LOS MAMIFEROS DE LA FAUNA LOCAL PASO OTERO (PLEISTOCENO TARDIO), PROVINCIA DE BUENOS AIRES. ASPECTOS PALEOAMBIENTALES y BIOESTRATIGRAFICOS

José L. Prado, Adriana N. Menegaz, Eduardo P. Tonni, Mónica C. Salemne

Abstract


This study deals with the characterization, palaeoenviromental interpretation and chronostratigraphic assignation of the mammals association from Paso Otero Local Fauna. This Local Fauna was found in continental sediments exposed along the banks of the river Quequén Grande, Necochea County (Buenos Aires Province) at lato 38°34' S. and long. 58°42' W. From the zoogeographic point of view, this area belongs to the Guayano-Brazilian Region, Pampean Dominion and it is phytogeographically located within the Chaquean Dominion, Pampean Province. The carrying sediments correspond to an ancient flood plain. They constitute the Guerrero Member of The Luján Fm. In this unit are identified two sectors: a) lower ""reddish-brown"", and b) upper ""green''; both have been characterized from the geological and faunistic points of view. The faunal assemblage is interpreted as a thanatocenosis whose individuals formed a relatively contemporaneous association, corresponding to the same environment. This
association is characterized by a great variety of herbivores, mainly grazing forms of open areas. There are several dominants species among the marnmals of the Paso Otero Local Fauna: Equus (Amerhippus), Lama guanicoe, Lama morphotype similar to Lama vicugna, Cervidae (morphotype ""a"" and ""b""), Macrauchenia patachonica and Toxodon platensis. They compose a typical association of the Lujanian Land-Marnmal Unit. The following hypothesis are formulated: Hl: Paso Otero Local Fauna is referable to the last part of the Late Pleistocene. It corresponds to the Lujanian Land Mammal Unit in the Pampean Region. H2: the faunistic differences between the ""reddish-brown"" and ""green"" sectors of the Guerrero Member of the Luján Formation evidence an ecological succesion corresponding to an environmental deterioration. H3: during the sedimentary deposition of the Guerrero Member of the Lujan Formation, the environmental conditions were arid or semiarid. The aridity increased from bottom to top of this unit. H4: mean temperatures lower than the present ones, or at least, biologically-useless winter mean temperatures (lower than 10°C) were verified at the end of the Late Pleistocene in the Pampean Region.

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