More and Scruton (1957)

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B U L L E T I N O F T H E A M E R I C A N A S S O C I AT I O N O F P E T R O L E U M G E O L O G I S T SVOL. 41. NO. 12 (DECEMBER, 1957). PP. 2723-2751. 16 FIGS.

M I N O R I N T E R N A L S T R U C T U R E S OF SO AIE R E C E N TU N C O N S O L I D AT E D S E D I M E N T S '

D . G. M0 0R E2 AND P. C. S CRU T0N 3San Diego, California, and Tulsa, Oklahoma

A B S T R A C T

Widespread occurrence of several different minor sedimentary structures in shallow-waterGulf of Mexico sediments has been shown by more than 2,000 cores and bottom samples. Minorinternal structures in two areas, one oft the east side of the Mississippi River Delta and the otheralong the central Texas coast, were found to be similar. Deposits in these two areas were subdividedinto those containing: (i) regular layers (thin beds or laminations), (2) irregular layers (rough orcrude layers and lenses), (3) mottles (discontinuous lumps, tubes , and pock ets), and (4) structurelesshomogeneous sediments, deyjending on the principal type that occurs.

Areal distributions of these different structures in the surficial sediments are mappable. Similarsedimen tary s tructures and sequences of structures occur in the open gulf and in the bays and sou nds.In the open gulf the structures occur in wide bands, and the sequences are developed through wideranges of water depths; in the bays and sounds the bands generally are narrower, and the sequencesare compressed into much smaller ranges of water depths.

The different types of structures are formed on or near the depositional surface, contemporaneousor nearly contemporaneous with deposition. The differences between depositional environmentswhich produce the various structures are differences in: (i) sediment sources, (2) in physical processesand their intensities, and (3) rates of deposition. Regular layers are characteristic of areas of rapiddeposition an d/o r relatively few bottom-living animals; they are either primaryformed by fluctuations of sediment, or secondaryformed by w ave or current winnowing. Irregular layers and mo ttlesare mostly secondary features, formed mainly by bottom-living animals altering existing sediments.Hom ogeneous deposits are either primary or secondary; they form b y extremely rapid deposition, uniform deposition, or by complete secondary reworking. The appearance of many normal marinesediments is due in large measure to burrowing and crawling organisms.

Structures similar to those in presently forming sediments of the Gulf of Mexico apparently weredeveloped in rocks of all ages when environmental conditions were proper. Knowledge of how thesestructures form, why they vary, and the relationships between them furnishes a valuable key forinterpreting deposition of ancient rocks.

INTRODUCTION

Proje ct 51 of the Am erican Pe trole um In st itu te , for the stu dy of recent continental shelf and nearshore marine sediments in the northern Gulf of Mexico,has been active at the S cripps Ins titu tion of Ocean ography since 1951. Two principal areas have been studied; one is on the east side of the active MississippiRiver Delta, and the other is a region of protected bays, barrier islands, andopen shelf on the central T exas coast near Ro ckp ort (Fig. i, also Figs. 8 and 9for detail). During the course of these studies more than 2,000 sediment samples

^ Contribu tion from the Scripps Institutio n of Oceanograph y by New Series No. 956. Thisinvestigation was supported by a grant from the American Petroleum Ins titute , Project 51 . M anuscript received, August g, 1957.

^ U. S. Na vy Electronics L abo ratory .

Pan American Petroleum Corporation. Acknowledgments. Field work and preliminary composition of this study were done while the writers were associated with the Scripps Institution ofOceanography. They are indebted to the Navy Electronics Laboratory and to the Pan AmericanPetroleum Corporation for time and facilities to complete the manuscript. Thanks also are due toF . P. Shepard for assistance in the Texas coast field work, to R. H. Parker for valuable help in thelaboratory tank experiments, and to D. M. Poole who photographed many of the cores studied inthis program. The manuscript was read and criticized by H. .\. Bernard, P. A. Dickey, M. K. Hanna ,N . A. Riley, and R. D. Russell of the A.P.I. 51 Advisory Committee and by F. P. Shepard andT j . H. van Andel, Project 51 directors.

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2 7 2 4 D. G. MOORE AND P. C. SCRUTON

have been collected, most of which were cores. Processing of these cores andother samples included visual study of their minor internal structures.*

To many geologists, the small internal structures of sedimentary rocks, formedwhen the sediments were first deposited and still soft and plastic, are among

their most interesting and puzzling features. One of the purposes of this paper isto describe those minor internal structures that occur in shallow-water depositsof the Gulf of Mexico and to discuss their distributions and origins. It is hopedthis discussion will contribute to a better understanding of these structures inmore ancient rocks. In addition, study of these sedimentary features has shownthat their type and character are closely related to the sedimentary environmentsin which they are formed. These structures are of such widespread distribution

OKLAHOMA

TEXAS

h-AEXICOiC/

A

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rv \ ALABAMA

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Mississippiy

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G U LF OF M e x i c o

FIG. I .Map of northwest Gulf of Mexico, showing locations of study areas.

and occurrence, both in recent sediments and in older rocks, as to deserve generalattention in environmental interpretation.

Some types of original sedimentary structures such as bedding, cross-bedding,ripple marks, animal tracks, shrinkage cracks, flow-casts, and features resultingfrom contemporaneous (wet) deformation are described and discussed in an

extensive literature. Several of the minor structures discussed here also have beennoted previously under various names, but they have not been discussed asextensively.

In the literature on minor structures such works as those of ilcKee (1939)and Thompson (1937) are noteworthy, because of the emphasis they laid on

* Min or internal structure s and small original sedim entary structu res are terms used here interchangeably to cover original li thologies or fabrics that are visible to the naked eye or with a handlens. They may be of primary origin or developed secondarily, but in either case, they are formedon or just beneath the de position al surface. As these te rm s are used here, the y exclude fabrics orstructures of later, diagenetic, origin such as those produced by chemical alteration or reorientationof particles through compaction or tectonic forces.


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INTERNAL STRUCTURES OF SEDIMENTS 2725

understanding of the processes that produce original structures, and the relationships these processes bear to the general sedimentary environment. Both theseworkers later were successful in applying their understanding of the processesthat produce different structures to the interpretation of ancient rocks (McKee,

1954; Thompson, 1949). Recent work by other geologists also has emphasizedthe importance of describing minor sedimentary structures and determining theenvironmental processes that produce them. In studying sediments of the tidalflats of the Dutch Wadden Sea, van Straaten (1951) ascribed the minor structureswithin the sediments to processes of these depositional environments and usedthis as background for interpreting older (Devonian) rocks. Stewart (1956)described some minor contorted structures in exposed sand flats of a tidal deltaand used laboratory experiments to demonstrate their formation by "air-heave."This is a mechanism active in only a few sedimentary environments.

Scruton (1955) has shown that depositional environments of the MississippiRiver Delta differ from one to another because of variations between three fundamental factors. These factors are: (i) the sources of sediment, (2) the processes(physical and chemical) that occur in them and their intensities, and (3) the rateat which deposition occurs. These three basic factors are dynam ic, and the y interact with each other in a complicated way to govern the kinds and amounts ofsediments deposited. Moore (1955) and Shepard and Moore (1955) have demonstrated that these same basic factors are responsible for variations in sedimentsin the central Texas coastal area. Rate of deposition in this area is much less variable than in the Mississippi Delta, however, and the fundamental importance of

this environmental factor is therefore less striking.D E S C R I P T I O N

The minor structures that have been studied are visible in the sedimentsprimarily because of textural variations, and secondarily because of differences incomposition and color. The structures have been subdivided into four basic typesdepending on their appearance on the flat surface of a cut or of a longitudinallysectioned core. The four basic types are: (i) regular layers, (2) irregular layers,(3) mottles, and (4) homogeneous sediments (Fig. 2).

No attempt has been made to fit these features into any of the proposed size

classifications of sedimentary structures (cf. Pettijohn, 1949, p. 120; McKee andWe ir, 1953; Ing ram , 1954; Gra y, 1955). Ho we ver, where am enab le to such classification, they would be called medium, thin, or very thin beds following Gray(1955, p. 147), as they generally are less than 10 cm. in thickness.

LAYERS

Layered structures, as the name implies, are layers or bands of coarse- andfine-grained sediments (Fig. 2), which may alternate in any order. These structures are tabular or lenticular in three dimensions. Individual layers generallyhave sharp or relatively sharp contacts with adjacent material and therefore


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2726 G. MOORE AND F. C. SCRUTON

REGULAR LA YE RS IRREGULAR LAYERS

Tabular or thin lenticular bodiesfn matrix of contrasting texture,horijontally- or c ross -bedded

I r r e g u l a r l e n t i c u U rb o d i e s in m a t r i x ofc o n t r a s t i n g t e x t u r e

M O T T L ES * Irregular lumps, t\jbs or poctiets in matrix of contrasting texture

D I S T I N C T IWDISTIWCT

Boundaries sharply defined

HOMOGENEOUS

Bounda ries poorly defined

O R I G I N L

S E D IM E N T R Y

S T R U C T U R E SUniform texturci no Visiblestructures-, particle st jescompletely mixed

F I G 2.Basic types of minor internal structures.

Stand out as distin ct uni ts from the general mass of sediment if it is uniform, orfrom adjacent layers if the sediment is variable. Two types of layered structu resare recognized: (i) regular, and (2) irregular (Figs. 2-4).

REGULAR LAYERS

Regular layers have relatively uniform thickness in core section, and adja cent

layers or sets of layers usually are nearly parallel. The layers are horizontal orinclined, and m ay be slightly curved. Thicknesses of individ ual layers generallyrange from a fraction of a millimeter to about 10 centimeters, and the thinnestones usually lens or pinch out in core section. Reg ular lay ers may be relativelyhomogeneous in texture, but ma ny coarse-grained layers, particularly thethicker ones, are thinly lamin ated or cross-laminated internally (Fig. 3). In general, regular layers present a neat, orderly, parallel or sub-parallel appea rance,regardless of their thickness.

IRREGULAR LAYERS

In contrast to regular layers, irregular layers present a disorganized appearance. Thickness of irregular-layered structures is ma rkedly non-uniform in core


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2 7 2 8 D. G. MOO RE AND P. C. SCRUTON

MP 2 6 3

MP 75

V)Xo

FIG. 4.Irregular layers. Cores showing irregular shapes of layers andabsence of cross-bedding.

s t ru c tu re s co m m on ly a re a f ew mi l l ime te r s t o seve ra l cen t im e te r s i n d i am e te r.In c ross sec t ion , i nd iv idua l l umps a re o rd ina r i ly, bu t no t necessa r i ly, c i r cu la r.

Tex ture o f t he i r r egu la r l umps , pods , t ubes , and l enses may be e i the r coa rse r

or f ine r t han the ma t r ix , o r t he re may be nea r ly equa l d i s t r ibu t ion be tweencoa rse and f ine lumps in the sed iment . Examples o f coa rse lumps in a f ine ma t r ixan d f ine lum ps in a coa rse m a t r ix a re show n in F igu re 5 . Te x tu res of i n d iv idu a ls t ruc tu re s range f rom c lean sand in a f ine ma t r ix to poor ly so r t ed sand in a ma t r ixof s i l ty c layey sand and f rom c lay in a c lean sand to sandy c lay in poor ly sor tedsand . She l l s and she l l f r agment s gene ra l ly a re p re sen t bu t commonly a re no t .

Th e re is no t en de ncy to wa rd hor i zo n ta l a l ign m en t of t yp ica l mo t t l e s . In fac t ,t he con t ra ry o rd ina r i ly i s t he case , and the re appea rs to be a p re fe r red ve r t i ca lo r i e n t a t i o n . Mo t t l e d s t r u c t u r e s b e c o m e i n d i s t i n g u i sh a b l e f r o m i r r e g u l a r l a y e r swhe re the re is som e hor i z on ta l a l ign m en t and an inc rease in regu la r i ty.


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0E 5 A

10

20

;m

0A 2 6 A A 5 3 B

10

A20

B

cm.

DISTINCTINDISTINCT

FIG. 5.Mottled structures. Examples of coarse mottles in fine-grained matrix (A), fine-grainedmottles in coarse matrix (B), and approxima tely equal distribution b etween coarse and fine sedime ntsin mottles and matrix (C). Striations on E5A and A26A are knife marks.

True mottles are not produced by distortion of soft sediments in sampling.They have been found with all types of sampling equipment and are well developed where there is no question of the undisturbed nature of the sample.

Two types of mottled structures have been recognized: (a) those with distinctbou nda ries, and (b) those w ith indistinct b oun darie s (Figs. 2, 5). Th eir differentiation is based on the amount of textural gradation between lumps and matrix;there is no precise division be tween the type s, and in places they co nstitute a con-


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2730 D. G. MOOR E AND P. C. SCRUTON

tinuous series. Sediments with indistinct mottling in turn grade into homogeneoussediments with further decrease in sharpness of contact and textural contrastbetween lumps and matr ix.

H O M O G E N E O U S S E D I M E N T S

Sediments with no visible internal structures complete the list of types normally found in the unconsolidated shallow marine deposits of the two Gulf Coastareas. These sediments are massive, and their relatively uniform texture may be

FINE COARSE

MP 7 8 MP 13FIG. 6 .Homogeneous deposits. Clay and sand. Striations are knife marks.


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fine-grained (clays and silty clays), coarse-grained (sands), or any intermediatetexture (Figs. 3 , 6) . Homogeneous sediments approach "textural maturity"(Folk, 1951) in the petrographic sense as the proportion of coarse material increases.

LATEEAL CONTINUITY

Duplicate and multiple cores between which layering might be traced weretaken within small areas to determine the amount of lateral continuity in layeredstructures. Individual mottled structures by definition are discontinuous.

Short duplicate cores from 200 stations in San Antonio Bay, Texas, werecompared by F. P. Shepard (1953) to determine continuity of sandy zones in thatarea. Generally the cores were collected only a few feet apart and at most only afew score feet. These observations showed that there is little tendency for irregular layers to persist laterally. Sixty of the 200 stations contained distinctiveirregular layers, but in only nine instances were layers repeated at the same orapproximately the same depth in the nearby duplicate core.

A double barrel, or bident, corer was used for collections in both the Mississippi Delta and Texas areas. Barrels of the bident corer were mounted 32 inchesapart, giving samples with constant lateral separation. These samples showedthat individual irregular layers, even though well developed in one core, couldnot be traced with certainty to the adjacent core. In most instances they alsoshowed that the zones in which groups of irregular layers occurred could betraced from core to core, although in lower San Antonio Bay even zones couldnot be traced with certainty (Fig. 7).

To test the continuity of regular layers, multiple cores were taken in "delta-front silts and sands" and "pro-delta silty clays" of the Mississippi Delta (Scru-ton, 1955, Fig. i). Sixteen of these cores were taken in a rectangular pattern ime ter apa rt in the bay between M ain Pass and B aptis te C ollette Bayou. Some ofthe individual regular layers were recognizable in as many as 9 or 10 of the 16cores. Some groups of layers or zones were traceable throughout all of the 16cores. Continuity of the regular layers in these very shallow-water samples wasgreater than that of regular layers in bident samples from "pro-delta silty clays"that are forming farther seaward in deeper water. In the silty clays the thin, indi

vidual, regular layers rarely could be traced between bident cores, but zones orgroups of layers usually extend from core to core.

Because the deposits are under water, trenching such as used by Thompson(1937) or McKee (1939) to test lateral development is not possible. However,methods other than coring were used in the continuity studies, and they haveyielded similar results. A large van Veen sampler (2 cubic-foot clam shell) wasused on the continental shelf offshore from the Texas barrier islands. These largesamples are virtually undisturbed when taken in fine sediments, and manyshowed zones of discontinuous mottled structures traceable across the entire


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2732 D. G. MOO RE AND P. C. SCRUTON

sample. Some samples contained large mottles of sand up to 4 or 5 inches indiameter which might be misinterpreted as thick layers in small-diameter cores.

Careful testing for small changes in bottom sediment was made in shallowwater outside small distributaries of the Mississippi Delta. This was done by

feeling the sediment with the hands, as it is impossible to see the bottom throughthe muddy water. It was found that thin, uniformly shaped, discontinuous lensesof more sandy material occurred on and below the sediment surface. These thinlenses ranged in diameter from a few inches to several yards.

A B

L T ' -

o

^ ^ .

r - ,

J 67 A B B S 2 4 8 A a BFIG. 7.Bident cores. Pair A shows lateral continuity of zones; pair B

shows lack of continuity.


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K^

^

m ^ i

asajy^arL E G E N D

1 3 REGULAR LAVER5

H IRRESULAR LAYERS

AREAL DISTRIBUTION

OF MINOR INTERNAL STRUCTURES

IN CENTRAL TEX AS AREAQ MOTTLES (DISTINCT INDISTINCT)

PE] H0MO6ENEOUS (FINE)

' ^ HOMOGENEOUS (COARSE)

o l i c i n r i M i c i t MI I I

STATUTt MILESCONTOURS IN FATHOMS

XFIG. g.Distributions of minor structures in central Texas bays,

lagoons, and Gulf of Mexico.


