The Triassic section of the West Texas High Plains is represented by the rocks of the Dockum Group. This section consists of up to 2,000 ft (61 O m) of complex elastic sequence composed of conglomerates, sandstones, and shales. These sediments were deposited by a variety of terrigenous depositional systems into a broad, shallow, fluvial-lacustrine basin stretching across what is now the Panhandle region of Texas. The location and geometry of the Dockum Basin probably reflect Paleozoic structural elements lying in an area roughly defined by the Midland Basin. It is bounded to the north by the Sierra Grande Arch and Amarillo Uplift and to the south by the Llano and Marathon Uplifts (Fig. 1). Most of the Triassic deposits of West Texas occur beneath younger deposits of the Llano Estacado. These rocks crop out along the Caprock Escarpment from Oldham County southward to Sterling County (Fig. 1). Terminology applied to the Dockum Group of West Texas has undergone considerable evolution. Presently, the Dockum Group of the West Texas High Plains is divided into two formations. These are, from oldest to youngest, the Tecovas and Trujillo formations (Fig. 2). In the southern outcrop areas, however, the formational divisions are difficult to identify.
Figures & Tables
One of six volumes generated by each GSA section for the Decade of North American Geology (DNAG) project, this Centennial Field Guide contains descriptions of 100 sites or site clusters representing outstanding geologic locations in Arkansas, Kansas, Oklahoma, and Texas.