Revista de la Asociación Geológica Argentina 63 (4): 549- 556 (2008) 549

JURASSIC PALEOCLIMATES IN ARGENTINA, A REVIEW

Wolfgang VOLKHEIMER1, Oliver W. M. RAUHUT2, Mirta E. QUATTROCCHIO3 and Marcelo A. MARTINEZ3

1 Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CCT - CONICET - Mendoza, Argentina. E-mail: [email protected] 2 Bayerische Staatssammlung für Paläontologie und Geologie, Munich, Germany. E-mail: [email protected] 3 INGEOSUR (Instituto Geológico del Sur)-CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas). Universidad Nacional del Sur, Departamento de Geología, Bahía Blanca, Argentina. E-mail: [email protected]; [email protected]

ABSTRACT New paleoclimatic evidence from palynologic and vertebrate proxies provides more detailed data on climatic change during the Jurassic in Argentina. Comparison with paleomagnetic data shows that the Neuquén basin shifted from the highest pale- olatitudes (50ºS), by the end of the Triassic until the end of the Sinemurian. During the Pliensbachian-Toarcian it moved northward, reaching the lowermost paleolatitudes (25ºS), and subsequently (Middle to Late Jurassic) the area moved again and attained eventually a position similar to its present-day position (30ºS). These movements are reflected in the Jurassic palyno- floras. The high frequency of the pollen genus Classopollis (Cheirolepidiacean gymnosperms) is of special paleoclimatic impor- tance in the Argentinian Jurassic, as it is indicative of seasonal aridity or semiarid conditions during large intervals of this Period. During the shift of the South American continent to the northernmost position, the arrival of an important group of Araucariaceae, represented by Callialasporites spp., in the Toarcian could indicate an amelioration related to more humid con- ditions. Jurassic dinocyst assemblages studied in the Neuquén basin have proved to be useful paleoclimatic and paleobiogeo- graphic proxies. Abundant remains of marine crocodiles in the Mid- and Late Jurassic of the Neuquén basin indicate warm water temperatures for this basin, probably in excess of 20° C. The occurrence of abundant turtles and other ectothermic vertebrates in the Middle Jurassic Cañadón Asfalto Formation of Chubut is in general accordance with the warm climate indi- cated for this unit by geologic evidence.

Keywords: Paleoclimate, Jurassic, Argentina, Vertebrate evidence, Palynology.

RESUMEN: Paleoclimas jurásicos en la Argentina, una revisión. Nuevas evidencias de indicadores paleoclimáticos (palinológicos y de vertebrados) suministran datos detallados sobre los cambios climáticos en el Jurásico de la Argentina. La comparación con datos paleomagnéticos muestra como, desde fines del Triásico hasta el Sinemuriano Tardío, la cuenca Neuquina derivó ocu- pando las posiciones más australes (50ºS). Durante el Pliensbaquiano-Toarciano se movilizó hacia el norte, alcanzando las más bajas latitudes (25ºS), para luego ocupar, durante el Jurásico Medio y Tardío, posiciones similares a las actuales (30ºS). Estos movimientos se reflejan en las palinofloras jurásicas. La alta frecuencia de polen del género Classopollis (Cheirolepidiaceae, gim- nospermas) es de especial importancia paleoclimatológica, ya que indica aridez estacional o condiciones semiáridas durante largos intervalos de este Período. Durante la deriva del continente sudamericano a su posición más septentrional en el Toarciano, la llegada de un importante grupo de araucariáceas, representado por Callialasporites spp., indicaría el comienzo de condiciones climáticas más favorables para este grupo de coníferas, relacionadas con condiciones más húmedas. También se ensayan el significado climático y la evaluación paleobiogeográfica de las asociaciones de quistes de dinoflagelados en la cuen- ca Neuquina. Frecuentes restos de cocodrilos marinos en el Jurásico Medio y Tardío de la cuenca Neuquina indican tempera- turas de aguas cálidas para esta cuenca, de probablemente más de 20ºC. La presencia de abundantes tortugas y otros vertebra- dos exotérmicos en el Jurásico Medio de la Formación Cañadón Asfalto de Chubut está de acuerdo con las condiciones de clima cálido generalizadas, indicadas para esta formación por la evidencia geológica.

Palabras clave: Paleoclima, Jurásico, Argentina, Paleovertebrados, Palinología.

INTRODUCTION nology. floras and palynofloras of Argentina is From a palynological viewpoint, the uni- given by Quattrocchio et al. (2007). This brief essay mainly intents to be a formity of Jurassic and earliest Creta- The paleoclimatic situation of Argentina critical revision of earlier contributions ceous floras appears to be more apparent during the Jurassic Period was conditio- on Jurassic paleoclimates of southwes- than real (Batten 1984). A modern re- ned by its geographic position in mid- tern Gondwana, especially through eva- view of the knowledge on distribution, paleolatitudes of southwestern Gond- luation of new data in vertebrate paleon- diversity, and paleogeographic and paleo- wana. Gondwana became part of the su- tology and continental and marine paly- environmental significance of Jurassic percontinent Pangaea in the Permian. 550 W. VOLKHEIMER, O. W. M. RAUHUT, M. E. QUATTROCCHIO AND M. A. MARTINEZ

The disintegration of Pangaea/Gondwa- The same tendency is registered offshore for these extinct thalattosuchians, it na during the Mesozoic is important for eastern Canada, at 25-30º northern pale- might be noted that recent amphibious the climatic evolution during the Jurassic, olatitude, possibly reflecting warming crocodiles seem to prefer water tempera- when drying occurred in Gondwana, trends in the Late Jurassic. tures in excess of 24° C (Markovick which was interpreted as indicative of 1998). Furthermore, longer spells of the breakdown of the Pangean Mega- c) Vertebrates temperatures below 18° C may lead to monsoon (Parrish 1993). organ malfunction in recent alligators, Vertebrates, especially ectothermic te- and feeding is already restricted at tempe- PALEOCLIMATIC rrestrial forms, have proved to be useful ratures below 22° C (Markovick 1998). If INDICATORS as climate proxies in palaeoclimatic stu- similar restrictions applied to metrior- dies of mainly Cenozoic environments hynchids, water temperature in the Neu- a) Sporomorphs (e.g. Markovick 1998, Böhme 2003), and quén basin did probably not drop below they might be helpful to interpret Me- 20° C for longer periods of time in the Large numbers of Classopollis pollen in sozoic climates as well (e.g. Vandermark et late Middle and Late Jurassic environ- Mesozoic deposits are generally thought al. 2007), though additional caution is ments in which these animals lived. The to reflect an abundance of representati- needed when dealing with extinct groups limits of a coldest month mean tempera- ves of Cheirolepidiacean gymnosperms (see Ostrom 1970). The record of Juras- ture of 5.5° C and a mean annual tempe- of lowland vegetation, when the climate sic vertebrates from Argentina is still ra- rature of 14.2° C found by Markovick was at least seasonally dry or semiarid ther patchy, though a variety of dino- (1998) for recent amphibious crocodiles (Batten 1975). Alvin (1982) suggests that saurs, marine crocodiles, and a few other are probably not applicable to the fully some species of cheirolepids undoub- groups have been reported. marine thalattosuchians. Temperatures in tedly were adapted to coastal environ- Although dinosaurs were sometimes excess of 20° C for the Neuquén basin ments and may have formed extensive used as climate proxies, allegedly indica- are also in accordance with data from