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Structural chronology of the Alleghanian in southeastern West

STUART L. DEAN Department of , 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 . 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 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 . boundary to the Roanoke sector recess and as the principal boundary Analysis of local and regional folds, , 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 () 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, . 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 , 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 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 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

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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 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.

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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. 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%

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(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.

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change. Mesoscopically, solution cleavage surfaces are undulose and are land, and West Virginia by Cloos (1951), Nickelsen (1966, 1979), typically closely spaced, ranging from a few millimetres to a few centime- Groshong (1975), Dean and Kulander (1972,1977,1978), Geiser (1974), tres apart. Consistent orientations of the strike of this cleavage aid in the Dean and others (1979), Engelder (1979a, 1979b), Engelder and Engelder delineation of fold trends north of the Glen Lyn syncline. Cleavage devel- (1977), and Engelder and Geiser (1979). Cleavage attitudes that fit both opment in Greenbrier limestone of the central Appalachians was appar- central and southern Appalachian fold structures are confined to a narrow ently initiated before folding, or very early in folding, given the presence of zone within, and near, the southwestern extension of the Covington lin- cleavage in very low-dipping Greenbrier limestone beds in the Union area eament (Fig. 2). South of the trend change, vertical, N10°E-trending (Fig. 2). In addition, the perpendicular relationship of cleavage to bedding solution cleavage transects the N60°E southern Appalachian structural in more intensely folded rocks in the same area supports this conclusion. grain. The fact that the cleavage there is not folded and related to southern Similar relationships dealing with early cleavage formation and other Appalachian structures indicates that central Appalachian folding and penetrative layer-parallel shortening effects have been documented or cleavage development overprinted earlier formed southern Appalachian suggested in the central Appalachians of , , Mary- folds.

Figure 5. Stylolites and stylolite teeth trends, southeastern Monroe County, West Virginia (area A, Fig. 1). Northeast-trending lines represent stylolites, and the barbed lines represent accompanying teeth trends.

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 n= 76 n -76 n »49 Contour Interval Contour Interval Contour Interval

>6% >6%

N 22 W

n = 49 n- 76 n »76 Contour Interval Contour Interval Contour Interval

221 m >6% >6%

Figure 6. (a) Lower hemisphere, equal-area plot of poles to stylolite seams, after folding, Williamsburg anticline (area B, Fig. 1). Central maximum reveals near-horizontal stylolites measured on near-vertical beds. (b) Lower hemisphere, equal-area plot of poles to stylolite seams, before folding, Williamsburg anticline (area B, Fig. 1). The two maxima show trends of N41°E and N63°E that are coincident with stylolite trends throughout the Greenbrier outcrop belt. (c) Lower hemisphere, equal-area plot of poles to joints, after folding, Williamsburg anticline (area B, Fig. 1). Central maximum reveals near-horizontal joints measured on vertical beds. (d) Lower hemisphere, equal-area plot of poles to joints, before folding, Williamsburg anticline (area B, Fig. 1). The maxima in the northwestern and southeastern quadrants reveal prefold trends of N30°E and N75°E that fit local stylolite orientations and the overall stylolite trends throughout the Greenbrier outcrop belt. The maximum in the northeastern and southwestern quadrants represents a N59°W- trending cross-joint set that was second formed to the N30°E set. (e) Lower hemisphere, equal-area plot of stylolite teeth trends after folding, Williamsburg anticline (area B, Fig. 1). Maximum in center of diagram represents vertical teeth on horizontal stylolites crossing vertical bedding. (f) Lower hemisphere, equal-area plot of stylolite teeth trends before folding, Williamsburg anticline (area B, Fig. 1). The maximum in the northwestern and southeastern quadrants trends N22°W and obliquely crosses the Williamsburg anticline axis.

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Figure 7. Bedding-plane view of sty- lolitized joints in Greenbrier limestone. Pens at left and right for scale. Arrows indicate joint propagation directions and hooking of joints into other joints prior to later stylolitization.

