The composition of Argentinian Jurassic marine ostracod and foraminiferal faunas: Environment and zoogeography

THE C O M P O S I T I O N OF A R G E N T I N I A N J U R A S S I C MARINE OSTRACOD A N D FORAMINIFERAI, FAUNAS: ENVIRONMENT AND ZOOGEOGRAPHY SARA C. BALLENT & ROBIN WHATLEY BALLENT S.C. & WHATLEY R. 2000. The composition of Argentinian Jurassic marine ostracod and foraminiferal faunas: environment and zoogeography. [La composition des faunes d'ostracodes marins et de foraminiferes du Jurassique d'Argentine: environnement et zoog6ographie]. GEOBIOS, 33, 3: 365-376. Villeurbanne, le 30.06.2000. Manuscrit d6pos6 le 31.03.1999; accept6 d6finitivement le 16.07.1999. ABSTRACT - The composition of Jurassic marine ostracod and foralniniferal assemblages from the Neuqu6n Basin is analysed. The absence of these microfossils from certain levels is attributed to a number of causes, such as inimical facies for their existence or for their preservation. Evidence is produced demonstrating that the absence of ostracods and the virtual absence of Foraminifera from such important Middle Jurassic sections as that at Chacay Melehue is due to their lower bathyal or abyssal palaeodepth. The relative success of filter and deposit feeders is shown to be probably related to palaeoxygen levels, with filter feeders being able to tolerate lower levels of oxygen concentration than their competitors. The palaeoecology of the various ostracod assemblages is compared and contrasted with that of their contemporary Foraminifera. While in the Liassic and the early Middle Jurassic there is a considerable general similarity between ostracod assemblages wordwide, throughout the remainder of the Jurassic there is evidence of the progressive isolation of southern South America, with consequent generic impoverishment and the absence or extreme rarity of many of the major families and genera of NW Europe. Conversely, there are no genera or supra-generic taxa endemic to Argentina. KEYWORDS: OSTRACODA, FORAMINIFERA, JURASSIC, ARGENTINA, ENVIRONMENT, ZOOGEOGRAPHY. RI~SUMt~ - La composition des associations d'ostracodes et des foraminif'eres matins du Jurassique du Bassin de Neuqu6n est analys6e. Certains niveaux sont d6pourvus d'ostracodes (et souvent aussi de foraminif'eres). On peut y voir plusieurs raisons, comme un faci6s hostile h la vie des organismes, ou h leur conservation. Dans le cas de coupes importantes du Jurassique moyen, comme celle de Chacay Melehue, cette absence est due h la bathym6trie: domaine bathyal inf6rieur ou abyssal. Le 'succ6s' relatif des formes filtrantes est probablement dfi au taux d'oxyg6ne dissous: les formes filtrantes en particulier sont capables de vivre ~ des concentrations d'oxyg6ne plus faibles que les autres. La pal6o6cologie des diff6rentes associations d'ostracodes est similaire ~ l'6chelle globale; plus tard, il y a 6vidence d'une isolation de plus en plus forte de la pattie m6ridionale de l'Am6rique du Sud. L'6ventail des genres s'appauvrit; de nombreux genres - et m4me familles - communs en Europe du NW sont dor6navant absents ou deviennent extr~mement rares. Inversement, on n'observe pas de taxons limit6s ~ l' Argentine. MOTS-CLI~S: OSTRACODES, FORAMINIFI~RES, JURASSIQUE, ARGENTINE, ENVIRONNEMENT,ZOOGI~OGRAPHIE.

INTRODUCTION The Neuqu6n Basin, in central-western Argentina, has provided most of the Jurassic ostracod and foraminiferal assemblages known at present in this country. The microfaunas are associated with wellknown ammonite zones and have been described and figured in several papers (Ballent 1985 'unpublished', 1986, 1987, 1991, 1992; Musacchio 1979). The aim of this contribution is to present an analysis, based on the study of several hundred samples mainly from outcrops in the Neuqu6n Basin, of the structure of early Mesozoic marine ostracod and foraminiferal assemblages. The study is based on the percentage of individuals of all the groups of Foraminifera and the following major groups of Ostracoda: Metacopina, Cladocopina, Platycopina and Podocopina; the latter being subdivided into the th r ee m a r i n e superfamilies: Cytheracea, Cypridacea and Bairdiacea. The Cytheracea, by far the most important post-Palaeozoic ostracods, are divided into their various families and each of these

major groups is analysed at the generic level in respect of their change through time.

LOCATION AND GEOLOGICAL FRAMEWORK OF THE NEUQUI~N BASIN The Neuqu6n Basin is located in central-western Argentina and eastern Chile, between latitudes 34°S and 41°S. It came into being during late Triassic-Jurassic times, when the sea invaded the central-western region of Argentina from the west and northwest and formed an em baym ent with a large eastward extension (Fig. 1). The succession exceeds 5000 m of marine and continental sedimentary rocks. It includes all the Jurassic stages, and is one of the best known Jurassic areas in South America. The sedimentary record has been the subject of several recent syntheses (Riccardi 1983; L egarret a & Gulisano 1989; Riccardi & Gulisano 1990), most of them being concerned with sequence analysis and palaeogeographical evolution (Legarreta & Uliana 1996).

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Lithostratigraphically, the units which correspond to the Hettangian to Callovian interval are all referred to the Cuyo Group, the Middle Callovian to Oxfordian interval is known as the Lotena Group, while the Kimmeridgian continental rocks and the marine and continental Tithonian deposits belong to the lower part of the Mendoza Group•

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Figure 2 shows the simplified stratigraphical column of the Jurassic of central-western Argentina and the relevant ammonoid zones from the same

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tral basin, evaporites were deposited. The Upper Oxfordian is characterized by the development of a thick and extensive evaporitic sequence, corresponding to a shallow hypersaline environment of marine origin• During the Kimmeridgian, complete desiccation of the basin occurred, with the deposition of continental clastic sediments. This episode lasted until the early Tithonian when a transgressive event brought marine conditions back to parts of the basin• Tithonian sediments are either clastic, carbonate marine, or continental in origin.

area. Ma Rosa Curic5

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FIGURE 1 - Base map showing Argentinian part of the Neuqu~n Basin (after Legarreta & Uliana 1996) and position of fossiliferous localities in which this paper is based• Carte schdma-

tique du Bassin de Neuqudn (d'apr~s Legarreta & Uliana 1996% avec emplacement des localitds fossili[~res.

During the late Triassic ? to earliest Jurassic, sedimentation was confined to isolated depressions which were filled with rocks of continental facies, much of which was pyroclastic and volcanic• These deposits are grouped under the name Precuyano or Precuyo, which may be coeval, although without physical continuity, with marine sediments of Hettangian to Sinemurian age (Legarreta et al• 1993)• Over most of the basin, marine deposition began in the Pliensbachian; however, in the Rio Atuel region, in southwestern Mendoza Province, the Hettangian and Sinemurian stages are both represented by marine strata (Riccardi et al. 1988)• Recently, the existence of marine Upper Triassic strata in the same area has been demonstrated by Riccardi et al. 1997. Marine conditions prevailed until the late Callovian over the greater part of the basin• However, the area of sedimentation became gradually reduced until, during the mid Callovian, the basin became isolated, resulting in the deposition of evaporites until its complete desiccation, with consequent continental deposits in the central part of the basin• Subsequently, there was an expansion of the depositional area brought about by a relative sea level rise and the uppermost Callovian, and much of the Oxfordian, are represented in the inner basin by deposits laid down in deep water to shelf environments while, contemporaneously in the cen-

One problem which we have encountered in our study of the Neuqudn Basin has been the absence of ostracods from a number of Jurassic stages. The Sinemurian has not yielded any ostracods, probably due to the extreme hardness of much of its strata• Along the upper Rio Atuel in southwestern Mendoza Province, marine Sinemurian deposits with common macro-invertebrate fossils comprise a relatively monotonous sequence of fine to very fine grained yellowish grey, quartz lithic and somewhat tuffaceous, sandstones and claystones, which are an unfavourable sediment type for the extraction of microfossils. Similarly, Ostracoda are unknown from the Toarcian and the Lower Aalenian. In both these cases, the strata comprise mainly dark grey, black and dark greyish brown claystones intercalated with tabular beds of fine-grained sandstones, which have yielded only a few lenticulinid foraminifers• However, notwithstanding the unfavourable type of sediments, the absence of ostracods may also be due to an insufficient density of sampling. The absence of ostracods from Upper Bajocian and Bathonian strata seems, however, to be due to different reasons. In 1970, one of us (R.W.) made an extensive collection of the Chacay Melehue section (see Fig. 1), amounting to some 150 samples• In the field and in hand specimen they seemed to be very promising• In the Upper Bajocian, the lithology is of black calcareous shales with irregular lamination and with interbedded tabular and irregular beds of greenish grey, medium to fine-grained sandstones (wackes) while the Bathonian is characterized by a monotonous succession of black shales, with calcareous concretions and tabular tuff and tuffaceous sand beds containing very abundant ammonites• None of these samples, however, despite their favourable response to standard micropalaeontological preparatory techniques, yielded a single ostracod; the only microfossils being a few (3 or 4) poorly preserved lenticulinid foraminifers• Subsequently (1980, 1986),

367 FIOURE 2 - Simplified stratigraphiSTAGE

cal column of the Jurassic of central-western Argentina (after Gulisano & Guti6rrez Pleimling 1994) and ammonoid zones (from Riccardi 1992). Coupe stratigra-

phique simplifide du Jurassique de l'Argentine du centre-ouest (d'apr~s Gulisano & Gutidrrez Pleimling 1994) et zones d'ammonites (Riccardi 1992).

BIOSTRATIGRAPHICAL UNITS

LITHOLOGY FORMATIONSGROUP I

Substeueroceras koenenl Z o n e Corongoceras alternans Zone Wladhausericeras iaternispiaostun Zone Aulaccsphinctes proxinms Zone Pseudolissocera$ zitteli gone ]

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one of us (S.B.) repeated the sampling and also failed to encounter ostracods in the Bathonian of the same section, but did encounter a small foraminiferal fauna in the Lower Callovian represented by pyritized and ill-preserved nodosarfids and polymorphinids. Whatley & Ballent (1994, p. 963) concluded that the absence of ostracods from this section was 'mainly because the section was at a palaeo-depth then inimical to colonisation by ostracods but not, given the excellent preservation of the ammonites, below the CCD'. Late Palaeozoic ostracods of the Thuringian Associations of Becker & Bless 1990 clearly lived in deep, cold water and inhabited the palaeopsychrosphere (Kozur 1972) probably into the early Triassic (see references to psychrospheric ostracods from Hungary in Kozur 1971, 1972 and more recently Monostori 1995). Becker's Thuringian Assemblage became extinct with the obliteration of the palaeopsychrosphere in the uppermost Palaeozoic/earliest Triassic and no truly deep, cold water fauna was able to evolve until the late Palaeocene, when the presence of polar ice brought to an end the thermospheric Mesozoic Ocean and made the reconstruction of the present day psychrosphere possible. During the Mesozoic there were no truly deep, cold water ostracod faunas as such, and even those described by such authors as Donze 1976 from the

Milt¢cerasZone Epophioceras Faunule Vermi . . . . . Zone Badouria canadensis Zone/

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Lower Cretaceous of the Vocontian Trough (Fosse Vocontienne), southeastern France, in spite of the deep water nature of parts of the sequence, are good examples of Mesozoic thermospheric ostracods. In the Neuqu4n Basin, the Upper Oxfordian and Kimmeridgian are represented mainly by continental sediments. The former ocurrs principally as evaporites with thick white gypsum deposits capping many sections. The Kimmeridgian is represented by fluvial and alluvial conglomerates and sandstones in the south and southwest and by lacustrine and playa lake deposits in the central area. Marine Tithonian strata are mainly represented by basinal and outer shelf shales, claystones, marls, micritic limestones and occasional sandstones which, although they yield very abundant epistominid foraminifers, contain an extremely poor ostracod fauna. Given these circumstances, the data on which the present study is based are clearly limited, being subject as they are to the apparent restriction of ostracods due possibly to inimical facies and/or inadequate sampling. Furthermore, none of the data sets take into account sample size, and therefore, only generalized conclusions are presented. These are summarized in figure 3, which shows the changing faunal composition of the Ostracoda at subordinal/superfamilial level and the fluctuating

368 0%

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CLADOCOPINA 100 0% 50 Abundant eplstomlnids

Abundant nodosariids. Agglutmatlng forms ~onfinant at certain levels

Ill preserved nodosarilds and polymorphinids

Scarce lsnticalinids Abundant nodosarlids. Subordinate polymopkinids, spiriliinids and involutinids. Scarce agglutiaating

Abundant nodcsariids Subordinate spirillinids and polymorphlnids

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FIGURE3 Changingostracodalcompositionat suborder/superfamilylevelin the Jurassic ofcentral-westernArgentina.Rdpartition -

et dvolution des sous-ordres ou super-families d'Ostracodes durant le Jurassique du centre-ouest de l'Argentine.

Stages

N u m b e r of species Cypridacea

Bairdiacea

Tithonian Mid-Late Callovian

0 2

1 0

E a r l y Callovian E a r l y Bajocian Aalenian-Bajocian boundary Late Pliensbachian

0 0 1

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C:(cheracea 6 13 (5 Bythocytheridae 4 Cytheruridae) 2 1 19 (13 Cytheruridae) 7 (3 Bythocytheridae 4 Cytheruridae)

FIGURE4 Diversity of Podocopina through the stages of late Early Jurassic and Late Jurassic of central-western Argentina. Diversitd des Podocopina du Lias supdrieur au Malta -

dans le centre-ouest de l'Argentine.

relative abundance (number of specimens) of the various taxomonic groups within the Hettangian to Tithonian interval. Figure 4 demonstrates the diversity of podocopinid families at the various ostracodiferous levels in the basin over the same interval. Figures 5 and 6 illustrate some selected ostracod species referred to in the text.

THE OSTRACOD FAUNAS

Riccardi et al. 1997, p. 233) in sediments dated on macropalaeontological evidence as late Triassic (Norian-Rhaetian). These ostracods are as yet undescribed. They were, however, first mentioned by Ballent (1994, p. 55) as being from the Triassic/Jurassic boundary, prior to the availibility of later macrofossil evidence. The ostracods comprise the metacopid O g m o c o n c h e l l a , probably represented by a single species and occurring as the overwhelming dominant taxon. The remainder of the ostracod fauna is very poorly preserved and seems to be of bythocytherids such as M o n o c e r a t i n a . Small, poorly preserved, infilled and often broken foraminifers are also present and include coiled H a p l o p h r a g r n o i d e s - l i k e agglutinated tests and a few nodosariids among the calcareous forms. JURASSIC

Hettangian As demonstrated by Ballent 1992, this fauna is monogeneric, comprising at least three different species of O g m o c o n c h e l l a , with O. e l l i p s o i d e a (JONES) being the most abundant. These ostracods have been found in levels within the W a e h n e r o ceras-Schlotheimia and B a d o u x i a c a n a d e n s i s zones of the Upper Hettangian (see Figs 2, 3).

