U.S. Geological Survey
GLORIA Mapping Program

U.S. EEZ Gulf of Mexico Region

GLORIA Geology Interpretation

Gulf of Mexico GLORIA geology interpretation map

Background

The GLORIA sidescan sonar images provide a unique view of the seafloor in the deep water of the Gulf of Mexico. The U.S. EEZ in the Gulf of Mexico can be divided into three major sedimentary provinces: a salt deformation province in the western section, the Mississippi Canyon and Fan system in the central section, and a carbonate province in the eastern section, which is separated from the terrigenous Mississippi Fan by the Florida Escarpment.

In the western Gulf the Sigsbee Escarpment marks the seaward edge of the salt deformation province. Seaward of the escarpment, patches of highly reflective (bright) seafloor with numerous lineations are interpreted as bedform fields formed by the reworking of debris from the escarpment. Diapirs have created numerous domes and isolated basins on the slope that have significantly influenced the paths of submarine canyons crossing the continental slope (mosaic #11). Seismic-reflection profiles across the escarpment suggest that a wedge of salt is overriding sediments that were deposited in the deep waters of the Gulf.

Landward of the escarpment, the continental slope has a very complex morphology, formed in response to intrusion by the salt. The continental shelf in the Gulf of Mexico prograded seaward during the Tertiary as a series of depocenters migrated eastward from the Rio Grand River area of Texas to the presently active Mississippi River area in the north-central Gulf. Loading of these Tertiary sediments onto an underlying salt layer has resulted in diapiric intrusion by the salt. Identifying salt domes and basins on the slope based on imagery alone is difficult. In some cases, the salt domes are highly reflective because of the inclination of the flanks on the crests, whereas in other instances basin floors are reflective, possibly because of differences in sediment texture.

In the central Gulf of Mexico, the Mississippi Canyon and Fan system is the dominant morphologic feature. The Sigsbee Escarpment cannot be identified because it is buried by sediments from the Mississippi Canyon. The Mississippi Canyon shows a highly reflective region on the GLORIA imagery because it is filled with debris-flow deposits.

The Mississippi Canyon shows as a highly reflective region that feeds onto the Mississippi Fan. Much of the surface of the fan comprises highly reflective deposits called depositional lobes, and these depositional lobes all seem to have been fed from a single meandering channel system that can be traced across the fan. The largest of these is a mass-wasting deposit on the middle to upper part of the fan. The low-backscatter regions around the margins of the fan are interpreted to be fine-grained hemipelagic deposits, whereas the high-backscatter regions on the fan correspond to areas where sand has been sampled. The surface of the fan to the west of the channel has a different acoustic character than that to the east. West of the channel the sea floor is covered by a series of southwestward-trending high-backscatter linear stripes whose origin is as yet undetermined. Detailed studies following up on the reconnaissance view provided by the GLORIA images suggest more intricate sedimentary processes than previously anticipated.

In the northeastern Gulf, a highly reflective area on the imagery marks submarine debris-flow deposits. A meandering channel (mosaic #13) shown as a bright sinuous line on the images emerges from the deposits and trends southward, parallel to the Florida Escarpment. The bright meandering channel is part of an elevated channel and levee system (levee ridge). The highly reflective debris-flow deposits from the Mississippi Canyon area are dammed by this elevated channel until the flow eventually overtops the levee and buries the channel. The southern extent of this channel and its deposits is masked by the debris-flow deposits.

The dominant feature in the eastern Gulf is the Florida Escarpment. The GLORIA imagery shows that the erosional morphology varies along the escarpment. North of 27^on (mosaic #14), the escarpment is dissected by a series of closely spaced canyons with tributary gullies. South of 27^on (mosaic #3), large box canyons with nearly vertical headwalls have been cut into the escarpment. Numerous scarps are present in the carbonate sediments above the escarpment. These scarps are the product of mass wasting of the carbonate sediments. Some of the scarps align with the canyons, suggesting that the canyons are conduits for mass-wasting products from the continental slope above.