RESUME OF STRUCTURAL CKOLOCY OK NOHTII AMKHK.\ 



IT 



The Ozark uplift developed into a broad, continuous arch with the 

 Nashville and Cincinnati arches, and the northern arms of the Cincinnati 

 arch, the Kankakee and Findlay arches, became well established. Gentle 

 , erosion probably occurred throughout this system of arches. 



Subsidence continued in the Appalachian trough area, and a maximum 

 of 4000 feet of sandstones, shales, and limestones accumulated. 



In the Maritime Provinces and Newfoundland, a basin sank within the 

 older Taconic and Acadian orogenic belts, and received about 5000 feet 

 of clastic sediments, presumably from a rising orogenic belt on the 

 i east. 



Pennsylvanian (Plate 7) 



3 The south-central part of the continent was one of considerable and 

 widespread unrest in Early Pennsylvanian time, and a number of ranges 

 and basins were formed. The Wichita Mountain system of Oklahoma and 

 northern Texas was uplifted together with the Ancestral Rockies of New 

 Mexico and Colorado. The Pecos and Diablo ranges in west Texas ap- 

 peared. The long, narrow Nemaha Range rose sharply, and at the same 



i time basins on the east sank. The previously formed La Salle anticlinal 



, belt was mostly buried. 



The trough of the deep basin in eastern Texas of latest Mississippian 

 and earliest Pennsylvanian time shifted northward to central Arkansas, 



, and over 10,000 feet of sediments accumulated there. 



The Arkansas basin was probably continuous with one in the southern 

 Appalachians, where 10,000 feet of sediments, mostly clastic, accumu- 

 lated. Such a thick and clastic deposit undoubtedly means vigorous uplift 

 immediately on the southeast and south. The area of deposition in the 

 southern Appalachians in Early Pennsylvanian time shifted to the 

 central Appalachians in Late Pennsylvanian time, and somewhat more 

 that 3000 feet of coal-bearing strata were deposited there. Although de- 

 position had proceeded at variable rates here and there during the 

 Paleozoic in the southern and central Appalachians, which lay to the 

 west of the Taconic orogenic belt, it is generally stated that more than 



j 30,000 feet of sediments had accumulated. In Late Pennsylvanian time 

 or possibly in Early Permian time, the thick succession of strata from 



Oklahoma and Arkansas to Pennsylvania suffered folding and thrusting 



toward the continental interior, and the Ouachita Mountains and ( lassical 

 Appalachian Mountains (Valley and Ridge Province) WOt brought 

 into being. 



The Marathon orogeny of west Texas occurred in Late Pennsylvania!! 

 time and several thrust sheets moved northward toward the shelf. The 

 Arbuckle Mountain system was formed hy considerable folding and 

 thrusting of the sediments of the Ardmore basin, and the structures 

 were appressed tightly against the early Wichita Range. 



In New England, the Maritime Provinces, and Newfoundland, sub- 

 sidence followed somewhat the same pattern as that of the Mississippian. 

 and coarse red Pennsylvanian elastics rest there on the 'laconic and 

 Acadian complex, and also in places in angular unconformity on the 

 Mississippian. 



Extensive subsidence occurred during the Pennsylvanian in the Cordil- 

 leran geosyncline with the deposition of more sand than in any time 

 since the Cambrian. A local basin in west-central Utah subsided greatly 

 and was filled in one place with about 25,000 feet of beds. The Antler 

 orogenic belt dominated the sedimentary conditions east of it, and coarse 

 elastics were spread there. Allochthonous masses were translated 25 to 75 

 miles eastward. 



The volcanic orogenic archipelago persisted along the west margin of 

 the continent, and was the source of volcanic contributions to the sedi- 

 ments of the adjacent seas, and the cause of unconformities and low- 

 grade metamorphism in the deposits. 



Ry Late Pennsylvanian time the Transcontinental Arch was almost 

 entirely overlapped and buried, and the Early Pennsylvanian uplifts of 

 Kansas, Oklahoma, and Texas were covered. Only the Ancestral Rockies 

 in Utah, Colorado, and New Mexico remained as islands above the ac- 

 cumulating sediments. 



Permian (Plate 8) 



An eugeosyncline of deep and broad proportions developed in 

 Permian time along the Pacific and was filled largely with volcanic ma- 

 terials. The Permian was a time of most extensive volcanism, and the site 



