Abstract: Subsurface Controls on Seafloor Vent/Seep-Related Geology, Deepwater Gulf of Mexico: Initial Results

ROBERTS, HARRY H.
Coastal Studies Institute, Louisiana State University Baton Rouge, LA 70803;
PAUL WEIMER and MARK G. ROWAN
Department of Geological Sciences, University of Colorado, Boulder, CO 80309

Within the deepwater Gulf of Mexico hydrocarbon province, improved seismic acquisition and processing have provided new comprehensive data sets for defining relationships between sediments, salt, and faulting. Sequential restoration techniques and physical modeling have advanced our understanding of how salt-sediment configurations evolve to their present configurations. Coincident with this emerging new subsurface framework, high quality data for determining surficial geology and the processes that impact it have also been collected, primarily for geohazards evaluations. The study reported here represents the first comprehensive attempt to link high resolution surficial geology to controlling subsurface geology and processes. Special attention is focused on seafloor responses forced by the surficial venting/seepage of hydrocarbons, other fluids, and sediment within a northern Green Canyon-Ewing Bank area covered by 3D-seismic and previously studied extensively. Sixteen surface sites accompanied by high resolution acoustic data and ground truth observations/samples acquired by research submersible represent the surface data set. Initial results of combining subsurface and surficial data sets indicate a first-order relationship with faults, conduits for gas and fluid flux to the seafloor. Faults linked to subsurface salt support the most numerous and active vent/seep-related features, perhaps because of frequent salt movements that open conduits to the surface by fault activation. Salt geometry and proximity to the seafloor are important factors. Salt stocks focus fluids and gases vertically while venting/seepage occurs around the edges of shallow salt sheets. Topography on the surface of deep salt sheets (> 1.5s TWT) and other types of salt bodies is an important determinant of numbers and types of conduits to the seafloor.

AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas