Structural chronology of the Alleghanian orogeny in southeastern West Virginia STUART L. DEAN Department of Geology, University of Toledo, Toledo, Ohio 43606 BYRON R. KULANDER Department of Geosciences, Wright State University, Dayton, Ohio 45435 JEFFREY M. SKINNER Wintershall Oil and Gas Corporation, 5 Post Oak Park, Suite 2000, Houston, Texas 77027 ABSTRACT The trend change between central and southern Appalachian extension of this same line of structural discontinuity, the Covington lin- structures is sharply defined in southeastern West Virginia. There, eament (Dean and others, 1979), extends into the Valley and Ridge of N30°-35°E trends coincident with major central Appalachian folds, Virginia at least to the Rich Patch anticline and possibly into the Shenan- such as the Browns Mountain anticline, end abruptly at N60°E- doah Valley (Fig. 1). The Covington lineament thus serves as the northern trending southern Appalachian structures along the St. Clair fault. boundary to the Roanoke sector recess and as the principal boundary Analysis of local and regional folds, cleavage, bedding-perpendicular between the central and southern Appalachians. stylolite seams and bedding, and fault slickenlines reveals that layer- The abrupt changes in trend and discontinuous nature of structures parallel shortening, directed N10°-30°W, occurred in nonfolded across the boundaries of the central-southern Appalachian juncture have Greenbrier Group (Mississippian) carbonates well into the present suggested to Rodgers (1970) that folds and faults of the southern sector Appalachian Plateau area. This structural event is early and is asso- predated deformation in the central sector. It is the intention of the present ciated with the evolution of southern Appalachian folds and faults study to clarify Alleghanian deformational chronology in this region south of the St. Clair fault. Central Appalachian folds and mesoscopic through structural analysis of Greenbrier Group carbonates (Mississippian) structures were superimposed on this early layer-parallel shortening in West Virginia. Folds, bedding-perpendicular stylolite seams, cleavage, fabric. This structural chronology indicates that southern Appalachian and slickenlines have been analyzed on a regional basis and in detail at two folds and faults predated the development of central Appalachian locations in the study area in West Virginia (Fig. 1, locations A and B). structures in the region. FOLDS AND CLEAVAGE INTRODUCTION With the exception of the Abbs Valley anticline and Hurricane Ridge Appalachian Plateau and Valley and Ridge structures show abrupt syncline, central Appalachian folds in Monroe County, West Virginia, changes in trend and continuity at the boundaries of, and within, the plunge out into the line of Appalachian juncture (southwestern extension V-shaped recess north and northwest of Roanoke, Virginia (Fig. I). The of the Covington lineament). The exact nature of the relationship of these northern boundary of this recess marks the junction between the central two structures to the trend change is unclear. The West Virginia Geologi- Appalachians, where folds dominate the structural framework with cal Survey county report for Mercer, Summers, and Monroe Counties N30°-35°E trends, and the southern Appalachians, where southeast- (Reger, 1925) shows virtually no structural relief at the Avis Limestone dipping thrust faults, with N60°E trends, are the major features. The (Upper Mississippian) level on these folds that is continuous from central southern boundary of this V-shaped sector is a linear zone marking the to southern Appalachian trends. Recent work by McDowell (1982) also abrupt termination of the Catawba syncline, Saltville fault, and Sinking suggests a lack of continuity of these structures across the trend change. It Creek anticline and the change in trend of the Pulaski fault. Rodgers seems clear that previous positioning of the axial traces is speculative (1970) and Lowry (1971) have discussed in detail the contrasting aspects across the trend change and that any interpretation of synchronism of between central and southern Appalachian structures. structural development across the trend change, based on this continuity, is To the northwest, the Roanoke sector recess converges in eastern inconclusive. Monroe County, West Virginia, to the position of the St. Clair fault. This South of the extension of the Covington lineament in Monroe thrust fault and the Glen Lyn syncline (McDowell, 1982), which has the County, Appalachian structures such as the St. Clair fault strike N60°E same trend and is immediately to the northwest, serve as the approximate parallel to this line of trend change. Particularly significant north of the boundary between the central and southern Appalachians in southeastern Covington lineament extension is the series of small folds, east of the West Virginia as well as marking the position of the Allegheny structural community of Union, that are developed on the southern terminus of the front. The trace of the St. Clair fault ends just across the West Virginia- Browns Mountain anticline (Fig. 1, area A; Fig. 2). None of these struc- Virginia state line in Alleghany County, Virginia, but the northeastern tures carries through into the southern Appalachians. Some larger folds Geological Society of America Bulletin, v. 100, p. 299-310,10 figs., February 1988. 299 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/100/2/299/3380083/i0016-7606-100-2-299.pdf by guest on 02 October 2021 STRUCTURES CITIES A.V. A. Abbs Valley Anticline R. P. A. Rich Patch Anticline C Covington B.V.A. Back Valley Anticline SC.A. Sinking Creek Anticline M Mar 1 in ton B.D. Bane Dome W.S.A. Warm Springs Anticline R Roa noke B.M.A. Browns Mt. Anticline W.A. Williamsburg Anticline U Union C.S. Caldwell Syncline W.M.A. Wills Mt. Anticline CT. S Catawba Syncline N.F. Narrows Fault G.L.S. Glen Lyn Syncline P. F. Pulaski Fault H.R.S. Hurricane Ridge Syncline S.F. Saltville Fault MM.A. Mann Mt. Anticline S C F. S t. C 1 a i r Fault P. S. Pedro Syncline Figure 1. Area of investigation, showing major tectonic elements, specific locations of areas A and B, the extent of the Roanoke recess, and the position of the Covington lineament. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/100/2/299/3380083/i0016-7606-100-2-299.pdf by guest on 02 October 2021 STRUCTURAL CHRONOLOGY OF ALLEGHANIAN OROGENY, WEST VIRGINIA 301 Figure 1. (Continued). such as the Pedro syncline, just to the east of the Browns Mountain trending folds are present north of the Covington lineament in Monroe structure, appear to swing into alignment with the N60°E trend of the County. The low amplitude and short wave length of Greenbrier Group extension of the Covington lineament. The verification of the continuity of folds in Monroe County also indicate that these structures are rooted this structure to the southwest as an extension of McDowell's (1982) Glen primarily at a Middle Devonian (lower Millboro-Marcellus) shale Lyn syncline requires additional field work, however. No major N60°E- décollement level, as postulated for the region by Roeder and others Figure 2. Fold and solution cleavage trends, southeastern Monroe County, West Virginia (area A, Fig. 1). Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/100/2/299/3380083/i0016-7606-100-2-299.pdf by guest on 02 October 2021 Figure 3. (a) Lower hemisphere, equal-area plot of poles to solution cleavage, southeastern Monroe County, West Vir- ginia (area A, Fig. 1). Maxima reveal trends of N62°E and N10°E. (b) Lower hemisphere, equal-area plot of poles to stylo- lite seams, southeastern Monroe County, West Virginia (area A, Fig. 1). Maximum shows a trend of N56°E. (c) Lower hemisphere, equal-area plot of stylolite teeth trends, southeastern Monroe County, West Virginia (area A, Fig. 1). Major maximum occurs at N13°W. Minor maximum also at N85°W. (d) Lower hemisphere, equal-area plot of bedding slick- enline trends, southeastern Monroe County, West Virginia (area A, Fig. 1). Maxima occur at N15°W, N42°W, and N85°W. (e) Lower hemisphere, equal-area plot of slickenline n = 275 n =240 trends on small, low-dipping bedding reverse faults, south- Contour Interval Contour Interval eastern Monroe County, West Virginia (area A, Fig. 1). Max- ima occur at N15°W, N40°W, and N77°W. 1-9% >9% 1-12% >12% N13W N 1 5 W N15 W N42 W N 77 W N85 W n=320 n = 180 n = 180 Contour Interval Contour Interval Contour Interval VP. y za A 1-1É >16% 1-9% >9% 1-6% Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/100/2/299/3380083/i0016-7606-100-2-299.pdf by guest on 02 October 2021 STRUCTURAL CHRONOLOGY OF ALLEGHANIAN OROGENY, WEST VIRGINIA 303 (1978), Dean and others (1979), Perry (1980), and Perry and others (1979). Solution cleavage is present in Greenbrier limestone throughout the Greenbrier outcrop belt of southeastern West Virginia (regional location map, Fig. 1) and is especially well developed near the trend change in Monroe County (Fig. 2). Figure 3a reveals trends of N62°E and N10°E at this locale that are attributable to southern and central Appalachian de- formational stresses, respectively, if deformational stresses are considered to be normal to structural trends. Figure 2 reveals that the N62°E-trending cleavage is only locally developed within the prominent central Appala- chian grain north of the Covington lineament and has been found no farther north than the community of Union, ~5 km north of this trend 5 10 15 MILES Figure 4. Trends of stylolite seams throughout the Greenbrier Valley in southeastern West Virginia. Long lines represent major regional systematic trends, and short lines represent the orthogonal stylolite set. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/100/2/299/3380083/i0016-7606-100-2-299.pdf by guest on 02 October 2021 304 DEAN AND OTHERS change.