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1 AN INTRODUCTION TO THE GEOLOGY OF THE SOUTHERN APPALACHIANS by George D. Swingle Professor of Geology, Department of Geology and Geography University of Tennessee, Knoxville, Tenn. Gatlinburg is located at the eastern border of Tennessee near the heart of the classic Southern Appalachians. This resort city, the gateway to the Great Smoky National Park, is situated The Blue in the foothills region of the Blue Ridge. Ridge physiographic province is flanked on the west by the Valley and Ridge and,on the east by the Piedmont. Valley and Ridge, in Tennessee Cumberland Atlantic Plateau, Coastal geologic the boundaries tifiable. region has a characteristic expression which reflects of the underlying by the rocks. and rather in part the For the most part between these regions are sharp and easily iden- A west to east traverse (line A-A' Figure 1), beginning reveals a tableland Plateau-Valley is bounded eastward Plain (Figure 1). topographic features and adjacent states, is the and the Piedmont Each physiographic distinctive West of the at the latitude of Gatlinburg on the Cumberland some 2000 feet in elevation. and Ridge boundary Plateau At the an abrupt escarpment, whose crest is 1000 feet above the general level of the Valley and Ridge, is quite conspicious. intervening Abruptly, The nearly parallel ridges and valleys of the Valley and Ridge are striking. at the southeast margin of this province Ridge front rises 1000 to almost 2000 feet. foothills in the vicinity of Gatlinburg the Blue The Blue Ridge at elevations of 2 .J vi ~ III .... ~ ~ ~ I _I \ -«>t> ,. ~ . ~~ !"Vo °0 >il9a.~ ~O 0'1 I - \.) ~. Y"..-z._., •• " ..~ I ~ .. L- . "'\ ~n,g ~ ~/ 4'" .J..NOWa'3ld ~'. I "- - '<""ti- I I 39CJ1~ ON'" ..A'3"VA n~"3..l."""d aN""~"39l11n.) 'If. r :11-'. I '/1 i ...; r.; __ ..-., I .,'-. ....--...-r" •• \, . \• • l.· .. Fig. 1 ' Major physiographic with -_ _ ... .- elements ot the Southern AppalaChians diagrammatic geologic cross section. 1« 3 generally 2000 to 3000 feet give way, less than 5 miles south- eastward, to the higher "and more rugged terrain of the Blue Ridge crestal mountains. Gatlinburg Mt. LeConte 6 miles southeast of is 6593 feet in elevation, south of Gatlinburg is at an elevation Clingmans Dome 10 miles of 6642 feet. These peaks are among the highest in the Southern Appalachians succeeded only by Mount Mitchell top is at 6684 feet. ward from Gatlinburg north of Asheville, The mountainous being N. C. whose Blue Ridge extends east- some 80 miles where its eastern border is marked by a sharp descent of some 2000 feet to the floor of the Piedmont. The Piedmont plain slopes gradually eastward, average elevation the Atlantic of 1000 feet at the foot of the Blue Ridge, to Coastal Plain. Unfortunately, the geology of several provinces which con- stitute the Southern Appalachians as are the physiographic more detailed western is not as readily understood elements. and complete In general our knowledge in the Plateau, is Valley and Ridge and Blue Ridge than in the eastern Blue Ridge and Piedmont regions. This is due in part to the availability topographic presence western from an maps, more abundant bedrock exposures of fossiliferous areas. and less metamorphosed of detailed and the rocks in the Because of these factors the western been studied more intensively result our knowledge areas have than those to the east and as a is more complete. Geologic The Appalachian Mountain element of the Southeastern Setting System, the dominant tectonic U. S. extends from the Cumberland 4 Plateau eastward miogeosynclinal eastward to the Atlantic deposits inferred Paleozoic "Appalachian and deformational revolution." extending However, late the sedimentary from late Precambrian Evidence for Precambrian including as in the sedimentary planed from the presumably sequences. the mountain throughout diastrophism plutonism, is found in the metamorphic deformation rocks history of this region is quite lengthy, and periods of deformation morphism of features of this system are to have resulted also quite complex, the Paleozoic. Composed to the west and eugeosynclinal many of the structural generally Coastal Plain. vulcanism and later and meta- and plutonic rocks as well After the late Paleozoic system was extensively eroded, pene- (perhaps 3 times) and the present landforms carved by differential erosion. Description of Tectonic Units Cumberland Plateau West of the Valley and Ridge this province prised of relatively flat-lying Pennsylvanian totaling a mile or more in thickness. features are the Pine Mountain distances westward. A spectacular sequence and Alabama. overthrusts along have moved short faulted anticline occurs near the middle of the region extending Tennessee and older sediments The main structural and Cumberland which upper layers of the sedimentary is mainly com- (Sequatchie) over 150 miles in Its axis is nearly straight, paralleling the main structural lineament of the Appalachians, and is essen- tially horizontal. The fold is breached by erosion resulting in 5 a valley, below 3 miles or so wide, whose the general floor is 1000 feet or more level of the Plateau. Valley In this province, and Ridge 40 or more miles is a generally comformable Pennsylvanian) sediments sequence thickness averages 3 or so miles. Imbricate dipping, repeat of the sequence thrusts, These faults are of large stratigraphic for hundreds of miles Appalachians. province coarsen and thicken generally carbonate southeastward sequence Ridge rocks although strongly crushed, cleavage is present eastern portions observed mainly the province. portion of the sediments which contrast to the northwest. are relatively southeast grain of the clastic in marked folded tightly in places to the The Valley and and locally unmetamorphosed. Weak fracture in select rock types near the middle of the region to throw and some extend in the southeastern have in their thrust blocks (Cambrian but which probably across along the structural The faults in Tennessee, of Paleozoic of varying segments across and but slaty .cleavage has not been in the rocks of this province. Blue Ridge This province east trending northwest east. can be conveniently segments, and the second, The crystalline latitude and other one dominantly of Gatlinburg, dominantly segment, into two north- sedimentary crystalline, in the to the south- about 30 miles wide is composed types of gneisses divided chiefly and schists at the of mica, hornblende plus granitic and 6 ultramafic intrusives. cambrian These rocks are considered and at least in part constitute upon which the sediments deposited. rocks). Lower Cambrian extends sedimentary is Precambrian Two sequences the basement complex of the eastern Blue Ridge were The dominantly near Gatlinburg, mainly Pre- portion of the Blue Ridge, (with but minor early Cambrian of chiefly clastic rocks are present, Chilhowee the Group, about a mile thick, which for several hundred miles along the eastern Blue Ridge, and the underlying Ocoee sediments which are areally quite restricted. The Ocoee clastics and possibly twice this amount. overlying Chilhowee, locally schists, different are at least five miles thick They are, in contrast with the metamorphosed to slates, phyllites, and have obviously environment The structural been deposited than the overlying Paleozoic in quite a rocks. features of this portion of the Blue Ridge are world famous, this being the classic Appalachian tremendous klippen. overthrusts as evidenced The Grandfather Gatlinburg, is evidence Blue Ridge. 75 miles n9rtheast of the 30 mile westward of transport of the the limestone-floored Cades, Wears and others) are windows Ridge thrust sheet and indicate westward approximating area of by several fenster areas and Mountain Window, Near Gatlinburg (Tuckaleechee, and horizontal cove areas in the Blue movements 10 miles. Piedmont This province, deciphered over 150 miles across, is the least of the Southern Appalachians. of its rocks is generally The surficial distri- known but their ages, stratigraphic, 7 structural and metamorphic The Piedmont which relationships are poorly understood. is commonly divided into somewhat generally Appalachians. parallel the northeast From the Atlantic Blue Ridge the more conspicious (I) The Carolina strike of the Coastal Plain westward slate belt, some 50 miles wide and area are characteristically strongly siltstones .and slates. is unknown but is probably altered. Precambrian dynamically The rocks of this felsic and mafic volcanics calated with partly tuffaceous are but slightly to the of these belts are: having a strike length of over 400 miles. thickness linear belts over 2 miles. metamorphosed interTheir These rocks but Dear plutons are Their age is unknown but they are presumably or early Paleozoic. (2) The Charlotte plutonic belt west of the slates is about 30 miles across and typified by rocks of approximately granitic composition. Paleozoic age, possibly These intrusives spanning are believed to be of several periods of that era. (3) The Kings Mountain belt~ a narrow dejective Late Precambrian erate or Early Paleozoic and schist, separates quartzite, zone of marble, conglom- the slate belt and the Inner Piedmont. (4) The Inner or Western dominated morphism zone. Piedmont, by mica gneisses and schists. of the Appalachians 50 miles wide, is Here the regional meta- peaks in the sillimanite-garnet The age of the rocks of this area was long believed Precambrian but the possibility of a Paleozoic age is now to be 8 entertained. significant Granitic rocks are also present here as well as ultramafic plugs and dikes. (5) The Brevard belt separates Blue Ridge. This belt, a narrow zone of phyllite, locally limestone, metamorphosed the Inner Piedmont is characterized and schist and by its rocks being less than those in adjacent belts. Some workers sur- mise that this belt is a major fault zone; others believe it is synclinal. Selected General References Guides to southeastern America. Hadley, geology: 1955, Geological Society of Jarvis B., and Goldsmith, Richard, 1963, Geology of the eastern Great Smoky Mountains,North Carolina and Tennessee: U. S. Geological Survey Prof. Paper, 349-B. King, Philip B., 1950, Tectonic framework of southeastern United States: Am. Assoc. of Petroleum Geologists, Bull. Vol. 34, No.4. King, Philip B, 1964, Geology of the Central Great Smoky Mountains, Tennessee: U. S. Geological Survey Prof. Paper 349-C. Rodgers, John, 1953, Geologic map of East Tennessee with explanatory text: Tennessee Div. of Geol. Bull. 58. Stuckey, Jasper L. and Conrad, Stephen G., 1958, Geologic map of North Carolina: Explanatory text for geologic map of North Carolina: North Carolina Division of Mineral Resources, Bull. 71.