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

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

Rio Grande do Sul

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 thepreservation pattern of molluscan assemblages. Although dominant species show differentmagnitude of damage, they still show similar trends in preservation along environmentalgradients. Moreover, differences in relative abundances do not bias the taphonomic profile ofthe defined taphofacies, probably favoured by high rates of cementation. Therefore, howmuch does relative abundance contribute to the definition of taphofacies in siliciclasticenvironments? The San Matías Gulf (SMG, Patagonia Argentina) is an ideal study area fortesting due to the dynamic mosaic of environments that were recorded throughout the LateQuaternary by molluscan assemblages. Those assemblages are dominated by one species ofbivalve, Amiantis purpurata; and based on its damage profile and the presence of certainmolluscan fauna was possible to identify different taphofacies. In this study, we found that thepreservation pattern of the dominant species, A. purpurata, is correlated to the second mostabundant species, Glycymeris longior, both showing different gradients in preservation.However, the accompanying fauna showed no correlation with. A. purpurata, they exhibitedpristine preservation. This mollusc fauna, with very low abundance, was possible to bestudied because of their good preservation which allowed to identify species ?characters. Thatgives us a clue that rare or exceptional fauna can be found because of their good or pristinepreservation, and therefore, show a different pattern concerning the most abundant species.However, their very low abundance do not affect the taphonomic signal of the assemblagebecause it is defined by the very abundant species. On the other hand, Late Pleistocene andHolocene assemblages were possible to be discriminated in terms of the quality ofpreservation in internal glossiness, where late Pleistocene assemblages are affected bydiagenetic processes. Finally, the most dominant species are the ones that worth to beanalyzed and will define taphofacies in assemblages dominated by one or two species.