Structure of the Salt Surface and Comparison to Bathymetry from 2-D Multichannel Seismic Data: Texas and Louisiana Continental Slope, Northwestern Gulf of Mexico

The seafloor morphology of the continental slope of northwestern Gulf of Mexico shifts, going from the smoother Texas offshore to the rugose central Louisiana slope. This change is considered to be a reflection of the structure of mobile Jurassic salt residing within the rock column. To test this hypothesis, the structure of the top of salt (ToS) across the Texas and western Louisiana slope has been interpreted and compared to the bathymetry using a regional grid of 2D industry multichannel seismic data. The 2D data, provided by TGS, were analyzed using Kingdom Suite software. Regional time-structure maps of seafloor and ToS surfaces were created from seismic time-picks along >61,000 km of survey lines. Analysis revealed that shallow salt occurs under roughly 80% of the continental slope within the study area and it is not uniformly distributed. Going from shelfbreak to Sigsbee escarpment, salt is increasingly more abundant seaward and forms an arc of nearly-continuous canopy on the project lower-slope. Additionally, shelfbreak-to-escarpment salt morphology varies west to east and the study area can be roughly divided accordingly, Texas versus Louisiana. For offshore Texas, tall, widely-spaced passive diapirs are near-surface on the upper-slope; then diapirs are closely-spaced, buried, and likely detached from the source-layer on the middle-slope; and, finally, basinward-leaning diapirs are coalesced and form canopy on the Texas lower-slope. On the Louisiana slope, salt is more widespread than in the west and dominant salt bodies are relatively evenly-spaced and elongate salt ridges or sheets; they gradually increase in width seaward and coalesce to form canopy on the lower-slope. Comparison of seafloor to ToS revealed that the preponderance of seafloor is coincident with ToS relief and that bathymetry corresponds to the transition in salt morphology that characterizes the study area. Additionally, narrow zones of seafloor deformation result from faulting above essentially all ridge-crests and sheet-edges across the Louisiana slope. This is intensified where near-surface salt structures fall along sediment pathways. Therefore, bathymetric relief can be a clue to finding shallow salt on the move, while a smooth seafloor is evidence that salt is absent, deeply positioned in the sediment column, or recently-inactive.