Recognition Criteria for Establishing a High-Resolution Sequence Stratigraphic Framework for High Net-to-Gross Slope Sandstones, Permian Brushy Canyon Formation, TX

Michael H. Gardner and Mark D. Sonnenfeld

Detailed outcrop studies of the Brushy Canyon Formation that integrate principles of both seismic stratigraphic and architectural element analysis have establish a slope stratigraphic framework. By analysis of cross-cutting relationships among multi-scale stratal discordances we recognize that the most laterally continuous slope discordance surfaces represent slump scars that confine the position of multistory channel-levee sandstone bodies to topographic lows. The stacking pattern of these sandstone bodies, bounded by laterally continuous slope discordance surfaces, is associated with changes in facies arrangements of mesoscale architectural elements that may help improve predictions of reservoir architecture from remotely sensed seismic and well-log data.

Deep-water strata of the Brushy Canyon Formation represent a lowstand wedge (3rd-order; 1 to 2 Ma) bypassed across a karsted carbonate platform. In slope strata, the lowstand wedge consists of three seismically resolvable, high-frequency sequences (4th order; 0.1 to 0.5 Ma), each containing up to six slope-discordance cycles (5th-order; 0.04 to 0.07 Ma). High- frequency sequences (HFS) are described by the stacking pattern of 5th-order cycles consisting of interlaminated siltstone and sandstone locally replaced by multistory channel-levee sandstone bodies bounded by high-relief and laterally continuous slope discordance surfaces.

The upper Brushy Canyon HFS contains six 5th-order cycles that how a basinward- to shelfward-stepping stacking pattern of slump-scar confined multistory channel-levee sandstone bodies. These show systematic changes in thickness, cycle symmetry, and channel-levee and channel-levee to slope facies proportions. Basinward-stepping cycles are characterized by more frequent and closely spaced slope discordance surfaces, with thicker slope successions separating channel-levee sandstone bodies from bounding slope discordances, lower channel-to-levee facies proportions, and increased cycle symmetry, relative to back-stepping cycles. Significantly, shelfward-stepping channel-levee sandstone bodies occur in a succession previously depicted as a single marine flooding surface. Detailed architectural element analysis of the most basinward-positioned channel-levee sandstone body shows an internal stacking pattern that mimics that of the larger-scale HFS.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California