Near-surface salt canopies play an important dual role in the northern Gulf of Mexico. When salt canopies inflate, they create bathymetric highs that divert sediment-carrying bottom currents at their flanks while creating sediment-starved habitats at their crests. Conversely, when canopies deflate beneath prograding slope sediments, displacement of the mobile salt accommodates large volumes of sediment in growth-faulted intraslope basins. These contrasting roles are manifest biostratigraphically both regionally, as large sequential changes in patterns of mapped accumulation rates, i.e., abnormally low rates succeeded by abnormally high rates, and locally, in individual wells, as changes from “stacked” or super-condensed section to expanded section. The latter is indicated in biostratigraphic data by unusual occurrences of index taxa, such as: (1) Miocene to Eocene taxa in younger section; (2) close succession of index taxa in high abundance zones within super-condensed sections, especially overlying younger expanded section; (3) reoccurrence of short-ranging (younger) taxa beneath older markers; (4) substantial reversals in total assemblage age, e.g., middle Miocene section overlying Plio-Pleistocene; (5) mixed, “jumbled” occurrences of index taxa; (6) intercalated stratigraphic “slices,” out-of-order, but internally consistent. These various observations are consistent with: (1) age limits of fossils from in-salt inclusions; (2) salt-rafted suprasalt super-condensed sections; (3) the tendency of displaced salt to override intraslope basin-fills; (4) minor age inversions related to repeat section associated with high-angle reverse faulting; and, (5) multiple or major age inversions, associated with imbricate thrust sheets and horizontal salt welds associated with extensive low-angle overthrusts.
SEPM/NAMS/AAPG: Biostratigraphic and Paleoenvironmental Analyses in Deep-Water Settings