Memoir 8—Stratigraphy and Paleontology of the Mississippian Sytem in southwestern New Mexico and adjacent southeastern Arizona

By A. K. Armstrong, 1962, 99 pp., 41 figs., 12 plates, 1 index.

The Mississippian system was studied in western Cochise County, Arizona, and in Luna, Hidalgo, and Grant Counties, New Mexico. The primary concern was with the Osage through Meramec Escabrosa Limestone, its stratigraphy, paleoecology, and biologic contents. The Escabrosa Limestone is regarded as a group and has been divided into two formations. These are, in ascending order, the Keating Formation, and the Hachita Formation. The Escabrosa Group has a minimum thickness of 650 ft in the Peloncillo Mountains and a maximum thickness of 1,000 ft in the Big Hatchet Mountains of New Mexico. In the area of this report, it is primarily an encrinite with minor amounts of microcrystalline limestone. These sediments represent almost continuos deposition through all of Osage and Meramec time. The strata were deposited over a slowly sinking shelf area in shallow normal-marine waters.

The corals, brachiopods, blastoids, and endothyrids collected from the Escabrosa Group are described and illustrated. The following new species were found: Chonetes klondikia, Unispirifer balki, Amplexizaphrentis sonoraensis, A. northropi, Vesiculophyllum sutherlandi, Lithostrotionella lochmanae, and Michelinia leptosphragma.

The late Meramec to middle Chester Paradise Formation was studied and part of its brachiopod fauna described. The Paradise Formation is an alternating series of medium-bedded limestones and shales, with a maximum thickness of 220 ft in the Big Hatchet Mountains. It thins rapidly to the north and to the west, and is only about 80 ft thick in the eastern Chiricahua Mountains of Arizona. The Helms Formation of Chester age was studied in the Franklin Mountains and its coral fauna, including the new coral species Koninickphyllum elpasoensis, described.