656 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



■Jutcrop Coleman Junction Ls 

 PENN PERMIAN CONTACT 



M -crop Range' U me5 ' one h , , 



BALCONES FAULT ZONE 



EAST TEXAS BASIN 



Fig. 41.5. Cross section from the Bend arch, central Texas, eastward to the Sabine uplift. 



uplift. The shallow structural sag on the west is the Tyler basin, just 

 described. A small and shallow syncline separates the Sabine uplift 

 from the gentle Monroe uplift in northern Louisiana and southern Ar- 

 kansas. The axis of each uplift trends northwest-southeast. The doming 

 started in Cretaceous time. The Sabine uplift was an island at the close 

 of the Early Cretaceous, and the Monroe uplift was an island during 

 much of Late Cretaceous time. The Sabine uplift especially was effected 

 by upward movements in post-Claiborne (post-middle Eocene) time, 

 and this doming with ensuing erosion has left a core of Midway (Pa- 

 leocene), Wilcox (early Eocene), and Claiborne (middle Eocene) sedi- 



ments surrounded by younger formations (Murray and Thomas, 1945). 

 See Fig. 41.6. 



Jackson Dome 



The Jackson dome is a sharp uplift in the subsurface in west-central 

 Louisiana. See Fig. 41.7. It is about 30 miles across. Local doming suffi- 

 cient upon erosion to expose the Upper Jurassic Cotton Valley forma- 

 tion occurred at the close of the Late Cretaceous. The amplitude of the 

 fold is about 10,000 feet, but the dips shown on Fig. 41.7 are excessive 

 owing to the grossly exaggerated vertical scale. 





