--> ABSTRACT: Compaction of Wilcox Sandstones to 14,500 Feet, by E. F. McBride, J. C. Wilson, and T. N. Diggs; #91022 (1989)

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Compaction of Wilcox Sandstones to 14,500 Feet

E. F. McBride, J. C. Wilson, T. N. Diggs

Changes in packing and porosity resulting from compaction were studied in 38 Wilcox sandstones from 12 cores. Burial depths, adjusted for erosion in updip areas, range from 1,100 to 14,500 ft. Neither quartz (x = 5.6%) nor carbonate cement (x = 2.9%) were introduced shallow enough or in sufficient abundance in the sandstones to significantly retard compaction. As a result, compaction continued to maximum burial depth and was the main cause of porosity decrease with depth (r = 0.82). As measured by increases in packing indices, sands compacted rapidly to depths of 2,500 to 4,000 ft (where intergranular volume averages approximately 30%) and more slowly and variably at greater depths. At all depths the amount of porosity lost by grain rearrangement was about twice the poros ty lost by ductile grain deformation or by pressure solution. Ductile grain deformation was identified as shallow as 1,100 ft (the shallowest sample) and pressure solution as shallow as 1,915 ft. At shallow depths, only clay rip-up clasts deformed ductily; at greater depths micaceous rock fragments, micas, and glauconite deformed also. Surprisingly, porosity loss by ductile deformation has only a poor correlation (r = 0.62) with total amount of ductile grains. Quartz is the main mineral that undergoes pressure solution, although feldspar and volcanic rock fragments locally pressolve also.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.