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Bulletin 112—Palynology and age of south Hospah coal-bearing deposits, McKinley County, New Mexico

By A. Jameossanaie, 1987, 65 pp., 4 tables, 17 figs.

Ninety-four samples from four core sections in the South Hospah coal-bearing deposits, McKinley County, NM, yielded a rich palynomorph assemblage. In this volume 172 species assigned to 91 form genera of spores, gymnospermous pollen, and angiospermous pollen are described. Two new genera of spores, eight new species, nine new combinations, and two new ranks are proposed. One hundred fourteen of the described palynomorphs are either stratigraphically restricted to the Cretaceous System, or their older reported occurrence is in the Cretaceous. The palynomorph assemblages indicate a Late Cretaceous (early Companion) age for the South Hospah deposits. According to palynological evidence, assignment of these strata to the Menefee Formation is appropriate. The source of some of the clastic material in the South Hospah deposits is interpreted based on the occurrence of palynomorphs recycled from older strata.

Most of the palynological studies pertinent to the Upper Cretaceous strata of western North America have been summarized. Only a few palynological studies have been published on the Cretaceous rocks of NM. The oldest coal-bearing unit in the San Juan Basin, NM, is known as the Mesaverde Group. It consists, in ascending order, of the Crevasse Canyon Formation with two coal-bearing members, and the Menefee Formation with a lower coal-bearing member and an upper, unnamed, coal-bearing member. The most economically significant coal in the basin is found in the stratigraphically higher Fruitland Formation. The study area is located on the South Hospah lease, about 19 road miles northwest of Crownpoint, adjacent to, and on the western side of, the Continental Divide, in the east-central part of McKinley County, NM. It includes sections in Orphan Annie Rock and Laguna Castilla quadrangles. The exposed rocks consist mainly of shale beds and crossbedded sandstones. These deposits have been assigned to the Cleary Coal Member of the Menefee Formation by both petroleum geologists and the coal geologists mapping the South Hospah lease area. The strata dip about 2-3º NNE towards the center of the San Juan Basin. Coal seams are exposed locally at the surface.

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