maria Village (Sheet 153 - Tav. I NE); log 76 Primo Campo, along the road from Passo della Forchetta to Rivisondoli Town, in the locality Primo Campo (Sheet 153 - Tav. IV SE); log 77 Borello I, along the road from National Road no. 154 to Borello Village, near the fountain at the side of the road (Sheet 153 - Tav. I SE); log 78 Borello II, about 200 m from log 77, towards Borello (Sheet 153- Tav. I SE); log 79 Agnone I, along the road from Agnone to Castiglione Messer Marino Village, about 1.5 km far from Agnone (Sheet 153 - Tav. II NE); log 80 Agnone II, about 1.5 km from log 79, towards

almost constant a t 4 <l>) an d internai structures; at the top there is a thin level (15 cm) of laminated siltstone.

Cross laminated layers are widespread only in log 79 an d 80, generally they are very thin; convolute laminations are present in layers l and 4 of log 80 only. In log 79 is peculiar a layer 233 cm thick which is graded ali along the thickness without any internai structure with exclusion of a cross laminated interval 20 cm thick.

Sole markings are always present but essentially with worm tracks an d load casts; flute casts were found in log 77 and 80 only. In the first log the direction is from N 70 E and in the second from E.

Grainsize curves are characterized by modal class varying between 2 and 4 <l>; only in log 79 and 80 the modal class is about -1 <l>. The curves are from platykurtic to very leptokurtic


with kurtosis varytng from 0.81 to 2.25 (FoLK and WARD 1957). Standard deviation varies from O. 75 to 2.00 and ali the beds are from moderately to poorly sorted. The lithology of the series is characterized essentially by marly sandstones and clayey marls with marls and marly siltstones just in few series.

CALCARENITIC TURBIDITES IN THE MOLISE APENNINES

by Giovanni Battista La Monica

In some areas of Centrai Southern Apennines (Molise Mountains) an d in particular in the Sheets 154 (Larino) and 161 (Isernia) of the Geologica! Map of Italy, the arenaceous Flysch, characteristic in more western and northern areas, is partially or completely replaced by a calcarenitic Flysch.

In this area the following six graphical logs were surveyed:

log 81 Altino, along the road from Roccascalegna t o Altino, just east of Altino Village (Sheet 14 7 Tav. II NE);

log 82 Villa Santa Maria, just west of Santa Maria Village, along the road (Sheet 153 - Tav. I NE); log 83 Carunchio, along the road from Carunchio to Furci Villages, a t km l 02 of the State Road no. 86 (Sheet 154 - Tav. IV NW); log 84 Trigno, along the road from Trivento to Palmoli Villages, after the bridge on Trigno River (Sheet 154 - Tav. IV SE);

log 85 Treste, along the road from Castiglione Messer Marino to Palmoli Village, after the bridge on Treste River, where the road bends on the right (Sheet 154 - Tav. IV SW); log 86 Fosso di Acquevive, in a small valley on the left of the road from Acquevive del Sannio Village to Frosolone Town, just south of the village (Sheet 161 - Tav. I NE).

In the area belonging to the Sheet Larino, the stratigraphical column begins with Paleogene sediments characterized by varying in colour shales with interbedded levels of siliceous sandstone, grey finely detrital limestone, marly limestone, and reddish or bluish chert (sometimes in lenses). These sediments, whose age might be U p per Cretaceous also, represent the lowest sequence outcropping in the area and it underlies a marly one which consists essentially of marls interbedded with sandstone and limestone. Sandstone, widespread in the surroundings of Castellino del Biferno,

FIG. 52 - Calcarenitic turbidites in the Molise Apennines (Langhian-Elvetian); in the photograph the exposure in which log Acquevive (no. 86) was surveyed. The sequence is made up essentially by two lithological types: calca reni tic limestone and mari, closely interbedded and whose thickness generally does not exceed 30 cm (just one calcareous bed is 60 cm thick). In each layer, in generai, the marly bed is thicker than the calcareous one and the different lithology is pointed out by a differential weathering that gives the outline of

the exposure, characterized by a series of steps.

- Torbidi ti calcarenitiche nell'Appennino molisano (Langhiano-Elveziano); nella fotografia è rappresentata la serie in cui è stato campionato il log Acquevive (n. 86). Si possono distinguere essenzialmente due tipi litologici: calcari finemente detritici e marne; questi due tipi Iitologici sono fittamente interstratificati in livelli di potenza generalmente inferiore a 30 cm (in tutta la serie soltanto uno strato calcareo è potente 60 cm). In ciascun banco, formato dall'assieme di uno strato calcareo e di uno marnoso, quello marnoso è di norma il più potente. Le differenze Iitologiche sono messe in luce anche dalla diversa azione operata dall'erosione; infatti i livelli calcarei, più resistenti, tendono ~ sporgere rispetto a quelli

marnost.

Civitacampomarano and Lupara, shows a fluviallacustrine fa ci es; sandy fraction is ma de essentially by quartz grains with windblown materia! charactenstlcs. Limestone microfauna consists of Nummulitae and Lepidocyclinae pointing out an Oligocene age.


With the end of Oligocene and at the bcginning of Miocene, facies becomes more and more calcareous. Miocene can be divided in almost four sequences: l) Very fine detrital limestone an d fine breccia with interbedded marly shales and marls (Upper Oligocene-Lower Miocene). 2) Calcarenites and fine breccias interbedded with limestone, grey marl and some calcareous sandstone levels (lower Middle l\1Iiocene). 3) Grey sandy shales and marls with some levels of almost loose sandstone. At the top of this sequence, and sometimes interbedded m the uppermost beds,

FIG. 53 - Calcarenitic turbidites in the Molise Apennines (Langhian-Elvetian); calcarenitic layer in the sequence where log Trigno (no. 84) was surveyed. The lower levels of this layer, overlaying a marly bed, consist of a cross lamination interval, about 3 cm thick, followed by a convolute lamination one (about 7 cm). At the top of the latter there is another parallel lamination interval thinner than the first one. The wavy lamination consists of a large trough (10 cm wide) and two narrower crests whose characteristic is to be bended in apposite direction. - Torbiditi calcarenitiche nell' Appennino molisano (Langhiano-Elveziano); strato calcarenitico nella serie in cui è stato campionato il log Trigno (n. 84). La parte inferiore dello strato, sovrastante un livello marnoso, è costituita da un intervallo a laminazione paral

At the base of layers worm tracks, fossi! and load casts are abundant; flute casts are present and point out a direetion of turbidites from N 65 W. Among internai structures grading is almost always present with a graduai transition from the base, represented by fine or coarse calcarenite, to the top of the layers characterized by marl or calcareous marl. Interval b of BouMA is rather frequent and generally in levels consisting of fine calcarenite. Interval d is no t frcquent, but when present i t often represents the top of the layers, lacking, in these istances, interval e. Also convolute lamination

lela, potente 3 cm, cui segue un intervallo a laminazionc convoluta c quindi un nuovo intervallo a laminazione parallela, ma meno potente del primo. L'intervallo a laminazione convoluta, potente circa 7 cm, presenta una struttura caratterizzata da ampie concavità (ampie circa 10 cm) e strette creste; la particolarità della struttu•a è costituita dal fatto che le creste

a fianco di ciascuna concavità sono rovesciate in direzione opposta.

there are levels of sandy materia! with a fluviallacustrine facies (surroundings of Carunchio Village). The whole sequence is Tortonian in age. 4) Coarse detrital limestone with Lucinae, sandy shale lacking of fauna, and sandy crystalline gypsum (Upper Miocene). This sequence, with an evaporite facies, probably represents the end of the Miocene sedimentary cycle. On l.VIiocene deposits there are Pliocene sediments characterized by a clear marine facies (shales and sandy shales rich in marine macro and microfauna).

The second of the Miocene sequences shows ali the characteristics of a Flysch deposit with a series of turbidites varying in thickness and grain size. The best exposures are along Trigno River where the series is regularly bedded with layers that only sometimes are very thick (more than 1 m) while in generai their thickness is less than 50 cm.

interval is rather frequent in levels lithologically characterized by a fine detrital limestone; convolute laminac are not very thin and in some case they may reach many millimeters in thickness. One of the convolute lamination intervals is shown in fig. 53 owing to the particular trend of the convolution. Laminae are folded in such a way to originate a wide through with two narrow crests at the sides and these crests are not bended in the same dircction but in an apposite one. As regards grain size at the base of the layers it is very variable from more than l mm to 0.250 mm.

Some different characteristics are shown in the exposures nearby Palmoli Village. Here the base of the layers always consists of graded sandstone coarser than 0.250 mm. Sometimes sandstone underlies a calcarenitic level finer than the base of the layers, but coarser than the uppermost le-

390 A. ANGELVCCI, E. DE ROSA, G. FIERRO, M. GNACCOLINI,. G.B. LA MONICA, ecc.

vels of the sandy bed; o n calcarenite there is c interval, consisting of fine sand and silt, and then d interval made up by marl and representing the top of the layer. Sometimes the base of the layers is always sandy, but represented by c interval with convolute or cross lamination. In these exposures sole marks are not frequent and they consist almost exclusively of load casts and worm tracks.

In the Sheet Isernia the more interesting area is located south of Isernia; here the stratigraphic column {SIGNORINI and DEVOTO, 1961) is the following: l) white crystalline limestone sometimes breccia like (Lower-Middle Paleocene, Maastrichtian); 2) closely bedded limestone with red cherty nodules and some interbedded shaly levels (Lower-Middle Eocene, Middle-U p per Paleocene); 3) shales and marls with interbedded calcarenite (Middle-Upper Eocene, Aquitanian); 4) conglomerate, breccia and calcarenite (Langhian); 5) marly limestone with interbedded marl (Helvetian); 6) sandstone with interbedded marly shale (Tortonian).

In this area, as we said above, one log (Fig. 52 and 54) was surveyed in the locality Fosso di Acquevive near Acquevive Village. Lithologically the series is characterized by the presence of calcarenite interbedded with calcilutite an d marls; thickness frequency distribution curves are generally skewed towards the classes representing thicker beds and they show a very high standard deviation for the marly beds, while standard deviation is not very high for the calcareous ones. Moreover the curve of the calcareous beds is unimoda! with modal class corresponding to 5-8 cm

FIG. 54 - A part of log Acquevive (no. 86) surveyed in the Calcarenitic turbidites of Molise Apennines. The log, about 3.5 m thick, consists of 21 layers, generally thicker towards the top. Sole markings, not very abundant, consist essentially of worm tracks and load castings, just one flute cast was found, but it was not well shaped and for this reason no current direction was measured. Among internai structures, grading is widespread, parallel lamination is less frequent and c interval (type c1) is present in two layers only. Grain size is not very coarse and at the base of the layers it does not exceed 2 <Il.

- Spezzone del log Acquevive (n. 86) campionato nelle torbidi ti calcarenitiche dell'Appennino molisano. Il log, potente circa 3,5 m, è costituito da 21 strati, generalmente più potenti verso l'alto della serie. Le impronte sulla superficie inferiore di strato non sono molto frequenti e sono rappresentate essenzialmente da impronte organiche ed impronte di carico. È stata rinvenuta una sola impronta di erosione su cui non è stato possibile effettuare alcuna misura di direzione di corrente. Fra le strutture interne la più frequente è la gradazione e quindi la laminazione parallela; l'intervallo c (tipo c1) è stato rinvenuto soltanto in due strati. La granulometria non è mai molto grossolana ed alla base degli strati non

supera i 2 <Il.

interval, and the one of the marly bed shows three modal classes (5-8; 21-24; 29-32 cm). Grading is very frequent at the base of the layers (86% of the observed layers), but this structure may be easily observed with microscopic analysis only because in the field it is not so clear owing to weathering and grain size that is often very fine. Thickness frequency distribution of graded intervals is bimodal with modal classes corresponding to 5-8 cm (18%) and 25-28 cm (2%). Also parallel lamination 1s very frequent (96% of the observed layers) in the calcareous beds and it corresponds to interval b

,--.,----,------,---,-----,---------- ------ - --

~ ~ ! LI~OGY ~ CASTS

300:::

21

600

c? r-r--+~7~~~~~ ~?

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150 ~ ~-19 t:±:i:::ti± ---150~-

1--1---+..:.L-'-'--'--f-'--i = -v-

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so

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of BouMA; thickness frequency distribution is unimodal with modal class corresponding to 1-4 cm. Interval c generally lacks, while interval d frequency distribution is 56% and it occurs in the marly bed; thickness frequency distribution of interval d is unimodal (modal class 1-4 cm) and characterized by a very low standard deviation. Interval e is almost always present (90%) and its thickness is very variable (from 5 to more than 40 cm).

Among sole marks very frequent are load casts and worm tracks; flute casts are not widespread, but generally they are well shaped so that it was possible to measure the turbidites direction (from N 12 E).

On the base of laboratory analyses it was ascertained a CaC03 percentage varying from 32% to 94%; residue insoluble in HCl is very poor and its percentage is generally lower than 40% and of this about 39% belongs to fractions whose grain size is finer than 0.062 mm. According to SHEPARD the residue may be defined as silty-clayey for some samples and as clayey-silty for the others. Grain size analyses were carried out on severa! samples an d the statistica! moments were measured; because of the hydrocloric disaggregation the insoluble residues only were studied.

AH the samples showed the same characteristics with mean and median grain size varying respectively between 6.80-8.20 an d 7 .l 0-9.1 O ; skewness is sometimes negative; standard deviation vari es between 1.30 and 1.70; kurtosis is generally lower than l.

Many thin sections were observed to determine the lithological composition according to FoLK classification of calcareous rocks. Generally the calcareous beds are biomicrites very rich in foraminifers, and the marly ones are micrites with scattered microfossils; i t is interesting to noti ce that the fauna percentage in the marly beds is higher towards the top of the layer.

MIOCENIC TURBIDITES OF SORRENTO PENINSULA

by Tullio Pescatore

The following sediments are cropping upwards in the mwcemc sequence of Sorrento Peninsula - Naples:

a) Punta Lagno Formation (BeANDONE & SGRosso 1965). Max thickness is 80 m, in some piace however <<Punta Lagno Formation >> is completely lacking.

Three members ha ve been distinguished: l) Calcarenites and fine grained glauconitic calcirudites with Ostrea, Pecten, Scutella, Miogypsina, Operculina, Amphistegina, Elphidium; 2) Glauconitic, cross laminated sandstones; 3) Coarse grained sandstones and conglomerates with calcareous pebbles. The transition among the above mentioned members occurs both vertically and laterally without a distinctive order. <<Punta Lagno formation >> is Miocenic, may be Langhian and transgressive on Upper Cretaceous neritic limestones.

b) Medium and coarse grained arkosic sandstones with calcitic cement. Thickness is 60-70 m. This part is more or less regulary bedded and some layers are up to 4-5 m thick. Large scale cross lamination is present at piace, with laminae up to 30-40 cm long and 2-3 cm thick.

c) Fine and medium grained arkosic sandstones with calcitic cement. The thickness is about 100 m. These deposits are very well stratified. Layers are 10-20 cm thick. In the upper part of these sandstones, graded beds of coarse grained sandstones or conglomerates with calcareous pebbles grading upwards to mudstones have been found. Burrows are sometimes present.

d) Greywakes. Total thickness is about 200 m. The sandstones are well an d thiny stratified;

siltstones and silty shales are interbedded with. Almost all the typical turbiditic structures like graded bedding, sole marks, parallel, cross and convolute laminations and so on are in the sandstones.

log 87 Marina della Lobra, 500 m, West of Massalubrense (Sorrento). Coordinates: Lat. 40° 36' 45" North; Long. 1° 53' 10" East (M. Mario).

Sandstones with interbedded siltstones and silty shales are outcropping. The bedding is regular and continous. The rocks are yellowish by weathenng. On the bottom of the layers groove casts were observed. In a layer groove casts are swerving of 15o.

Grading is frequent: sometimes i t is graduai, sometimes the lower part of the layer is not or poor graded. The transition to well graded part of the bed often occurs correspondingly to the pelitic interval and or above the intervals with lamination. More rarely, the transition is corrisponding to the start of lamination intervals.

Parallel, cross and convolute laminations are frequent, intervals of lamination are mainly in the thicker layers of the outcrop. Convolute lamina-


FrG. 55 - Turbidites of Sorrento Peninsula, Marina della Lobra; log no. 87. Graded bed with erosional channels filled by silty sediments with convolute

laminations.

- Torbiditi della Penisola Sorrentina, Marina della Lo bra; log n. 87. Strato gradato con canali d'erosione riempiti da materiale siltoso con laminazioni convolute.

tion in this log is never very complex and often changes laterally to cross lamination.

Sometimes convolutions form the filling of erosional channels located in the graded intervals of the beds (Fig. 55). More complicated convolutions are on the contrary, characteristic of thin silty layers and occur to the whole laycr. Some of them starts with current laminations, followed by very thick peli tic intervals; other layers consist only of pelitic interval.

It is to be noticed that, the same bed can show repeated intervals of parallel, cross and convolute lamination. Ali these intervals are separated by an erosion surface; convolute laminati o n occurs in the 40 and 100 micron grain size class (Fig. 56, 57 and 58). Repetition on these intervals can be explained by velocity variations as the structures are occurring under different fl.ow regimes. The grain size however could have so much infl.uenced the sedimentary structures that, for small grain size classes, different structures could have occurred in a turbidity current with a more and more decreasing velocity. The former hypothesis seems to be the more feasible and is also supported by the convolutions filling the erosional channels in the graded interval of the layers and this implies sedimentation and subsequent erosion of the current transported materia!.

The lower part of the layer showed in fig. 58 is formed by three intervals with erosional surfaces among them. They are three individuai amal-

gamed beds or eventually severa! part of the same bed settled by a single turbidity current. Layer thickness is betwcen 7 and 130 cm; more frequent values belong to 16-32 cm class: the frequency distribution trend is unimodal.

log 88 S. Agata, 500 m North of the town, along the Sorrento-Priora-S. Agata road. Coordinates: Lat. 40° 36' 39" North; Long. 1° 55' 22" East (M. Mario).

Sandstones with interbeddcd siltstones and mudstones. Structures on the bottom of the layer as in prcvious log consist only of groove casts and secondarily of load casts. Graded bedding is generally prcsent in almost ali the layers. There is a distinct grain size step in the upper part of

l --- T-~ l LAMINATIONS l GRti.IN SIZE l~ ti l l l~

~ l l l ~ l : l l ~ ~ - 115 d 4 [AAAI, 1, of'', 6 e

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Frc. 56 Turbidites of Sorrento Peninsula, Marina della Lobra; log no. 87 (upper part). The layers no. 2-4-11 show multiple current laminations. In the layer no. 11 cross lamination is recurrent 4 times, convolute lamination twice. In the layer no. 4 parallel lamination is recurrent 3 times, cross lamination twice, convolute lamination twice. In these current intervals grading is sometimes evident (layer no. 4), sometimes

poor (layer no. 11).

- Torbiditi della Penisola Sorrentina, Marina della Lo bra; log 87. G Ii strati n. 2-4-11 presentano ripetizioni negli intervalli da corrente: nello strato n. 11 la laminazione obliqua è ripetuta 4 volte e la laminazione convoluta 2 volte; nello strato n. 4 la !ami nazione parallela è ripetuta 3 volte, l'obliqua 2 volte, la convoluta 2 volte. In questi intervalli da corrente è presente a volte una gradazione dei clasti (strato n. 4), a volte la gradazione

è appena accennata (strato n. 11).


the layer corrisponding either to the pelitic interval or to that o ne with laminations; grading 1s poor at the base while is marked in the upper part of the layers. When the layer starts with current

FIG. 57 - Turbidites of Sorrento Peninsula, l\1arina della Lo bra; log no. 87. Sandstone grading upwards

to silty shale (see fig. 58).

- Torbiditi della Penisola Sorrentina, Marina della Lobra; log n. 87. Arenaria gradata passante verso l'alto

ad argilla siltosa (vedere fig. 58).

FIG. 58 Sketch from r---- _ fig. 57. Intervals: t---=--=-.--_-~-=-=-------1 i) siltstone grading upwards r- _ to silty shale t----------------1 h) siltstone with parallel la- - - !l mination ~ ~ -~ g

g) siltstone with cross lami-nation passing laterally to ~~ ~ convolute lamination (no- 1---/-==--=-----'<c~---· _/_-_ ______, d tice the irregular erosional

~ surface) f) coarse grained siltstone with parallellamination ··.~c--.· ... · .... · ~.'/! .. . 1· .· ... e) silty sandstone with cross // .L-- / ~ lamination passing laterally to convolute lamination (notice the irregular erosional surface) d) fine grained sandstone with cross lamination c) medium grained sandstone grading upwards to fine grained sandstone with convolute lamination in the

b

upper part of the interval b) medium coarse grained sandstone grading upwards to medium grained sandstone with large convolute lamination a) coarse graincd sandstone grading upwards to medium coarse sandstone.

- Disegno illustrativo della fig. 57. Intervalli: i) siltite passante ad argilla si !tosa; h) si !ti te a laminazione parallela; g) si !ti te con !ami nazione obliqua che passa lateralmente a laminazione convoluta (superficie d'erosione irregolare); f) siltite a grana grossa a laminazione parallela; e) arenaria siltosa con laminazione obliqua che passa lateralmente a laminazione convoluta (superficie d'erosione irregolare); d) arenaria a grana fine con laminazione obliqua; c) arenaria gradata da media a fine con laminazione convoluta nella parte alta; b) arenaria gradata da medio-grossa a media con laminazione convoluta a grande scala; a) arenaria gradata da grossa a medio-grossa.

lamination intervals, grading occurs only in the pclitic interval.

Parallel, cross and convolute laminations are well developed but repetition, as in the previous log, are lacking. In some layers there is a complete sequence of intervals; in others only the graded interval occurs; laycrs starting with interval of lamination followcd by pditic interval are frequent.

The more charactcristic layers of this log consist of siltstones with an interval of convolute lamination at the base of the bed followed by a pditic interval. Convolutes change upward to parallei and cross laminations. Recumbent convolute laminations are more distinct than those of the prcvious log and seem to be caused by more eddied currcnts than in log n. 87.

I n addition i t is possible to noti ce rather frequcntly layers with lacking or reverse grading, till thickncsscs exceeding 10 cm, because of the dccrcasing by friction of the current near the bottom. Layer thickness is between 10 and 100 cm, with modal value of the 16-32 cm class; the frequency distribution trend is unimodal.

WESTERN CILENTO FL YSCH

by Tullio Pescatore

The second group of logs has been surveyed in Western Cilento, in the area between the Alento river Vallcy and Punta Licosa. In this area the western Cilento flysch crops out with almost solely turbiditic deposits, about 4.000 m thick.

The stratigraphic sequence consists of three formations: c) S. Mauro Formation (Miocene ?-Eocene) b) Pollica Formation (Lower Eocene-Upper Cretaceous) a) S. Venere Formation (Middle and Lower Cretaccous).

a) S. Venere Formation: thin bedded argillites, siltstones, sandstones and arenaceous limestones. Limestone-claystone sequences have been found in the layers of the lower part of this formation and sandstone-clay siltstone sequences in the layers of the upper part. The sequences have to be related to distai part of tubidity currents. The thickness 1s 600-700 m. A measure of flute casts showed paleocurrent direction from NorthWest. b) Pollica Formation. Two members are distinguishcd. Member A : fine and medium grained


sandstones interbedded with siltstones and mudstones. Sandstones are normally graded; there are also some arenaceous layers with erosional channels poorly or no graded. The former are considered turbidites the latter fluxoturbidites. The Member A thickness is 300-400 m.

Member B: medium and coarse grained sandstones interbedded with siltstones and mudstones. Some Jayers are graded (turbidites) other are not (fluxoturbidites). The former are tabular, the latter lenticular in shape. In the upper part of the Member B there are frequently intraformational slumps (sands flows, plastic glides, pebbly mudstones). Thickness ranges about 500 m. The direction of sediment supply in this formation is from South-West.

c) S. Mauro Formation. Two members are distinguished. Member A : alternations of sandstones and marls. Both arenaceous and marly layers have typical sequence of distai or intermediate parts of turbidity currents. In the upper part of the Member A there are sandstones with fluxoturbidites structures. The Member A thickness ts ranging from 1.100 to 1.200 m.

Member B: alternations of sandstones and conglomerates. Sandstones show turbidity or fluxoturbidity structures. Conglomerates in which matrix is prevailing, are connected with submarine slides. The Member B sequences are therefore to be related to intermediate and or proximal parts of turbidity currents. Thickness is ranging from 1.000 to 1.200 m. Prevailing direction of sediment supply is from East; nevertheless some structures with direction from South West were found.

The described sequences show two large sedimentological cycles in the stratigraphic succession of western Cilento Flysch. The first cycle include <<S. Venere Formation >> and <<Pollica Formation >>; their turbiditic deposits are passing up from distai stages into proximal ones. In the second cycle S. Mauro Formation there are again distai deposits at the base passing up into proximal ones. These two cycles can be related to regional tectonics modifying both basin morphology ( changes in paleocurrents directions) and source areas (variation in sediment litology).

log 89 Pioppi (S. Venere Formation), AcciaroliCasaivelino Marina road, km 46.900. Coordinates: Lat. 40o 10' 22" North; Long. 2° 37' 49" East (M.Mario).

Siltstones and mudstones are prevailing, sandstones are infrequent. Parallei Iamination is very frequent as well as cross Iamination, generally with an angie Iower than 10°. At the base of the Iayers cross lamination either gradually changes to parallel Iamination or is interrupted by an erosional surface and the parallei Iamination overlies it unconformably. This phenomenon is related to an increasing in current velocity. In the first case this rise is graduai and therefore also the transition from cross to parallel is graduai. In the second case the rise is abrupt and causes the erosional surface. Sometimes convolute laminations change sideways and downwm:d'ò. t<l cross lamination: crests and troughs following each other regularly was observed; in the upper part, they tend to upset according to current direction. The erosional surface interrupting the convolute Iaminas proves the increasing of current veiocity. Layers thickness varies between 40 and 50 cm.

log 90 Galdo (S. Mauro Formation, Member A), Acciaroii-Mercato Road, 750 m after Galdo village. Coordinates: Lat. 40o 13' 00" North; Long. 2° 36' 17" East (M. Mario).

Aiternation of turbiditic sandstones, marly sandstones and marls. Marls are prevailing and often form the upper part of the arenaceous Iayers. Grading is frequent. In the marly layers often the base is a calcareous siltstone. On the bottom of the marly and arenaceous Iayers flute casts were found. These structures normally show a paleocurrent direction from East, some of them however indicate a direction from South West.

More frequently, wavy lamination were found in the interval of current ripple lamination. The wave height is very small (2-3 cm) as compared to their length (20-30 cm). Ripples are irregular and often change upward to parallel lamination. This wavy lamination, possibiy, is related to the grain size of the sediment because it is Iocated only in the marly silty bed.

Laboratory tests prove the wavy lamination occurs in the distai parts of turbidites currents (DzuLYNSKI & WALTON 1965). This fact does not contrast with the generai features of the deposits, as they are interpreted as typical of distai part of turbidites.

Layers thickness varies between few cm and 4 m. Thicker Iayers are mainly composed of


marls. Frequency distribution shows two peaks in two contiguos classes: 8-16 cm and 16-32 cm. It is a bimodal distribution with very similar modal values. This could be related with the different lithology of the deposits and the different sour ce of sediments.

log 91 S. Mauro (S. Mauro Formation, Member A), Acciaroli-Mercato road, 500 m West of S. Mauro village. Coordinates: Lat. 40° 13' 21" ~Wn+.l.>.·, Long. 2° 35' 53" East (M. Mario).

This sequence is similiar to the latter described one. Alternation of turbiditic sandstones, arenaceous marls and marls. Convolute lamination consists of irregular wavy laminae. Wavy laminae sometimes change upwards to convolute. At places, the parallel lamination changes upwards to wavy lamination or, viceversa.

Some couples of layers are particularly interesting. The bottom of each upper layer in the couples in very irregular and it is clear the upper layer eroded not uniformly the top of the underlying one. In addition the erosional and the dragging action of the current, giving rise to the upper layer of the couples, not only eroded the underlying layer but also caused the beginning of the convolution in it. In the following stages the differential load more and more deformed these structures (Fig. 59, 60). Layer thickness varies from 2 m to 5-6 cm. Frequency distribution is bimodal with a peak corrisponding to 32-64 cm class and another

FrG. 59- Western Cilento Flysch; log no. 91. Graded sandstone with convolutions (lower layer) and graded sandstone with erosional channels deformed by load (upper

layer).

- Flysch del Cilento occidentale; log n. 91. Arenaria gradata con convoluzioni nella parte alta (strato inferiore) e arenaria gradata con canali di erosione defor-

mati dal carico (strato superiore). w

FIG. 60- Western Cilento Flysch; log no. 91. Same couple of graded layers of fig. 59. Notice the erosional

channels deformed by load.

- Flysch del Cilento occidentale; log n. 91. Stessa coppia di strati di fig. 59. Notare i canali di erosione

deformati dal carico.

to the 8-16 cm class. The former peak is characteristic of marls and the latter of the sandstones.

log 92 Selva (S. Acciaro li-Mercato Lat. 40° 15' 16" (M. Mario).

Mauro Formation, Member B), road, km 3.000. Coordinates: North; Long. 2° 34' 30" East

Alternations of turbiditic sandstones, siltstones and mudstones. Slumping phenomena are also present. Sandstones are medium or coarse grained, graded or poorly graded. In the lower part of this log truncated sequences lacking of the pelitic interval were quite frequently observed. Sequences consisting only of the upper pelitic interval and complete sequence were also found. There is therefore an alternation of distai, intermediate and proximal stages. The last two are prevailing. In a layer the interval of convolute lamination is repeated. The same phenomenon has been observed in the log measured in Sorrento Peninsula.

A couple of layers shows a well developed amalgamation. A layer consists of a graded sandstone an d upwards has an interval of parallel laminati o n; the other layer consists of a fine grained sandstones grading upwards to mudstone and starts with grain size just larger than that of the top bed of the underlying layer. The boundary between the two layers is clear when marked by flute casts, but lateratly disappears. The thickness of layers varies from 7 cm to 70 cm. Frequency distribution is unimodal with a peak corrisponding to the 16-32 cm class.


NUMIDIAN FL YSCH

by Forese Carlo Wezel

The Numidian Flysch of Sicily is represented by a thick (about 2,000 m) sequence of alternating brown pelites and graded quartzarenites, which crops out in the north-eastern part of the island. The sicilian outcrops represent only a part of the formation which, according to literature (see OGNIBEN, 1960 and 1964; CAIRE & lVIATTAUER, 1960; DuRAND DELGA, 1962; etc), is present, in a more or less continuous way, along a strip which covers about 2,500 km from Gibraltar through Morocco, Algeria, Tunisia and Sicily reaching Lucania (Southern Italy). In the Nèbrodi Mts. and the Madonìe Mts. the formation is autochthonous and folded to form a wide, asymmetric anticlinorium having the southern side thinner and sometimes faulted and a W-E direction. The formation age, established on the basis of planktonic foraminifera, falls between Middle Oligocene (WEZEL, 1966) and, probably, Lower Burdigalian (WEZEL, in press; see also OGNIBEN, 1960), both inclusive. The localities where logs have been surveyed in this formation are shown in fig. 1.

From the lithologic point of view the formation can be divided in Sicily into three intervals. The lowermost and the topmost ones are reprcsented by thin alternations of brown pelite and thin quartzarenite or quartz-siltstone beds while the middle part consists of very thick multiple quartzarenite layers with thin clayey partings, alternating with intervals of rhythmic quartz-siltstone and pelite beds. This paper deals with the sedimentological description of the middle interval of the formation.

From the petrographic point of view these sandstones are characterized by a high compositiana! stability. More than 90-95% is composed of quartz. The rest is represented by fcldspars, mica, glauconite and heavy minerals. Among the latter, the ultra-stable zircon-tourmaline association strongly prevails. Contrasting with this great stability in minerai composition, quartz grains (mainly monocrystalline) have sometimes a frequent undulose extinction which is characteristic of more immature sandstone (BLATT & CHRISTIE, 1963). This anomaly is probably due to post-depositional folding. Contacts between the quartz grains are sometimes of microstylolitical type, which proves a rather advanced diagenesis. In the parautochthonous outcrops south of the Madonìe-Nèbrodi Mts. the Numidian Flysch is often decemented,

probably because of percolation of water along fissures; in fact, some instances are also known in which a norma! calcitic cement is present.

From the textural point of view the quartzarenites show three mai n features: l) poor sorting of the quartz grains, contrasting with the quartzarenite composition; 2) fair percentage of quartz grains smaller than 30 Il. (5 phi), i.e. presence of a quartz matrix; 3) high degree of roundness of quartz grains.

These sandstones contain a great number of grain size classes between clay-silt and granules. The median varies between 0.1 and 4.0 mm, the coarser part usually exceed\ug 0.5 mm. Percentage of thc pelitic part usually falls between 5 and 15%. Cumulative curves, obtained with sieving data and drawn on phi-probability paper, show a centrai part not well sorted in respect to the tails (platikurtosis) and, in a generai way, show an upward convexity proving a positive skewness. As the grain size of the sediment decreases this convexity is less and less marked: fine sediments can also be negatively asymmetric. In almost all sandstones sorting is poor and ranges between l and 2 phi.

It is very interesting to notice that median diameter and standard deviation are directly related. This relation is probably of V type, very similar to the one found in submarine deposits sedimented by norma! tractive currents in any type of environment (INMAN, 1949; GRIFFITHS, 1951; FOLK & WARD, 1957; WEZEL, 1964). As for the Numidian Flysch, grain size analyses proved the existence of the left side of the V trend with a best sorting corresponding to 2-3 phi. Such a relation seems to be missing in deposits due to experimentally produced turbidity currents and in Pliocene turbidites of Ventura Basin (KuENEN & lVIENARD, 1952; see also PASSEGA, 1957). This fact seems to require an explanation.

Half, or more than half, quartz grains of any size, is sub-rounded (WADELL in d ex: 0.26-0.40). The roundness degree, unusually high for a flysch, together with a sometimes frosted aspect of grain surface, show that the materia! is originated from a sediment which underwent aeolian abrasion.

Therefore, from the compositional-textural point of vie w the N umidi an sandstone shows features completely different from those of the other flysch: high compositional stability, poor sorting and marked grain roundness. It could be defined as << quartzwacke >> (sensu GrLBERT in WrLLIAMSON et al., 1954) with rounded grains, a name which,


however, puts a shadow on the most decisive compositional characteristic. Therefore, here will be spoken of > or of (i graded quartzarenite >>.

Within the Numidian Flysch of Sicily, beds are separated by characteristic piane and parallel surfaces with more abrupt contact with the underlying pelites than with the overlying ones. As a whole, they show a remarkable latera! continuity. Thickness varies usually between 50 and 100 cm. Frequency distribution of thickness is of lognormal type.

Abouta 10-15% of observed layers is macroscopically homogeneous, while ali others show graded bedding, consisting of an upward decline in coarse grain size mixed with finer quartz matrix. Sometimes, on the contrary, a decrease in percentage of coarse grains occurs. Six descriptive types of graded bedding have been observed till now in Numidian Flysch (fig. 61; see WEZEL, 1967).

Type l consists of a norma! > grading with ali grain size classcs included between coarse ones at the base of the bed and finer ones which make up the quartz matrix that is present in all parts of the layer. This type has been observed in 2/3 of layers.

Type 2 consists of a norma! (i sharped >> grading with a sudden change from the coarse size of the bottom to the top one caused by the lack of some grain size classes (middle and coarse sand). This type is not very frequent.

Type 3 consists of an inverted abrupt grading with a sudden upward change from a grain size of about 0.5 mm to about 0.8-0.9 mm. This type was observed in a few layers.

Type 4 is here defined as (i unipolar >> repeated grading. There are usually two (or even three) graded units lying one on the other, separated by a distinct surface. Both have upward shaded grading. The unit lying on the other one (roughly in the middle of the layer) usually has a grain size coarser than the o ne a t the base of the layer. This type was observed in about 1/6 of studied layers. Thickness of concerned layers varies between 60 and 100 cm.

Type 5 consists of a structure in which there is a coarse (grain size even exceeding 1 mm) strip roughly located in the middle of the layer from which a drop in grain size occurs both upward and downward. This type of internai structure could be called: (i bipolar >> repeated grading. This type was observed in a few layers more than l m thick.

Type 6 is a more complex type of repeated grading in which it is possible to observe a double unipolar grading overlying an interval consisting of a bipolar grading which could be called (i convergent >>. This type was observed in a few, very thick layers.

Repeated grading does not seem to be explainable by means of superposed multiple layers as no interbedded day was ever observed between the different graded units within the layer. Moreover there is no sign whatever that a subsequent erosion took piace. The contact between the two graded units is usually p lane and horizontal; only in Mt. Sàlici (W of Mt. Etna) load-casts are present. The recurrence of graded cycles within the same layer may be explained by assuming that each graded interval is a single sedimentation unit (OTTO in PETTIJOHN, 1957, p. 159). The repetition would be caused by sedimentation due to closely subsequent current pulses.

As far as the type of depositing current is concerned, during the last years ali graded beds have generally been related to transport and deposition due to turbidity currents. In reality, there seem to be two types of graded bedding: the first o ne caused by norma! tractive currents and the other one due to turbidity currents (PETTIJOHN, 1957, p. 171 ). The latter should have the following features: (l) fine grains distributed throughout the layer, (2) upward increase in grain sorting and (3) layers having an abrupt lower contact and a graduai upper one. Following this limitation of the grading concept which corresponds to the originai definition (KUENEN & MIGLIORINI, 1950), most of observed psammitic Numidian beds seem to have been deposited by turbulent suspensions.

H orizontal lamination (or micro-stratification) is very rare over the graded interval. Laminae are represented by changes in quartz grain sizes. The fact that lamination is so rare seems to indicate a lack of tractive currents sorting the bottom materia! according to grain size or composition. It is very interesting to notice that, according to PETTIJOHN (1957, p. 172), normally graded layers, especially if coarse-grained, should lack internai lamination.

Within almost all homogeneous layers and within some graded ones flattened shale pebbles with a rounded surface (size varying between a few mm and 25-30 cm) have been found. Usually they are not present on the bottom of the layers and lie parallel or sometimes transverse to the bedding piane. They prove that an erosion on the clayey

398 A. ANGELUCCI, E. DE ROSA, G. FIERRO, M. GNACCOLINI, C.E. LA MONICA, ecc.

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FIG. 61 - Some pieces of logs surveyed in the Numidian Flysch in which the six different types of grading and the grain size variation of the coarsest grains along the layer thickness are schematically shown. I t is to be noticed that also using an arithmetical scale for maximum size decline curve, the shape of the curve is always convex towards the top. Graded intervals are made up by poor sorted quartz grains and show the textural features characteristic of turbidites. The different types of grading (numbers inside small circles a t the side of the lithological column) are: 1- norma! shaded grading; 2- norma! sharped grading; 3- inverted grading; 4- unipolar repeated grading; 5- bipolar repeated

grading; 6- complex repeated grading (after WEZEL, 1967).

- Spezzoni significativi dei logs misurati nel Flysch Numìdico che mostrano schematicamente i 6 tipi descrittivi di gradazione distinti e le variazioni, all'interno dei banchi, delle dimensioni dei granuli maggiori stimate sul terreno (linee a tratti, scala logaritmica). Da notare che anche in scala aritmetica la curva di decrescita dei diametri maggiori è in prevalenza del tipo convesso verso l'alto come appare in questa figura. Le unità gradate sono composte da granuli quarzosi mal classati e con caratteri tessiturali analoghi a quelli dei depositi ritenuti di origine torbiditica. Tipi di unità gradate (numeri entro circoletti a fianco della colonna litologica): 1- gradazione normale sfumata; 2- gradazione normale netta; 3- gradazione inversa; 4- gradazione ripetuta uni polare; 5- gradazione ripetuta bipolare; 6- gradazione ripetuta complessa.

Gli strati senza numero a fianco non mostrano una gradazione macroscopica (da WEZEL, 1967).

SEDIMENTOWGICAL CHARACTERISTICS OF SOME !TAL/AN TURBIDITES 399

bottom, upcurrent of the sedimentation site, occurred.

In Sicily (Mt. Sàlici area) and in Lucania (Stigliano area) Numidian layers are sometimes irregularly stratified and consist of coarse materia! (up to quartz-rudite). Numerous and sometimes thin and lenticular coarse beds either homogeneously or very irregularly graded, were observed within the layers. Load-casts are frequent in the underside of these. Such irregular structures are present in some areas only, occurring in regular layers.

They could perhaps be explained by means of a total transport along the bottom under conditions similar to those of the slides. Such particularly coarse materia! would seem to imply proximity to the source area and a lateral supply in the Numidian miogeosyncline (WEZEL, 1967).

On the bottom of Numidian quartzarenites current marks are sometimes visible.

Flute-casts are mainly found on bottom surfaces of layers more than l m thick. They show an asymmetric section with a sharp up-current end and a longer slightly inclined side on the opposite part. The two sides join at a height from the layer base roughly corresponding to 1/3 of the total lenght of the cast. Flutes length varies between a few cm and 40 cm. In the clearer instances the large casts are tongue-shaped, isolated or in couples, parallel and rather spaced. Smaller casts (about 10 cm long) are, on the contrary, gathered in groups and their downcurrent side may be spiralled. Their orientation constantly indicates a current direction towards ESE.

Current-crescents are rather rare, some of them having been found on the bedding plane of thick layers, about lS cm long, either isolated or associated with flute-casts. They indicate a current direction towards ESE. As no pebbles are present they are probably due to a turning of the current around resistant parts of the clayey bottom.

A single structure of the frondescent-casts type (TEN HAAF, 19S9) has been found on the bedding plane of a layer S.20 m thick cropping out at Grotta Fumata (W of Mt. Etna). It has an arborescent shape with several branches diverging more or less fan-wise from a single trunk. These branches have crenulate margins. The entire cast is very flat (height from the base: 1-l.S cm), about l.S m long, and with branches opening toward ESE. According to DzuLYNSKI & WALTON (1963, p. 294) who produced it by means of artifìcial turbidity currents, this frondescent-cast would be

originated by the sand flow o n the soft sea-floor. Scour channels are present as probably recti

linear and parallel wide elongate ridges similar to enormous groove-casts. Their sections are nearly symmetric and strongly rounded, from a few decimeters up to 2 m wide and little less than 10 to SO cm deep. It seems that their direction is parallel to the other current marks (WNW-ESE).

Deformational structures are also present. They are transfìguration and deformation marks of afready existing current marks and originai marks due to differential sinking of coarse materia! in a finer substratum. When these marks are continuous and regular they appear as small crests of fine sand (grain size about 0.1 mm) intruded in a coarser materia! with quartz grain size about 0.5-1 mm. Crests, up to 8-10 cm high, are not straight but remarkably inclined, all o n the same side; their height is varying. Sometimes they are narrow and sharp separated by wide, rounded troughs. In Numidian Flysch they are generally present along the surface which separates two repeated graded units within the layers. Sometimes instead of these regular and oriented marks (<< load-crests >>

or, according to KELLING & WALTON, 19S7, << flamestructures >>) one can fìnd isolated small parts of coarse materia!, more or less lenticular, under the separation surface between the two graded units. Sometimes the small parts are rig-wise bended with the fìnest sandy materia! in the core.

Both structures seem to be caused by vertical sinking due to overload. As for load-crests besides this cause there also can be the existence of a tractive movement of the current (KuENEN & MENARD, 19S2).

The inclusions of successions of layers (usually 2-3 m X 1-2 m) chaotically embedded within the Numidian pelites, present more or less everywhere, are related to slumpings and to other intraformational disturbances.

Finally, in the Numidian Flysch sandstone dikes are frequently found in Geraci Siculo and Mistretta areas. Those from Geraci have already been described in detail by COLACICCHI (19S9). They are subvertical quartzarenite layers which cut for many meters horizontal alternations of quartzarenite and brown pelite with a sinuous and winding trend. Thicker dikes are SO cm thick. Quite similar dikes have been found in the Numidian Flysch in Tunisia (GOTTIS, 19S3). Their origin is related to seismic shocks which could also have caused the starting movement of turbidity currents down a slope.


<< REITANO FL YSCH ))

by Forese Carlo Wezel

<<Reitano Flysch )) (OGNIBEN, 1960) is a formation belonging to an allochthonous complex, probably orogenically transported from North, which overthrusted the largely contemporaneous autochthonous Numidian Flysch. The <<Reitano Formation >>

consists of a regular alternation of fddspathic sandstones more or less rich in rock fragmcnts, and of grey-blackish clays and marls. Its appearance is largely similar to the << Macigno Formation >> of the Northern Apennines.

The two studied logs have been suryeyed in the north-western edge of Reitano outcrop, bctwcen Castel di Tusa and Pettineo (fig. 1).

About half of the observed layers are gradcd and can generally be ascribed to the abovc mentioned type l. No repeated gr2ding has been observed. Grain size is rather fine at the base of the layers, usually varying bctween 0.25 and 0.50 mm. Sorting is poor and tends to increase toward the top of the layer.

Horizontal lamination (b interval) is abundantly present and consists of an alternation of lighter laminated layers 1-1.5 mm thick with darker and thicker (2-3 mm) oncs. The former ones are mainly composed of quartz grains and fcldspars, very fine silt-sand sized ( maximum diamcter 0.15 mm), and of some fragments of mica. The latter ones are richer in mica, usually 0.5 mm long and lying parallel to the bedding planes. The contact between two laminated layers is not abrupt. Sorting seems rather good and better than the one observed in graded intervals. Lamination genesis is thought to be related to a tractive movement that sorted the grains according to their composition.

Cross-lamination ( c1 an d c2 intervals) division is a thin interval within the layers nearly always less than 5 cm thick. I t consists of small successions of cross laminated layers made of fine sand. The successions are at bottomwards and topwards separated by strongly wavy surfaces, sometimes converging. Waves are asymmetric and have spaced crests, a few cm to about 10 cm (transverse current ripples). Laminae are all inclined on the same side, thus indicating a current direction which seems parallel to the direction of groove-casts in nearby layers. Cross-lamination is exclusively present in thin laminated layers while it is mtssmg in the thicker layers in which the graded interval

1s present. Some layers are composed only of an interval of cross-lamination with or without an overlying interval of convolute lamination.

The convolutions (c3-c5 intervals) consist of wavy laminae more and more corrugateci and irregular towards the top of the layer. They were found both over the interval of cross-lamination and over the interval of horizontal lamination (more frequent instance). In both cases convolutions are at thc upper part of the layer. Thic"kness of interval of convolute lamination varies between l and 70 cm.

Frc. 62 - Convolute lamination with wide symmetrical troughs an d vertical narrower crests; this interval overlies another interval with parallel or gentle waved lamination. Thesc structures were found in two beds of fine grained fcldspathic graywacke in the << Reitano Flysch >>

(log no. 97). lt is to be noticed also the deformation of laminae inside the trough at the upper right side of

the photograph (corrugateci convolute lamination).

- JV[icrostratificazione convoluta di tipo semplice a larghe conche simmetriche e più strette creste verticali sovrastante un intervallo a microstratificazione orizzontale e leggermente ondulata in due strati di fine arcose micaeea del << Flysch di Reitano>) (log n. 97). Da notare la deformazione dei microstrati entro la conca che si osserva nella parte superiore destra della foto (micro-

stratificazione contorta).

From the morphologic point of view the convolutions can be divided into two types. The first one consists of strongly wavy laminae bended to form wide symmetric troughs joined by vertical narrower crests always symmetric and sometimes with a ftat top (fig. 62). The second type is more irregular and shows asymmetric troughs and sharp and inclined crests (fig. 63).

When convolutions are present together with ripples, the two structures are roughly parallel and convolute crcsts stand vertically over current ripple crests (fig. 64 ).

SEDIMENTOLOGJCAL CHARACTERISTICS OF SOME ITALIAN TURBIDITES 401

FIG. 63 - Contact between graded interval (lower level) and laminated intervals (upper levels) in two layers of <<Reitano Flysch l) (log no. 96). In the upper layer there are small platy shale pebbles and in the lower one intervals with wavy and convolute lamination (asymmetrical troughs and bended narrow crests); corrugate d convolute lamination also is present. The contact between the two successive layers shows that there was an erosion of the finer top levels of the lower layer by the high-fiow-regirne current which sedimented the graded interval of the upper layer. The length of the pencil

is 14 cm.

- Contatto fra la parte inferiore gradata e la parte apicale microstratificata di due successivi banchi del << Flysch di Reitano l) del log n. 96. Da notare nel banco sovrastante i piccoli ciottoli argillosi appiattiti e in quello sottostante la successione delle parti a microstratificazione ondulata, convoluta (conche asimmetriche e strette creste aguzze e inclinate) e contorta (microstrati disordinatamente corrugati). La saldatura tra i due banchi indica che vi è stata una brusca erosione della più fine porzione sommi tale del banco inferiore ad opera della corrente, a probabile

alto regime di flusso, che depositava il materiale gradato sovrastante. La lunghezza della matita è di 14 cm.

These convolute laminations are abruptly interrupted by an erosional surface immediately over which the graded interval of the subsequent layer is found (fig. 63). As shown by the photograph, the erosion may affect different levels of the convolute interval.

It is interesting to notice that sometimes, starting from inclined laminae (current ripples), convolute crests inclined on the same side as laminae occur upwards. This clearly proves that deformation of a single lamina occurred simultaneously with the deposition and, moreover, i t proves the existence of some horizontal tractive movement of the cur-

FIG. 64 - A layer of << Reitano Flysch l) (log no. 96), whic shows a lower interval of crosslamination (current from left) and overhanging intervals with wavy, convolute and corrugateci con volute lamination. The small thickness of the layer and the lack of the graded interval seem to indicate a sedimentation by low-fiow-regime current and a successive reworking by norma! tractive currents (laminae, alternatively rich and poor in mica, are better sorted than graded

intervals). See fig. 62 also.

- Strato del << Flysch di Reitano l) (log n. 96) costituito da una parte inferiore a microstratificazione obliqua (corrente da sinistra verso destra) sor

rent. It seems therefore probable that the convolutions have been originated by deformation processes of laminae similar to those responsible for the load-casts (see load-crests).

Clayey inclusions are usually present in the graded interval, where they are generally 5 cm long and l cm heigh, lying parallel to the stratification. They are usually not present at the base of layers. However, a large shale fragment, 17 cm long, has been observed at the base of a layer. Shale pebbles are rare in the laminated intervals and consist of tiny clayey fragments.

montata da successive parti a microstratificazione ondulata, convoluta e contorta. Il ridotto spessore dello strato e la mancanza dell'intervallo gradato alla base fanno pensare a deposizione ad opera di una corrente a basso regime di flusso e ad un possibile successivo rimaneggiamento ad opera di normali correnti trattive (i microstrati, alternativamente ricchi e

poveri in miche, appaiono meglio classati rispetto a quelli gradati). Confronta anche la fig. 62.


Marks wbicb can be related to organic traks were only occasionaly found. Among the more interesting ones, the presence of tracks of Helmintoidea type (but having a spiralled and concentric trend) are to be stressed. These marks may be ascribed to Nereites s.l.

Groove-casts are present as continuous and parallel rectilinear ridges of various lenght and height. In general tbey are not associateci witb flute-casts while sometimes they are associateci with small, discontinuous bounce-casts.

Bounce-casts are usually lower than 10 cm in lengtb. These casts are sbort, symmetric and spindle-sbaped and are associateci witb groovecasts witb wbicb tbey can be confused. Tbey bave a direction parallel to grooves and may be very numerous on the undersurface of a same layer.

Dendritic-casts (<< dendritic pattern >>, KuENEN, 1957) bave been found on tbe undersurface of a layer of tbe << Reitano Flyscb >>, some bundred meters S of tbe log area. They cover all tbe exposed surface (fig. 65) whicb is grooved by arborescent groups oriented in the same direction and parallel to the current direction indicated by the groovecasts. Eacb group consists of a set of numerous, very narrow, short (around 10 cm long) furrows rougbly parallel. They are all converging in tbe same direction towards a centrai, more continous furrow and tbe wbole covers tbe entire outcrop.

FrG. 65 - Dendritic-casts at the base of a layer which overlies another layer with groove and bounce-casts (<<Reitano Flysch >>). Current direction was from the upper right corner. The photograph was taken about 1 km far from the locality where log no. 97 was

surveyed.

- Dendritic-casts alla base di un banco del << Flysch di Reitano>> a sua volta sovrastante uno strato con la superficie basale striata da groove-casts e bouncecasts. Scorrimento della corrente probabilmente dall'alto verso il basso e da destra verso sinistra. << Flysch di Reitano >) affiorante 1 Km circa a Sud

del log n. 97.

Tbe bifurcation of brancbes from tbe centrai stem shows angles of about 10-15°.

Sucb a structure implies tbe occurrence on the muddy sea-floor of small vertical and parallel ridges whicb separate wider cbannels witb a flat bottom. The origin and preservation of tbese ridges is difficult to be explained without assuming some subsequent magnification by load casting (TEN HAAF, 1959). Anybow DZULYNSKI & WALTON (1963) bave been able to experimentally produce tbese dendritic-casts with the sole flow of a current. From tbe experiment carried out by tbese two Autbors tbe following conclusions are drawn: ( 1) tbe concerned casts are current scour-markings due to slow currents, (2) tbey can result either from converging (more common instance) or from diverging of tbe stream-lines. Tbese casts can therefore be used to determine only tbe line of movement of tbe depositing current but not its direction.

Load-casts are visible in some outcrops, on tbe bedding piane of about l m thick layers. Tbey consist of elongate channels wbose section is very wide (up to SO cm in diameter) separated by tbin sharp crests wbicb pierce up to 30 cm in tbe arenaceous layer; they are originai clayey intrusions of << diapiric >> type. Tbe iso-direction of these load-crests proves tbat deformation took piace simultaneously to a tractive movement of tbe current.


FINAL REMARKS

Considerations about each formation are given in the paragraph which they belong; for this reason in this chapter we give just the more generai data regarding turbidite deposits. Some of these data were elaborateci by computer and they represent just a first result; different kinds of analyses are now under way.

Analyses carried out at the present time regard ~'<-~T).ti.ally a linear correlation between intervals and their frequency, sole markings and their frequency, layer thickness and base grain size, layer thickness an d thickness of each interval in the layer, frequency of a single interval or groups of intervals within each layer, frequency of cl> 2 , 3, 4 , 5 levels within c interval and of their possible combinations.

Intervals frequency

Intervals, number of times they appear in 1888 layers, their frequency distribution regardless if they are single or in group within the 1888 layers, and their frequency distribution percentages made on the total of 4363 intervals are shown in tab. I.

TAB. I

Frequency Frequency lntervals Frequency distribution distribution

on 1888 on 4363 layers intervals

a 705 37.34 16.15

b 618 32.73 14.17

cr 615 32.57 14.09

Cz 40 2.12 .91

C3 205 10.86 4.69

C4 151 8.00 3.46

cs 56 2.97 1.28

d 470 24.89 10.78 e 1503 79.61 34.37

Besides the pelagic interval (e), the more frequent one is the current ripple lamination interval (c) that we divided in five levels of which the more frequent is cr and then c4• It is interesting to notice that among the different c levels the one characterized by a more confused structure is also the more rare ( c2 an d c5).

Sole markings

Among sole marks the worm tracks and load casts are respectively the more frequent, while ftute and groove casts and erosion channels are less frequent as it is clear from tab. II. Organic and scour marks are frequent in the layers whose average grain size is about 2.5 ID; average grain size of the base of layers with loading casts and tool marks is coarser and about 1.9 ID. Shale fragments, nodules, and lenses in the sandy beds are not frequent (3.7%) and they were found in layers whose average base grain size is about 1 ID.

TAB. II

Frequency Casts Frequency distribution

on 1888 layers

---·--~·- ----

Worm tracks 183 9.7

Loading casts 117 6.2

Tool marks 77 4.1

Scour marks 54 2.9

Correlation between layer thickness and base grain size

The analysis pointed out that there is no correlation between these two parameters. However it is to be noted that this result may be due to the kind of measurements (in the field and with comparison samples) and to the large number (about ten) of studied formations, which, sometimes, show quite different characteristics. The trend of the regression line is sub-horizontal.

Correlation between layer thickness and thickness of each interval

Total thickness of each layer is controlled essentially by the thickness of the graded interval and of e interval, but, also for these two intervals, variance is always high.

Frequency of the single intervals and of groups of intervals

As it is clear from tab. III, 30 layers only (1.58%) are characterized by a complete sequence of intervals; 705 layers begin with the graded interval and 280 are characterized by the presence of both the graded and the b interval.


Intervals

a

b c d e

ab a c ad a e be be cd ce de

ab c ab d a be a cd ace ade be d bee bde c de

ab cd a bee ab de a c de be de

a be de

TAB. III

Frequency

93 13 33 2

216 11 18 20

204 20 98 65

369 72 19 17

106 7

51 17 19 95 21 77 12 61 24 15 47 30

Frequency distribution

on 1888 layers

4.92 .68

1.74 .10

11.44 . 58 .95

1.05 10.80 1.05 5.19 3.44

19.54 3.81 1.00 .90

5.61 .37

2.70 .90

1.00 5.03 1.11 4.07

.63 3.23 1.27 .79

2.48 1.58

Besides sequences truncated at the top or at the base, already observed by many Authors, there

are sequences lacking of some of the intermediate intervals (for istance, sequences of the type Ta-c-d-e; Ta-b-d-e; Ta-c-e; etc.).

Frequency of Ct, z, 3, 4, 5 levels and of their combinations within c interval

From tab. IV in which levels, their frequency for the 1888 studied layers, and their frequency distribution percentages are reported, clearly appears that level c1 is the most frequent .

Levels

CJ

Cz

CJ

C4

cs CtCz

CtC3

CtC4

CtCs

C3C4

C3C5

C4C5

CtCzC4

C1C3C4

CtCJCs

C3C4C5

C1C3C4C5

TAB. IV

Frequency

525 37

139 104 28 2

43 27 12 5 4 2 l 4 l 8 l

Frequency distribution

on 1888 layers

27.80 1.95 7.63 5.50 1.48 .lO

2.27 1.43 .63 .26 .21 .10 .05 .21 .05 .42 .05

Groups of two or more levels are very rare and just in one layer the complete sequence from c1

to c5 ts present.

RIASSUNTO

Scopo del lavoro è stato quello di esaminare le caratteristiche sedimentologiche di alcune torbiditi italiane; ad esso hanno contribuito tutti i ricercatori del Gruppo di Ricerca per la Geologia dei Sedimenti del Consiglio Nazionale delle Ricerche. Gli Autori hanno studiato alcune sezioni appartenenti al maggior numero possibile di formazioni senza tener conto delle età; particolarmente è stato esaminato: lo spessore e la frequenza degli intervalli (vedi pag. 346) definiti da BouMA (1962); le dimensioni granulometriche della base di ciascun strato; la presenza di noduli argillosi e di impronte basali e di strutture interne; la distribuzione percentuale granulometrica per ogni singolo livello. Con particolare cura è stato analizzato l'intervallo c di BoUMA

che è stato diviso in cinque ttpt: cross lamination (fig. 64), deformed cross lamination (fig. 14), wavy lamination (fig. 5), convolute lamination (iìg. 11), corrugated convolute lamination (fig. 10).

L'area studiata si estende dalle Alpi alla Sicilia e include buona parte dell'Appennino. Le formazwni studiate sono le seguenti:

Flysch del Friuli e della Venezia Giulia (Paleogene) Flysch del Bellunese (Paleogene) Flysch delle Prealpi bergamasche (Cretaceo) che include il Flysch di Pontida, le Arenarie di Sarnico e il Flysch di Bergamo


Formazione delle <<Ardesie >> negli Appennini liguri (Cretaceo inferiore) << Flysch ad Elmintoidi >> nelle Alpi Occidentali (Cretaceo superiore) Torbiditi delle Langhe in Piemonte (Miocene); comprendono la Formazione di Cassinasco e la Formazione di Cortemilia << Arenarie Superiori >> negli Appennini della Liguria orientale (Cretaceo superiore-Paleocene) Arenarie di Bismantova negli Appennini emiliani (Miocene) Formazione del << Macigno >> negli Appennini centro-settentrionali (O ligocene) Formazione della << Pietraforte >> negli Appennini centro-settentrionali (Cretaceo superiore)

- << Marnoso Arenacea >> negli Appennini romagnoli (Miocene medio)

- << Formazione Argilloso-Arenacea>> negli Appennini laziali-abruzzesi (Miocene medio-superiore) T or bi diti calcarenitiche nell'Appennino molisano (Miocene medio) Torbiditi della penisola sorrentina Flysch del Cilento occidentale Miocene ?)

(Miocene) (Cretaceo-

- Flysch Numìdico delle Madonìe e dei Nèbrodi (Oligocene medio - Miocene inf.)

- << Flysch di Reitano>> dei Nèbrodi (OligoceneMiocene medio).

Sono state esaminate 97 sezioni per uno spessore di 602 m ed un totale di 1888 strati ; la loro ubicazione è riportata in fig. l. Le granulometrie sono state effettuate in parte in campagna con l'aiuto di comparatori e in parte in laboratorio mediante setacciatore per le parti grossolane e pipetta per le frazioni più sottili; i campioni per le analisi granulometriche sono stati prelevati essenzialmente dagli intervalli a, b e c.

I dati ottenuti sono stati parzialmente elaborati mediante un calcolatore IBM 7040 in base a programmi di correlazione lineare (l) ed in particolare sono state analizzate: le correlazioni fra gli

(1) Gli Autori esprimono i loro sentiti ringraziamenti al Prof. DE VITo, Direttore del Centro di Calcolo dell'Università degli Studi di Roma e alla D.sa MARCHIORO per l'assistenza prestata durante l'elaborazione dei dati.

intervalli presenti e le loro frequenze di apparizione, la frequenza delle impronte di fondo, lo spessore degli strati in relazione alla granulometria basale, lo spessore degli strati in relazione allo spessore di ciascuno degli intervalli, la frequenza di ciascun intervallo e di gruppi di intervalli, la frequenza dei singoli livelli o di gruppi di livelli distinti nell'ambito dell'intervallo c di BouMA.

Come risulta dalla tab. I, oltre all'intervallo pelagico (e), il più frequente fra gli intervalli di BoUMA è quello di tipo c, generalmente rappresentato dai livelli c1 e c4• È interessante notare che fra i diversi livelli di tipo c il più raro è quello che presenta una struttura più complicata (c5). Fra le impronte d,: fondo (tab. II) più frequenti sono quelle organiche e quelle dovute a fenomeni di carico. Inoltre le impronte organiche e di erosione sono generalmente presenti in strati con granulometria basale di circa 2,5 cD, mentre quelle di carico e di trascinamento si ritrovano in strati la cui granulometria di base è di circa 1 , 9 cD.

In generale non si è notata alcuna correlazione fra lo spessore degli strati e la granulometria di base; è però da tenere presente che questo risultato può essere stato falsato sia dal metodo di misurazione della granulometria (in campagna e mediante campioni di paragone), sia dal fatto che sono stati accomunati i dati ottenuti per molte formazioni ( circa 10) spesso con caratteristiche molto diverse. Nella correlazione fra lo spessore degli strati e quella dei singoli intervalli si è ottenuta sempre una varianza molto elevata, ad ogni modo lo spessore totale sembra essere controllato essenzialmente dallo spessore degli intervalli a ed e. L'analisi della frequenza dei singoli intervalli e di gruppi di intervalli ha messo in luce alcuni fatti interessanti: soltanto 30 strati su 1888 presentano la sequenza completa di tutti gli intervalli; circa metà degli strati iniziano con l'intervallo a; oltre a sequenze troncate alla base o al tetto (già osservate da altri Autori), sono frequenti anche sequenze in cui mancano uno o più degli intervalli intermedi (tab. III). Fra i diversi livelli in cui è stato suddiviso l'intervallo c di BouMA il più frequente è quello del tipo c1 ; il raggrupparsi di due o più livelli rappresenta un fatto sporadico e soltanto una volta (su 1888 strati) è stata rinvenuta la sequenza c, c, c4 c, mai quella completa (tab. IV).

Manoscritto presentato nel Giugno 1967

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SEDIMENTOLOGICAL CH.4RACTERISTJCS OF SOME /TAL/AN TURBIDITES 409

APPENDIX

GRAPHICAL LOGS OF THE SURVEYED SEQUENCES. All the data measured or observed in the field are shown in these graphical logs and they were used in this work either for the description of the sequences and for the statistica! elaboration. The meaning of each column is as follows: 1 - number of the series, 2- number of each layer in the series, 3 - thickness of each layer in millimiters, 4 - occurrence of sole markings ( 4a: organi c casts; 4b: tool marks; 4c: scour marks; 4d: load casts), S - thickness of intervals with different internai structures (Sa: graded bedding; Sb: parallel lamination, Sct: cross lamination; Scz: deformed cross lamination; Sc3: wavy lamination; Sc4: convolute laminati an; Sc5 : corrugateci convolute laminati an; Sd: parallel lamination in fine sediments; Se: peli tic interval), 6 - occurrence of shaly fragments, nodules and small lenses, 7 - average grain size of the base of each layer (in phi). (Leggenda in Italiano a pag. 420)

! 4

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SEDIMENTOLOGICAL CHARACTERISTICS OF SOME ITALIAN TURBIDITES

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E. DE ROSA - A. RIZZINI - Prealpl Flysch near Bergamo Coniaciano

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G. FIERRO - "Ardesie" in the Ligurian Apennines

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G. FIERRO - "Flysch ad Elmintoldl" In the Western Alps Cenomaniano - Maestrichtiano

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M. GNACCOLINI - Langhe Turbidites in Piedmont Miocene inferiore n-r- -: 4 . 1 --- --~5---- ~ -~ 1

! l ' 21_11

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E. DE ROSA- A. RIZZINI - Prealpi Flysch near Bergamo Santoniano

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E. DE ROSA - A. RIZZINI - Prealpi Flysch near Bergamo Turoniano

a 1 d ~~-----+~+-~---+--~--+--+~~~~~--r---+-+--j

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G. FIERRO - "Arenarie superiori" in the Apennines et Eastern Liguria - Albiano - Paleocene

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G. C. PAREA ·''Arenarie superiori" in the Apennines of Eastern Liguria · Cenomanlano · Turonlano

4

1 2 3 ab cd

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3 701' l' ? l ?

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46 20 2 310 3 30 4 70 5 85 ? 6 50 7 160 8 25 9 600

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G. C. PAREA : Bismantova Sandstones in the Emilian

4

Apennines · Langhiano

970 10(

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l

l l

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G. FIERRO- "Macigno" in the Middle- Northern Apennines Oligocene medio - superiore

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G, C, P AREA- "Macigno" in the Middle- Northern Apennines Oligocene medio- superiore

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G_ C_ P AREA - "Pietraforte" in the Mi dd le- Northern Apennines Senonlano

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1,5

A. RIZZINI- "Marnoso-Arenacea" In the Romagna Apennines Langhiano - Elvezlano

4 5

1 2 3 ab cd a b c, c, c3 c. Cs d e 6 7

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10 250 30 no 4,0 Il 590 300 so 240 0,0 12 680 + 280 400 0,0 13 130 60 70 4,0 14 400 + 80 40 280 2,0 15 470 50 420 4,0 16 700 + +. 300 100 50 250 0,0 17 250 50 200 4,0 18 900 + 200 100 600- 2,0 19 780 80 700 4,0 20 400 50 350 4,0 21 8.50 l- 700 150 + 0,0 22 300 + 150 150 4,0 23 950 + 400 200 100 250 0,0 24 430 80 350 4,0 25 130 50 80 4,0 26 540 80 120 2,0 27 200 80 120 4,0 28 330 80 250 4,0 29 170 170

l 59 l 14300 l 12450 l ':j 14300 0,0

2 2400 50 0,0 3 3600 l 3100 100 400 + 0,0 4 2200 2200 0,0 5 350' + 350 0,0 6 6401 + 190 450 2,0 7 4580 3600 700 2SO fO,O

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lO 1220 120 1100 4,0 11 1840 1800 4,0 12 2700 + 150 50 2500 4,0 13 570 70 500 4,0 14 2210 + 110 2100 4,0 15 1960 60 1900 4,0 16 2300 100 2200 4,0 17 1650 50 200 200 1200 2,0 18 1500 120 1400 4,0

G. C. PAREA- "Marnoso-Arenacea" in the Romagna Apennines Langhlano- Elveziano_

-----·------ ------ -~······ .. 4 5

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SEDIMENTOWGICAL CHARACTERISTICS OF SOME ITALIAN TVRBIDITES 417

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- Locs GRAFICI DELLE SERIE ANALIZZATE. Tutti i dati misurati od osservati sono stati riportati su logs grafici che poi sono serviti di base sia per la parte descrittiva del lavoro che per l'elaborazione statistica. La leggenda delle singole colonne in cui ciascun log è stato suddiviso è la seguente: 1 - numero della serie, 2 - numero di identificazione di ciascuno strato nella serie, 3 - spessore in millimetri dei diversi strati, 4 - presenza di impronte sulla superficie basale degli strati (4a: impronte organiche; 4b: impronte di trascinamento; 4c: impronte di erosione; 4d: impronte di carico), S - spessore degli intervalli con strutture interne (Sa: gradazione; Sb: laminazione parallela; Sct: !ami nazione incrociata; Scz: laminazione incrociata deformata; SCJ: laminazione ondulata; Sc4: laminazione con voluta; Scs: laminazione con voluta ribaltata; Sd: laminazione parallela in materiale fine; Se: intervallo pelitico), 6- presenza d'inclusi d'argilla, 7- granulometria media alla base dei diversi strati (in phi).

Documents

B. MARTINIS, G.C. PAREA, T. PESCATORE, A. RIZZINI, F.C ... 6/GR_6_345_420_Angelucci et al.pdfof Mollusca, Corals, macrophoraminifers, etc. (DAI NELLI 1912, FABIANI 1915). Also microfauna