Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143

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Palaeogeography, Palaeoclimatology, Palaeoecology

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An incised valley fill and lowstand wedges in the Upper Devonian Foreknobs Formation, central Appalachian Basin: Implications for Famennian glacioeustasy

Wilson S. McClung a,⁎, Clifford A. Cuffey b, Kenneth A. Eriksson c,DennisO.TerryJr d a 3165 Orion Drive, Colorado Springs, CO 80906, United States b Chevron USA Inc., 15 Smith Rd, Midland, TX 79705, United States c Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, United States d Department of Earth and Environmental Science, Temple University, Philadelphia, PA 19122, United States article info abstract

Article history: The supposition that the Late Devonian Gondwanan glaciation should be recorded in more temperate regions by Received 24 September 2015 black shales, incised valleys, and lowstand wedges is tested with reference to the Foreknobs Formation (late Received in revised form 6 January 2016 Frasnian to early Famennian) of the central Appalachian Basin (USA). The upper (early Famennian) portion of Accepted 7 January 2016 the Foreknobs Formation in a proximal strike belt in eastern West Virginia contains an erosionally based, coarse, Available online 18 January 2016 conglomeratic, incised valley fill (IVF) that is underlain and overlain by strata deposited in a relatively deep- marine, ramp setting. A signal of sea-level drawdown is in the form of conglomeratic, hummocky cross- Keywords: fi fl Late Devonian strati ed (HCS) storm event beds underlying the IVF, suggesting the proximity of a gravely uvial point source Foreknobs Formation up-paleoslope. Within a more distal outcrop 66 km (41 miles) to the west, and at about the same stratigraphic Wedge-top horizon, the Foreknobs Formation exhibits a relatively thin succession of black shale that was deposited as sea- Incised valley fill level fell, resulting in the concentration of nutrients that caused anoxic conditions. Overlying the black Lowstand wedge shale are several erosionally based lowstand wedge deposits comprised of cyclic conglomeratic, braided- High frequency sequence stream facies which fine-upward to dark gray shales deposited within estuarine environments. The genetically Icehouse related proximal IVF and the lowermost distal lowstand wedge formed during a major 3rd-order eustatic sea- level fall (35–45 m) consistent with published 3rd-order sea-level curves. Lowering of sea-level (base-level) resulted in steeper stream gradients which caused incision and transportation of gravel from the wedge-top depozone of the foreland basin down to the basinward-migrated shoreline. Inferred depositional environments of the distal lowstand wedge are consistent with interpretations from regional subsurface mapping west of the most distal outcrop belt. From inferred magnitudes of sea-level falls and the physics of ice-sheets, calculations of areal extents of ice over Gondwana suggest that an early Famennian inferred sea-level fall of 35–45 m translates to an area of ice which is only half of the reported area of late Famennian ice. The data are consistent with step-wise increases in magnitude of sea-level fluctuations during deposition of the Upper Devonian Foreknobs Formation within a period of time transitional between Middle Devonian greenhouse conditions and the later icehouse conditions of the Late Paleozoic. © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction abundant subaerial exposure surfaces (some imprinted on subtidal strata), abrupt shifts of fluvial deposits over relatively deep marine During time intervals that icehouse conditions prevail on Earth, deposits (or vice-versa), and cyclothems (e.g., Heckel, 2008; Kabanov large-scale continental glaciations result in both high-magnitude and et al., 2010; McClung et al., 2013; Cecil et al., 2014). high-frequency sea-level fluctuations (e.g., Heckel, 2008; Rygel et al., Incised valley fills (IVFs) and genetically related (down-paleoslope) 2008; Catuneanu et al., 2009; Montañez and Poulsen, 2013). The lowstand wedges also form during icehouse conditions (glacial– stratigraphic record of icehouse conditions in more temperate climates interglacial cycles) in response to sea-level (base level) fall and rise is characterized by the vertical juxtaposition of sediments deposited (e.g., Allen and Posamentier, 1993; Dalrymple, 2006; Tesson et al., under greatly differing water depths. Characteristics may include 2011; Belt et al., 2012). Within foreland basin settings, steepened fluvial gradients caused by the lowering of base-level (formation of ice) are ⁎ Corresponding author. Tel.: +1 719 339 4860. capable of transporting gravel from the wedge-top depozone to E-mail address: [email protected] (W.S. McClung). the marine environment, bypassing a relatively wide alluvial plain

http://dx.doi.org/10.1016/j.palaeo.2016.01.014 0031-0182/© 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 126 W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143 dominated previously by sandy and muddy meandering and low- deposits comprising the IVFs were inferred to be a product of the largest sinuosity streams and rivers (Ver Straeten, 2010). The coarser sediment sea-level falls during the deposition of the Foreknobs Formation, and is deposited at the new shoreline which migrated basinward (seaward), therefore, are of particular interest in order to further understand the creating a lowstand wedge. During subsequent transgression related to nature of glacioeustasy during the transition from Middle Devonian melting of ice, the coarse sediments of the lowstand wedge and back- greenhouse to the icehouse conditions of the Late Paleozoic ice age. filled incised valley are drowned beneath marine strata (e.g., Allen and Because glacial ice is largely drawn from ocean water, there are strong Posamentier, 1993; Dalrymple, 2006). These stratigraphic relationships correlations between ice areal extent, ice volume, and magnitude of are well documented from both the Carboniferous and Quaternary sea-level fluctuation (Cuffey and Paterson, 2010). The conglomeratic stratigraphic record, and are convincingly correlated to continental- strata of the Foreknobs Formation, with well-constrained estimates scale glaciation during both of those time intervals (e.g., Allen and of sea-level fluctuation (McClung et al., 2013), provide an ideal opportu- Posamentier, 1993; Heckel, 2008; Tesson et al., 2011, Belt et al., 2012; nity to tie the stratigraphic record to glacial ice volumes and their areal Cecil et al., 2014). extents. The estimates of glacial ice extent and ice volume can then be Both the late Frasnian and late Famennian (Late Devonian) compared with both the Carboniferous and the step-wise increase of have been identified as times of glaciation (Racheboeuf et al., 1993; Cenozoic glaciation from greenhouse to icehouse conditions. Censier et al., 1995; Crowell, 1999; Caputo et al., 2008; Isaacson et al., Whereas McClung et al. (2013) discussed the overall sequence 2008; McGhee, 2014). Although the Frasnian glaciation has been de- stratigraphy of the Foreknobs Formation, this study expands on the con- emphasized due to lack of direct evidence (Playford et al., 2012), the cepts of our previous work by focusing on a cross-section perpendicular sedimentary record of continental glaciation on Gondwana in the late to depositional strike that illustrates the relationship of a proximal IVF Famennian is unequivocal with glacial deposits of this age reported and genetically related distal lowstand wedges. We focus on three mea- from South America and Africa (Caputo et al., 2008). Contemporaneous, sured sections — proximal (eastern), medial, and distal (western), of the but smaller-scale, glacial deposits are also known from the Appalachian Upper Devonian Foreknobs Formation (Fig. 1) with the purpose of: Basin of North America (Brezinski et al., 2008, 2009, 2010). Correspond- (1) constructing a sequence stratigraphic framework for the proximal ingly, Devonian global sea-level curves constructed by several workers IVF and distal lowstand wedges which can be related to the sequence (Johnson et al., 1985; Haq and Schutter, 2008) suggest low-magnitude stratigraphic framework proposed by McClung et al. (2013) as well as greenhouse-type sea-level fluctuations in the Middle Devonian which to published global sea-level curves; (2) proposing a model that relates were followed by moderate sea-level fluctuations in the Late Devonian, the transport of gravel to the offshore marine environment with falls in particularly in the late Frasnian to late Famennian. The increasing mag- base-level, thus providing a genetic link between conglomeratic storm nitudes of sea-level fluctuations in the Late Devonian are transitional to event beds and an overlying incised valley in the most proximal section; the higher magnitude sea-level fluctuations of the Carboniferous and (3) explaining the derivation and transport of gravel across a relatively are interpreted to be the consequence of increasing glacial episode ice low-gradient alluvial floodplain dominated by meandering and low- volumes (McClung et al., 2013). sinuosity streams and rivers; (4) arguing that the evidence for signifi- According to Isaacson et al. (1999) and Isaacson et al. (2008), the cant sea-level falls during the late Frasnian and into the Famennian effects of Gondwanan glaciation should be recorded in rocks of more reflects the transition from greenhouse to icehouse conditions during temperate regions in the form of black shales, incised valleys, and the Late Devonian; and (5) calculating estimates of areal extents of lowstand wedges deposited during times of sea-level drawdown glacial ice from magnitudes of sea-level fluctuations during the late related to ice formation. The Foreknobs Formation (late Frasnian to Frasnian and early Famennian and comparing these areas with what is early Famennian) comprises the uppermost marine strata of the south- known of published areal extents of late Famennian, Carboniferous, ernmost portion of the Catskill clastic wedge of the central Appalachian and Cenozoic ice. Basin (Ettensohn, 1985; Ver Straeten, 2010) and is an ideal succession in which to test this hypothesis because it was deposited at 30 to 45 2. Stratigraphic nomenclature degrees south latitude under temperate climatic conditions (Blakey, 2008; Scotese, 2008). The Foreknobs Formation locally contains con- The stratigraphy of the upper marine strata of the Catskill clastic glomeratic deposits, particularly within the upper portion of the forma- wedge in the southern-most central Appalachians (West Virginia and tion, which McClung et al. (2013) interpreted as IVFs. The conglomeratic Virginia) was extensively studied by Dennison (1970, 1971, 1985).

Fig. 1. Study area and location of measured sections: Shenandoah Mountain, WV: proximal section; Briery Gap Rd., WV: medial section; Elkins, WV: distal section. Stars indicate locations of the 3 measured sections. See Appendix A for section location details. W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143 127

These strata are named the Greenland Gap Group, including a lower the Hampshire Formation further east. Boswell et al. (1988) includes Scherr Formation and an upper Foreknobs Formation (Dennison, both the Cannon Hill and Rowlesburg Formations within the Hampshire 1970)(Fig. 2). Where described along the Allegheny Front in West Group. For simplicity, we herein consider the Cannon Hill beds to be the Virginia, the Foreknobs Formation is divided into five named members: uppermost part of the Foreknobs Formation and the Rowlesburg beds to Mallow, Briery Gap, Blizzard, Pound, and Red Lick (in ascending order) be the Hampshire Formation. (Dennison, 1970; McGhee and Dennison, 1976). The Foreknobs Stratigraphic nomenclature in the subsurface west of Elkins Formation, comprised predominantly of olive to gray marine shale (Appalachian Plateau region) is complicated for several reasons. First, with local sandstones, red shales, and conglomerates, spans the late the various formations become progressively younger westwards. Frasnian and early Famennian and approximately correlates with the Second, the rocks in this region were first encountered in oil and gas Rhinestreet through Dunkirk interval in the New York state section wells more than a century ago and were named with informal driller's (Rickard, 1975; Filer, 2002; McClung et al., 2013). Along the Allegheny names which are different to what has been used in outcrop studies to Front, the Frasnian–Famennian boundary is within either the Pound the east (Boswell et al., 1988). Third, through well log correlation, Sandstone Member or the lower Red Lick Member based on inverte- names from New York state and Ohio were extended southward brate occurrences, including brachiopods (McGhee, 1977; Clausen and (Filer, 2002). A thorough summary of the nomenclature is beyond the McGhee, 1988; Rossbach, 1992; Brame, 2001; Rossbach, 2001). Due to scope of this paper, but relevant names are included in Fig. 2. lack of high resolution conodont or ammonoid biostratigraphy, more precise placement is not possible. Further to the west in Ohio, the 3. Methods Frasnian–Famennian boundary has been identified immediately below the Dunkirk–Huron Shale on the basis of conodont biostratigraphy This investigation is a detailed re-examination of three of the ten (Over, 2002)(Fig. 2). The Foreknobs Formation is overlain by measured sections of the Foreknobs Formation studied by McClung Famennian-age red, continental strata of the Hampshire Formation of et al. (2013), and an additional measurement of the Elkins section is the Catskill clastic wedge which is in turn overlain by the Mississippian- available within McColloch and Schwietering (1985) (Figs. 1, 3–5; age Price–Pocono Formation (Brezinski et al., 2009, 2010). Appendix A). All three sections are exposed along, or close to, Rt. 33 in In the westernmost outcrop belt, in the vicinity of Elkins, West West Virginia. Field observations included bedding thickness, grain Virginia, the stratigraphy is somewhat different. Here the lower portion size and sorting, color, sedimentary and pedogenic structures and of the Foreknobs Formation is comprised mainly of shale and siltstone vertical trends thereof, nature of contacts/bounding surfaces, and with less sandstone, and individual members are difficult to recognize. biota. A total of 16 lithofacies were identified, described, and grouped Above the main portion of the Foreknobs Formation and below the into four facies associations based on genetic processes and stratal red Hampshire Formation is an interval consisting of prominent gray- relationships (Table 1; Figs. 6, 7). Paleosols were identified and charac- white quartzose sandstones and conglomerates, dark gray carbona- terized by macro- and micro-morphological features such as presence ceous shales, olive gray marine shale, and rare “redbeds.” These strata of root traces, ped structure, slickensided curvilinear fracture planes, were named the Cannon Hill Formation by Boswell et al. (1988) due and differences in color (following Brewer, 1964; Fitzpatrick, 1993; to their different appearance as compared to this interval within other Munsell Color, 2009). The paleosols observed in this study are classified sections (Fig. 2). The overlying continuous “redbeds” are named the using USDA Soil Taxonomy (Soil Survey Staff, 1998) and labeled on a Rowlesburg Formation (Boswell et al., 1988) which are equivalent to scale of 1 to 4 with 4 having the greatest degree of pedogenesis. The 4

Fig. 2. Stratigraphic nomenclature of the diachronous Catskill clastic wedge in West Virginia (stratigraphic units are not drawn to scale with regard to time). Stratigraphy is based on Dennison (1970); McGhee and Dennison (1976); McGhee (1977); Clausen and McGhee (1988), Boswell et al. (1988), and Filer (2002). Incised valley fill symbol within Red Lick Member at Shenandoah Mountain section indicates stratigraphic position of proximal IVF. The same symbols within the upper Foreknobs Formation (=Cannon Hill Formation) at Elkins indicate position of distal IVFs/lowstand wedges. 128 W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143

Fig. 3. Proximal Foreknobs Formation measured section at Shenandoah Mountain showing vertical relationships of lithofacies and facies associations. Enlargement of the upper portion shows details of storm event conglomeratic HCS sandstone beds (lithofacies A3b) (754–771 m) below the conglomeratic proximal IVF (lithofacies D1 of facies association D) (776– 786 m). Contorted and slumped marine offshore strata (774–776 m) immediately below the erosional base of the IVF are interpreted to be the result of cut bank failure. Letters and numbers in legend refer to facies associations and lithofacies, respectively (see Table 1).

soil orders recognized are Entisol (=1), Entisol to Inceptisol (=2), 4. Time, magnitude of sea-level fluctuations, and cyclicity moderately developed Vertisol (=3), and strongly developed Vertisol (=4). For detailed descriptions and interpretations of the paleosol Within this study, we will use the terminology of parasequences/ data, refer to Table 2 in McClung et al. (2013). high frequency sequences (HFSs), 4th-order sequences, and composite W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143 129

Fig. 4. Medial Briery Gap measured section showing vertical relationships of lithofacies and facies associations. Note the enlarged section from 596 to 650 m with numerous paleosols within the 604–613 m interval as well as at 636 m. See Fig. 3 for legend. All paleosols are level 1 to 2 (Entisols and Inseptisols) and are intercalated with fluvial redbeds (facies association C). More mature paleosols may have been eroded and re-worked by fluvial processes. F/F = Frasnian–Famennian boundary by McGhee (1977).

sequences (terminology of Mitchum and Van Wagoner, 1991) to de- et al., 2012; Wendler et al., 2014; Laurin et al., 2015). McClung et al. scribe the 5th-, 4th-, and 3rd-order (orders of Vail et al., 1991)cyclicity (2013) proposed a detailed correlation of the Foreknobs Formation within the Foreknobs Formation (McClung et al., 2013). It is significant across outcrop belts using laterally persistent patterns in this cyclicity. that the inferred three orders of cyclicity are interpreted to have tempo- The correlations are corroborated by a sea-level curve for the Foreknobs ral periodicities which are similar in time to the eccentricity and axial Formation, constructed by McClung et al. (2013),whichcorrelates obliquity of Milankovitch cyclicity (e.g., Jovane et al., 2006; Horton closely with the Haq and Schutter (2008) 3rd-order global sea-level 130 W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143

Fig. 5. Distal Elkins measured section showing vertical relationships of lithofacies and facies associations. Note drillers names: Benson (F/F = Frasnian/Famennian boundary at 7 m), Balltown, Warren, Elizabeth, and Bayard (see Fig. 2). Also note the expanded vertical scale as compared to the Shenandoah Mountain (Fig. 3) and Briery Gap (Fig. 4) sections. See Fig. 3 for additional legend information; F/F = Frasnian–Famennian boundary by Clausen and McGhee (1988).

