Journal of South American Earth Sciences, Vol. 1, No. 4, pp. 373-418, 1988 0895-9811/88 $3.00 + 0.00 Printed in Great Britain Pergamon Press plc

Cretaceous paleogeography and depositional cycles of western South America

C. E. MACELLARI

Earth Sciences and Resources Institute, University of South Carolina, Columbia, SC 29208, USA*

(Received for publication January 1988)

Abstract - -The western margin of South America was encroached upon by a series of marine advances that increased in extent from the Early Cretaceous to a maximum in the early Late Cretaceous for northern South America (Venezuela to Peru}. In southern South America, however, the area covered by the marine advances decreased from a maximum in the Early Cretaceous to a minimum during mid-Cretaceous time, followed by a widespread advance at the end of the period. A series of unconformity-bounded depoeitional cycles was recognized in these sequences: five cycles in northern South America, and six (but not exactly equivalent) cycles in the Cretaceous back-arc basins of southern South America (NeuquSn and Austral, or Magallanes, Basins). Both widespread anoxic facies and maximum flooding of the continent in northern South America coincide in general terms with recognized global trends, but this is not the case in southern South America. Here, anoxic facies are restricted to the Lower Cretaceous and seem to be controlled by local aspects of the basin evolution and configuration. The contrasts observed between northern and southern South America can be explained by differences in tectonic setting and evolution. To the north, sediments were deposited around the tectonically stable Guayana-Brazilian Massifs, and thus registered global "signals" such as anoxic events and major eustatic changes. The southern portion of tim continent, on the contrary, developed in an active tectonic setting. Here, the mid-Cretaceous Peruvian Orogeny over- printed, to a large extent, world-wide trends and only the earliest and latest Cretaceous conform to global depositional patterns.

ResumenbE l margen oeste de Sudam~rica fue cubierto per una sorie de avances maritm~ tlUe involu- craron ~ireas progresivamente mhs extensas a partir del CretAcico temprano hasta alcanzar uu Inaximo en el Cretkcico tardio temprano en el norte del continente (Venezuela a Per0). En el sur de Sudttmbrica, sin embargo, el area cubierta per las transgresiones cretbcicas decreci6 a partir de un m6ximo en el CretAcico m6s temprano hasta el Cret~cico medio, pero una extensa transgresibn cubri6 una gran parte del con- tinente al finalizar este periodo. Varies cielos deposicionales soparados per sendas discordaneias regionales se reconocieron en estas secuencias: cinco ciclos para el norte de Sudam~rica y seis ciclos (aunque no exactamente equivalentes) en las cuencas de tras-arco cret4tcicas del sur de Sudam6rica. Tanto facies an6xicas de gran extensibn, come la edad en que se verifie6 la m6xima inundacibn del norte de Sudam~rica coinciden en t~rminos generales con tendencias globales, pore eete no es el case on el sur del continente. Aqtti, las facies an6xicas estAn restringidas al Cret~cico int'erior y estAn aparentemente controladas per aspectos pecuiiares de la evoluci6n y configuraci6n de dichas cuencas. Los contrastes observados entre el norte y el sur de Sudam6rica pueden ser explicados per diferencias en su ubicacibn y evoluci6n tectbnicas. En el norte, los sedimentos fueron depositaries alrededor de los macizos de Guayana y Brasil, tectbnica- monte estables, que registraron eventos globales, tales come episedios an6xieos y eustaticos. Per el con- trario, la porcibn sur del continente se desarroll6 en un ambiente tect6nico active. Aqui, la orogenia Peruviana del CretAcico medio se sobreimpuso en gran medida a los eventos globales, y solamonte durante el Cret~cico mbs temprano y el m6s tardIo los sedimentos se depositaron de acuerdo a patrones deposi- cionales globales.

INTRODUCTION

THE WESTERN MARGIN of South America was covered by several successive marine advances during Creta- ceous time. Sediments deposited during these events are widely exposed along the Andes and preserved in the subsurface of subandean basins. Cretaceous rocks in these basins are of great economic importance as they provide the source and, in many cases, the reservoirs for the largest accumulations of hydro- carbons of the western margin of the continent.

The objectives of this work were to recognize com- mon patterns of basin infill along the extensive con- tinental margin, and to contrast and possibly explain different depositional trends observed in northern

*Present address: Pecten International. P.O. Box 205, Hous- ton, TX 77001 USA

and southern South America. These tasks were ap- proached in two ways: the first involved the recon- struction of detailed paleogeographic maps; the second included recognition and correlation of un- conformity-bounded depositional cycles or sequences of regional significance (sensu Vail et al., 1977).

This study was based mostly on published infor- mation, field work in Venezuela, Colombia, and southern Argentina and Chile, and limited unpub- lished subsurface information for Colombia and por- tions of Argentina.

Various criteria were used for recognition of the cycles. In surface outcrops, cycles usually present three distinctive intervals or surfaces. A transgres- sive deposit, usually containing reworked phosphatic fragments, iron nodules, or reworked fauna from un- derlying sediments, is found at the base of many sequences. This basal unit, deposited on top of the "transgressive surface," indicates the initiation of a

.qq.q

374 C.E. MACELLARt

relatively rapid rise in sea level and may be present on top of the lowstand deposits in the deepest portion of the basin or directly above the sequence boundary on the updip portion of the basin (Haq et al., 1987; Vail, 1987). The second surface is the maximum flooding surface, which is usually associated with a condensed zone. Since the basin is deprived at this time of clastic input due to the increased distance from the source of sediments, sedimentation is char- acterized by chemical deposits (glauconite), high concentrations of pelagic material, or the develop- ment of hardgrounds due to the absence of sedimen- tation (Haq et al., 1987). The third recognizable surface in outcrop is the sequence or cycle boundary, which is represented by an obvious unconformity or by more subtle changes. In the deeper portion of the basin, the sequence boundary is conformable and is characterized by a change from progradational de- posits to more massive aggradational sequences (Haq et aI., 1987). Other criteria used for the recognition of these cycles include paleontological hiata, marked changes in the map distribution of coastal onlap of sediments, and basin-wide marked changes in litho- logy.

These cycles are the result of the interaction of tec- tonic and thermal subsidence, variations in sedimen- tary input, and eustatic sea-level fluctuations. Even though no attempt has been made to evaluate the origin of these cycles, they are comparable in mag- nitude to the second-order cycles of Haq et al., (1987). The degree of certainty about the exact definition of these cycles varies from well documented to specu- lative. However, it is hoped that this kind of analysis may provide a regional framework to understand and predict local aspects of the Cretaceous stratigraphy of western South America.

DISTRIBUTION OF CRETACEOUS SEDIMENTS

Areal Distr ibut ion

Cretaceous sediments were deposited over a large portion of western South America in a variety of tectonic settings. Even though these sediments were deposited in the Pacific (or "active") South American margin, the Guayana and Brazilian Massifs provided a stable platform for sediments deposited to the east of these basins. To the west, however, sedimentation during the Early Cretaceous took place mostly in a back-arc setting that changed to a foreland basin setting during the Late Cretaceous, following the uplift and deformation of the ancestral Andes.

Depositional troughs in northern South America are oriented NE/SW, coinciding with the distribution of Jurassic red beds in rapidly subsiding grabens (cf. Maze, 1984). These are the Trujillo, Machiques, Uri- bante, and Bogot~ Troughs (Fig. 1). Also controlling the distribution of these sediments was a series of NW/SE-trending paleohighs (M6rida Arch, Arauca Arch, Santander Massif, and Vaup6s-Natagaima

High; Fig. 1) of major importance in the migration and entrapment of hydrocarbons on a regional scale. The greatest thickness of Cretaceous sediments has been reported for the Bogot~ Trough (over 15,000

Fig. 1. Generalized isopach map of CrvLuceous sedimunLs of" the western margin of South America showing major paleohighs.

Cretaceous paleogeography and depositional cycles of western South America 375

meters cited by BOrgl, 1961e). However, only half this value was measured in the area recently (E. Cardozo and L. Sarmiento, pets. commun., 1987).

South of the Vaup~s High, Cretaceous isopachs trend NW/SE, parallel to the orientation of major tectonic features. The most prominent of these tec- tonic features is the Marah6n Geantieline that separated the East Peruvian and the West Peruvian Troughs during a large portion of the Cretaceous (Benavides, 1956).

In southern Peru, Bolivia, and northern Argentina and Chile, Cretaceous sedimentation was restricted to a series of relatively isolated but rapidly subsiding basins (Reyes, 1972; Salfity, 1982). South of this area, a major NW/SE-trending paleohigh (the "Cra- t6geno Central" of Bracaccini, 1960) separated the Chaco-Paran~ Basin from the Neuqu~n Basin. In southernmost South America, the Rio Chico or Dun- geness High was also oriented NW/SE and separated the San Jorge Basin from the Austral (Magallanes) Basin to the south.

! :.

Cretaceous rocks are preserved in several basins of western South America that became isolated during the Cenozoic. These Cenozoic basins preserving Cre- taceous strata are classified here as follows (Fig. 2).

Oceanic Basins. These are basins in which Creta- ceous sediments were deposited on top of oceanic crust that was later obducted onto the continent. Included in this group are basins located in north- western and western Colombia and in western Ecua- dor. These rocks have been subjected to a variable degree of metamorphism (Bourgois et al., 1987; among others).

