Jurassic Overlap in Western New Mexico

Abstract

ABSTRACT Southward changes in Jurassic stratigraphy along the east side of the Cebolleta Mesa give a clear picture of the nature of the southern margin of Jurassic deposition in western New Mexico. Results of the measurement of nine sections are shown graphically and discussed in terms of the structural and stratigraphic relations of the units. The Wingate sandstone is divided into three members and the Morrison formation into four. These members thin and become coarser southward and progressively overlap a positive area in that direction. The wedge of Jurassic rocks lies between the Chinle shale (Upper Triassic) and the Dakota (?) sandstone (Upper Cretaceous). Its disappearance southward is due (1) to thinning against a positive area and (2) to truncation by the pre-Dakota erosion surface.