--> --> Outcrop to Subsurface Linkages, Canyon and Cisco Groups, Eastern Shelf of the Permian Basin

AAPG Southwest Section Annual Convention

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Outcrop to Subsurface Linkages, Canyon and Cisco Groups, Eastern Shelf of the Permian Basin

Abstract

Coastal-plain, incised-valley, shelf, and shelf-edge depositional facies in the Missourian Canyon Group and Virgilian-Wolfcampian Cisco Group are well- documented in outcrops in north Texas. This study links outcrops in this stratigraphic succession to subsurface slope and basin-floor systems in a ~12,000 mi2 (~31,000 km2) area in the southern part of the Eastern Shelf of the Permian Basin. The Canyon Group (base Palo Pinto Limestone to top Home Creek Limestone) is mostly an aggradational, carbonate-bank succession with locally prominent reef facies. The bank/reef interval, age-equivalent to the Horseshoe reef complex, is as much as 1,540 ft (~470 m) thick in northeastern Coke County and forms an irregular shelf margin. Reef buildups also occur in local pinnacles on the platform. Canyon basin-floor facies are equivalent to the lower part of the Cline shale (“Wolfcamp D”) and are dark, organic-rich (˃2% TOC) mudrocks. The Cisco section consists of a cyclic series of thirteen mudrock, limestone, and sandstone facies (top of the Home Creek to top Coleman Junction Limestone). It forms a progradational succession from the eastern edge (Bunger Limestone) to the central part of the study area (Coleman Junction Limestone). The top of the Home Creek Limestone coincides with a regional downlap surface for progradational lower Cisco shelf strata. Progressive upward decrease in height of shelf-margin clinoforms indicates that accommodation decreased in the upper Cisco Group. The Pennsylvanian–Permian (Virgilian–Wolfcampian) boundary is at the top of the Cline Shale in the basin and slope, occurring onshelf above the Crystal Falls Limestone. The Wolfcampian section is ~700 to 850 ft [~210 to 260 m]) thick on the shelf and expands basinward to 3,500 ft (~1,070 m) thick into a “foredeep” area. However, it is thinner in the deeper part of the basin (<500 ft [<152 m]). Slope facies closest to Virgilian and lower Wolfcampian shelf margins are mostly siliciclastic mudrocks and sandy turbidites. The Wolfcampian (upper Cisco) basin system to the west comprises (1) siliciclastic, thin turbidites and hemipelagic mudrocks in the lower Wolfcampian and (2) carbonate debris-flow deposits and turbidites in the upper part. In contrast, the Virgilian (lower Cisco) basin succession constitutes organic-rich mudrocks of the upper Cline Shale.