The present general outline includes not only the peri-atlantic basins but also the Andean. .... one in the westem coast of South America, equivalent to the.
1
«ANNALES DU MUSI!UM D'HISTOIRE NATURELLE DE NICE- TOME IV -1976»
C. Nclñct::
~
OUTLINE OF CRETACEOUS STRATIGRAPHY OF ARGENTINA Norberto MALUMIÁN Ana María BÁEZ Univenidad de Buenos Aires Dto Geologia and Consejo Nacional de Investigaciones CientliJCas y Técnicas
ABSTRACT The mid-Cretaceous stratígraphy of Argentina, including recent data, is outlined. This is aimed at relating the major stratigraphical and palaeontological events connected with the origin of the South Atlantic Ocean. A prooounced synchronism among tectonic movements, fauna! breaks and the major episodes in the development of the South Atlantic Ocean in Barremian-Aptian. and Cenomanian-Turonian times are demonstrated. The present general outline includes not only the peri-atlantic basins but also the Andean.
INTRODUCTION The aim of this paper is to provide a general idea of the Cretaceous stratigraphy of Argentina. With íhis end in view, we give a swnmary of the geology of the Cretaceous sedimentary basins. We . have particularly emphasized recent results and new information on collections · currently under study which are of interest in casting light on the major events connected with the origin of the South Atlantic Ocean. We lay no claim to completeness in our treatment of the palaeontology and stratigraphy. lt is evident that the main events connected with the origin and evolution of the South Atlantic are reflected not only in the basins along the Atlantic margin but also in those of the Andes ; the two have synchronous histories. In contrast with most of the sedimentary basins, the Austral basin contains an almost complete Cretaceous sequence. There are changes in the microfauna that may well be explicable as being related to the events marginal to the evolution of the South Atlantic. lt should bere be mentioned that a stratigraphical standard scheme has yet to be developed for Argentina. The early work of Groeber on the Neuquén Basin brought to light the fact that the stratigraphical sequences encountered did not coincide with those known from Europe. The marine part of the Austral basin is suitable for the development of a stratigraphical standard. Recently, Flores et aL ~ 19731 have worked out in sorne detail the Argentinian part of the basin and Natland et aL, (19731 have proposed a succession of stages for the Chilean part. Microfaunas are relatively abundant and they are gradually proving useful for establishing stages and for erecting a zonational scheme, permitting correlations within the southem hemisphere. The relationships between the macro- and microfaunas have yet to be worked out. Generally speaking, the continental formations need to be given stratigraphically studied and much remains to be done on their faunas and floras. Sorne of the work whlch has been done needs revision as the criteria employed at the time do not meet modem standards and requirements. Thus, a new evaluation of the ages and lenghts of stratigraphical discontinuities is badly needed. In spite of these difficulties, we have attempted to sketch in simple terms the general correlational picture, usin1!¡ moet importan\ tonDAtions. As reguds to the stratigrap · breaks, these have only been possible to estimate ín very broad terms, especially for the continental sequences.
XXVII. 1
SAN JORGE., COLORADO AND SALADO BASINS These basins are characterized by their Cretaceous continental sedimentation, interrupted by the Miranic phase and equivalent moveRUlnts and by a Maastrichtian ingression related to the Huantraico phase. San Jorge Basin : Fonnatioas and Lithology Light greenish glauconitic rich sandstooes and claystones, par· Salamanca Fm. tiaUy calcareous
Sandstones, siltstones and claystones, grayish, greenish ; local Chubut Gr. red beds ; tuffs ; dark grey clays. Grey or green tuffs, claystones and subordinate tuffaceous sandstones. Mina del Cannen Fm. Locally with reddish or variegated intervals. Colorado Basin: Formation and Lithology Green, grey, or dark grey claystones, generally calcareous Pedro Luro Fm. Red, brown, green or variegated claystones and siltstones, with Colorado Fm. sandstones generally crossbedded. Dark brown, purplish, red siltstones, claystones and shales ; Fortin Fm. subordinate sandstones. Salado Basin: Formation and Lithology Grey claystones and sandstones with anhydrite and gypsum Red, green or variegated fine to coarse sandstones alternating with General Belgrano Fm layers of purple, greenish-grey variegated claystones. Conglomerates. Red. brown and purple sandstones and claystones partly with light greenish decolouration zones ; Rio Salado Fm. generally micaceous. Arapey lavas (in Uruguay and Table 1 sub-basins.) AUSTRAL or MAGALLANES BASIN.
This basin differs considerably from the nearby basins if its marine sedimentation is compared with the continental sedimentation in Golfo de San Jorge, Colorado and Salado Basin of southeastem Argentine and Neuquén Basin of westem Argentine. Recently, comprehensive stratigraphic studies, mainly based on foraminifers in .t he NNW of the Isla Grande de Tierra del Fuego (Flores et al. 19731 and the Chilean part of the basin (Natland et al., 197 41, have been carried out. Natland et al. (op.cit.) with a more complete view of the basin proposed a stage system, considering the oldest stage (Rinconian) to be of Oxfordian-·Kimmeridgian age; however, according to the known record of the anunonite genus Favrella, present in that stage and afso in the Esperanzian, its age could be Hauterivian-Barremian. (Ric· cardi, 1970). This ammonite has been found in the Esperanzian Stage, which contains the same microfauna as the Pampa Rincón Formation, indicating a similar age to that assigned by Riccardi, (Malumian and Masiuk, 1975a). In general, the foraminiferal assemblag~ of the Austral or Magallanes Basin have the characteristics of the Austral province or geobioprovince of Scheibnerová ( 1971, 197 2a ). This microfaunal province presents problems of correlation with the known Cretaceous zonations of warmer regions because it lacks diagnostic planktonic keeled foraminifera, nannoconids, etc. typical of warm waters. The foraminiferal assemblages are characterized by benthonic forms, sorne of which may prove good for correlation when given detailed study. Within this Auatral province. different regions can be recognized; at Ieast. thé Magallanean microfaunas show enough charactersitics to be diHerenciated from those of the Great Artesian Basin of Auatralia. The foraminiferal assemblage of the Pampa Rincón Fm. is peculiar, being similar to that of the Majunga Basin,
Madagascar, (Sigal etaL, 1970; Malumián and Masiuk, 1973, 197 5a). Two species are very common : Pseudopolymorphina martinezi (Caflón and Ernst J and thé Lenticulina nodosa Reuss-Astacolus gibber Espitalié and Sigal group. More than 50 per cent of the specimens coming from different levels of this formation in different parts of the basin belong to these two species. The Lenticulina nodosa-Astacolus gíbber group was recently studied by Bartenstein (197 4), who cited it also in Somalia and South Africa, and recolmized it as a guide group, with a wide distribution, for the Lower Cretaceous. On the other hand, Pseudopolymorphina martinezi appears to be an endemic species, in spite of its high frequency and wide distribution in the Austral Basin. lt has neither been recognized in Madagascar nor in Africa (Brenner, pers. comm., Jan. 1975). The low diversity of this assemblage has been explained as a result of it having inhabited a smalllandlocked sea in an unstable enviroment .( Malumián and Masiuk, 1975a ). The faunal affinities of Tierra del Fuego and Africa during Hauterivian-Valanginian times led Gordon (19731 to propose the existence of an eastward current in the belt of the westerly winds comparable with the present one. The Lenticulina nodosa-Astacolus gíbber group is represented iu the Pratian stage (Barremian?) by Lenticulina reyesi Catión and Emst, in the deeper p~ of the basin. This stage is not represented in the NNE region of the Isla Grande de Tierra del Fuego where a paleontological break occurs : the microfaunas of the Nueva Argentina Fm. have no elements in common with those of the Pampa Rincón Fm. This is remarkable considering that most Cretaceouslenticulinids are long-ranging forms. Moreover, the foraminifers of the Nueva Argentina Fm .. show no affinities with those from Madagascar (cf. Sigal, 1956; Malumián and Masiuk, 1975b ). The Malagasymicrofaunas indicate warmer waters than those of Tierra del Fuego. This difference during Aptian-Albian times could be explained by postulating a warm current flowing southwards along the eastem coast of South Africa, equivalent to the present Mozambique and Agulhas currents, and a cold northward one in the westem coast of South America, equivalent to the present Peruvian current (Gordon, 1973). An altemative explanation would be a different position of the continente at the time. A third possibility is that both these altematives may have existed. The Nueva Argentina Fm. (Tenerifian stage : Vicutla Fm.; Capas del Hito XIX). contains the oldest planktonic foraminifers of the basin. In its upper section it becomes calcareous, this being one of the rare carbonates in the basin. The foraminifers are not well known because of their poor preservation due to recrystallization. In the Chilean part of the basin, the upper part of the Tenerifian Stage has been characterized by the occurence of Pullenia natlandi Caflón and Emst, but this species is rare in the argentinian part of the basin and in the present work it is considered a junior synonym of GlobigerineUoides gyroidinaeformis Moullade, 1966. This planktonic species was initially described from the "Fosse Vocontienne" and found in the &arly and Middle Albian of Germany (Risch, 1971) and in the Leg 27 of the Deep Sea Drilling Proyect (Krasheninnikov, 1974). Other typical calcareous species are Clbicides cf. djalfaensis Sigal and Discorbis minima Vieaux; Natland et al., 1974). In addition, agglutinated foraminifers, specially those belonging to the genua Tritaxia, become common towards the top of the sequence. The overlying formation , Arroyo Alfa, contains a well studied microfauna (Malumián and Masiuk, 1975b) which also contains typical agglutinated foraminifers of the genua Tritaxia(v. gr.. T. porteri Catión and Emst).ltseems thatthe Auatral Basin has agglutinated forms which show, as other Aptian.Cenomanianforaminifers. a clear evolutionary transformation that wiU permit the finer chronologicál subdivision in this basin. The initial forms of the Tritaxia group
XXVII. 2
have a uniserial stage with a triangular cross section, which gradually becomes circular. The forros, whose uniserial stage is completely circular are morphologically identical to the "Clavulinoides" gaultinus Morozova group, known from Cretaceous flysch of Europe (including Russia), where they also display evolutionary changes (cf.Neagu, 1962). Other forros with a well known evolutionary development are Spiroplectinata annectens (Parker and Jones) and S. complanata (Reuss), cf. Grabert, 1959; and these also oc· cur in this formation. All these elements can be used to produce a more precise stratigraphy in the temperate-cold regions, and particularly in the Austral Basin. The calcareous foraminifers of the Arroyo Alfa Formation are characterized by species also present in Zululand, South Africa, (e.g. Lini(Ulol(avelinella africana Lambert and Scheibnerová, cf. Lambert and Scheibnerová, 1974), and others present also in the Great Artesian Basin of Australia (e.g. "Discorbis" sp.nov., in Scheibnerová, 1972b; Scheibnerová et aL, in prep.). Discorbis mínima Vieaux sensu Cafton and Emst, could be referred to this latter species. There are also new species of the genera Lingulogavelinella and Valvulineria, anda new genus of the Family Discorbidae; (Malumián and Masiuk, 1975b ). It is important to mention that the microfaunas of the Nueva Argentina and Arroyo Alfa Forroations were compared with material from the Sergipe Basin (cf. Petri, 1962), kindly sent by Dr. Setem· brino Petri. No similar forros were found. The overlying Cabeza de León Fm ; (almost equivalent ot the Chilean Rinconian Stage), lacks the typical elements of the Arroyo Alfa Fm., thus another important microfaunal break occurred. The Cabeza de León Fm. has a Lower zone ("A" zone of chart) which is characterized by the last occurrence of the Gavelinella (Berthelina) group. This group occurs from the Arroyo Alfa Fm. ~pwards. A new species of Pseudoespiroplectinata, that could have descended from the spiroplectinates of the Arroyo Alfa Fm. defines that zone. Thedevelopment of the subgenus Berthelina, the occurrence of large Hedbergella (v.gr. "Globigerina" wenzeli Cafton and Ernst) and certain forms close to Praeglobotruncana, with weak keels (forros being currently studied by Malumián and Masiuk) indica tes that the "A" zone probably cannot be younger than Turonian. Another microfaunal break occurs between zones "A" and "B". Foraminifers similar to sorne described from Santonian·Campanian deposits of Australia and New Zealand (cf. Belford, 1960; Hornibrook, 1968) characterize the latter. In its lower part are found keeled foraminifera belonging to the Globotruncana "llapparenti" group, similar to those described by Edgell (1957) and Belford ( op.
cit. in Australia and by Douglas and Rankin (1969 Ion the island of Bomholm in the Boreal Province. "Planulina" rakauroana FinJa y ( :Planulina popenoi (Trujillo) sensu Caftón and Ernst) characterize the ben· thonic foraminifers of the "B"zone. This species, typified by a spiroumbilical and curved aperture in the apertura! face, belongs to a new genus which includes "Gavelinella" compressa Sliter from the Campanian of California (Malumián and Masiuk, in press). The "C" zone exhibits a noteworthy development of agglutinated forar:-_:nifers. The assemblage is known from the Antarctic (Ross Island, where it is associated with ammonites of probably middle Campanian age; Olivero, 1975) and also from the Southem portion of the continent (Santa Cruz Province); Malumián et al., 1971 ; 1972. It is worth noting the occurrence of Austral foraminifers of similar ages in the present latitude of 6° 02' 4" N in the Atlantic Ocean ( Scheibnerová, 1973) that could be related to this zone. Another salient fact becomes evident when the dissimilarity between the Cam panian·Maastrichtian microfaunal assemblages from southern and Northem Patagonia is considered.The former are characterized by the presence of species also occurring in New Zealand and Australia, but not recorded from Northem Patagonia. The occurrence of benthonic forros belonging mainly to Cassidulinacea and Buliminacea (Bertels, 1968, 197 2a) clearly characterizes the latter. This has been checked by one of the present authors (N.M.). Moreoever, the rare forros common to both regions are typically cosmopolitan species. Such microfaunal differences can hardly be explained by a difference in age or purely enviromental grounds. Groeber ( 1959, 1963) pointed out that transcontinental connections did not exist between the Maastrichtian seas of the Austral and the Northem Patagonian Basins. According to that author, the marine communication could only have taken place along Juan Fernandez Land from the Pacific side, while from the Atlantic, the coast may have bor· dered the Deseado Massif which reached the Malvinas Islands. This continental barrier, if it indeed existed with a similar position of its present day relict elements, should have separated both seas alongmore than 2,500 km. In the present continental portion of the Magallanes Basin (Santa Cruz Province), the microfaunas are poorer and less well developed (Malumián and Masiuk, 197 3). In the SC-1 well (Malumián etaL, 1971 ; 1972) the ostracod Novocythere santacruciana Rossi de Garcfa, probably of Albian age, was found. lt is similar to Majungaella pyritiformis Bate and Bayliss ( 1969 )from the
Austral Basm : formations and lithology Patagonia Austral, Santa Cruz province* * Claystones and reddish tuff, Cardiel Fm. subordinate gray sandstones.
Isla Grande de Tierra del Fuego*
Silty claystones and argillaceous siltstones
Claystones
Cabeza de Léon Fm.
Yellowish grey claystones and siltstones
Mata Amarilla Fm.
Yellow sandstones
Piedra Clavada Fm.
Arroyo Alfa Fm. Río Mayer (outcrop)
Biomicrites and biomicritic claystones
Nueva Argentina Fm.
Dark Claystones
Pampa Rincón Fm.
Sandstones and claystones
Springhill Fm.
Dark pelites
* **
or San Martín Fm. (Subsurface ).
From Flores et al. 1973 Ruaso and Flores (19721, modified ; Campo Bola Fonnation, because of its glauconitic ·and rounded quartz content (cf. Riggi, 1969 ; MalumiA~ et al., 19711 could be co!IAidered Tertiary. Also from Riccardi 09711and Leanza.(19721 Table 2
XXVII. 3
Aptian-Alhian ofTanzania.Recendy, Krommelhein 09751 erected the Majungaellini tribe, with a mainly Gondwanic distribution, !ncluding the similar genera: Novocythere and Tickalaracythere, the former from the Austral Basin and the latter from the Great Artesian Basin of Australia.
radimetrically dated (114, lOO and 96m.y., all+-5m.y.l, thus indicating that the accumulation of sediments must have commenced in the Barremian (Valencio etal., 19751. These basalts could be contemporaneous with those of the Chaco-Parana basin which are overlain discordantly by terrestrial deposits-referred to Late Cretaceous.
Invertebrate faunas. The marine invertabrates from the present continental portion of the Austral Basin are better known than those from the insular part. The species have been listed in the classical work on Patagonian geology by Feruglio (19491. Only the most recent studies on this topic will be mentioned here. Palaeogeographic interpretations have been made on the basis of the occurrence of Gryphaea balli (Stefaninil, which is also known from Oxfordian-Lower Kimmeridgian deposits of Ethiopia, Somalia and India (Cecioni and Charrier, 197 41. According to these authors, the transgression began in Oxfordian-Kimmeridgian times, varying the age of these deposits as the sea gradually transgressed: thus younger deposits occur on the rigid core of the continent (Deseado "Massif"l. Riccardi ( 19701 has pointed out that Favrella, one of the most controversia! fossils, is also present in extraPatagonian areas abd is not endemic as claimed by other authors (cf. Hallam, l%71.
The Las Curtiembres formation overlies concordandy the foregoing la Yesera Formation. It is also continental. The radiometric dating of basalts in the upper third of the for· mation indicates a Middle Campanian age (78, 77 m.y. +· 5m.y.l (Valencio et aL, 19751. Anurans have been collected from these beds: Saltenia ibanezi (Reig, 1959; Parodi Bustos et aL, 1960; Báez, 19751. These fossils have Gondwa· nan affinities indicating faunistic relationships with Africa. In addition, plants and fish remains have been recorded, but these are too poorly preserved to permit identification.
Leanza and Leanza 09731 erected a new genus: Pseudofavrella to include the extramagellanian species, accepting Brüggen's idea (19501 ofthe existence of "Juan Fernandez Land" in Mid Cretaceous times ·in order to ex· plain the faunistic differences between the Austral and Neuquén Basins. Maccoyella bonarelli (Leanzal, of probable Aptian age, is similar to M. incuroata (Etheridgel of Australia,This genus has palaeogeographical significance as it appears to be restricted to a narrow strip between palaeolatitudes of 50° and 60° (Waterhause and Riccardi, 197 Ol In the Patagonian Andes, the following ammonites zones (Leanza, 19701 havebeenrecognized: (Lower Cenomanianl Mantelliceras yrigoyeni (Upper Alhianl Puzosia vegaen.~is (Lower Alhianl Hatchericeras patagonense
Sanmartinoceras patagonicum
(Upper Aptianl
Tropaeum deeckei
(Lower Aptianl
Leanza ( l969b l described the ammonite Peroniceras santacrucense, related to P. buergli Leanza from Colombia, from the Mata Amarilla Formation, thus proving the Coniacian age of the formation. The Upper Cretaceous deposits contains the well known Lahillia Iuisa Wilckens fauna, whose Austral affinities have been widely accepted. NORTHWESTERN BASIN This basin forms part of a unit which extends up to Bolivia, northern Chile, Paraguay and Peru in which Cretaceous deposition took place. In Argentina, these sediments constitute part of the Salta Group, consisting of a thick sequence of continental sediments (with, a marine ingression from the Pacific of short durationl which lie with an angular disconformity on rocks of Precambrian and , or, Palaeozoic age. The three basal formations are grouped into the Pirgua Subgroup; these formations cannot be recognized in all parts of the basin, The La Yesera Formation is continental, interpreted by Reyes and SaHity 097 31 as being a piedmont deposit. F ossils have not been found in this formation ; it is provisionally referred to the Cenomanian on the grounds of stratigraphical position and correlations of the overlying beds with similar sequences in BoliviaandPeru (ReyesandSalfity.Op. cit.). Recendy, basaltic beds in the lower part of the formation have been
The overlying formation, Los Blanquitos, is also terrestrial and may have a basal unconformity (Reyes and Salfity, 19731. The upper part of the formation has yielded bones of sauropod dinozsaurs, titanosaurians, assigned with reservation to the genus Antarctosaurus (Bonaparte and Bossi, 19671. It is possible that these deposits could be equivalent in part to the Neuquén Group (see the Neuquén basinl. With a regional unconformity between the preceding for· mations are overlain by the Balhuena·subgroup. The basin was invaded by the Pacific Ocean,, although the evidence available suggests that the depth of the transgression was not great. There is also a possibility that there were periods of regression. In the southem part of the sedimentational realm, there is a marked terrestrial in~ fluence and there are levels with plants, altemating with levels containing gastropods, so-called "melanids" (Danieli and Porto, 1968 ; Lencinas and SaHity, 19751, remains of dinosaurs, camosaurian teeth and crocodilian remains (Bonaparte and Bossi, 19671. A level representing a marginal marine environment has yielded ganopristinid Pucapristis branisi, Schaeffer, 1963, in Benedetto and Sanchez, 1972, and the clupeid Gasteroclupea branisai Signeux (Leanza, 19691. These species have been observed in the El Molino Formation of Bolivia which is correlated to the Argentinian Yacoraite F ormation, at least in part (Russo and Rodrigo, 1965; Leanza, 1969; Reyes and Salfity, 19731. Likewise, teeth of the picnodontid Coelodus ton-
1Northwestern l Cretaceous Basin : fonnations and lithology Oolitic and dolomitic limestones. Yellowish and greenish clay. Calcareous sandstones with intercalated black shales.
Yacoraite Fm.
Yellowish or whitish medium or coarse sandstones, somewhat calcareous.
LechoFm.
Conglomeratic layers (Q = pink granite and gneiss l Whitish-pink, medium to coarse sandstones with conglomerates of Q and granite
Los Blanquitos Fm.
Basaltic flows, dykes and sills. Reddish brown mudstones, claystones and shales with Las Curtiembres Fm. layers of fine conglomerates. The pelitic content with intercalated sandstones increases upwards Reddish-brown medium to conglomeratic sandstones. Polymictic conglomerates with clasts of phyllite, quarzite.
La Yesera Fm.
Table3 XXVII. 4
coensis Benedetto and Sánchez (1972) have been found in mainly bone-beari~~ beds in grey to black shales which also contain other fish,~ . as well as crocodilian vertabrae. Beds similar to "bone beds" in which several kinds of vertebrates occur have also been recorded from the El Molino (Schaef· fer, 1963 ; Branisa et al., 1964). The entire Yacoraite Formation contains beds of stromatolithic limestone, just as is the El Molino Formation. The mi· cropaleontological analysis has shown the presence of charophytes correlatable with an association recorded from the Vilquechico Formation of Pero (Porochara gildemeisteri Koch and Blissenbach and Porochara ovalis (Fritzsche) (Grambast, 1967). According to this evidence, at least those levels of the Yacoraite Fm., with P. gildemeisteri and Amphyochara sp. could be of U pper Cretaceous age, possibly Campanian-Maastrichtian. N evertheless the Late Cretaceous age of the whole unit should be verified by the systematic analysis of the charophytes present in its upper portion (Mussachio, 1972). Recently, Méndez and Viviers (197 3) reported the sparse oc· currence of ostracods and benthic foraminifers in out· crop and subsurface samples. Among their provisional determinations we quote the following : Discorbis aff. cretacea Franke, "Valvulineria infrequens Morrow", "V. allomorphinoides (Reuss) ", "V. marianosi Trujillo", ··'Lingulogavelinella frankei (Bykova) ", "Orostella turonica Butt" and "Bilingulogavelinella sp. ". According to Méndez and Viviers ( op. cit.), the association displays affinities with associations from the Upper Cretaceous (Senonian). It should, however, be noted that the above association contains lingulogavelinellids typical of the transicional Austral and Boreal biogeoprovinces which cannot be younger than turonian (Scheibnerová, 1972). This family is well represented in the Austral basin in the Nueva Argentina and Arroyo Alfa Formations (ranging from Aptian ? to Early Cenomanian), without having been found in the sediments referred to the Turonian. This poses an intriguing problem as the Yacoraite Formation is dated as Late Campanian to Maastrichtian in age, even if decisive data are not yet available.
The lithological characteristics of the formations in the Northwestern Basin are given in Table 3.
NEUQUÉN BASIN
A marine cycle of sedimentation was initiated in the Kimmeridgian with an incursion from the Pacific in connexion with which the formations comprising the Mendoza Group were deposited : Va ca Muerta, Quintuco, Mulichinco and Agrio. The Vaca Muerta Formation, of Early Tithonian age, contains abundant pelecypods, ammonoids and fish (the latter have yet to be studied). Recently, remains of ichthyosaurs have been collected and metrior!Jynchid crocodiles (Gasparini, pers. comm.). The complex Vaca Muerta For· mation and Quintuco Formation has yielded ? Purranisaurus potens Rusconi, a representative of this family, according to the results of Gasparini (1973). Mem· bers of that group also occur in beds assigned to the Callovian in Chile (Chong Diaz and Gasparini, 1975). Apart from this record, the group is known to range in Europe from Upper Jurassic to Lower Cretaceous. The presence of trocholinas in the Upper Tithonian of the Neuquén Basin suggests temperate waters (Malumián and Masiuk, 1973). The sediments were deposited in a liitoral environment in the south and in an infraneritic environment to the north. The Quintuco Formation contains abundant bivalves, in· cluding trigonids as well as ammonites which indicate a Tithonian to Middle Valanginian age. The environment of deposition appears to have been the same as
XXVII . 5
that of the foregoing formation. The increase in the arena· ceous content in its upper part points to a regressive tendency which became accentuated during the deposition of the Mulichinco Formation. This latter formation includes deltaic deposits and litoral sediments in its southem ex· tensions and epi-neritic deposits in its northern parts. There are ammonites, pelecypods and turritellids as well as tree trunks and the remains of poorly preserved vertebrates. The formation has been dated as Valanginian to Early Hauterivian. The Agrio Formation (Hauterivian to Early Barremian) has yielded corals, ammonites, pelecypods, gastropods and echinoderms. The teeth of picnodontiform fish have been found. The similarity between the trigonids from the Andean and Magallanes Geosynclines led Fuenzalida ( 1964) to conclude that the faunas were in contact in Tithonian· Late Valanginian times. Uhlig (1911 ) noted the affinities between the fossils of the Mulichinco and Agrio Formations and those of the Uiten· hage F ormation in South Africa. Hallam ( 1967) pointed out the similarity between the trigonids of South Africa and the Neuquén Basin. Reyment (1972) suggested the existence of a marine faunal connexion between the two regions in the Valanginian on the grounds of the close affinities in the molluscan associations of the Mulichinco and Agrio Formations and the Uitenhage Formation of Late Valanginian age. A regional uplift alter the deposition of the Agrio Formation caused the withdrawal of the sea, followed by the deposition of Huitrin Formation, with abundant lacustrine limestones and evaporites. The invertebrates found in this formation are of little biostratigraphical use, although of environmentalsignifican· ce. Melania macrochüenoides Doello Jurado1 Corbicula sp. and other pelecypods indicate freshwater or brackish conditions. The palynological analysis has shown the presence of angiosperm polleo in the upper part of this unit. On regional grounds, these levels have been referred to Middle Albian (Volkheimer and Salas, 1975). Cytheracean and darwinulidan ostracods of Barremian age have been described from the La Amarga Formation ( = Huitrín Formation) ; the association has a local aspect (Musacchio, 1970a). New species of Cypridea have also been recorded (Musacchio, 1972). The age determination a~ees with that yielded by the charotypes, of which we cite Atopochara trivolvis aff. triquetra and Triclypella aff. calcitrapa (Musacchio, 1971 ). In deposits corresponding to the La Amarga Formation, and which represent a flood plain, remains of dinosaurs have been reported (Parker, 1965 fide Digregorio, 1972). The transgressive cycle of sedimentation which continued up to the deposition of part of the Huitrin Formation ter· minated with a change in environment as evidenced by the appearance of red·beds, following OD this sequence. This is coincident with a change in the regional dip to the east. It should be noted that there are several opinions about the lithostratigraphy of the beds overlying the Huitrín Formation. In this paper, we follow the sub· division put forward by Cazau and Uliana (1973). The Rayoso and Bajada Colorada Formations were deposited in a fluviatile and lacustrine environment, including pseudodeltaic and flood plain phases. The known fossil content is inadequate to permit dating and only bone fragments and carboñaceous plant material with occasional freshwater pelecypods have been recorded. Recently, well preserved remains of dinosaurs have been found in Bajada Colorada (Ramos, per. comm.). The ostracods from the Rayoso Formation described by Musacchio in Musacchioand Chebli (1975) belongto a new genus and species : Rayosoana quilimalensis and its family attribution is still uncertain, therefore they have little chronological significance. According to their stratigraphical position, these units
Neuquén Basin : fonnations and lithology Yellowish claystones
JagüelFm.
Grey-yellowish-green claystones and mudstones. Conglomeratic sandstones.
AllenFm.
Red mudstones, with levels of calcareous concretions and geodes of calcite. "Ondulites ". Cross-bedding. Variegated sandstones. Polymitic conglomerates.
Rio Colorado Fm.
Red mudstones with altemating light sandstones, light sandstones. Polymitic conglomerates.
Rio Neuquén Fm.
Quartzoze medium coarse yellow sandstones. Conglomeratic sandstones. Mn concretions. Red sandstones. Acid to mesosilicic vulcanites. Polymitic conglomerates.
Rio Limay Fm. NORTH Red claystones Fine to medium reddish sandstones Variegated claystones with layers of gypsum
Red claystones with suhordinate conglomeratic layers Sandstones. Green marls with calcareous concretions and limestones. Sandstones with conglomeratic lenses. Cross-bedding Argillaceous sandstones, green limestones and sandy marls. Red sandstones and conglomerates. Torrential and cross-bedding.
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Dolomitic limestone with layers of gypsum. Gypsüerous sandstones with layers of gypsum. Argillaceous sandstones with layers of salt.
Agrio Fm.
Gypsum. Dolomites. Dark grey claystones, shales and marls. Suhordinate limestone.
Mulichinco Fm.
Limestones and coquina light sandstones with fine to medium conglomerates.
------~------------------------------~----------------------
Limestones and oolitic limestones. Calcareous and marly sandstones. Cross-bedding
Greenish shales and claystones with intercalated sandstones and argillaceous tuffs. Fine to medium yellowish brown siliceous sandstones.
Quintuco Fm.
Sandy levels increasing upwards.
Vaca Muerta Fm.
Bituminous marls and shales.
From : Marchese, 1970 : Digregorio, 1972 ; Cazau and Uliana; 1973.
Tahle4
Huene, Argyosaurus superbus Lydekker. These species carne from the Neuquén Basin, as well as notosuchid Notosuchus terrestris Smith Woodward crocodiles (Gasparini, (19711, cynodontosuchid crocodiles : Cynodontosuchus rothi Smith Woodward (Gasparini, 19721 and the booid snake Dinylisia patagonica Smith Woodward (Estes etal., 19701.
have been considered of Cenomanian-Coniacian age ; however the lower boundary could be extended back to Albian in the light of the above evidence. The N euquen Group, a thick continental sequen ce, lies unconformably above the Rayoso Formation. In every formation of this group, dinosaur remains and also, frequently, large pieces of opalized wood have been found. Generally, these remains show evidence of transport. In the uppermost levels of Río Limay Formation, turtles, crocodiles and freshwater pelecypods have been recorded (Cazau and Uliana, 19731. Although the presence of large sauropods in these deposits is known since the last century, being the characteristic feature of this sequence ("Dinosaur-beds" 1, the knowledge of their faunas is based largely on the studies of Lydekker (18931 and von Huene (19291. Unfortunately, no revisions of that material ha ve been made nor new collections studied in order to correlate the different taxa with the present stratigraphical scheme. Besides, the taxonomic criteria used are questionable, making the palaeobiogeographical considerations based on them weak.
The ecological conditions which permitted the existence of those forms in the Neuquén Basin should have been quite general, not only in the present Argentina but also in other areas of South America. Titanosaurid remains have been recorded in the Viftita Formation, Province of Coquimbo, Chile. They were referred to Antarctosaurus cf. wichmannianus von Huene (Casamiquela et al., , 19691. According to its faunal content and stratigraphical position, that unit was considered at least partially equivalent to the Neuquén Group (Casamiquela et al., op. cit. l. Sauropod remains assigned with sorne doubt to Antarctosaurus were also cited in the Northwestern Basin (Bonaparte and Bossi, 19671. Laplatasaurus araukanites, Antarctosaurus wichmannianus and Argyrosaurus superbus were recorded in Uruguay, in sandstones which unconformably overlie the Serra Geral Basalts (fide Padula, 19721. The genus Antarctosaurus (A. brasiliensis Arid and Vizotto 1 is a)so present in U pper Cretaceous deposits of Southern Brazil (Arid and Vizotto, 19711.
Von Huene, in bis study and revision of the Cretaceous saurischian and ornitischian dinosaurs of Argentina, considered as "Dinosaur beds" the continental strata overlying the "Transitional Gypsum" or Huitrín Formation (op. cit.., table : 111, although he stated that most of the material carne from the upper levels of the continental series which overlie the unconformity (op. cit. : 81. He mentioned the presence of titanosaurid sauropods : Titanosaurus australis Lydekker, Antarctosaurus wichmannianus von Huene, A.giganteus von Huene, Laplatasaurus araukanites von NOIHHW, rlffN CfffT ACIOIII UIIN PALIOCINI
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