Facies and Architecture of the Upper Permian (Upper Guadalupian) Capitan Foreslope, Guadalupe Mountains, West Texas

Ted Playton¹ and Charles Kerans^2
1Chevron Energy Technology Company, San Ramon, CA
²University of Texas at Austin, Austin, TX

Oligophotic, microbially-dominated boundstone reefs are documented to extend down the slope profile below the influence of high frequency sea level fluctuations. Questions remain regarding the impact of such reef systems on foreslope development and linkages to accommodation change. Outcrops in the Guadalupe Mountains, west Texas expose Upper Permian (Upper Guadalupian) prograding platforms with deep (150-200 m water depth) skeletal-microbial boundstone reefs and associated foreslopes (Capitan Formation).

Fourteen measured sections tied to interpreted photomosaics and 100 samples were collected within a 7 km2 study area with well-exposed Upper Guadalupian Capitan foreslope strata. Foreslope deposits are dominated by 1-3 m thick, lenticular breccias with abundant reef-derived clasts. Internal to clinothems, breccia beds exhibit a hierarchy of compensational, backfilling architecture from the toe-of-slope to the reef, representing repeated upslope accretion in response to intra-slope positive topography generated from prior deposits.

The composition and architecture of the Capitan foreslopes indicate sustained, small-scale gravitational failure of the reef as the dominant resedimentation process. Single collapse events that produce individual breccia beds do not correlate with platform-top high frequency cycles and are substantially less in duration. This suggests autocyclic processes, including boundstone reef accretion, generation of local instability, gravitational failure, and filling of the slope profile, that are independent of high frequency accommodation changes and reflect the deep, oligophotic reef assemblage. Thus, Capitan foreslope exposures reveal that reef type is an autonomous control to consider regarding foreslope development, and also provide an outcrop analogue for reservoirs in similar settings, such as those in the Pricaspian Basin, Kazakhstan.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery