WHERE AMIANTIS PURPURATA RULES, THE OTHERS HAVE NO SWAY: TAPHOFACIES DEFINED BY THE PRESERVATION PROFILE OF THE DOMINANT SPECIES

BAYER, M. SOL; BALSEIRO, DIEGO; MUÑOZ, DIEGO F.

Imbé

Workshop; 2nd Workshop on Actualistic Taphonomy; 2021

Centro de Estudos Costeiros, Limnológicos e Marinhos, CECLIMAR, UFRGS Litoral Norte

We are aware that in modern tropical carbonate environments taphofacies are defined by the preservation pattern of molluscan assemblages. Although dominant species show different magnitude of damage, they still show similar trends in preservation along environmental gradients. Moreover, differences in relative abundances do not bias the taphonomic profile of the defined taphofacies, probably favoured by high rates of cementation. Therefore, how much does relative abundance contribute to the definition of taphofacies in siliciclastic environments? The San Matías Gulf (SMG, Patagonia Argentina) is an ideal study area for testing due to the dynamic mosaic of environments that were recorded throughout the Late Quaternary by molluscan assemblages. Those assemblages are dominated by one species of bivalve, Amiantis purpurata; and based on its damage profile and the presence of certain molluscan fauna was possible to identify different taphofacies. In this study, we found that the preservation pattern of the dominant species, A. purpurata, is correlated to the second most abundant species, Glycymeris longior, both showing different gradients in preservation. However, the accompanying fauna showed no correlation with. A. purpurata, they exhibited pristine preservation. This mollusc fauna, with very low abundance, was possible to be studied because of their good preservation which allowed to identify species ?characters. That gives us a clue that rare or exceptional fauna can be found because of their good or pristine preservation, and therefore, show a different pattern concerning the most abundant species. However, their very low abundance do not affect the taphonomic signal of the assemblage because it is defined by the very abundant species. On the other hand, Late Pleistocene and Holocene assemblages were possible to be discriminated in terms of the quality of preservation in internal glossiness, where late Pleistocene assemblages are affected by diagenetic processes. Finally, the most dominant species are the ones that worth to be analyzed and will define taphofacies in assemblages dominated by one or two species.Financial support for this study was provided by Agencia Nacional de Promocion Cientifica y Tecnologica (ANPCyT-FONCyT) PICT 2016-2951 awarded to S. Bayer. This is a contribution to PUE 2016 (CICTERRA ? CONICET).