Taphonomic comparison between two fossiliferous concentrations (shell beds) from the Coastal Plain of Rio Grande do Sul State, Brazil

Abstract

Taphonomic features on fossils accumulations are the result of the depositional context in which the remains were preserved. Under this focus, two places characterized by the occurrence of shell beds in the southern coastal plain of Rio Grande do Sul State were tested. One of them, known as “concheiros”, is located at the present coastline, and the other, called “Passo da Lagoa”, is exposed near 6 km landwards and in levels 4 m high, separated from “concheiros” by a coastal lake and a sandy barrier formed in the Holocene. The fossil material was analyzed and compared regarding its physical integrity, abrasion, bioerosion, dissolution and taxonomic composition, including the ichnofossils involved in the bioerosional activity. The taphonomic similarities suggested common hidrodynamic process and beach environments to their genesis and their relation with the transgressive events that marks the end of Pleistocene and the beginning of Holocene in the area. The study is the first contribution to taphonomic analyses to those deposits, characteristics of Rio Grande do Sul southern coastal plain.

Key words: taphonomy, taphofacies, shell beds, bioerosion, Entobia ichnofacies, coastal plain of Rio Grande do Sul State.