curve, as well as to the Johnson et al. (1985) eustatic sea-level curve. a fine member comprised of interbedded dark gray shale and sandstone Magnitudes of sea-level fluctuations responsible for of each scale of (lithofacies D4) (e.g., Figs. 5:170–186 m, 8). cyclicity, as well as the depositional origin and derivation of the tempo- ral scale of these cycles, are discussed in detail by McClung et al. (2013). 4.2. 4th-order sequences A summary, however, is necessary here because the authors have expanded the types of cycles discussed and have given each cycle type Fourth-order sequences range from 20 to 100 m thick with durations a reference code for ease of discussion (Fig. 8). of approximately 375 Kyr, and are primarily the consequence of sea- level fluctuations of 25–35 m (McClung et al., 2013). Three primary types of 4th-order sequences are typical of the Foreknobs Formation. 4.1. 5th-order parasequences/high frequency sequences (HFSs) Type 4BA 4th-order sequences consist of a sharp-based conglomeratic shoreface sandstone (facies association B), overlain by multiple, stacked Parasequences/HFSs are typically less than 20 m thick with Type 5AA parasequences, capped by a sharp-based conglomeratic durations of approximately 65 Kyr, and are the consequence of sea- shoreface sandstone (e.g., Figs. 4:340–435 m, 8). Type 4CA 4th-order level fluctuation of 10–15 m (McClung et al., 2013). Three primary sequences consist of multiple, stacked HFSs comprised of facies associa- types of parasequences/HFSs are typical of the Foreknobs Formation. tions A and C. Within the lower portion of these 4th-order sequences, Type 5AA parasequences consist of stacked, upward-coarsening succes- parasequences are dominated by marine offshore strata (facies associa- sions comprised of marine offshore to shoreface lithofacies (facies tion A), whereas within the upper portion of these 4th-order sequences, association A: lithofacies A1, A2a, A3a &/or A3b, and A4) (e.g., Figs. 3: HFSs are dominated by fluvial redbeds (facies association C) (e.g., Figs. 3: 0–75 m, 8). Type 5CA HFSs consist of a basal erosional surface overlain 680–735 m, 8). Parasequence/HFS thicknesses systematically increase by fluvial redbeds (facies association C), that are in turn overlain by and then decrease upward through each Type 4CA 4th-order sequence. marine offshore (facies association A: lithofacies A1, A2a, and A3a) Paleosols are locally developed at bounding surfaces of these sequences. (e.g., Figs. 3:685–730 m, 8). Type 5DD HFSs are comprised of an Type 4DA 4th-order sequences are restricted to the uppermost erosional scour overlain by a lower coarse member of channelized portion of the Foreknobs Formation at Elkins, and are inferred to have conglomeratic sandstone (lithofacies D2) which is, in turn, overlain by resulted from sea-level fluctuations of 35 –45 m. The bases of these W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143 131 sequences are sharp and irregular, and overlie marine offshore strata lower two of which contain numerous conglomeratic HCS sandstones (facies association A: lithofacies A1, A2a, A2b, and A3a). The lower (lithofacies A3b) (Figs. 3:744–771 m, 6A, B, 9). portion of these sequences primarily consists of single or multiple The conglomeratic HCS sandstones (lithofacies A3b, see Table 1) stacked Type 5DD HFSs, whereas the upper portion primarily consists are interpreted to have been deposited under storm conditions in an of multiple stacked Type 5AA parasequences (e.g., Figs. 5: 193–227 m, 8). offshore environment immediately down-paleoslope of a gravelly shoreface and high-gradient fluvial source. The conglomeratic HCS sandstones signal lowering of sea-level (base-level) resulting in gravel 4.3. 3rd-order composite sequences transport from the wedge-top depozone to the marine environment by higher-gradient streams. Rip currents transported and deposited Composite sequences are upwards of 125–300 m thick with gravel seaward and modern offshore transport of gravel has been durations of approximately 1.12 Myr, and are the consequence of sea- observed in water as deep as 18 m during peak storm conditions level fluctuations of either 25–35 m or 35–45 m, depending upon (Gillie, 1983; Hart and Plint, 1989). The conglomeratic HCS sandstone which facies are involved (McClung et al., 2013). Three primary types beds were deposited in an intermediate depositional environment of composite sequences are typical of the Foreknobs Formation. Type with intermediate flow regime, between proximal higher energy 3BABA composite sequences consist of stacked, thinning-upward Type conglomeratic storm beds deposited within a proximal shoreface 4BA 4th-order sequences (e.g., Figs. 3:0–280 m; 8). Type 3CC composite depositional setting and lower energy non-conglomeratic storm beds sequences consist of westward-extending tongues of stacked HFSs deposited within a more distal setting (cf., Leithold and Bourgeois, dominated by fluvial redbeds (facies association C) typically sandwiched 1984; Hart and Plint, 1989; Cheel and Leckie, 1992; Leckie, 1994) between marine offshore strata (facies association A) (e.g., Figs. 3:400– (Fig. 6C). Deformed and convoluted offshore marine strata (lithofacies 580 m, 8). A1, A2a, A3a) of the third and uppermost (truncated) parasequence Type 3DADA composite sequences are restricted to the uppermost overlying the conglomeratic HCS sandstones and immediately beneath portion of the Foreknobs Formation at Elkins and are primarily the base of the fifth composite sequence (IVF) are interpreted to have comprised of stacked Type 4DA 4th-order sequences (e.g., Figs. 5: been produced by possible cut-bank failure of the margin of the overly- 170–338 m, 8). The bases of these composite sequences are sharp and ing incised valley (Figs. 3: 774–776 m, 7A). Note that the highest, or irregular, and overlie marine offshore strata (lithofacies A1, A2a, A2b, fourth 4th-order sequence, present in the Briery Gap section appears and A3a of facies association A). One variant of the Type 3DADA to have been removed by erosion in the Shenandoah Mountain section composite sequence is found at Shenandoah Mountain, where coarse (Figs. 3:776m,9, 10). conglomerate (lithofacies D1) directly overlies marine offshore facies In the distal facies belt, represented by Elkins, the majority of association A at 776 m (e.g., Figs. 3: 776–823 m, 8). The Type 3DADA the fourth composite sequence is comprised of fine-grained offshore composite sequence is inferred to be the consequence of sea-level marine sediments of facies association A (lithofacies A1, A2a, A3a) fluctuations of 35–45 m (McClung et al., 2013). making cyclicity difficult to recognize (Figs. 5:0–164 m). The fourth (highest) 4th-order sequence at Elkins, however, is readily identifiable 5. Depositional history and sequence stratigraphy with black shale (lithofacies A2b) forming its uppermost part (Figs. 5: 166–170 m, 9). Black shale immediately underlying the fifth composite 5.1. First through fourth (3rd-order) composite sequences sequence is interpreted to signal sea-level drawdown with concentra- tion of organic material causing anoxia (cf., Halbertsma, 1994; Isaacson The lower two-thirds of the Foreknobs Formation, up to the base of et al., 1999; Schieber and Riciputi, 2004; Isaacson et al., 2008)(Figs. 5: the Pound Sandstone Member, consists of three composite sequences 154–164, 166–170 m, 9). (Figs. 8, 9, 10). These composite sequences are predominantly of the Type 3BABA comprised of stacked, thinning-upward Type 4BA 5.2. Fifth (3rd-order) composite sequence 4th-order sequences, the bases of which are marked by sharp-based conglomeratic shoreface sandstones (facies association B). Facies The fifth composite sequence includes the lower half of the Cannon association B formed as a result of 25–35 m sea-level falls (McClung Hill Formation at Elkins and the upper portion of the Red Lick Member et al., 2013), resulting in a forced regression (cf., Catuneanu et al., at Briery Gap and Shenandoah Mountain. The base of this composite 2009) and transport of gravel by higher-gradient streams from the sequence marks the beginning of a fundamental change in lithofacies, wedge-top depozone of the foreland basin to the shoreline where the cycle types, and depositional facies belts across the study region. The gravel was incorporated into the shoreface depozone (cf., McClung base of this sequence is represented by an erosional surface at the prox- et al., 2013). Similar successions have been described within the correl- imal Shenandoah Mountain (Figs. 3:776m,9) and distal Elkins sections ative Frasnian–Famennian Lock Haven Formation of north-central (Figs. 5:170m,9), and a paleosol at the intermediate Briery Gap section Pennsylvania by Castle (2000). It is important to note that the thinner (Figs. 4: 603 m, 7B, 9). The erosional surfaces record a higher magnitude shoreface sandstones (lithofacies A4) of upward-coarsening Type 5AA sea-level fall than is recognized in the Foreknobs Formation up to this parasequences were deposited under highstand conditions and do not horizon. At this time, a sea-level fall subaerially exposed most of the contain gravel (Fig. 8; Table 1). ramp, causing the shoreline to shift westward to just west of Elkins. The Pound Sandstone Member, plus the overlying lower and middle McClung et al. (2013) inferred this sea-level fall to be 35–45 m, based parts of the Red Lick Member, comprise the fourth composite sequence on conglomeratic braided stream strata (facies association D) erosionally (Fig. 10). In the middle facies belt, represented by Briery Gap, the fourth overlying marine offshore strata of facies association A at both the composite sequence consists of four Type 4BA 4th-order sequences proximal Shenandoah Mountain and distal Elkins sections. (Figs. 4:435–603 m, 9, 10). Note that only the basal portion of the fourth During the time of the sea-level lowstand at Elkins and just land- or highest 4th-order sequence is present at Briery Gap with the upper ward (east) of the shoreline, river valleys cut into marine black shale portion removed by erosion (Figs. 4: 603 m). In the proximal facies (lithofacies A2b). These river valleys widened into estuaries filled with belt, represented by Shenandoah Mountain, this fourth composite gravelly braided streams and marshes (lithofacies D2–D5). At Elkins, a sequence consists of three 4th-order sequences (Figs. 3:599–776 m, 9, succession of four 4th-order sequences overlie the erosional scour; 10). The lower two 4th-order sequences are of the Type 4CA with the constituting the fifth composite sequence (Figs. 5:170–338 m, 9, 10). sequence boundary at 743 m represented by a paleosol (Figs. 3, 9). The first two 4th-order sequences are Type 4DA (Figs. 5:170–192, The third and uppermost 4th-order sequence is comprised of three 192–227 m, 9). Type 5DD HFSs comprising the lower portions of the upward-coarsening marine offshore parasequences (Type 5AA), the Type 4DA 4th-order sequences consist of channelized conglomeratic 132 ..MCuge l aaoegah,Pleciaooy aaoclg 4 21)125 (2016) 446 Palaeoecology Palaeoclimatology, Palaeogeography, / al. et McClung W.S.