coastal forests as the main components ting warm climates (e.g. Romer 1961, Col- oxygen isotopes, which indicate tempera- of a halophytic, salt-marsh community. bert 1964), they seem to be poorly suited tures between 24 and 27° C (Gasparini et Cheirolepidiaceae occupied a wide range for these purposes, due to uncertainties al. 2002). of warm and semiarid habitats, and some regarding their physiology (Ostrom The Cañadón Asfalto Formation has groups were probably associated with 1970). Indeed, recent finds of even sau- yielded one of the most important verte- freshwater environments (both lakes and ropod dinosaurs at high latitudes (see brate faunas from the Middle Jurassic of rivers), or even inhabited freshwater stre- Smith and Pol 2007) indicate that dino- Gondwana (see Bonaparte 1979, Rauhut am banks or low-lying areas dissected by saurs cannot reliably be used to interpret et al. 2001). Vertebrates recorded include braided streams that may have dried out paleoclimates. The same applies to other a diverse dinosaur fauna (Bonaparte seasonally or irregularly (Alvin 1983). groups, such as the pterosaurs, and cau- 1979, 1986, Rauhut 2002, 2005) and a va- Other Cheirolepidiaceae may have been tion is even needed when interpreting cli- riety of other groups, such as anuran am- characteristic for higher, better drained mates on the basis of larger taxonomic phibians (Báez and Nicoli 2008), turtles soils. Maximal abundances of Classopollis units that have living representatives, but (Sterli 2008), and mammals (Rauhut et al. have been correlated with evidence of are represented in the fossil localities 2002, Rougier et al. 2007a, b). Interes- warmth and aridity (Vakhrameev 1981, under study solely by lineages that lie tingly, no crocodile remains have been 1987). outside the radiation of the recent forms, confidently identified from this forma- such as crocodiles (Ostrom 1970, Marko- tion so far. However, this might be due to b) Dinoflagellate cysts vick 1998). Keeping these restrictions in ecological reasons other than climate, mind, some observations on possible cli- since geological evidence indicates a ra- The Liassic until Bajocian Jurassic dino- matic implications of the Jurassic verte- ther warm climate for this formation (see cyst assemblages of the Neuquén basin brates from Argentina will be offered. above). It cannot be ruled out, though, (Fig. 1) are characterized by low specific Marine crocodiles, mainly of the family that very high temperatures, in combina- diversity and predominance of acavate Metriorhynchidae, have been reported tion with at least seasonal aridity, might proximate cysts. Chorate/acavate ratios from both the Middle and the Late Ju- have been a limiting factor for crocodi- increase during the Callovian and the rassic of Argentina, principally from ma- lians in the Cañadón Asfalto Formation Tithonian and specific diversity increases rine sediments of the Neuquén basin (see Colbert et al. 1946). The abundant during the Jurassic. Chorate species are (Gasparini 1985, 1992, Gasparini et al. turtles found in the Cañadón Asfalto getting common in the Callovian and in- 2005, Pol and Gasparini 2007). Although Formation (see Sterli 2008) are consis- crease during the Late Jurassic (Fig. 2). the cautions noted above certainly apply tent with rather warm climates; in recent Jurassic paleoclimates in Argentina, a review. 551

