Geochemical environments of continental shelf-upper slope sediments in the northern Gulf of Mexico

Geochemical environments were characterized for 14 sites along the northern Gulf of Mexico continental shelf and upper slope, in an effort to examine the relationship between sediment geochemistry and carbonate shell taphonomy in a long-term study—Shelf and Slope Experimental Taphonomy Initiative (SSETI). Three groups of environments of preservation (seep, near-seep, and shelf-and-slope) were identified based on their geochemical characteristics (i.e., oxygen uptake rate and penetration depth, pore-water saturation states, and carbonate dissolution fluxes). Diffusive oxygen uptake rate increased in the order of shelf-and-slope, near-seep, and seep, although carbonate dissolution flux did not show significant correlation with O2 flux, presumably due to non-diffusive behavior at some sites. Using pore-water saturation indices with respect to aragonite and calcite and sedimentation rates, we defined a semi-quantitative parameter, carbonate dissolution index (CDI), to predict carbonate preservation potential during the taphonomic processes. Our limited database suggests that both the seep and the shelf-and-slope sediments may have higher carbonate preservation potential than the near-seep sediments.

► We examined sediment geochemistry in the northern Gulf of Mexico shelf & slope area.
► Depositional environments are categorized following sediment geochemistry.
► Compressed undersaturation window was observed in petroleum seep sediments.
► We proposed a concept—carbonate dissolution index for taphonomy studies.