TRIASSIC

Pliensbachian

Triassic marine ostracods were unknown from Argentina until a unique mention by Ballent (in

This presents a mixed fauna of metacopids, platycopids, marine cyprids, bairdiids and cytherids. The

369

FIOURE 5 1. Ogmoconchella ellipsoidea (JONES),MLP-Mi 714, Arroyo Malo, late Hettangian, carapace, right lateral view 2. Cytherella concentrica FIELD,MLP-Mi 1069, Sierra Pintada, late Pliensbachian, carapace, right lateral view. 3. Cytherella praetoarcensis BOOMER, MLP-Mi 1070, Sierra Pintada, late Pliensbachian, carapace, left lateral view. 4. Cytherelloidea circumscripta (BLAKE),MLP-Mi 555, Sierra Pintada, late Pliensbachian, carapace, right lateral view. 5. Cardobairdia posteroprolata AINSWORTH,MLP-Mi 718, Picfin Leuffi, late Pliensbachian, carapace, right lateral view. 6. Isobythocypris cf. elongata (TATE & BLAb), MLP-Mi 559, Picfin Leuff~, late Pliensbachian, carapace, right lateral view. 7. Paracypris redcarensis (BLAKE),MLP-Mi 561, Estancia Santa Isabel, late Pliensbachian, carapace, right lateral view. 8. Liasina lanceolata (APosTOLESCU),MLP-Mi 1071, Sierra Pintada, late Pliensbachian, carapace, right lateral view. 9. Monoceratina sp. B, MLP-Mi 573, Trapial Mahuida, late Pliensbachian, carapace, right lateral view. 10. Procytherura celtica AINSWORTH,MLP-Mi 673, Picfin Leuffi, late Aalenian-early Bajocian, carapace, left lateral view. 11. Procytherura euglyphea AINSWO~TH, MLP-Mi 670, Picfin Leuf~, late Aalenian-early Bajocian, carapace, left lateral view. 12. Procytherura bispinata BALLENT,MLP-Mi 678/2, Picfm Leuffi, late Aalenian-early Bajocian, carapace, right lateral view. 13. Eucytherura argentina BALL~NT,MLP-Mi 654, Picfin Leuffi, late Aalenian-early Bajocian, carapace, left lateral view. 14. Eucytherura transversiplicata (BATE& COLEMAN),MLP-Mi 656, Picfin Leuffi, late Aalenian-early Bajocian, right valve, external view. 15. Eucytherura pichia (BALLENT),MLP-Mi 645/2, Picfm Leuffi, late Aalenianearly Bajocian, right valve, external view. Repository: MLP-Mi= Museo de Ciencias Naturales de La Plata-Micropaleontologia. Scale bar=100 #m. 1. Vue lat~rale droite. 2. Vue latgrale droite. 3. Vue latgrale gauche. 4. Vue latgrale droite. 5. Vue lat~rale droite. 6. Vue latgrale droite. 7. Vue latgrale droite. 8. Vue latgraIe droite. 9. Vue latgrale droite. 10. Vue latgrale gauche. 11. Vue latgrale gauche. 12. Vue lat~rale droite. 13. Vue lat~rale gauche. 14. Valve droite, vue externe. 15. Valve droite, vue externe. -

370 basal beds are barren but platycopids (Cytherella), cyprids (Liasina, Paracypris) and bairdiids (Cardobairdia) soon appear in some number (Lan6s, pers. com. 1996). Notable by their absence, however, are the metacopids and cytherids, while the Cypridacea are the dominant group with 53 % of the total number of specimens. This fauna was found in the late early Pliensbachian Dubariceras Zone (see Figs 2, 3). It is succeded by that of the late Pliensbachian Fanninoceras Zone (Figs 2, 3) where the fauna of the preceeding zone, at the generic level, remains the same but is augmented by the metacopids (Ogmoconcha and Ogmoconchella) and the cytherids (Monoceratina, Eucytherura, 'Procytherura'), the platycopids (Cytherelloidea) and the bairdiids

('Bairdia'and Isobythocypris).

Late Aalenian-early Bajocian This fauna, which occurs around the boundary between the two stages (Puchenquia malarguensis Zone), is strongly dominated by the Cytheracea with the Platycopina (Cytherelloidea), Cypridacea (Paracypris) and Bairdiacea (Bairdiacypris and Bythocypris) comprising together only 4.5 % of the total number of individuals. The Cytheracea, however, comprise twelve genera and nineteen species and, with 95.5 % of the fauna are clearly the most dominant group of any interval in the Argentinian Jurassic (Fig. 4). The most important genera are Para-

doxorhyncha, Eucytherura, Procytherura, Hemiparacytheridea and Gramannicythere and four inde-

terminate taxa, ostracods A, B, C and D (see Ballent 1991) whose affinities have been discussed by Boomer & Ballent 1996.

Early Bajocian The ostracod fauna of the Emileia giebeli Zone is impoverished in both abundance and specific diversity. It comprises only the platycopids Cytherella and Cytherelloidea and a species of the cytherid Ektyphocythere. The platycopids make up 23.5 % and the cytherids 76.5 % of the fauna, which is indicative of warm water shelf conditions.

Early Callovian After a considerable gap (late Bajocian, Bathonian, early Callovian) in which ostracods are unknown in the Neuqu6n Basin, the fauna of the Bodenbenderi and Proximun Standard Zones remains sparse in both species and abundance. The Platycopina and the Cytheracea are the only groups to occur here, the former represented by a single species of Cytherelloidea, which makes up 63.6 % of the fauna. The Cytheracea are represented by only two species in low numbers (Ektyphocythere australis BALLENT and ?Procytherura sp.).

Mid-Late Callovian The Rehmannia patagoniensis Horizon is typified by more abundant ostracods and by the presence, for the first time in the Argentinian Mesozoic, of the Myodocopida in the form of a single specimen of the cladocopid genus Polycope (Musacchio 1979). The Cypridacea also reappear, for the fist time since the late Aalenian, again in the form of two species of Paracypris. These constitute only 7.1% of the fauna, the same as the Platycopina, represented by species

of Cytherella and Cytherelloidea. The dominant Cytheracea (84.3 %) are represented by the genera

Monoceratina, Eucytherura, Procytherura, Ektyphocythere and 'Progonocythere'. All thirteen cytheracean species are shelf dwellers. Around the level of the Callovian-Oxfordian boundary, the genus Sondagella has been recovered; this is a typical Upper Jurassic-Lower Cretaceous taxon restricted to southern Gondwanaland. Its record in the Middle Jurassic of the Neuqu6n Basin seems to be the oldest for the genus.

Tithonian The only Tithonian ostracods known by the authors are from the subsurface of the eastern part of the Neuqu6n Basin. They are not abundant and are represented by cytheraceans including an as yet undescribed species of a genus similar to Polydentina and platycopids with Cytherella sp. From the same deposits, Simeoni (in Mancefiido 1993, p. 62) mentioned cytheraceans (neither described nor illustrated) of the genera Monoceratina, Paracytheridea, Parariscus and Sondagella and the bairdiacean 'Bythocypris'. OSTRACODAL P A L A E O E C O L O G Y In the late Hettangian, the total number of specimens belong to the genus Ogmoconchella (see Fig. 3). Ogmoconchella is a member of the extinct Metacopina suborder, which, by virtue of the similarity of their morphology to the extant Platycopina, are also considered to have been filter-feeders and, due to their alimentary strategy, would have possessed the ability to suvive in times of reduced oxygen by virtue of passing a greater volume of water across the respiratory surface (Boomer & Whatley 1993; Lethiers & Whatley 1994, 1995; Whatley 1991, 1995; Whatley et al. 1994). Boomer & Whatley (1993) and Whatley et al. (1994), studying the Liassic metacopids of the Mochras section in North Wales and of outcrops in NE Spain respectively, noted that the metacopids seemed to have a mutually exclusive relationship with the Platycopina. It was also evident that, as with platycopids, when metacopids were present in large number, other ostracods of different feeding strategies were rare or absent (see comparative diagram showing different feeding strategies of extant Ostracoda in Whatley 1995, Fig. 1). Boomer & Whatley (1993, p. 375) and Whatley et al. (1994, p. 740) concluded that the mutual exclusivity of the two groups was due to their preference for different water depths and suggested that the metacopids preferred shallower water than the platycopids. Whatley (1995) suggested that this exclusive relationship based on different water depths preferences obtained until the final global extinction of the Metacopina, which took place at different times in different places between the late Pliensbachian and early Toarcian and that, from then onwards, platycopids were able to occupy the filter-feeder niche in shallower waters. Since the demise of the metacopids, the platycopids have become the only filter-feeding marine benthonic ostracods. Whatley et al. (1995) demonstrated the significance of platycopids in warm water littoral

371

FIGURE 6 - 1. Paradoxorhyncha neuquenensis (BALLENT),MLP-Mi 93, Pict~n Leuffi, late Aalenian-early Bajocian, carapace, left lateral view. 2. Ektyphocythere australis BALLENT, MLP-Mi 500/4, Paso del Carro Quebrado, early Bajocian, carapace, left lateral view. 3. Hemiparacytheridea sp, MLP-Mi 655, Picdn Leuf(1, late Aalenian-early Bajocian, right valve, external view. 4. Cytherella sp. C, MLP-Mi 651, Paso del Carro Quebrado, early Bajocian, carapace, left lateral view. 5. Cytherelloidea sp. A, MLP-Mi 652, Paso det Carro Quebrado, early Bajocian, carapace, left lateral view. 6. Monoceratina sp. 2 MUSACCHIO,MLP-Mi 726, Picfin Leuffi, mid-late Callovian, carapace, left lateral view. 7. Monoceratina sp. cf. M. vulsa (JoNEs 8~ SHERBORN),MLP-Mi 1072, Maria Rosa Curic6, mid-late Callovian, carapace, right lateral view. 8. Eucytherura leufuensis MvsAcc}{io, MLP-Mi 727, Picdn Leuffi, mid-late Callovian, carapace, left lateral view. 9. Eucytherura sp., MLP-Mi 1073, Maria Rosa Curic5, mid-late Callovian, carapace, left lateral view. 10. "Progonocythere" neuquenensis MUSACCHIO, MLP-Mi 1074, Pic~n Leuffi, mid-late Callovian, carapace, left lateral view. 11. Sondagella sp., MLP-Mi 621, Mallin de la Cueva, Callovian-Oxfordian boundary, carapace, right lateral view. 12. Polydentina ? sp., MLP-Mi 1075, YPF.Nq.PC.EC 24 (El Caracol) borehole, 2080-2090 metres below surface, Entre Lomas Area, Tithonian, carapace, left lateral view. Repository: MLP-Mi = Museo de Ciencias Naturales de La Plata-Micropaleontologia. Scale bar=100 #m, 1. Vue latgrale gauche. 2. Vue latdrale gauche. 3. Valve droite, rue externe. 4. Vue latgrale gauche. 5. Vue latdrale gauche. 6. Vue latgrale gauche. 7. Vue latdrale droite. 8. Vue latdrale gauche. 9. Vue latgrule gauche. 10. Vue latgrale gauche. 11. Vue latdrale droite. 12. Vue latgrale gauche.

372 environments, Whatley (1988) having already demonstrated their effective absence from shallow cold waters. For example, it is probably due to depth that metacopids are absent from the typical Liassic ostracod assemblages of deep, perhaps bathyal conditions, of the western Pontides, Turkey (Lord & Lamnourne 1991). In the late Pliensbachian, as shown in figure 3, the two filter-feeding groups, Platycopina and Metacopina, occur together, which, as stated above is uncommon. This occurrence represents the last for the suborder Metacopina which became globally extinct at this time, except in Wales, where they persist into the Lower Toarcian (Boomer 1991). The cooccurrence of Ogmoconcha-Ogmoconchella and CythereUa-Cytherelloidea, however, amounting to the 21% of the fauna, is not sufficient to signify a major period of lowered oxygen levels. The Cytheracea, Cypridacea and Bairdiacea are of equal importance with some 25 % of the total number of specimens each, although the former, with seven species, is the most diverse (see Fig. 4). The presence of species of the cytherids Monoceratina and two cytherurid genera is suggestive of shelf conditions. Around the Aalenian-Bajocian boundary, the Cytheruridae is clearly the dominant family with a number of species being characterized by small and delicate carapaces. The composition of the cytherid fauna points to an environment of deposition on the shelf with clear, well-oxygenated waters, while the presence of Cytherelloidea, a well-known warm water indicator (Sohn 1962) indicates inner rather than outer shelf in a subtropical or warmer environment. The dominance of Platycopina in the early Callovian, could possibly represent an example of the platycopid signal (Whatley 1991 ), where filter-feeding ostracods, because of their system means of alimentation, are able to obtain sufficient oxygen to survive in an 02 depauperate environment where other ostracods, with different feeding strategies were unable to exist. However, in this case, the actual number of ostracod specimens (fifteen) recovered is insufficient to be certain. C O M P A R I S O N WITH COEVAL OSTRACOD F A U N A S

The basic constitution of Argentinian Hettangian and Pliensbachian ostracod assemblages is essencially the same as those typical of epicontinental shallow marine environments as far apart as northwestern Europe and western Australia, for example. They comprise the same combination of healdiacean metacopids and Cytheracea, accompanied by Bairdiacea and platycopids. Deeper water assemblages, such as those from the Tethys described by Lord & Lamnourne 1991, are different in that they lack the cytheracean component. The Cytheracea seem not to have evolved the ability to live at deeper bathyal and abyssal depths until after the Early and Middle Jurassic (Whatley & Ballent 1994). Despite the general similarity of European and Argentinian Liassic ostracod faunas (Whatley & Ballent 1994; Boomer & Ballent 1996), from the Middle Jurassic

onwards there is an increasing divergence. The generic diversity of European and North American Middle and Upper Jurassic Ostracoda is of an order of magnitude greater than that of South America. To a certain degree this may be explicable in terms of environment. However, the principal reason is zoogeographical. For example, such families as the Progonocythereidae (Lophocythere, Neurocythere, Glyptocythere, etc.) so very generically diverse in the Middle Jurassic and early Upper Jurassic of Europe are very sparsely represented in Argentina (the single possible example being 'Progonocythere neuquenensis' MUSACCmO,from the Middle Callovian) and the equally important Schulerideidae, Protocytheridae and the so-called Upper Jurassic brachycytherids (Macrodentina, Polydentina) and cytherideinids (Galliaecytheridea, Vernoniella), so very abundant in NW Europe are also virtually absent. Many of the numerous genera described by Bate between 1963 and 1969 (see also Bate 1978) from the British Bajocian and Bathonian are confined to Great Britain and NW Europe. While to a certain extent this may be due to facies control and the prevalence of restricted marine conditions in parts of the British region at this time, the fact that many other European genera of entirely marine character are also absent from Argentina points to endemism on a continental scale. Conversely, there are no generic or supra-generic ostracod taxa that are endemic to the Argentinian Jurassic. After the global extinction of the Metacopina, which in Argentina took place in the late Pliensbachian, it was not only the platycopids which were able to exploit the niches they vacated. The Cytheracea probably owe much of their major adaptive radiation in the Toarcian to the demise of the metacopids (Whatley & Stephens 1976; Whatley 1986, 1988, 1990). In the Middle Jurassic of Argentina, from the Aalenian-Bajocian boundary to the mid-Upper Callovian the dominant family were the cytherurids, while in NW Europe the Cytheruridae, although always present, were never dominant and only seem to have achieved a relatively high level of importance in the post-Liassic in the Callovian/Oxfordian (whatley 1965). At the present day, while cytherurids, typified by such genera as Semicytherura, are sometimes very important in shallow water, it is in slope and abyssal plain environments that they achieve their acme of diversity, mainly through the agency of

Cytheropteron. THE F O R A M I N I F E R A

A few Haplophragmoides-Ammobaculites-like infaunal agglutinated foraminifers occur together with the metacopid ostracods in the WaehnerocerasSchlotheimia and Badouxia canadensis zones of the Upper Hettangian. In the late Pliensbachian Fanninoceras Zone, the foraminifers are represented by highly diverse nodosariids and subordinate spirillinids, all with calcareous tests (Ballent 1987). Among the most common nodosariids taxa are Prodentalina pseudocommunis (FRANK.),Ichthyolaria terquemi bicostata (D'ORB.), I. terquemi sulcata (BORN.), Marginulina prima prima D'ORB., Planularia protracta (BORN.)

