Circular 139—Clay minerals in east-central New Mexico

By H. D. Glass, J. C. Frye, and A. B. Leonard, 1973, 14 pp., 8 figs., appendix.

Representative samples were analyzed for clay mineral composition and evaluated for identifiable sediment sources. Samples of Pleistocene deposits from east-central New Mexico were analyzed for clay mineral composition, and representative samples of Tertiary, Triassic, and Permian rocks were analyzed for evaluation of sediment sources. Throughout the region montmorillonite, illite, and kaolinite were found to be most widespread and abundant, and are shown to be detrital minerals from identifiable sources. Sepiolite was present only in the pond and lake deposits of the High Plains area. Attapulgite occurs in the Ogallala Formation and in middle to early Pleistocene soil profiles on alluvial deposits. Corrensite was present in three localities: a Triassic sandstone, late Wisconsinan sediment fills in basins developed in Permian rocks, and Holocene terrace deposits of the Pecos River valley.

During the summers of 1971 and 1972, Frye and Leonard spent several weeks in the field in east-central New Mexico, under auspices of the New Mexico Bureau of Mines and Mineral Resources, investigating Pliocene and Pleistocene deposits. As part of this project, 129 samples were collected for clay mineral analysis. Geographic distribution of the sample localities is shown. Most of these samples were collected from late Pleistocene deposits, many of which were from the fillings of short-lived ponds and lakes of Woofordian age, but other samples came from earlier Pleistocene deposits, from the widespread Ogallala Formation, and from the older bedrock of Triassic and Permian age. We present here the results of X-ray analyses of these samples as a reconnaissance of the clay mineral compositions of the region.

East-central New Mexico includes the western part of the High Plains. The High Plains extend from South Dakota southward across Nebraska, Kansas, Oklahoma, Texas, and New Mexico, to the Pecos Valley of Texas. The part of the High Plains that includes west-central Texas and east-central New Mexico, stands as an Ogallala-capped plateau, generally called the Llano Estacado, above the erosional plains to the east, to the north along the broad valley of the Canadian River, and to the west along the Pecos River valley, bounded by prominent, sharp, high escarpments. On the south the High Plains merge with a portion of the Edwards Plateau.

The study area discussed here extends from central Lea County, and the northern part of Eddy County, northward to the north line of Curry County, and southern Guadalupe County, and westward from the Texas state line to the western side of Pecos River valley through De Baca and Chaves Counties. The eastern part of this area is within the High Plains but the western part lies in the broad belt that comprises the valley of the Pecos River.