Regional distribution and chemical characterization of Permian Capitan fore-reef slope dolomite: Implications for paleohydrology

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

OSTI ID:6645158

Melim, L A ^[1]

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1. Southern Methodist Univ., Dallas, TX (USA)

Dolomitized fore-reef slope facies recently have become significant targets for petroleum exploration in the Permian basin and elsewhere. Despite this, very little is known about the dolomitization process that largely controls porosity distribution in this facies. An integrated field, petrographic, and geochemical study has been conducted in the fore-reef slope strata of the Permian Capitan Formation to provide insight into this problem. Dolomitization of the Capitan fore-reef slope facies ranges from 0 to 100%. Regionally, the variation is related to stratigraphic age, with older forereef slope facies more dolomitized than younger facies. This generalization is consistent throughout the Guadalupe Mountains and appears to continue into the subsurface. On a local scale, more permeable beds were the first dolomitized, and within these, dolomitization decreases downslope. In the Capitan reef facies, dolomitization is restricted to vertical karst breccia pipes and other zones of high primary porosity. The majority of Capitan dolomite is finely crystalline (5-30 {mu}) with average {delta}{sup 18}O = 0.9 and {delta}{sup 13}C = 5.9. A second coarser (130-{mu}) dolomite generation is also present but is not as volumetrically important. The relative positive (for the Late Permian) {delta}{sup 18}O values indicates an evaporitively concentrated dolomitizing fluid. The most likely paleohydrologic model for the main phase of forereef slope dolomitization calls for descending hypersaline brines passing through the reef facies in vertical karst breccia pipes and then following permeable beds down the foreslope. Several sources are possible for these brines, with the most likely being the hypersaline back-reef lagoonal environment.

• OSTI ID: 6645158
• Report Number(s): CONF-900605-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 74:5; Conference: Annual convention and exposition of the American Association of Petroleum Geologists, San Francisco, CA (USA), 3-6 Jun 1990; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CARBONATE ROCKS
DIAGENESIS
PERMIAN BASIN
TEXAS
BRINES
DOLOMITE
GEOLOGIC FORMATIONS
HYDROLOGY
PERMEABILITY
REEFS
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
FEDERAL REGION VI
GEOLOGIC STRUCTURES
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
ROCKS
SEDIMENTARY ROCKS
USA
580000* - Geosciences