373 and Paralingulina tenera tenera (BORN.); polymorphinids (mainly Eoguttulina liassica (ST~ICK.) and the spirillinids SpiriUina and Conicospirillina trochoides (BERTH.) occur in flood proportions. Around the Aalenian-Bajocian boundary (Puchenquia malarguensis Zone) the foraminifers are very abundant, diverse and well preserved (Ballent 1997, 1999). Calcareous forms are represented by 48 species; among them, the ornamented nodosariids with taxa such as Ichthyolaria lignaria (TERQ.),Nodosa-

ria mutabilis TERQ.,Lenticulina quenstedti decorata BALL., Lenticulina quenstedti violetae BALL.,Astacolus dorbignyi (ROEM.) and Planularia beierana (G~MB.);polymorphinids (mainly Eoguttulina liassica STRICK.)~spirillinids (Spirillina infima (STRICK.)) and involutinids (Trocholina unica BALL.) occur in flood abundance at certain levels. In the upper part of the section, only infaunal agglutinated forms are represented, such as Reophax and Ammobaculites. A few nodosariids are present throughout the early Bajocian. Foraminifers are most diverse in the Emileia giebeli Zone with several species of ornamented Lenticulina. Foraminifers are absent in the late Bajocian and Bathonian and are only poorly known in the early Callovian (Bodenbenderi Standard Zone), where they occur in only a few samples and are represented by pyritized and ill-preserved nodosariids and polymorphinids. In the Middle Callovian (Rehmannia patagoniensis Horizon), a rich and diverse fauna of foraminifers are present (Musacchio 1979; Simeoni 1995). More than 70 species of benthic foraminifers have been identified; nodosariids are dominant and very diverse; the infaunal agglutinated forms, with free (Reophax, Ammobaculites, Haplophragmiun) and attached tests (Tolypammina), dominate over nodosariids at certain levels. Although the presence of some Tithonian nodosariids have been noted by Simeoni (in Mancefiido 1993, p. 63) the present study is confined to samples of boreholes in the eastern part of the Neuqu~n Basin from which an exclusive fauna of abundant epistominids has been recovered in the dark shales of the Tithonian Vaca Muerta Formation. FORAMINIFERAL PALAEOECOLOGY Palaeoecological interpretations of Jurassic foraminiferal assemblages are difficult to make due to a general lack of direct modern-day analogues. The predominant group of Foraminifera in the Jurassic were the lagenids, which are believed to have occupied a far more diverse range of habitats than their living representatives. These groups in the Recent occupy deeper water settings than in the Jurassic. Nevertheless, some conclusions may be drawn by studing the foraminiferal assemblages in relation to the sediment type, since, as in the case of the ostracods, their presence is largely facies-controlled. In the Upper Hettangian, small Haplophramoides - Ammobaculites like specimens are the only foraminifers and this is coincident with low-oxygen

conditions in a sequence characterized by off shore, dark, pyritized mudstones. Both taxa have a planispiral chamber arrangement and rounded periphery, which are typical features of the Subgroup 3a of Nagy (1992), who recognized agglutinated foraminiferal morphogroups in Jurassic North Sea deltas. According to Nagy (op. cit. p. 120), Haplophragmoides is among the most common taxa in the Jurassic black shales of Scotland and Spitsbergen and is one of the genera which disappear last with increasing organic carbon content, suggesting that it could tolerate dysaerobic conditions immediately below the sediment-water interface. In the late Pliensbachian, the dominance and diversity of nodosariids suggest normal marine shelf conditions in a sequence characterized by brownish siltstones. This corresponds, within the various types of Jurassic foraminiferal assemblages of Gordon (1970), to Group A1. Jurassic nodosariids seem to have preferred normal marine shelf conditions, particularly in areas of argillaceous sedimentation (see references in Copestake 1989). Polymorphinids (mainly represented by Eoguttulina liassica) occur in flood abundance at certain levels. According to Shipp & Murray (1981, p. 130) 'the significance of this group is not clear, but as they often occur in large numbers, there may be some distinct factor, such as salinity or clarity of water, affecting their distribution'. The other subordinate group, the Spirillinina, includes the planispiral Spirillina and the conical trochospiral Conicospirillina. The occurrence of Spirillina in modern lagoons, principally on algae, and the presence of the conical Recent Patellina as a vagrant phytal genus are referred to by Nagy (1992). Around the Aalenian-Bajocian boundary, the faunas are dominated by nodosariids with floods of spirillinids, polymorphinids and involutinids at certain levels. As stated above, they indicate essentially shallow marine conditions with clear and well oxygenated waters in a sequence of greenish and greyish siltstones. Gordon (1970) and Shipp & Murray (1981) have interpreted the floods of spirillinids as indicative of shallowing. Small infaunal agglutinated forms (Reophax and Ammobaculites) are only present to the top of the section. They suggest progressively more restricted conditions from the normal marine environment, probably shallow water with reduced salinity. In the Middle Callovian, the faunas are characterized by highly diverse nodosariids suggesting normal marine conditions in a sequence of brownish and greenish siltstones. The levels in which small agglutinated forms dominate are interpreted as shallowing. The Tithonian faunas are characterized by the unique presence of very abundant specimens of Epistomina. This asssociation could correspond to Group A3 of Gordon (1970); (Assemblages with conspicuous calcareous species other than nodosariids). According to Gordon (1970, p. 1697), in these cases one of the most common genera is Epistomina 'which in Jurassic strata often appears in large numbers when the sediment is a dark grey clay or

374 shale', even though its depth significance is variable. One of us (R.W.) has noted abundant monotypical faunas of Epistomina in the Callovian part of the Oxford Clay in Southern England (Whatley 1965 unpublished), which he attributed to reduced oxygen. Tyszka (1994) analysed the response of Middle Jurassic foraminifers to dysoxic/anoxic conditions in the Polish Carpathians. He included the epistominids in his Morphogroup C-1, characterized by bi/plano-convex trochospiral test and epifaunal habit, and correlated the acme of abundance of this group with low/medium oxygen levels. Similarly, there are examples in which Epistomina is thought to represent open marine shelf conditions with reduced oxygen levels, such the cases referred to by Bartenstein & Brand (1951); Bettenstaedt (1962) and Malumi~n & N~fiez (1983) for Lower Cretaceous marine microfaunas. In Argentina, the high abundance of monotypic Epistomina is coincident with the accumulation of several hundred metres of euxinic sediments, mainly marly shales and laminated deposits, of the Vaca Muerta Formation. This has been interpreted as due to renewed marine flooding and widespread anoxia (but actually kenoxia) around the late Jurassic and early Cretaceous in the Neuqu~n Basin (cf. Legarreta & Uliana 1996). CONCLUSIONS This contribution presents an analysis of the structure of early Mesozoic marine ostracod assemblages from the Neuqu~n Basin in central-western Argentina. The study reflects a correlation between the changing faunal composition of the Ostracoda at subordinal] superfamilial level and the environmental changes in the sequence within the Hettangian to Tithonian interval. The only time when the Metacopina dominate was in the Hettangian and this is interpreted as a time of low-oxygen conditions in a sequence characterized by dark, pyritized mudstones. It is acknowledged that this was a filterfeeding extinct group which would have possessed the ability to survive in reduced oxygen conditions by virtue of passing a greater volume of water across the respiratory surface. In the late early Pliensbachian, the Cypridacea and the Bairdiacea were dominant; in the late Pliensbachian the presence of the Cytheracea, almost equally abundant as the Cypridacea and Bairdiacea, seems to represent near to off shore marine facies in a sequence characterized by brownish siltstones. Around the Aalenian-Bajocian boundary, the Cytheracea (mainly Cytheruridae) with small and delicate carapaces were dominant representing more than 90 % of the total number of specimens. They indicate essentially shallow marine conditions with clear and well oxygenated waters in a sequence of greenish and greyish siltstones. Throughout the early Bajocian, the Cytheracea were dominant, although poorly diverse, with accompanying Platycopina. They are associated with restriction to near-shore facies in a sequence of calcareous sandstones and arenaceous marls to shallow and high energy environment. The dominance of Platycopina in the early Callovian may represent low-oxygen events, perhaps related to relatively high sea-level. This is possibly an

