TALBERT, SAMUEL J., and STACY C. ATCHLEY , Baylor University, Waco, TX
A sequence stratigraphic framework is provided for the, Lower Cretaceous (Albian) Fredericksburg Group in central and, north Texas based upon a dataset of forty-two outcrop-measured sections and eleven water-well resistivity logs. Outcrop results indicate the Fredericksburg is partitioned into at least 5 regionally, correlative parasequence sets and therefore indicates the potential for predictable reservoir compartmentalization within subsurface equivalents.
The Fredericksburg Group accumulated as a carbonate shelf comprised of six shallow marine facies. Facies are distributed within a cyclic hierarchy of parasequences and parasequence sets that stack into a lower-order composite sequence. The lower composite sequence boundary is overlain by lowstand nonmarine-to-marginal-marine siliciclastics of the Paluxy and Antlers Formations within the northern portion of the study area. Lowstand siliciclastics are truncated by a transgressive ravinement surface, and overlain by retrogradational parasequence sets of the transgressive systems tract (parasequence sets 13: Bull Creek, Bee Cave and Cedar Park Members of the Walnut Formation). The succeeding highstand systems tract is initiated at the composite sequence maximum flooding surface (lower portion of the Keys Valley Member of the Walnut Formation), and is comprised of progradational parasequence sets (parasequence sets 35: middle and upper Keys Valley Member, Comanche Peak Limestone, Edwards Limestone). The highstand systems tract has the highest proportion of potentially reservoir-prone margin shoal and rudistid buildup facies. Reservoir-prone facies are often interbedded with deeper-water lower reservoir quality facies across parasequence set boundaries, and are spatially offset in a basinward direction due to progradational stacking.
AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas