TAPHONOMY ON THE CONTINENTAL SHELF AND SLOPE: EIGHT-YEAR TRENDS—GULF OF MEXICO AND BAHAMAS

In 1993-1994, SSETI (Shelf and Slope Experimental Taphonomy Initiative) deployed skeletal remains in a range of environments of deposition (EODs) over a range of depths and sediment types. Eight years later, in 1999-2001, SSETI retrieved skeletal remains from 41 locations on the Bahamas and Gulf of Mexico continental shelf and slope. Across all sites and species, the dominant taphonomic process was discoloration. Dissolution was of penultimate importance but the cumulative impact over 8 yr was insufficient to produce a significant loss in shell weight in any EOD. Maximum dissolution intensity was normally observed on the outer shell surface; the inner and outer shell surfaces are inherently different in their time course of shell deterioration. Most taphonomic processes operated independently. Dissolution could be decomposed into independent components discriminating pitting from the development of a chalky surface.

Discoloration dissembled into five distinct processes: fading without discoloration, and discoloration to brown-to-red, orange/orange-mottled, green/green-mottled, and gray-to-black. Taphonomic signature after 8 yr was nearly exclusively a function of deployment location but EOD-level characteristics were insufficiently discriminative to delineate environments of preservation (EOP); hence our use of the acronym EOP. Depth did not exert a single significant effect on any taphonomic factor, likely because burial has taken some shallow-water arrays out of the photic zone. Trends in taphonomic signature cannot be explained by any simple combination of sediment type and degree of exposure. The discrepancy between expectation gleaned from visual observation of sediment type and biotic regime and the reality of definitive dissimilarity in taphonomic signature suggests that EOPs and EODs are not synonymous concepts. Certainly, although the desire to relate taphofacies to EOD is understandably important, the details of this conflation are still illusory.