88 Berrones Et Al. 1993 - 2nd ISAG

8/6/2019 88 Berrones Et Al. 1993 - 2nd ISAG

1/4

Second ISAG, Oxford (UK), 1 231911 993 283

STRATIGRAMIY OF TIIE CELICA-LANGONESASIN(SOUTIIWESTERN ECUADOR- NORTHSVESTERN PERU).T1I:CTONIC IMILICATIONS.

Gerardo BERRONESEtienneJAILLARD (), Marta ORDO REZ (l),Peter BENGTSON (3),Stalin BENITEZ (1, Nelson JIMENEZ l ) nd Italo ZAMBRA NO (l).

(1) Petroproduccibn, Km 6, 5 via a la Costa, casilla 10829, Guay aquil, Ecuador.(2)Misibn ORSTOM , Rusia y Eloy Alfaro,Apartado postal 17.11.06596, Quito, Ecuador.(3 ) Geologisch-Palaontologisches nstitut, Im NeuenheimerFeld 234W, 6900 Heidelberg, Germany.

RESUMEN En la Cuenca de Celica-Lancones, se distingue una serie sedimentaria occidental,queconstituye la coberhwa del Bloque Amotape-Tahuin, y una serie oriental en parte v oic hic a perteneciendo ala mu gen andina. Esthnseparadas por m a sutura tectbnica, que involucra rocas maastrichtianas. Por Io tan-to, la colisibn del Bloque Amotape-Tahuin con la margen andina ocurrib despues del Maastrichtiauo, proba-blemen te en el Eoceno basal.KEY-WORDS :Late Cretaceous, Paleogene, A ndean m argin, Terrane, Accretion.

INTRODUCTIONThe Andes are classically divided into Central, liminalAndes without accretions nor ophiolites, and Northern and Sou-thern Andes, which underwent obduction andlor accretion ofoceanic andor continental terranes. Moreo ver, the tectonic rota-tions are clockwise in the Northern Andes, whereas they arecounter-clockwise in the Central Andes (Kissel et al. 1992). The-refore, the Peru-Ecuador border, that roughly coincides with theNorthem to Central Andes transition (Mourier 19881, is a key

area to understand the tectonic behaviour of the Andean marginand of the alloc htonous terranes.GEOLOGICALETTING

The Cretaceous series of the Celica (Southwestern Ecua-dor) and Lancones (Northern Peru) zones were interpre td as theinfilling of a back-arc basin located on the suture of the Amo-tape-Tahuin Block (ATB), accreted to the Andean margin at the Fis. 1: Lucation sketch.1:PaleozoicJurassic-Cretaceous boundary (Mourier 1988, fig. 1). In these rocks;:retaceousr Ce2ica-Lanconesinterpretations, western facies unconformably overly the Paleo- Basin y 3: early Tertiary rocks of the An-dean nmrgin.


2/4

284 &?corad ISAG, Oxford (UK), 1-23/9/1993

m ie rocks of the ATB, and laterally grade eastward into volcanic and volcaniclastie deposits, which are se-parated from the Andean margin by important faults (Kennerley 1973, Morris & A l e m h 1975, Bristow &Hoffstetter 1977, ReyesBr Caldas 1987, Mourier 1988). Paleomagnetic studies indicate that the ATB under-went a northward drift of hundreds of kilometers and a *l lO' cloclcwise rotation since the Paleozoie, whe-r a s the Cretaceous rocks of the "Celica-Lancones Basin" raord ed a * 60' rotation, without significant mi-gration (Mourieret al. 1988).New stratigraphie, sedimentologic and structural field data, asw d l as partial geologic survey in thesuadorian part of the "Celica-Lancones Basin" led to dist inp ish two tectonic units, separated by a majorteetonic suture. The western series eonstitutes the stratigmphic cover of the ATB, w hereas the eastern onerepresents the sedimentation of the Andean continental active m g i n .TRATIGRAPIIY

Th e Cretareous-Balmgenne sedimentary cover of t h e Amo tap cTah u inBlock.Bisconformably overlying the Paleozoie rocks of the E astern side of the ATB, is a thick, undated seriesof deltaic ( y ) shales and sandstones , overlain by mature, coarse-grained luvial sandstones. They are csrrela-tive with the early Cretaceou s Goyllarisqu izga Gp of the West-peruvian m ug in (Benavides 1956, GigantalFm of Mourier 1988, Huay1lap;unspa Gp of Myers 1980). A marine transgression then deposited shales,sandstones and limestones, eorrelative with the late A ptian-earliest Albian transgression of Pem (Inca an dPariahuanca F m , Benavides 1956, Wilson 1963). They are overlain by black laminated, bituminous limes-tones, which yielded middle Albian am monites (Bristow & Hoffstetter 1977), coeval with si m il a depositsof Peru (Chulee-Pariahmbo and Pmanga-Muerto F m , Benavides 1956, Reyes $r.Caldas 1987).These areoverlain by a thiclc series of blaclc s h a h and fe ldqa thie sandstones, interpreted as low densiyhwbidites representing the erosion of a continental cristalline basement with a noticeable volcanic contami-nation. These are known as the Copa Sombrero Gp in Northwestern Peru, and are d a t a i as Cenomamian(Olsson 1934) to Campanian (Morris & Alemin 1975)(fig. 2). InEcuador, they are capped by a 10 0 rn-thickconglomerate correlative with the Campanian Tabloaes Fm of Peru (Reyes & Caldas 1987), an d then byblack shales, with thin-bedded turbidites intercalations a d imestone nodules, dated as Maastrichtian i nPeru (Pazul, Monte Grande Fm, Olsson 1934, Reyes & Caldas 19$7)(fig.2).

