PALAIOS, 2019, v. 34, 405–423 Research Article DOI: http://dx.doi.org/10.2110/palo.2019.020

SEDIMENTOLOGY AND CARBON ISOTOPE (d13C) OF – BOUNDARY INTERVAL STRATA, APPALACHIAN BASIN (, USA)

1, 2 1 ANYA V. HESS AND JEFFREY M. TROP 1Department of and Environmental Geosciences, Bucknell University, Moore Avenue, Lewisburg, Pennsylvania 17837, USA 2Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854, USA email: [email protected]

ABSTRACT: Silurian–Devonian boundary interval strata deposited during the expansion of land plants record a major perturbation of the carbon cycle, the global Klonk Event, one of the largest carbon isotope excursions during the Phanerozoic. In the Appalachian Basin, these marine strata record the regional buildup to the Acadian Orogeny. This study reports new sedimentologic, paleontologic, ichnologic, and carbon isotope data from an exceptional quarry exposure in central Pennsylvania, USA, a historically understudied area between better-documented outcrops .500 km away to the southwest (West , Virginia, ) and northeast (New York). spanning the continuous 113-m thick outcrop are dominantly carbonate and fine-grained siliciclastic strata interpreted as being deposited in supratidal through subtidal environments, including oxygen-limited environments below storm wave base. They record parts of three transgressive-regressive cycles, in the (1) upper Silurian , (2) upper Silurian–Lower Devonian through lower Mandata Member of the Old Port Formation, 13 and (3) Lower Devonian Mandata through Ridgeley Members of the Old Port Formation. Micrite matrix d Ccarb 13 analyses exhibit a large, positive d Ccarb excursion (.5% amplitude). Outcrops of this interval in the Appalachian Basin occur in two belts, between which correlation has been historically challenging. The regional correlation presented herein is based on carbon-isotope trends and is more consistent with published and volcanic ash ages, an improvement over published correlations based on lithostratigraphy. Transgressive- regressive trends at the central Pennsylvania study site are not consistent with regional trends, indicating that local controls (tectonics, supply) rather than global (eustasy) dominated depositional patterns in the Silurian– Devonian boundary interval in the Appalachian Basin.

13 INTRODUCTION perturbation to the global carbon cycle, with rising values in d Ccarb representing the evolving isotopic composition of global dissolved The Silurian–Devonian transition was a time of major change in the 13 inorganic carbon (d CDIC). Proposed drivers of the Klonk Event include global biosphere. Vascular land plants had evolved by the late Silurian and global regression and the of exposed, isotopically heavy diversified rapidly in the Devonian. In the late Silurian–Early Devonian, Silurian carbonate platforms (Saltzman 2002) or enhanced burial of arthropods transitioned to land and impacted soil development (Kenrick et organic carbon from newly evolved terrestrial biota (Malkowski and Racki al. 2012). These changes coincided temporally with an overall increase in 2009). However, coupled chemostratigraphic-sedimentologic studies atmospheric oxygen that led to a peak in atmospheric oxygen content spanning Silurian–Devonian strata needed to evaluate these potential (Lenton et al. 2016; Lu et al. 2018). In the Appalachian Basin, the drivers are generally lacking. Silurian–Devonian boundary interval has recently been the focus of renewed interest as the advent of modern techniques (-lead The carbon isotope excursion has been of recent interest in the , carbon isotope chemostratigraphy) allows for more Appalachian Basin, where it was originally documented in advanced, quantitative analysis (Kleffner et al. 2009; Husson et al. 2016; (7%; Saltzman 2002; Husson et al. 2016) and more recently in New York McAdams et al. 2017). (Husson et al. 2016). However, there still exists a geographic gap of .500 A major perturbation to the carbon cycle, the Klonk Event, is also km between Appalachian Basin sites (Fig. 1). The Silurian–Devonian recorded at the Silurian–Devonian boundary, as a significant carbon boundary interval has been understudied in most of Pennsylvania, isotope excursion. Carbon isotope analyses of bulk marine carbonates particularly with regards to modern methods, for a number of reasons. 13 Temporally, the period boundary is a natural stopping point, and many (d Ccarb) document a positive carbon isotope excursion as much as 7% in amplitude, making it one of the largest such excursions during the studies are restricted to either Silurian (e.g., Smosna and Patchen 1978; Phanerozoic. The excursion has been documented in sections around the Brett et al. 1990; Bell and Smosna 1998; McLaughlin et al. 2012) or world: the in the Great Basin of Nevada and (3.0%; Devonian strata (e.g., Diedrich and Wilkinson 1999; Ver Straeten 2007, Saltzman 2002, 2005) and the Arbuckle Mountains of Oklahoma (3.3%; 2008; Ver Straeten et al. 2011). Geographically, outcrops occur in two Saltzman 2002); the Czech Republic and France (3.8–4.0%; Buggisch and belts, a northern belt in New York and parts of New Jersey and Mann 2004; Buggisch and Joachimski 2006); and Ukraine (.6%; northeastern-most Pennsylvania, and a southern belt spanning the Virginia- 13 Malkowski et al. 2009). The similar shape and magnitude of the d Ccarb West Virginia border, the western tip of Maryland, and southern and central excursions has led previous workers to argue that it represents a Pennsylvania (Fig. 1). Outcrops in central Pennsylvania are generally poor

