Jurassic lacustrine and palustrine environments in Argentina: a review.

VOLKHEIMER, W.; QUATTROCCHIO, M.E.; CABALERI, N.G.; NARVÁEZ, P.L; SCAFATI, L.; MELENDI, D.L.

Konstanz

Congreso; 5th International Limnogeological Congress; 2011

The International Association of Limnogeology

We compare and correlate Jurassic continental palynobiotas of southern and central-western Argentina, to review their environmental and climatic significance and to characterize some time-slices through paleoclimatic multi-proxy mapping, considering lithogenetic, isotopic, palynologic, megafloristic,  invertebrate and vertebrate paleodata. The differences between both areas could be related with the sheere size of the Gondwana  supercontinent configuration (as expressed by Parrish). In general, the continental interior (Cañadón Asfalto Basin) would be expected to have been dry, with strongly seasonally distributed temperatures, while the western coast of the continent, during the marine transgressions in the Neuquén Basin, would be expected to have been moist. In central Patagonia, early in the Middle Jurassic, and associated with a magmatic arc, after deposition of the volcano-sedimentary Lonco Trapial Formation, began the sedimentary filling of Jurassic continental depocenters in the Cañadón Asfalto Rift Basin (named Cerro Cóndor, Llanquetruz and Fossati). Lacustrine and fluvio-deltaic sediments, bearing a continental Middle Jurassic palynobiota, filled the Cerro Cóndor depocenter, while a Late Jurassic palustrine palynobiota characterized  the Fossati  deopocenter. Also, continental and coastal palynomorph assemblages of the back arc Neuquén Basin were considered: a Callovian deltaic swamp palynoflora at Sierra de Chacaico, Callovian continental coastal siltites at Arroyo Picún Leufú locality and a Late Oxfordian coastal saltmarsh palynobiota north of Zapala (Neuquén province). Palynostratigraphic, palynofacial and statistic studies show tendencies in diversity at the species level and in suprageneric groups. A Late Jurassic (Late Oxfordian) time-slice is specially surprising, due to the large regional extension of  lithogenetic climatic proxies, which indicate extreme aridity: the thick gypsum and anhydrite deposits of the evaporitic coastal Auquilco Formation, which extend from the southern end of the Sierra de la Vaca Muerta (Neuquén Province) in the south, through western Mendoza and San Juan provinces, crossing to Chile and southern Perú. These evaporites correlate to extended deposits of eolian sandstones on the eastern side of the continent. The eolianites are present between Minas Gerais (Brazil), at the northern end of the Paraná Basin, and the Chaco-Paraná Basin of northeastern and central Argentina. They represent the enormous Botucatú paleodesert and are the register of the largest paleodesert known  in the geologic history. Towards the south, in central Patagonia, their time equivalents are palustrine wetland environments with  locally hydrophile palynologic assemblages (trilete spores) of ferns and bryophytes and in some cases with dominance (>80%) of planctonic coccal green freshwater algae (Botryococcus spp.). The presence of Classopollis spp. and Ephedripites sp. indicates a macroenvironment with a certain degree of aridity.