STYLOLITES N60°-75°E- and N30°-45°E-trending sets of stylolite seams are not surfaces of solution cleavage but, instead, are interpreted to represent Stylolite seams perpendicular to bedding pervade the Greenbrier early-formed vertical joints created in response to regional southeastward limestone outcrop belt (Fig. 4). Regional systematic trends of N30°-45°E extension before Alleghanian folding. It is felt that these interpreted joint and N60°-75°E are present, and each set commonly shows development surfaces then experienced later in response to early of a nonsystematic, near-orthogonal stylolite set. Locally, in southeastern Alleghanian compressional stresses. Monroe County, only one set of seams, trending N56°E, is prominent Fundamental morphological differences exist between the solution (Figs. 3b, 5). In spite of the closeness of this value to the local N62°E trend cleavage and the stylolitized joints. The stylo-joints are wider spaced (15 of solution cleavage, a common origin is not indicated. Both the cm to > 1 m apart), and their surfaces are irregular but commonly sutured.

Figure 8. Bedding-plane view of sty- lolitized joints in Greenbrier limestone. Major stylolite running from upper right to lower left trends N30°E. Second- formed stylolitized joint trends east-west and abuts N30°E stylo-joint. Pen shows stylolite teeth direction and reveals that N10°W lateral compressive styloli- tized both earlier formed joints at the same time.

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Indicating an early joint origin are the consistent regional trends of the stylolite seams, which do not fit a causal relationship to the variable trends of local and regional fold axes (Fig. 4). Similarly, in moderately and steeply folded strata, the stylolites remain perpendicular to bedding. Anal- ysis of a series of asymmetric to overturned folds on the western flank of the Williamsburg anticline (Fig. 1, area B) illustrates the early origin of these stylolite seams. Figures 6a and 6b show the trend of stylolite seams after folding and restored to a prefolding orientation, respectively. Figures 6c and 6d show nonstylolitized joints in dolomite and shale beds on the same structures after folding and before folding. After restoration to

0 5 10 15 MILES

Figure 9. Stylolite teeth trends throughout the Greenbrier limestone outcrop belt, southeastern West Virginia. Regional N10°-30°W trends dominate and obliquely cross central Appalachian structures well into Monroe and Greenbrier Counties, West Virginia.

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study of joints on the of West Virginia, which reveals a joint geometry in Mississippian and shale as well as Greenbrier limestone throughout all of southeastern West Virginia that fits an early southeasterly extensional mode of formation. Trends of extension joints in all Mississippian formations are distinctly different from joint trends in Pennsylvanian coals immediately west and northwest of the Greenbrier outcrop belt (Kulander and others, 1980). First-formed Mississippian limestone joints are oriented N56°E. Mississippian sandstone and shale joints also trend subparallel to southern Appalachian structures, with orientations of N65°-80°E. First-formed Pennsylvanian coal joint (face cleat) trends are N30°-35°W. These marked differences in trend indicate that different stress fields existed between the times of formation of Missis- sippian and of Pennsylvanian joints. Mississippian joints fit an extensional pattern caused by subsidence to the southeast, whereas trends of nearby Pennsylvanian coal joints indicate the same lateral compressive stresses associated with southern Appalachian mountain building that stylolitized the earlier formed limestone extension joints. Extensional stresses appear to be related to southeastward subsidence, caused by tectonic loading and sedimentation associated with the devel- opment and northwestward advance of southern Appalachian thrust sheets, according to the work of Donaldson and Shumaker (1980). Re- gional stratigraphie thickening of