Distribution and Character of Soft-Sediment Structures within a Paleo-Submarine Mass Transport Complex and Implications for Reservoir Geometry Prediction, Permian Cutoff Formation, West Texas

Robert Amerman, Eric P. Nelson, and Michael H. Gardner
Colorado School of Mines, Golden, CO

Paleo-topography produced by a huge paleo-submarine mass transport complex (MTC) controls the geometry and lithology of overlying deep-water siliciclastic reservoir strata (Permian Brushy Canyon Formation). Sedimentological and structural data collected across a 6-km transect suggest that the MTC was formed by multiple mass transport events (MTEs) of previously deposited carbonate turbidites. Seven “strato-structural” units were recognized and mapped and exhibit unique geometries, facies, and structural characteristics. Structures include variable-scale (mm- to decameter) folds, faults, and lineations resulting from the intersection of cm-scale folds and faults with bedding planes. These structures are locally concentrated within MTE bodies. Blocks in MTE bodies contain previously formed mm- to cm-scale structures. Such blocks are up to several meters thick, with lateral dimensions of at least 10s of meters. Mesoscopic complex deformation zones associated with fault ramps may indicate the presence of macroscopic structures. MTE bodies show a generally north–south transport vector and a pattern of waning volume and degree of deformation through time. Structural style is dominated by shortening, which caused Cutoff thickness to double over a distance of 20+ km and produced local highs that concentrate Brushy Canyon sandstone deposition within the intervening topographic lows. As the geometries and cumulative thicknesses of all MTE bodies controlled depositional patterns in overlying sandy sediment gravity flows, the distribution of soft-sediment structures within an MTC may provide a tool for predicting sand body geometry and lithology.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005