OUACHITA, MARATHON, AND COAHUILA SYSTEMS 



235 



W-E SECTION PASSING 2 KM. NORTH OF LA DIFUNTA 

 K 



POST-PERMIAN PRE-CRETA. 

 GRANITE INTRUSION 



CRETACEOUS 



POST- PERMIAN ' PRE-'WeTACEOUS GRANITE INTRUSION 



WSW-ENE SECTION PASSING I KM. NORTH OF THE NORIA DE MALASCACHAS 



MILES 



! Fig. 14.11. Cross sections near Las Delicias, Coahuila, Mexico. The Permian strata consist of 

 1 interbedded conglomerate, graywacke, sandstone, shale, limestone, and intermediate and basic 



, detritus from these and older rocks accumulated in the western part of 



1 the area either contemporaneously with the reefs or as a clastic wedge 



i on the flank of an early Permian uplift. The coarseness and unsorted char- 



j acter of the boulder conglomerates indicate that the boulders must have 



] been transported by unusual processes. During the remainder of Permian 



time, the geosyncline received deposits of clay from Llanoria on the east, 



flows of lava from fissures in the basin to the west, and volcanic detritus 



derived from the reworking of pyroclastic deposits and possibly by action 



of waves on the lava flows. 



lavas. The graywacke and lava make up about 60 percent of the sequence. After R. E. King 

 ef al., 1944. 



At some time beween Late Permian and Late Jurassic, the Pennsvl- 

 vanian (?) and Permian rocks were intensely folded and overthrust. See 

 cross section, Fig. 14.11. If the deformation took place in Late Permian 

 time, it was the last phase of orogeny affecting the sediments of the Paleo- 

 zoic geosyncline. Possibly it occurred in Early Jurassic or Triassic time, but 

 not as late as the Nevadan disturbance (Late Jurassic), because the 

 Upper Jurassic Oxfordian sediments rest unconformably upon the trun- 

 cated Permian. The geosyncline is shown as deformed in Late Permian 

 time on the tectonic map of Plate 8. See Chapter 17 and Fig. 17.9. 