turtles, even cold-adapted species do not occur in areas with warm month mean temperatures below 17.5° C (Tarduno et al. 1998). d) Paleolatitudes and paleomagnetic data

Comparison of paleoclimatic conclu- sions with data on paleolatitudes from paleomagnetic studies shows a good co- rrespondence of paleoclimatic data and paleomagnetic latitudes. A paleomagnetic study in four ammonite-bearing marine sedimentary sections (Iglesia Llanos et al. 2006) shows that during the Middle and Late Jurassic, the South American conti- nent eventually attained a position similar to its present-day position (Fig. 3). But Figure 1: Location map showing the that during the Hettangian-Sinemurian position of the localities and regions the 50º S-latitude was crossing the Neu- mentioned (Río Limay region of nor- thern Patagonia, Neuquén basin, Sierra quén basin, suggesting a cold climate in de Chacai Co, Mendoza region, this basin during the earliest Early Juras- Cañadón Asfalto basin). sic (Spalletti et al. 1999, Gómez-Pérez 2003). Based on the palynofloras this shift could be correlated with the distribution of so- me Jurassic floras. The Sinemurian - Ear- ly Toarcian microflora from the Los Pa- tos Formation in the north of the basin (Volkheimer et al. 1978) and the Pliensba- chian microflora of the Sierra de Cha- caico Formation in the south (Volkhei- mer 1974, 1980) reflect the passage from a position of the Neuquén basin from 50º S to 25º S. The lower member of the Los Patos Formation (lowermost Pliens- bachian - Sinemurian) exhibits a content of Classopollis not higher than 60 % on average (at 50º S), while the Upper Mem- Figure 2: Number of species in various encystment modes and total specific diversity in the ber (Late Pliensbachian - Early Toarcian) Jurassic and earliest Cretaceous of the Neuquén basin (adapted from Quattrocchio 1986). For and Sierra de Chacaico Formation show methodology see Quattrocchio (1984). the highest percentages of Classopollis (91 in arroyo Lapa, Neuquén (Volkheimer During the Late Jurassic (and Early Cre- and up to 99 %). 1971). The arrival of the new group of taceous) a broad arid belt, whose most During the shift of the South American Araucariaceae, represented by Callialas- conspicuous feature was the Botucatú continent to the northernmost position, porites spp., in the Toarcian (Volkheimer desert, (studied by Bigarella and Sala- another important microfloral change and Quattrocchio 1981) could indicate muni 1964), extended from approxima- can be registered: The first appearance of an amelioration related to more humid tely 15º to 30º of southern paleolatitude. the Callialasporites "complex" (Araucaria- conditions. This conclusion could be ex- Evaporites of considerable thickness and ceae) is documented in the earliest Late tended to Australia, where the same pat- distribution along the Pacific margin Toarcian associated with Araucariacites tern of Classopollis and the Callialasporites complete the picture of this warmarid australis and A. pergranulatus, for example "complex" is observed (Monteil 2006). region. Only in southern Patagonia pre- 552 W. VOLKHEIMER, O. W. M. RAUHUT, M. E. QUATTROCCHIO AND M. A. MARTINEZ

vailed moist conditions, as indicated by arborescent ferns and products of ancient weathering (Volkheimer 1969, 1970a, b). The Jurassic magmatic paroxysm was the immediate predecessor of a large scale Gondwanaland disintegration (Uliana and Biddle 1988). Those basins close to the western margin of South America continued to accumulate marine deposits during the Neocomian. Large areas of the southern South American interior became depositional sites for non-marine clastic material. The Late Jurassic to Neocomian sequen- ce records active crustal stretching in areas along the present margins of the South Atlantic. By 130 Ma the first ocea- nic floor was formed in the South Atlantic (Rabinowitz and LaBrecque 1979, Gerrard and Smith 1982). Figure 3: By the end of the Triassic until the end of the Sinemurian, the studied region (Neuquén SUMMARY OF JURASSIC basin) was at its southernmost position (c. 50º S). From then on, it moved northward at about 20 PALEOCLIMATES cm yr-1 and reached its northernmost location (c. 25º S) in the Pliensbachian. Subsequently, the area moved again to the south at 10 cm yr-1 and eventually attained c. 30º S by the end of the Jurassic, which is similar to its present-day position (from Iglesia Llanos et al. 2006). a) Early Jurassic paleoclimates of hygrophile elements: bryophyte/pteri- the Cañadón Asfalto Formation is of Neuquén basin: The Sinemurian - Early dophyte spores, associated with compa- special value for paleoclimatic considera- Toarcian palynoflora from the Los Patos ratively smaller amounts of conifer pol- tions. The abundant mega- and microflo- Formation in the north of the basin and len (Zavattieri et al. 2008). ral evidence (Volkheimer et al. 2001) sug- the Pliensbachian microflora of the Sie- A fundamental feature of the climatic gest warm climatic conditions during the rra de Chacaico Formation in the south evolution of the Jurassic in the southern Middle Jurassic of this region. The Chei- of the same basin reflect the passage Andean region is the gradually increasing rolepidiaceae dominated the spectrum, from a position of the Neuquén basin at aridity during this Period. A cool climate associated with Araucariaceae. Warm and 50º S to 25º S, taking into account the is inferred for the Neuquén basin for the relatively humid climatic conditions are cheirolepidiacean pollen content, which earliest Early Jurassic, based on the gene- indicated by high percentages of the rises from 41.5 % in the lower member ral absence of carbonate deposits and a thermophilic Cheirolepidiaceae, associa- to 91 % of Classopollis in the upper mem- high siliciclastic input into the basin (Spa- ted with Araucariaceae, which need rela- ber (Volkheimer et al. 1978), indicating lletti et al. 1999, Gómez-Pérez 2003). The tively humid conditions. increasing warmth and aridity during the Middle and Late Liassic of the andean Lacustrine carbonates (marls and algal li- deposition of the Los Patos Formation. and pre-andean regions of Neuquén and mestones) are frequent in this formation. The relative abundance of the thermo- Mendoza were characterized by moist cli- They are good climatic indicators, "be- philic Classopollis (reaching 25 % as the matic conditions, as shown by the fre- cause they are restricted to generally dry maximum of the total spectrum of paly- quency of coal and well preserved fossil climates where the ground waters are not nomorphs) in the Late Toarcian Nestares floras. unduly acid" (Fairbridge 1967). However, Formation of the Río Limay region of thin coal seams found in parts of the Ca- northern Patagonia probably reflects the b) Middle Jurassic paleoclimates ñadón Asfalto sequence also indicate local environments. The presence of short periods of more humid conditions warm (-temperate) and humid conditions Central Patagonia: Cañadón Asfalto basin: In at least in the basal parts of the formation. (at least temporarily) is also compatible central Extra-Andean Patagonia the con- The conchostracans from this formation with the composition of associated paly- tinental volcano-sedimentary sequence are occurring in banded shales. As an nomorph assemblages consisting mainly of mainly siliciclastic lacustrine strata of example, fifteen or more successive sea- Jurassic paleoclimates in Argentina, a review. 553

sons are represented in a thickness of 19 Formation) were deposited. During the cm of sediment. This points to a seaso- Callovian a return to moister conditions nal sedimentation rate of 1 mm or less. occurred, probably related to a marine Other evidence, as growth bands, points ingression. In the southern part of the to wet-dry cycles in the water bodies in- Neuquén basin thin coal seams are wi- habited by the conchostracans studied by dely distributed, bearing an abundant pa- Tasch (in: Tasch and Volkheimer 1970). lynoflora with many representatives of Cabaleri et al. (2005) studied a saline pale- the hygrophile ferns (Volkheimer 1972). olake of the Cañadón Asfalto Formation A hypothetic scenario for the Middle Ju- near the village of Cerro Condor, middle rassic in the southern part of the Neu- valley of the Chubut River. Within a la- quén basin was proposed by Quattro- custrine facies association they observed cchio et al. (2001), on the basis of sedi- an extensive biohermal belt (500 m long mentary facies and palynological data ob- and 39 m thick), showing three growth- tained from the study of eight stratigra- stages of microbial communities: a core phic sections. The analysis of the terres- facies with discontinuous stromatolite la- trial palynological assemblages (102 spe- minae, formed by green filamentous al- cies of sporomorphs) shows that certain gae, interbedded with mudstone; a flank plant groups dominated the scenario, in facies (up to 22 m thick), made up by particular the Cheirolepidiaceae, Arauca- Figure 4: The South American arid belt during stratiform stromatolites with intercala- riaceae and Podocarpaceae and to a lesser the Late Jurassic (adapted from Volkheimer, tions of Magadi-type chert laminae and a degree Cyatheaceae, Osmundaceae, Ma- 1969). Paleolatitudinal position of the conti- nent during the Late Jurassic is from Iglesia top facies assemblage, consisting of thick rattiaceae, Dipteridaceae, Lycopodiaceae, Llanos et al. (2006). hemispheroidal stromatolites, interbed- Schizaeaceae, Anthocerotaceae, Riccia- ded with Magadi-type chert and affected ceae, Cycadales/Bennettitales, Caytonia- Middle Jurassic. by desiccation processes, presenting ceae and Gnetales. In addition to the The sedimentary facies and the palynolo- crack systems and caliche covers, indica- conventional approach using percentage gic assemblages of the Middle Jurassic ting arid conditions and a gradual transi- values, principal component analysis depositional sequences (García et al. tion from eulittoral to supralittoral envi- (Martínez et al. 1996) proved to be an 1994) at Sierra de Chacaico are conside- ronments (Cabaleri and Armella 2005). excellent and complementary tool, be- red, taking into account the Classopollis The biohermal belt favoured the forma- cause it reduced the data set into definite content. This genus is dominant in all the tion of the pan lake of Cañadón Carrizal. groups of representative taxa. assemblages, with increasing frequencies Cycles present a sedimentation pattern Quattrocchio et al. (2001) used modern from the offshore-prodelta deposits, to a that responds to climatic variations. The analogues, the Chilean-Argentinian fo- maximum in the stream mouth bar. This paleoenvironmental history of the lake is rest and the Planalto of southern Brazil, genus is here considered as a coastal pro- defined by a succession of five cycles to explain the paleoclimatic and paleoen- xy related to extraordinary flooding of that lead to the progressive reduction of vironmental conditions during the Mid- the delta plain. In this scenario Classopo- the water body, each cycle being shallo- dle Jurassic. In the Planalto (about 1000 llis acts as a clastic component, sensitive wer than the previous one and ending m above sea level) the Araucariaceae and to increments of the sedimentary input. with evaporites. Podocarpaceae grow together, but the Classopollis reaches up to 90 %, associated The same authors emphasize that the latter disappear with an increase of tem- with bars of the prodelta deposits. mentioned succession of different cycles perature and humidity farther north in of expansion-contraction during the evo- Brazil. The influence of acid effusives of c) Late Jurassic paleoclimates lution of the lake is a consequence of the the Serra Geral Formation conditions the tectonic history of the basin, which was low pH of the soils. In the Neuquén ba- During Kimmeridgian times, approxima- interpreted as a pull-apart structure (Silva sin, rhyolites of the Choiyoi Group (Per- tely 150 to 155 My ago, as a consequence Nieto et al. 2002), characterized by diffe- mian-Triassic) and other acid rocks of of the Araucanian Movements, the pale- rential movements of small blocks that the basement could have been the subs- ogeography and climate of South Ame- delimit horsts and grabens. tratum of the ancient Araucariaceae. Ac- rica underwent fundamental changes. A Neuquén basin: During late Bajocian times, cording to the above mentioned assess- series of marginal basins began to subsi- in a context of marine regression and ment, they proposed a plateaus scenario de near the eastern border of the conti- drying out of the basin, widespread sul- with warm to temperate conditions and nent. phatic rocks (the gypsum of the Tábanos variable precipitation rates through the Neuquén basin and related areas: The world- 554 W. VOLKHEIMER, O. W. M. RAUHUT, M. E. QUATTROCCHIO AND M. A. MARTINEZ

wide marine transgression was reflected climate proxies in general concerns the For example the income of a new group by the important marine ingression of fact that all groups represented belong to of the Araucariaceae in the Toarcian is the Tithonian sea in the Neuquén basin. extinct lineages with no close living rela- postulated to have been associated with The Tithonian Berriasian microfloras of tives, and, thus, their climatic preferences moist conditions. the Neuquén basin are very similar and and necessities remain speculative (see There is also an increasing need to un- correspond to the Equisetosporites -Trisac- Ostrom 1970). This is especially true for derstand the taphonomic processes that cites Assemblage (Volkheimer and Pöthe groups such as ichthyosaurs or plesio- act upon the palynomorphs, in order to de Baldis 1982). The only difference bet- saurs, which do not have any living rela- obtain accurate paleoclimatic and paleo- ween Tithonian - Berriasian microfloras tives, and for the dinosaurs, the living environmental interpretations. is the lower diversity of the later (Vol- representatives of which (the birds) are kheimer 1980, Quattrocchio et al. 2003). highly specialized physiologically. Al- ACKNOWLEDGEMENTS The sporomorph assemblages show mar- though also not unproblematic, other ked change only at the Berriasian/Valan- groups that have more similar living rela- We wish to acknowledge the Consejo ginian boundary, by the appearance of tives, such as anurans, turtles, and croco- Nacional de Investigaciones Científicas y the conspicuous and abundant Cycluspha- diles might help to interpret general as- Técnicas (CONICET) for economic era psilata (Riccardi et al. 1990). pects of Jurassic climates, although cau- support (PIP 5222 and PIP 5297); IANI- A large region of southern South Ame- tion is advisable in interpreting their im- GLA-CCT-CONICET-Mendoza for rica was subject to extremely arid condi- plications. Thus, abundant marine croco- laboratory facilities, to the Secretaría tions during the Late Jurassic (Fig. 4) and diles in the Middle and Late Jurassic of General de Ciencia y Tecnología de la parts of the Early Cretaceous. In the the Neuquén basin indicate warm water Universidad Nacional del Sur (SEGCyT), Chaco-Paraná basin a large paleodesert, temperatures in this basin, and the pre- Bahía Blanca, for economic support, to documented by eolian sandstones, exten- sence of turtles and other ectothermic Drs. E. Schrank and Z. Gasparini for ma- ded from Minas Gerais (Brazil) to Uru- vertebrates, such as frogs, in the Cañadón ny useful comments and corrections and guay (Bigarella and Salamuni 1964) and Asfalto Formation of Chubut also indi- to Lic. Paula Narváez for correction of central Argentina (Padula and Min- cate a rather warm climate for this unit. the manuscript. gramm 1968, Volkheimer 1967). The pa- In both cases, these interpretations are in leoclimatic scenario of an extremely arid agreement with other lines of evidence, WORKS CITED IN THE TEXT region was complemented by thick gyp- both geologic and palaeontologic, so that sum and anhydrite deposits of Late the vertebrates seem to reliably reflect Alvin, K.L. 1982. Cheirolepidaceae: biology, Oxfordian age, which extended from the climatic conditions. structure and paleoecology. Review of Pa- Zapala (Neuquén Province, Auquinco 2) Beside the thermophilic character pre- laeobotany and Palynology 37: 71-98. Formation) to Mendoza and San Juan viously postulated for the Cheirolepidia- Alvin, K.L. 1983. Reconstruction of a Lower provinces and continued to southern ceae, dominant in almost all the palyno- Cretaceous conifer. Botanical Journal of the Perú. Again marine regression (increa- logical assemblages through the Jurassic, Linnaean Society 86: 169-176. sing continentality) was accompanied by it is important to analyze the facies in Báez, A.M. and Nicoli, L. 2008. A new species of an increase of aridity. which these pollen grains occur. For Notobatrachus (Amphibia, Salienta) from the Biohermal limestones of Middle Oxfor- example, in marine deposits of the Mid- Middle Jurassic of northwestern Patagonia. dian age (La Manga Formation, Neuquén dle Jurassic (Neuquén basin) they show Journal of Paleontology 82 (2): 372-376. basin) indicate warm and shallow oceanic increasing frequencies from the offsho- Batten, D.J. 1975. Wealden palaeoecology from waters in large areas of this basin. re-prodelta deposits, to a maximum in the distribution of plant fossils. Proceedings the stream mouth bar. Principally they of Geologists' Association 85 (for 1974): 433- CONCLUSIONS are considered as a coastal proxy related 458. to extraordinary flooding of the delta Batten, D.J. 1984. Palynology, climate and the 1) The use of vertebrates as paleoclima- plain. In this case Classopollis acts as a development of Late Cretaceous floral pro- tic proxies in the Jurassic of Argentina is clastic component, sensitive to incre- vinces in the Northern Hemisphere; a review. currently severely restricted. One reason ments of the sedimentary input. Classo- Fossils and Climate: 127-163. for this is the very patchy Jurassic record pollis reaches up to 90 % associated with Bigarella, J.J. and Salamuni, R. 1964. Paleowind of especially terrestrial vertebrates in bars of the prodelta deposits. Patterns in the Botucatú Sandstone (Triassic- Argentina, with the only good fauna For paleoclimatic inferences it is impor- Jurassic) of Brazil and Uruguay. 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