Proximal Pericratonic Basins. This extensive sys- tem of basins envelops the western margin of the Guayana-Brazilian Massifs. Because of their loca- tion to the east of the Andes, these have also been called "subandean" basins. Cross-basinal arches separate this area into a series of basins, namely: Barinas-Apure, Llanos, Putumayo, Oriente, Mara- fi6n, Ucayali, and Madre de Dios. Sedimentation here is characterized by the dominance of clastic intervals. These basins have great economic signifi- cance as they contain extensive hydrocarbon re- serves.

Distal Pericratonic Basins. These basins represent the western continuation of the pericratonic basins from which they became separated during the late Cenozoic Andean orogeny. In general, the distal pericratonic basins are characterized by finer grained sediments and much thicker sequences than those found to the east. Thick intervals of shale and

BASIN CLASSIFICATION

PASSIVE MARGIN ~ OCEANIC

PROXlNJ~. PERICRATONIC

~ DISTAL PERICRATONIC

INTRA-CRATONIC

~ ACTIVE MARGIN ~ BACK-ARC

~ [~ SEDIMENTARY INPUT

i o . . . i . /~v ' " ".. ~ . .~o o,

2

". oooOO : ooOO

Classification of Basins

AU8TRAL

0 6001Gr

Fig. 2. Classification of pressnt-day major sedimentary basins on the basis of Cretaceous rocks present.

376 C.E. MACELLARI

limestone are common here. The presence of excel- lent source rocks for hydrocarbons and the scarcity of Cretaceous elastic reservoirs are characteristic of these basins. Basins included within this group are the Maracaibo, Middle Magdalena, Upper Magda- lena, Santiago, and Huallaga.

buco, and Rio Negro Formations. To the west, the basal elastics (Tambor Formation) are followed by more distal marine sediments of the Rosa Blanca Formation (Julivert, 1968; Zambrano et al., 1971; Gonzalez de Juana et al., 1980; Garcia Jarpa et al., 1980; among others).

Intracratonic Basins. A major NW/SE paleogeo- graphic high separated the pericratonic area around the Brazilian Massif from the Cretaceous back-arc basins of southern South America. Cretaceous sedi- mentation within this high was characterized by mostly continental deposits capped during the latest Cretaceous by a short-lived marine transgression. Both sources and reservoirs of hydrocarbons are associated with this brief event. Basins included in this group are the Titicaca Basin of southern Peru, the Subandean Basin of Bolivia, and the Northwest Basin of Argentina.

"Active Margin Basins." These basins developed at the edge of the South American plate. Because of their position near the zone of convergence of the Nazca and South American plates, these basins are characterized by complex tectonics and marked facies variations. Included in this group are the Talara Basin of northwestern Peru (Olsson, 1934; Travis et al., 1976) and the Navidad fore-arc basin of coastal Chile (Cecioni, 1979; among others).

Back-Arc Basins. The Neuqu~n and Austral Ba- sins underwent a similar tectonic evolution, both developing as back-arc basins during Late Jurassic- Early Cretaceous times. However, the Neuqu~n and Austral Basins differ in that the former contains thick "middle" Cretaceous continental deposits, whereas the latter basin registers marine sedimen- tation throughout the Cretaceous. In both basins, sources and the most important reservoirs of hydro- carbons accumulated during the early stages of the Cretaceous transgression.

Passive Margin Basins. These basins developed on the Atlantic margin of South America as the con- tinent rifted apart from South Africa. These basins are not considered in this study, with the exception of brief references for comparative purposes.

PALEOGEOGRAPHY

The Cretaceous paleogeographic evolution of wes- tern South America is summarized in Figs. 3-8.

Pre-Barremian (Fig. 3)

Venezuela and Colombia. Sedimentation during earliest Cretaceous time was restricted to the major depocenters of the area - - namely, the BogotA, the Uribante, and, possibly, the Machiques Troughs. These sediments are characterized by quartz and feldspathic arenites included in the Caqueza, Area-

Ecuador and Peru. Well-documented earliest Cre- taceous rocks in this portion of South America are primarily restricted to the West Peruvian Trough. A continuous belt of fluvial to deltaic facies was depo- sited adjacent to the western edge of the Marafi6n Geanticline (Chimu, Etuancane, and Cotacucho For- mations) (Dalmayrac et al., 1980; among others). Progressively deeper water facies have been found toward the center of the basin, with a mostly shaley deposition in the northern portion and limestone pre- dominant to the southwest (Santa Formation) (Bena- vides, 1956). Farther south, predominantly silici- elastic deposition took place in a shallow marine environment (Yura Group) (Vicente et al., 1982), and active volcanism occurred along the coast in a strip extending from Lima to Nazca (Myers, 1974).

Argentina and Chile. During the Berriasian- Hauterivian interval, the back-arc basins of Argen- tina and Chile were covered by an extensive marine advance that began in the Tithonian. In the Neu- qu6n Basin, deep basinal limestones and shales of the Vaca Muerta Formation were followed by slope sediments of the Quintuco Formation and shallower water carbonates and elastics of the Loma Montosa Formation (Mitchum and Uliana, 1985; among others). Reefal facies (Chachao Formation) develo- ped to the northeast of the basin (Legarreta et al., 1981).

Extension in the back-arc portion of the Austral Basin resulted in the intrusion of ophiolitic bodies (Dalziel et al., 1974; among others). Lowermost Cre- taceous sediments include a basal sandstone (Spring- hill Formation) followed by black shales (ltio Mayer and Pampa Rinc6n Formations). These sediments are replaced farther north by shallow marine sand- stone (Apeleg or basal Coyhaique Formations) (Plosz- kiewicz and Ramos, 1978; Skarmeta and Charrier, 1976).

At the northern part of the passive margin, the Chaco-Paranfi Basin is characterized by deposition of clean eolian sands (Tacuaremb6, San Crist6bal, Botucat~ Formations), overlain by extensive tholei- itic basalt flows (Russo et al., 1980). These volcanics are indicative of the initial extension prior to the opening of the Atlantic Ocean. Farther south, the San Jorge Basin recorded widespread lacustrine and fluvial sedimentation (Pozo D-129 Formation) (Lesta et al., 1980a). A series of smaller continental basins

Fig. 3. Pre-Barremian palvogvographic map. Data for nor- thern South America from several authoru; data Ibr euuthern South America modified from Malumi~n et al. {1983) and Riccardi { 1987 ).

Cretaceous paleogeography and depositionai cycles of western South America 377

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PRE-BARREMIAN

MARINE CHERT/GREYWACKE/ OPHIOLITE

~ 1 LIMESTONE (SHALE)

~ SHALE (LIMESTONE)

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SANDSTONE

CONTINENTAL SANDSTONE-SHALE

~- - ] NO DEPOSITION

V ANDESITES

BASALTS

ALKALINE ROCKS

+ GRANITES

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APPROXIMATE SCALE

100 0 500km.

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associated with alkaline rocks developed along the "Crat6geno Central Argentino."

Barremian-Cenomanian (Fig. 4)

Venezuela and Colombia. Cretaceous sediments extended over an increasingly larger area during the Barremian. A characteristic feature of these rocks include the presence of evaporites interbedded in dif- ferent environmental settings (Julivert, 1968; Garcia Jarpa et al., 1980; among others). Thick elastic facies of the Rio Negro Formation were deposited in the Trujillo, Machiques, and Uribante Troughs. In the Guajira Peninsula, however, quiet marine deposition predominated (limestones of the Yuruma Forma- tion). During this time, the M6rida Arch (which separates the Trujillo and Uribante Troughs) and the Santander Massif remained as positive features. In Colombia, sandstones were deposited east of BogotA, but they were replaced by fine-grained sediments (Villeta and Paja Formations} to the west.

During the late Aptian-Albian, a large portion of the continental margin was blanketed by quartz sandstones derived from the Guayana Massif (Aguar- diente, Une, and Caballos Formations). Those sand- stones were deposited in a deltaic to shallow marine environment, and covered the Putumayo and Upper Magdalena Basins as well as the Santander Massif and the M6rida Arch for the first time. The sand- stone belt was replaced to the west by finer grained sediments that include carbonatic intercalations (Villeta, Simiti, and Lisure Formations). Turbidites and basic volcanics were possibly the dominant rocks deposited in western Colombia.

Ecuador and Peru. During Aptian-early Albian times, the Oriente Basin orEcuador as well as a large portion of Peruvian territory, including the MarafiSn Geanticline, were covered by quartz sandstone deri- ved from the Guayana and Brazilian Massifs (Fig. 4). These sediments were flushed westward through an extensive fluvio-deltaic system (ltolltn Formation in Ecuador and Cushabatay, Goyllarisquizga, and Far- rat Formations in Peru). In Ecuador, coeval sedi- ments were possibly deposited to the west in the now metamorphic portion of the Cordillera Real (Faucher and Savoyat, 1973). Farther west, in Ecuador, an andesitic volcanic arc was active from the Aptian to the Late Cretaceous. This volcanic arc probably res- ted on oceanic crust to the north but on continental crust to the south (llenderson, 1979}. Still farther west, the Romeral Fault separated the rocks of the volcanic arc from pillow basalts of the PifiSn For- mation (Fig. 5). The Pifibn Formation has been interpreted as the distal, oceanic portion of the vol- canic arc (Henderson, 1979) or, alternatively, as an accreted portion of oceanic crust (Feininger and Bristow, 1980; Feininger, 1982; Feininger and Seguin, 1983). In southern Peru, non-marine red bed deposition predominated during this time (Murco, Huancane, and Cotacucho Formations). The only Aptian-early Albian, well-defined marine facies were

378 C.E. MACELLARI

APTIAN-ALBIAN

MARINE ~ CHERT/GREYWACKE/

OPHIOLITES

LIMESTONE (SHALE) i i !

~ SHALE (LIMESTONE)

~ ANDSTONE-SHALE

SANDSTONE

~ VOLCANIC ARC

CONTINENTAL

~ SANDSTONE-SHALE

V ANDESITES

BASALTS

+ GRANITES

APPROXIMATE SCALE

100 0 500 km.

~.-:--:; . . . . . /

N

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i,/

: |

V ~ V /

deposited in the Lima area where the Farrat sand- stones are replaced by marine shales and limestones of the Pamplona Formation.

During the later part of the Albian, Cretaceous seas invaded most of Ecuador and Peru (Fig. 5). In the Oriente Basin, this event is reflected in the basal portion of the Nape Formation. In Peru, the new transgression is reflected in the marine shales of the Esperanza-Raya Formation of the Marafibn, Ucayali, and Huallaga Basins of Peru. Farther east and south, however, these sediments are replaced by del- taic facies included in the Agua Caliente Formation. Of special interest during this time interval is the development of widespread anoxic conditions in western Peru. These are evidenced in the bitumin- ous limestones of the Pariatambo Formation (central and northeastern Peruvian Andes) and the Muerto limestone of northwestern Peru. To the south, as well as to the east, these anoxic facies are replaced by better oxygenated, mostly calcareous sediments. These are the Ferrobamba (Abancay) and Arcur- quina Formations to the south (Marocco, 1978) and the Crisnejas Formation to the east in the MarafiSn Geanticline (Benavides, 1956).

During the Albian, red bed sedimentation (Cota- cucho Formation) continued in southern Peru, as well as in the Altiplano area. These facies are re- placed to the west by red shale and gypsum deposits of the Moho Formation and by shallow marine lime- stones and quartzites of the Arcurquina Formation (Newell, 1949; Audebaud et al., 1976; Dalmayrac et al., 1980).

The late Albian marine advance was followed by a general regression in Ecuador and Peru (Fig. 6). This regression is clearly reflected in the East Peruvian Trough where most of the area was covered by a elas- tic wedge (Agua Caliente Formation) derived from the Guayana and Brazilian cratons. Anoxic condi- tions had completely disappeared by the latest Albian. Predominantly shale and marl facies (Pullu- icana Group) enclose a limestone facies (Jumasha Formation) deposited east of the West Peruvian Trough and on top of the MarafiSn Geanticline. Mar- ine volcanic activity continued in the coastal area (Casma Group), but at a much less impressive pace than during middle Albian time.

Marine sedimentation continued in southern Peru during the late Albian-Cenomanian. This is evi- denced in the shales and limestones of the Ferrobam- ba and Arcurquina Formations (Fig. 6). A short- lived marine incursion occurred during Cenomanian times in the Altiplano area (Ayavacas Limestone of the Moho Formation). Farther east, however, red bed deposition of the Cotacucho facies continued, with the exception of a thin dolomite intercalation that may correlate with the Ayavacas event (Laubacher, 1978).

Fig. 4. Aptian-Albian paleogeographic map. Data for northern South America from several author~; data for southern South America modified from Malumi~n et aL (1983) and Riccardi (1987).

Cretaceous paleogeography and depositional cycles of western South America 379

LATE MIDDLE ALBIAN

I

/ (

/

/

BRAZIL

0

i,'. ,.,.~ r r ' ' -T "~ i i I n I I u 1

Trujillo~ . , o= ; ~- ~ :_ o . . ~' : "= ,, :~. Z,:= " " '

: *%

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Shale-l imestone ---,. ~ :;i Bituminous limestone :

Evaporites ;:

Red beds __

Andesite-volcaniclastics

Basic lavas & volcaniclastics

No deposition 0 KM I I t

80 76 W

300 I

Fig. 5. Late middle Albian paleogeography of Ecuador and Peru.

Argent ina and Chile. In Barremian-Albian times, the Neuqu~n and Austral Basins developed differ- ently. The Neuqu~n records the presence of progres- sively shallower sedimentation that ended with the

deposition ofevaporites (Huitrin Formation) and con- tinental red beds (Rayoso Formation). Concurrent active andesitic volcanism took place to the west in Chile (Aberg el al., 1984; Ramos and Ramos, 1979).

380 C.E. MACELLARI

Gua'

LATE ALBIAN-CENOMANIAN

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Sandstone "~",~" """~ =' ; "

Shale ;' " ,~ Hxxet Limestone

Limestone-shale '..'~ I

Turbidites ., Red beds 'E.

w

Andesite-volcaniclastics

Basic volcanics & volcaniclastics

No deposition 0 KM 300 I t I t

BRAZIL

80 76W 72

Fig. 6. Late Albian-Cenomanian paleogeography of Ecuador and Peru.

Marine sedimentation continued in the Austral Basin (Rio Mayer, lower Pampa RincSn, Hito XIX, Nueva Argentina, and Vicufia Formations), with the exception of continental tuffaceous sediments (Divi- sadero Formation) deposited to the north. These rocks were affected by a mid-Aptian tectonic event

that resulted in the first uplift of the Andes to the west (Ramos, 1976; Aguirre Urreta and Ramos, 1981). This event coincided with extensive pluton- ism (Su~rez, 1979; Aguirre, 1985) and volcanic acti- vity (Ramos, 1978) in the southern Andes.

Cretaceous paleogeography and depositional cycles of western South America 381

In the Northwest Basin, conglomeratic sedimenta- tion took place in the block-faulted Alemania Sub- Basin where several basalt flows were extruded in association with the earlier phases of sedimentation (Reyes, 1972; Valencio et al., 1976). All the eastern passive margin basins (Atlantic) are characterized by continental sedimentation possibly initiated in Bar- remian-Albian times (Rio Salado Formation, Salado Basin, Fortin Formation, Colorado Basin) (Lesta et al., 1980b; Urien and Zambrano, 1973; Zambrano, 1980).

Turonian-Santonian (Fig. 7)

Venezuela and Colombia. The maximum exten- sion of the Cretaceous transgression in northern South America occurred during Turonian-Santonian times, coinciding with a worldwide highstand of sea level (Kauffman, 1979; Jenkyns, 1980; Haq et aI., 1987). Uplift of the Cordillera Central of Colombia also commenced during this interval as a result of the mid-Cretaceous (Peruvian) orogeny (Steinmann, 1929; Btirgl, 1961a; Campbell and B0rgl, 1965; Julivert, 1968; Irving, 1975). Three depesitional pro- vinces are recognized between this semi-emergent arc and the South American craton: a coastal area composed of proximal clastic facies (Escandalosa and eastern facies of the Guadalupe Formation); a shelf belt composed of intercalations of sandstone, shale, porcellanite, and phosphorite (Navay and western facies of the Guadalupe Formation); and a pelagic belt (outer shelf-slope), characterized by organic-rich black shale, thinly bedded bituminous limestone, and chert (La Luna and Villeta Formations) deposited in anoxic conditions (Catchcart and Zambrano, 1967; Gonz~tlez de Juana, et al., 1980; Macellari and DeVries, 1987).

Thick turbidite packages were deposited during Turonian-Santonian times at the edge of the South American plate. Examples are found exposed along the Cordillera Occidental of Colombia (Barrero, 1979) and at the northern termination of the Andes (Barquisimete Trough, NE portion of Fig. 7; Renz, 1960b; Stephan, 1977).

Ecuador and Peru. Turonian-Coniacian sedimen- tation in the Oriente Basin is recorded in the lime- stones and shales of the Napo Formation (Fig. 7). In the southwestern portion of Ecuador and in north- western Peru, the Copa Sombrero Formation repre- sents turbiditic sedimentation in a narrow trough (Lancones syncline and its northward extension; Fisher, 1956; Morris and Aleman, 1975}. A thick prism of coeval sediment that had been winnowed from the shelf was laid down by turbidity currents on the deeper continental slope to the west (Feininger

Fig. 7. Turonian-Santonian paleogeographic map. Data for northern South America from several authors; data for southern South America modified from Malumi6n et al. (1983) and Riccardi (1987).

MAGUGHI

~ESOANDALO8A

~::.:::.;.:::.. / ~ADALUPE

./'

....... l',.'" '".

....... v,. / o 600Ktl

JUMASHA-

FERROBAMB

-%

TURONIAN- SANTONIAN

TINENTAL DEPOSIT? . . ~ CHERT, OPHIOUTES ,

& TURBIDITES ~ ("

BLACK SHALE (BI- ~, TUMINOUS LIME- ( STONE, CHERT) I TURBIDITES

SANDSTONE-SHALE ~.1 r" I (PORCELLANITE) ~ARomm- I

~o~'~,~, MATA I SANDSTONE ~#'LL" I

I MO--

BASALTS /

SAE$ I/4--E

382 C.E. MACELLARI

and Bristow, 1980). The andesitic volcanic arc con- tinued its activity during Turonian-Coniaeian times (C61ica-Macuchi Formations), and a thick volcani- clastic sequence was deposited in the Costa region (Cayo Formation) (Bristow, 1975).

