TAPHONOMIC VARIATION AMONG CARBONATE AND SILICICLASTIC DEPOSITIONAL ENVIRONMENTS IN THE NORTHERN GULF OF MEXICO

Understanding the taphonomic processes affecting organic remains can enrich our understanding of potential biases in the deep time fossil record. These biases may also alter paleoecological interpretations of younger material, including Holocene records increasingly used by conservation paleobiologists to guide ecological management and restoration efforts. For this study we compared the taphonomic characteristics of molluscan death assemblages from across the northern Gulf of Mexico. Our transect spans inner shelf environments from Louisiana to Florida and represents both a sediment and nutrient gradient. Relatively high rates of siliciclastic sedimentation and nutrient enrichment characterize coastal Louisiana and Alabama. In contrast, lower rates of predominantly carbonate sedimentation and lower nutrient levels characterize the panhandle of Florida and the west Florida shelf offshore Tampa. Molluscan shell material was scored for size, thickness, articulation, fragmentation, edge modification, encrustation, internal and external luster, bioerosion, and dissolution. All bioclasts larger than 2 mm, including both fragmentary and whole shells, were scored. There were higher levels of certain damage types, such as encrustation, bioerosion, dissolution, and loss of luster, in the carbonate-dominant settings of Florida versus the siliciclastic settings of Louisiana and Alabama. Disarticulation, fragmentation, and edge modification were consistently high across all sites and did not vary with substrate type. Although some taphonomic variables (e.g. encrustation) showed a significant positive correlation with bioclast size, most did not. The taphonomic differences that we observed are consistent with studies conducted previously at lower latitudes, which found lower quality shell preservation in carbonate versus siliciclastic environments (Best & Kidwell 2000). Our results indicate that taphonomic processes vary between these broad-scale depositional settings, which may reflect differences in bioclast residence time, sedimentation rates, time averaging, pore water chemistry, species life habit, and/or human activities. The taphonomic biases introduced as a result of these environmental differences should be taken into consideration when making paleoecological interpretations.