Lower Cisco Formation (Pennsylvanian- Virgilian) Paleokarst, Wolf Flat Field, Palo Duro Basin, Texas

R. C. Trentham, R. F. Lindsay, R. C. Price, and D. D. Pack

Wolf Flat field produces from karstified Lower Cisco Formation at the rimmed northeast shelf margin. Mounds, peripheral skeletal debris, and oolitic facies form the vertical/lateral succession. Mounds are composed of crinoids, bryozoans, corals and algae. Skeletal packstone/grainstones surround mounds, with back-mound wackestone. Ooid grainstone formed in high-energy passages onto the shelf and cap shallowing-upward cycles.

Karstification resulted from two 100+ ft (30+ m) sea level drops, that dropped in a step-by-step manner to form ~20 porous intervals that extend through all facies and lithologies in the field. Aragonitic mound and skeletal grainstone/wackestones experienced intense dissolution. Calcitic ooid grainstones dissolved less and form cave roofs and floors. Dissolution was in two phases: first, small vertically oriented pipes formed, resembling a "swiss cheese" texture; second, was intense lateral dissolution that created a "sponge" texture, with porosities up to 60-70%. Eventually, collapse breccias formed, with some clasts transported in the karst system.

Porosity was reduced by vadose silt, breccia clasts, speleothem cements, transgressive shale infilling, and burial saddle dolomite. Portions of the field nearest the rimmed margin were dolomitized.

^dgr¹⁸O is within the range of early meteoric diagenesis and ^dgr¹³C is negative and becomes more negative toward the exposure surface.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California