Journal
GEO-MARINE LETTERS
Volume 22, Issue 4, Pages 204-209Publisher
SPRINGER
DOI: 10.1007/s00367-002-0114-x
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A synthesis of high-resolution (Chirp, 2-7 kHz) subbottom profiles in the Ulleung Basin reveals patchy distribution of shallow (< 90 in subbottom depth) gassy sediments in the eastern basin plain below 1,800-m water depth. The shallow gases in the sediments are associated with acoustic turbidities, columnar acoustic blankings, enhanced reflectors, dome structures, and pockmarks. Analyses of gas samples collected from a piston core in an earlier study suggest that the shallow gases are thermogenic in origin. Also, published data showing high amounts of organic matter in thick sections of marine shale (middle Miocene to lower Pliocene sequence) and high heat flow in the basin plain sediments are consistent with the formation of deep, thermogenic gas. In multichannel deep seismic profiles, numerous acoustic chimneys and faults reflect that the deep, thermogenic gas would have migrated upwards from the deeper subsurface to the near-seafloor. The upward-migrating gases may have accumulated in porous debrites and turbidites (upper Pliocene sequence) overlain by impermeable hemipelagites (Quaternary sequence), resulting in the patchy distribution of shallow gases on the eastern basin plain.
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