Walchian conifers from the Mid-Late Pennsylvanian Conemaugh Group in the Appalachian Basin: Stratigraphic and depositional context, and paleoclimatic significance

International Journal of Coal Geology 171 (2017) 153–168

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Walchian conifers from the Mid-Late Pennsylvanian Conemaugh Group in the Appalachian Basin: Stratigraphic and depositional context, and paleoclimatic significance Ronald L. Martino Department of Geology, Marshall University, Huntington, WV 25755, United States

a r t i c l e

i n f o

Article history: Received 6 August 2016 Received in revised form 28 December 2016 Accepted 11 January 2017 Available online 12 January 2017 Keywords: Walchia Paleoclimate Cyclothems Sequence stratigraphy

a b s t r a c t Walchian conifers are indicators of seasonally dry habitats of the Euramerican subtropics and tropics and are of considerable value in tracking both short term and long term Pennsylvanian-Permian paleoclimatic changes in central Pangea. Walchian conifer macrofossils first appeared in North America during the Middle Pennsylvanian, but are rare in central Pangean coal basins until the Permian. An abrupt climate change occurred near the Desmoinesian-Missourian boundary that was characterized by global warming, stronger seasonality, and shorter wet phases. This change coincided with the regional extinction of most tree lycopsids and the appearance of widespread, high chroma, calcic vertisols and aridisols. Only four occurrences of Walchia have been reported from the Pennsylvanian of the Appalachian Basin: 1) 7-11 Mine of eastern Ohio, 2) Rennersville in southwest Pennsylvania, and 3) Charleston and 4) Cedar Run, both in southern West Virginia. This paper uses recently acquired outcrop data to more fully document and reevaluate the depositional and stratigraphic context of the West Virginia assemblages and their paleoclimatic and paleogeographic implications. The Cedar Run Walchia assemblage occurs in olive mudshale of an abandoned fluvial channel-fill 15.8–16.9 m above the base of the Ames Limestone, indicating an early Virgilian age. It consists of compressions and impressions of branches and branchlets of Walchia, Lepidophylloides, Cordaites, and rare neuropteroid pinnules. The channel-fill at this location is a component of the Grafton Sandstone incised valley-fill previously described from the study area. Correlation of paleosol-bounded, marine-cored cyclothems in the study area with their nonmarine cyclothem equivalents at Charleston, West Virginia indicates the Walchia previously reported at the Mahoning coal horizon, occurs between the Brush Creek and Bakerstown coals, and is therefore Missourian, not late Desmoinesian, and similar to the revised age for the 7-11 Mine Walchia reported from eastern Ohio. Late Pennsylvanian, upland (or dryland) conifer communities were comprised of Walchia, Cordaites, and Sigillaria which produced a forest with seed ferns as an understory. The Cedar Run assemblage was probably transported into the valley from adjacent, well-drained coastal plain uplands formed during valley incision, and deposited within the early transgressive systems tract. It is also possible that Walchia expanded into the valleys when drainage became ephemeral during more arid climatic phases. The revised correlations of Appalachian Basin Walchia horizons indicate their appearance closely followed, rather than predated the abrupt climate change and extinctions at the Desmoinesian-Missourian boundary. © 2017 Elsevier B.V. All rights reserved.

1. Introduction The late Middle and Late Pennsylvanian strata of the Appalachian Basin have been the focus of much attention because they record both short-term climate cycles related to glacioeustasy and longer term trends related to 1) the northward drift of Pangea across the equator, 2) orographic effects of the rising Appalachian Mountains, and 3) possibly atmospheric changes in carbon dioxide (Donaldson et al., 1985; Cecil, 1990; Frakes et al., 1992; Heckel, 1994; Otto-Bleisner, 2003;

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DiMichele, 2014). Plant fossils provide a snapshot of paleoclimatic conditions. A full understanding of their spatial and temporal distributions and their sedimentologic context is essential to the accuracy of interpretations regarding paleoclimate trends and cycles and evolutionary patterns. The importance of their sequence stratigraphic context in accurate paleoenvironmental reconstructions has also become apparent (e.g. Demko et al., 1998; Falcon-Lang et al., 2009; Gastaldo and Demko, 2010). The paleoenvironmental and paleoclimatic significance of Walchia has received much attention over the past three decades and the various interpretations have been recently been reviewed in detail by DiMichele (2014). Walchia was a primitive conifer represented by woody trees with small, helically arranged, needle-like leaves 1–5 mm

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in length (Taylor, 1981). The xeromorphic traits of Walchia, like most modern conifers (thick cuticle, needle like leaves with low ratio of surface area to volume), enabled it to retain moisture and inhabit welldrained soils, and drier climates (Lyons and Darrah, 1989a). Walchia is a key taxon and is widespread in Permian strata. In contrast, relatively few occurrences are know from the Mid-Late Pennsylvanian of North America. The term ‘Methuselah taxa’ was recently suggested for sporadic, anomalous occurrences of genera, like Walchia, many millions of years older than their more temporally continuous, established range (Looy et al., 2014). They are named for Methuselah, the oldest man (929 years) in the book of Genesis in the Hebrew Bible. Methuselah floras are typically found in seasonally dry facies in between vertically adjacent wetland floras. It has been postulated that Methuselah floras may have first appeared in upland areas with low preservation potential, and periodically migrated into basinal lowlands during seasonally drier portions of glacioeustatic climate cycles (e.g. Dolby et al., 2011; DiMichele, 2014; Looy et al., 2014). The earliest unequivocal walchian conifer macrofossils occur in Middle Pennsylvanian (middle Desmoinesian) strata of the North American Illinois Basin (Plotnick et al., 2009; Falcon-Lang et al., 2009). Walchian pollen (Potonieisporites) has been reported from the Late Mississippian (early Namurian) of Britain and Nova Scotia (Bharwadjwa, 1964; Neves and Belt, 1971; Mapes and Gastaldo, 1986). Walchia has been reported from the Pennsylvanian of Colorado, Illinois, Oklahoma, and Kansas (Elias, 1942; Rothwell, 1982; Winston, 1983; Lyons and Darrah, 1989a, 1989b; Falcon-Lang et al., 2009). Only four occurrences have been reported from the Late Pennsylvanian of the Appalachian Basin: one in Ohio (7-11 Mine, McComas, 1988), one in Rennersville, Pennsylvania (Darrah, 1969, 1975) and two in West Virginia (Charleston: Lyons and Darrah, 1989a, 1989b; Cedar Run, Martino and Blake, 2001; Fig. 1). The stratigraphic context of the Ohio occurrence has recently been revised (Easterday, 2004; Falcon-Lang et al., 2011; Belt et al., 2011), but the West Virginia occurrences have yet to be clearly documented. The objectives of this paper are to fully document the paleobotanical and stratigraphic context of the Cedar Run Walchia assemblage (Martino and Blake, 2001) and re-evaluate the stratigraphic correlations for the Charleston and 7-11 Mine occurrences and their paleoclimatic and paleogeographic implications.

2. Geologic setting Strata in the study area crop out in the Central Appalachian Basin at the southwest end of the Dunkard Basin Synclinorium (Spencer, 1964; Merrill, 1988). Downwarp of the Dunkard Basin may have occurred during, as well as after, the deposition of the Conemaugh Group (Merrill, 1988). The Appalachian foreland basin extends from Quebec to Alabama, covering an area of about 536,000 km2 (Ettensohn, 2008). During the Middle-Late Pennsylvanian, thrust-loading in the Appalachian Orogen caused basin subsidence which helped provide sediment accommodation space (Quinlan and Beaumont, 1984; Greb et al., 2008). The rate of subsidence was greatest in eastern West Virginia and decreased northwestward toward the cratonic platform in Ohio and Kentucky. Transgressive-regressive cycles each lasting several million years, referred to as tectophases, resulted from tectonic loading and relaxation. Higher frequency, glacioeustatic transgressive–regressive cycles are superimposed on the tectophases (Busch and Rollins, 1984; Busch and West, 1987; Heckel, 1994, 1995; Ettensohn, 2008; Greb et al., 2008). During the Late Pennsylvanian the Central Appalachian Basin was positioned within a few degrees of the equator (Blakey, 2007; Rosenau et al., 2013). During the Middle and Late Pennsylvanian, rivers flowed west and north across West Virginia, draining the Allegheny Orogen. Channel belts in the tropical coastal plain were flanked by flood basin lakes and swamps during the wetter parts of glacial-interglacial cycles (Arkle, 1974; Donaldson, 1979; Martino, 2004, 2015). 3. Stratigraphic and depositional framework The late Middle to Late Pennsylvanian Conemaugh Group extends from the top of the Upper Freeport coal to the base of the Pittsburgh coal (Fig. 2). It was historically referred to as ‘the lower barren measures’ because there are relatively few minable coals in this stratigraphic interval (Wanless, 1939). The Conemaugh Group does contain several high volatile bituminous coals with total sulfur of 1–3%. These are usually minable only in the northern Appalachian Basin (Repine et al., 1993). Where the Ames Limestone is present, the Conemaugh Group is divided into the Glenshaw and Casselman Formations; where absent, as is the case in the Charleston area of West Virginia, it is the

Fig. 1. Location map showing the four known Pennsylvanian-age Walchia occurrences in the Appalachian Basin of the eastern U.S.

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Fig. 2. Stratigraphic framework for the Conemaugh Group and composite stratigraphic section for the Cedar Run study area showing level of Walchia interval at Cedar Run relative to the Ames Limestone based on sections at locations 1–5 (Figs. 3 and 7). Time scale is based on Davydov et al. (2010) and Richards (2013). The position of the Westphalian-Stephanian stage boundary is not accepted by some workers.

Conemaugh Formation. The Glenshaw Formation in Wayne County, West Virginia and vicinity is 80 m thick. It consists mainly of fluvial, deltaic, and estuarine sandstones and flood basin mudrocks and occasional thin coals and marine limestone and shale (Martino et al., 1996; Martino, 2004, 2015). The Casselman is 90 m thick and extends from the Ames Limestone to the base of the Pittsburgh coal. It is lithologically similar to the Glenshaw (Donaldson, 1979), except that it is predominantly nonmarine. The Conemaugh Group is late Desmoinesian to early Virgilian in age and recent workers have correlated it with the Westphalian D to Stephanian B of Western Europe (Eble et al., 2009; Falcon-Lang et al., 2011). Wagner and Lyons (1997) suggested the presence of a major unconformity near the base of the Conemaugh based on the absence of plant megafossils found in Western Europe. They concluded that essentially all of the Conemaugh was late Stephanian C or Autunian in age.

The absence of Western European taxa in the Appalachian Basin and the apparent stratigraphic gap was subsequently interpreted to be the result of different paleobiogeographic and climatic factors between Western Europe and North America rather than a major unconformity (Blake et al., 2002; Falcon-Lang et al., 2011). The uplift and deformation associated with the Allegheny-Hercynian Orogeny during the Late Pennsylvanian fragmented the tropical floral belt. Biotic migration was obstructed between Europe and North America causing increasingly endemic floras which hinder interregional correlations. Biostratigraphy is further complicated by the alternation of wetland and dryland floras during cyclothems; during dryland phases extrabasinal forms can temporarily appear in lowland regions in place of the wetland taxa (e.g. Falcon-Lang et al., 2009; Falcon-Lang and DiMichele, 2010; Looy et al., 2014). Due to the current uncertainty regarding the relationship of the Desmoinesian-Missourian boundary in North America to the

