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USGS2000

Seismic reflection results from the GYRE 1997 cruise of the Bryant Canyon on the Louisiana Gulf Coast

The Texas-Louisiana continental slope is one of the few remaining frontiers for hydrocarbon exploration within the US Exclusive Economic Zone. This area has a complex seafloor morphology and highly discontinuous shallow stratigraphy that are the result of deformation by the highly mobile Louann salt that underlies much of this margin shoreward of the Sigsbee Escarpment.Gas hydrates exist both on the sea floor and at depth throughout the gas hydrate stability zone which extends to several hundred meters beneath the sea floor at greater water depths. Multibeam bathymetry, GLORIA sidescan sonar imagery, and site-specific studies have identified the presence of faults, mass-wasting deposits, variable sediment types, and gas hydrates exposed on the seafloor. The expression of these features on the seafloor suggests a tectonically active area. The distribution of these different processes and their relation to the subsurface stratigraphy and tectonic setting are not well understood, yet an understanding of these issues is essential as exploration extends into this deep-water area. To address the questions of surficial processes and their connection with deeper structures underlying this continental margin, a three-week cruise was conducted by the USGS in April, 1997 aboard the RV GYRE. The study area focussed on Bryant Canyon, a former submarine canyon, through which turbidity currents transported sands from a shelf-edge delta upslope of the study area to the Bryant Fan on the rise seaward of the base of the slope. The cruise was divided into two parts. The first part was devoted to collecting seismic-reflection profiles across parts of the canyon system to define the shallow stratigraphy and to determine the presence and distribution of gas hydrates in this area. Approximately 555 km of single-channel seismic-reflection data were collected during this first part of the cruise. A track map showing the locations of the profiles, low-resolution images of the profiles, and the SEG-Y format of these data are all presented on this CD-ROM. During the second part of the cruise, 38 piston cores were collected to describe the shallow subsurface facies of the study area. The coring data will be availible in an open file report to be published by Hans Nelson.

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