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James M. Borer1,
Michael H. Gardner1
(1) Colorado School of Mines, Golden, CO
Abstract: Submarine fan architecture along a slope to basin profile, Brushy Canyon Formation, West Texas
The linkage between submarine channel and fan evolution exists because fans are constructed from channelized and channel-derived deposits. Slope and basin-floor deposits in the Permian Brushy Canyon Formation form a depositional profile, along which changes in facies architecture are compared across eight fan conduits that obliquely intersect the 45-km outcrop belt in progressively more basinward positions. Eight siltstone-bounded 4th-order cycles, each forming up to 50-m thick successions, can be correlated across fan conduits, show a 70% net increase in sand content basinward, and represent deposits that had geomorphic expression as submarine fans within the 3rd-order Brushy Canyon fan complex. Associated with the basinward increase in sand content is a down-profile equilibration of sandstone volumes inside and outside of channels, complexes and conduits. These fan-scale depositional patterns record "build," "cut," "fill," and "spill" phases of bypass and deposition.
The preservation of build-cut-fill-spill depositional phases varies according to position on the depositional profile and/or position in a depositional cycle that records profile migration. The percentage of build- and spill-phase deposits increase down profile to increase sand percent. Slope and upper basin-floor settings have steep gradients that promote sediment bypass producing cut-fill-spill motifs with little or no build-phase deposits. Sandstone percent is low overall, but locally is high in intraslope depressions confining composite channelform sandbodies. Spill-phase deposits are poorly developed because topographic depressions are large and rarely backfill. Stratigraphic motifs change basinward along the basin-floor profile from complex build-cut-fill-spill, to build-fill-spill, to simple build-spill patterns. Recognition of these changing patterns is important because each depositional phase records different sedimentologic processes and energy trends that directly control the type, distribution, and correlation length of architectural elements and facies.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana