WICHITA AND ANCESTRAL ROCKIES SYSTEMS AND THE TEXAS FORELAND 



245 



ham (1955) finds evidence by way of conglomerates, unconformities, 

 and fault offset of fold axes that the deformation there began in Deese 

 ( Mid-Pennsylvanian) time, culminated in late Pennsylvanian, and con- 

 tinued on into early Permian by tilting the Lower Pontotoc conglomerate 

 beds up to 40 degrees. 



The Arbuckle anticline was thrust far northeast of its original position 

 and overrode a considerable distance onto the Hunton-Tishomingo uplift. 

 The magnitude of the overthrusting decreased a great deal within a short 

 distance from southeast to northwest where crustal shortening was taken 

 up mainly by complex folding. It probably follows that the thrust along 

 its strike continued for a considerable distance southeast under what 

 is now the Ouachita Mountains. The Tishomingo anticline was shoved 

 northward in an overthrust second in magnitude only to the one in 

 the southeast end of the Arbuckle anticline, and overrode the syncline 

 to the north. The Franks graben, Wapanucka syncline, and other minor 

 folds and thrusts were formed in the Hunton arch. 



Tomlinson ( 1929 ) has estimated the amount of crustal shortening in 

 the Ardmore basin as 16 miles; and Dott (1934), whose theory of 

 structural evolution the above summary depicts, suggests in his illustra- 

 tion (Fig. 15.6) a net shortening at right angles to the trend of the struc- 

 tures, in late Pennsylvanian time only, of several scores of miles. It is, 

 therefore, probably incorrect to show the positions of structural elements 

 as they existed in times past in the places where the features now re- 

 pose, but so many uncertainties attend the construction of palinspastic 

 maps (Kay, 1945) in this region that it seems best for present purposes 

 to crown the elements so as to conform to their present geographic 

 positions. Such has been done on the tectonic maps of Plates 6, 7, and 

 8. 



During the great late Pennsylvanian phase, marine deposits of Canyon 

 age and older were highly tilted on the flanks of the Arbuckle Mountains, 

 and during the following Cisco time erosion removed a sedimentary 

 mantle probably 3 miles thick, and cut into granite. The granite thus 

 removed was distributed in beds of Wo If camp age over wide areas. North 

 central Texas was affected to some extent at this time, as shown by 

 thinning over the Matador arch. 



TEXAS FORELAND 



Definition 



The Texas Foreland, as here defined is the fairly undeformed portion 

 of the earth's crust north and west of the Ouachita-Marathon orogenic 

 belt, south of the Wichita system, and west of the Laramide cordillera. 

 See Fig. 14.1. It is characterized by broad arches, basins, platforms, and 

 shelves. It appears to be a small part of the Central Stable Region cut 

 off by the Wichita system. In reference to the Precambrian rock area 

 Flawn (1959) has designated large parts of it as the Texas craton. Con- 

 siderable igneous activity and probably deformation occurred in Pre- 

 cambrian time, but from the beginning of the Paleozoic era to the 

 present it has been a fairly stable region with practically no igneous 

 activity. 



For purposes of discussion the Texas Foreland may be considered to 

 have two divisions, the Central Texas and the West Texas-New Mexico. 



Central Texas 



Texas Arch. During Cambrian and Early Ordovician time Texas was 

 mostly a shelf region of carbonate deposition. The carbonate deposit 

 known as the El Paso limestone in New Mexico, the Ellenburger in West 

 Texas and the Arbuckle in Oklahoma and adjacent north Texas, 

 thickens southeasterly from a thin layer on the northwest to a massive 

 deposit over 2000 feet thick at the edge of what may have been the 

 continental shelf at the time. The Oklahoma basin lay to the north and 

 the West Texas basin to the west. In about Mid-Ordovician time a 

 broad and gently emergent peninsula extending southeastward through 

 Texas rose (Adams, 1954). See the map of Fig. 15.7 and stratigraphic 

 column of Fig. 15.9. 



The subsurface outcrops as indicated on the map are interpreted to 

 be depositional edges, with the peninsula, as large as Florida, emergent 

 throughout the long period of time. The deposits in general gradually 

 encroached on the peninsula; the Simpson, Viola, Montova. Sylvan, and 

 Hunter being Upper Ordovician and Silurian, and the Woodford De- 

 vonian. The lithologies are remarkably similar on either side of the arch. 



