5. 



CENTRAL STABLE REGION 

 OF THE UNITED STATES 



other structures of the Central Stable Region, with few <-\( eptions, formed 

 during the Paleozoic era, and many of them yield < \ idenoe ol a prolonged 

 history of development. 



Up to Pennsylvania!! time, there was a certain bilateral symmetry to 

 the stable region, with a great medial transcontinental arch, and basins 

 and smaller arches on either side. An approximate parallelism of a s<n<s 

 of arches with the Ouachita and Appalachian orogenic belts was existent 

 and is still apparent today. 



During Mississippian, Pennsylvanian, and Permian time, great overlaps 

 on some of the arches occurred. Others were either not completely buried 

 or have since been partially exhumed by erosion. In some areas the 

 Triassic overlapped on the Central Stable Region beyond the limits of the 

 Permian, and especially in late Cretaceous time did epeiric seas exten- 

 sively invade the region of arches and basins. 



The large arches and basins are rippled and checked with numerous 

 folds and faults; and these, with the unconformities created by the great 

 overlaps, constitute immensely valuable structures for oil and gas accumu- 

 lation. The strata also contain great coal deposits and numerous other 

 nonmetallic mineral resources. Each basin and each arch will, therefore, 

 be considered separately. The geologic and tectonic maps of Chapter 

 3 will be especially helpful in relating the diastrophic histories of the 

 various major structures, and should be referred to repeatedly. 



GENERAL CHARACTERISTICS 



The Central Stable Region of the United States is made up of a founda- 

 tion of Precambrian crystalline rock previously described, with a veneer 

 of sedimentary rock. The veneer varies greatly in thickness from place 

 1 to place. For the most part, the Central Stable Region has suffered vertical 

 movements, and broad basins and arches have formed. Some of the 

 basins have more than 10,000 feet of strata in them, and in the cores of 

 some of the arches the Precambrian crystalline rock is exposed. Some of 

 the arches and sharper uplifts are not expressed in the surficial layers and 

 have been revealed only by drilling operations. The arches, basins, and 



PRE-DEVONIAN BASINS 



The basins of greatest extent and deepest subsidence in early Paleozoic 

 time were the geosynclines along the western and eastern margins of the 

 continent. Each constitutes an important part of our continent and will 

 be discussed in separate chapters: the Paleozoic Cordilleras geosyncline 

 in Chapter 6, and the Appalachian geosyncline in Chapters 7. 8, 11. 12. and 

 13. Refer to the map of Plate 2, Chapter 3, in the following paragraphs. 



The Appalachian geosyncline subsided most in West Virginia, Virginia, 

 Tennessee, and Alabama. In a small area across the border of Virginia 

 and Tennessee, sediments accumulated to a thickness in excess of 25.(KX) 

 feet during Cambrian, Ordovician, and Silurian time. A distinct sag in the 



37 



