SOUTHERN AND CENTRAL APPALACHIANS 



127 



recrystallized 1000-1100 m.y. ago. This correlates in time with the Gren- 

 ville orogeny of Ontario and Quebec. 



2. The continental margin was subparallel with the present, but may 

 have been extended by a continental shelf and slope type of deposit in 

 times following the Grenville orogeny, particularly in Late Precambrian 

 and Early Cambrian time. This was the time of accumulation of the 

 Ocoee series and the Chilhowee group. 



3. The Atlantic margin of the continent was beset with deformation 

 beginning in the last part of early Ordovician time, and the previous 

 region of sedimentation now was elevated and became the source land 

 of sediments to the west. See Fig. 8.31. A great fan or wedge of clastic 

 sediment was spread northwesterly from the Great Smoky region during 

 the Middle Ordovician and another one in Late Ordovician time in New 

 England. The crustal deformation must have been mostly elevatory at 

 this time because the metamorphic and plutonic activity occurred some- 

 what later. The New England clastic wedge records part of the Taconian 

 orogeny as defined, but no name has been proposed for the Middle 

 Ordovician uplift. 



4. Clastic sedimentation on a large scale shifted during Silurian 

 and Devonian time to New York, Pennsylvania, and West Virginia, and 

 another great fan of sediments was deposited there, also derived from 

 uplifted lands on the east. See Fig. 8.32. The Silurian and Lower Devo- 

 nian elastics were not very thick, about 5000 feet, but then a flood of 

 sediments reached 10,000 feet in thickness in late Devonian time. Strong 

 compression and plutonic tectonism started in early Devonian time, ac- 

 cording to the isotope age measurements, but evidently high mountains 

 were not created until the beginning of the Late Devonian. 



Figure 8.33 is an idealized section of the southern Appalachian system 

 and illustrates the central belt of most profound Devonian metamorphism 

 and plutonism. This, when much eroded, became the crystalline Pied- 



CUMBERLAND 

 PLATEAU 



BlUC RIDGC PICDM0NT PROVINCt 



VALLCY 1 RIDCt ..tferomorphic f flutomc belt 



\ V. 1 ill Coro/mo i/ofe 



PROVINCE 



He/t 



ATLANTIC COAJT- 

 al plain 



Fig. 8.33. Idealized cross section of the southern Appalachian Mountains system. After P. B. 

 King, 1950a. 



mont. The age of the Carolina slate belt sediments is unknown but evi- 

 dently older than the Devonian tectonism. It may be speculated that they 

 were a collateral eastern deposit of the Middle Devonian clastic wedge 

 on the west of a medial uplift, but their age must be known first before 

 they can be correctly fitted into the picture. 



5. Uplift of the orogenic belt was general along its entire length 

 during the Mississippian and sediments were carried westward and added 

 to the miogeosyncline. However, in Early Pennsylvania!! time uplift was 

 particularly great in the southern Piedmont and another thick wedge 

 accumulated on the west. Later, sedimentation shifted to the West 

 Virginia and New York and considerable clastic material of continental 

 environment accumulated during Late Pennsylvanian and Permian time. 



6. The eastern part of the miogeosyncline including the thickest parts 

 of the clastic wedges and the eastern part of the great Cambro-Ordovician 

 carbonate sequence was then compressed and cast into folds and thrusts 

 as exemplified in the Valley and Ridge province of Fig. 8.33. The de- 

 formation is generally referred to as the Appalachian orogeny. It may 

 have started in Mid- or Late Pennsylvanian time in the south but farther 

 north Valley and Ridge deformation could not have occurred until the 

 close of Pennsylvanian time, and it may not have happened until near 

 the close of the Permian. 