In the East Peruvian Trough, the marine advance is reflected in the shales and limestones of the Chonta Formation. This unit grades toward the craton into a deltaic system that includes pro-delta muds and delta-top facies (proto-Amazon delta; Soto, 1979). Farther west, the Chonta Formation becomes more limestone-rich and is replaced by the Jumasha and the Cajamarca Formations. These limestone facies are continued south in the Ferrobamba and Arcurquina Formations. Limestone facies were part- ly replaced by shale deposition during the Santonian. The Chonta Formation in this interval is mostly composed of shales and is continued westward into the marls of the Celendin Formation. A thick eva- poritic sequence was deposited in southern Peru during the Santonian (Querque and Chilcana For- mations; Jenks, 1948; Vicente, 1981). Farther east, in southern Peru, these evaporitic facies are replaced by the red beds of the upper portion of the Moho and Cotacucho Formations (Newell, 1949; Audebaud et al., 1976). The Peruvian movements initiated during the Santonian are reflected in the uplift of a large portion of the coastal area of Peru.

Argentina and Chile. Turonian to early Cam- panian sedimentation in the Neuqu~n and Austral Basins was controlled by the initial uplift of the Andes, which provided an important western source of sediments. The Neuqudn Basin records exclu- sively continental sedimentation during this time (Neuqu~n Group). The intrusion of granitic rocks was extensive along northern Chile; this was associ- ated with widespread andesitic volcanism im- mediately to the east (cf. Aguirre, 1985).

In the Austral Basin, marine sedimentation con- tinued after a depositional hiatus that extended approximately from the late Cenomanian to the early Coniacian (Malumi#~n, 1968; Malumi~n etal., 1971; Flores etal., 1973). This hiatus is possibly related to the extensive magmatic activity (Ramos, 1976; Ploszkiewicz and Ramos, 1978) and intense folding and uplift associated with the closure of the marginal basin that gave rise to the "Paleoandes" to the west (Cecioni, 1957; Dalziel et al., 1974; Winslow, 1980). Sedimentation in the center of the basin, however, seems to have been interrupted only by a much shorter hiatus (Biddle etaL , 1986). A rapidly subsiding foredeep developed immediately to the east of the newly uplifted cordillera, where a turbiditic sequence was deposited (Punta Barrosa and Cerro Toro Formations), but platform deposition continued to the east (Palermo-Aike Formation). Regressive facies are well displayed in the northern portion of the Austral Basin (Mata Amarilla Formation), pos- sibly replaced northward by continental pyroclastic deposits (Cardiel Formation).

Continental sedimentation continued in the Northwest Basin, this time extending to the rest of the sub-basins (Pirgua Subgroup), but the Salto Jujeiia Dorsal, located in the center of the basin, remained as a positive feature (Salfity, 1982).

During the Coniacian-Campanian interval, the Atlantic basins were also characterized by continen- tal deposition. However, marine facies are recorded in the eastern portion of the Colorado Basin (Zam- brano, 1974, 1980; MalumiAn et al., 1983).

Campanian-Maastrichtian (Fig. 8)

Venezuela and Colombia. A marked regression occurred during the Campanian-Maastrichtian inter- val in northwestern South America. Particularly important was the uplift of a portion of the Cordillera Central following the Peruvian movements. For the first time, then, two sources of sediments are obser- ved: an eastern source provided by the Guayana Massif, and a more restricted western source pro- vided by the ancestral Cordillera Central. Sediments include sandstone to the east and south (Monserrate, Guadalupe, and Burguita Formations) and shale to the west and north (Umir and Col6n Formations). The elastic influence decreases to the northwest where a limestone-shale sequence predominates (Guaralamai Formation) (Renz, 1960a; Rollins, 1965). Turbidites were deposited during this time interval in western and northwestern Colombia (Duque-Caro, 1984).

Ecuador and Peru. In western Ecuador, uplift associated with shortening and deformation of the back-arc basin resulted in metamorphism in the present Cordillera Real (Feininger, 1975, 1982). In the Oriente Basin, sediments were derived from two sources. To the east, a fluvial system transported quartz sands from the Guayana and Brazil ian Massifs (Vivi~n Formation). In the southwestern part of the Oriente Basin and in the northwestern part of the Marafi6n Basin, these sandstones are followed by the Maastrichtian Cachiyacu shales, which were deposited during a brief but widely distributed marine transgression. These facies were replaced to the west by a red bed sequence of mostly continental origin that was derived from the newly uplifted Andes (Tena Formation). These sediments truncate progressively younger beds in an eastward direction. Thus, the red bed facies appeared in the Santonian in the Cordillera Occidental of Peru (Chota and Casapalca Formations), but only in the latest Maastrichtian in the Oriente (Tena Forma- tion) and Ucayali Basins (Huchpayacu Formation) (Tschopp, 1953; Benavides, 1956; Wilson, 1963; Huerta-Kohler, 1982).

Fig. 8. Campanian-Maastrichtian paleogeographic map. Data from northern South America from s~veral authors; data from southern South America modified from MalumiAn etal. (1983) and Riccardi (1987).

Cretaceous paleogeography and depositional cycles of western South America 383

.)

CAMPANIAN-

MAASTRICHTIAN

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VOLCANICS

LIMESTONE-SHALE

~ SHALE

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~ SANOSTONE-SHALE

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I I NON-DEPOsITION

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APPROXIMATE SCALE

100 0 500km.

CAZAOOR

In central Ecuador, a trough developed to the west of the Cordillera Real where the Maastr icht ian turbidites of the Yunguilla Formation were deposited (Bristow, 1973; Feininger and Bristow, 1980). In the Costa area, deeper-water facies persisted during this period (chert of the Guayaquil Member of the Cayo Formation; Sigal, 1969; Bristew, 1975).

Possibly the same marine advance reflected in the Cachiyacu shales of the Marafi6n Basin is recorded in the Petacas Formation of the Talara Basin (Cruzado Castafieda, 1980). By the end of the Maastrichtian, most of Ecuador and Peru had become emergent.

Argentina and Chile. An extensive marine ad- vance over large portions of southern South America took place during the Maastrichtian (cf. Uliana and Biddle, in press). For the first time, an Atlantic- derived transgression covered a large portion of Argentina, and the Andes began to develop as the continental divide. This marine ingression is re- corded in the Neuqu~n Basin (Jaguel and Malargue Formations) and in its eastern continuation into the Colorado Basin (Pedro Luro Formation). Regressive facies punctuated by oscillations and marine ad- vances were deposited in the Austral Basin during this time (Arbe and Hechem, 1984b; Macellari, et al., in review). This resulted in the deposition of deltaics (La Anita Formation) to the northwest, and inner and outer shelf rocks to the south (Cerro Cazador and Fuentes Formations).

A shallow marine transgression also reached the Northwest Basin (Lomas de Olmedo Sub-Basin) where the oolitic and stromatolitic limestones of the Yacoraite Formation were deposited (Marquillas et al., 1984, among others). This short-lived trans- gression coincided with a similar episode observed in southern Peru (Vilquechico Formation) and Bolivia (El Molino Formation) where a transgression had possibly entered from the Atlantic Trough into the Chaco Paran~ Basin (cf. Salfity et al., 1985).

In Chile, a rapidly subsiding fore-arc basin develo- ped along the western edge of the active (Pacific) margin (Navidad Basin) (Cecioni, 1979; Bir6- Bagoczky, 1982; Stinnesbeck, 1986). Extensive an- desitic volcanism took place in the arc to the east of this basin.

Continental sedimentation continued in the San Jorge Basin, but the new marine advance is recorded in other passive margin basins, the Colorado, Salado, and Chaco-Paran~ Basins (Malumi~n et al., 1983).

CRETACEOUS CYCLES

Several regional unconformity-bounded cycles have been recognized in the Cretaceous of western South America (Figs. 9 and 10). The stratigraphy of the pericratonic and back-arc basins is discussed for three different major areas: northern South America from Venezuela to Peru, the Neuqu~n Basin of Argentina, and the Austral Basin of Argentina and Chile. The "oceanic" basins of northwestern South

384 C.E. MACELLARI

[2 i:i':::" HAUTERIVlAN [ IVALANGIIIIA'~ I BERR/AS/A" I "l

~ CHERT--PORCELLAHI~E i: I : i u~esTo .E

s v ~

~ 81LTSTONE ~ 8ANOSTONE

MULICHINC?~ -,- .-_ ----- _

Fig. 9. Stratigraphic chart and correlation of cycles in the pericratonic and back-arc basins of western South America.

America, as well as the "intracratonic" basins of cen- tral South America, are not included in this discus- sion because of insufficient data for this kind of analysis in the former case, and lack of precise age dating in the latter.

Northern South America

Five depositional cycles of regional distribution preserved in the pericratonic to distal pericratonic basins are recognized in northern South America. The stratigraphy of this area is discussed in some detail as this is the first time that these cycles are documented on a regional scale. Regional strati- graphic sections depicting these cycles are presented in Figs. 11-17.

Venezuela and Colombia. The five depositional cycles found in Venezuela and Colombia are detailed below.

Cycle I (Tithonian to Valanginian): Sedimen- tation during the earliest portion of the Cretaceous was restricted to localized NE/SW-trending grabens that originated during initial extension in a rifting stage of evolution of the area (Stainforth, 1969; Favre, 1983a,b). No break in sedimentation is observed at the Jurassic/Cretaceous boundary. The exact age and limits of this cycle are poorly defined due to the lack of detailed biostratigraphic data to correlate between isolated exposures.

The initial marine advance entered through the Bogota area and progressed rapidly to the northeast (B(irgl, 1961c; Etayo-Serna, et al., 1976; Favre, 1985). In the eastern portion of the Cordillera Oriental of Colombia, sedimentation started with deposition of the Caqueza Group. This group includes up to 250 meters of a poorly sorted basal conglomerate followed by 2500 meters of shales and siltstones with interca- lations of orthoquartzites and limestones that indi- cate the initial transgressive episode (Hubach, 1945; Renzoni, 1967; Miller, 1979). The group contains diagnostic Tithonian to Valanginian ammonites.

Farther north along the NE/SW-trending graben, in the Sierra Nevada del Cocuy, the marine advance is recorded in the Macanal Shale, which was de- posited rapidly under inner shelf conditions (Favre, 1985; Fig. 14). To the east, this sequence is replaced by a coarser clastic sequence (Rio Ele Conglomerate). To the west, in the Villa de Leiva area, similar clastic facies are included in the braided fluvial and delta plain sandstones of the Arcabuco Formation. This unit is followed by the shallow marine shales of the Cumbre Formation (Galvis and Rubiano, 1985; Ren- zoni, 1985b).

Although precise age dating is lacking, it is pos- sible that Cycle 1 rocks may have been deposited in the Uribante Trough of southwestern Venezuela (the basal portion of the Rio Negro Formation; see Fig. 1). This unit comprises arkosic sandstones of consider- able thickness (Renz, 1959; Ramirez and Campos, 1972; Garcia Jarpa et al., 1980).

Cretaceous paleogeography and depositional cycles of western South America 385

H S DISTAL PER ICRATONIC eAS lHS /

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Fig. 10. Stratigraphic chart and correlation of cycles in the distal pericratenic basins and western Peru; see Fig. 7 for explanation of symbols.

Cycle 2 (Valanginian to Upper Aptian): Subsi- dence during Cycle 2 deposition changed from being confined and tectonically driven during the earlier part of the cycle, to being more widespread and thermally driven at the end of the cycle (Fabre, 1983a,b).

In Venezuela, deposition of the Rio Negro Forma- tion continued in the Uribante Trough and was initiated in the Machiques Trough (Figs. 1, 12, 13). This is a time-transgressive unit that displays a major variation in thickness - - from 2000 meters in the Machiques Trough to only a few meters in the platform area of the Maracaibo Basin and up to 1500 meters in the Uribante Trough. The formation is composed of polygenic conglomerate, with sandstone and light grayish claystone intercalations with some evaporitic intervals, and contains a restricted shal- low water bivalve assemblage (Renz, 1959; Richards, 1968; Garcia-Jarpa et al., 1980).

The flooding of the continental margin during Cycle 2 deposition resulted in the accumulation of

limestone and shale over a large area (lower Cogollo Group, and Ap6n Formation; Figs. 12 and 13). [n the Sierra de Perij~ (Machiques Trough), these rocks are followed by the Machiques Member of the Ap6n For- mation, representing the maximum flooding event during Cycle 2. These are well-laminated, bitumin- ous, dark blue-gray limestone with abundant cal- careous concretions and a predominant pelagic fauna deposited in an anoxic environment (Renz, 1959, 1981). This unit was paleontologically dated as late Aptian (Sutton, 1946).

The Ap6n Formation is much thinner in the Mara- caibo Platform and comprises well bedded, micritic, skeletal limestones interbedded with marly lime- stones deposited in a neritic, well aerated but quiet environment (Renz, 1981; Fig. 12). Toward the east and southeast in the Andes, the Ap6n Formation displays a progressive terrigenous influence and a rapid decrease in thickness from that found in the Machiques Trough (Trump and Salvador, 1964; Garcia-Jarpa et al., 1980). These rocks are capped by

386 C.E. MACELLARI

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upper Aptian, gray, partly micaceous, sandy shale approximately 20 meters thick (Guaimaros Shale), deposited during the peak of Cycle 2 (Renz, 1959, 1981; Fig. 13).

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Cretaceous paleogeography and depositional cycles of western South America 389

East of BogotA, Cycle 2 was initiated with a trans- gressive quartz sandstone (Caqueza Sandstone of Miller, 1979; or the Alto de Caqueza Formation of Renzoni, 1967; see Fig. 3). The Caqueza Sandstone is Hauterivian in age (Hubach, 1957; Biirgl, 1961a) and is followed by the shales of the Fomeque Formation that represent the peak of Cycle 2 sedimentation. This unit comprises 700 meters of dark gray, iron- rich, occasionally gypsiferous silty shale with inter- calations of calcareous, micaceous siltstone, fine- grained, carbonaceous sandstone, and hard, fine- grained orthoquartzite (Renzoni, 1967).

In the Middle Magdalena Valley, sedimentation started with the Tambor Formation (Figs. 10, 14, 15), which rests unconformably on Jurassic red beds. This unit includes 350 to 650 meters of conglo- merates and quartz sandstones interbedded with red and gray mudstones that were deposited in several continental to shallow marine settings ranging from braided to high-sinuosity rivers, alluvial plain, and tidal fiat (Bueno, 1979; Renzoni, 1985a). The age of the basal deposits is generally accepted as Valan- ginian-Hauterivian (Morales et aL, 1958; Julivert, 1961, 1968; Bueno, 1979; Taborda, 1979). Well established marine conditions were achieved during deposition of the overlying unit, the Rosa Blanca Formation. This unit is composed of up to 400 meters of thinly bedded, medium- to dark-gray wackestones, micrites, biomicrites, grainstones and biomicrudites, representing shallow marine to intertidal and supra- tidal deposits (Taborda, 1979; Cardozo and Ramirez, 1985). Ammonites reported from this formation in- dicate a Hauterivian-Barremian age (Morales et a[., 1958).

The upper portion of Cycle 2 in the Middle Magda- lena Basin area is composed of 125 to 625 meters of black, thinly laminated, frequently micaceous and slightly calcareous shales commonly containing gyp- sum intercalations (Paja Formation; Julivert, 1958; Reyment, 1981; Forero and Sarmiento, 1985). Barremian to Aptian ammonites are reported for this unit (Morales eta[., 1958; Julivert, 1968).

Cycle 3 (Upper Aptian to Mid-Cenomanian): Deposition during this cycle occurred at a time of generalized subsidence controlled by the thermal cooling of an increasingly rigid crust (Fabre, 1983b). This, combined with a high stand of sea level, resul- ted in the flooding of several paleohighs that had remained emergent during the earlier portion of the Cretaceous.

Sedimentation in the Barinas Basin was initiated with deposition of the Aguardiente Formation (Figs. 9 and 12), a unit 55-93 meters thick composed of glauconitic, well bedded calcareous sandstones inter- calated with well laminated shales and gray, crys- talline limestone (Gaenslen, 1962). An Aptian?- Albian age has been determined for this unit in the Barinas Basin (Russomano and Velarde, 1982). This sequence is overlain by the Cenomanian-Turonian Escandalosa Formation, which is 55-262 meters thick with max imum values increasing toward the

Uribante Trough. Four members are recognized in this formation but only the lower two are included in Cycle 3. Member S, composed of a micaceous, car- bonaceous shale, forms a regional, 6-24 meter thick guide unit that represents the max imum flooding of Cycle 3 transgression (Russomano and Velarde, 1982). This is followed by Member R, a glauconitic interval with intercalations of crossbedded sandstone and minor dark shale (approximately 40 m thick) that resulted from the progradation of shallow marine clastics during the final portion of Cycle 3.

In the southern Venezuelan Andes Basin, Cycle 3 was initiated with the basal transgressive sand of the lower to middle Albian Aguardiente Formation (Notestein et al., 1944; Figs. 12 and 13). South of the M6rida Arch, this formation is composed of 300 to 500 meters of light colored, hard, medium to thickly bedded sandstone interbedded with carbonaceous shale and siltstone, with glauconite becoming more abundant up-section (Trump and Salvador, 1964). North of the M6rida Arch, equivalent beds contain thick intercalations of calcareous sandstone (Peflas Altas Formation; Renz, 1959; Fig. 13). The Pe6as Alias Formation represents a tidally dominated, highly destructive delta with long strings of sand perpendicular to the coast (Bartok et al., 1981). The max imum flooding event of Cycle 3 in the southern Venezuelan Andes is recorded in the anoxic facies of the La Grita Member of the Capacho Formation (Renz, 1959). This member (upper Albian to lower Cenomanian) is composed of 10-15 meters of well bedded black limestones that may represent a con- densed zone at the peak of Cycle 3. The upper portion of Cycle 3 in this area is represented by the lower portion of the Seboruco shales of the Capacho For- mation (Renz, 1959, 1977; Figs. 12 and 13).

