Quarterdeck 3.1
Recent Graduate

Seismic stratigraphy and salt tectonics of the Alaminos Canyon area, Gulf of Mexico

by Suzanne M. Hewitt

The goal of my research was to study salt distribution and the interrelationship between the movement of salt, development of slope basins, and sediment distribution within the Alaminos Canyon area, Gulf of Mexico. The Alaminos Canyon area is a region of complex seafloor topography located at the transition between the continental slope and rise. By studying this area, we can gain a better understanding of the geologic processes within the slope environment and provide information for future exploration.

Due to the depth of the seafloor within the study area, direct sampling of sediment and rock is difficult. The results of this study were based solely on the interpretation of data obtained through seismic reflection surveys. These surveys generate data which provide information about geologic structures below the seafloor. To produce the necessary contour maps of the underlying structure and stratigraphy, I interpreted seismic sections processed from the seismic reflection data.

Contour maps of the salt indicated that the study area contains shallow canopies of salt. Salt canopies are composite structures formed by lateral fusion of salt stocks, tongues or lobes. The canopies were classified as salt lobe canopies due to their characteristic lobate shape and preferred flow direction downslope. Salt lobe canopies characterize the eastern and western margins of the Alaminos Canyon area, while the central region represents a transition zone between these canopies. As these salt lobe canopies move downslope, they tend to deform overlying sediment and mask earlier depositional and structural records.

I identified several large salt-free areas where the lobes of the salt sheet have not fused together. The Alaminos and Rio Perdido Canyons are salt-free areas between the lobes of the distal front of the salt sheet. The present configuration of these canyons is governed by the movement of the salt lobes which surround their perimeters. Information about the origin and evolution of these canyons has been masked by the movement of this salt.

As the salt forms canopies, it greatly influences how sediment is deposited within and transported through the slope environment. The salt sheet interacts with slope sediment deposition by forming well-developed intraslope basins which inhibit the transport of sediment downslope. These basins consist of remnants of submarine canyons blocked by salt uplift and depressions formed by subsidence in response to salt withdrawal. The basins have trapped thick deposits of sediments, reducing the amount of sediment that can be transported beyond the slope environment. Even when salt uplift does not successfully block downslope sediment transport, it strongly influences the direction. Within the study area, salt has formed channelized topographic lows through which sediment moves into the basins and beyond the slope environment.

The results of my study show that salt in the Alaminos Canyon study area has played the dominant role in the formation of intraslope basins, basin morphology, and sediment transport. Due to the lateral movement of the salt canopy, the structure and depositional record prior to the formation of the salt canopy has been masked.

Oceanography, Texas A&M University

URL=http://oceanography.tamu.edu/Quarterdeck/QD3.1/Hewitt/hewitt.html
Updated July 24, 1995