ABSTRACT: The Post-Fusselman Karst of the Northern Franklin Mountains, West Texas and South-Central New Mexico

COLLEARY, WILLIAM M., Colorado School of Mines, Golden, CO, JAMES W. CRAFTON, Colorado School of Mines, Golden, CO, and Gas Research Institute, Chicago, IL, and J. T. FARRARO, and DAVID V. LeMONE,* University of Texas at El Paso, El Paso, TX

The uppermost Fusselman Formation (Crazy Cat Member) at Anthony's Gap in the northern Franklin Mountains exhibits extensive karsting as documented by the presence of such features as sinkholes, breccia-filled solution channels, and preserved terra rosa. Karst control, post-El Paso as well as post-Fusselman, probably is developed by jointing resulting from recurrent fault movements in a pattern inherited from an ancestral Precambrian framework. The post-Fusselman karsting (Middle Silurian-Middle Devonian) in the Franklins developed over more than 40 m.y. The Fusselman represents the uppermost Tippecanoe sequence, and the disconformably overlying Canutillo Formation is the basal Kaskaskia in the Franklin Mountains.

Overlying the Fusselman karst is a thin transgressive unit interpreted to be a silicified lag deposit. The unit has been observed to be only sporadically deposited in local swales and reaches a maximum thickness on the order of 30 cm. This dark-brown to black unit contains subrounded dolomitic pebbles of the Fusselman, as well as scattered fossil material, which in the vertebrates includes apparent teeth and bone material. This lag deposit is interpreted to represent an initial transgressive or flooding surface. This deposit has produced a significant radioactive "hot" gamma-ray spike in a profile taken through the formation using a hand-held scintillometer. The top of the Fusselman in the Permian basin typically is marked on subsurface well logs by a "hot" gamma-ray spike.

AAPG Search and Discovery Article #91018©1992 AAPG Southwest Section Meeting, Midland, Texas, April 21-24, 1992 (2009)