International Geologiical Congress - Oslo 2008

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GAH-03 Exploration and assessment of gas hydrates

 

High resolution seafloor environmental characterization of methane seeps in the Mississippi canyon near Atwater valley 13/14, Gulf of Mexico

 

Joan Gardner, US Naval Research Lab (United States)
Patrick Hart , US Geological Survey (United States)
Rick Hagen, US Naval Research Lab (United States)
Mike Czarnecki, US Naval Research Lab (United States)
Clyde Nishimura, US Naval Research Lab (United States)
Debbie Hutchinson, US Geological Survey (United States)
 

 

The purpose of this project was to conduct detailed surface mapping of one of the areas drilled by the Joint Industry Project with ChevronTexaco to understand gas hydrates in the Gulf of Mexico.

The gently sloping, mostly flat floor of the Mississippi Canyon is interrupted by mounds and depressions that presumably reflect the complex geology and geohydrology related to turbidite deposition and pervasive salt tectonism. The seafloor mounds we mapped in this study occur in approximately 1300 water depth along the floor of the Mississippi Canyon in lease block areas Atwater Valley 13 and 14. . High resolution sidescan sonar (100 kHz and 500 kHz) backscatter imagery, and chirp sub-bottom profiler data were collected using the DT1 deep-towed oceanographic mapping instrument, concentrating on the region directly adjacent to and surrounding two mounds identified as, mounds D and F, and in the region directly adjacent to and surrounding the mounds. The backscatter data have been mosaiced and normalized to provide information on the shape and extent of the mounds, the possible lateral extent of fauna, such as mussel and clam fields on the mounds, possible seep related flows and the occurrence of carbonate material. The extent of a mudflow can be mapped on the southeastern side of mound F. Previously collected bottom camera images have been used to ground-truth the backscatter information. Coincident with the collection of backscatter information was the collection of very high-resolution bathymetric data.

Together, the backscatter and bathymetric data show extremely high-resolution detail about the shape, relief, and morphology of the mounds. This information, coupled with porewater chemistry and heatflow data form a coherent picture of possible mechanics for fluid venting and flora/fauna of the seeps in this region.

 

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