A progressive increase in limestone is observed to- ward the Maracaibo Platform during Cycle 3. These sediments are included in the Mercedes Member of the Aguardiente Formation, in the upper ApSn, Lisure, and Maraca Formations, and in the undif- ferentiated Cogollo Group, representing mostly shallow marine sedimentation (Rod and Maync, 1954; Richards, 1968; Renz, 1977, 1981; Bartok et al., 1981). These are followed by the La Aguada Member of the La Luna Formation, which is composed of 60 meters of dark gray massive limestone with large calcareous concretions and black shale that contain upper Albian to Cenomanian ammonites (Renz, 1981). Cycles 3 and 4 are poorly differentiated in this rapidly subsiding area.

In the Llanos Basin of Colombia, Cycle 3 was initiated with the deltaic Une-Ubaque sandstones (Fig. 14). The Une is composed of approximately 500 meters of quartz sandstone with siliceous cement, quartz conglomerate, and medium- to fine-grained clayey sandstone with carbonized debris (e.g., P~rez and Bolivar, 1985). This unit is replaced in the north by the lithologically similar Ubaque Formation (Miller, 1979).

Toward the west, these sediments are replaced by deeper water facies preserved in the western margin

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Cretaceous paleogeography and depositional cycles of western South America 399

West Peruvian Trough is the Inca Formation, which is composed of 90 meters of interbedded, brownish gray, oolitic, arenaceous, and ferruginous limestone and yellowish-green fossiliferous shale with minor intercalations of quartz sandstone and ferruginous siltstone (Benavides, 1956; Figs. 19 and 20). This unit is possibly replaced to the east by the Goyllaris- quizga Formation. Farther south, the unit becomes less ferruginous and increasingly calcareous, and it passes into the Pariahuanca Formation (Wilson, 1963}. To the southwest, in the Lima area, wide- spread volcanic activity started at this time and extended to the end of the Albian or possibly the Cenomanian. The rocks originated during this event are included in the Casma Group (Myers, 1974; Guevara, 1980; Atherton et al., 1983).

The basal transgressive unit in the Mara~6n Geanticline is formed by the quartz sandstone of the Goyllarisquizga Formation. However, it is unclear whether this unit represents only the basal portion of Cycle 3 or if it includes older intervals as well (McLaughlin, 1924; Benavides, 1956; Wilson, 1963).

In the northern portion of the West Peruvian Trough, the Chulec Formation was deposited on top of the Inca Formation as deeper water conditions began to develop. The Chulec is composed of 500 meters of fossiliferous, light gray marls with inter- bedded massive gray limestones that contain a lower middle Albian macrofauna (Benavides, 1956). These rocks are followed by a lower interval of friable brownish shale with intercalations of massive limestone-bearing abundant thick-shelled bivalves, and an upper interval of thinly bedded limestones. The maximum flooding of the West Peruvian Trough during Cycle 3 resulted in the deposition of anoxic, black bituminous shales with thin intercalations of fetid limestones and chert (Pariatambo Formation; Cobbing et al., 1981; see Fig. 5).

In the northern portion of the Marafi6n Geanti- cline, the Chulec and Pariatambo Formations are replaced by the Crisnejas Formation, which consists of 200-300 meters of calcareous shale and sandstone with intercalations of limestone (Benavides, 1956; Fig. 2O).

A normal oxygenated environment was re-estab- lished during the late Albian concurrent with emer- gence at the margins of the trough (Cobbing, et al., 1981). These regressive sediments are included in the Pulluicana Group, which is composed of approxi- mately 900 meters of wavy bedded, nodular, argilla- ceous limestone with intercalations of sandstone and calcareous shale (see Fig. 6). The Pulluicana Group was deposited in a shallow marine environment and contains late Albian to mid-Cenomanian ammonites (Benavides, 1956).

In the East Peruvian Trough, as now preserved in the Marafi6n, Ucayali, and Huallaga Basins, the basal unit of Cycle 3 is included in the Cushabatay Formation (Figs. 20 and 21). This formation is composed of 100-450 meters of crossbedded, white quartz sandstone with intercalations of siltstone and micaceous shale with plant remains and coal hori-

zons (Huerta-Kohler, 1982; Zegarra, 1982). These sandstones are interpreted to have been deposited in fluvial to deltaic environments in the Marafi6n Basin (Kummel, 1948; Pardo and Zt~fiiga, 1976; Soto, 1979). In the Huallaga Basin, the lower portion of the unit was deposited in a fluvial environment, but the upper portion represents coastal barrier sands (Huerta- Kohler, 1982}. Only the upper portion of the unit has yielded age-diagnostic palynomorphs, which indicate an Albian age (sominario and Guizado, 1976). The maximum flooding event of Cycle 3 resulted in the deposition of the Esperanza Formation (see Fig. 5). This unit is composed of 20-200 meters of black fos- siliferous shale, with occasional glauconitic as well as sandstone and limestone intercalations. These shales contain ostracods, foraminifers, bivalves, and gastropods which indicate deposition in lagoonal to shallow marine environments (Soto, 1979}. Palyno- morphs present here indicate an Albian age (somin- ario and Guizado, 1976). To the east and southeast, the Esperanza is replaced by sandstones and shales containing plant fragments and abundant mica (Raya Formation).

The upper part of Cycle 3 is represented by the pro- gradation of a deltaic system (Agua Caliente Forma- tion; Soto, 1979; see Fig. 6). This unit is composed of 50-500 meters of medium- to coarse-grained to con- glomeratic massive to crossbedded quartz sandstone, with occasional intercalations of black shale with abundant iron concretions and plant remains (Martinez, 1980). This unit is considered Albian in age on the basis of limited diagnostic palynomorphs (Seminario and Guizado, 1976).

Cycle 4 (Upper Cenomanian to Lower Campan- Jan?): The boundary between Cycle 3 and Cycle 4 is not clearly expressed in the West Peruvian Trough, but a new deepening trend was established with deposition of the Quillquih~n Group (Figs. 19 and 20). This unit consists of 100 meters of brown shales and marls interbedded with rusty yellowish lime- stones, followed by bluish-gray limestones and marls (Benavides, 1956). The Quillquifi/m Group repre- sents deposition in a neritic environment transi- tional between the shallower deposits of the Pullui- cana Group and the deeper sediments of the over- lying Cajamarca Formation. These sediments con- rain an upper Cenomanian to lower Turonian fauna (Benavides, 1956).

The overlying Cajamarca Formation was depo- sited during the peak of Cycle 4 and consists of about 300-500 meters of gray-brown, very fine grained limestones and well stratified bluish marls with very thin shaley intercalations. A rich macrofauna was collected in the Cajamarca Formation that indicate a mid- to late Turonian age (Benavides, 1956). Toward the Marafi6n Geanticline, the Pulluicana and Quill- quifi~n Groups and the Cajamarca Formation are replaced by the Jumasha Formation (Fig. 20). This unit consists of 1000 meters of bioclastic and pelletal limestone and dolomite, with intercalations of very fine grained carbonate and siltstone (Wilson, 1963).

400 C.E. MACELLARI

The Jumasha Formation was deposited in a relative- ly shallow water environment devoid of clastic input.

The Cajamarca Formation of the West Peruvian Trough and the Jumasha Formation of the Marafi6n Geanticline were followed by the fossiliferous Conia- cian to lower Santonian Celendin Formation, con- sisting of up to 300 meters of gray and yellowish, cal- careous shale and siltstone with intercalations of nodular limestone (Benavides, 1956). The Celendin Formation was deposited in a shallower water set- ting than was the preceding unit (Benavides, 1956).

In the East Peruvian Trough, Cycle 4 was initi- ated either in the upper part of the Agua Caliente Formation or in the overlying marine shales depo-

sited during the new marine advance (Fig. 21). These are dark gray shales with interbeds of sand- stone, siltstone, and limestone that are included in the Chonta Formation. The Chonta Format ion varies from a thin (100 m), predominantly sandy sequence to the southeast to a thick (1600 m), pre- dominantly shale and limestone sequence to the northwest in the ancient Amazonian delta of the Marafl6n Basin (Soto, 1979). The Chonta is divided into three members: a lower shale interval, followed by a middle, mostly micritic, limestone interval, and an upper gray shale and micritic l imestone unit (Fuentes, 1980). The Chonta contains an abundant macro- and microfauna that indicate an Albian to

550 meters

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Fig. 21. Generalized well-log signature, oil occurrence, and Cretaceous cycles of the northeastern Mara56n Basin (modified from Del Solar, 1982).

Cretaceous paleogeography and depositional cycles of western South America 401

Santonian age (Knechtel et al., 1947; Kummel, 1948; Seminario and Guizado, 1976; Pardo and Zfifiiga, 1976; Huerta-Kohler, 1982).

Cycle 5 (Upper Campanian to Maastrichtian): By the end of the Santonian, the western portion of the West Peruvian Trough had been uplifted and provided the source for a continental red bed molassic sequence known as the Chota Formation in northern Peru and as the Casapalca Formation in central Peru (Benavides, 1956). The age of these red beds is not clearly established, but a Campanian to Paleocene age is generally accepted (Cobbing et al., 1981).