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tares in the deeper parts of the bays are distinct mottles, whereas those in theshallower water are of the indistinct type grading shoreward into coarse homogeneous sediments, as previously described. In the open gulf seaward of the barrierislands (Fig. 9) mottles are forming in a broad band roughly parallel with the

coast in water depths greater than about 50 feet. This band is irregular in outlineand extends seaward into water 120-300 feet deep.

In the Mississippi Delta area, mottles occur in sediments of both the soundand the open gulf (Fig. 8). In Breton Sound they are found predominantly in abelt jus t landw ard of the ba rrier islands. Th e dep th of. wa ter ranges from ab ou t4 to 20 feet. In the open gulf m ottle s occur in a band lying seaw ard of the ban dof irregular layers. The band of mottles also extends around the fine-grained deltadeposits. On the landward side of this band the mottles are mostly distinct, andthey grade into indistinct mottles on the seaward side away from the delta.Water depths in the open gulf where mottles are forming range from about 15feet near Breton Island to about 350 feet on the outer shelf on the east.

HOMOGENEOUS SEDIMENTS

Homogeneous, structureless, fine-grained clays and silty clays are being deposited seaward from the Mississippi Delta in water depths greater than about120 feet (Fig. 8). These fine homogeneous deposits occur as a large lobe on theshelf east of the delta. Fine-grained homogeneous beds also occur in the deepestpa rts of southern Breto n Sound where water de pths are between 18 and 27 feet.In the Texas area (Fig. 9) fine-grained homogeneous sediments are found only inthe deepest pa rts of Aransas and San Antonio bay s and in water deeper than ab out

120 feet in the open gulf.Relatively coarse, virtually homogeneous sediments are forming short dis

tances seaward of the mouths of North Pass, Pass a Loutre, and Southwest Passof the Mississippi Delta. These sediments are mixtures of silt, clay, and sand, andthey are being deposited at a very high rate.

Coarser-grained homogeneous sediments (sands or coarse mixtures of sand,silt, an d clay) are found bo th land w ard an d seaw ard of the barrier islands in eachof the study areas. Coarse, homogeneous, texturally mature deposits extend fromapproximately the island shorelines seaward into about 75-90 feet of water eastof Gosier and Breton islands and from near the shore seaward to depths of 30-45feet off the Texas islands. The sands seaward of the barrier islands are coarsestand best sorted near shore; seaward they generally become progressively finerand more poorly sorted, and minor internal structures begin to occur. On thelandward side of the barrier islands the sands are homogeneous in the shallowestwater. In the Texas bays homogeneous sands fringe the narrow beaches, and theyare found in the shallowest parts of Breton Sound.

SUMMARY OF DISTRIBUTION

Different areas of the sea and sound floors were found to contain differentminor sedimentary structures. These structures are arranged in an order that is


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(1922) desc r ibed o ff t he de l t a o f t he Frase r Rive r. From the Guada lupe De l t ai n t o u p p e r S a n An t o n i o B a y t h e r e is a su c c e ss i on of s e d i m e n t a r y s t r u c t u r e ss imi l a r t o th i s , b u t t he zone of i r r egu la r l aye rs is e i the r p oor ly de ve lop ed o r p oor lyp r e se r v e d .

Seaw ard f rom th e Tex as ba r r i e r i s l ands (F ig . 9 ) t he r e is a zone of hom og ene ous" m a t u r e " s a n d s . I n 3 0 - 4 0 fe e t of wa t e r a fe w ir r e g u l a r- l a y e r e d s t r u c t u r e s b e g i nto appea r which inc rease seaward fo rming a zone o f i r r egu la r- l aye red sed iment s .T h e se , i n t u r n , c h a n g e g r a d u a l l y o u t w a r d i n t o s e d i m e n t s c o n t a i n i n g m o t t l e ds t r uc tu r e . In s ti l l deep e r wa te r f a r th e r o ff shore , t he re i s an a rea of ho m og ene ou sf ine -gra ined sed im en t s . F igu re 10 show s how a p a r t o f t h i s sequenc e of m ino rs t r u c t u r e s a p p e a r s i n c o r e s . T h i s s i m p l e o u t wa r d s e q u e n c e v a r i e s l o c a l l y n e a rsec on da ry sources of she lf sa nd . A rou nd these th e re i s a sma l l - sca le repe t i t i o n oft h e m a j o r o u t w a r d s e q u e n c e . A se q u e n c e of m i n o r i n t e r n a l s t r u c t u r e s so m e wh a ts imi l a r t o tha t o f t he Texas a rea occurs eas tward f rom the ba r r i e r i s l ands nor thof the Miss i ss ipp i De l t a .