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Westphalian-Stephanian boundary in Europe (Wagner and Lyons, 1997; Falcon-Lang et al., 2011), the regionally recognized stage names for North America will be used going forward. The Glenshaw Formation in the study area contains nine, paleosolbounded allocycles averaging 8–9 m in thickness (Martino, 2004, 2015). Thick, mature, calcic vertisols and calcisols are interpreted to have formed as interfluvial sequence boundaries (IFSBs) during falling stage systems tract (FSST), lowstand systems tract (LST) and early transgressive systems tract (TST) during sediment bypassing and negative accommodation. Rising sea level/base level and wetter climatic conditions caused rising water table and gley overprinting. The paleosols are overlain by thin coals, and fresh, brackish and marine shales and limestones. Lakes and shallow seas filled with coarsening-upward sequences during the HST. Incised valley-fills (IVFs) 20–35 m thick were cut during FSST and early LST and filled with multistory fluvio-estuarine channel facies during late LST and early TST. The Grafton Sandstone along the Big Sandy River is a multistory, incised valley-fill up to 20 m thick (Martino, 2004). Individual channelfills commonly display epsilon cross-bedding with sets 7–9 m thick which indicate lateral accretion normal to the paleoflow direction. Cross-stratification from several Grafton outcrops in the study area indicates average flow directions from 249 to 335 degrees. Paleohydraulic analysis of a Grafton paleochannel 9.4 km (5.85 miles) SSW of location 5 indicates a low gradient, suspended or mixed load meandering river (sinuosity = 1.9) with a width of 49 m and depth of 5.5 m in crossovers between meander bends (Martino et al., 1985). Similar results were reported by Morton and Donaldson (1978) for a Grafton Sandstone paleochannel in northern West Virginia. 4. Paleoclimate and glacioeustasy During the Early to Middle Pennsylvanian, the tropical climate in the central Appalachian Basin varied from perhumid (everwet) to wet subhumid (long wet season/short dry season; precipitation regime terminology from Cecil, 2003). During the Late Pennsylvanian there was significantly less rainfall, and the climate fluctuated between humid subtropical to semiarid (Donaldson et al., 1985; Cecil, 1990). A sharp change occurred near the Desmoinesian-Missourian boundary and was characterized by global warming, stronger seasonality, and shorter wet phases. It coincided with the regional extinction of most arborescent lycopods and the appearance of widespread, high chroma, calcic vertisols and aridisols. Aridity was greatest during deposition of the Conemaugh Group (Donaldson et al., 1985; Cecil, 1990; Pfefferkorn et al., 2008). This paleoclimate change had a major impact on coal resources. Coals of the Conemaugh Group likely formed under moist subhumid (wet-dry seasonal) climates and tend to be thinner, laterally discontinuous, and higher in sulfur and ash than Early to Middle Pennsylvanian coals in the Appalachian Basin which formed under wetter (humid-perhumid) climates (Cecil et al., 1985; Milici, 2005). Subregional differences in paleotopography and subsidence rates likely influenced where and how thick peat could accumulate (Lyons and Darrah, 1989a, 1989b). Only the greater highstands (major cyclothems) invaded the Appalachian Basin due to its high shelf position relative to midcontinent basins. The major cyclothems have an average duration of 400,000 years and resulted from glacioeustatic sea level cycles and climate variations associated with the eccentricity of the earth's orbit (e.g. Busch and Rollins, 1984; Busch and West, 1987; Greb et al., 2008; Heckel, 1995, 2008). The amount of rainfall in tropical Pangea varied during cyclothems and impacted the composition of tropical vegetation. Viewpoints vary as to what stage of the sea level cycle wetter and drier phases occurred (e.g. Falcon-Lang, 2004; Dolby et al., 2011; Horton et al., 2012; DiMichele, 2014). In the Conemaugh, polygenetic paleosols indicate that drier conditions were associated with falling sea level and lowstands, whereas wetter conditions were associated with transgressions and highstands (Martino, 2004, 2015). Pteridosperms, lycopods

and tree ferns were prevalent during humid to subhumid climates associated with interglacial phases (late TST and HST). Gymnosperms including conifers, cordaitaleans and pteridosperms were widely developed during drier and more seasonal climate associated with glacial maxima and associated lowstands of sea level (Falcon-Lang et al., 2009; Falcon-Lang and DiMichele, 2010). Thus, in general, wetland floras developed at or near glacial highstands while ‘dryland’ floras were prevalent and expanded into lowlands at or near glacial maxima (Falcon-Lang et al., 2011). The relatively uniform oxygen-18 and carbon-13 isotopic composition in growth layers of spiriferid brachiopods from the Ames Limestone indicates a consistently moist subtropical climate with minimal seasonality existed during the Ames sea level highstand (Roark et al., 2015).

5. Results and discussion 5.1. Cedar Run Walchia assemblage The Cedar Run Walchia assemblage was collected from a temporary excavation along a gas pipeline trench near the base of the Casselman Formation. The exposure existed in May–June 1999 and was located approximately 15 m north of Cedar Run Road and 0.6 km (0.37 miles) northeast of its intersection with West Virginia Rt. 52 (location 1, Fig. 3). A total of 15.33 kg including 77 plant-bearing samples was recovered before the site was reclaimed in July. The Cedar Run flora occurs in pale olive (Munsell Hue 5Y, Value 6/3), clayshale and mudshale. The facies is thin bedded and laminated. The flora consists of compressions and impressions of branches and branchlets of Walchia, grass-like leaves of Lepidophylloides, palm-like leaves of Cordaites and isolated neuropteroid pinnules. Lepidophylloides occurs as isolated pinnules and as clusters of subparallel pinnules representing branchlets of the tree Sigillaria (Figs. 4–7). Fieldwork in 2016 revealed Lepidophylloides and rare root traces in olive shale 1.1–1.5 m below the level of the Walchia horizon at location 1. The stratigraphic position of the Cedar Run Walchia was originally projected as 8.5 m above the Ames Limestone (Martino and Blake, 2001) based on its elevation compared to structural contours of Merrill (1988) on the Ames Limestone; this position would put it in the paleosol-capping, lacustrine roof shale that directly overlies the Ames marine zone at nearby locations (Martino and Blake, 2001; Martino, 2004). Additional fieldwork at the Cedar Run location and four nearby exposures in 2016 has helped clarify the stratigraphic and depositional context (Figs. 3, 8). The Ames marine zone of the Glenshaw Formation contains a distinctive, ledge-forming, calcareous crinoidal sandstone facies in Wayne County, West Virginia and adjacent Boyd County, Kentucky (Merrill, 1988, 1993; Martino et al., 1996; Martino, 2004). At the Cedar Run locality, this marker bed is 1.1 m thick and its top crops out 5.5 m below Cedar Run Road along a steep embankment. The base of the Walchia interval occurs 5.3 m above the road. This places the stratigraphic interval between the top of the crinoidal sandstone and the Walchia floral zone 10.8 m at locality 1. The interval between the base of the Ames Limestone and the top of the crinoidal sandstone is 5.0–6.1 m at locations 3 and 5. Using this interval, the Walchia horizon at location 1 occurs 15.8 to 16.9 m above the base of the Ames Limestone (Figs. 2, 8), slightly higher stratigraphically than the 8.5 m initially concluded by Martino and Blake (2001). The Walchia horizon at locality 1 is recognized as occurring within a paleochannel fill of the Grafton Sandstone IVF rather than in strata that are truncated by the IVF because 1) the strata that are 15.8–16.9 m above the Ames Limestone at all nearby localities (Martino, 2004) are above the base of the IVF, and 2) the large scale, inclined bedding that occurs 3–5 m below the Walchia horizon (recently identified from a construction site photograph) is similar to the epsilon cross-strata seen in paleochannels at the same stratigraphic level at locations 2 and 4 which also contain plant fossils (Figs. 8, 9).

