Modern biogenic gas-generated craters (sea-floor “pockmarks”) on the Bering Shelf, Alaska

Abstract

Research Article| December 01, 1979 Modern biogenic gas-generated craters (sea-floor "pockmarks") on the Bering Shelf, Alaska HANS NELSON; HANS NELSON 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar D. R. THOR; D. R. THOR 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar M. W. SANDSTROM; M. W. SANDSTROM 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar K. A. KVENVOLDEN K. A. KVENVOLDEN 3U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information HANS NELSON 1U.S. Geological Survey, Menlo Park, California 94025 D. R. THOR 1U.S. Geological Survey, Menlo Park, California 94025 M. W. SANDSTROM 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90024 K. A. KVENVOLDEN 3U.S. Geological Survey, Menlo Park, California 94025 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1979) 90 (12): 1144–1152. https://doi.org/10.1130/0016-7606(1979)90<1144:MBGCSP>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation HANS NELSON, D. R. THOR, M. W. SANDSTROM, K. A. KVENVOLDEN; Modern biogenic gas-generated craters (sea-floor "pockmarks") on the Bering Shelf, Alaska. GSA Bulletin 1979;; 90 (12): 1144–1152. doi: https://doi.org/10.1130/0016-7606(1979)90<1144:MBGCSP>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract As many as 1,340 small craters per square kilometre cover the sea floor of Norton Sound in the northeastern Bering Sea. The craters are circular pits, 1 to 10 m in diameter and less than 1 m deep, observed on sonographs over 20,000 km2 of northern Norton Sound sea floor. Craters typically are associated with acoustic anomalies, near-surface peaty mud, and gas-charged sediment.The peaty mud is a thick (>1.5 m), nonmarine pre-Holocene deposit that is now covered by a 1- to 3-m-thick layer of Holocene marine mud in the area of the craters. The peaty mud (2% to 8% organic carbon) contains abundant biogenic methane [C1/(C2 + C3) = 256 to 7,669] with carbon isotope (δ13C) values of −69‰ to −75‰- Decomposition of organic debris in the peaty mud apparently charges the mud with gas. The peaty and gassy zones attenuate sound waves and cause acoustic anomalies on high-resolution seismic profiles in the area with craters.The craters are forming now, as shown by the disruption of modern ice gouges by the craters. In the absence of storms, the gas apparently is trapped in the peaty mud in a saturated state by the cover of Holocene mud. Periodically, possibly during storms, the gas escapes through the thin Holocene cover and forms craters. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.