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Abstract: Relationship of Laramide and Basin and Range Structures in the Pedregosa Basin, Southwestern New Mexico

J. Chang, K. C. Miller, S. Thompson, III, G. R. Keller

The Pedregosa basin of southwestern New Mexico has long been recognized as a frontier hydrocarbon exploration target. The Paleozoic sedimentary rocks contain petroleum source and reservoir units that correlate with important producing zones in the Permian basin of west Texas and southeastern New Mexico. Factors that are commonly considered to limit the petroleum potential of the region include multiple episodes of deformation, heating due to local igneous intrusion and volcanism, and fresh-water flushing. Laramide (Late Cretaceous-early Tertiary) fold-and-thrust traps are structural targets. Subsequent fracturing by Basin and Range (late Tertiary) normal faulting may have partially destroyed the Laramide traps.

Seismic reflection and gravity data from the Playas and Hatchita valleys in southwestern New Mexico constrain the structural styles of Laramide shortening and later Basin and Range extensional deformation. These data show that Precambrian basement was involved in Laramide thrusting. This observation refutes the interpretation of some previous workers who interpreted the Precambrian basement surface as a regional decollement for Laramide thrusting.

An east-west seismic profile that crosses the southeast end of the Little Hatchet Mountains images a range-bounding listric normal fault and associated antithetic faults beneath the Hatchita Valley fill. Near the range, "antithetic" faults show a normal sense of motion, but farther east, faults are reverse. The latter may be high-angle Laramide structures or unusual features of Basin and Range deformation. The major range-bounding fault is steeply dipping

near the surface, but becomes a low-angle listric fault at a depth of about 10 km.

AAPG Search and Discovery Article #90980©1994 AAPG Southwest Section Meeting, Ruidoso, New Mexico, April 24-26, 1994