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Circular 160—Late cenozoic sediments, molluscan faunas, and clay minerals in northeastern New Mexico

By J. C. Frye, A. B. Leonard, and H. D. Glass, 1978, 32 pp., 5 tables, 18 figs.

Companion to Circular 161. Discusses Pliocene, Pleistocene, and Holocene stratigraphy, paleontology, and clay-mineral assemblages; stratigraphic zonation of the Ogallala Formation is extended north to the Colorado border and correlated with the floral zones occurring in the Ogallala Formation throughout the region. Detailed clay-mineral analyses are also included. Northeastern New Mexico contains a variety of late Cenozoic strata that is observable at few places on the North American continent. The surficial rocks of this region range from late Tertiary to late Quaternary basaltic flows, interspersed with Pliocene, Pleistocene, and Holocene sediments, faunas, and floras; all are in a setting of a complex erosional topography in Triassic to Cretaceous bedrock. The topographic complexity has been caused not only by structural warping and by lava flows that periodically diverted drainage, but also by stream piracy and diversions that were initiated by the warping and changed gradients in the Plains region (to the east, southeast, and south), and by pulsating climatic changes.

In order to understand the present complex relation in this region, it is necessary to consider the stratigraphic relations of the late Tertiary and Quaternary sediments, their relation to the basalt flows and erosional history, and the climatic events interpreted from the clay-mineral suites and the molluscan fossil assemblages. The area described in this report is bounded on the north by Colorado, on the east by Oklahoma and Texas, on the south by I-40-US-66, on the northwest by the volcanic terrain north and south of Capulin, and on the west by the western edge of the Mosquero-Roy-Abbott Ogallala upland. The bedrock below the Cenozoic deposits of the region consists of Triassic, Jurassic, and Cretaceous rocks. Except for a small area in the northwestern part of the region that is tributary to Purgatoire drainage, the region is drained by the east-flowing Cimarron River and the by the Canadian River system.

A study of the Pliocene, Pleistocene, and Holocene stratigraphy, paleontology, and clay mineral assemblages was made for the northeastern part of New Mexico. The stratigraphic zonation of the Ogallala Formation, using clay-mineral assemblages developed farther south in the state, is extended to the northern border and paleontologically correlated with the floral zones identified regionally throughout the Ogallala Formation. The stratigraphic relations of several basalt flows to the Ogallala as well as to Pleistocene deposits is included. Earliest Pleistocene deposits (Nebraskan) are sparse, but deposits of Kansas to mid-Pleistocene age are extensive in the area to the north and east of the Canadian River. Wisconsinan to Holocene terrace deposits occur along virtually all of the valleys of the region; they have yielded 48 collections of fossil molluscs, and nine samples have been dated by radiocarbon analysis. The molluscan assemblages are compared through an age range from 27,000 to less than 1,000 B.P. with the living fauna and with fossil assemblages of similar age southward in New Mexico. Clay-mineral data for the Pleistocene and Holocene deposits are presented in the appendix, and the contrasting erosional histories of the several drainage systems are discussed.

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