--> ABSTRACT: Lowstand Carbonate Reservoirs: Upper Pennsylvanian Sea Level Changes and Reservoir Development Adjoining Horseshoe Atoll, by A. M. Reid, S. T. Reid, S. J. Mazzullo; #90996 (1990).

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ABSTRACT: Lowstand Carbonate Reservoirs: Upper Pennsylvanian Sea Level Changes and Reservoir Development Adjoining Horseshoe Atoll

A. M. Reid, S. T. Reid, S. J. Mazzullo

The majority of carbonate reservoirs comprising the Horseshoe Atoll were deposited as reefs and skeletal sand banks during sea level highstands of glacio-eustatic origin, during Canyon (Missourian) and Cisco (Virgilian) deposition. During lowstands, previously deposited carbonate rocks were exposed subaerially to intense meteoric dissolution and karstification creating the pore systems typical of most Horseshoe Atoll fields. Detailed biostratigraphic and sedimentologic studies and recent discoveries adjoining the Horseshoe Atoll have documented the deposition of in-situ and associated intraclastic limestone reservoirs deposited in former slope and basin locations concomittant with periods of sea level lowstand. Our data suggest that the deposition of such reservoirs occur ed throughout the Late Pennsylvanian and accompanied sea level drops of as great as 200 m. To date, productive lowstand reservoirs have been identified in rocks of the middle lower, upper lower, and upper middle Missourian, and the lower lower Virgilian. These deposits are represented by porous reefs, skeletal sandstones, and porous-to-tight intraclastic limestones previously referred to as satellite or pinnacle reefs. These deposits, subsequently onlapped and buried by deep-water shales, comprise potentially prolific stratigraphic-trap reservoirs in basinal areas seaward of the Horseshoe Atoll.

AAPG Search and Discovery Article #90096©1990 AAPG Southwest Section Meeting, Wichita Falls, Texas, March 11-13, 1990