Regional geology and Cenozoic history of Pecos region, southeastern New Mexico

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.

Condensed listing of surface boreholes at the Waste Isolation Pilot Plant Project through 31 December 1995

“…WIPP 17,20,23, and 24 were planned but not drilled because the technical justifications for these holes were satisfied by data obtained from earlier boreholes. WIPP 25 through WIPP 30 were drilled specifically to define the geology and hydrology of the Nash Draw area, a broad, shallow topographic depression west of the WIPP site (Bachman, 1980). were studied extensively because some units contain groundwater.…”

Basic Data Report for Drillhole SNL-12 (C-2954)

“…SNL-12 is distant from an outcrop of Lava Creek B ash found at the top of the Gatuña by Bachman (Bachman, 1980;Izett and Wilcox, 1982) along Livingston Ridge. The Gatuña at SNL-12 does not provide any direct clues to its age, but it may represent younger portions of the unit range, as is believed the case for much of the upland Gatuña deposits.…”

Basic Data Report for Drillhole SNL-3 (C-2949)

“…SNL-3 is located east of an outcrop of Lava Creek B ash found at the top of the Gatuña by Bachman (Bachman, 1980;Izett and Wilcox, Basic Data Report for Drillhole SNL-3 (C-2949) DOE/WIPP 03-3294…”