Mississippian and Lower Pennsylvanian formations as documented by these workers, as well as by Ferm and Cavaroc (1969), Ferm (1974), Arkle (1974), and DeWitt and McGrew (1979), support this concept by revealing depo-axes to the southeast in southwestern Virginia. Where stylolite seams do not contain a thick clay selvage, a sutured contact of pits and columns (that is, "teeth"), representing differential pressure solution, reveals the direction of lateral compressive stress (CTI), a analysis technique previously used in other regions by Blake and Roy (1949), Park and Schot (1968), Arthaud and Mattauer (1969), Choukroune (1969), Schafer (1974), and Geiser and Sansone (1981). Figure 8 shows stylolite teeth with the same orientations crossing stylolite seams of different orientations. The teeth trend is measured as a linear Figure 10. Greenbrier limestone exposure on the southeastern fabric element. overturned limb of the Hurricane Ridge syncline near Bluefield, West The oblique manner in which stylolite teeth cross most stylolite seams Virginia (extreme southeastern corner of Fig. 9). Overturned bedding (Figs. 5, 8) and the consistent local and regional trends (Figs. 3c, 9) of dips from upper left to lower right. Stylolite seams are all perpendicu- stylolite teeth support the concept of early joint formation followed by lar to bedding, and stylolite teeth are all parallel to bedding. stylolitization. The imposition of stylolites on joints occurred before fold- ing, or during earliest fold growth, because stylolite teeth always show a parallel relationship to bedding, even in steeply folded . Figure 10 shows a typical outcrop of Greenbrier limestone on the southeastern over- turned limb of the Hurricane Ridge syncline near Bluefield, West Virginia. It is significant that the orientation of stylolite teeth is exactly parallel to a prefolding attitude, the stylolite seam trends are coincident with those of bedding and that the stylolite seams (that is, early-formed joints) are the unfolded joints, as well as with trends of regional stylolite seams perpendicular to bedding. throughout the Greenbrier limestone outcrop belt shown in Figure 4. Regional stylolite teeth show trends of N10°-30°W and N50°-70°W Figure 6d also reveals a N59°W-trending cross-joint set that was second throughout the Greenbrier limestone outcrop belt, revealing lateral com- formed, as shown by abutting relationships to the N30°E set. Local fea- pressive stress directions that fit both southern and central Appalachian tures associated with the stylolite seams also support an early joint origin. structural trends (Fig. 9). Furthermore, the presence of the N10°-30°W Figure 7 shows apparent hooking relationships of stylolite seams, a charac- stylolite teeth trend north of the Covington lineament indicates that layer- teristic feature in jointed rocks. parallel shortening in Greenbrier limestone, associated with southern Ap- The strike of the stylolite seams is parallel to Mississippian isopach palachian deformation, extended far north of the line of Appalachian trends (DeWitt and McGrew, 1979), which also supports the interpreta- juncture, possibly as far as the present site of Marlinton, West Virginia. tion of early extension joint development. A -joint origin for these This extent of N10°-30°W-trending stylolite teeth to Marlinton, West seams does not appear to be valid because the seams are not favorably Virginia, projects southeastward to the northeastern plunge-out of the Rich oriented for shear failure caused by deformational stresses related to either Patch anticline, the last of the major southern Appalachian folds imme- southern Appalachian or central Appalachian folds and faults. In addition diately south of the Covington lineament in Alleghany County, Virginia. to the near orthogonal relationship of many pairs of seams (Fig. 4), sup- Accordingly, the authors feel that southern Appalachian deformational porting evidence has been presented by Kulander and others (1980) in a stresses were translated perpendicular to the Covington lineament into the

