1989 NMGS Spring Meeting: Abstract-2118

STRATIGRAPHY OF THE CRETACEOUS BISBEE GROUP IN THE CENTRAL PELONCILLO MOUNTAINS, HIDALGO COUNTY, NEW MEXICO Steven N. Hayden1 and Spencer G. Lucas2 1Department of Geology, University of New Mexico, Albuquerque, NM, 87131 2New Mexico Museum of Natural History, P.o. Box 7010, Albuquerque, NM, 87194 Gillerman (1958, NMBMMR Bulletin 57) named four formations for strata of the Bisbee Group (Aptian-Albian) exposed in the central Peloncillo Mountains. The type section of Gillerman's McGhee Peak Formation is on McGhee Peak in the SW1/4 SE1/4 SW1/4, sec. 34, T24S, R31W and consists of 107 m of interbedded siliceous conglomerate, sandstone and siltstone. We correlate these strata with the Glance Conglomerate and Morita Formation of the Bisbee Group, but because of interbedding of Glance and Morita lithologies we are unable to recognize separate formations. The McGhee Peak Formation is homotaxial with the Hell to Finish Formation of the Big and Little Hatchet mountains to the east, but we refer to this interval in the central Peloncillo Mountains as the Glance/Morita Formation. We designate a type section for Gillerman's Carbonate Hill Formation in the NE1/4 SE1/4 SW1/4, sec. 34, T24S,R21 W where it consists of 49 m of brownish gray to graylimestone and siltstone. In other sections near the Carbonate Hill Mine (E1/2, sec. 34; T24S, R21W) it may be as much as 90 m thick and contains a late Aptian marine invertebrate fauna dominated by Ostrea, Exogyra, turritelloid gastropods and parahoplitid ammonoids. Gillerman's Carbonate Hill Formation is equivalent to the Mural Formation of the Bisbee Group and the oyster limestone and reef limestone members of the U-Bar Formation in the Big Hatchet Mountains. In the central Peloncillo Mountains, we abandon the term Carbonate Hill Formation in favor of Mural Formation. Gillerman's Still Ridge Formation type section runs from the SW1/4 SE1/4 NW1/4 to the SE1/4 NW1/4 NW1/4,sec. 34, T24S, R21W. Its base is not exposed, it is 116+ mthick and consists of interbedded limestone siltstone and limestone- pebble conglomerate. We equate it to part of the Mural Formation and with the suprareef limestone member of the U-Bar Formation in the Big Hatchet Mountains. We thus abandon the term still RidgeI Formation in favor of Mural Formation. Gillerman's Johnny Bull Sandstone type section is in the NW1/4 SW1/4, sec, 4, T25S, R21W. This also is an incomplete section, being in fault contact with the Mural Formation at the base and with Precambrian granitoid rocks at the top. The Johnny Bull here consists of 241+ m of metamorphosed, interbedded sandstone, siltstone and shale. The Johnny Bull correlates with thecinturaI Formation of the Bisbee Group and with the Mojado Formation of the Big and Little Hatchet mountains. We thus abandon the name Johnny Bull in favor of Cintura. Drewes and Thorman (1980, USGS Map I-1220) misidentified this unit as the Morita Formation at its type section. Hayes (1970, USGS Professional Paper 658-B) correlated it with the Ringbone Formation of the Little Hatchet Mountains, which is of Late Cretaceous age. However, the Bobcat Hill Conglomerate, which overlies the cintura Formation in the central Peloncillo Mountains, has yielded , Late Cretaceous dinosaur fossils and is the apparent correlative of the Ringbone. Keywords: stratigraphy pp. 15 1989 New Mexico Geological Society Annual Spring Meeting April 7, 1989, Macey Center.

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