3D Seismic Architecture of Slope Turbidites and Their Evolution with Coeval Bathymetry in The Gulf of Mexico
Ryan, Kieran M.
Univesity of Adelaide
The northern Gulf of Mexico continental margin has been one of the worlds most active regions in the exploration and exploitation of hydrocarbons for the last century. The last 20 years have seen a shift in the focus of exploration from the shelfal, to the continental slope environment following the advance of deepwater exploration and development techniques. Successful exploitation of the deepwater environment requires the development of an understanding of the geological processes that influence sediment dispersal and deposition on the continental shelf.
The area under study is located on the northern Gulf of Mexico continental slope extending from the shelf/slope break to the lower slope and covers an area of approximately 42,000 km2. The area is covered by a number of 3D seismic surveys, merged using a series of tie lines to form a regional survey. The study covers parts of three Minerals Management Service protraction areas, including Mississippi Canyon, eastern Green Canyon and northern Atwater Valley. Seismic analysis included the mapping of the sea floor and a shallow horizon corresponding to the 0.1 Ma Sangamon biomarker, as well as isochron and amplitude extraction maps indicating the distribution of sedimentary gravity flows throughout the study area.
Three areas of distinct bathymetry are identified and related to the underlying mobile salt. Extremely variable bathymetric relief consisting of steep sided ridges and deep valleys dominates the western study area from the middle to lower slope. This is related to the well-developed salt diapirism in the area and failure of the upper slope. The eastern study area exhibits a more typical concave up slope profile, grading from 1.2degrees on the upper slope to 0.8degrees on the lower slope. This is ascribed to the less deformed underlying salt sheets and canopies. The centre of the study area is characterised by the elongate, smooth bathymetry caused by the sedimentary fill of the Mississippi Canyon, the primary conduit for sediment bypass to the basin floor during the Late Pleistocene.
Root-mean-square amplitude extractions and coherency slices indicate the control of coeval bathymetry on slope sedimentation in the study area. The thickest sediment packages are located in the deep mini basins of the western study area and are interpreted as slope turbidites generated from upper slope failure. Sediments in the eastern study area are continuous and laterally extensive. The Mississippi Canyon exhibits various stages of development including a major erosional phase and stages of deposition by channelised turbidites and mass transport flows.
Sediment distribution is related to the style of allochthonous salt within the study area, steep sided salt diapirism is associated with confined, thick sediment deposits while laterally extensive salt canopies induce thinner, more continuous sedimentation. Analysis of the salt distribution alone can give insight into the depositional styles of sediments both above and below salt structures and thus aid in identification of exploration targets.