248 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



different types of deposits and which were probably tectonically unlike. 

 Refer to Figs. 14.1 and 15.12. Some were basin areas, like the Delaware 

 basin in which a total of 10,000 feet of sediments accumulated. Others 

 were shelf areas. Akin to the shelves were several narrow masses, or 

 platforms, lying between the basins. The basins were areas of greater 

 subsidence; the platforms and shelves, areas of lesser subsidence. The 

 Central Rasin Platform was covered with 2000-4000 feet of sediments, 

 as were also the shelf areas. The provinces appear to have been inherited 

 from the pre- Wolfcamp foreland features, and each platform is underlain 

 by one of the more important pre-Wolfcamp uplifts. The Permian tectonic 

 features may have been formed during a time of dominant crustal ten- 

 sion, following the pre-Wolfcamp time of dominant crustal compression 

 (King, 1937). The basins were centers of accumulations of clastic rocks, 

 first black shales and later sandstones, and the total thickness of beds 

 deposited in them was greater than elsewhere. Limestone tended to form 

 over all the higher standing areas. Landward, because of climatic condi- 

 tions that favored evaporation, evaporites were laid down in the fringing 

 seas. On the margins of these seas, red-beds were deposited which were 

 derived from the bordering lands. 



The subsidence in Permian time that led to the burial of the Penn- 

 sylvanian ranges also resulted in the burial of the Matador and Amarillc— 

 Wichita ranges to the north, and the northern part at least of the folded 

 and thrust Marathons. Much of the sediment in the extensive Permian 

 basin came from the Ouachitas which were actively being elevated at 

 this time. Some debris from the Marathons reached surprising distances 

 northward. The subsidence was regional in aspect and accentuated the 

 Concho arch. 



Extending across the larger features of the Marathon foreland and im- 

 parting a distinctive grain to their surfaces are numerous minor tectonic 

 features in which the linear element dominates. These include the 

 flexures in the Guadalupe Mountains region, the minor folds on which 



Fig. 15.11. Concho arch, Bend axis, and Llano uplift, after Cheney and Goss, 1952. Forma- 

 tional contacts generalized. Heavy contours are isopachs on the Paleozoic interval below the 

 Strawn formation and illustrate the nature of the resulting Concho arch in Mid-Pennsylvanian 

 time. 