Table 1 Lithofacies and facies associations. *Fluvial sedimentary structure types and architectural element interpretations after Miall (1992).

Lithofacies Lithology Bedding characteristics Fossils Facies association architecture Depositional environment Water depth

Facies association A: marine offshore to shoreface Bioturbated Mudrock; gray-green Typically gradational base; bioturbation, Rare in-situ brachiopods Occurs as coarsening-upward successions Slow rates of accumulation with 15–50 m mudrock (A1) no preserved sedimentary structures ranging in thickness from 4 to 30 m; lower burrowing and browsing organisms and thicker portions dominantly lithofacies below fair-weather wave-base: offshore Shale (A2a) and Shale; gray-green; black Typically gradational base; fissile No biota A1 and A2 with upward-increasing Absence of organisms and/or rapid rate 15–50 m black shale (A2b) shale in Elkins section from interbeds of A3 and/or A3b; in some cases, of accumulation below fair-weather 154 to 170 m successions abruptly capped by lithofacies wave-base: offshore; black shale A4, with a thin basal transitional interval; deposited during times of abundance of mica and plant fragments increase upward flora, concentration of nutrients, and (for example, Fig. 3: Shenandoah Mountain anoxia coupled with falls in sea-level HCS sandstone Sandstone; very fine- to Sharp and irregular base; conglomeratic Rare brachiopod/crinoid 0–74 m). Storm event beds; deposition by 15–50 m (A3a) and medium-grained; lags plane-laminated and/or low-angle bioclastic lags, plant fragments waves/storms above storm wave-base conglomeratic conglomeratic lags in cross-bedded; massive, plane-laminated, and below fairweather wave-base: HCS sandstone Shenandoah Mtn. section or HCS; typically grade upward to shale or conglomeratic HCS sandstones deposited (A3b) from 754 to 771 m and mudrock, rare symmetrical-rippled (10–30 down paleoslope of relatively Elkins section from 210 to cm wavelength) caps; rare flute-casts and high-gradient fluvial source: offshore 225 m; gray-green ball and pillow structures Amalgamated, Sandstone; very fine- to Sharp and irregular base; amalgamated, Rare marine fossils, plant Deposition by waves/storms well above 2–15 m cross-bedded medium-grained; plane-laminated to HCS to trough cross- fragments storm wave-base to unidirectional sandstone (A4) gray-green stratified; uncommon symmetrical-rippled currents above fairweather wave-base: caps proximal offshore to upper shoreface – 143 Facies association B: sharp-based conglomeratic shoreface sandstone Sharp-based Sandstone; fine- to very Sharp-based, locally irregular; amalgamated, Rare marine fossils, common Occurs as sandstone bodies ranging from 2 Deposition by waves/fair weather 2–15 m conglomeratic coarse-grained; massive, plane-laminated/HCS/trough/ plant fragments to 19 m thick; consists of thick interval of processes within lower to upper sandstone (B1) conglomeratic; gray-green tabular cross-stratified, common lithofacies B1 capped by lithofacies B2 (for shoreface near and above fair-weather symmetrical-rippled (10–30 cm wavelength) example, Fig. 4: Briery Gap 435–450 m). wave-base caps; rare flute and gutter casts at base Pebbly bioturbated Sandstone; very fine- to Typically gradational base; thin bedded, Scattered brachiopods, crinoid Transgressive sheet sandstone recording Drowning sandstone (B2) medium-grained; scattered bioturbated, uncommon large wavelength ossicles base-level rise and ravinement surface due to quartz pebble and mudrock symmetrical ripples (~50 cm wavelength); (TRS) transgression clasts; gray-green rare siderite nodules

Facies association C: fluvial redbed Heterolithic Interbedded red shale, Typically laminated with centimeter- to Rare rootlets, burrows; rare fish Occurs as 0.5 to 50 m thick intervals; Overbank fines (OF) flanking fluvial Above redbeds (C1) siltstone, and sandstone decimeter-scale sharp-based fining-upward scales (Hyneria sp.) along dominated by lithofacies C1, with scattered channels sea-level (very fine-grained) successions; rare mudcracks, asymmetrical laminae lenses of lithofacies C2; lithofacies C2 may ripples (Sr); locally capped by pedogenic fine up into lithofacies C1; commonly alteration (Fl, Fm, Fsc) capped by thin lithofacies C3 (for example, Reddish-gray Sandstone; fine- to Sharp-based, planar to irregular; Locally abundant Archaeopteris Fig. 3: Shenandoah Mountain 400–450 m). Fluvial channel deposits, including: Above sandstone (C2) medium-grained; plane-laminated (Sh) or cross-bedded (St, plant fragments laminated sand sheet (LS); sandy sea-level rare mudstone clasts Se, Ss); locally channelized bedform (SB); lateral accretion (LA) and quartz pebbles; reddish-gray Bioturbated Sandstone; very fine- to Sharp-based; thin bedded, bioturbated; Scattered brachiopods, crinoid Transgressive sheet sandstone recording Drowning sandstone (C3) medium-grained; scattered rare siderite nodules ossicles base-level rise and ravinement surface due to mudrock intraclasts; (TRS) transgression gray-green

Facies association D: proximal IVF and distal IVF (distal = estuarine) Coarse conglomerate Conglomerate (pebbles and Sharp and irregular based; numerous Large plant and wood fragments Occurs in two modes: single units of Gravel bars and bedforms (GB): braided Above (D1) cobbles) and conglomeratic channel-shaped, concave-up scoured up to 25 × 5 cm disseminated lithofacies D1 overlain by lithofacies stream, proximal IVF sea-level sandstone (medium- to surfaces (Gt); large-scale tabular (Gp) throughout. D5 (Fig. 3: Shenandoah Mountain: coarse-grained); gray and trough cross-stratification; 776–788 m); or multistoried occurrences

pebble imbrication (Gm); also of lithofacies D2 overlain by lithofacies 125 (2016) 446 Palaeoecology Palaeoclimatology, Palaeogeography, / al. et McClung W.S. local lenticular (up to 6 cm thick) coaly D3, D4 or Facies Association A (for pods example, Fig. 5: Elkins: 338–391 m); Channelized Sandstone (medium- to Sharp and irregular base; numerous Abundant plant fragments up to commonly, lithofacies D2 fines up into Sandy bedform (SB); lateral accretion At or slightly conglomeratic coarse-grained); internal channel-shaped concave-up 10 × 2 cm sometimes associated lithofacies D4 (LA): channel bedform of braided above sandstone (D2) conglomeratic (quartz scoured surfaces (Se), some overlain by with disseminated pyrite and stream, distal IVF sea-level pebbles and mudrock dark gray carbonaceous mudrock; pyrite nodules clasts); gray to gray-white medium-scale trough (St) and tabular (Sp) cross-stratification Skolithos-burrowed Sandstone (medium- to Gradational base; Skolithos Ichnofacies Skolithos burrows Marine drowning of distal IVF channel Drowning sandstone (D3) coarse-grained); preserved; channelized bedform due to conglomeratic; gray to transgression gray-white Interbedded dark Shale/mudrock, dark Mudrock/shale typically bioturbated (Fsc, Abundant plant fragments Overbank to estuarine margin marshes At or slightly gray shale and gray/black, carbonaceous; C), with cut (b1 m relief) and fill features (Archaeopteris) up to 10 × 2 cm (OF in part) above sandstone (D4) interbedded with (Fl); sandstones thin bedded to massive, with rare associated sea-level; sandstone (very fine- to lenticular and discontinuous, disseminated pyrite and pyrite some marine fine-grained) lenses, asymmetrical-ripple cross-laminated (Ss, nodules in shale/mudrock; rare influence gray-white Fl) linguloid brachiopods in sandstone Pebbly bioturbated Sandstone, very fine- to Typically gradational base; thin bedded, Scattered brachiopods, crinoid Transgressive sheet sandstone recording Drowning sandstone (D5) medium-grained; scattered bioturbated, uncommon large wavelength ossicles base-level rise and ravinement surface due to quartz pebbles and wave ripples (~50 cm wavelength), rare (TRS) transgression mudrock intraclasts; siderite nodules gray-green – 143 133 134 W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143

Fig. 6. Conglomeratic HCS sandstone (lithofacies A3b) (refer to Table 1). (A) Marine offshore conglomeratic HCS sandstone (lithofacies A3b of facies association A) deposited down- paleoslope from a gravelly fluvial source. Erosional base overlain by gravel lag, overlain by HCS sandstone and wave-ripples. Card is 5 × 8 cm. Shenandoah Mountain: 758 m (see Fig. 3). (B) Close-up of cross-bedded basal gravel lag of lithofacies A3b. 11 cm pen for scale. (C) Comparison of depositional setting of “proximal coarse-grained” and “distal fine-grained storm beds” of Cheel and Leckie (1992) with the inferred intermediate storm bed of this study (lithofacies A3b of facies association A), which is characterized by a basal plane-laminated to low-angle cross-stratified conglomeratic lag directly overlain by HCS sandstone with rare capping wave ripples (see Table 1). sandstone (lithofacies D2) which commonly fine-upward into interbed- were characterized by very broad mouths and relatively low relief ded dark gray shale and sandstone (lithofacies D4) (Fig. 7C). Although valley walls, thus producing a lowstand wedge which was progradational facies association D is interpreted to be fluvial in origin, the rare over the region of sediment debouchment at the shoreline. This type of presence of linguloid brachiopods, Skolithos-burrowed sandstone estuary morphology is in sharp contrast with that of Late Cenozoic, (lithofacies D3), and overlying marine offshore strata (facies association deeply incised passive-margin valleys caused by drawdown of A) record the interplay of fresh and marine water which is consistent sea-level below the shelf break which were then back-filled during with previous interpretations of incised-valley estuaries near the shore- subsequent sea-level rise (cf., Blum, 1994; Li et al., 2006; Simms et al., line (e.g., Allen and Posamentier, 1993; Dalrymple, 2006; Dalrymple 2006). and Choi, 2007; Koch and Brenner, 2009)(Fig. 5:170–186, 192–203 m). Up-paleoslope, on the subaerially exposed ramp, rivers incised The upper portions of the Type 4DA 4th-order sequences consist downward creating low-relief, but prominent valleys. Such incised of one or more Type 5AA parasequences recording marine flooding valleys were localized, and therefore are rare in outcrop; one such and highstand. The marine portion of the two Type 4DA 4th-order example of an incised valley is at Shenandoah Mountain, the erosional sequences extend progressively eastward. The lowest example is base of which forms the base of the fifth composite sequence (Figs. 3: confined to outcrop at Elkins (Figs. 5:186–192 m, 9) whereas the 776 m, 9). The provenance of gravel within lithofacies D1 and D2 at upper example extends eastward to Briery Gap (Figs. 4: 612–633 m, Shenandoah Mountain and Elkins was most likely from the wedge-top 9) but is not recorded at Shenandoah Mountain. depozone of the foreland basin. Transport of gravel more than 100– Due to the gentle foreland basin ramp gradient, fluvial incision 175 km from the wedge-top depozone to the shoreline is consistent resulting from sea-level falls was not of high relief. Resulting estuaries with the larger magnitude sea-level fluctuations near, and above, the W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143 135

Fig. 7. Outcrop photographs of lithofacies and facies associations (refer to Table 1). (A) Marine offshore strata (lithofacies A1, A2a, and A3a of facies association A) overlain erosionally by coarse conglomerate (lithofacies D1 of facies association D: proximal IVF): inferred to record a 35–45 m S-L fall. White dashed lines indicate contorted and convoluted bedding (interpreted to be the result of cut-bank failure) of facies association A underlying erosional incision. Shenandoah Mtn: 767–783 m (see Fig. 3). (B) Sharp-based conglomeratic shoreface sandstone (lithofacies B1 of facies association B) overlying an erosional bounding surface (dashed line) above marine offshore strata (lithofacies A1, A2a, and A3a of facies association A). Fluvial redbeds (lithofacies C1 and C2 of facies association C), with interbedded paleosols, overlie sharp-based conglomeratic shoreface sandstone. Bedding is dipping steeply to left (west). Briery Gap: 596–610 m (see Fig. 4). (C) Stacked braided-stream fluvial cycles comprised of channelized conglomeratic sandstone (lithofacies D2) overlain by interbedded dark gray shale and sandstone (lithofacies D4) of facies association D (distal IVF: estuarine). Note the concave-up scour overlain by interbedded dark gray shale and sandstone. Note the 1.5 m scale. Elkins: 192–197 m (see Fig. 5). (D) Coarse conglomerate (lithofacies D1: proximal IVF) of facies association D. 15 cm pen for scale. Shenandoah Mtn: 783 m (see Fig. 3).

Frasnian–Famennian boundary in the uppermost Foreknobs Formation parasequences at Elkins (Figs. 5:270–338 m, 9) and Briery Gap (Fig. 10)(McClung et al., 2013). Gravel was transported to the marine (Figs. 4:637 –648 m, 9). Further up-paleoslope, the rise in sea-level environment within incised valleys during times of low sea-level and initially caused back-filling and aggradation of gravelly sediment filling was facilitated by storms and floods (cf., Clifton, 2003; DeCelles, 2012). in the incised valleys, thus forming the IVF at Shenandoah Mountain The surrounding interfluve surface of the IVF is exposed down- (Figs. 3:776–786 m, 7D, 9). paleoslope at Briery Gap (Figs. 4:603m,9). Within the medial Briery Maximum sea-level rise flooded the entire width of the ramp to a Gap section, no conglomeratic braided stream strata are present point east of Shenandoah Mountain resulting in deposition of the Type although five, weakly developed, vertic paleosol profiles are recogniz- AA parasequences (Figs. 3:788–821 m, 9) above the IVF at Shenandoah able within fluvial redbeds (facies association C) (Figs. 4:603–612 m, Mountain. During subsequent 3rd-order highstand, the shoreline 7B, 9). The paleosols exposed at 603 to 612 m are interpreted to be prograded westward, resulting in aggradation of red fluvial cycles of the interfluve surface(s) associated with the base of the fifth composite the Hampshire Formation overlying marine offshore strata at both sequence at Elkins and Shenandoah Mountain (Fig. 10). More mature Shenandoah Mountain and Briery Gap (Figs. 9, 10). In contrast, the paleosols may have been present but were possibly removed by fluvial Elkins area remained marine throughout the entire sea-level highstand processes. of the fifth composite sequence. The third 4th-order sequence at Elkins (Figs. 5: 227–256 m, 9) The marine portion of the sea-level highstand is very thin at consists of multiple Type 5DD HFSs overlain by several HFSs comprised Briery Gap (Figs. 4: 637–648 m, 9), especially considering it is down- of facies association C (fluvial redbeds). Overlying this third 4th- paleoslope from Shenandoah Mountain (Figs. 3:786–821 m, 9). The order sequence is a very mature paleosol (well-developed Vertisol) at thin marine section is consistent with a lack of accommodation and 256 m (Figs. 5, 9) which forms the base of the fourth 4th-order the presence of an inferred forebulge which had developed in this sequence. These red facies are interpreted to have been deposited region during the deposition of the Famennian-age Red Lick Member. higher on the floodplain than the underlying estuarine deposits of facies Filer (2003) argued for a forebulge from a thinning he observed in the association D. entire Red Lick Member based on east-to-west stratigraphic cross- The lower portion of the fourth 4th-order sequence at Elkins sections he constructed across the state of West Virginia. Based on (Figs. 5:256–338 m, 9) is comprised of multiple fluvial redbed (facies his cross-sections, the Red Lick Member is thinnest within a region association C) HFSs which are interpreted to record fluvial aggradation which includes the Briery Gap section and thickens to the west and associated with initial sea-level rise and transgression. Sea-level rise east. Greater subsidence within the foredeep to the east was most likely continued and flooded the shoreline, estuaries, and floodplain areas responsible for the thicker marine section up-paleoslope at Shenandoah of the ramp, resulting in the development of marine Type 5AA Mountain. 136 W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143

Fig. 8. Types of 5th-order parasequences/high frequency sequences (HFSs), 4th-order sequences, and 3rd-order composite sequences within the Upper Devonian Foreknobs Formation of the Appalachian Basin Acadian clastic wedge.

5.3. Sixth (3rd-order) composite sequence study that Filer (2003) argued for the development of a forebulge with- in the region of the Briery Gap section, he also argued for a backbulge The sixth composite sequence includes the upper half of the Cannon basin to the west in the region of Elkins. This argument was based on Hill Formation at Elkins and consists of additional occurrences of facies a thickening of the Famennian section in this region as compared to association D. At Elkins, marine offshore strata (facies association A) of that of the thinner forebulge to the east within the region of the Briery the sea-level highstand portion of the fifth composite sequence are ero- Gap section. sionally overlain by channelized conglomeratic sandstone (lithofacies D2 of facies association D) (Figs. 5: 338 m, 9); forming the base of 5.4. A test of foreland basin ramp gradient the sixth composite sequence. This sequence boundary is presumably within the lower part of the Hampshire Formation redbeds at Briery A comparison with modern ramp analogs permits an independent Gap and Shenandoah Mountain. Within this sixth composite sequence, check of the inferred 3rd-order sea-level fall of 35–45 m which at least two 4th-order sequences are developed. The lower sequence is produced the incised valley at Shenandoah Mountain (Fig. 9: 776 m) interpreted to be of Type 4DA comprised of Type 5DD HFSs overlain and the basal lowstand wedge at Elkins (Fig. 9:170–270 m). This com- by at least one incomplete Type 5CA HFS (Figs. 5: 338–394 m, 9) The parison is based, in part, on an estimate of the ramp gradient. Modern upper 4th-order sequence is comprised of a basal well-developed foreland basin ramps dip at angles from 1′/mile (Arafura Sea off the paleosol (strongly-developed Vertisol) overlain by a series of Type Fly Platform of New Guinea) (Alongi et al., 2011)to4.5′/mile (eastern 5DD HFSs (Figs. 5:395–416 m, 9), which are interpreted to record the Persian Gulf) (Kämpf and Sadrinasab, 2006); an average of 2.75′/mile lowstand and transgressive portions, respectively, of that sequence. will be used for this exercise. Since the rocks immediately underlying During the subsequent 3rd-order highstand, red fluvial strata of the the IVF at Shenandoah Mountain (Fig. 3: ~770–776 m; facies association Hampshire Formation prograded over the top of the braided stream A) were deposited below fair-weather wave base (water depth at least estuarine deposits. 5–15 m) (McClung et al., 2013), a reasonable inference is that the Recognition of the location of a backbulge basin within the region of shoreline was approximately 16–19 km (10–12 miles) further east. Elkins during the Famennian provides a possible explanation for the This distance can be added to the 66 km (41 miles) between Shenandoah location of lowstand wedges described herein. The development of a Mountain and Elkins. Thus, the shoreline would have shifted approxi- backbulge basin may have produced the subsidence and accommoda- mately 84 km (52 miles) westward as a result of the sea-level fall. The tion necessary for the deposition of the lowstand wedges. In the same product of this distance and the 2.75′/mile gradient is 43 m (143′) W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143 137

Fig. 9. Correlated cross-section of the three measured sections. Note the IVF near the top of the proximal Shenandoah Mountain section and the genetically related lowstand wedge in the distal Elkins section. The medial Briery Gap section displays a correlative interfluve environment defined by multiple paleosols. Note dashed correlative tie-lines that correspond to the 4 sequential times within Fig. 12.SeeFigs. 3 and 5 for legend. which is the amount of sea-level fall between the two locations. This association B. Facies associations A and B, represented by the value is within the 35–45 m range estimated based on lithofacies western and central depozones, respectively, comprise the bulk of juxtaposition. the dominantly marine Foreknobs Formation. The eastern depozone is characterized by extensive sandstone-poor areas that are dissected by 6. Comparison of subsurface mapping relatively narrow, east–west trending and westwardly bifurcating sand- stone bodies. This eastern depozone is inferred to correspond to redbed A previous subsurface study of the Upper Devonian Foreknobs and fluvial strata of facies association C, or conglomeratic strata of facies Hampshire Formations provides support for our depositional interpre- association D, depending on which 3rd-order cycle is considered. The tation of lowstand wedges within the upper portion of the Foreknobs east–west trending sandstones, or conglomerates, are considered to Formation (=Cannon Hill Formation) at Elkins. In the subsurface have been deposited within river channel or estuary systems oriented (Appalachian Plateau region) west of Elkins, Boswell and Donaldson perpendicular to the paleoshoreline (Fig. 11A, B). (1988) used over 400 gamma-ray logs from hydrocarbon wells to The Balltown sand at Elkins is interpreted to record the deposition of construct sandstone isolith maps of the “drillers' named” sandstone a sharp-based conglomeratic shoreface sandstone (facies association B). intervals (Figs. 2, 9, 11). The abundance of relatively closely spaced The isolith of this interval corroborates this interpretation with abun- wells, as compared with more widely-spaced outcrops, makes this an dant sandstone parallel to depositional strike which is in alignment ideal region for mapping the three-dimensional geometries of sand- with the location of the Elkins outcrop section (Figs. 2, 11C). stone bodies. The lowstand wedge estuary deposits (facies association D) of The “drillers' named” intervals display three sandstone geometries, the fifth and sixth composite sequences at Elkins are analogous to the or depozones, distributed from west to east across northern West westernmost distal portions of the river channel sandstone bodies Virginia, and are best illustrated by isolith maps of the Fifth and Gordon (westernmost portions of eastern fluvial depozones). The isolith maps sandstones (Figs. 2, 11A, B) (Boswell and Donaldson, 1988). The of the lowstand wedge estuary deposits, represented by the Warren, western-most depozone is characterized by shale, with little to no Elizabeth, and Bayard sands, indicate Elkins is immediately to the east sandstone, and is considered to correspond to the marine offshore of the central depozone in a position where estuarine strata would be shale-dominated facies association A (Fig. 11A, B). The central deposited (Figs.2,11D, E, F). The IVF at Shenandoah Mountain is analo- depozone, approximately 16 to 32 km wide, is characterized as a gous to the proximal part of the river channel sandstone bodies (eastern sandstone belt which trends approximately north–south parallel to depozones) (Fig. 11A, B). This analogy provides further evidence of a depositional strike (Fig. 11A, B) and which is interpreted to correspond close genetic relationship between the IVF at Shenandoah Mountain to the sharp-based conglomeratic shoreface sandstones of facies and the lowermost lowstand wedge at Elkins. In addition, the Briery 138 W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143

Fig. 10. Cross-section showing the relationship of our inferred 3rd-order composite sequences to the eustatic sea-level curves of Johnson et al. (1985) and the Smith and Jacobi (2001) modification. Our interpretation of sea-level fluctuations is very similar to the Smith and Jacobi (2001) curve from geology in Allegany County, NY. Placement of F/F (=Frasnian/ Famennian boundary) on curve is from Sandberg et al. (1988) and Bond and Wignall (2008). Vertical scales of S-L curves have been adjusted slightly to fit the stratigraphy. F/F noted on Elkins and Briery Gap sections based on brachiopod biostratigraphy by Clausen and McGhee (1988) and McGhee (1977), respectively, and correlated to the Shenandoah Mountain section by McClung et al. (2013). Time scale from Kaufmann (2006).SeeFigs. 3 and 5 for legend.

Gap measured section would be located within the eastern depozone volume, number of ice sheets, ice sheet volume, thickness and areal but within a relatively sandstone-poor area between major fluvial extent, and the proportions of Earth's surface represented by land channel sandstone bodies, thus explaining the lack of evidence for IVF versus sea (Cuffey and Paterson, 2010). It is important to note that as or lowstand wedge deposits at Briery Gap. the number of ice sheets increases for a given area of ice, the total volume of ice and associated magnitude of sea-level fall decreases 7. Depositional model in relation to sea-level change (Crowley and Baum, 1991; Isbell et al., 2003; Cuffey and Paterson, 2010)(Appendix B). A series of four depositional models of the Foreknobs Formation Using a set of equations and logic of Cuffey and Paterson (2010) and from the upper portion (sea-level highstand) of the fourth composite Cuffey pers. Comm. (2014, 2015) (Appendix B), it is possible to calculate sequence to the upper portion (sea-level highstand) of the fifth approximate areas of proposed late Frasnian and early Famennian ice composite sequence are displayed in Fig. 12. These models sequentially from inferred changes in sea-level derived from facies juxtaposition. illustrate the sea-level conditions during this time interval and develop- These areas can then be related to areas of late Famennian, Carboniferous, ment of the proximal incised valley fill at Shenandoah Mountain and the and Cenozoic ice reported by previous workers. To produce the average genetically related lowstand wedge at Elkins. For each of the four inferred sea-level falls of 25–35 and 35–45 m (4th- and 3rd-order, models, stratigraphic horizons (in meters) are given for the three respectively) that McClung et al. (2013) inferred from vertical facies sections which can be compared to those on the measured sections juxtaposition, we estimate that ice sheets with areal extents of 5.6– (Figs. 3, 4, 5) and correlation cross-section (Fig. 9). The Time 1 panel 7.4 × 106 km2 and 7.4–9.1 × 106 km2, respectively, existed during the of Fig. 12 also indicates the position of the different depozones of the late Frasnian and early Famennian (Table 2). foreland basin discussed in this study (wedge-top, foredeep, forebulge, Volumes of ice in the Late Paleozoic and Cenozoic continue to be and backbulge basin). debated, in part due to limited preservation of direct evidence as well as the number of ice sheets present at any particular glacial episode, 8. Relation of sea-level fall to areal extent of glaciation particularly on Gondwana during the Late Paleozoic. Nevertheless, several workers have estimated the areal extent of ice sheets during As described herein, and by McClung et al. (2013), the Foreknobs the Late Devonian. McGhee (2014) estimated the area of a proposed Formation provides a record of Frasnian to Famennian sea-level fluctu- late Frasnian Gondwanan ice sheet to be in the range of 8– ations of different magnitudes. In addition, the Foreknobs Formation 11 × 106 km2 (Table 2). Furthermore, Isaacson et al. (2008) concluded provides these constraints at a time when Earth's climatic regime was that the latest Famennian glaciation extended over an area of at least in transition from the Middle Devonian greenhouse to the Late Paleozoic 16 × 106 km2 in Gondwana, including large areas of both South icehouse. America and Africa (Brazil, Bolivia, northern Argentina, Niger, and the Glacial ice is largely drawn from ocean water and there is a strong Central African Republic) (Table 2). The latter estimate does not include relationship between total ice volume and magnitude of sea-level fall the area of glacial deposits within the central and northern Appala- (e.g., Rygel et al., 2008; Cuffey and Paterson, 2010). This relationship, chians described by Brezinski et al. (2008, 2009, 2010),soweregardit however, involves mathematical relationships between ocean water as a conservative estimate. W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143 139

Fig. 11. Upper Devonian sandstone isolith maps of various “driller's intervals” which are equivalent to the Foreknobs and Hampshire Formations further east. Maps prepared by Boswell and Donaldson (1988) and Boswell et al. (1988) using wireline logs from over 400 hydrocarbon wells within the Appalachian Plateau region (no Devonian outcrops). (A) and (B) The Fifth and Gordon sandstones display three depozones interpreted to represent western marine (very little to no sandstone), central paralic or shoreface (north to south sandstones), and eastern fluvial depositional systems (east to west sandstones separated by little to no sandstone). Both the Fifth and Gordon sandstones are within the fluvial Hampshire (=Rowlesburg) Formation at Elkins (see Fig. 2). (C) Balltown, (D) Warren, (E) Elizabeth, and (F) Bayard display western marine and central paralic, or shoreface depositional systems, and are within the upper Foreknobs Formation at Elkins (star labeled “E”). Warren, Elizabeth, and Bayard sandstones at the Elkins section are interpreted to represent the westernmost portions of the eastern fluvial depozones. Isolith contours in meters. “BG” and “SM” stars denote locations of Briery Gap and Shenandoah Mountain sections. Contoured values are sandstone thickness in meters (C.I. = 6 m).

The two areas of ice sheet extent herein calculated from inferred sea- glaciation as reported by Isaacson et al. (2008) (Table 2). These infer- level falls are similar to McGhee's (2014) estimate for the area of late ences are consistent with the proposal of growing Gondwanan ice Frasnian glaciation, but are less than half the area of late Famennian sheets during late Frasnian to late Famennian glacial episodes. The 140 W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143

Fig. 12. Sequential idealized models of deposition during high-to-low sea-level (35–45 m fall) and back to high sea-level (35–45 m rise) during the early Famennian within the Acadian foreland basin. Depozones of the foreland basin (wedge-top, foredeep, forebulge, and backbulge basin) are labeled on the Time 1 model (terminology of DeCelles, 2012). Approximate stratigraphic horizons corresponding to the 4 time intervals are shown in Fig. 9 (also refer to Figs. 3, 4, and 5). Locations of the three measured sections are designated as follows: E = Elkins, BG = Briery Gap, SM = Shenandoah Mountain. Time 1 represents sea-level highstand immediately prior to the base-level (sea-level) fall which caused erosion and formation of the incised valley at Shenandoah Mountain and Elkins. Time 2 represents falling base-level (sea-level) with deposition of black shale (lithofacies A2b) at Elkins and conglomeratic HCS beds (lithofacies A3b) seaward of fluvial incision at Shenandoah Mountain. Time 3 represents maximum sea-level lowstand with deposition of a lowstand wedge (lithofacies D2– D4) at the distal Elkins section and erosion of an incised valley at the proximal Shenandoah Mountain section. Time 4 represents subsequent sea-level highstand with marine offshore strata (facies association A) overlying the lowstand wedge at the distal Elkins section and the IVF (lithofacies D1 and D5) at the proximal Shenandoah Mountain section. greater areal extent of the late Famennian ice sheet reported by Isaacson from the Late Devonian into the Carboniferous are consistent with the et al. (2008) would have produced larger magnitude sea-level fluctua- global eustatic sea-level curve constructed by Johnson et al. (1985) tions (Table 2). This is corroborated by latest Famennian incised valleys and the 3rd-order sea-level curve by Haq and Schutter (2008) which in- that are 75–90 m deep which are present in both North America and dicate the magnitude of sea-level fluctuations increased in a step-wise Europe (e.g., Van Steenwinkle, 1993; Pashin and Ettensohn, 1995), manner from the Frasnian into the Famennian, and continued into the and have been inferred to be the result of glacioeustasy. The calculated Carboniferous related to an increase in ice volumes (McClung et al., areal extents of ice in the late Frasnian to early Famennian are also 2013)(Fig. 10). The time period of this transition was approximately considerably less than the maximum areal extent of ice sheets during 65 Myr (early Late Devonian to Middle Pennsylvanian) (Walker et al., the Carboniferous (up to 40 × 106 km2) which produced sea-level fluc- 2013). tuations N100 m (e.g., Otto-Bliesner, 1996; Heckel, 2008)(Table 2). The increasing trends of both ice sheet extent and magnitude of These inferences regarding the increasing areal extent of ice sheets sea-level fluctuations from Middle Devonian into the Carboniferous

Table 2 Areal extents of ice calculated from inferred sea-level equivalents and vice-versa: see Appendix B. Note the general increase in areal extent of ice (and magnitude of sea-level fluctuations) during the Cenozoic leading to glacial maxima during the Pleistocene. Note similar inferred trend during the Late Devonian leading into the Late Paleozoic ice age.

Late Paleozoic Cenozoic

Areal extent of ice Sea-level Areal extent of ice Sea-level equivalent equivalent

Carboniferous–Permian 13.4–40 × 106 km2 Crowley and 48–183 m Pleistocene 23.5–45 × 106 km2 Litt et al. 114–254 m Baum (1991); González-Bonorino (if 6 ice sheets) (2008); Anderson et al. (2013) (if 6 ice sheets) and Eyles (1995); Otto-Bliesner (1996); Isbell et al. (2003) Latest Famennian 16 × 106 km2 Isaacson et al. 70 m Miocene 12–15 × 106 km2 Huybrechts 59–77 m (2008) (if 3 ice sheets) et al. (1991); Alley et al. (2005) (if 3 ice sheets) Early Famennian 3rd-order, inferred from 7.4–9.1 × 106 km2 calculated 35–45 m McClung et al. (2013) using 35–45 m (if 1 ice sheet) Late Frasnian 8–11 × 106 km2 McGhee (2014) 38–57 m Oligocene 7–13 × 106 km2 Zachos et al. 33–71 m (if 1 ice sheet) (2001); Wilson et al. (2013); (if 2 ice sheets) 4th-order, inferred from McClung et al. (2013) 5.6–7.4 × 106 km2 calculated 25–35 m Pollard et al. (2013) using 25–35 m (if 1 ice sheet) W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143 141 parallels the trend observed during the Cenozoic (Table 2), and corrob- ice sheets. Thanks also to colleagues Shane Prochnow and Henry orates our interpretation that the Late Devonian was a time of transition Posamentier for many insightful discussions and to Andrew Bush, from greenhouse to icehouse climatic conditions. The major difference Katharine Lee Avary, Ron McDowell, Brian Willis, Thomas Rossbach, is the span of time over which the greenhouse to icehouse transition and the late John Dennison for their help during various stages in the occurred. The Cenozoic greenhouse to icehouse transition of approxi- preparation of the manuscript. The authors thank Peter Isaacson, an mately 35 Myr is approximately half the 65 Myr interval between the anonymous reviewer, and T. Algeo for their critical reviews of the early Late Devonian to Middle Pennsylvanian. It is well known that paper. Finally, C.A. Cuffey would like to thank Chevron USA Inc. for giv- greenhouse conditions existed during the Cretaceous, Paleocene, and ing him permission to publish this paper. into the Eocene. The Antarctic ice sheet first developed at approximately 34 Myr (latest Eocene or earliest Oligocene), followed by the initial Appendix A. Locations of Foreknobs Formation measured sections inception of the Greenland ice sheet at 6–7 Myr (latest Miocene), followed finally by the Laurentide and Fennoscandian ice sheets at 1. Shenandoah Mountain (proximal section), WV, Pendleton County, 2.5 Myr (Pleistocene) (e.g., Lewis et al., 2008; Cuffey and Paterson, located along Rt 33 on the west flank of Shenandoah Mountain 2010; McClung et al., 2013; McGhee, 2014). A similar transition of approximately 4.0 km (2.5 miles) west of the Virginia–West Virginia increasing areal extents of ice sheets most likely occurred during the state line and 7.4 km (4.6 miles) east of Brandywine, West Virginia. Late Devonian leading into the Late Paleozoic ice age. Lat 38.599264, Long −79.17984. 2. Briery Gap (medial section), WV, Pendleton County, located 9. Conclusions approximately 33 km (20.5 mi) west of the proximal section and exposed along the Allegheny Front outcrop belt on Briery Gap Road Vertical juxtaposition of lithofacies, bounding surfaces, and stacking just 1.6 km (1.0 mile) west of the intersection of Rt 33 between patterns within the Frasnian–Famennian-age Foreknobs Formation Circleville and Riverton, West Virginia. Lat 38.729012, Long permit recognition of parasequences/HFSs (5th-order), 4th-order −79.465442. sequences, and composite sequences (3rd-order), as well as a record 3. Elkins (distal section), WV, Randolph County, located approxi- of moderate-magnitude sea-level fluctuations during the late Frasnian mately 27 km (16.8 mi) west of the medial section along the 4-lane which transitioned to increasing magnitudes of sea-level fluctuation Route 33 just east of Elkins, West Virginia. The base of the section is into the Famennian. This step-wise increase in magnitude of sea-level 250 m west of the Kelly Mountain Road turnoff. Lat 38.914344, fluctuation is consistent with published global sea-level curves. Long −79.782457. The Famennian-age conglomeratic IVF within the upper portion of the Foreknobs Formation in the proximal Shenandoah Mountain section Appendix B. Relationships of sea-level change, ice volume, and and the genetically related conglomeratic lowstand wedges in the distal glacial ice sheet area Elkins section were deposited following moderate magnitude sea-level falls. The sea-level falls lowered base-level sufficiently for the shoreline Given a change in sea-level as a starting point: to migrate approximately 84 km basinward, causing fluvial incision and allowing for gravel to be transported from the wedge-top depozone Δs=sea level rise RE =radius of Earth=6370km ƒo =fraction across a low-gradient sandy and muddy alluvial plain of the foredeep of Earth's surface covered by ocean to a marine environment in the backbulge basin of the foreland basin. Area of ocean surface ¼ A ¼ ƒ 4πR 2 o o E Gravel and sand were deposited by braided streams within perennially ≈ ðΔ Þð Þþð1 Δ ÞðΔ Þ V w s Ao 2 s Ao second component of equation wet incised valleys near the shoreline during sea-level lowstands and accounts for change in surface area of ocean as shoreline moves; factor shaly estuarine strata were deposited during times of transgression. 1 of 2S applies (strictly) for linear slopes The IVF at the proximal Shenandoah Mountain section erosionally over- lies a shaly marine offshore section containing HCS storm event beds Given the relationship between volume of water and volume of fl with gravel lags. The source of the gravel was from the same uvial ice, we can convert water volume to ice volume: source (incised valley) which eroded into the marine beds. The absence of more proximal gravelly shoreface or braid-delta facies indicate a Vi ¼ total ice volume substantial base-level fall (35–45 m) which caused basinward erosional incision and removal of these beds. Vw ¼ equivalent water volume ≈ Vi½¼915=1000 0:915Vi ¼ cdVi From what is known of the physics of ice-sheets and reported areal extents of late Famennian to Carboniferous ice, our inferred sea-level For an ice cap, there is an approximate relationship between ice changes and associated areal extents of late Frasnian to early Famennian 3 2 volume V1 in km and ice area A1 in km ; thus we can estimate ice ice compare favorably to the trend of ice build-up during the Cenozoic. area from ice volume: The areas of ice needed to produce the inferred 25–35 and 35–45 m sea- level falls (related to 4th- and 3rd-order cyclicity, respectively) during 1:23 logV1 ¼ 1:23½¼ logA1−1 ½logðÞ A1=10 the latest Frasnian and early Famennian are approximately half the reported areas of late Famennian ice. Areas of Carboniferous and γ : V ¼ cA with c ¼ 1=101 23 ¼ 0:0589 γ ¼ 1:23 Cenozoic (specifically the Pleistocene) ice are double that of reported 1 1 late Famennian ice. These data substantiate a step-wise increase in 2 magnitude of sea-level fluctuations from the Frasnian into Famennian In terms of Diameter D of a circular ice cap, A1 ¼ðπ=4ÞðD1 Þ γ−1 0:23 which we attribute to a step-wise increase in total volume of ice during And average thickness is V=A ¼ H ≈ cA1 ¼ cA1 glacial episodes. For multiple ice caps, total ice volume = X γ γ γ Acknowledgments Vi ¼ cA1 þ cA2 þ …: ¼ c Ai i The data base for this study is W. McClung's 1983 VPI&SU MS thesis γ but the interpretations are revised and updated. Many thanks to Richard If ice caps all of same size Vi =cNA where N = number of ice caps γ γ Bambach for directing the project. The authors express their thanks to Combining Vi=cNA =(1/cd)(Vw)→VW=cdcNA =Δs[Ao+½ ΔAo] γ γ Kurt Cuffey at U.C. Berkeley for critical information on the physics of →Δs=(cdcNA )/(Ao+½ΔAo) probably ΔAo≪Ao ,soΔs≈cdcNA /Ao 142 W.S. McClung et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 446 (2016) 125–143

And substituting further: Caputo, M.V., Melo, J.H.G., Streel, M., Isbell, J.L., 2008. Late Devonian and Early Carbonifer- ous glacial records of South America. In: Fielding, C.R., Frank, T.D., Isbell, J.L. (Eds.), Re- solving the Late Paleozoic Ice Age in Time and Space. Geol. Soc. America Special Paper γ γ γ Δ ≈ =ƒ π 2 ¼ ðÞπ= 2 =ƒ π 2 – s cdcNA o4 RE cdcN 4 D o4 RE 441, pp. 161 173. Castle, J.W., 2000. Recognition of facies, bounding surfaces, and stratigraphic patterns in γþ γ ¼ πγ−1=4 1 c cN=ƒ R 2 D2 foreland-ramp successions: an example from the Upper Devonian, Appalachian d o E – Basin. U.S.A. J. Sediment. Res. 70, 896 912. 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