Physiographic Divisions and Differential Uplift in the Piedmont and Blue Ridge G£b :LOG-! A-L SURVEY P R O FC S SI ON A L PAPER Physiographic Divisions and Differential Uplift in the Piedmont and Blue Ridge ByJOHNT. HACK GEOLOGICAL SURVEY PROFESSIONAL PAPER 1265 A study of the topography and other surface features of the Piedmont and Blue Ridge, as related to late tectonic history UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1982 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES G. WATT, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging in Publication Data Hack, John Tilton, 1913- Physiographic divisions and differential uplift in the Piedmont and Blue Ridge. (Geological Survey professional paper ; 1265) Bibliography: p. Supt. of Docs. no. I 19.16:1265 1. Physical geography-Piedmont (U.S.: Region) 2. Physical geography-Blue Ridge Mountains. 3. Isostasy. I. Title. II. Series. GB124.P53H33 551.4'3'0975 82-600079 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, DC 20402 CONTENTS Page Abstract _______ 1 Southern Blue Ridge province _. .____________ 27 Introduction ____ 1 Chilhowee-Walden Creek belt. ._____________ 28 Plan of report _ 2 Mountain highlands ______________ 28 Regional setting _ 6 Brevard zone and Hendersonville bulge __ 30 Piedmont Lowlands ___________________________________ 10 Intermontane basins ________ 32 Stream patterns and evidence for sedimentary overlap ____ 11 Mount Rogers area _____________ 34 Quantitative analysis of drainage patterns _________ 12 New River plateau _____ _ 34 Regional physiographic features related to the Pine Blue Ridge escarpment ______________ 35 Mountain belt ______________________ 14 Differential movement along the Fall Zone ________ 14 Dan River capture ________________ 38 Northeastern Highlands _____________________ 15 Linville River ________________ 40 Southwestern Highlands ____________________ 20 Evolution of the escarpment ______ 44 Foothill zone ___________________________ 23 Time frame of late tectonism _________ 45 Northern Blue Ridge Mountains ________________ 25 References cited _____ 46 ILLUSTRATIONS Page FIGURE 1. Map of the Southeastern United States, showing subdivisions of the Piedmont and Blue Ridge ________________ 3 2. Generalized lithologic map of the Piedmont and Blue Ridge provinces _____________________________ 4 3. Averaged topographic map of part of the Southeastern United States _______________________________ 5 4. Relief map of the Piedmont and Blue Ridge provinces ______________________________________ 7 5. Drainage map of part of the Appalachian Highlands _________________________________________ 8 6. Topographic profile across the Blue Ridge and Piedmont from Salem, Va., to the Durham Triassic and Jurassic basin ____ 9 7. Topographic profile across the Blue Ridge from Johnson City, Tenn., to South Mountains, N.C _________________ 10 8. Profiles of 14 streams in the Piedmont Lowlands ___________________________________________ 15 9. Profiles of five streams in the Northeastern Highlands _____________________________________ 16 10. Map of the Patapsco River basin, Maryland ______________________________________________ 17 11. Logarithmic profile of the Patapsco River, Md ____________________________________________ 18 12. Logarithmic profile of the Appomattox River, Va __________________________________________ 19 13. Transverse profiles of two valleys in the Patapsco River basin ___________________________________ 20 14. Profiles of some first-order tributaries in the Patapsco River basin _______________________________ 20 15. Averaged topographic map of the Southwestern Highlands _____________________________________ 21 16. Simplified topographic and geologic maps of the Southwestern Highlands ____________________________ 22 17. Longitudinal profiles of the Tallapoosa and Coosa Rivers ______________________________________ 23 18. Logarithmic profile of the Tallapoosa River ______________________________________________ 24 19. Profile and geologic map along the crest of the Northern Blue Ridge ________________________________ 26 20. Map of the Southern Blue Ridge province _______________________________________________ 28 21. Profiles along two trench valleys ____________________________________________________ 30 22. Map showing large trench valleys and basins in part of the Mountain highlands _________________________ 31 23. Geologic map of the basin of the French Broad River _______________________________________ 33 24. Map showing the asymmetry of the drainage system of the Southern Blue Ridge province ____________________ 36 25. Strip maps showing the southeastern margin of the Southern Blue Ridge province _______________________ 37 26. Map of the headwaters area of the Dan River _____________________________________________ 39 27. Profile of the headwaters of the Dan River _______________________________________________ 40 28. Map of the Linville River and surrounding areas ______________ ____________________________ 42 29. Profile of the Linville River _______________________________________________________ 43 TABLES Page TABLE 1. Mensuration data for drainage basins of the Piedmont and three selected basins in the Coastal Plain 13 2. Comparison of topography at four locations in the Asheville basin __________________ 34 ill PHYSIOGRAPHIC DIVISIONS AND DIFFERENTIAL UPLIFT IN THE PIEDMONT AND BLUE RIDGE By JOHN T. HACK ABSTRACT Northwest of the Piedmont Lowlands, the topography and relief are higher, and in some places, the rise is gradual, forming a Foothill zone The Piedmont and Blue Ridge are dynamic landscapes that have between the Piedmont Lowlands and the high Blue Ridge. This zone is undergone substantial change since the orogenies that ended in late morphologically more complex than the Piedmont Lowlands. North of Paleozoic or, as some believe, early Mesozoic time. The southern Blue the Roanoke River, the foothills are commonly chains of isolated hills Ridge region south of Roanoke, Va., lies on the crest of a topographic and ridges generally underlain by resistant rocks. The hills increase in uplift that corresponds to the eastern continental drainage divide. To height near the Blue Ridge, an indication that they owe their height to the north, this uplift and divide cross the Appalachian Valley and form tectonism of late geologic age. South of the Yadkin River, the hills are the crest of the Appalachian Plateaus as far north as central Penn­ believed to be residual, the remnants of a larger highland that has been sylvania. The northern Blue Ridge Mountains as well as parts of the only partially reduced to the lower relief of the general Piedmont sur­ Piedmont are on the eastern part of the uplift area. The southeastern face. margin of the uplift corresponds to a line within the Piedmont physiographic province that extends northeastward from the The Blue Ridge physiographic province has two subdivisions. The Tallapoosa River at the Fall Zone and crosses the Rappahannock River Northern Blue Ridge Mountains are underlain by resistant rocks and in effect form the easternmost range of the Valley and Ridge province. at the Fall Zone. The differential elevation on either side of this line is Three different rock types form the crest in various places; the dif­ sharp in some places, as, for example, northeast of Atlanta, Ga. In other places, the difference in elevation is difficult to detect, and, in ef­ ferences in their resistance as well as in the width of outcrop belts fect, the line becomes a broad monoclinal slope. determine the altitude of the range. North of Chester Gap in northern Virginia, the lower altitude of the range may be related in part to dif­ The region as a whole can be divided into at least six broad ferences in uplift history over a broad region. subregions that have somewhat different histories in late geologic The Southern Blue Ridge province is a complex area. Part of it, the time. New River basin, is essentially a plateau that owes its relative height The Piedmont Lowlands subprovince, southeast of the uplifted area, to resistant rocks crossed by the New River downstream from the Blue is dominated by a monotonous topography of low rounded ridges and Ridge itself. The southern part is underlain by massive and resistant ravines largely underlain by saprolite on crystalline rocks. Isolated gneiss and metasedimentary rock and has relief exceeding 1,100 m. ranges of hills of greater relief are scattered across the region; those Rock control has a strong influence on forms locally. Deep trenchlike investigated are directly related to the presence of erosionally resist­ valleys follow weak-rock outcrop areas like the carbonate rock of the ant rocks. Stream patterns as well as broad topographic forms indicate Murphy marble belt as well as fracture zones or shear zones along that although the southern part of the Piedmont Lowlands was prob­ faults. The Asheville basin may be partly controlled by the outcrop of ably once covered by younger sediments, this area has been exposed to weak rocks but also by intersecting shear zones. erosion for a long time. In North Carolina, the inner part of the Pied­ The Southern Blue Ridge province is bounded on its southeast mont Lowlands has strongly trellised stream patterns, which suggest margin by a bold escarpment that corresponds to the major drainage that subaerial erosion was active for an even longer time period, divide. As shown by a major piracy by the Dan River, at least the perhaps since the latest