In the bays o f t he cen t ra l Texas coas t and in Bre ton Sound the sequence o fse d i m e n t a r y s t r u c t u r e s o u t wa r d f r o m t h e b a r r i e r i s l a n d sh o r e a r e s i m i l a r t o t h o sejus t desc r ibed in the open gulf, b u t t h e d e p t h z o n a t i o n is g r e a t l y c o m p r e s se d w i t hthe re su l t t h a t t h e i r r egu la r- l ay e red zon e i s ve ry na r ro w or miss ing . C oa rseh o m o g e n e o u s s e d i m e n t s g e n e r a l l y a r e f o u n d i n t h e sh a l l o we s t wa t e r n e a r sh o r e .T h e y g r a d e o u t wa r d i n t o m o t t l e d a n d i r r e g u l a r l y l a y e r e d s e d i m e n t s i n d e e p e rwa t e r. T h e d e e p e s t p a r t s of t h e b a y s a n d so u n d c o n t a i n f in e - g ra i n ed h o m o g e n e o u ss e d i m e n t s .

O R I G I N

Mi n o r s e d i m e n t a r y s t r u c t u r e s r e g u l a r l a y e r s , i r r e g u l a r l a y e r s , m o t t l e s , o rh o m o g e n e o u s s e d i m e n t s m a y b e e i t h e r p r i m a r y o r s e c o n d a r y i n o r i g i n . P r i m a r yminor s t ruc tu re s a re fo rmed a t t he t ime o f in i t i a l depos i t ion by va r i a t ions inam ou nt an d k in ds of sed im en t s f rom a s ing le ( s imple ) source o r by a l t e rn a t in gdepos i t ion o f con t ra s t ing sed iment s f rom two or more (compound) sources . Sed im e n t s w i t h p r i m a r y r e g u l a r l a y e r s a n d p r i m a r y h o m o g e n e o u s s e d i m e n t s a r e c o mm o n , wh e r e a s p r i m a r y i r r e g u l a r l a y e r s o r m o t t l e s a p p a r e n t l y a r e u n c o m m o n a n dp r o b a b l y f o r m o n l y u n d e r sp e c i a l i z e d a n d u n u su a l c o n d i t i o n s .

Seconda ry minor s t ruc tu re s a re p roduced a f t e r i n i t i a l depos i t ion bu t be fore

the sed im ent is bu r i ed be yo nd the reach of phy s ica l p rocesses ac t ive on and j us tbe ne a th the sea floor. Th ey a re fo rmed b o t h by pa r t i a l o r com ple te de s t ru c t io n ofp r e v i o u s l y f o r m e d p r i m a r y s t r u c t u r e s a n d b y r e so r t i n g o r u n m i x i n g of h o m o g en e o u s s e d i m e n t s . Se c o n d a r y s t r u c t u r e s o f a l l k i n d s a r e b y f a r t h e m o s t c o m m o nse d i m e n t a r y s t r u c t u r e s i n b o t h t h e Mi s s i s s i p p i De l t a a n d R o c k p o r t , Te x a s , a r e a s .

B o t h p r i m a r y a n d s e c o n d a r y s t r u c t u r e s m a y o c c u r i n t h e s a m e l o c a l a r e a .P r o v i d e d c o n t r a s t i n g s e d i m e n t s a r e a v a i l a b l e , t h e s t r u c t u r e t h a t f o r m s d e p e n d son the processe s tha t do m in at e the loca l sea floor a t the t im e i t i s form ed a nd onthe loca l r a t e o f depos i t ion . Tab le I summar izes the p rocesses tha t fo rm most o fthe d i f fe ren t s t r uc tu r e s .


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INTERNAL STRUCTURES OF SEDIMENTS 2 7 3 9

TABLE I. PROCESSES THAT FORM M O S T M I N O R INTERNAL SEDIMENTARY STRUCTURES

(Capitalized methods are considered most important)

o w < w J >.S z *Dz1

- ^ M O T T L E S 1 -

' 11

;s?h5is"NtT-|

\ 1* v

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Documents

More and Scruton (1957)