The neogene succession cropping out betwen Peña s Azules and Ovejería Chica zones in Cajón Valley, Catamarca.

Acta geológica lilloana 21 (2): 2009

Abstract

This work describes the stratigraphic detailed profile of Peñas Azules-Ovejería Chica that involves all the Miocene-Pliocene succession and it is framed in the research that analyzes evidences of possible biogenic origin of the calcretes. This sedimentary succession crops out at Cajón Valley in discordance over the Quilmes range peneplain. It is divided in three alloformations which have discordant contacts to each other. Peñas Azules Aloformation (Sequence I), 288 meters, is characterized by fine and middle brown sandstones, with tuff paraclasts and some thin conglomeradic levels. The paleocurrent direction is to NE. It owns its name to the blue colour prese nt at the upper of the deposits. Playa del Zorro Alloformation (sequence II), 927.3 meters, is constituted by fine and middle calcretized sandstones, with bioturbation, ryzhoconcretions and it is alternating with conglomeradic and coarse sandstones levels. There are some very thin (decimeters) tuff layers. Fluvial paleochannels were also observed. The paleocurrent direction is to SE. Totoral Alloformation (Sequence III), 174.75 meters, presents conglomeradic levels at the base with many volcanic clasts. Toward the top of the succession, the sandstones are finner and the disperse clasts are principly metamorphic and granitic composition. The paleocurrent direction is to NE.