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BROADHEAD, RONALD F., New Mexico Bureau of Mines and Mineral Resources, a Division of New Mexico Tech, Socorro, NM 87801

ABSTRACT: Petroleum Systems in Pennsylvanian Elevator or Basins of New Mexico

The Tucumcari, Estancia, Vaughn, and Carrizozo Basins are located in northeast and central New Mexico. These basins began to form during the Early to Middle Pennsylvanian. Tectonic development continued through the Early Permian. They were formed along the flanks of the late Paleozoic Sierra Grande and Pedemal uplifts in a strike-slip setting.

These basins were dominated by shallow-shelf deposition. Along the boundaries with adjoining uplifts, these basins have component elevator basins, long, narrow, and structurally deep troughs bounded by high-angle faults. Bounding faults have vertical offsets that can exceed 5,000 ft. Basin length ranges from 20 to 50 miles and width ranges from 5 to 15 miles.

Early to Middle Pennsylvanian strata in the elevator basins are gray to black shales and sandstones. The shales are mature petroleum source rocks. Total organic carbon (TOC) can exceed 9% in black shales. Kerogens range from gas-prone woody types to oil-prone amorphous types. Greater depth of burial in the elevator basins as compared to the adjoining uplifts and shelf areas has resulted in optimum thermal maturation within the basins. Hydrocarbons generated within the basins have migrated upward along the bounding faults and into reservoirs on adjacent shelves as well as being trapped within sandstones in the elevator basins. If rates of subsidence exceeded rates of deposition, then the source rocks within the elevator basins are oil prone kerogens and reservoirs on the adjoining shelf include fringing reefs. If rates of deposition exceeded rates of subsidence then source within the elevator basin are gas prone and reservoirs on the adjoining shelf are primarily sandstones.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico