Geologic and geophysical investigation of a portion of the upper continental slope, northwest Gulf of Mexico
Casby, Susan Margaret
Master of Arts
The continental slope in the northwest Gulf of Mexico ranges in width from 11 kilometers (59 nautical miles) off the Rio Grande to 24 kilometers (13 nautical miles) off Louisiana. Throughout its Cenozoic history, this continental margin has increased its limits through the progradation and aggradation of clastic sediments on a broadly downwarped and subsiding basement. Eustatic changes in sea level in response to Pleistocene climatic fluctuations have provided for the deposition of these transgressive and regressive deposits. Rapid Pleistocene sea level changes are responsible for accelerated deposition and extension of the continental margin. Eustatic lowering of sea level moved the site of nearshore sedimentation to the outer edge of the continental shelf. Shelf outbuilding occurred as deltas prograded over the shelf-slope break. Growth faults cut the sediment column in response to this rapid sedimentation. Transgressive seas decreased the sedimentation rate, calling a halt to this outbuilding sequence. The continental slope in the northwest gulf is also marked by diapiric uplifts of variable size. Drilling in the late 196’s confirmed the hypothesis that these are salt diapirs. These intrusions greatly affect the surrounding sedimentation, especially in the basins, or synclines, which they create. This particular study correlates high resolution seismic profiles with drill core data in a selected location on the outer continental shelf and upper continental slope off the Texas Gulf coast. Textural, micropaleontologic and paleomagnetic information obtained from these drill cores combined with sparker data to yield a history of the Late Pleistocene to Recent in this area. The analysis of shelf edge progradation and its relationship to sedimentation and structural activity on the continental slope yielded additional information with respect to the Pleistocene to Recent depositional history.