--> Abstract: Diagenetic and Sedimentolgical Aspects of Pinda (Albian) Dolomites: Offshore West Africa, by W. C. Dawson, T. C. O'Hearn, and E. E. Hiatt; #90987 (1993).

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DAWSON, WILLIAM C., and T.C. O'HEARN, Texaco Inc., Houston, TX; E. E. HIATT, Univ. Colorado, Boulder, CO

ABSTRACT: Diagenetic and Sedimentolgical Aspects of Pinda (Albian) Dolomites: Offshore West Africa

The Pinda Formation is a transgressively onlapping, upward-shoaling, carbonate sequence developed on a structural hinge along offshore Angola. Pinda carbonates consist of interstratified oncoid-ooid grainstones and packstones and skeletal packstones and wackestones. Mixed carbonate/siliciclastic lithofacies are developed locally. Collectively, these sparsely fossiliferous Pinda carbonates represent subtidal deposition on a restricted marine, westward sloping ramp.

The Pinda carbonate sequence underwent a complex diagenetic history and was pervasively dolomitized during progressive burial. Petrographic and geochemical data reveal evidence of multiple dolomitization events: penecontemporaneous, mixing-zone, and late burial. Evidence of late dolomite recrystallization is also apparent. The generalized paragenetic sequenceincludes: mechanical compaction, marine cementation, meteoric cementation, anhydrite cementation, stylolitization and fracturing, saddle dolomite precipitation, MVT mineralization, and late anhydrite cementation/replacement. Cementation and dolomitization alternated with multiple dissolution events. Consequently, Pinda reservoirs are characterized by extreme textural variability. Porosity developed preferentially in oncoid-ooid pa kstones and skeletal wackestones. Moldic and intercrystalline porosity are predominant. Paleoflow reconstructions suggest that early Pinda diagenetic fluids (marine and mixed marine-meteoric) flowed downdip (i.e., westward), whereas late (basinal-derived) fluids migrated updip (i.e., eastward).

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.