DILLON, WILLIAM P., U.S. Geological Survey, Woods Hole, MA; KRISTEN FEHLHABER, U.S. Geological Survey, Woods Hole, MA; and MYUNG W. LEE, U.S. Geological Survey, Denver, CO

ABSTRACT: Gas Hydrates - Their Distribution and Significance in Sea-Floor Sediments of the U.S. Atlantic Margin

Gas hydrates bind immense volumes of gas (mostly methane) in ocean-floor sediments. They represent a possible major energy resource; they probably have had an important influence on sea-floor slope stability and they may, at times, supply a significant greenhouse gas to the atmosphere. We have mapped hydrates along the U.S. Atlantic margin from South Carolina to New Jersey, by using more than 7,500 km of digitally-recorded seismic profiles. Hydrate volume is estimated by seismic modeling, employing the measured reduction of reflection amplitude, which apparently is caused by cementation of strata by gas hydrate. Because this model implies velocities, we can generate an isopach map of the hydrate-cemented surface layer of sediment. Estimates show large amounts of gas. At the location o greatest concentration, hydrates may contain 600 TCF of gas within a 2,800-sq km area. High concentrations of gas hydrate occur in two settings: (1) areas of rapid sedimentation, as at the Blake Ridge and continental rise hills, where we anticipate greater biogenic gas generation and the possibility of upward recycling of hydrate gas as deposition occurs, and (2) areas of diapirs and associated faulting along the seaward side of the Carolina Trough, where fractures may provide migration pathways for thermogenic gas from depth. Thickness of the hydrate-cemented layer and volume of hydrate are decreased at landslide scars, indicating that hydrate breakdown may be a cause and/or effect of landsliding. Because methane is a strong greenhouse gas, landslide processes may release enough methan to affect global climate significantly.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.