--> ABSTRACT: Subsurface Study of Lower Tuscaloosa Formation at Olive Field, Pike and Amite Counties, Mississippi, by Gary J. Wiygul and Leonard M. Young; #91042 (2010)

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Subsurface Study of Lower Tuscaloosa Formation at Olive Field, Pike and Amite Counties, Mississippi

Gary J. Wiygul, Leonard M. Young

Olive field is located on the Amite-Pike county line in southwestern Mississippi. The field was discovered by Shell Western Exploration and Production Inc., and produces from a stratigraphically trapped sandstone within the lower Tuscaloosa Stringer Member. The Stringer Member consists of alternating sandstones, siltstones, and shales, and averages 76 m thick at Olive field. The Stringer Member represents a transgressive sequence deposited on eroded Washita Fredericksburg sediments and is overlain by middle Tuscaloosa marine shales.

The coarse to fine-grained sandstones are quartz-rich with a high percentage of sedimentary rock fragments. Most of the sandstones are shale arenites. However, many rock fragments were greatly altered, and could not be identified with confidence; many may be of volcanic origin. The sandstones are cemented by quartz overgrowths, iron-rich carbonate cement, and chlorite. Sandstones commonly exhibit a high, preserved, interparticle porosity, that is characteristic of lower Tuscaloosa sandstones. This interparticle porosity is attributed to chlorite, which occurs as an isopachous cement that coats grains and reduced nucleation sites for quartz overgrowths.

The Stringer Member was subdivided into five zones in this study, based on lithology and electric-log responses. The lower three zones were deposited in a fluvial environment. The sandstones were deposited as point bars and channel sands in a meandering system. Siltstones and shales represent overbank deposits, flood-basin deposits, and channel-fill deposits. The upper two zones consist of sediments deposited at or near sea level. Finely laminated shales and siltstones represent marsh and bay deposits. The top zone is a thin continuous sand body that represents a remnant beach deposited before major marine transgression occurred.

AAPG Search and Discovery Article #91042©1987 GCAGS and GC-SEPM Section Meeting, San Antonio, Texas, October 28-31, 1987.