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Abstract: Effects of Relative Sea Level Changes on Facies and Diagenetic Variability of a Pennsylvanian Outcrop and Near-Surface Reservoir Analog, SE Kansas (Missourian, Drum Limestone)

Irene Gomez-Perez, Howard R. Feldman, Evan K. Franseen, J. A. (Toni) Simo

The Drum Limestone contains facies that are an analog to important petroleum reservoirs elsewhere in the Mid-continent. It consists predominantly of an oolitic shoal and algal buildup complex deposited at the seaward edge of a shale delta. This study integrates outcrop, core, well log, petrographic, and high-resolution reflection seismic data to understand the role of relative sea level fluctuations in the depositional and diagenetic history of the Drum reservoir facies.

The Drum Limestone forms an E-W belt 30 km wide, is up to 21 m thick, and thins to less than one meter thick both up-dip and down-dip of the depositional shelf edge. The basal contact of the Drum Limestone is regionally erosive and interpreted to represent a relative sea level drop. The erosion surface is overlain by a basal oolite with lithoclasts. Two-thirds of the Drum oolite facies coexisted partially with algal-bryozoan buildups, in shallow-waters at the shelf edge. Ooids were likely transported by tidal and wave currents to paleotopographic lows forming basinward prograding (SSW direction) clinoforms. Landward, Drum facies grade to stromatolites, and basinward the oolite pinches out.

An interpreted relative sea level fall at the end of this Drum depositional stage resulted in a sharp, regionally traceable surface with evidences of likely subaerial exposure in shelf positions, and represented basinward by an oolitic lithoclastic breccia capped by an incipient hardground. The surface is overlain by Drum trough-crossbedded (N-NE direction) bioclastic oolitic facies interbedded with shales, deposited during a relative sea level rise. This upper third of oolite deposition was influenced by siliciclastic input from the south that eventually overtook carbonate sedimentation.

Facies and diagenetic changes documented for the Drum Limestone analog are providing important details on reservoir heterogeneities at a scale important for Mid-continent reservoirs.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France