This report is preliminary and has not been edited or reviewed for conformity with U.S. Geological Survey standards and nomenclature.Report prepared in cooperation with the U.S. Nuclear Regulatory Commission under Interagency Agreement AT(49-25)-1000. Contents

No abstract

This report summarizes the Cenozoic history of the Pecos drainage in the Delaware basin, southeastern New Mexico, and incorporates an outline of the dissolution and karst development in Permian evaporites in the region. Evaporites include anhydrite, gypsum, halite and related minerals. They are included in the Castile, Sal ado and Rustler Formations of Late Permian (Ochoan) age. These formations have been transgressed by strata of the Dockum Group of Late Triassic age and unnamed formations of Early Cretaceous age. Complex karst features include collapse sinks, karst mounds (new term), karst domes (new term) and caves. Karst mounds are erosional remnants of regional breccia. Karst domes are structural features which have formed on a very irregular dissolution surface. They are analogous to towers, kegelkarst or mogotes in tropical regions except that karst domes are almost buried by their own dissolution residue. Breccia chimneys are collapse sinks which have formed over the Capitan aquifer system. They appear to be the result of unsaturated water rising under a strong hydraulic head through fractures and dissolving upward into the evaporite sequence. Breccia chimneys, karst mounds and karst domes studied during this work were formed during middle Pleistocene time. Dissolution has been an active process in the Delaware Basin at least since Triassic time and it is impractical to attempt to calculate a rate of dissolution for the basin. Earlier estimates of the rate of dissolution are considered to be conservative. Subsurface evidence does not suggest that deep dissolution is presently an active process in the Castile Formation beneath the thick beds of Salado salt. Pleistocene glaciation in the northern and central United States was probably accompanied by "pluvial" periods in southeastern New Mexico. PIuvials are characterized by less extreme temperatures, less evaporation and more effective moisture than at present.

The Permian salt basin in the Western Interior of the United States is defined as that region comprising a series of sedimentary basins in which halite and associated salts accumulated during Permian time. The region includes the western parts of Kansas, Oklahoma, and Texas, and eastern parts of Colorado and New Mexico.

Issued by Sandm National Laboratories, operated for the United States Department of Energy by Sandm Corporation. NOTICE: This report was repared aa an account of work sponsored by an agency of the United States kvernment. Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their emplo makes any warranty, express or implied, or assumes any legal IiaG; or responsibility for the accuracy, completeness, or usefulness of any information, a aratus, product, or p-disclosed, or represents that its use woufi'not infringe privately owned righta. Reference herein to any specirc commercial d u c t , pmce%s, or seMca by trade name, trademark, manufacturer, or o&erwise, does not neceasaril constitute or imply ita endorsement, recommendation, or favoring by the 6nited Statea Government, an agency thereof or any of their contractors or subcontractors. The views a n i opinions expressed herein do not neeeasarily state or reflect those of the United States Government, any agency thereof or any of their contractors or subcontractors.