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Fig. 3. Topographic map showing outcrop locations 1–5. Contour interval = 20 ft. The Walchia assemblage from Wayne County was collected from bedrock that was temporarily exposed in a gas pipeline trench at Locality 1 (red star) in May and June of 1999. Rob Thompson, a civil engineer for Columbia Gas Transmission at the time, reported the location of the collection site; based on his description, the Walchia interval was 15 m (~50 ft.) north of Cedar Run Rd. at an elevation of 184.5–185.7 m (605–609 ft.) above sea level (latitude = 38.327421, longitude −82.563500).

5.2. Flora of correlative Grafton Sandstone paleochannels

Fig. 4. Walchia piniformis frond showing branches with short, helically arranged, needlelike leaves, Cedar Run site, locality 1.

At location 2, 0.84 km (0.52 miles) west of the Cedar Run site at locality 1, a nearly complete 15.5 m section extending upward from the crinoidal sandstone was measured (Fig. 8). Using the 10.8 m interval between the top of the crinoidal sandstone and the Walchia horizon at location 1, the projected Walchia-equivalent interval occurs within a 6.75 m thick channel-fill. The lower 4.5 m consists of medium-coarse sandstone that grades up to very fine sandstone. Epsilon cross-beds enclose medium to large scale trough cross-stratification and ripple crosslamination. Reactivation surfaces are common. This 4.5 m thick sandstone is overlain by a 2.25 m thick abandoned channel facies consisting of olive green shale/dark greenish gray mudstone. This channel-fill is truncated by another channel-fill sandstone, and both are part of the Grafton Sandstone IVF (Fig. 8). Calamites, Annularia stellata, and Pecopteris were found along a 5 cm thick interval in the shale (Fig. 9). At location 4, 1.51 km (0.94 miles) southwest of the Cedar Run Walchia locality, a complete section from 0 to 16.3 m above the crinoidal sandstone was measured and combined with the section through the Ames marine zone at location 3. Using the 10.8 m interval from the top of the crinoidal limestone to the Walchia horizon at locality 1, the projected Walchia-equivalent interval occurs within a 3.4 m thick, pale yellow mudstone (Fig. 8) in the upper portion of a channel-fill. The lower 4–5 m of the channel-fill consists of cross-stratified sandstone and correlates with the Grafton Sandstone Member of the Casselman Formation. The paleochannel-fill is overlain by a 3.2 m thick red/olive

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Fig. 5. Walchia piniformis from locality 1. A, C. Walchia fronds. B, D. Walchia branchlets. Scale bar is 5 mm.

variegated hackly mudstone paleosol with abundant micritic limestone nodules in the lower 40 cm. Plant fossils are restricted to a 10 cm thick interval near the top of the channel-fill. Cordaite leaves are common and Lepidophylloides is rare (Fig. 9). 5.3. Flora from below the Grafton Sandstone incised valley-fill A second floral horizon occurs below the Grafton Sandstone IVF at locations 2 and 4. The flora are preserved in the lower part of a 2.2 m thick, gray to dark gray shale. The shale occurs directly above a calcic vertisol that overlies the Ames marine zone and it is truncated by the Grafton Sandstone IVF. At locality 2, this assemblage includes Lepidophylloides, Cordaites, Pecopteris, and Neuropteris ovata. At locality 4, the shale contains Cordaites, Lepidophylloides, and Pecopteris (Fig. 10). This shale correlates with the Duquesne coal which in eastern Ohio is overlain by the marine Skelly Limestone (Sturgeon and Hoare, 1968). 5.4. Charleston Walchia Walchia and Cordaites were reported by Lyons and Darrah (1989a, 1989b) from a carbonaceous shale about 7.5 m above the lowest red bed in the Conemaugh Formation at Charleston, West Virginia as described by Englund et al. (1979). The exact location and stratigraphic section of the Charleston Walchia was not included. Lyons and Darrah (1989a, 1989b) concluded that the Charleston Walchia occurred at the Mahoning coal horizon. However, the absence of minable coal and marine units makes it difficult to confidently correlate within the

Conemaugh Formation in the Charleston area using traditional lithostratigraphy. Furthermore, the Mahoning coal cannot be identified with confidence at Charleston because it is thin and discontinuous, and the Mahoning coal horizon tentatively identified is usually truncated by the Upper Mahoning Sandstone (Windolph, 1987). Recent work involving the correlation of paleosol-bound allocycles from Charleston downdip to Huntington and Flatwoods, West Virginia indicates that the Twomile Limestone of I. C. White (1885) is likely equivalent to the Upper Brush Creek Limestone (Martino, 2015). A composite section of the Conemaugh Formation from the north side of Charleston indicates that the Brush Creek coal horizon is present 7.5 m above the lowest redbeds (Fig. 11). This coal is discontinuous in the Charleston area. Kosanke (1988) reported the palynomorph Laevigatosporites globosus from carbonaceous shales at three horizons north of Charleston that have been correlated to the Charleston section. These horizons occur near interfluvial sequence boundaries 2, 5 and 6 in Fig. 10. Lycospora is absent in these beds and last occurs in the Mahoning coal (Fig. 2; Eble et al., 2009). The Brush Creek coal is distinguished from the Mahoning coal below by the absence of Lycospora, and from the Bakerstown above by the presence of Laevigatosporites globosus and Punctatosporites granifer (Peppers, 1996; Eble et al., 2009). Since the first occurrence of L. globosus without Lycospora is ~ 20 m below the Twomile Limestone and this first happens in the Brush Creek coal, the Charleston Walchia reported by Lyons and Darrah (1989a, 1989b) must be above the Brush Creek coal and below the Bakerstown coal. If the first occurrence of L. globosus without Lycospora occurs between the Mahoning and Brush Creek coals, it is possible that the Charleston Walchia may be associated with the Brush Creek coal horizon, but it

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Fig. 6. Walchia piniformis from locality 1. A. Walchia frond. B–D. Walchia branchlets. Scale bar = 5 mm.

would still be Missourian in age and not Late Desmoinesian as postulated by Lyons and Darrah (1989a, 1989b). 5.5. 7-11 Mine Walchia Walchia was reported from a 1.5 m thick, dark gray-black shale at the 7-11 Mine north of East Liverpool, Ohio (Mapes and McComas, 1984; McComas, 1988). Wagner and Lyons (1997) reexamined this assemblage and found abundant Walchia as well as Cordaites, Sigillaria brardii, and fern and pteridosperm fragments. Associated taxa reported by McComas (1988) included Lepidostrobophyllum, Sigillariostrubus, Annularia asteris, Calamites, Asterotheca, Pecopteris unita?, Ptychocarpus, Spiropteris, Alethopteris, Aphlebia, Cyclopteris orbicularis, Neuropteris ovata, Odontopteris aequalis, Cordaites, Gomphostrobus, Walchiostrobus, and Samaropsis. The Walchia-bearing shale has a thin coal at the base which was queried as the Brush Creek coal (McComas, 1988). The Walchia interval is part of a fine-grained incised valley-fill up to 28 m thick that truncates the Mahoning coal and overlying 18 m of strata (Easterday, 2004; Falcon-Lang et al., 2011, Fig. 2; Belt et al., 2011, Fig. 13). Lycospora, which is absent in this coal (Easterday, 2004), last occurs in the Mahoning coal, which is consistent with the Brush Creek coal correlation. Both the flora and palynoflora associated with the lower 11 m of the IVF are early Missourian in age (Belt et al., 2011). The Walchia-bearing shale is overlain by a fossiliferous shale identified as the Lower Brush Creek marine unit by McComas (1988). The presence of the ammonoid

Pennocereas seaman (Mapes and McComas, 2010) and the conodont Idiognathodus cancellosus confirm the correct correlation as Lower Brush Creek (Work et al., 2007; Falcon-Lang et al., 2011). The thin coal beneath the walchian shale is limited to the valley-fill and therefore cannot be strictly lithostratigraphically correlated with the Brush Creek coal horizon. However, its position above a 2.7 m thick paleosol with limestone nodules and directly beneath the Lower Brush Creek transgressive sequence suggests the coal and overlying walchian shale are genetically related to the lower Brush Creek Cyclothem. The 7-11 Mine Walchia interval is younger (early Missourian) than the late Desmoinesian Mahoning roof shale age presumed by Lyons and Darrah (1989a, 1989b) when they correlated it with their Charleston Walchia horizon. 5.6. Rennersville Walchia Darrah (1969, 1975) reported four specimens of Walchia (Lebachia sp.) from a fine grained sandstone at Rennersville southwest of Pittsburgh, Pennsylvania. The sandstone was located above the Clarksburg Limestone in the upper Casselman Formation. The Walchia was considered a rare component of the assemblage. Common taxa included Lescuropteris moorii, Pecopteris polymorpha, P. aborescens, Neuropteris ovata and Sphenophyllum oblongifolium. Other taxa present were Callipteridium cf. pteridium? (questioned by Wagner and Lyons, 1997), Danaeites emersoni, Pecopteris feminaeformis, Sphenopteris minutisecta, Alethopteris grandini, Odontopteris reichiana, Macroneuropteris

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Fig. 7. Flora associated with Walchia from Cedar Run, locality 1. A, B, D: isolated neuropteroid pinnules. C, E. Strap-like Cordaites with Walchia branchlet. F: grass-like leaves of Lepidophylloides (foliage from Sigillaria). Scale bar = 5 mm.

scheuchzeri, and Cordaites. The stratigraphic and depositional context of this assemblage is not known. The age is early Virgilian, but younger than the Cedar Run Walchia.

5.7. Implications for revised correlation of Appalachian Basin Walchia The previously reported and revised stratigraphic positions of the four Walchia occurrences in the Appalachian Basin are shown in Fig. 12. The oldest occurrences from the Glenshaw Formation (Charleston, 7-11 Mine) were originally thought to be from the level of the Mahoning coal and late Desmoinesian in age. From the preceding data, it appears that both are younger and correlate with the Brush Creek coal roof shale or lower Brush Creek cyclothem making them early Missourian in age. The Cedar Run and Rennersville Walchia

occurrences in the Casselman Formation are slightly younger, correlating with the early Virgilian stage. These results provide a more coherent picture of the timing of paleoclimatic changes in the Appalachian Basin and the migration of walchian conifers into this region. The first appearance of Walchia, instead of preceding other indicators of increasing dryness (extinction of wetland-centered lycopods, first appearance of calcic vertisols), closely follows these events (Fig. 12). The first red beds are associated with the Mahoning coal horizon, and the earliest widespread calcic vertisols occur below the Brush Creek coal (Martino, 2004, 2015); the Desmoinesian-Missourian boundary occurs between these two coals. Thus, walchian conifers were already established in subtropical paleolatitudes and more western regions of the midcontinent during the Middle Pennsylvanian (Lyons and Darrah, 1989a, 1989b), and migrated to the Appalachian Basin as climate/sea level cycles involved longer dry seasons along the equator.

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Fig. 8. Stratigraphic sections from locations 1–5 in Fig. 3. Correlations are made across the study area using the top of the crinoidal sandstone as a datum, which was discovered at the Cedar Run Walchia locality in 2016. The crinoidal sandstone is a shallow marine facies found along the Big Sandy River that is developed in the upper part of the Ames marine zone. A composite section was constructed for locations 3 and 4 due to their close proximity and continuous exposure between them. The stratigraphic interval between the Walchia horizon and the regionally developed Ames Limestone was determined by adding the interval between it and the crinoidal sandstone at locality 1 to the interval between the top of the crinoidal sandstone and the base of the Ames Limestone at localities 3 and 5.

5.8. Paleoecology The xeromorphic traits of most modern conifers (thick cuticle, needle like leaves with low ratio of surface area to volume) enables them to retain moisture, inhabit well-drained soils, and tolerate drier climates (Lyons and Darrah, 1989a). Walchia was restricted to seasonally dry habitats in subtropical to tropical Euramerica (Ziegler et al., 2002) and is considered to be an indicator of semiarid settings where only 1–2 wet months occurred per year (DiMichele et al., 2010). Walchian conifers may have occupied upland areas continuously, and expanded into lowland areas during the drier phase of the cyclothems (Phillips and Peppers, 1984; Falcon-Lang et al., 2009; Dolby et al., 2011, DiMichele, 2014). Their rarity in Late Pennsylvanian strata has been attributed to be due at least in part to the lower preservation potential of flora that inhabited well-drained soils (Looy et al., 2014). The flora associated with the Cedar Run Walchia includes Cordaites, Lepidophylloides and rare neuropteroid pinnules. Cordaites, like Walchia, was a coniferophyte with well-developed xeromorphic features

(Clement-Westerhof, 1988; Rothwell et al., 1997). Cordaites inhabited peat swamps, clastic swamps, upland/dryland regions, and slopes of river valley walls. Its large, tough, strap-like leaves were fairly durable during transport (Falcon-Lang and Bashforth, 2004, 2005). Some Cordaites had deep root systems that enabled them to inhabit moisture-stressed clastic substrates (Bashforth et al., 2014). Lepidophylloides includes the grass-like leaves arborescent lycopods (Gillespie et al., 1978), and Sigillaria is the only lycopod that survived into the Missourian and Virgilian. Though Sigillaria was typically associated with wetlands, it was tolerant of seasonally drier conditions and lowered water tables due to deep-reaching adaptations in its stigmarian root system (Phillips and DiMichele, 1992; Pfefferkorn and Wang, 2009). Sigillaria is often preserved in fluvial channel sandstones suggesting that some species grew along stream margins, perhaps on levees (Gastaldo, 1987; Phillips and DiMichele, 1992). Calamites was an arborescent plant up to 30 m in height which inhabited lake margins and point bars of meandering rivers. The hollow stems of mature Calamites commonly filled with mud forming pith casts (Gillespie et al., 1978; Mapes

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Fig. 9. Flora from abandoned fluvial channel-fill mudstones at locations 2 (A–C) and 4 (D). Scale bar = 5 mm. A. Annularia carinata, Calamites, and Pecopteris. B, C. Annularia carinata. D. Cordaites.

and Gastaldo, 1986). Annularia carinata represents foliage of Calamites (Kerp and Fichter, 1985; DiMichele et al., 2010). Pecopteris and Neuropteris are seed ferns (pteridosperms) that included shrubs and small trees. They are common elements in Pennsylvanian, tropical wetland floras. Late Pennsylvanian swamps were dominated by tree ferns and the lycopod Sigillaria, with pteridosperms as an understory (DiMichele, 2014). During the Late Pennsylvanian, Walchia, Cordaites, and Sigillaria are often found together in what earlier workers interpreted as ‘upland assemblages’ (Scott and Chaloner, 1983; Rothwell and Mapes, 1988; Stewart and Rothwell, 1993), though more recent workers prefer the term ‘dryland’ (e.g. Looy et al., 2014). The branches and leaves of upland trees may have been detached during storms and swept downstream during high rainfall and runoff, ultimately accumulated in abandoned fluvial channels. Previous studies have documented allochthonous Walchia assemblages in lowland lake and swamp facies (Rothwell and Mapes, 1988; Mapes and Rothwell, 1988) and even marine limestone (Leisman et al., 1988). In the Illinois Basin, Middle Pennsylvanian conifers including Walchia have been described from incised fluvial channel-fills, and are interpreted to have grown on the interfluves or within the channels themselves during dry conditions associated with glacial lowstand (Falcon-Lang et al., 2009). Walchian conifers in growth position have been described from Missourian coastal facies in New Mexico (FalconLang et al., 2015). Limited palynologic sampling of Desmoinesian cyclic strata from Nova Scotia suggests that conifers including Walchia were the dominant forms of vegetation on a well-drained interfluve and dry alluvial plain during lowstand and early transgressive systems tracts (Dolby et al., 2011).

5.9. Plant taphonomy Studies of modern depositional settings indicate that fossilized plants may represent flora living at or near the site of deposition (i.e. autochthonous/parautochthonous) or flora that were transported from upstream or upland locations (allochthonous; Gastaldo et al., 1987; Gastaldo and Degges, 2007). Preservation potential is highest in fluvial, upper delta plain, and lacustrine settings (Dodd and Stanton, 1990). Different plant parts have highly variable floating times. For example, experimental work has shown that leaves may be saturated in a few days to a few months (Spicer, 1981; Ferguson, 1985). Evergreen branches and needles often can float for several months, increasing the likelihood of sustained transport over a significant distance (Spicer and Greer, 1986). In the modern Mobile Delta of Alabama, fascicles of Pinus from upland pine savannah communities have been found in crevasse splay channel deposits (Gastaldo et al., 1987).

5.10. Depositional model for the Cedar Run Walchia assemblage During deposition of the Conemaugh Group, a low relief coastal plain with poorly drained interfluves prevailed during late TST and HST (Martino, 2004, 2015). During FSST and LST, rivers incised their valleys (Fig. 13) creating relief on the order of at least 20–35 m based on the preserved thickness of IVFs. The total maximum relief is likely to have been significantly greater than the preserved thickness of the IVFs, when sediment compaction is taken into account and also that the interfluves were being eroded as the valleys filled. The dryland/upland flora may have developed on well-drained interfluves, topographically

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Fig. 10. Flora from paleosol-capping shale facies a locations 2 and 4. Scale bar = 5 mm. A. Pecopteris. B. Pecopteris cf. oreiopteridia. C–E. Neuropteris ovata. F. large Cordaites.

higher areas of a dissected lowland (Fig. 14). A similar scenario is envisioned for conifer-dominated assemblages from the Mid-Late Pennsylvanian Sydney Mines Formation of Nova Scotia (Dolby et al., 2011). The excellent preservation of the Cedar Run Walchia and lack of size sorting indicates minimal physical, biologic or chemical degradation. Interfluve runoff could have easily introduced coniferous vegetation into rapidly filling valleys requiring transport of several km or less. Mass wasting could also have played a role in transferring the conifers as the valleys were widened over time (e.g. Falcon-Lang et al., 2009; Fig. 14). A large, paleovalley wall slump block is preserved in the Glenshaw Formation along Rt. 52 at Prichard, 5 km south study area (Martino, 2004, Fig. 17). The Cordaites and Sigillaria may have populated the wetlands of the valley floor, but could also have coexisted with Walchia along the valley walls or interfluves.

Looy et al. (2014) reviewed the taphonomic factors that controlled the preservation of plant fossils in Late Paleozoic strata, and concluded that Methuselah occurrences of drought-tolerant plants such as walchian conifers likely represented normally extrabasinal (i.e. upland) elements living above base level that migrated into the basinal lowlands during drier parts of the climate cycle. Their model (Looy et al., 2014, Fig. 2) was based on a static, flat coastal plain that persisted through wet and dry climatic phases. It overlooks the significant relief that develops in coastal plains along the depositional strike due to fluvial incision during FSST and persists during LST and early TST. During these times, it is likely that walchian conifers inhabited well-drained upland interfluves and valley walls adjacent to the river basins. Slope failure and flash flooding could have transported them as little as a hundred meters to the valley floor where they were quickly buried in standing

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water, with rapidly increasing accommodation and rising water table during TST enhancing their preservation potential. The juxtaposition of well-drained upland or valley wall substrates within rapidly filling

valleys (Fig. 14) provides a very plausible alternative to the drylandlowland concept, particularly for rare, anomalous, Methuselah-type occurrences.

9 80

70 SM,O 8

60 7

50

L. globosus

6

IVF

40

30

SM,O

5

SM,O 4

Twomile Ls. L. globosus

Walchia of Lyons and Darrah

Brush Cr. C.

7.5 m lowest red bed 20 L. globosus

2 10

0m

Mahoning Ss.

IVF

Shale

Coal

Silty shale, bedded mudstone

Carbonaceous shale/claystone

Cr

Crinoid plates

Hackly mudstone

Micritic limestone nodules

Br

Brachiopods

Siltstone

Siderite nodules

Bi

Bivalves, marine

Ripple cross-lamination

Root traces

G

Gastropods, marine

Parallel lamination

Cs

Conchostracans

Trough cross-stratification

SM

Spirorbid Microconchids

Compound cross-stratification

Hummocky cross-stratification O

Ostracods

Limestone

Burrows

P

Plants

Argillaceous limestone

Quartz pebbles

T

Shark Tooth

1-9

Interfluvial sequence boundaries

Fig. 11. Composite section of lower Conemaugh in the Charleston area with paleosol-bounded cyclothems which have been correlated with marine-cored cyclothems to the north and west of Charleston (modified from Martino, 2015). Lyons and Darrah (1989a, 1989b) reported Walchia from a carbonaceous shale 7.5 m above the lowest red beds at or above the Mahoning Sandstone which they believed to be the Mahoning coal horizon.

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Fig. 12. Stratigraphic position of Appalachian Basin Walchia occurrences and associated paleoclimatic data (red bed paleosols, calcic vertisols, extinction of most lycopods). Relative wetness curve is based on abundance of known bituminous coal resources from eastern U.S. coal basins (modified from Phillips et al., 1985). Stars show the four occurrences of Walchia in the Appalachian Basin (7-11 = 7-11 Mine, Ch = Charleston, CR = Cedar Run, R = Rennersburg). Dashed arrows point to revised stratigraphic positions based on this study.

6. Conclusions

1) The Cedar Run Walchia is only the fourth Walchia occurrence from Pennsylvanian strata of the Appalachian Basin, and only the second occurrence to be accompanied by a detailed description of its stratigraphic and sedimentologic context.

2) The Cedar Run floral assemblage occurs 15.8–16.9 m above the base of the Ames Limestone and is early Virgilian in age. It includes Walchia, Cordaites, Lepidophylloides, and rare neuropteroid pinnules preserved in an abandoned channel-fill mudstone that is part of the Grafton Sandstone incised valley-fill. This is slightly higher stratigraphically than was initially reported, and revises the flood basin lake interpretation of Martino and Blake (2001).

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SEQUENCE STRA

FACIES ASSOCIATIONS Valley incision, pedogenesis on interfluves under dry, seasonal climate. FSST/LST/EARLY TST Valley filled by stacked fluvial channels with fluvial-estuarine transition.

MFS

HST

Rising water table with rising sea level and less seasonal, wetter climate gleys and drowns soils forming histosol + lakes, bays, and seaway. MFS

SB 1

LATE TST Valley incision, pedogenesis on interfluves FSST/LST/EARLY TST under dry, seasonal climate. Onset and peak of of glaciation. Valley filled by stacked fluvial channels with fluvial-estuarine transition during deglaciation and rising sea level .

IFSB

SB1

subhumid

IVF TST

Lake or sea filling by crevasse splays and deltas produces coarsening upward sequence locally truncated by crevasse and delta channels. Interglacial sea level highstand.

HST

T

TS ly ar

e

sea level

late

semiarid

subhumid

histosol

IVF TST

LATE TST

IFSB

SB2

SB 2

inter fluve exposure- paleosols IFSB calcisol/calcic vertisol va y e lle lat FS lley i va ing T ST ncis ill S f T ion rly ea

HST

FS

ST

LST

water table

Fig. 13. Sequence stratigraphic model for paleosol-bounded, eccentricity-driven, fourth-order sequences in Conemaugh Group and related moisture regimes that affected vascular plants (modified from Martino, 2015). Sea level curves, systems tracts and water table conditions are shown. Symmetric sea level curve is used for simplicity, but is likely to be strongly asymmetric for glacioeustatic cycles since ice sheets melt more rapidly than they grow (Catuneanu, 2006). The Cedar Run Walchia is interpreted as mass wasting into an abandoned fluvial channel from an adjacent valley wall or upland as the Grafton Sandstone incised valley was filling during early TST.

Fig. 14. Paleoenvironmental model for origin of the Cedar Run Walchia assemblage in an abandoned fluvial channel. Interfluvial sequence boundaries occur at the top of thick, mature, welldrained paleosols (IFSB = interfluvial sequence boundary; SB 9, 10, and 11 from Martino, 2004, Fig. 12). A = Calamites, B = medulosan pteridosperms, C = tree ferns, D = walchian conifers, E = Cordaites, F = Sigillaria (modified from Falcon-Lang et al., 2009). Sigillaria and Cordaites could inhabit basin floor wetlands and well-drained coastal plain uplands, while Walchia was restricted to well-drained uplands. Topographic relief may have been 30 m or less. The occurrence of Walchia at a single location and the abundance of well-preserved fronds and branchlets make it more plausible that an entire tree fell into the channel via a slump block from the valley wall. Valley-fill sequence not to scale. The Grafton IVF downcuts to Harlem coal north of the present study area.

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3) It is possible that Walchia, Sigillaria, and Cordaites populated the drainage basin (lowland/dryland origin) when water tables were seasonally low due to the semiarid climate during or near glacial maximum. However, it appears more likely that it was derived from proximal, well-drained interfluves or valley walls through mass wasting associated with valley-widening. 4) The flora of the lacustrine shale that caps the calcic vertisol directly above the Ames marine zone consists of tree ferns and Cordaites. The rising water table associated with wetter climatic conditions and rising sea level drowned interfluvial paleosols forming lakes as part of the TST. 5) The earliest reported occurrences of Walchia in the Appalachian Basin from Charleston, West Virginia and the 7-11 Mine in Ohio are early Missourian in age and not late Desmoinesian as previously thought. The appearance of walchian conifers between the Brush Creek and Wilgus coals follows the mass extinction of nearly all arborescent lycopods near the Desmoinesian-Missourian boundary and the earliest development of calcic vertisols and aridisols in the Conemaugh Group of the Appalachian Basin. Acknowledgements I am greatly indebted to Robert D. Thompson for 1) bringing the Cedar Run Walchia location to my attention, 2) facilitating the description of the Walchia location and stratigraphic interval, and 3) assisting in the recovery of additional fossils from the site. James Bowling and Robert D. Thompson, Jr. also helped in the collection of fossils. Elaine Martino recognized the potential significance of the fossils when they were first excavated and was instrumental in their recovery and preservation. She is also due thanks for her patience and support throughout this project. Mitch Blake provided copies of field notes that helped correlate Kosanke's pollen-bearing horizons to the Charleston Walchia occurrence. Paul Lyons provided input on the proposed Stephanian unconformity in the Appalachian Basin and shared his current knowledge of the stratigraphic context and location of the Charleston Walchia occurrence. William DiMichele provided encouragement and generously assisted with the identification of plant taxa. Annalisha Johnson provided invaluable guidance on drafting illustrations. The clarity of this paper was significantly improved due to thorough and thoughtful reviews by William DiMichele, Martin Gibling, and Stephen Greb. Various phases of this study were supported by the Petroleum Research Fund (PRF 34516-B8), the West Virginia Geological and Economic Survey, and Marshall University. References Arkle Jr., T.A., 1974. Stratigraphy of the Pennsylvanian and Permian Systems of the central Appalachians. In: Briggs, G. (Ed.), Carboniferous of the Southeastern United States. Geological Society of America Special Paper 148, pp. 5–29. Bashforth, A.R., Cleal, C.J., Gibling, M.R., Falcon-Lang, H.J., Miller, R.F., 2014. Paleoecology of Early Pennsylvanian vegetation on a seasonally dry tropical landscape, (Tynemouth Creek Formation, New Brunswick, Canada). Rev. Palaeobot. Palynol. 200, 229–263. Belt, E.S., Heckel, P.H., Lentz, L.J., Bragonier, W.A., Lyons, T.W., 2011. Record of glacial–eustatic sea-level fluctuations in complex middle to late Pennsylvanian facies in the Northern Appalachian Basin and relation to similar events in the Midcontinent basin. Sediment. Geol. 238, 79–100. Bharwadjwa, D.H., 1964. On the organization of Spencerites, Chaloner, and Edosproites Wilson and Coe with remarks on their systematic position. The Paleobotanis 13, 85–88. Blake Jr., B.M., Cross, A.T., Eble, C.F., Gillespie, W.H., Pfefferkorn, H.W., 2002. Selected plant megafossils from the Appalachian region, eastern United States: geographic and stratigraphic distribution. In: Hills, L.V., Henderson, C.M., Bamber, E.W. (Eds.), Carboniferous and Permian of the World: Canadian Society of Petroleum Geologists Memoir 19, pp. 259–335. Blakey, R.C., 2007. Carboniferous–Permian paleogeography of the assembly of Pangaea. In: Wong, T.E. (Ed.), Proceedings on the XVth International Congress on Carboniferous and Permian Stratigraphy, Utrecht, 10–16 August 2003. Royal Dutch Academy of Arts and Sciences, pp. 443–456. Busch, R.M., Rollins, H.B., 1984. Correlation of Carboniferous strata using a hierarchy of transgressive- regressive units. Geology 12, 471–474. Busch, R.M., West, R.R., 1987. Hierarchal genetic stratigraphy: a framework for paleoeceanography. Paleoceanography 2, 141–164. Catuneanu, O., 2006. Principles of Sequence Stratigraphy. Elsevier, Amsterdam, The Netherlands (375 p).

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