98 



STRUCTURAL GEOLOGY OF NORTH AMERICA 







East-central Ten- 

 nessee (Chilhowee 

 Mountain) 



Northeastern Ten- 

 nessee (Johnson, 

 Carter and Unicoi 

 Counties) 



Northern Virginia 

 (Elkton and Har- 

 pers Ferry areas) 







Shady dolomite 

 (in Miller Cove) 



Shady dolomite 



Tomstown dolomite 





— 



3 



o 



E 



s 



o 



o 



Hesse quartzite 



Erwin 

 quartzite 



Antietam 



c 



Murray shale 



quartzite 



£ 



cS 



Nebo quartzite 







Nichols shale 



Hampton shale 



Harpers shale 



o 



Cochran 

 conglomerate 



Unicoi formation 

 (with basalt flows 

 1000-1500 feet 

 below top) 



Weverton 

 quartzite 





Loudoun formation 

 (with tuffaceous 

 slate and rare 

 flows) 



c 



.5 



£ 



CIS 



CJ 



<1) 



s- 





Ocoee series 



Volcanics of Mt. 

 Rogers area 



Cranberry granite 



Injection complex 



Fig. 8.1. 

 1949. 



Formations of the Chilhowee group in Tennessee and Virginia. From P. B. King, 



Major Sedimentary Divisions of the Miogeosyncline 



Lower Cambrian Marine Clastics. The oldest beds of the Cambrian, 

 referred to as basal Cambrian, are conglomerates, arkoses, and shales, 

 that pass upward into quartzites. They make up the Chilhowee group 

 (Fig. 8.1) and attain a thickness of 5000 to 6000 feet. Tentative correla- 

 tions with metamorphic units of the Piedmont suggest that these strata 

 of the miogeosyncline grade southeasterly into eugeosynclinal facies 

 in the manner illustrated in Fig. 8.2. 



The basal Chilhowee beds rest in places unconformably on the vol- 

 canics and greenstones of the Ocoee series, and hence are believed to be 



part of the Lower Cambrian sequence. They are limited to a trough 

 which runs the length of the central and southern Appalachians and 

 are absent over the foreland or shelf region. 



Cambrian and Lower Ordovician Carbonates. The miogeosyncline 

 with its clastic deposits from Alabama to Pennsylvania became one 

 dominantly of limestone and dolomite deposition. Some 9000 feet of 

 carbonates representing the remainder of the Lower Cambrian, the entire 

 Middle and Upper Cambrian, and the Lower Ordovician accumulated 

 to a fairly uniform thickness up and down the entire trough. In the 

 southern and northern ends of the geosyncline carbonate deposition 

 continued into Middle Ordovician time. A correlation chart of the im- 

 portant formations of this period is given in Fig. 8.3. The carbonates 

 grade into shale facies toward the northwest side of the miogeosyncline 

 and the shelf in the manner illustrated in Fig. 8.4. 



The basal Cambrian clastics and the succeeding thick carbonate 

 sequence are typically miogeosynclinal and correspond in distribution 

 approximately with the later orogenic belts of the Blue Ridge and 

 Valley and Ridge provinces (King, 1959). The clastics were derived from 

 an emergent stable interior, and the carbonates were deposited on a 

 broad continental shelf, evidently without off-lying tectonic lands or a 

 volcanic archipelago. The eugeosynclinal equivalents of the carbonates, 

 if ever deposited, are not yet clearly recognized in the Piedmont. 



Middle Ordovician Clastic Wedge. The regimen of erosion and sedi- 

 mentation characterized by an emergent interior and a gently sub- 

 merging continental border gave way abruptly in Middle Ordovician 

 time to a reversed situation in which an uplifted borderland now 

 furnished the sediments to a subsiding inside basin. The sediments were 

 mostly clastic (Fig. 8.5), and the main source was in western Virginia, 

 western North Carolina, and eastern Tennessee. A great fan of sedi- 

 ments is visualized to have apexed in this region in about the Great 

 Smoky Mountains area and extended radially to the west, northwest, 

 and north (P. B. King, 1959). See Fig. 8.31. It spread considerably 

 beyond the later deformed belt of the Valley and Ridge province, and 

 unlike the Cambrian and Lower Ordovician sediments was not confined 

 to an elongate basin parallel with the continental margin. The wedge 



