236 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



The folded rocks were intruded by batholiths of granite and grano- 

 diorite before Oxfordian time. 



Structural Trends 



The dominant strike of the beds in the northern part of the main Per- 

 mian area is N. 35° to N. 50° E. The strike of secondary cleavage is 

 N. 75° E. and may indicate the trend of the axis of the folds. In the south- 

 ern part of the Permian area the strike of the beds swings sharply to 

 S. 40° E. R. E. King et al. (1944) suggest that this may mean that the 

 Las Delicias area is a salient part of a mountain arc in the Paleozoic struc- 

 ture which possibly controlled the outline of the Coahuila peninsula of 

 Upper Jurassic and Lower Cretaceous time. Post-Cretaceous folds in con- 

 tinuation of this S. 40° E. trend may have been controlled by Permian 

 folds, and thus indicate the trend of the older structures. King's sug- 

 gestion is illustrated on the tectonic map. 



Relation to Marathon System 



On previous pages it has been explained that the folding and thrusting 



in the Marathons reached a climax in late Pennsylvanian time. See Plate 7. 

 Thereafter the compressed structures were deformed only by epeirogenic 

 uplift. The Pennsylvanian and older rocks were deeply eroded, and even- 

 tually Permian deposits overlapped them progressively southward. The 

 tectonic map of the Permian shows the previously deformed belt as one 

 of epeirogenic uplift. The Permian Delaware and Marfa basins were con- 

 tinuous with the Coahuila Permian basin; but while saline residues were 

 being deposited in the northern basins, waters of normal salinity persisted 

 in the south basin and probably replenished the evaporating waters to the 

 north. After the Permian deposition in both the north and south basins, 

 the folding and intrusions of the Coahuila area occurred. 



The Coahuila structures have commonly been tied to the Marathon 

 belt, which lies 250 miles to the north. The Permian volcanics and the 

 post-folding granitic intrusions present characteristics foreign to the 

 Ouachitas and Marathons in late Paleozoic time, and the writer is inclined 

 to favor a connection with the early Nevadan belt of western Nevada and 

 California, where the same characteristics hold. This correlation, however, 

 presents problems in working out logical map relations. 



