VARIATION IN TAPHONOMIC SIGNATURES BETWEEN BIOFACIES AND SYSTEMS TRACTS: IMPLICATIONS FOR ORDOVICIAN BIODIVERSITY ESTIMATES (Invited Presentation)

Modern taphofacies analysis often focuses on the loss of information and biases that are produced by local environmental conditions at the time of deposition. The integration of taphonomic signals with sequence stratigraphic architecture at a macroscale could play an important role in understanding the dynamics of GOBE-related biodiversification estimates. Multivariate similarity analyses were used to assess sample sites in the Ordovician Bromide Formation, based on taphonomic signature, lithofacies, and inferred sequence regime (TST vs HST). Previous biofacies and diversity analyses on Bromide Formation trilobites have shown that in most biofacies, rarefied alpha diversity and gamma diversity of middle and outer ramp HST deposits are greater than in the TSTs, with biofacies replacement occurring in a downramp direction. Diversity patterns do not agree with model predictions and other data sets that indicate low beta and high alpha diversity in the TST, likely because of taphonomic degradation. We tested the degree of taphonomic degradation using trilobite-specific taphonomic variables, including sorting, fragmentation, encrustation, and sclerite size ratios. The results of the multivariate analyses suggest that samples within the TST are characterized by abrasion and fragmentation, and during early HST conditions, well-articulated trilobite exoskeletons preserved by obrution deposits are lightly imprinted by taphonomic processes. These data show that large-scale changes in sea level can influence alpha, beta, and gamma diversity profiles, necessitating sequence stratigraphic control to test hypotheses related to GOBE diversification sources, dispersal between paleocontinents, and concurrent pules of dispersal with large-scale transgressions.