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Title: Reflux revisited

The samples and data for this project are derived from 22 test holes drilled to a maximum depth of 91 m, and from rock exposures representing the carbonate section through the Miocene. Dolomite on St. Croix exists in a highly localized region of outcrops and subsurface occurrences in a Miocene-Pliocene reef tract and its related facies. Bioclasts in the dolomitic strata commonly show surprisingly good preservation of microstructure, particularly in large benthic forams and coralline algal clasts. The dolomite is stoichiometrically calcium-rich and exists as euhedral rhombs ranging from 2 to 30 ..mu..m in diameter. The surficial dolomitization occurs in reef, lagoonal, and platform facies that rim the predevelopment shoreline of a coastal lagoon. In the subsurface, dolomitized rock follows the lithifield undersurface of the same lagoon. This spatial distribution of dolomitization suggests a causal relationship between the lagoon hydrology and the process of the dolomitization. The preliminary Sr/sup 87//Sr/sup 86/ isotopic composition of the dolomite is 0.70888, which corresponds to Miocene-Pliocene seawater values, and suggests a Miocene-Pliocene age for the dolomitization event. Stable isotopic values average +2.3 o/oo for delta/sup 13/C and +4.1 o/oo for delta/sup 18/O, both relative to the PDB standard. These data imply that dolomitization tookmore » place by reflux of Pliocene fluids enriched in /sup 18/O. The dolomitization was confined to a fault-bounded region, and affected reef, lagoonal, and platform carbonates.« less
Authors:
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Publication Date:
OSTI Identifier:
6591935
Report Number(s):
CONF-880301-
Resource Type:
Conference
Resource Relation:
Conference: Annual meeting of the American Association of Petroleum Geologists, Houston, TX, USA, 20 Mar 1988
Publisher:
American Association of Petroleum Geologists,Tulsa, OK
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; 03 NATURAL GAS; DOLOMITE; PETROGENESIS; NATURAL GAS DEPOSITS; MINERALOGY; PETROLEUM DEPOSITS; VIRGIN ISLANDS; PETROLEUM GEOLOGY; BENTHOS; BIOGEOCHEMISTRY; CARBONATE ROCKS; CHEMICAL COMPOSITION; EXPLORATION; ISOTOPE RATIO; MINERALIZATION; MIOCENE EPOCH; PETROCHEMISTRY; PLIOCENE EPOCH; REEFS; STRONTIUM 86; STRONTIUM 87; ALKALINE EARTH ISOTOPES; ALKALINE EARTH METAL COMPOUNDS; AQUATIC ORGANISMS; BETA DECAY RADIOISOTOPES; CALCIUM CARBONATES; CALCIUM COMPOUNDS; CARBON COMPOUNDS; CARBONATE MINERALS; CARBONATES; CENOZOIC ERA; CHEMISTRY; ELECTRON CAPTURE RADIOISOTOPES; EVEN-EVEN NUCLEI; EVEN-ODD NUCLEI; FEDERAL REGION II; GEOCHEMISTRY; GEOLOGIC AGES; GEOLOGIC DEPOSITS; GEOLOGIC STRUCTURES; GEOLOGY; HOURS LIVING RADIOISOTOPES; INTERMEDIATE MASS NUCLEI; ISLANDS; ISOMERIC TRANSITION ISOTOPES; ISOTOPES; LESSER ANTILLES; MAGNESIUM CARBONATES; MAGNESIUM COMPOUNDS; MINERAL RESOURCES; MINERALS; NORTH AMERICA; NUCLEI; OXYGEN COMPOUNDS; RADIOISOTOPES; RESOURCES; ROCKS; SEDIMENTARY ROCKS; STABLE ISOTOPES; STRONTIUM ISOTOPES; TERTIARY PERIOD; USA; WEST INDIES 020200* -- Petroleum-- Reserves, Geology, & Exploration; 030200 -- Natural Gas-- Reserves, Geology, & Exploration