Paleoecologic implications of chemoautotrophic molluscan-dominated assemblages on the Louisiana continental slope
- Texas A and M Univ., College Station (United States)
Dense chemoautotrophically based molluscan communities are common at sites of active petroleum seepage in the Green Canyon and Garden Banks lease blocks on the Louisiana upper continental slope. The presence of dense molluscan aggregations has important implications for paleoecology because the continental slope is generally though of as a geologic setting depauperate of macrofossils. Liquid and gaseous petroleum seepage, primarily along faults associated with salt diapirism, provides localized nutrient input which facilitates high molluscan productivity. Authigenic carbonate, formed due to methane oxidation, occurs at and below the sediment-water interface in areas of molluscan concentrations. Trophic structure of these bivalve-dominated communities is based on three separate carbon pathways: chemoautotrophy, utilizing either H{sub 2}S or CH{sub 4}, or autotrophy, utilizing organic food sources. The largest quantity of preservable molluscan biomass is produced by infaunal lucinid and thyasirid clams which utilize H{sub 2}S. Thyasirid and lucinid clams form extensive three-dimensional shell beds which can extend for several tens of meters. Second and third in terms of preservable biomass are vesicomyid clams and mytilid mussels which utilize H{sub 2}S and CH{sub 4} respectively. Vesicomyid clams form shell pavements at a smaller scale then the lucinid and thyasirid shell beds. The least amount of preservable biomass is produced by autotrophs including trochid and nerite gastropods, limid bivalves, crabs, and starfish. Energy flow requirements for benthic communities on the oligotrophic continental shelf and slope settings of the northern Gulf of Mexico require a localized nutrient enrichment, such as a petroleum seep, to support dense concentrations of large individuals. This relationship of nutrient enrichment to enhanced biomass productivity probably also was a dominant factor in the formation of similar autochthonous benthic assemblages in the fossil record.
- OSTI ID:
- 5874711
- Report Number(s):
- CONF-910403-; CODEN: AABUD
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 75:3; Conference: Annual meeting of the American Association of Petroleum Geologists (AAPG), Dallas, TX (United States), 7-10 Apr 1991; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
AUTOTROPHS
BIOGEOCHEMISTRY
CONTINENTAL SLOPE
PETROLEUM DEPOSITS
LOUISIANA
BIOLOGICAL EVOLUTION
FOSSILS
MOLLUSCS
PALEONTOLOGY
SEEPS
ANIMALS
AQUATIC ORGANISMS
CHEMISTRY
CONTINENTAL MARGIN
DEVELOPED COUNTRIES
FEDERAL REGION VI
GEOCHEMISTRY
GEOLOGIC DEPOSITS
INVERTEBRATES
MINERAL RESOURCES
NORTH AMERICA
RESOURCES
USA
020200* - Petroleum- Reserves
Geology
& Exploration
580000 - Geosciences