example of the 'platycopid signal' (Whatley 1991). Ostracods were comparatively more abundant in the mid-late Callovian; the Cytheracea were dominant and account for more than 80 % of the total of specimens; the Platycopina and the Cypridacea with equal 7.5 % each and the very rare Cladocopina, represented by Polycope. This fauna is coincident with shallow marine facies in a sequence of brownish and greenish siltstones. Tithonian ostracods include cytheraceans and platycopids with Cytherella, with very abundant epistominid foraminifers in a sequence of dark shales. These palaeoecological conclusions coincide with those from the contemporary Foraminifera. The basic constitution of Argentinian Hettangian and Pliensbachian ostracod assemblages is essentially the same as those of typical epicontinental shallow marine environments as far apart as northwestern Europe and western Australia. Throughout the remainder of the Jurassic there is an increasing divergence of ostracod faunas with evidence of the progressive isolation of southern South America. Strongly calcified progonocytherids, Schulerideidae and Protocytheridae, very generically diverse in the Middle and Upper Jurassic of Europe, are very sparsely represented in Argentina; the so-called Upper Jurassic brachycytherids (Macrodentina, Polydentina ) and cytherideinids (Galliaecytheridea, Vernoniella), very abundant in NW Europe, are also virtually absent. Conversely there are no genera or supra-generic taxa endemic to Argentina. A c k n o w l e d g e m e n t s - The authors thank very especially Dr. Oertli (Bizanos, France) for the carefully reading of the manuscript, suggesting improvements and French abstract and figure captions. R. Whatley acknowledges the agreement between the Royal Society and the Argentinian Science and Technology Research Council (CONICET) which allowed him to work on this paper in the Museo de La Plata. Partial support was provided by a grant to S. Ballent from Universidad Nacional de La Plata.

REFERENCES AINSWORTHN.R. 1986 - Toarcian and Aalenian Ostracoda from the Fastnet Basin, offshore Southwest Ireland. Geological Survey of Ireland Bulletin, 3: 277-336. ..... 1987 - Pliensbachian Ostracoda from the Fastnet Basin, offshore Southwest Ireland. Geological Survey of Ireland Bulletin, 4: 41-62. APOSTOLESCUV. 1959 - Ostracodes du Lias du Basin de Paris. Revue de l'Institut Fran¢ais du Pgtrole, 14: 795-826. BALLENTS.C. 1985 - Taxonomic y bioestratigraffa de los microfSsiles calc~reos del Jur~sico inferior y medio de la Repfiblica Argentina. Unpublished doctoral dissertation. Facultad Ciencias Naturales y Museo, Universidad Nacional de La Plata, 272 p. ..... 1986 - Una nueva especie del g~nero Ektyphocythere Bate (Ostracoda) en el Jur~sico medio de la provincia del Neuqu~n, Argentina. Notas del Museo de La Plata, 21, Pal. 105: 40-46. ..... I987 - Foraminfferos y ostr~codos del Jur~sico inferior de Argentina. Revista del Museo de La Plata (Nueva Serie), Paleontologic, 9: 43-130. ..... 1991- Ostr~codos del Jur~sico medio (Limite AalenianoBayociano) en la provincia del Neuqu~n, centro-oeste de Argentina. Revista EspaTtola de Micropaleontologia, 23: 21-56. ..... 1992 - Metacopina (Ostracoda) del Hettangiano superior en el sudoeste de la provincia de Mendoza, Argentina. Ameghiniana, 29: 153-157. ..... 1994 - New marine microfaunas from the Triassic-Jurassic boundary in the Atuel River area (Mendoza, Argentina). In

Symposium IGCP 322 Correlation of Jurassic Events in South

375 America. 4 th International Congress on Jurassic Stratigphy and Geology, Abstracts, p. 55. ..... 1997 - Lenticulina quenstedti (GOMBEL) (Protista-Foraminifera) from t h e Middle J u r a s s i c of w e s t e r n Argentina. Ameghiniana, 34: 453-460. ..... 1999 - Foraminiferos del Jur~sico medio (Limite AalenienseBajociense) del c e n t r o - o e s t e de A r g e n t i n a . S i s t e m ~ t i c a . Revista Espa~ola de Micropaleontolog[a, 31: 129-153. • WHATLEYR. 1996 - Marine ostracods as a chronoecological tool. Their application to t h e A n d e a n J u r a s s i c sequences of Argentina. 13 ° Congreso Geol6gico Argentino y 3 ° Congreso de Exploracign de Hidrocarburos (Buenos Aires), Actas, 5: 143149. BARTENSTEINH . & BRAND E. 1 9 5 1 - Mikropal~iontologische U n t e r s u c h u n g e n z u r S t r a t i g r a p h i e des n o r d w e s t d e u t s c h e n Valendis. . . . . .

Abhandlungen der Senckenbergischen Naturforschenden Gesellschaft, 485: 239-336. BATE R.H. 1963a - Middle J u r a s s i c O s t r a c o d a from N o r t h Lincolnshire. Bulletin British Museum (Natural History), Geology, 8: 173-219. ..... 1963b - Middle J u r a s s i c Ostracoda from S o u t h Yorkshire. Bulletin British Museum (Natural History), Geology, 9: 19-46. ..... 1964 - Middle J u r a s s i c Ostracoda from t h e Millepore Series, Yorkshire. Bulletin British Museum (Natural History), Geology, 10: 1-34. ..... 1965 - Middle J u r a s s i c O s t r a c o d a from t h e Grey L i m e s t o n e Series, Yorkshire. Bulletin British Museum (Natural History), Geology, 11: 73-134. ..... 1967 - The B a t h o n i a n U p p e r E s t u a r i n e Series of E a s t e r n England. Bulletin British Museum (Natural History), Geology, 14: 21-66. ..... 1969 - Some B a t h o n i a n O s t r a c o d a of E n g l a n d w i t h a revision of t h e J o n e s 1884 a n d J o n e s & S h e r b o r n 1888 Collections. Bulletin British Museum (Natural History), Geology, 17: 377437. ..... 1978 -The J u r a s s i c P a r t II- A a l e n i a n to B a t h o n i a n . In BATE R.H. & ROBINSON E. (eds), A Stratigraphical Index of British Ostracoda: 213-258. Seel H o u s e Press, Liverpool. ..... & COLEMANB.E. 1975 - U p p e r Lias Ostracoda from R u t l a n d a n d H u n t i n g d o n d h i r e . Bulletin Geological Survey of Great Britain, 55: 1-42. BECKER G. & BLESS M.J.M. 1990 - Biotope indicative f e a t u r e s in Palaeozoic ostracods: a global p h e n o m e n o n . In WHATLEYR. & MAYBURY C. (eds), Ostracoda and Global Events: 421-436. C h a p m a n & Hall, Cambridge. BETTENSTAEDT F. 1 9 6 2 - E v o l u t i o n s v o r g ~ n g e bei fossilen Foraminiferen. Mitteilungen Geologisches Staatsinst., 31: 385460. BOOMER I.D. 1991- Lower J u r a s s i c ostracod biozonation of t h e Mochras Borehole. Journal of Micropalaeontology, 9: 205-218. . . . . . & BALLENTS. 1996 - Early-Middle J u r a s s i c ostracod migration b e t w e e n t h e n o r t h e r n a n d s o u t h e r n h e m i s p h e r e s : F u r t h e r evidence for a proto Atlantic-Central America connection. Palaeogeography, Palaeoclimatology, Palaeoecology, 121: 53-64. ..... & WHATLEYR. 1993 - O s t r a c o d a a n d dysaerobia in t h e Lower J u r a s s i c of Wales: t h e r e c o n s t r u c t i o n of p a s t oxygen levels. Palaeogeography, Palaeoclimatology, Palaeoecology, 99: 373379. COPESTAKEP. 1989.- Jurassic. P a r t 6. T h e H e t t a n g i a n to Toarcian (Lower Jurassic). In JENKINS D.G. & MURRAY J.W. (eds),

Stratigraphical Atlas of Fossil Foraminifera, Second edition: 129-188. Ellis Horwood Ltd, Chichester. DONZE P. 1976 - S u r u n mode d'dlaboration d'espbces nouvelles chez le genre Protocythere (ostracode) d a n s le Crdtacd infdr i e u r vocontien. Abhandlungen und Verhandlungen des Naturwissenschaftlichen Vereins in Hamburg, NF, 18/19 Suppl.: 239-246. FIELD R.A. 1966 - Species of t h e family Cytherellidae (Ostracoda) from t h e Lower Lias of S o u t h Dorset, England. Senckenbergiana lethaea, 47: 87-105. GORDON W.A. 1970 - Biogeography of J u r a s s i c Foraminifera. Geological Society of America Bulletin, 81: 1689-1704. GULISANOC.A. & GUTII~RREZPLEIMLINGA . R . 1 9 9 4 - The J u r a s s i c of t h e N e u q u d n Basin. a) N e u q u d n Province. Field Guide. Secre-

tarla de Mineria de la Nacidn-Direccidn Nacional del Servicio Geol6gico, Publicaci6n 158 & Asociaci6n Geol6gica Argentina, E, 2: 7-111.

HERRIG E. 1979 - Ostracoden a u s d e m Ober-Domerien von G r i m m e n westlich von Greifswald. Geologie, 18: 999-1126. JONES T.H. 1872 - On some Bivalve E n t o m o s t r a c a from t h e Lias ('Infralias') of Yorkshire. Quarterly Journal Geological Society London, 28: 146-147. . . . . . & SHERBORN C . D . 1 8 8 8 - O n some Ostracoda from t h e Fuller's E a r t h Oolite a n d Bradford Clay. Proceedings Bath Natural History Field Club, 6: 249-278. KOZUR H. 1971- Die Bairdiacea der Trias. I-III. Geologie und Pal~ontologie Mitteilungen Innsbruck, 1, 3: 1-27. ..... 1972 - Die B e d e u t u n g t r i a s s i s c h e r Ostracoden for stratigraphische u n d pal~ioSkologische U n t e r s u c h u n g e n . Mitteilungen Gesellschaft Geologische Bergbaustud, 21: 623-660. LEGARRETA L. & GULISANO C.A. 1989 - An~lisis estratigr~fico secuencial de la Cuenca N e u q u i n a (Tri~sico superior-Terciario inferior). In CHEBL1G. ~,~ SPALLETTIa. (eds), Cuencas Sedimentarias Argentinas. Serie de Correlacidn Geoldgica, 6: 221-243. & ULIANAM.A. 1996 - The J u r a s s i c succession in west-central Argentina: s t r a t a l patterns, sequences and paleogeographic evolution. Palaeogeogphy, Palaeoclimatology, Palaeoecology, 120: 303-330. ..... , GULISANO C.A. & ULIANA M.A. 1993 - Las secuencias sedim e n t a r i a s jur~sico-cret~cicas. In RAMOS V.A. (ed.), Geologla . . . . .

recursos naturales Relatorio 12 ° Congreso Geol6gicoArgentino & 2 Congreso Exploraci6n de Hidrocarburos: 87-114. LETHIERS F. & WHATLEYR. 1994 - The u s e of Ostracoda to reconst r u c t t h e oxygen levels of Late Palaeozoic oceans. Marine Micropaleontology, 24: 57-69. . . . . . & WHATLEYR. 1995 - Oxygdnation des e a u x et ostracodes illtreurs: application au Devonien-Dinantien. Geobios, 28: 199207. LORDA.R. & LAMNOURNED.C. 1991 - Lower J u r a s s i c ostracods from the w e s t e r n Pontides, Turkey. Geologica Romana, 27: 381-387. MALUMI~,NN. & Ni~EZ C. 1983 - Foraminfferos de a m b i e n t e anSxico de la Formacidn Rfo M a y e r (Cret~cico inferior), provincia de S a n t a Cruz. Ameghiniana, 20: 367-393. MANCE~IDO M.O. 1993 - Palaeontology a n d Biostratigraphy. In RICCARDI A . C . & DAMBORENEA S . E . ( e d s ) ,

IGCP 322 Correlation

of Jurassic Events in South America. Boletin 1 First Conference Proceedings and Abstracts: 48-65. MONOSTORI M. 1995 - E n v i r o n m e n t a l significance of t h e A n i s i a n Ostracoda f a u n a from t h e Forr~s Hill n e a r EelsoSrs (Balaton Highland, T r a n s d a n u b i a , Hungary). Acta Geologica Hungarica, 39: 37-56. MUSACCHIOE.A. 1979 - Datos paleobiogeogr~ficos de a l g u n a s asociaciones de foraminfferos, ostr~codos y carofitas del Jur~sico medio y Cret~cico inferior de Argentina. Ameghiniana, 16: 247-271. NAGY J. 1992 - E n v i r o n m e n t a l significance of foraminiferal morphogroups in J u r a s s i c N o r t h Sea deltas. Palaeogeography, Palaeoclimatology, Palaeoecology, 95: 111-134. RICCARDI A.C. 1983 - The J u r a s s i c of A r g e n t i n a a n d Chile. In MOULLADE M. & NAIRN A.E.M. (eds), The Phanerozoic of the World. 2. The Mesozoic B: 201-263. Elsevier, A m s t e r d a m . ..... 1992 - B i o s t r a t i g r a p h y of w e s t - c e n t r a l A r g e n t i n a . In WESTERMANNG.E.G. (ed.), The Jurassic of the Circum Pacific: 139-141. C a m b r i d g e U n i v e r s i t y Press. ..... & GULISANOC.A. 1990 - U n i d a d e s l i m i t a d a s por discontinuidades. Su aplicaciSn al Jur~sico andino. Revista de la Asociacidn Geoldgica Argentina, 45: 346-364. . . . . . , DAMt]ORENEA S.E., MANCE~IDO M . O . & BALLENT S.C. 1 9 8 8 H e t t a n g i a n o y S i n e m u r i a n o m a r i n o s en Argentina. 5 ° Congreso Geol6gico Chileno, 2: C359-C373. DAMBORENEAS.E., MANCEI~IIDOM.O., SCASSO R., LAN~S S. & IGLESIA LLANOSM.P. 1997 - P r i m e r registro de Tri~sico m a r i n o fosilifero de la Argentina. Nota breve. Revista de la Asociaci6n Geol6gica Argentina, 52: 228-234. SHIPP D. & MURRAYJ.W. 1981 - Jurassic. P a r t III. The Callovian to Portlandian. In JENKINS D.G. & MURRAYJ.W. (eds), Stratigraphical Atlas of Fossil Foraminifera: 125-144. Ellis Horwood Ltd., Chichester. SIMEONI M. 1995 - MicrofSsiles calc~reos m a r i n o s jur~sicos de la Formacidn Lotena en Picdn Leufd (Neuqudn), Argentina. 6 ° Congreso Argentino de Paleontologfa Bioestratigraffa, Actas: 255-264. SOHN I.G. 1962 - T h e ostracod g e n u s CythereUoidea, a possible indicator of p a l e o t e m p e r a t n r e . Geological Survey Professional Paper, 450-D, 162: D-144-D 147. . . . . .

.,

376 TATER. & BLAKEJ.F. 1876 - The Yorkshire Lias, 475 p, London. TYSZKAJ. 1994 - Response of Middle Jurassic benthic foraminiferal morphogroups to dysoxic/anoxic conditions in the Pieniny Klippen Basin, Polish Carpathians. Palaeogeography, Palaeoclimatology, Palaeoecology, 110: 55-68. WHATLEY R. 1965 - Callovian and Oxfordian Ostracoda from England and Scotland. Unpublished Doctoral Dissertation, University of Hull, 648 p. ..... 1986 - Biological Events in the evolution of Mesozoic Ostracoda. Lecture Notes in Earth Sciences, 8, Global Bio-Events: 257-265. Springer Verlag, Berlin. ..... 1988 - Patterns and rates of evolution in Mesozoic Ostracoda. In HANAIT. et al. (eds), Evolutionary biology of Ostracoda, its fundamentals and applications. Proceedings of the 9 th International Symposium on Ostracoda, Shizuoka, Japan 1985. Developments in Palaeontology and Stratigraphy, 11: 10031020. Kodansha/Elsevier, Tokyo. ..... 1990 - Ostracoda and Global Events. In WHATLEYR. & MAYBURYC.A. (eds), Ostracoda and Global Events, Proceedings of the 10th International Symposium on Ostracoda, Aberystwyth, 1988: 3-24. Chapman & Hall, Chichester. ..... 1991- The platycopid signal: a means of detecting kenoxic events using Ostracoda. Journal of Micropalaeontology, 10: 181-185. ..... 1995 - Ostracoda and oceanic palaeoxygen levels. Mitteilungen aus dem Hamburg Zoologischen Museum Institut, 92: 337353. ..... & BALLENTS. 1994 - Bi-hemispherical distribution of Jurassic Ostracoda: Palaeogeographical implications. In Pangea: Global Environments and Resources. Canadian Society of Petroleum Geologists, Memoir, 17: 961-966. . . . . . & STEPHENS J.M. 1976 - The Mesozoic Explosion of the Cytheracea. In HARTMANNG. (ed.), Proceedings of the 5th International Symposium on Evolution of Post-Palaeozoic Ostracoda. Abhandlungen und Verhandlungen des Naturwissenschaftlichen Vereins in Hamburg (HF), 18-19 Suppl.: 63-76. ..... , ARIASC.F. • COMAS-RENGIFOM.J. 1994 - The use of Ostracoda to detect kenoxic events: a case history from the Spanish Toarcian. Geobios, M~m. sp. 17: 733-741. ..... , COOKEP.C.B. & WARNE M.T. 1995 - The Ostracoda from Lee Point on Shoal Bay, Northern Australia: Part 1- Cladocopina and Platycopina. Revista Espa~ola de Micropaleontologia, 27: 69-89. S.C. BALLENT Consejo Nacional de Investigaciones Cientificas y T&nicas Departamento Paleontologla Invertebrados Museo de La Plata, Paseo del Bosque s/n 1900 La Plata, Argentina

R. WHATLEY D e p a r t m e n t of Geology University of Wales U.K.Aberystwyth, Cardiganshire, SY23 3DB

APPENDIX

- List of species

Late Hettangian

Ogmoconchella ellipsoidea (JONES, 1872) Ogmoconchella sp. 1 (in Ballent & Whatley 1996) Ogmoconchella sp. 2 (in Ballent & Whatley 1996) Early Pliensbachian

Cytherella praetoarcensis BOOMER,1991 Cardobairdia posteroprolata AINSWORTH, 1987 Liasina lanceolata ( A P o S T O L E S C U , 1959) Paracypris sp. (in Ballent 1987) Late Pliensbachian

Cytherella praetoarcensis BOOMER,1991 Cytherella concentrica FIELD,1966 Cytherelloidea circumscripta (BLAKEin TATE & BLAKE,1876) 'Bairdia' donzei HERRIG,1979 Bythocypris? sp. A (in Ballent 1987) Bythocypris? sp. B (in Ballent 1987) Isobythocypris sp. cf. L elongata (TATE& BLAKE,1876)

Cardobairdia posteroprolata AINSWORTH,1987 Paracypris redcarensis (BLAKE,1876) Paracypris sp. A (in Ballent 1987) Paracypris sp. B (in Ballent 1987) Liasina lanceolata (APoSTOLESCU,1959) Monoceratina sp. B (in Ballent 1987) Monoceratina sp. C (in Ballent 1987) Monoceratina sp. D (in Ballent 1987) Eucytherura isabelensis BkLLENT, 1987 Eucytherura sp. A (in Ballent 1987) Eucytherura sp. B (in Ballent 1987) 'Procytherura' sp. (in Ballent 1987) Ogmoconcha sp. (in Ballent 1987) Late Aalenian-Early Bajocian

Cytherelloidea sp. (in Ballent 1991) Paracypris redcarensis (BLAKE, 1876) Bairdiacypris triangularis AINSWORTH,1986 Bythocypris? sp. (in Ballent 1991) Paradoxorhyncha neuquenensis (BALLENT, 1991) Eucytherura argentina BALLENT,1991 Eucytherura transversiplicata (BATE • COLEMAN,1975) Eucytherura pichia (BALLENT, 1991 ) Eucytherura sp. (in Ballent 1991) Eucytherura sp. A (in Ballent 1991 ) Eucytherura sp. B (in Ballent 1991 ) Eucytherura sp. C (in Ballent 1991) Procytherura euglyphea AINSWORTH,1986 Procytherura celtica AINSWORTH,1986 Procytherura bispinata BALLENT,1991 Procytherura nov. sp. BALLENT& WHATLEYin prep. Hemiparacytheridea sp. (in Ballent 1991) Ektyphocythere australis BALLENT,1986 Grammanicythere sp. (in Ballent 1991) Ostr~codo Ostrficodo Ostr~codo Ostr~codo

A (in Ballent B (in Ballent C (in Ballent D (in Ballent

1991) 1991 ) 1991) 1991)

Early Bajocian

Cytherella sp. A (in Ballent 1985) Cytherelloidea sp. A (in Ballent 1985) Cytherelloidea sp. B (in Ballent 1985) Ektyphocythere australis BALLENT,1986 Early Callovian

Cytherelloidea sp. (in Ballent & Whatley 1996) Ektyphocythere australis BALLENT,1986 Procytherura? sp. (in Ballent & Whatley 1996) Mid-late Callovian

Cytherella sp. A (in Ballent & Whatley 1996) Cytherella sp. B (in Ballent & Whatley 1996) CythereUa sp. (in Musacchio 1979) Cytherelloidea sp. (in Musacchio 1979) Paracypris sp. 1 (in Musacchio 1979) Paracypris sp. 2 (in Musacchio 1979) Monoceratina sp. 1 (in Musacchio 1979) Monoceratina sp. 2 (in Musacchio 1979) Monoceratina? sp. 3 (in Musacchio 1979) Monoceratina sp. cf. M. vulsa (JONES & SHERBORN,1888) Monoceratina? sp. (this paper) Eucytherura? leufuensis MUSACEHIO,1979 Eucytherura sp. (this paper) Procytherura sp. (in Ballent & Whatley 1996) Procytherura nov. sp. BALLENT& WHATLEYin prep. 'Progonocythere' neuquenensis MUSACCHm,1979 Ektyphocythere australis BALLENT,1986 Gen. et sp. indet. (in Musacchio 1979)

Polycope sp. (in Musacchio 1979) Sondagella sp. (Callovian-Oxfordian Boundary) (in Ballent 1985)

Tithonian

Cytherella sp. (this paper) Polydentina? sp. (this paper) Monoceratina sp. 118 (Simeoni in Mancefiido 1993) 'Bythocypris' sp. 107 (Simeoni in Mancefiido 1993) Paracytheridea sp. 101 (Simeoni in Mancefiido 1993) Parariscus sp. 118 (Simeoni in Mancefiido 1993) SondageUa sp. (in Ballent 1985) Gen. indet. 92 (Simeoni in Mancefiido 1993)