New Mexico Geological Society Annual Spring Meeting — Abstracts

The Pennsylvanian section at Bell Hill in the southern San Mateo Mountains of southern Socorro County, New Mexico (sec. 16, T8S, R4W and vicinity), has long been considered the thickest Pennsylvanian section (~ 800 m thick) in south-central New Mexico and the focal point of a late Paleozoic San Mateo depositional basin. Kottlowski (1960) first described the Paleozoic section at Bell Hill (his Eaton Ranch section) as 808 m of Pennsylvanian strata on Proterozoic basement and overlain by the lower Permian Abo Formation. Furlow (1965; Kelley and Furlow, 1965), however, interpreted the section differently, as ~ 91 m of Cambro-Ordovician strata resting on the basement, overlain by ~732 m of Pennsylvanian strata beneath the Abo Formation. We restudied the Pennsylvanian section at Bell Hill and determined that the Pennsylvanian section is thinner than previously reported, only 495 m thick. At Bell Hill, the Pennsylvanian strata overlie a thin (~ 70 m thick) lower Paleozoic section that consists of the Cambro-Ordovician Bliss Formation and the Ordovician El Paso Group (Sierrite Member of the Hitt Canyon Formation) and Montoya Formation (Cable Canyon and Upham members). The Middle Pennsylvanian Red House Formation unconformably overlies the Montoya Formation, and is at least 31 m thick (structural complications prevent a certain estimate). It is overlain by the Gray Mesa Formation, which is 158 m thick and divisible into the Elephant Butte (at least 18 m thick), Whiskey Canyon (53 m thick) and Garcia (87 m thick) members. The overlying Bar B Formation is 306 m thick, substantially thicker than to the south, and accounts for most of the relatively great thickness of the Bell Hill Pennsylvanian section. The Bar B Formation is overlain by the Bursum Formation, ~ 18 m thick, which is overlain by the Abo Formation. Fusulinid and conodont biostratigraphy indicate that at Bell Hill the Red House Formation is Atokan, the Gray Mesa Formation is Desmoinesian and the Bar B Formation is Desmoinesian-Virgilian. The new estimate of the thickness of the Pennsylvanian section at Bell Hill requires redrawing the late Paleozoic San Mateo basin as an east-west-oriented trough instead of a single, localized depocenter.

References

Furlow, J. W., 1965, Geology of the San Mateo Peak area, Socorro County, New Mexico [M. S. thesis]: Albuquerque, University of New Mexico, 83 p.

Kelley, V. C. and Furlow, J. W., 1965, Lower Paleozoic wedge edge in south-central New Mexico: New control: Geological Society of America Bulletin, v. 76, p. 689-694.

Kottlowski, F. E., 1960, Summary of Pennsylvanian sections in southwestern New Mexico and southeastern Arizona: New Mexico Bureau of Mines and Mineral Resources, Bulletin 66, 187 p.