OUACHITA, MARATHON, AND COAHUILA SYSTEMS 



227 



D' 



ARKANSAS VALLEY 



COASTAL PLAIN OUACHITA MOUNTAINS 



window .Jockfork ,' . WINDOW „ 



BOSTON MOUNTAINS 



-Cambrian 'S'S'->, '-/c/\'\> 



)° 



Mississippion 



Formations in Ooachitas 

 Atoka -formation 

 Johns Volley shale 

 dock fork sandstone 

 Stanley shale. 

 Coney shale 

 Arkansas novacu/ite 

 Missouri Mountain slate 

 Blaylock sandstone Silurian 



Polk Creek shale 

 Big fork chert 



Womble shale (Stringtownj \ Ordovician 

 Bloke ly sandstone 

 Mazarn shale i 



Crystal Mountain sondstoneX Cambrian 

 Collier shale J 



Formations in Arkansas Valley 

 Boggy shale 

 5a van a sandstone 

 McAlester shale 

 Hartshorne sandstone 

 Atoka formation -9,ooo' 

 thick in southern part 



L Pennsylvanian 



Vertical t horizontal scale in miles 



Fig. 14.4. North-south cross section through Ouachita Mountains and Arkansas Valley. Section D-D', Fig. 

 14.1. Somewhat idealized from Miser, 1929, and Hendricks et a/., 1936. 



are common (Croneis, 1930). Their south sides are generally down, 

 thereby augmenting the basin structure. 



The thrust faults appear to die out eastward into Arkansas where a 

 fold complex indicates also considerable compression. See Fig. 14.6. 

 An anticlinorium is the dominant structure in the approximate center of 

 the exposed fold belt. The minor folds on the major anticline are sharp 

 and mostly asymmetrically inclined northward. Two large anticlines with 

 amplitudes of 7000-10,000 feet dominate the belt north of the intricately 

 folded anticlinorium. Precambrian rock is nowhere exposed in the 

 Ouachitas — a condition similar to that in the Valley and Ridge province 

 of the Appalachians. 



In Arkansas it is not clear just where the line should be drawn 

 separating the folds of the Arkansas Valley basin and those of the 

 Ouachitas. The Choctaw thrust is considered the northern boundary of 



the Ouachitas in Oklahoma. Numerous folds in the Arkansas Valley 

 basin sediments are conspicuous on the Tectonic Map of Oklalioma 

 (Arbenz, 1956). 



The turn of the thrusts of the west end of the Ouachitas to the south 

 is very conspicuous. The number of thrust slices increases also, and it 

 appears that the strata were more crowded here than elsewhere. The 

 junction with the Arbuckles is unfortunately covered by the Cretaceous 

 sediments, but a number of wells and some geophysical work help to 

 explain the obscure relationship. The strike of the structures and trend 

 of the Arbuckles is nearly at right angles to the southward veering 

 Ouachita structures, and the formations are in part conspicuously differ- 

 ent. The problem of the relation of the Arbuckles to the Ouachitas will 

 be taken up later. 



No rocks or structural elements resembling the Rlue Ridge or the 



