C/sup 13/-depleted authigenic carbonate buildups from hydrocarbon seeps, Louisiana Continental Slope

Conference · Wed Mar 01 04:00:00 EST 1989 · AAPG Bull.; (United States)

OSTI ID:5795516

Roberts, H H; Sassen, R; Aharon, P; Carney, R

Geohazard and geochemical survey data consisting of high-resolution profiles, side-scale sonographs, drop cores, dredge samples, and borings have substantiated the consistent association between carbonate buildups and hydrocarbon seeps on the Louisiana continental slope. Analyses indicate a range of carbonate mineralogies including aragonite, Mg-calcite, and dolomite that are extremely depleted in the C/sup 13/ isotope (/approximately/dC/sup 13/ values to /minus/48/per thousand/ PDB). Microbial oxidation of methane (biogenic and thermogenic) and crude oil creates a source of pore water CO/sub 2/ containing isotopically light carbon, which triggers carbonate precipitation. Geophysical and geochemical evidence suggests that both surface and subsurface lithification is taking place. Recent observations and samples collected using a Pisces class research submersible confirm the abundance of C/sup 13/-depleted sedimentary carbonates and massive authigenic buildups associated with the tops and flanks of shallow salt diapirs and gas hydrate hills. Although chemosynthetic communities (including tube worms and bivalves) with isotopically light carbon in tissues have been described from gas seeps, bacterial mats sampled from several seep areas using a submersible have /delta/C/sup 13/ values of /minus/28 to /minus/ /per thousand/ PDB, suggesting a crude oil contribution to microbial biomass. Lithoherms 15 m in vertical dimension are not unusual on dome crests. These features dominate mesoscale sea-floor topography on the slope and have important short-term impacts on platform locations as well as pipeline routing. They are of long-term importance as sites for low sea level reefs. Moreover, these observations provide new insight into the earliest stages of salt-dome cap-rock evolution.

• Research Organization: Louisiana State Univ., Baton Rouge (USA)
• OSTI ID: 5795516
• Report Number(s): CONF-890404-
• Conference Information: Journal Name: AAPG Bull.; (United States) Journal Volume: 73:3
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
ALKALINE EARTH METAL COMPOUNDS
ALKANES
CALCITE
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON 13
CARBON COMPOUNDS
CARBON ISOTOPES
CARBONATE MINERALS
CARBONATE ROCKS
CARBONATES
CHEMICAL REACTIONS
CONTINENTAL MARGIN
CONTINENTAL SLOPE
DOLOMITE
EVEN-ODD NUCLEI
FEDERAL REGION VI
GEOLOGIC DEPOSITS
HYDROCARBONS
ISOTOPES
LIGHT NUCLEI
LOUISIANA
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
METHANE
MINERAL RESOURCES
MINERALS
NORTH AMERICA
NUCLEI
ORGANIC COMPOUNDS
OXIDATION
OXYGEN COMPOUNDS
PETROLEUM DEPOSITS
RESOURCES
ROCKS
SALT DEPOSITS
SEDIMENTARY ROCKS
STABLE ISOTOPES
USA