Evolution of reef and atoll margin carbonates, upper Eocene through lower Miocene, Enewetak, Marshall Islands

Conference · Mon Feb 01 00:00:00 EST 1988 · AAPG Bull.; (United States)

OSTI ID:6014956

Saller, A H; Schlanger, S O

Two wells drilled along the margin of Enewetak Atoll penetrated approximately 1000 m of upper Eocene, Oligocene, and lower Miocene carbonates. Strontium isotope stratigraphy indicates relatively continuous deposition of carbonate from 40 Ma to 20 Ma. Depositional environments show a gradual basinward progradation of facies with slope carbonates passing upward into fore-reef, reef, back-reef, and lagoonal carbonates. Slope strata contain wackestones and packstones with submarine-cemented lithoclasts, coral, coralline algae fragments, benthic rotaline forams, planktonic forams, and echinoderm fragments. Fore-reef strata are dominantly packstones and boundstones containing large pieces of coral, abundant benthic forams, coralline algae fragments, stromatoporoids( ), and minor planktonic forams. Reef and near-reef sediments include coralgal boundstones and grainstones with abundant benthic forams. Halimeda and miliolid forams are common in lagoonward parts of the back reef. Sponge borings, geopetal structures, and fractures are common in reef and fore-reef strata. Lagoonal strata are wackestones and packstones with common mollusks, coral, coralline algae, and benthic forams (rotaline and miliolid). Diagenesis has extensively altered strata near the atoll margin. Aragonite dissolution and calcite cements (radiaxial and cloudy prismatic) are abundant in fore-reef, reef, and some back-reef strata. Petrographic and geochemical data indicate aragonite dissolution and calcite cementation in seawater at burial depths of 100 to 300 m. Dolomite occurs in slope and deeply buried reefal carbonates. Most dolomitization occurred at burial depths of more than 1000 m in cool marine waters circulating through the atoll. lagoonal strata are not significantly altered by marine diagenesis and still contain abundant primary aragonite and magnesium calcite.

• Research Organization: Unocal Science and Technology, Brea, CA (USA)
• OSTI ID: 6014956
• Report Number(s): CONF-880301-
• Journal Information: AAPG Bull.; (United States), Vol. 72:2; Conference: Annual meeting of the American Association of Petroleum Geologists, Houston, TX, USA, 20-23 Mar 1988
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
MARSHALL ISLANDS
REEFS
DEPOSITION
ALGAE
CALCITE
CARBONATE ROCKS
CORALS
DISSOLUTION
FOSSILS
GEOCHEMISTRY
MIOCENE EPOCH
STRATIGRAPHY
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CENOZOIC ERA
CHEMISTRY
CNIDARIA
GEOLOGIC AGES
GEOLOGIC STRUCTURES
GEOLOGY
ISLANDS
MICRONESIA
MINERALS
OCEANIA
OXYGEN COMPOUNDS
PLANTS
ROCKS
SEDIMENTARY ROCKS
TERTIARY PERIOD
020200* - Petroleum- Reserves
Geology
& Exploration