Origin of Smackover Dolomites: Southwest Alabama

Conference · Tue May 01 00:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6857953

Benson, D J ^[1]

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1. Univ. of Alabama, Tuscaloosa (USA)

Dolomite is a major component of the Upper Jurassic Smackover Formation in southwest Alabama Dolomite comprises most of the unit in updip areas and across paleohighs. The amount of dolomite decreases basinward where dolomite is restricted for the most part to the upper and lower parts of the Smackover. Paragenetic relationships indicate that the majority of the replacement dolomite formed early in the diagenetic history of the Smackover, prior to or contemporaneous with deposition of overlying Buckner evaporites. On the basis of isotopic composition, two major types of replacement dolomite can be identified. Type 1 dolomites are characterized by positive (0.0 to +3.1{per thousand} PDB) {delta}{sup 18}O values. They are restricted to the uppermost and lowermost parts of the Smackover in the depositional basins, but comprise virtually the entire Smackover section over paleohighs. Type 2 dolomites are characterized by negative ({minus}0.1 to {minus}5.9{per thousand}) {delta}{sup 18}O signatures and comprise most Smackover dolomite in downdip areas. {delta}{sup 13}C values for both types range from +6.4 to +2.6 and show a regular downward decrease within the Smackover. The distribution, timing of formation, and isotopic composition of the dolomites indicate two distinct mechanisms were responsible for dolomite formation. The isotopically heavy type 1 dolomites were brine derived and formed during refluxion of brines from Smackover and Buckner sabkhas or brine pools. The type 2 dolomites formed from mixed marine and meteoric waters. Dolomitization occurred in isolated mixing zones that developed around shoal complexes during short-term falls of eustatic sea level. The distribution of dolomite and specific dolomitization mechanisms in any area are a function of eustatic sea level fluctuations and paleotopography.

• OSTI ID: 6857953
• Report Number(s): CONF-900605--
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Vol. 74:5; ISSN AABUD; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
58 GEOSCIENCES
580000 -- Geosciences
ALABAMA
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
DIAGENESIS
DOLOMITE
EVAPORITES
FEDERAL REGION IV
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
JURASSIC PERIOD
LEVELS
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MESOZOIC ERA
MINERAL RESOURCES
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
PETROLEUM DEPOSITS
RESERVOIR ROCK
RESOURCES
ROCKS
SEA LEVEL
SEDIMENTARY ROCKS
USA