Abstract The Southern Great Plains physiographic sub-province lies south of the Cimarron River, which crosses the plains at ~37° N latitude (Fig. 1). The sub-province is bounded on the west by the Southern Rocky Mountains Province and Sacramento section of the Basin and Range Province. On the east the Great Plains are bounded by the Caprock Escarpment and are separated from the Gulf Coastal Plain by the Balcones Escarpment. The southern Great Plains physiographic sub-province is divided into the Pecos Valley and Raton sections on the west, the High Plains section on the east, and the Edwards Plateau on the south. “In the public mind the Great Plains are thought of as a vast monotonous plain that lacks scenic interest, but has to be crossed to reach the scenic Rocky Mountains to the west“ (Thornbury, 1965, p. 287). Whereas this region clearly lacks areas of high relief and thus scenic wonders, it does contain some of the most extensive deposits of Tertiary and Quaternary sedimentary and volcanic rocks that have been recognized in North America. These units are commonly well exposed along the banks of stream systems being incised into the Great Plains and in the high scarps that bound the High Plains. Numerous descriptions of the Quaternary geology and geomorphology of the Southern Great Plains have been published since the first reports became available late in the 19th and early 20th centuries (Johnson, 1901; Baker, 1915). Of these, useful reviews or

Abstract Blanco Canyon and Mount Blanco are located along the eastern Caprock Escarpment of the Southern High Plains (Llano Estacado) in the Texas Panhandle near Crosbyton, Texas. The Blanco Canyon exposures are along U.S. 82 where it crosses lower Blanco Canyon east of Crosbyton (Fig. 1). Within a distance of 5.5 mi (8.9 km), the highway descends from the High Plains through the Bridwell and Couch Formations (Ogallala Group) to Triassic red beds before climbing back onto the High Plains surface. The route passes near the Bridwell and Couch type sections and is flanked by several excellent roadside exposures. Outcrops at four Blanco Canyon localities are discussed in this chapter. Collectively, they document the buildup and subsequent dissection of the Southern High Plains since late Miocene time. Mt. Blanco can be reached by traveling north from Crosbyton on Farm Road 651 across the High Plains surface (Backwater Draw Formation). At 7.8 mi (12.5 km) the road descends into Blanco Canyon. Below the escarpment the highway crosses the mouth of Crawfish Creek, a major reentrant of Blanco Canyon. As the road descends the side of the canyon, the white beds of the Blanco Formation are apparent to the left and right just below the reddish sands of the Backwater Draw Formation. After descending into the canyon, turn left (west) on Farm Road 193 and drive 0.7 mi (1.1 km) to Mt. Blanco, which is the conical erosional remnant on the south side of the road.

Abstract 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.

Abstract Lake Tanganyika provides an excellent opportunity for understanding tectonic and climatic influences on sedimentation in a rift lake. Each tectonic setting within rift half-graben basins generates a predictable range of lithofacies architectures. Escarpment-margin (boundary-fault) drainages are small and steep, producing small fan deltas and thick, although not broad, sublacustrine fan complexes. Most water and sediment derived from escarpments is diverted away from the rift basin, although it may reenter along an adjacent half-graben basin margin. Drainages crossing hinge ramps or platforms are larger and well integrated. Deltaic sands on these platforms may form sheets or be channelized into older alluvial valleys. Delta positions are poorly constrained by structure, and portions of the platforms may be clastic-sediment bypassed. Fault-bounded interbasinal ridges, termed accommodation zones, are clastic-sediment starved. They are predominantly areas of pelagic sedimentation but may become areas of littoral carbonate accumulation at appropriate lake levels. Rift-axial streams drain moderately large areas under very low gradients. Their deltaic positions are highly constrained by rift structure, providing for abundant clastic-sediment supply across the axis. A predominance of interflows and underflows generates strong density currents across most lake margins. Asymmetry in lithology and strata thickness is the result of lake-level fluctuations interacting with varying rates of sediment accumulation, much of which is structurally influenced. Differences in sequence geometry have implications not only for interpreting ancient rift-lake deposits but also for deposition of economically viable reservoir facies and their juxtaposition with source rocks and caprocks. Several environments deserve more attention as exploration analogs than they have previously received. Platform and axial-margin sand bodies (clastic and carbonate), accommodation-zone carbonates, and turbidites or contourites derived from platform or axial sources all have considerable potential as reservoir facies.