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Alan Cooper1, Patrick Hart1, David Twichell2
(1) U.S. Geological Survey, Menlo Park, CA
(2) U.S. Geological Survey, Woods Hole, MA

Abstract: Gulf of Mexico gas hydrates - a potential link to shallow flows and continental-slope stability

In April 1999, we recorded 800 miles of high-resolution seismic-reflection data over 1500 mi.2 of the upper continental slope in the northern Gulf of Mexico, to study gas hydrates and sea-floor stability. Multichannel data were collected using a 15 in3 water gun, and single-channel data using a Huntec boomer and deep-tow chirp transducer. Structure and stratigraphy of the continental slope are dominated by salt-related faulting and diapirism, resulting in diverse mini-basin morphology and sediment basin-fills. Massive gas hydrate deposits occur at the sea floor on crests of many diapirs, but subsurface hydrate occurrences are rarely reported. Gas is widespread. Gas deposits, which create high-amplitude and chaotic seismic facies, are mapped in other studies in the Mississippi Canyon region only a few hundred feet below hydrate deposits cored at the sea floor. Such facies are common in our seismic data, and occur mostly in 'deformed' stratal units of variable thickness between well-layered strata. The 'deformation' results mostly from sediment movement, faulting, and acoustic gas-related distortion. In places, seismic-reflection data show faults, stratal failures and changes in slopes that occur in slide zones extending from the sea floor into 'deformed units'. Large areas of the uppermost sedimentary section may have moved (and be moving?) downslope along these slide zones. At one location, an active water-flow was encountered in the 'deformed' unit. Because the 'deformed' units lie within the gas-hydrate stability zone, are associated with likely gas, gas-hydrate and possibly active water-flows, we suggest that the development, and dissociation, of hydrate deposits is causally linked to many subsurface and sea-floor failures in this part of the Gulf of Mexico. Detailed coring of the 'deformed' units is needed to determine the specific link.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana