Geochemical conditions in sediment containing gas hydrates of active and passive continental margins
Conference
·
· Am. Assoc. Pet. Geol., Bull.; (United States)
OSTI ID:5909371
Two sites of the Deep Sea Drilling Project in contrasting geologic settings provide a basis for comparison of the geochemical conditions associated with marine gas hydrates in continental margin sediments. Site 533 is located at 3191 m water depth on a spitlike extension of the continental rise (Blake Outer Ridge) on a passive margin in the Atlantic Ocean. Site 568, at 2031 m water depth, is in upper-slope sediment of an active accretionary margin (Middle America Trench) in the Pacific Ocean. Both sites are characterized by high rates of sedimentation (greater than 30 m/m.y.), and the organic carbon contents of these sediments generally exceed 0.5%. Anomalous seismic reflections that crosscut reflections from sedimentary layers and parallel reflections from the sea floor suggested the presence of gas hydrates at both sites. During coring, small samples of gas hydrate were recovered at subbottom depths of 238 m (Site 533) and 404 m (Site 568). The principal gaseous components of the gas hydrates were methane, ethane, and CO/sub 2/. Residual methane in sediments at both sites usually exceeded 10 ml per liter of wet sediment. Carbon isotopic compositions of methane, CO/sub 2/, and followed parallel trends with depth, suggesting that methane formed mainly as a result of biologic reduction of oxidized carbon. Salinity of pore waters decreased with depth, a likely result of gas hydrate formation. The small samples of gas hydrates observed visually in cores confirm that gas hydrates are present at these sites, but much of the direct evidence for gas hydrates may be destroyed during the coring and recovery process.
- Research Organization:
- Geological Survey, Menlo Park, CA
- OSTI ID:
- 5909371
- Report Number(s):
- CONF-850322-
- Conference Information:
- Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 69:2
- Country of Publication:
- United States
- Language:
- English
Similar Records
Gas hydrates at two sites of an active continental margin
Gas-hydrate horizons detected in seismic-profiler data from the Western North Atlantic
Gas hydrates of outer continental margins
Conference
·
Thu Feb 28 23:00:00 EST 1985
· Soc. Pet. Eng. AIME, Pap.; (United States)
·
OSTI ID:5192657
Gas-hydrate horizons detected in seismic-profiler data from the Western North Atlantic
Journal Article
·
Sun May 01 00:00:00 EDT 1977
· Am. Assoc. Pet. Geol. Bull.; (United States)
·
OSTI ID:7099721
Gas hydrates of outer continental margins
Conference
·
Tue May 01 00:00:00 EDT 1990
· AAPG Bulletin (American Association of Petroleum Geologists); (USA)
·
OSTI ID:6685339