Geología y bioestratigrafía del límite Mio-Plioceno en el sur de la Región Pampeana: la cuenca del Quequén Salado como caso de estudio

BEILINSON, ELISA; GASPARINI, GERMÁN; TOMASSINI, RODRIGO; ZÁRATE, MARCELO; DESCHAMPS, CECILIA; RABASSA, JORGE

San Miguel de Tucumán

Congreso; XX Congreso Geológico Argentino; 2017

Universidad Nacional de Tucumán

The geological history of the deposits exposed in the Quequén Salado River valley (QS), is reconstructed on the basis of stratigraphic, sedimentologic and paleomagnetic analyses, as well as the study of the fossil vertebrates. This is a crucial area for the understanding of the evolution of the Pampean Region during the late Miocene-early Pliocene interval, and to test the validity of the biochronologic and biostratigraphic schemes, especially the "Irenense". A geological model is proposed: a case of headward erosion that explains the spatial distribution of facies and fossils, being the youngest in the distal sector of de middle basin and the oldest in the lower basin. The sedimentary record represents the distal end of a distributary fluvial system draining from the Ventania ranges. The Paso del Indio Rico section is key to understand the stratigraphic meaning of the Miocene-Pliocene boundary (the Huayquerian and Montehermosan stages/ages). In this sense, two biozones stratigraphically overlapping were recognized: the Xenodontomys ellipticus Range Zone (late Miocene-early Pliocene; late Huayquerian), and the Eumysops laeviplicatus Range Zone (early Pliocene; Montehermosan). Geologic and paleontologic evidence reject the validity of the "Irenense" as a biostratigraphic unit because according to the proposed geologic model, it would be represented by the Xenodontomys ellipticus Range Zone in the lower basin of the QS and by elements of the Eumysops laeviplicatus Range Zone in the middle basin.