Abstract

STERREN, Andrea F.. Carboniferous and lower Permian shell beds in Precordillera Argentina: Temporal variations and relationships with the trends proposed for the Fanerozoic. Ameghiniana [online]. 2008, vol.45, n.2, pp.303-320. ISSN 1851-8044.

Taphonomic and biodiversity studies of Carboniferous and Permian shell beds recorded in several sections from the Río Blanco-Paganzo and Calingasta- Uspallata basins are carried out. Two parameters of bioclastic accumulations are analyzed: taxonomic composition and thickness. The analysis of the taxonomic composition revealed that molluscan-dominated concentrations predominate in both periods, being rhynchonelliform-dominated ones more abundant during the Carboniferous than during the Early Permian. The distribution of thickness ranges exhibits a relative increase through the studied interval, reaching a maximum of 30 cm. Studied bioclastic deposits, are relatively thin and are composed of distinctive elements of the Modern Fauna; hence they could be included in a "mixed" style. On taxonomic grounds the transition between styles appeared to take place toward the ending of the Paleozoic, and might have been driven by a biotic factor related to the relatively early diversification of infaunal bivalves. The increase in thickness documented in the studied interval is the result of the sedimentary dynamics in different areas of the basins. Patterns of biodiversity among mollusks and brachiopods show significantly higher levels of richness in the Permian than in the Carboniferous, a feature that is also evident in the composition of fossiliferous concentrations. The superposition of styles herein documented suggests that the Neopaleozoic is a key interval to test the local expressions of global models.

Keywords : Shell beds; Taphonomy; Temporal trends; Carboniferous-Early Permian; Argentine Precordillera.