On he western side of the ATB (Talara Basin), a major hansgressiva unconformity (Sandino Fm) isoverlain by Campanian to Palmcene marine s h a h (Redomdo Fm, Mal Paso Gp , Gonzalez 1976). These aredisconfonmably overlain by coarse-graimed, continental, polygenic conglomerates (M0gol16~ m) gradingwestward into shallow-marine sandstones and shales of w l y Eocene age (Salina Gp, Gsnmlez 1976, S-ranne 1987).Th e Cretaceous toPaleogenes e r i a of t h e A n d a n continental margin.

The lowem ost unit is a thick series of massive, faulted and al te rd andesites,mcribsd to the Celica Fm .Although it is crosscut by granites dated as Aptian (1 14-1 11Ma K-Ar ages, Kem erley 1973), he Celica Fmis thought to correlate with the A lbian volcanics of Western Peru (Casma9,yers 1980 , Soler 1991).The Celica Fm is overlain by sandstones and greywackes (* 200 m), and then by thick-bedded, coarse-grained volcanidastic high-density turbidites (* 1500-2000 m), with few thin intercalations of lavas andblack laminnted limestones. We propose to cal1 this m i t the Alamor Group (fig. 2). A poor microfauna lo-cally indicates a post-Albian, probably Turonian age. Though the basal contact has not been obsewed, thelack of important deforma tion and alteration within this unit indiea tes that the CeIica Fm was defom ed be-fore its deposition.The Naranjo Fm (a 150-200m) aconforrnably overlies either the Celica Fm or the Alamor Gp. It be-gins with Iransgressive pebbly mark containing Santonian ammonites, followed by coarsening-upward se-quencesof marls, fossiliferous limestones and grauwackes, of shallow-marine shelf to deltaic environment.'Ille u p p r part of the unit yielded a late Cam panian or eiuly Maastrichtian microfauna (fig. 2).The Casanga Fm (* 200400 m) consists of shales, thin-bedded turbiditie grauwacke s and nodular limes-tones of m arine shelf environment. It differs from the underlying strata by the presence of coanse-gainedconglomeratic lenses an d beds, tha t ref le t the progradation of coastal alluvial fans. The Casanga Fmcontains a poor ate Cretaceous microfauna, and would be mainly of M aastrichtian age (fig. 2).h l l y , t is unconformably ov ala in by undated, red-coloured, continental shales, siltstones and volcani-clastic beds, which S em o belong to the Sacapalca Fm, that crops out farther East. Th e latter is made up of


3/4

Second ISAG, Oxford (UK), 1-23/9/1993 285

thick subaerialandesitic lowswith intercalations of fluvial redbeds, crosscut by an early E ocenepluton (49 Ma, Kennerley 1973).It is thus probably coeval withthe Llama and Porculla volcanicsof Northern Peru (Reyes & Cal-das 1987, Mourier 1988).This volcanic series is overlainby the undated CatamayoFm. tcomprises regressive sedimentarysequences, grading from coastal-marine shales to fluvial coarse-grained conglomerates (fig. 2).The latter mainly contain clastsof metamorphic rocks, and thuscontrast with the. underlying,rnainly volcaniclastic formations.Southerly, the Sacapalca Fm isoverlain by lacustr ine lackshales and turbiditic grauwackes,with abundant slumpingsandolistolites belonging to the un-dated GonzanamB Fm. ts rela-tionship with the Catamayo Fm isU n k n O W .The latter formations are un-conformably capped by the pro-hably Oligocene volcanic flowsof the Loma Blanca Fm.

AMOTAPE COVER CATAMAYO

SACAP AL"

3Op:UO&wp:

P4

Maasmrichtion7

!2O4PIOO

VJ

The Maastrihtian slices. Fis. 2: Stratigraphiesketch of the Celica-hncones series.The above-described series areseparated by a major fault, whithin which are pinched discontinuo us slices ofblack-coloured, thin-beddedturbidites and cherts, which have been locally dated as Maastrichtian (Bristow & Hoffstetter 1977)(fig. 2).These areususally affected by tight folds associated with well-developped axial plane cleavage.TECTONICNTERPRETATIONSThe eastern, Andean series differs from the western, ATB cover, through : 1) the presence of an earlyCretaceous volcanic "basement", (2) the dominant volcanic nature of the detritism throughout late Creta-ceous and Paleocene (?) times and (3) the presence of a mixed carbonatedetritic shelf during Senonian

times. These major differences indicate that they belonged to quite different paleogeograp hic doma ins, andthat they cannot have deposited in a sarne "Celica-LanconesBasin" of Cretaceous and Paleocene age.In spite of still poor stratigraphic data, the eastern series re co rd 4 al1 the major early Andean geodynamicevents (Jaillard 1993, fig. 3). T he thick andesitic Celica Fm probably represents the products of the Albiansubduction-reiated volcanic arc,which is well known along the Peruvian m g i n (Casma Gp , Quilmana Fm,Soler 199 1). Its deformation before the deposition of the Ala mor Gp woulde result from the late Albian-ear-ly Cenomanian Mochicacompressive phase of Peru (Mgard 1984).The subsequent accumulation of thick,coarse-grained deposits (Alamor Gp) indicates the creation of a subsident roug h (fig. 3), possibly related todextral wrench movements eg . Soler 1991). The Coniacian (?)unconformity below the Naranjo Fm is cor-relative with theearly Peruvian phase, defined n Southwestem Peru (Jaillard 1993). The appearance of con-glomerates in the Casanga Fm seems to be coev al with the late Campanian major Peruvian phase. The lateMaastrichtian or Paleocene regression, the intense volcanic activity of probable Paleocene age (Sacapalca


4/4

286

Fm), and the marine transgres-sionofpossible Eocene age(Catamayo Fm) still nwd strati-graphie confirmations, before toattempt correlations with Ande-an eventsknown elsewhere.Whichever the case, the Celieaseries is one of the quite scarceexamples of a completesedi-mentary seriesdeposited in aforearc setting hroughou t hewhole centralAndes.

and ine-zraincd urhidit

The early Crebceous to Albi- Fig. 3: Tectonic interpretationsof the lateCreeaceous-Paleogetreevo-an facies of the ATB cover are lution oftlte Afnotape and Andean series.comparablewith hose of theWest- Peruvian m g i n , and it probably belonged to this latter at this time (fig. 3). SinceCenommian timesonwards, the turbiditic sedimentation on the ATB differs totally from that of the Andeanmargin.This dras-tic change could be interpreted as the beginning of the nortlwa rd m igration of the ATB. As a matter of fact,late Cretaceous times are a period ofv ery oblique, nortllward convergence, which wo uld have induced dex-tral wrenching dong the Andean margin. This eould also account for the coeval creation of the Alamor,possibly pull-apart basin (fig. 3) .

The presence of Maastrichtian rocks in the suture between the two units demonstrates that these c m o thave been emplaced in their presant-day location before M aastrichtian times. Therefore, the hypothesis ofthe latest Jurassic to earliest Cretaceous collision of the ATB must be left out. The age of the accretion ofthe ATB could be indicn ted by the irruption of the early Eoc em coarse-grained deposib (Mogoll6n Fm) inthe Western side of theATB (Talara Basin).

The Celica-Lancones a r a comprises two distinct late Cretaceous-Paleogene sedimentary series an d canno longer be consiclerd as a "Basin" of that age. Th e western unit represents the cover of the Am otape-Ta-huin Block, whereas theeastern one is a well-p reserv d example of anAndean series in a arc to fore-arc set-ting. The pre.sence of deformed M aastrichtian slices betwm n both units indicates that the accretion of th eAmotape-Tahuin terrane occurred after Maastrichtian times, probably n ear the Palemene-Eocene boundary.

BENAVIDES,V., 1956,AmericcznMuseunl of Natrrral Hiseory Bulletin ,108,352-494, New York.BWSTOW, C R . & H O F F S T E R E R , R., 977,LexiqueIntem. Stratig., CNR S ed.,VQ, 410 p.. Pais.GONZALEZ, G., 1976,Dr Thesis, Univ. San Agustin, 225 p.? Arequipa.JAILLAWD, E., 1993, in : Cretaceoustectonicsin theAndes , u t h Evol. Sei. ser., View eg, Wiesbaden .MENNERLEY, J.B., 1973,LondonInstitute of Geological Sciences, Report 23,34p., London.MISSEL, C. tal., 1992, Bull. Soc. gC;ol.France, 163,371-380, Paris.MORRIS, R.C. BL ALEMAN, A.R., 1975,Bol. Soc. geol. PerG, 48,4964, LimaMO URIER , T., 1988,Dr Thesis Sei., Univ. Paris XI, 29.5 p., Orsay.MOU RIER, T. et al., 1988,Eaah Planer. Sci. lert , 8 8 , 182-192,Amsterdam.MYERS, J.S., 1980,Boletin INGEIISMET,33 , 145 p., Lima.OLON, A.A., 1934, Wdletin of American Paleontology , 20 , 104p., New-York.REYES, L.& CALISAS, J., 1987,Bol. hs t. GeoL M x Met, ,A, 39,83 p., Lima.SRANNE, M., 1987, IFEA - Pe t r o p d , u n pu bl .Report, 73 p., Lima.SOLER, P., 1991,Dr Thesis Sei., Univ. Paris VI, 950 p., Paris.W kS ON , J .J., 1963,hnerican Association of Petroleum Geologists Bulletin ,47, 1-34,Tulsa.

Documents

88 Berrones Et Al. 1993 - 2nd ISAG