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Seafloor Deformation in the South Caspian Sea: A Potential Proxy for Gas Hydrate Dissociation and Climate Change

Christopher C. Amos, Camelia C. Knapp, and James H. Knapp
University of South Carolina, [email protected]

The presence of buried gas hydrates in the South Caspian Sea has been interpreted using 2-D seismic reflection data. Evidence for buried gas hydrates consists of a shallow (300-500 m below seafloor) comparatively high velocity zone approximately parallel to the seafloor bounded by a positive-polarity reflector at the top and a high-amplitude negative-polarity reflector at the base. The position of gas hydrates fall within the stability field predicted for the South Caspian Basin. New industry quality 3-D seismic data are being used to determine the relationship between the presence of gas hydrates and an approximately 2,500 km2 late-Pleistocene zone of seafloor deformation and submarine slumping in the South Caspian Sea, named the Absheron Allochthon. Welllogs from the South Caspian Sea offshore Azerbaijan are being correlated with the 3-D seismic data to determine the age and origin of the Absheron Allochthon. The history of sea level changes in the Caspian Sea in the past ~700 ka emphasizes a major ~100 m drop in sea level during the latest deglaciation (late Pleistocene). Preliminary results show that the Absheron Allochthon may have formed through catastrophic failure of the western South Caspian continental slope as a result of dissociation of underlying buried gas hydrates. If this proves to be true, then repeated, remarkably rapid global warming events in the Caspian Sea during the late Quaternary were likely due to rapid marine gas hydrate (clathrate) dissociation rather than exhalation from wetlands.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas