Update of the paleofaunistic and paleofloristic diversity of La Cantera Formation (Early Cretaceous, San Luis): a lacustrine environment in central Argentina

ARCUCCI, A.; RIVAROLA, D.; PRAMPARO, M.B.; PETRULEVICIUS, J.; CODORNIU, L.; SALLENAVE, A.S.; PUEBA, G.G.

Mendoza

Congreso; GONDWANA 12"Geological and Biological Heritage of Gondwana"; 2005

Academia Nacional de Ciencias, CONICET, ANPCYT, Asoc.Geologica Argentina

La Cantera Formation (Del Gigante Group, San Luis Basin) crops out in a restricted area on the eastern side of the southern tip of Sierra del Gigante, in the northwest of San Luis Province. It is composed by green-grey siltstone and claystone, laminatede with red-brown sandstone and grey claystone interbedded at the top, having a measured thickness of 31 meters at its type locality. The prevailing sedimentary palaeoenvironments are of lacustrine type associated to ephemeral fluvial deposits. Althought the presence of fossil material in this Formation was previously known (se complete list in Arcucci et al. 2002, p.120), a systematic collection has been done in the area by our team in order to characterize the biotic aspects of the ancient lake to determine an accurate palaeoenvironmental model of this kind of continental basins. An important number and variety of fossil remains were collected, including palynomorphs, plants, arthropods, and fishes. La Cantera Formation has provided an imporetant palynofloristic assemblage studied by Prámparo (1990;1994). The presence of primitive anguiosperms with very distinctive morphologies and affinities (mainly Afropollis) allowed considering the studied microflora as transitional between the Northern Gondwana (Dicheiropollis etruscus/Afropolllis) and Southern Gondwana (Trisaccites) cretaceous palynofloral provinces, and assigning La Cantera Formation to the Late Aptian reaching probably the EArly Albian. It is remarkable that this Formation also yields diverse and relatively well preserved plant microfossils which consist of at least three angiosperm morphotypes (leaves and reproductive structures) and numerous remains (mainly stems) of Sphenophyta (Equisetaleans). Insects were found in high numbers. Most of them are Heteroptera, represented by new species of the aquatic ambush predator taxon Notonectidae. These specimens are considered to be exuviae of different nymph instars of Notonectinae and Anisopinae. Specimens of both taxa seem to live together as modern representatives (Petrolevicius et al., 2005). Other insects as Orthoptera, Coleoptera, Diptera and Trichoptera caddis are less abundant. Ostracods are abundant and concentrated in some levels. Fishes are also very abundant, and are preserved mostly articulated. The preliminary results showed that they are represented by basal actinopterygians and neopterygians. Among the actinopterygians, a probable coccolepid and a non-acipenseriform chondrostrean were identified. Among the actinopterygians, at least three species are present, probably closely related to basal telepsteans and pholidophoriforms (Arcucci et al., 2002) Arcucci, A., Rivarola, D., Codorniu, L., Sallenave, A.S. and Puebla, G. G., 2002. Diversidad de la asociación biótica en el paleoambiente lacustre de la Formacion La Cantera (Aptiano) de San Luis, Argentina. 2do Simposio sobre el cretacico de América del Sur, San Pablo, Brasil. Actas: 119-122.