Stratigraphy and paleontology of the middle sector of Rio Quinto Basin (Miocene-Pleistocene), San Luis, Argentina

Acta Geológica Lilloana 25(1-2)2013

Abstract

The hidrogeologic Rio Quinto basin originates in the south of the San Luis Ranges and forms the northern edge of the Mercedes basin whose sedimentary succession corresponds to Meso-Cenozoic. Eolian and alluvial-eolian Holocene deposits broadly cover the region, so the best strati- graphic records correspond to the Quinto riverbed and streams linked to it. The Neogene basal clastic calcareous sequence is identified as Paso de las Carretas Formation, without fossil remains and underlies the conspicuous clastic succession of Río Quinto Formation, which corresponds to plains deposits with permanent streams, developing extended floodplains. This formation presents a rich fossiliferous assemblage consisting of No- toungulata, Rodentia, Cingulata, Litopterna and Xenarthra, involving Huayquerian, Monteher- mosan and Chapadmalalan stages/ages. Through an important hiatus in the lower Pleistocene, linked with climatic conditions relat- ed to the Last Glacial Maximum and Late Glacial Pleistocene, were deposited Fraga, Alto Grande and Barranquita formations. The first two, of an intermittent river and isolated records of fossil megafauna (Tardigrada, Proboscidea), whereas, Barranquita Formation over- fill the sequence with fine eolian deposits.