BRAQUIÓPODOS CARBONÍFEROS EN LA SIERRA DEL TONTAL, PROVINCIA DE SAN JUAN, ARGENTINA

Abstract

The brachiopods from Casa de Piedra Formation are presented in this paper. This formation outcrops on top of the Tontal mountain range 20 km east of Hilario, Calingasta county, San Juan province. These are glacimarine deposits due to a progressive marine regression and consecutive regressive and transgressive events, which end in a stromatolitic structure, coquina and limestone deposits. We were able to locate five fossiliferous levels occurring along aproximately 400 m of thickness. The fossils are: Productella sp.,Aseptella ? sp. and undetermined gastropods and bivalves in level n° 1; Cancrinella ? sp., gastropods and bivalve coquinas in levels n" 2 and n" 3; several species of bivalves in level n° 4, and undetermined spiripherides and Septosyringothyris aff. S. saltensis Lech in level n° 5. The age of Casa de Piedra Formation may span early and late Carboniferous. The level in which Productella sp. occurs is the latest of the early Carboniferous, and the level with Cancrinella ? sp. and Septosyringothyris aff. S. saltensis is late Carboniferous. As for the palaeogeographicallocation of Casa de Piedra Formation, we conc1ude that during great part of the Carboniferous a positi ve orographic element ("Protoprecordillera") limiting the ingression of the sea towards the Paganzo Basin did not exist.