In the East Peruvian Trough, Cycle 5 commenced with the transgressive Vivi6n Formation, which forms the most important reservoir of the Marah6n Basin. This unit is composed of 50-300 meters of yellow-brown to white, coarse- to fine-grained, cross- bedded sandstone with minor intercalations of black shale with plant remains. These sediments represent an extensive braided fluvial system developed in an arid climate, followed by coastal barriers deposited at the initiation of the new transgression (Del Solar, 1982). The continuation of the Cycle 5 transgression resulted in deposition of the Cachiyacu Formation. This unit is composed of black shales, marly clay- stone and siltstone containing a brackish to marine fauna (Kummel, 1948; Kohl and Blissenbach, 1962}. The sequence is poorly dated due to the absence of diagnostic fossils, but a Maastrichtian age is accep- ted for the Cachiyacu Formation and a Campanian- Maastrichtian age for the underlying Vivi6n Forma- tion (Kummel, 1948; Kohl and Blissenbach, 1962). The Cachiyacu Formation is capped by red beds (Huchpayacu Formation; Huerta-Kohler, 1982) that represent the first important clastic influx derived from the uplifted Andes.

Neuqu~n Basin

Because of its economic importance, its excellent exposures, and its relatively easy access, the Neu- qu6n is one of the best known basins of South America. The early stage of development took place in an intra-arc setting with the extrusion of volcanics together with the development of extensive horsts and grabens (Digregorio et el., 1984). The Neuqu6n Basin, with its complexly block-faulted paleogeo- graphy, was covered by up to 6000 meters of Jurassic and Cretaceous, mostly marine sediments. These sediments represent three major sedimentary cycles (Jur6sico, Andico, and Riogrfindico) as defined in the works of Groeber (1929, 1946, 1953; Fig. 22). The cycles document transgressive/regressive events sep- arated by two major tectonic pulses: the late Kim- meridgian Araucanian phase, and the "mid-Creta- ceous" Peruvian phase - - the latter associated with the intrusion of large granodioritic bodies (Stipanicic and Rodrigo, 1970; Ramos and Rgmos, 1979).

Extension initiated during the early Mesozoic was followed by thermal subsidence in a back-arc setting during the Jurassic to the earliest Cretaceous ("Jut-

~sico" and lower "Andico" cycles). During the later portion of the Cretaceous (upper Andico and Rio- gr~ndico cycles), sedimentation took place in a fore- land basin setting (Digregorio et el., 1984).

Several sequence-stratigraphic syntheses of the basin have been presented recently (Legarreta et el., 1981; Gulisano et el., 1984; Mitchum and Uliana, 1985; Gulisano and Legarreta, 1987). In the present work, the Cretaceous stratigraphy is subdivided into six second-order cycles, following the scheme out- lined by Gulisano and Legarreta (1987).

Cycle 1 (~Lower Mendocian" - - K immer idgian to Lower Valanginian). The basal unit is represented by the continental Tordillo Formation, which is com- posed of red and gray-green conglomerate and sand- stone, followed by green siltstone (Digregorio and Uliana, 1980; Allen et el., 1985). This unit rests with angular unconformity on top of the "Jur~sico" cycle (Leanza et el., 1977; Leanza, 1981; Figs. 22, 23, 24).

The basal clastics are followed by a series of pro- gradational depositional sequences, with fluvial to shallow marine facies to the east-southeast and basinal facies to the west-northwest (Gulisano et el., 1984; Mitchum and Uliana, 1985). The basinal facies are included in the Vaca Muerta Formation. These are dark gray and black shales, locally highly organic and bituminous (Weaver, 1931), deposited under at least partially anoxic conditions. The Vaca Muerta increases rapidly in thickness from east to west, from approximately 20 to more than 600 meters. The top of this unit becomes younger from south to north, ranging from early to late Tithonian, to Berriasian, to early Valanginian in successive sections (Leanza, 1973, 1981; Leanza and Hugo, 1977; Mitchum and Uliana, 1985). The outer shelf facies, which laterally replace and overlie the basinal facies, are included in the Quintuco Formation. These are dark gray and black, partly bituminous shales that become more silty toward the basin margins. Thicknesses range from 400 meters to the south to 750 meters near the center of the basin (Gulisano et al., 1984). To the east and north of the basin, the Quintuco grades, respectively, into the Loma Montosa Formation (oolitic grainstones), and the Chachao Formation (bioclastic calcirudites, packstones, and calcarenites), which represent mid- shelf sedimentation (Zilli et el., 1979; Uliana et al., 1977; Mombrfi et al., 1979; Carozzi et al., 1981; Legarreta et el., 1981; Legarreta and Kozlowski, 1981; Ploszkiewicz and Orchuela, 1982).

The more proximal facies of Cycle 1, which later- ally replace and overlap the previous facies, are included in the Mulichinco Formation (Fig. 22). This unit consists of 230-450 meters of sandstones and conglomerates with thin limestone intercalations that represent shallow marine, deltaic, and continen- tal environments (Leanza et al., 1977; Leanza, 1981; Gulisano et al., 1984). The Mulichinco Formation ranges in age from late Berriasian in the southeast, to Valanginian in the northwestern portion of the basin (Leanza and Hugo, 1977; Leanza, 1981).

402 C.E. MACELLARI

~AASTRICH- TIAN

CAMPANIAN

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CONIACIAN

ALBIAN

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Fig. 22. Generalized stratigraphic column of the Neuqu~n Basin showing distribution of cycles and hydrocarbon producing units; Groeber's cycles shown on the right.

Cycle 2 CMid-Mendocian" - - Upper Valanginian to Lower Hauterivian). The second cycle was depo- sited on top of the Intra-Valanginian unconformity. Sedimentation in Cycle 2 was initiated with low- stand deposits of the upper part of the Mulichinco Formation (Gulisano et al., 1984), and the trans- gressive facies are represented by the Agrio Forma- tion (Fig. 22). This unit is divided into upper and lower members of similar lithology, separated by the

Avil~ Sandstone. In the southern part of the basin, the Agrio is composed of micritic limestone, grain- stone, coquina, and calcareous sandstone, which are replaced by carbonaceous shale toward the center of the basin. On the margin of the basin, the Agrio represents a shallow marine to fluvial and possibly lacustrine environment (Dellap~ et al., 1979). In the northern portion of the Neuqu~n Basin, the Agrio ranges from dark shales and micritic limestone to the

Cretaceous paleogeography and depositional cycles of western South America 403

A

SCHEMATIC STRATIGRAPHIC SECTION MENDOZA GROUP

SOUTHERN NEUQUEN BASIN

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A,

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Fig. 23. North-south stratigraphic section of the Mendoza Group (Cycles 1-3) in the southern portion of the Neuqu6n Basin (modified from Leanza et aL, 1977).

STRATIGRAPHIC SECTION MENDOZA GROUP

NORTHERN NEUQUEN BASIN C C '

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A A A A A A A

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,., " ~ fossillferous limestone ~,~

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TITHONIAN >< /" ~ gray-green clastlcs " k BA~ilN I .~ .~.~l l ' - o ,.,oo

KIMMERIDGIAF ~ u.

(~ deposltionel cycle

Fig. 24. East-west stratigraphic section of the Mendoza Group (Cycles 1-3) in the northern portion of the Neuqu~n Basin (after Legarreta et al., 1981 ).

404 C.E. MACELLARI

west, to skeletal and oolitic limestones grading into gray calcareous sandstone to the east (Legarreta et al., 1981; Mombrfl et al., 1979). West of this area, in Chile, facies encompassing Cycles 1 and 2 are in- cluded in the Lo Vald6s Formation. This unit shows a marked shallowing event at the cycle boundary (Hallam et al., 1986).

Cycle 3 ("Upper Mendocian" - - Upper Hauterivian to Lower Aptian?). This cycle was initiated with the Avil6 Member of the Agrio Formation, which is a lowstand deposit (Figs. 22, 23, 24). This unit is well represented in the interior (western) portion of the basin, but is absent to the east. These sands are followed by the marine shales of the upper Agrio For- mation. Regression at the end of Cycle 3 is defined by the appearance of coarser clastic facies (Troncoso Sandstone; Dellap6 et al., 1979). To the east, Cycle 2 and 3 rocks are replaced by the proximal clastics of the Centenario Formation (Digregorio, 1972).

Cycle 4 (~Huitriniano" - - Lower Aptian? to Mid- Cenomanian?). Deposition during this cycle took place in more restricted marine conditions. The base of the cycle is represented by the Huitrin Formation, composed of up to 500 meters of gypsum and carbon- ate with minor conglomerate, sandstone and shale. The depositional environment has been interpreted as sabkha, lacustrine, and fluvial. An increase in clastics occurs toward the east and southeast where this unit is replaced by the upper Centenario Formation. Even though no diagnostic fossils have been reported, an Aptian-Albian age is generally accepted for the Hutrin Formation (Uliana et al., 1975; Volkheimer and Salas, 1975; Digregorio and Uliana, 1980; Malumi~n et al., 1983).

The overlying Rayoso Formation (=Ranquiles and Cafiad6n de la Zorra Formations of Uliana et al., 1975} is composed of up to 900 meters of conglo- merate and reddish sandstone and shale, with minor amounts of gypsum and salt. The depositional en- vironment ranges from fluvial to lacustrine and possibly deltaic (Digregorio, 1972). Fossils include dinosaur bones, wood fragments, and freshwater bivalves (Digregorio, 1972). The upper boundary of Cycle 4 coincides with a regional unconformity associated with a major diastrophic face (Stipanicic and Rodrigo, 1969; Uliana et al., 1975). There is no agreement, however, on how much time is missing between Cycles 5 and 6. According to Riccardi (1987), this hiatus extended from the early Ceno- manian to the Coniacian, whereas Gulisano and Legarreta (1987), considered sedimentation to have been almost continuous.

Cycle 6 ("Neuqueniano" - - Mid-Cenomanian? to Lower Campanian?). This cycle was deposited in a continental setting, and is included in the Neuqu6n Group (Digregorio, 1972; Fig. 22). These sediments lap on top of older rocks in an easterly and south- easterly direction (Uliana et al., 1975). The Neuqu6n Group is up to 1400 meters thick and is divided into

three formations m the Rio Limay, Rio Neuqu6n, and Rio Colorado m representing three successive sedi- mentary cycles. Each cycle starts with sandstone and conglomerates and is capped by red mudstone (Cazau and Uliana, 1972).

Cycle 7 ("Malalhueyan" - - Upper Campanian? to Paleocene). These sediments herald the onset of the first Atlantic-derived transgression into the basin (cf. Wichmann, 1927; Bertels, 1979; Uliana and Dellal~, 1981). The basal unit of Cycle 7 is the Allen For- mation, approximately 65 meters thick, which is composed of light gray sandstone and conglomeratic sandstone, followed by claystone with intercalations of sandstone, and finally by tuff and stromatolitic limestone (Andreis et al., 1974; Uliana and Dellap6, 1981). The Allen Formation is interpreted as a sand flat environment close to the shoreline (lower mem- ber), followed by a mixed flat setting in a tidal environment (middle member), and finally capped by a restricted and hypersaline marginal sabkha envi- ronment (Andreis et at., 1974).

Clearly defined marine conditions were estab- lished during deposition of the overlying Jaguel For- mation, which represents an open shelf environment distant from the source of clastic input (Bertels, 1970). This unit is composed of 95 meters of green to yellowish green, monotonous, massive, partly friable siltstone and well laminated clays (Uliana and Dellap6, 1981).

Austral Basin

The Austral (or Magallanes) Basin originated during a Triassic to Jurassic extensional episode (Gust et al., 1985), which was immediately followed by the formation and infill of a marginal basin ("Rocas Verdes") to the west of the basin (Dalziel et al., 1974; Dalziel, 1981). This event was followed by a time of thermally driven subsidence just after the emplacement ofophiolitic bodies in the Rocas Verdes Basin. During the Late Cretaceous, a thick sedimen- tary package was deposited in a foreland setting following uplift of the Andes and the formation of a foredeep adjacent to the uplifted orogen.

The Cretaceous sequence of the basin has recently been subdivided into depositional sequences by Biddle et al. (1986) on the basis of seismic, strati- graphic, and well data, and by Arbe (1987) based mostly on outcrop data. Here, the Cretaceous se- quence is divided into six second-order cycles. How- ever, the lack in many cases of diagnostic fauna or correlation between ambiguously dated isolated out- crops makes it difficult to establish with certainty the age of several of the cycle boundaries. The cycles presented here agree in general with those outlined previously.

Cycle 1 (Tithonian to Lower Aptian). This cycle was initiated with the Springhill Formation, which is the main hydrocarbon reservoir of the basin. This unit is comprises a lower, continental, member com-

Cretaceous paleogeography and depesitional cycles of western South America 405

posed of subangular, medium- to coarse-grained quartz sandstone with a tuffaceous matrix, and an upper portion which is composed of well sorted, cross- bedded, glauconitic quartz sandstone with clay matrix and shell fragments and represents beach and shallow marine deposition during the transgressive phase of Cycle 1 (Thomas, 1949; Cecioni, 1955; Riccardi, 1977; Robles, 1982, 1984; Miller et al., 1982; Hinterwimmer et al., 1984). Macro- and micro- paleontologic data indicate that this unit is time- transgressive, becoming younger toward the north of the basin (Fig. 25). Thus, these sediments are Oxfordian to Kimmeridgian to the south, in Chile (Sigal et al., 1970; Natland et al., 1974), Tithonian to Berriasian in the Lago Argentino area (Blasco et al., 1979), Berriasian in the Lago San Martin area (Riccardi, 1977), and up to Valanginian in the Lago Belgrano area (Aguirre Urreta and Ramos, 1981). The lack of more precise age control does not allow the determination of whether this sand represents a single unit or if, as proposed by Biddle et al. (1986), it includes a series of backstepping intervals.

A thick package of basinal sediments (Rio Mayer Formation) was deposited as the basin continued to subside (Figs. 9 and 25). These are dark gray to black laminated shales with minor limestone intercala- tions that were deposited under partially anoxic con- ditions (Riccardi, 1971; Riccardi and Rolleri, 1980; Nullo et al., 1981). The Rio Mayer shales thicken considerably from a few meters to the north (Aguirre Urreta and Ramos, 1981) to over 700 meters in the Lago San Martin area to the south (Riccardi and Rolleri, 1980). In the southwestern portion of the basin, similar facies are included in the Zapata For- mation (Katz, 1963), whereas in the subsurface they are included in the Palermo Aike Formation (Russo and Flores, 1972) or into the Pampa RincSn Forma- tion (= Lower Inoceramus Shale; Flores et al., 1973).

The maximum flooding during Cycle 1 took place in the late Hauterivian (Riccardi, 1987). After this event, the northern portion of the basin was pro- graded by a coarsening upward clastic sequence (Rio Belgrano Formation). This unit, which ranges from the Barremian to the lower Aptian, is composed of green sandstone with intercalations of shale, and it is replaced by coarser crossbedded sandstone toward the top, deposited in shallow marine to intertidal settings (Ramos, 1979). In the Lago Cardiel area, this interval is represented in the lower portion of the Cerro Pelado Member of the Piedra Clavada For- mation (Ramos, 1982).

Cycle 2 (Mid-Aptian to Mid-Cenomanian? ). A new sedimentary cycle was initiated in the mid-Aptian. To the north of the basin, the Rio Tarde Formation was deposited unconformably on top of previous rocks (Ramos, 1979). This sequence includes 320 meters of conglomerates at the base and purple mudstones and tufts to the top deposited in a continental setting (Ramos, 1979). Farther south, these sediments grade into the sandstones of the Piedra Clavada Formation,

which include a marine intercalation near its base (Ramos, 1982}. In the Lago San Martin area, similar sediments are included in the Kachaique Formation, with a well developed marine fauna near its base containing lower to mid-Albian ammonites (Riccardi et al., 1987}.

The basal transgressive units are followed by the north to south progradation of beach, tidal, and flu- vial sandstones and finally red mudstones and tufts (Cardiel Formation). In the south of the basin, how- ever, the Rio Mayer Formation continued to be depo- sited without noticeable break. Because of the lack of diagnostic fossils in the north and uncertainties in the exact provenance of the fauna to the south, the upper limit of Cycle 2 remains poorly constrained. However, the youngest fossils found in this cycle are possibly Cenomanian in age (Riccardi 1979}.

Cycle 3 (Mid.Cenomanian? to Mid-Coniacian? ). The initiation of this cycle coincided with a major tectonic event that resulted in the closure and deformation of the marginal basin located to the west of the basin. This event gave rise to the "Paleoandes" and the concurrent formation of a foredeep im- mediately adjacent to the east (Dalziel et al., 1974; Winslow, 1980; Wilson, 1983}. This event is reflected in a paleontological hiatus extending from the upper Cenomanian to the lower Coniacian present in large portions of the basin (Malumi~n, 1968; Malumi~n et al., 1971; Flores et al., 1973; Riccardi, 1984). A thick turbidite sequence was deposited in this new depo- center (Punta Barrosa Formation in Ultima Esper- anza, and basal Cerro Toro Formation in Lago Argentino; Cecioni, 1957; Katz, 1963; Arbe and Hechem, 1984a). Toward the northern basin edge, these turbidites are possibly replaced by gray and green siltstone and shale of the Mata Amari l la Formation (Russo and Flores, 1972; Leanza, 1972). This unit contains diagnostic Coniacian ammonites (Leanza, 1969}.

Cycle 4 (Mid-Coniacian? to Mid-Campanian?) . The contact between Cycle 3 and Cycle 4 was recog- nized in the Lago Argentino area by Arbe and Hechem (1984a), and it is also represented in the subsurface (Biddle et al., 1986). Large amounts of sediment were dumped below wave base by turbidity flows on a deep sea fan system in the western margin of the depositional trough adjacent to the uplifted cordillera (Scott, 1966; Winn and Dott, 1979; Dott et al., 1982). These sediments are included in the Cerro Toro Formation (Katz, 1963} and comprise more than 2000 meters of turbidites transported southward along a major trough (Scott, 1966; Vilela and Csaky, 1968; Winn and Dott, 1979}. The Cerro Toro and equivalent units contain Santonian to lower Cam- panian ammonites (Katz, 1963; Leanza, 1963, 1967; among others). At the northern basin edge, these sediments were possibly replaced by greenish cal- careous sandstone (El Alamo Formation) bearing a similar ammonite fauna (Leanza, 1967, 1972).

CR

ET

AC

EO

US

S

Ult

ima

Esp

ere

nza

MA

ASTR

ICH

TIA

N

CA

MPA

NIA

N

8A

NTO

NIA

N

CO

NIA

CIA

N

TUR

ON

IAN

CEN

OM

AN

IAN

ALB

IAN

APTIA

N