Geomorphic development of the Canadian River Valley, Texas Panhandle: An example of regional salt dissolution and subsidence THOMAS C. GUSTAVSON Bureau of Economic Geology, The University of Texas, Austin, Texas 78713 ABSTRACT dian River Valley is primarily the result of regional salt dissolution and subsidence that have been active throughout the late Tertiary and Quater- Development of the Canadian River Valley in the Texas Pan- nary. The Deaf Smith County nuclear waste repository site, one of three handle resulted mostly from regional subsidence following dissolution recently identified sites, is located in the southern part of the study area of Permian bedded salts. Salts of the Clear Fork, Glorieta, San (Fig. 1). Andres, and Seven Rivers Formations have undergone dissolution along the margins of the Palo Duro, Dalhart, and Anadarko Basins. GEOLOGIC SETTING The Canadian River Valley follows a zone of subsidence for >208 km (130 mi) across the High Plains. High solute loads (3,000 ppm Late Paleozoic tectonic movements resulted in the Amarillo Uplift, chloride) in the Canadian River and historical development of sink- the Cimarron Arch and the Bravo Dome, and the adjacent Palo Duro, holes indicate that dissolution and subsidence processes are still active. Dalhart, and Anadarko Basins (Fig. 2) (Birsa, 1977). By middle Permian Evidence that these processes have been active in the region since the time, these basins were essentially filled, and the area evolved into an middle Tertiary includes Pliocene lake sediments and Quaternary extensive marine shelf, covering the northern portion of the Permian basin, terrace alluvium that have been deformed by dissolution-induced sub- where salt and other evaporites accumulated (Dutton and others, 1979; sidence as well as former sinkholes filled with lacustrine sediments of Handford and Dutton, 1980). The area was differentially uplifted during the lower Ogallala Formation (Miocene). the Triassic to form the fluviolacustrine basin of the Dockum Group and was uplifted again during the Late Cretaceous-early Tertiary, which re- INTRODUCTION sulted in the middle Tertiary erosional surface and later deposition of the Ogallala Formation (McGowen and others, 1979; Seni, 1980). The Canadian River, with headwaters in northeastern New Mexico, The Canadian River region is underlain by Permian, Triassic, Ter- flows south along the western margin of the Central High Plains (Fig. 1). tiary, and Quaternary strata (Fig. 3). Permian sediments consist of dolo- At its intersection with the Conchas River, the Canadian River turns mite, red beds, and thick evaporite sequences of salt, anhydrite, and gypsum east-northeast across the High Plains of New Mexico and the Texas Pan- (Presley, 1979a, 1979b, 1980a, 1980b; McGillis and Presley, 1981; Ho- handle at a high angle to the regional southeasterly slope. In Texas, the vorka, 1983; Boyd and Murphy, 1984). Triassic Dockum Group strata Canadian has incised through the Tertiary Ogallala Formation and into consist of nonmarine sandstones and mudstones (McGowen and others, Triassic and Permian strata to form a valley which is as much as 64 km 1979). Triassic and locally Permian strata are overlain unconformably by (40 mi) wide and 300 m (1,000 ft) deep. This valley has developed since Tertiary fluvial and eolian clastics of the Ogallala Formation (Seni, 1980). the end of deposition of the Ogallala Formation 3 to 5 m.y. ago (Schultz, The Ogallala Formation is overlain locally by late Pliocene lacustrine 1977). The High Plains north of the valley of the Canadian lie -75 m (250 sediments of the Rita Blanca Formation and is mantled by Quaternary ft) lower than do the High Plains south of the valley. These conditions eolian sands and silts of the Blackwater Draw Formation (Anderson and suggest that the position and, possibly, the development of as much as 208 Kirkland, 1969; Reeves, 1976; Holliday, 1984). km (130 mi) of the length of the Canadian River Valley may be struc- Gustavson (1982), Gustavson and Finley (1982,1985), and Dolliver turally controlled where it crosses the High Plains. (1984) have stated that the path of the Canadian River in the Texas In order to understand the geomorphic development of this part of Panhandle and eastern New Mexico was strongly influenced by dissolu- eastern New Mexico and the Texas Panhandle, several questions must be tion of Permian bedded salt and collapse of overlying strata. The position answered, including the following. (1) Why did the Canadian River Valley of several segments of the Canadian River Valley outside of the Texas develop at a high angle to the regional southeasterly slope of the Southern Panhandle has been attributed to adjustment to bedrock structure. In High Plains? (2) Why are the High Plains on the northern side of the eastern New Mexico, Spiegel (1972) attributed the morphology of the Canadian River Valley 75 m (250 ft) lower than are the High Plains on the Canadian River Valley to the river's adjustment to mid-Pleistocene normal southern side of the valley? (3) How was a stream as small as the Canadian faults. Fay (1959) suggested that the present-day course of the Canadian River able to incise such a large valley? River in western Oklahoma is a result of the river's adjustment to the strike This study, which is part of an ongoing research program designed to of Permian rocks exposed across the regional surface slope and of stream determine the feasibility of disposing of high-level nuclear waste in bedded piracy. Brown (1967) offered an alternative explanation, suggesting that Permian salt in the Texas Panhandle, tests the hypothesis that the Cana- the river has adjusted to deeply buried structures in western Oklahoma Geological Society of America Bulletin, v. 97, p. 459-472,10 figs., April 1986. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/97/4/459/3445145/i0016-7606-97-4-459.pdf by guest on 02 October 2021 460 T. C. GUSTAVSON 100° 103° 37° DO' Contour intervals: Texas 200 ft EXPLANATION N.M. OK. New Mexico 500 ft Caprock Escarpment TX. Deaf Smith Waste Isolation 30 60 mi Site —Il — -h 50 100 km Figure 1. Physiography of eastern New Mexico and the Texas and Oklahoma Panhandles. Dashed lines tie topographic contours across the Canadian River Valley (Breaks). If the strike of contour lines on the Southern High Plains is projected across the Canadian River Valley, it is apparent that the northern side of the valley is -75 m (250 ft) lower in elevation than is the south rim of the valley. U.S. Department of Energy stratigraphic test wells include Stone and Webster Engineering Corporation No. 1 Mansfield (A), No. 1 J. Friemel (B), No. 1G. Friemel (C), and No. 1 Detten (D) wells, and the DOE/Gruy Federal No. 1 Rex White well (E). Qtl = Quaternary terrace containing Lava Creek B Ash. following dissolution and collapse of Permian anhydrites. Walker (1978) GEOMORPHIC PROCESSES stated that the Canadian River Valley formed during the Pleistocene by headward erosion into the High Plains. Dissolution Tierra Blanca ("reek, which lies south of the Canadian River, is also thought to be structurally controlled (Gustavson and Budnik, 1985) Downstream from the Ute reservoir in eastern New Mexico (Fig. 1), (Fig. 1). Like the Canadian River, Tierra Blanca Creek flows northeast the solute load of the Canadian River reaches 3,000 ppm chloride (U.S. across the regional southeast slope of the High Plains. It overlies a Geological Survey, 1969-1982). The U.S. Bureau of Reclamation (1S>79) northeast-trending zone of subsidence induced by dissolution of salts of the estimated that >55,000 metric tons of sodium chloride are carried annu- Seven Rivers Formation. ally by the Canadian River to Lake Meredith, Texas. Gustavson and others Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/97/4/459/3445145/i0016-7606-97-4-459.pdf by guest on 02 October 2021 GEOMORPHIC DEVELOPMENT OF CANADIAN RIVER VALLEY, TEXAS 461 l&ïS'ff Basement structural high Figure 2. Regional structural elements, Texas Panhandle and eastern New Mexico. The peripheral salt dissolution zone in the Palo Duro and Anadarko Basins, along the margins of the Glorieta through Seven Rivers salt limit lines, follows the upturned edges of Permian strata along the basin margins, which illustrates that dissolution of salt tends to occur in structurally high areas where salts are nearest to the surface. The study area occurs along the Amarillo Uplift and Bravo Dome. (1982) found that sinkholes had occurred historically along the Canadian several lower, undated terraces indicate that incision has been active River Valley in the study area wherever the valley is underlain by Permian throughout the late Quaternary. bedded salts. These data confirm that salt dissolution is locally an active process beneath the Canadian River Valley and suggest that subsidence is PROCEDURES accompanying dissolution. To test the hypothesis that dissolution of Permian salt and subsidence Erosion and Deposition have controlled the development of the Canadian River Valley in the study area, the likelihood that salt was present in areas where it is now absent Until recently, the Canadian River, which lies at the floor of a broad, must be established. Also, structures attributed to dissolution-induced sub- V-shaped valley flanked by bedrock exposures, was probably incising its sidence must be separated from tectonically induced structures. valley. Unpaired terraces, which contain 610,000-yr-old Lava Creek B The Tubb interval of the Clear Fork Group underlies all salt-bearing Ash (Izett and Wilcox, 1982), lie -60 m (200 ft) above the river on the units suspected of having been affected by dissolution. A structure-contour south side of the valley near Lake Meredith (Fig. 1). These terraces and map on the Tubb interval, therefore, will show deformation of Permian Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/97/4/459/3445145/i0016-7606-97-4-459.pdf by guest on 02 October 2021 PALO DURO DALHART ANADARKO AGE BASIN BASIN BASIN WEST a CENTRA -i—i—i—i—i—I- ~i 1 I I—i I i i 1 i i—'— QUATERNARY Blockwoter Draw Fm.