Spatial distribution of geotechnical properties in surficial marine sediments-Northwestern slope region, Gulf of Mexico

Abstract

The northwestern portion of the Gulf of Mexico continental slope features approximately 90 intraslope basins offshore Texas and Louisiana. Domes of high elevations, sometimes resulting in a difference of 1000 meters from top to bottom, separate these basins. Considering the recent turn of interest to deeper water petroleum prospects, knowledge concerning the surficial sediments in this area is currently of major economic importance. The continental shelf to the north of this region has been studied in great detail due to its vast stores of petroleum. However, the continental slope and rise have received relatively little attention. Recent studies have interpreted a conglomerate of high-resolution seismic data, but very few sediment samples were used for ground truthing. A suite of 182 piston cores from the northwestern continental slope and continental rise were used in this study, with the intent to identify, illustrate and describe the recent sediments unique to that region. In addition, this study set out to identify the depositional environment of that region, and reflect on surface sedimentation patterns, regional and local. In order to achieve these goals, this study employed select geotechnical tests, shear strength measurements, lithologic descriptions, and high-resolution imagery by x-radiography. Utilizing a geographic information system (GIS), this study attempted to provide a digital database of such sediment physical properties, allowing for convenient analysis purposes in the future. The GIS revealed that a veneer of low shear strength, homogenous clay blankets much of the study area. Erosional patterns were not discovered on a regional scale, but local patterns do exist. The shortest cores retrieved in this study came from locations along basin walls where slumps and slides are common. Alaminos, Bryant, and Keathley Canyons are three large, north-south trending systems of valleys and basins that are believed to have transported much sediment to the abyssal plain within relatively recent periods of geologic time. The only silty sediments encountered in this study were retrieved from these three general locations. In general, the study illustrated that highly localized sedimentation environments occur along the continental slope due to the topographic highs and lows in this region.