Late Cenozoic sediments, molluscan faunas, and clay minerals in northeastern New Mexico

Abstract

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.