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central Appalachians at least as far as Marlinton, West Virginia. Work by CONCLUSIONS Wheeler (1978) on disc folds in the Millboro Shale of Middle Devonian age on the Browns Mountain anticline shows separation angles on slip Thin-skinned deformation has effected primarily a twofold deforma- planes that also fit southern Appalachian compressive stress orientations tional chronology at the juncture of the central and southern Appalachians well into the central Appalachians. in southeastern West Virginia and to the northeast in the Valley and Ridge Analysis of stylolite teeth on the western flank of the Williamsburg of Alleghany County, Virginia. A line perpendicular to strike, drawn anticline (Figs. 6e and 6f) shows that the N22°W teeth direction is unre- northwestward from the northeastern plunge-out of the Rich Patch anti- lated to the development of this fold because the teeth are not perpendicu- cline along the Covington lineament, coincides with the last observed lar to the overall N30°E fold trend at location B. Furthermore, Figure 6e N10°-30°W stylolite teeth measurements at Marlinton, West Virginia, as shows a pronounced maximum of vertical stylolite teeth, representing the detectable extent of southern Appalachian deformation compressive readings from stylolite seams on vertical and near-vertical limestone beds. stresses in this area. Restoration of bedding to horizontal (Fig. 6f) about the N30°E fold axis Mesoscopic rock-fabric data support the interpretation that southern migrates the vertical maximum into coincidence with the N22°W stylolite Appalachian folds and faults in the area formed before central Appala- teeth trend, clearly indicating that the N22°W trend formed first and was chian structures for the following reasons. subsequently rotated during later central Appalachian folding, which also (1) Throughout most of the Greenbrier Group outcrop belt in south- developed the N50°-70°W stylolite teeth elsewhere throughout the region. eastern West Virginia, layer-parallel tectonic stylolite teeth, trending The Williamsburg anticline exposures illustrate the fact that overprinting N10°-30°E, are oblique to central Appalachian folds, illustrating that they and different teeth trends at the individual outcrop are not commonly seen, formed in response to a different compressive from that asso- possibly because the accumulation of silt and clay along the initially devel- ciated with central Appalachian structures. The N10°-30°E trend of the oped stylolite seams may have prevented formation of well developed stylolite teeth is normal to southern Appalachian folds and faults in the teeth in response to a later compressive stress event, even though addi- region and is compatible with deformational stresses associated with the tional pressure solution did occur. Geiser and Sansone (1981) have development of southern Appalachian structures. In areas of folded rock pointed out, in carbonate rocks of the Umbrian Apennines of Italy, that north of the trend change, stylolite teeth remain parallel to bedding and undulous stylolite seams, without teeth, appeared to be restricted to rocks exhibit the same N10°-30°E trend after the strata have been unfolded having high insoluble residues. Another explanation for limited overprint- about central Appalachian fold axes. ing may lie in the elimination of bedrock intergranular and early joint (2) Stylolite teeth are present on, and cross, widely spaced in the initial pressure-solution process, thereby inhibiting addi- N30°-45°E- and N60°-75°E-trending stylolite seams that are every- tional pressure solution from another tectonic event. Where overprinting is where perpendicular to bedding. At nearly all locations, the stylolite teeth found, the N50°-70°W teeth trend is superimposed on the N10°-30°W are oblique to these seams, indicating that the seams existed before stylolite trend. teeth development. These stylolite structures are interpreted to be styloli- Locally, in extreme southeastern Monroe County, limited stylolite tized joints. They best fit an extension joint origin because they are parallel teeth data also suggest late-phase lateral compressive stress oriented at high to subparallel to Mississippian depo-axes shown in southwestern Virginia angles to the northwest (that is, N85°W) (Figs. 3c, 5). At a few locations by various workers. These stylolite seams preceded central Appalachian where timing can be established by overprinted stylolite teeth, with regard structural development because they reveal the same trends in folded to local N13°W and N50°W teeth trends, the N85°W trend is last formed central Appalachian rocks for the cases in which these strata are restored and therefore represents last stage Alleghanian compressional in to horizontal by unfolding about central Appalachian fold axes. The stylo- the area. The approximate north-south strike of solution cleavage near the joints are also subparallel to nonstylolitized joints in all Mississippian trend change line (Fig. 2) supports this interpretation as well as suggesting formations in southeastern West Virginia. It is implied that extension joint that some solution cleavage oriented at high angles to the north may be origin was pre-Pennsylvanian because the trends of both stylo-joints and late formed as well. nonstylolitized joints in Mississippian strata are distinctly different from Pennsylvanian joint trends. SLICKENLINES (3) North of the St. Clair fault and Glen Lyn syncline in area A near Union, West Virginia, slickenlines on bedding planes and small reverse Slickenlines were measured on bedding planes, small reverse faults, faults show multiple slip directions. Here, N40°-42°W and N77°-85°W and cleavage and stylolite seams in the Greenbrier outcrop belt of south- slickenline trends are most commonly overprinted on a N15°W trend. eastern Monroe County. Figure 3d reveals three dominant trends, N15°W, This first-formed N15°W-trending set of slickenlines fits deformational N42°W, and N85°W, on approximately horizontal bedding planes. These stresses associated with southern Appalachian structures. trends closely fit the three directions of stylolite teeth (Figs. 3c, 5). Figure (4) South-southeast of Union, West Virginia, vertical and near- 3e shows slickenline trends on small, low-dipping, bedding wedge (re- vertical central Appalachian solution cleavage fabric obliquely crosses the verse) faults. Here, again, the slickenlines are oriented N15°W, N40°W, Glen Lyn syncline, clearly revealing later development, and a different and N77°W and parallel the trends of stylolite teeth. Where multiple slip deformational stress field, than that which formed the Glen Lyn syncline, a directions are found on bedding or fault surfaces, the N15°W set is most southern Appalachian fold. commonly overprinted by the N42°W set. Similarly, these two sets are overprinted by the N85°W set. Slickenlines on cleavage faces and stylolite ACKNOWLEDGEMENTS seams were found mainly on those features oriented at moderate to high angles to the northeast (that is, greater than N30°E). These slickenlines are The authors have benefited from discussions with Peter Geiser, Peter horizontal to subhorizontal, and the development of calcite steps consist- Lessing, John Rodgers, and Russell Wheeler. Patrick Heider and David ently reveals a right-lateral sense of shear. This observation also indicates Mustafaga made useful suggestions for the preparation of the various that last-phase Alleghanian stresses in this area of the central-southern diagrams. The manuscript has been significantly improved through review Appalachian junction were oriented approximately east-west. by Robert Milici, Robert McDowell, and Avery Drake.

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