Wolfcampian and Early Leonardian Fore-Shelf Carbonate Debris Production, Permian Basin, West Texas: ABSTRACT

Abstract

Since 1980, a number of Wolfcampian and early Leonardian oil fields have been discovered in a previously unexplored carbonate environment of the Permian basin i.e. basinal fore-shelf debris. These fields range up to 25 MMBOE in size. The Permian basin formed during the Early Pennsylvanian through the earliest Leonardian. Carbonate buildups dominated shelf-edge deposition and a syntectonic wedge of shelf debris was shed into the basins during both high and low sea level stands. Combined eustatic and tectonic sea level fluctuations of over 300 ft have been documented. The geometry, texture, and seismic expression of the debris changes with depositional slope, which ranges from very steep fault-block edges on the Central Basin platform to gentle ramps on the eastern shelf. Productive, low-stand deposits derived from steep shelf edges, consist of turbidite grainstones; clean, very coarse, lithoclastic, debris flaws; and allochthonous slide blocks. These deposits were derived from point sources on the eroded shelf and have a single-lobe or multi-lobe fan geometry. Debris clasts commonly display subaerial lithification and leaching. Lowstand fans extend 4-8 mi into the basin. Productive, lowstand deposits derived from ramp settings have a submarine channel geometry and consist dominantly of grainstone and packstone. Porosity has been enhancedmore » by late subsurface solution. Nonproductive, highstand deposits were derived from a line source and have an apron geometry. These deposits consist of thinly bedded shaly, bioclastic turbidites with no evidence of lithification before final transport.« less