THE TAPHONOMIC BAHAMIAN STORY: UNVEILING THE CONSEQUENCES OF SPECIES ABUNDANCE ON TAPHOFACIES IN SAN SALVADOR ISLAND

MARÍA SOL BAYER; DIEGO BALSEIRO; DIEGO FERNANDO MUÑOZ; SANDRA GORDILLO

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

International Palaeontological Association

Several contributions have underscored the importance of how intrinsic variations affect the final taphonomic attributes of shell deposits. Other studies have shown that the composition of shell supply only affects the intensity of each attribute but not its actual ranking. Although these are promising results for taphofacies analysis, we still cannot confidently asses that taphofacies are free from biological biases. If species with different taphonomic responses differ dramatically in their abundances among rather similar environments, contrasting taphofacies could be identified for the same environment without reflecting real differences. In this contribution we study how intrinsic differences influence the definition of taphofacies in San Salvador Island. For this goal we studied (1) intrinsic differences between species in the ranking and intensity of taphonomic attributes, and (2) the effect that differences in species relative abundances bear upon the definition of taphofacies. Seven beaches were sampled around the island based on their geographical position with respect to the wind trades (windward or leeward), their environmental features based on the presence or absence of rock patches (sandy or rocky beaches) and beach zones (three equidistant samples from the maximum level of spring tides to the minimum level of the normal tide, and samples from the subtidal zone). We studied taphonomic attributes (fragmentation, abrasion, teeth preservation, muscle scars, color, external glossy, external cementation, internal glossy, internal cementation and biological incrustation) in the four most abundant bivalve species, and calculated their relative abundance. Using multivariate analysis, two taphofacies were recognized among geographical location and two between beach types, but none between beach zones. Intrinsic differences in the intensity of taphonomic attributes were commonly observed withing taphofacies, while differences in the ranking of taphonomic variables were seldom observed between taphofacies. To further test whether taxa's relative abundance influenced the definition of taphofacies, we tested the correlation between samples' taphonomic response taking and not taking into account the taxa's abundance. A mantel test indicated that both were significantly correlated. Differences in taxa's abundance couple to intrinsic variation seem to have little effect on the whole sample taphonomic signature. Therefore, two scenarios appear to be possible, either (1) intrinsic differences among taxa, or (2) differences in their relative abundances, were not strong enough to bias the taphonomical signature of the samples. However, because taphonomic signatures based on each single taxon are also correlated between all four taxa, the first scenario seems to be the most probable one.