ABSTRACT

A backstripping analysis of the Shell Main Pass 154 well offshore Mississippi-Alabama provides new insights into the post-middle Jurassic subsidence and depositional history of the northeastern Gulf of Mexico. The analysis was carried out using paleontological and lithological data provided by Shell Offshore Inc. tied to a sequence stratigraphic framework developed for the area. Paleobathymetry estimates were made by combining the well data with a seismic stratigraphic analysis and data from previous studies. The result is a tectonic subsidence curve that differs somewhat from a previously published curve for the same well. Subsidence during the Jurassic-earliest Cretaceous rifting and seafloor spreading phases of Gulf evolution follows a normal passive margin tectonic subsidence curve. Post-seafloor spreading subsidence rates increased during the late-Early Cretaceous, which corresponds to a Gulf-wide buildup of thick carbonate platforms that rimmed the entire Gulf of Mexico basin. This event can not be correlated with any regional tectonic event. Continued thermal subsidence during the Late Cretaceous to early Tertiary contributed to creating bathyal environments with water depths of ~800-1200 meters, which persisted into Early Miocene times. An anomalous uplift of the area is reflected in the curve from Eocene to Early Miocene, which can not easily be explained but could be due to regional Laramide stresses or deep salt movement. Latest Cenozoic subsidence could be due to deep salt withdrawal and/or flexural loading by an adjacent thick Plio-Pleistocene depocenter.