Massive gas- and oil-related carbonates of Louisiana continental slope

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

OSTI ID:5877497

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

Recent submersible research on the tops of salt diapirs at the shelf edge (/approximately/150 m) and upper slope (/approximately/300 m) confirms the occurrence of massive carbonate buildups (to /approximately/20 m relief) in these environmental settings. Samples collected from shallow and deep study sites in the Green Canyon area indicate that the foundation of the massive buildups is authigenic carbonate characterized by isotopically light carbonate carbon, a characteristic that relates their origin to the biodegradation of hydrocarbons. Fault systems associated with the salt diapirs function as conduits for migration of gas and oil to the sea floor. Gas and sediment samples collected from seeps using a submersible indicate that both biogenic and thermogenic gas seepage occurs, as well as crude oil. Bacterial mats are common to the sea floor of seep areas. Mat samples provided /delta//sup 13/C values of /minus/28 to /minus/31 /per thousand/ PDB, suggesting an association with crude oil rather than methane. At water depths greater than about 500 m, gas hydrates form distinctive mounds containing isotopically light carbonate clasts, slabs, and massive rocks in addition to sediments and frozen gas. The chaotic internal structure of shallower massive carbonate mounds (/approximately/350-150 m) suggests an origin related to the collapse of hydrate hills and continued carbonate cementation of the components into massive buildups. Through time, vertical movement of salt diapirs and sediment stripping subject hydrates to a shallower environment characterized by an unfavorable temperature and pressure regime. Progressively shallower dome crests at the shelf edge are capped with biogenic carbonates related primarily to low sea level reef-building organisms.

• Research Organization: Louisiana State Univ., Baton Rouge (USA)
• OSTI ID: 5877497
• 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
03 NATURAL GAS
030200 -- Natural Gas-- Reserves
Geology
& Exploration
CARBON 13
CARBON ISOTOPES
CONTINENTAL MARGIN
CONTINENTAL SLOPE
EVEN-ODD NUCLEI
FEDERAL REGION VI
GEOLOGIC DEPOSITS
ISOTOPES
LIGHT NUCLEI
LOUISIANA
MINERAL RESOURCES
NATURAL GAS DEPOSITS
NORTH AMERICA
NUCLEI
PETROLEUM DEPOSITS
RESOURCES
SALT DEPOSITS
STABLE ISOTOPES
USA