Late Cenozoic Geomorphic Evolution of the Texas Panhandle and Northeastern New Mexico -- Case Studies of Structural Controls on Regional Drainage Development

Salt dissolution has affected parts of the Upper Permian Salado, Seven Rivers, San Andres, Glorieta, and upper Clear Fork Formations beneath the Pecos River valley in eastern New Mexico and has been active beneath the Canadian River valley and the Rolling Plains of the Texas Panhandle. Extensive dissolution of the salts of the Salado and Seven Rivers Formations has also occurred beneath the Southern High Plains. Cumulative thickness of salt lost to dissolution exceeds 150 m (500 ft) along the western, northern, and eastern margins of the Palo Duro Basin. Dissolution and subsidence occurred during deposition of the Tertiary Ogallala Formation, but Ogallala deposition kept pace with subsidence. After Ogallala deposition during the late Pliocene, surface subsidence created lacustrine basins along trends of relatively rapid dissolution. Preserved lacustrine sediments contain Blancan faunas (which confirm a basin age of at least late Pliocene). Continued subsidence along trends of relatively rapid dissolution overlying the structural margins of the Palo Duro and Anadarko Basins during the late Tertiary and early Quaternary formed a series of subsidence basins that diverted many of the streams that flowed southeasterly across the Southern High Plains. As a result of subsidence, the headwaters of the ancestral Brazos River were diverted during the middle to late Pleistocene from a southeastern drainage through the Portales paleovalley to a southern drainage through the Pecos Valley. The present headwaters of the Canadian River are probably a former tributary of the Pecos-Portales-Brazos River system that was diverted to the northeast along a subsidence trough caused by dissolution during the late Pliocene or early Quaternary.On the High Plains surface, several lacustrine basins (Frio Draw, Tierra Blanca Creek, and Yellow House Draw) lie above areas where accelerated salt dissolution has apparently occurred. These features overlie apparent structural depressions of the Alibates Formation, which is stratigraphically above the salt-bearing units. Most of the features also overlie either paleostream valleys or closed depressions on the middle Tertiary erosional surface. Faunal evidence suggests that the present stream valleys formed as early as the late Pliocene. Lacustrine basins probably formed between the late Pliocene and the early Pleistocene. The basins and stream valleys probably owe most of their form to normal fluvial and eolian erosion. Their location, however, is most likely the result of dissolution-induced subsidence.A large system of late Quaternary alluvial fans that built eastward from the Caprock Escarpment is being extensively dissected. This suggests that much of the drainage on the Rolling Plains in the Texas Panhandle developed during the late Pleistocene and Holocene. The parallelism between major stream segments and the dissolution fronts of Permian salt-bearing units indicates that much of the drainage is controlled by dissolution-induced subsidence. Furthermore, minor stream segments parallel the preferred orientations of numerous subsidence basins that are on the surface of the alluvial fans. Both straight segments of minor streams and long axes of subsidence basins are aligned parallel to the preferred orientations of the regional fracture system. Dissolution was probably accelerated along fracture trends, resulting in the development of subsidence basins that parallel fracture trends and, in turn, leading to the alignment of drainage when subsidence basins were incorporated into the drainage network.