Rocky Mountain Section–58th Annual Meeting (17–19 May 2006)

Paper No. 2
Presentation Time: 9:20 AM

SUBMARINE MASS TRANSPORT COMPLEX EVOLUTION AND CONTROL ON OVERLYING SILICICLASTIC DEPOSITION, PERMIAN CUTOFF FORMATION, WEST TEXAS


AMERMAN, Robert, Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401, NELSON, Eric P., Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401, GARDNER, Michael H., Department of Earth Sciences, Montana State University, P.O. Box 173480, Trapenhagen 200, Bozeman, MT 59717 and TRUDGILL, Bruce, Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80401, ramerman@mines.edu

In the Delaware Basin, the Williams Ranch Member of the Cutoff Formation consists of six offlapping, basinward-stepping lithologic units of highstand carbonate turbidites deposited across a drowned Early Permian carbonate platform, then partially redistributed in slumps on the slope and basin floor. Slumps are intercalated with undeformed carbonate turbidites; the ratio of slumps to undeformed sediment increases basinward. Upslope evacuation scars correlate to downslope slump bodies. Gravity flow deposition and subsequent mass movement caused basinward thickening of the Williams Ranch Member and caused the toe of slope to shift 2 km basinward relative to the underlying Bone Spring Limestone. This shift controlled landward pinchouts of the overlying Permian Brushy Canyon Formation channel and sheet sandstone bodies.

Williams Ranch Member deposition both responded to and modified inherited bathymetric relief created by tectonism and/or by deposition. Williams Ranch isopach thicks correspond to larger underlying lows and smaller overlying highs and exhibit a higher ratio of undeformed to slumped sediment and a higher percentage of soft-sediment folds relative to soft-sediment truncation surfaces. These slump “pile-ups” appear to be concentrated in inherited lows. Slump bodies show a general southward transport vector, with significant local variation possibly reflecting underlying bathymetric influence. With repeated slump events, “pile-up” zones resulted in local positive bathymetry. Brushy Canyon sand fairways and ponded sheets are focused in bathymetric lows, and sands are sidelapped against highs atop the Williams Ranch Member.