Published Online: September 2019 Copyright Ó 2019, SEPM (Society for Sedimentary Geology) 0883-1351/19/034-405

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Dorobek and Read 1986); herein, the terms ‘northern outcrop belt’ and ‘southern outcrop belt’ refer to these areas that have been historically well studied. Regional correlations have been published for the southern outcrop belt (Dorobek and Read 1986) and for the northern outcrop belt (Rickard 1962; Epstein et al. 1967; Laporte 1969). Nomenclature and facies changes between the two outcrop belts make correlation difficult, and no basin-wide correlation scheme has been universally adopted (e.g., Smosna 1988). An exceptional, continuous quarry exposure of Silurian–Devonian boundary interval strata near the town of Winfield in central Pennsylvania (herein referred to as Winfield Quarry; Figs. 1, 2) provides a unique opportunity to fill the temporal and geographic gap. The purpose of this study is to (1) document the sedimentology, , and lithostratig- raphy of Winfield Quarry strata in order to reconstruct depositional environments and relative sea-level change, (2) document the chemo- stratigraphy and carbon isotope excursion in the context of that detailed sedimentology, paleontology, and stratigraphy, and (3) use the chemo- stratigraphic-lithostratigraphic framework to improve regional stratigraphic correlations and provide additional constraints on a major perturbation to the ancient geologic carbon cycle.

GEOLOGIC SETTING

Paleogeographic and Tectonic Setting

The Appalachian foreland basin, shaped by plate convergence, spanned much of eastern North America throughout most of the Paleozoic. During the late Silurian–Early Devonian, the basin was at ~308S latitude (Kent and Van Der Voo 1990; Witzke 1990), making it an environment conducive to carbonate . The foreland basin first formed in the FIG. 1.—Map of the eastern United States showing outcrop belts of Silurian– Middle , when the Taconic orogeny marked initial closure of the Devonian boundary interval strata (compiled from King et al. 1974; Denkler and Iapetus Ocean and collision of an island arc with eastern Laurentia. Harris 1988; Miles 2003; Kleffner et al. 2009). Circles indicate sites of existing Taconic deformation in New England was most intense from ~496 to carbon isotope studies from this interval. ~428 Ma, with metamorphism and roughly coincident development of the foreland basin ranging from ~480 to ~455 Ma in the southern since they are less resistant to weathering. Many previous studies are Appalachians and New England (Hatcher 2010 and references therein). restricted to either the New York-New Jersey part of the northern outcrop The Silurian–Devonian transition in the Appalachian Basin was a time belt (e.g., Epstein et al. 1967; Kleffner et al. 2009) or the Virginia-West of diminished clastic input that allowed marine organisms to flourish, Virginia-southernmost Pennsylvania part of the southern outcrop belt (e.g., resulting in a variety of carbonate facies throughout the basin (e.g., Laporte

FIG. 2.—Photograph of the quarry exposure at Winfield, Pennsylvania, described in section WQ1. Dashed black lines indicate approximate formation boundaries. Abbreviation: Fm. ¼ Formation.

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FIG. 3.—Stratigraphic correlation chart for upper Silurian–Lower Devonian strata throughout the southern and northern outcrop belts of the central Appalachian Basin. Bold text indicates formations, italicized text indicates members, plain text indicates not specified, from source publications. Abbreviation: Grp. ¼ Group.

1969; Dorobek and Read 1986). In the central Appalachians, where this is divided into the New Creek-Corriganville, Mandata, and Ridgeley study focuses, the late Silurian through Early Devonian historically has Members (Inners 1997). Stratigraphic nomenclature used in Pennsylvania been considered a time of tectonic quiescence between the Taconic and for this interval is broadly similar to that used throughout the southern Acadian orogenies (Rodgers 1967; Johnson 1971; Dorobek and Read outcrop belt but differs significantly from that used in the northern outcrop 1986). However, some researchers have suggested that Acadian orogenesis belt (Fig. 3). began as early as the late Silurian and would therefore have coincided with The Tonoloway Formation consists of evaporitic shelfal carbonates and deposition of the strata discussed herein (Ebert and Matteson 2003; Ver is correlative in the subsurface to thick and anhydrites in West Straeten 2007). Virginia and New York (Smosna et al. 1976; Mount 2014). Strata During the Acadian orogeny, a series of terranes collided with the northern part of the eastern margin of Laurentia. This transpressional, immediately overlying the Tonoloway are regionally referred to as the zippered collision progressed southward through time, affecting areas from , but this can be problematic for correlation as the term present-day Newfoundland through Georgia. It culminated in the closure of encompasses different formations and members in the southern and the Rheic ocean when Baltica (present-day Europe) collided with Laurentia northern outcrop belts (Fig. 3) (e.g., compare Rickard 1962 with Dorobek in the early part of the (~345 Ma) (Ver Straeten 2009; and Read 1986), and the term is not used herein. Hatcher 2010 and references therein). In West Virginia, Virginia, and Maryland, the contact between the Keyser and Tonoloway Formations is unconformable at the basin edges Stratigraphy and conformable in the basin center. The Keyser Formation is broken into three members (Fig. 3). Lowermost is the Byers Island Member, which The exposure at Winfield Quarry includes the upper Silurian Tonoloway Formation, upper Silurian to Lower Devonian Keyser Formation, and consists of fossiliferous, nodular carbonates. The overlying Jersey Shore Lower Devonian Old Port Formation (Fig. 3). These formation Member contains a variety of carbonate facies with diverse designations have been adopted from Inners (1997), the most detailed assemblages but is distinguished by its abundant coral-stromatoporoid existing study of upper Silurian–Lower Devonian strata in central buildups along the basin margins. Finally, the La Vale Member is a Pennsylvania. The Keyser Formation is divided into the Byers Island, laminated, mudcracked carbonate with minor stromatoporoid biostromes Jersey Shore, and La Vale Members (Head 1969). The Old Port Formation (Head 1969).

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In the southern outcrop belt, the Byers Island Member is termed the the Coeymans and Kalkberg Formations (Kleffner et al. 2009, using lower Keyser Formation (Fig. 3) and is aggradational open-marine combined biostratigraphy and carbon isotope stratigraphy). carbonates with skeletal banks around the basin edges and bioturbated, Volcanic ashes (bentonites) have been used to correlate the Silurian– nodular carbonates toward the basin center. Skeletal banks consist of coral- Devonian strata over limited distances (e.g., Rickard 1962; Smith and Way stromatoporoid mud mounds and framestones. The middle part of the 1988). In the southern outcrop belt, Smith and Way (1988) first described a Keyser Formation in West Virginia is regressive Clifton Forge set of three ash beds that occur in the Corriganville (Bald Hill Bentonites A on the eastern basin margin and grades basinward into the Big Mountain and B) and Mandata (Bald Hill Bentonite C) Members of the Old Port and correlative skeletal carbonates (Dorobek and Read 1986). These Formation at the type section near Hollidaysburg, Penn., 84 miles west- clastic units do not extend into Pennsylvania (Head 1969) and their southwest of Winfield Quarry. In the northern outcrop belt, the Kalkberg correlation to the carbonate there is ambiguous (e.g., compare Bentonite, an ash bed in the New Scotland Formation, has been dated by Head 1969 and Dorobek and Read 1986). The La Vale Member is McAdams et al. (2017) using U-Pb analysis of zircons, placing it in the equivalent to the upper Keyser Formation in the southern outcrop belt, middle Lochkvian (Early Devonian) at 417.6160.12 Ma. Smith and Way which consists of transgressive skeletal carbonates and contains coral- (1988) correlated this bed to their Bald Hill Bentonite A in the stromatoporoid mud mounds and framestones (Dorobek and Read 1986). Corriganville Member of the southern outcrop belt. McAdams et al. The Old Port Formation consists of four members in Pennsylvania, in (2017) note, however, that the number of volcanic ash beds in the Lower stratigraphic order from oldest, the New Creek-Corriganville, Mandata, Devonian of the Appalachians makes correlation of individual beds Shriver, and Ridgeley Members (Inners 1997) (Fig. 3). The New Creek potentially problematic. Member consists of regressive skeletal banks. The Corriganville Member Carbon isotope stratigraphy was recently used by Husson et al. (2016) to is a transgressive cherty carbonate. The Mandata and Shriver Members are correlate between a section in West Virginia and four sections in New York. transgressive basinal and transgressive-to-regressive cherty carbon- Their correlation shows that facies and the stratigraphic packages based on ates, respectively. The Ridgeley Member is a basin-wide that them are diachronous across the basin, that the Keyser Formation is represents the first substantial influx of clastic sediment resulting from the correlative with the Rondout, Manlius, and parts of the Coeymans Acadian Orogeny in the central Appalachian Basin (Dorobek and Read Formations of New York, and that the New Creek-Corriganville Members 1986). are correlative with the Kalkberg, New Scotland, and Becraft Formations Outside of Pennsylvania, the term Old Port Formation is not used and its of New York. The Winfield Quarry section provides an opportunity to members correspond to named formations. In Maryland, the New Creek refine this correlation between the northern and southern outcrop belts. Formation interfingers with the uppermost Keyser Formation and is equivalent to the Elbow Ridge sandstone at the eastern edge of the basin. Field Site The Corriganville Member is equivalent to the Healing Springs sandstone at the eastern edge of the basin in Virginia. The Mandata and Shriver The field site for this study is a quarry approximately 2 km west of Members are equivalent to cherty carbonates of the Licking Creek Winfield, Pennsylvania, in Union County (N 40.898168, W 076.893078) Formation nearer the basin margin in the southern outcrop belt. Outside of (Fig. 2). It was active a few years prior to the data collection phase, central Pennsylvania, the Ridgeley Member is equivalent to the Oriskany providing a fresh rockface. It was inactive during the data collection Formation. phase of this project (2007) and has since been reopened; the base of the The northern outcrop belt is oriented parallel to depositional dip, with original section has been removed. A well-exposed stratigraphic section more proximal facies to the west. Facies are time transgressive and timelines (WQ1) was measured on a bed-by-bed basis using a Jacob’s staff at the typically span multiple formations or members (Rickard 1962; Laporte west end of the quarry. Refer to Hess (2008) for an additional, less 1969; Husson et al. 2016). The Cobleskill Formation (Fig. 3) consists of extensive section spanning only the Old Port Formation. The stratigraphic massive, fossiliferous carbonates, including stromatoporoids and corals, and section and geochemical data from the western exposure are discussed grades westward to less fossiliferous, thin-bedded dolomites. The Rondout herein. and Manlius Formations represent a transgressive-regressive cycle consist- ing of shallow-water and stromatoporoid-coral biostromes and Geochemical Methodology bioherms and associated lagoonal facies (Rickard 1962; Laporte 1969; Belak 1980). The Coeymans, Kalkberg, and New Scotland Formations are A total of 63 micrite samples were analyzed from the lower 88 m of the progressively deeper water facies, transitioning to open marine by the WQ1 section, spanning the Tonoloway Formation through the Shriver Kalkberg and New Scotland Formations (Laporte 1969). Member of the Old Port Formation. Only samples devoid of fossil fragments, fractures, and veins were selected. samples were broken Regional Stratigraphic Correlations using a rock hammer in a cleaned room to provide a fresh surface. Powder was extracted from this surface using a Dremel drill with a diamond-dust- The units discussed above have been correlated thus far mainly using coated drill bit, while continually monitoring to ensure no material other lithostratigraphy (Fig. 3). The Keyser Formation is typically correlated in than micrite was sampled. Powder was deposited and sealed directly into the northern outcrop belt to portions of the Cobleskill, Rondout, and glass vials. Between samples, the rock hammer and drill bit were sanitized Manlius Formations, and the Old Port Formation is typically correlated to using a solution of 10%-diluted hydrochloric acid. portions of the Manlius, Coeymans, Kalkberg, and New Scotland Isotope analyses were conducted in the Stable Isotope Ratios in the Formations (Head 1969; Laporte 1969). Environment, Analytical Laboratory (SIREAL) in the Department of Conodont biostratigraphy, volcanic ashes, and carbon isotope stratigra- and Environmental Science at the University of Rochester. Samples were phy have also aided correlation of this complicated stratigraphy. Based on pretreated with 30% H2O2 to remove organic material, followed by three the first occurrence of the conodont woschmidti, the Silurian– rinses with deionized water and a final rinse with methanol. Analyses were Devonian boundary has been placed in the upper Keyser Formation in run on a Thermo Electron Corporation Finnegan Delta plus XP mass Virginia and West Virginia (Helfrich 1978; Denkler and Harris 1988). In spectrometer in continuous-flow mode via the Thermo Electron Gas Bench the northern outcrop belt, it has been variously placed in the Rondout peripheral and a GC-PAL autosampler. Samples were loaded into 4mL tubes Formation (Denkler and Harris 1988), the lower Coeymans Formation with pierceable, self-healing rubber septa with PTFE liners. Tubes were then (Tucker et al. 1998), and either within the Manlius Formation or between flushed with UHP helium at about 100 mL/minute for 10 minutes.

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100% phosphoric acid was injected through the septum manually with a 16- settings. A similar environment is inferred for in situ stromatolites at gauge needle and syringe. All samples were vortexed to insure complete Winfield Quarry. mixing of the sample and the acid. Tubes were loaded into a block heated to This facies contains a low-diversity assemblage of unabraded , 708C. Samples reacted for at least 45 minutes but never more than 12 hours chiefly eurypterids, gastropods, and ostracods. This suite of sedimentary before they were analyzed. Carbon dioxide gas evolved from the reaction structures indicates deposition in an environment that was above fair- with the acid was then drawn into the instrument for analysis. Carbon and weather wave base (symmetrical ripple laminae), within the photic zone oxygen isotopic results are reported in permil relative to VPDB (Vienna Pee- (stromatolites and cryptalgal laminae), within the tidal range (heterolithic Dee Belemnite) and normalized (Coplen 1994) on scales such that the bedding), with intermittent subaerial exposure (mudcracks) and more carbon and oxygen isotopic values of NBS-19 are 1.95 permil and -2.2 extended periods of exposure in the supratidal zone (). Not all permil, respectively, carbon and oxygen isotopic values of NBS-18 are -5.01 sedimentary features are present in all instances of this facies, and specific permil and -23 permil, respectively, and the carbon isotopic value of depositional environments are interpreted for units on a case-by-case basis L-SVEC is -46.6 permil. Average precision (1-sigma) is 0.06 and 0.10 for (refer to Inferred Depositional Setting and Relative Sea-Level Fluctuations carbon and oxygen isotopes, respectively. For repeat analyses, the average of section). the carbon and oxygen isotope values is discussed herein. Biomicrite to Biosparite Facies (F2a).—The biomicrite to biosparite SEDIMENTOLOGY facies is characterized by the presence of megascopic fossils or fossil fragments in a micrite matrix (Fig. 4H, 4I). Fossils are open-marine fauna Facies consisting of gastropods, , bivalves, bryozoans, rugose corals, Sedimentary facies are defined on the basis of , sedimentary , and sparse ostracods. In many instances, fossils are concentrated structures, paleontology, and ichnology, particularly as they relate to the in pods likely formed by or winnowing of fines. In some interpretation of depositional environments. Winfield Quarry strata consist instances, weathered surfaces appear mottled (Fig. 4H), also possibly of four : micrite, biomicrite and biosparite, sandy intrabiosparite, resulting from bioturbation. The varying degrees of abrasion and and shale. Seven sedimentary facies representative of different depositional orientation of fossils indicate deposition in open marine settings from environments are identified on the basis of lithology, sedimentary subtidal but above fair-weather wave base, for beds with highly abraded structures, ichnofabrics, and fossils (Table 1, Figs. 4, 5). See Hess fossils, to lower energy environments between fair-weather and storm wave (2008) for additional photographs of facies and fossils. base, for beds with abundant unabraded fossils. Some instances contain symmetrical ripples (Fig. 4J), indicating deposition above fair-weather Massive Micrite Facies (F1a).—The massive micrite facies is wave base. characterized by a lack of fossils and physical , Some beds contain cm-scale fining-upwards successions, which form though some instances contain low-diversity, high-abundance ichnologic under waning-flow conditions, and could be interpreted as either tidal assemblages of Chondrites and Zoophycos trace fossils (Fig. 4A, 4B). The channels near to where the fossils were abraded or as turbidity flows majority of this facies is interpreted as having been deposited in low- formed below normal wave base and distal to the environment in which the energy, subtidal environments below storm wave base. The lack of body fossils were abraded. From the association of these beds with relatively fossils indicates an inhospitable environment. Zoophycos has been linked shallow facies and their lack of definitive deep-water indicators, they are to low-oxygen, though not entirely anoxic, conditions (Marintsch and interpreted as tidal-channel deposits (refer to Inferred Depositional Setting Finks 1978; Bromley and Ekdale 1984), especially when they occur in high and Relative Sea-Level Fluctuations for more details). abundance and low diversity, as here. While Chondrites and Zoophycos traces in more recent deposits occur in deep water, Paleozoic strata with Sponge-Coral- Biomicrite to Biosparite Facies (F2b).—The these traces can have formed in a variety of water depths, from lagoonal to sponge-coral-crinoid biomicrite to biosparite facies is characterized by the below storm wave base (Ekdale 1988; Frey et al. 1990). On the basis of its presence of sponges (stromatoporoids) and(or) corals (Fig. 4K, 4L). thickness (~20 m) and association with relatively deep water under- and Stromatoporoids are discontinuous, overturned, and abraded, in some overlying units, the package of this facies with Chondrites and Zoophycos places including oncolites with concentric growth strata (Fig. 4L). These traces is interpreted as having been deposited below storm wave base, in deposits also contain tabulate and rugose coral, crinoids, and highly oxygen-limited conditions (Fig. 6). For micrites lacking trace fossils, their abraded, unidentifiable fossil fragments. These are interpreted as - environmental interpretation is based on the sedimentology and paleon- flank deposits formed in an environment with sufficient wave energy to tology of interbedded lithofacies, with some units deposited in waters rotate oncoids and abrade fossils, above fair-weather wave base and potentially as shallow as the intertidal zone. Refer to the Inferred within the photic zone. Some intervals contain shale partings, which may Depositional Setting and Relative Sea-Level Fluctuations section for more indicate slack water suspension fallout associated with tides or lulls in details. wave energy. While no framework reefs are present in Winfield Quarry strata, they have been documented in correlative strata (e.g., Cole et al. Micrite with Sedimentary Structures Facies (F1b).—The micrite 2015). with sedimentary structures facies is characterized by the presence of physical and organic sedimentary structures including mudcracks, Sandy Intrabiosparite Facies (F3).—The sandy intrabiosparite facies evaporites, heterolithic bedding, intraclasts, sparse fenestrae, stromato- consists of coarse-- to -size and calcareous clasts with lites, and cryptalgal laminae (Fig. 4C–4F). Stromatolites and cryptalgal sparse disarticulated brachiopods and crinoid ossicles (Fig. 5A). The lack laminae are domal on a millimeter to decimeter scale. In one instance, of finer grained indicates that wave energy was sufficient to stromatolites form a continuous layer of laminated, low-domal mounds. winnow away mud-sized particles from the depositional environment. This Laminae thicken toward the crests of mounds (Fig. 4G), a key indicator facies is interpreted as having been deposited in an open marine, above of microbial origin (Riding 1999), and these are interpreted as in situ fair-weather wave base environment. mounds under Riding’s (1999) definition. They are the ‘‘laterally linked hemispheroids’’ type of Logan et al. (1964), which in the Shale with Fossils and Ichnofabrics Facies (F4a).—The shale with modern of Shark Bay, Australia, form in protected, low-energy, intertidal fossils and ichnofabrics facies is a medium to dark gray shale and

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TABLE 1.—Summary of facies documented in stratigraphic section WQ1.

Interpreted depositional Facies Lithology Bed thickness Bed geometry Sedimentary structures Ichnologya Megafossilsb Associated shale environment

1a: Massive micrite micrite-argillaceous thin to thick tabular to nodular none Chondrites and Zoophycos none shale partings to intertidal–subtidal below micrite (in some units prevalent) interbedded shales storm wave base; some units oxygen limited 1b: Micrite with micrite-argillaceous finely laminated tabular, nodular, mudcracks, evaporites, none sparse ostracods where not shale partings to intertidal–supratidal sedimentary structures micrite to thick or lenticular heterolithic bedding, laminated, sparse fossil interbedded shales convolute, ripple or fragments, bryozoans, cryptalgal laminae, eurypterids, stromatolites intraclasts, sparse hummocks, sparse fenestrae 2a: Biomicrite to (sparse)(intra)biomicrite thin to thick tabular to nodular pods and discontinuous bands sparse Chondrites; sparse–packed, highly sparse shale partings subtidal, dominantly above biosparite to (intra)biosparite or of micrite, rare evaporites, mottling and abraded–unabraded to interbedded thin fair-weather wave base packed (intra) sparse micrite intraclasts, concentration of fossils gastropods, brachiopods, shales Trop J.M. and Hess A.V. biomicrite, non- to laminae, symmetrical wave in pods possibly bivalves, ostracodes, very argillaceous ripples, or hummocky resulting from bryozoans, rugose corals, cross-stratification and bioturbation crinoidsc fining-upwards sequences; nodules abundant in some layers 2b: Sponge-coral-crinoid (intra)biomicrite to medium nodular to oncolites and soft-sediment none stromatoporoids, tabulate none to shale partings subtidal above fair-weather biomicrite to biosparite biosparite stromatolitic deformation in some units, and rugose corals, to thin shales wave base, within the thrombolites crinoids, sparse photic zone ostracodes, unidentifiable fossil fragments 3: Sandy intrabiosparite coarse-sand to granule thick massive centimeter-scale fining none sparse disarticulated none subtidal above fair-weather sandy intrabiosparite upwards sequences brachiopods, crinoids wave base 4a: Shale with fossils and dark gray shale and thin tabular and fissile generally none, one 2-cm Chondrites, nondescript ostracodes, sparse mollusks N/A low energy, subtidal below ichnofabrics calcareous siltstone thick layer with chert ichnofabrics and brachiopodsd storm wave base, nodules oxygen limited 4b: Barren shale black shale thin tabular and fissile none none abundant lingulid N/A low energy, subtidal below brachiopods in one fair-weather wave base, interval oxygen limited

a Dr. Tony Ekdale identified many trace fossils. b Dr. Carl Brett identified many megafossils. c Identifiable fossils include Discomyorthis, Acrospirifer cf. murchisoni, Schuchertella cf. brachyprion, Costellirostratapeculiaris, Leptocoelia flabellites, possibly Meristella laevis, Pentamerus cf. gypidula, and ‘‘Schuchetella’’ woolworthiana. d Identifiable fossils include Coelospira dichtoma, Actinopteria cf. communis, Dalegina oblata, Coelospira, and possibly a small, narrow rhynchonellid (Stenorhynchus), Chonostrophiella, Leptaena rhomboidalis, Orbiculoidea cf. disca, Tyersella perelegans, and Discomyorthis. PALAIOS PALAIOS SEDIMENTOLOGY AND ISOTOPE STRATIGRAPHY OF SILURIAN–DEVONIAN STRATA 411

FIG. 4.—Photographs of key features of facies F1 and F2 used in identifying depositional environments, in order of facies listed in table 1. A) Zoophycos mottling on bedding-plane surface of block, Shriver Member of Old Port Formation F1a. B) Close-up view of bedding-plane surface showing arcing Zoophycos traces (arcs indicated by white arrows), same interval as Figure 4A. C) Mudcracks (m) on bedding plane surface and horizon of evaporites (e) on cross-section view, Tonoloway Formation F1b. D) vugs (e) and laminations, Tonoloway Formation F1b. E) Stromatolite bed, Tonoloway Formation F1b. F) Heterolithic bedding (h) and scours (s), La Vale Member of Keyser Formation F1b.

siltstone with fossils, including ostracods and very sparse mollusks and it can tolerate (Bromley and Ekdale 1984). This facies therefore brachiopods, and in many instances intense Chondrites bioturbation (Fig. represents deposition in an environment below storm wave base in 5B, lower three-quarters of Fig. 5C). Fossils include Orbiculoidea and oxygen-limited waters (Fig. 6). nuculid bivalves, which can indicate an oxygen-limited environment (Brett et al. 1991). The Chondrites ichnofacies is also common in Barren Shale Facies (F4b).—The barren shale facies is characterized oxygen-limited areas, even exceeding Zoophycos in the degree of dysoxia by dark gray to black shale lacking macrofossils and biogenic and

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FIG. 4.—Continued. Photographs of key features of facies F1 and F2 used in identifying depositional environments, in order of facies listed in table 1. G) In situ stromatolite mounds, New Creek-Corriganville Members of Old Port Formation F1b. H) Gray and tan mottling, possibly from bioturbation, Keyser Formation F2a. I) Crinoidal biomicrite, Keyser Formation F2a. J) Symmetrical wave ripples, Byers Island Member of Keyser Formation F2a. K) Tabulate coral (t) and crinoids (c), Keyser Formation F2b. L) Stromatoporoids, likely not in growth position, La Vale Member of Keyser Formation F2b.

sedimentary structures (upper quarter of Fig. 5C). The dark color of this WQ1 section (Fig. 6). The lack of sedimentary structures indicates facies is likely due to high concentrations of organic material, and it deposition in a low-energy environment. While these conditions can may therefore represent oxygen-limited conditions that would have occur in both lagoonal and offshore settings well below the influence of precluded the presence of bacteria able to break down this organic fair-weather and storm wave base, regional correlation of the Mandata matter. The lack of fossils and biogenic structures supports this Member, in which a large part of the facies occurs, indicates that it is a interpretation (Bromley and Ekdale 1984), and this facies is interpreted deep-water equivalent of being shed from the mountains to the to represent the most oxygen-deprived environment preserved in the east (Smosna 1988).

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FIG. 5.—Photographs of key features of facies F3, F4, and F5 used in identifying depositional environments, in order of facies listed in Table 1. A) Coarse sand- to granule- size quartz clasts and abraded fragments (bf), New Creek-Corriganville Members of Old Port Formation F3. B) Chondrites burrows on bedding-plane surface, Mandata Member of Old Port Formation F4a. C) Compacted Chondrites burrows (c) and brachiopod fragments (bf) of facies F4a, overlain by dark, barren shale of facies F4b at top quarter of frame, Mandata Member of Old Port Formation. D) Bentonite (altered volcanic ash) (orange), Mandata Member of Old Port Formation.

Instances of this facies outside of the Mandata Member are thin (,2m) assemblage indicates a stressed environment, perhaps due to changes in and are associated with shallower-water facies. One contains abundant oxygenation or salinity. These units are interpreted as representing lingulid brachiopods, which are associated with nearshore dysaerobic dysaerobic, below-fair-weather wave base environments, shallower water environments (Kammer et al. 1986), and the low-diversity, high-abundance than for the bulk of this facies.

FIG. 6.—Summary of features observed in the studied stratigraphy and corresponding interpretations of bottom-water oxygenation during deposition. See Table 1 for description of facies.

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FIG. 7.—Stratigraphic section WQ1 from Winfield Quarry, PA. Abbreviations: Fm. ¼ Formation; Mbr. ¼ Member.

Possible Volcanic Ash.—In addition to the sedimentary facies, eight Inferred Depositional Setting and Relative Sea-Level Fluctuations beds of what may be bentonites (altered volcanic ash) are also preserved in This section summarizes the stratigraphic distribution of the facies WQ1. They are thin (,10-cm thick), -rich (sticky when wetted), and documented in the previous section (Fig. 7) and relative sea-level weather bright orange, often leaching color to underlying beds (Fig. 5D). fluctuations inferred from the upsection facies changes (Fig. 8A–8C). The thickest horizon, in the Mandata, was sampled and yielded doubly terminated euhedral zircons (see Online Supplemental File) indicative of Tonoloway Formation.—The base of WQl consists of ~7mof airfall ash. Tonoloway Formation laminated micrite (F1b; Fig. 7). Laminae show the

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FIG. 8.—Stratigraphy, relative sea level, transgressive-regressive cycles, and for section WQ1, Winfield, PA, and equivalent strata south of Pennsylvania and in New York based on lithologic correlation (Fig. 3). A) Generalized stratigraphy for section WQ1. Silurian–Devonian boundary age is from Cohen et al. (2008); boundary is

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convex geometry of cryptalgal laminae and stromatolites, evaporites, and Keyser Formation La Vale Member.—The La Vale Member is mudcracks are also abundant. Laminae are lacking in some portions of this biomicrite, biosparite, and argillacous biomicrite (F2a). A return to non- stratigraphic package. Identifiable fossils are for the most part limited to reef margin biomicrites stratigraphically above the reef margin unit may sparse ostracods, with unidentifiable fossil fragments also present. These indicate a relative sea-level fall and a return to environments similar to strata are interpreted to represent deposition in shallow-water intertidal to those inferred from strata below the reef-margin package. Alternatively, sea supratidal environments, including carbonate tidal flats (Fig. 8B). level may have continued to rise, as depositional environments would have An exposure ~580 m along strike from the base of section WQ1 along been broadly similar both landward and seaward of the reef. Starting at the north wall of Winfield Quarry contains an exceptionally well-preserved ~45 m, fossils are gradually more abraded upsection and cm-scale fining- eurypterid Lagerst¨atte ~2 m below the top of the Tonoloway Formation upwards successions are noted at ~50 m. Based on the stratigraphic (Vrazo et al. 2014). The exceptional exposure in the quarry allowed for context and lack of definitive deep-water features, they are interpreted as physical tracing of this bed to the WQ1 section. Upon close inspection, two having formed by waning flow in tidal channels and bars, indicating that by partial eurypterid fossils of the taxa noted by Vrazo et al. (2014; this point relative sea level had begun to fall. Upsection, strata grade into Eurypterus cf. remipes) were found in the Tonoloway Formation of WQ1 laminated micrite (F1b), argillaceous micrite (F1a), and finally a package and it is likely that the 3.2-m-thick covered section 2 m below the contact of micrite and interbedded shales from ~61 to 64 m in which the micrites between the Tonoloway and Keyser Formations correlates to the Lager- exhibit mudcracks, cm-scale cut-and-fill structures, sparse fenestrae, and st¨atte exposed along strike within Winfield Quarry. heterolithic bedding with -sized particles showing ripple-scale multidi- In the uppermost 1.5 m of the Tonoloway Formation, sedimentary rectional planar crossbedding (F1b). The variations observed in the La Vale structures are lacking and the concentration of evaporites gradually Member are consistent with tidally influenced nearshore environments and decreases. The boundary between the Tonoloway and the Byers Island indicate an overall regressive trend culminating with interbedded micrites Member of the Keyser Formation is marked by an increase in fossil and shales at the top of the unit deposited in an intertidal environment abundance and diversity from sparse ostracods in the Tonoloway to frequently subject to subaerial exposure and tidal influence. bryozoans, brachiopods, bivalves, gastropods, ostracods, and rugose corals typical of F2a in the Keyser. This transition is gradational from 5.9 Old Port Formation New Creek and Corriganville Members.—A to 7.6 m and the formation boundary is picked at 7.6 m in WQ1, the point distinct contact separates the Keyser and Old Port Formations at 64 m where the rate of increase in fossil abundance slows. The loss of above the base of the section. Interbedded micrites and shales of the evaporites and mudcracks and the increasing fossil abundance and uppermost Keyser Formation occur below ~lmofin situ mounded diversity indicate freshening and minor relative sea-level rise across the stromatolites (F1b) of the New Creek-Corriganville Members of the Old contact between the Tonoloway and Keyser Formations. Port Formation. It is an apparently conformable contact with shallow marine facies above and below and no evidence of or prolonged Keyser Formation Byers Island Member.—The Byers Island exposure. In situ stromatolites are interpreted to have formed in a protected Member is distinguished by the nodularity of its beds (Head 1969). It is intertidal environment. biomicrite (F2a) with normal marine fauna and is interpreted to represent Above the in situ stromatolites is a ~1-m-thick cross-bedded, sandy deepening to a subtidal above fair-weather wave base environment. The intrabiosparite (F3) representing siliciclastic input into the basin and upper contact of this member is chosen at 12.8 m, where consistently similar to that described by Inners (1981) ~1 m above the contact in the nodular strata become more sporadically nodular. Bloomsburg and Mifflinville Quadrangles ~15 km to the east. The sandy unit is overlain by a series of biosparite, micrite, and biomicrite strata with Keyser Formation Jersey Shore Member.—Fossils in the nodular moderate to sparse, dominantly abraded fossils, which indicate a deepening biomicrite (F2a) of the Jersey Shore Member are fragmented and randomly to a shallow subtidal environment above fair-weather wave base. oriented. They become less prevalent upsection to about 23 m and are lost entirely from 13 to 15 m where there is a package of massive micrite (F1a). Old Port Formation Mandata Member.—An abrupt transition to Two stromatoporoid-bearing units (F2b) are at 17–18 m and 26–31 m, and shale and siltstone at ~71 m marks the contact between the New Creek- the lower contains oncoids while the upper contains fragmented fossils that Corriganville and Mandata Members. Packages of dark gray bioturbated become increasingly abundant and diverse upsection. The covered section shale with sparse fossils (F4a) and black, barren shale (F4b) are punctuated at 23–26 m is exposed in nearby parts of the quarry, where it contains by tens-of-centimeter-thick beds of nodular micrite and biomicrite. stromatoporoids, Favosites corals, and abundant crinoid ossicles; it is Together, these facies indicate deposition in a subtidal environment below inferred to also be facies F2b. The presence of oncoids and stromatop- storm wave base following a rapid relative sea-level rise at the base of the oroids indicate that these formed in a high-energy environment within the Mandata Member. Black shales are interpreted to represent times when photic zone during continued relative sea-level rise. As the corals and bottom waters were the most inhospitable to normal marine fauna, oxygen stromatoporoids are mainly not in life position, these units are interpreted limited, and conducive to preservation of organic material. Micrite, as reef-margin deposits that would have formed adjacent to reefs. Above biomicrite, and fossiliferous shale with Chondrites bioturbation are the covered section in WQ1, stromatoporoids are present up to 31 m and interpreted to represent times of oxygen limitation, but to a lesser degree other fossils are fragmented and increasingly abundant and diverse. The than during deposition of facies F4a (Fig. 6). Precipitated pyrite is common top of the stromatoporoid-bearing strata at 31 m was chosen as the throughout this member, further supporting the interpretation of oxygen- boundary between the Jersey Shore and overlying La Vale Member. limited, likely euxinic conditions. At a time when global atmospheric and

approximate. See Figure 7 for explanation of symbols. B) Interpreted relative sea-level curve for section WQ1. Gray shading indicates interpreted oxygen limitation during deposition, with darker shading indicating increasing oxygen limitation. C) Transgressive-regressive cycles from section WQ1 (black), south of Pennsylvania (blue, from Dorobek and Read 1986), and New York (red, from Laporte 1969 and Belak 1980). D) Isotope data from section WQ1 (black) and West Virginia (light blue and dark blue, Saltzman 2002 and Husson et al. 2016, respectively) plotted relative to stratigraphic position. Red box indicates peak carbon isotope values in New York (Husson et al. 2016). Abbreviations: Fm. ¼ Formation; Mbr. ¼ Member, FWWB ¼ fair-weather wave base; SWB ¼ storm wave base; VA ¼Virginia; WV ¼ West Virginia; MD ¼ Maryland; PA ¼ Pennsylvania; NY ¼ New York.

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2 FIG. 9.—Carbon versus oxygen isotope values with trendlines and R values for all data and for each facies. Symbol color and shape by facies. Trendline for facies F2a excluded due to insufficient data. Refer to Table 1 for facies information.

surface-water oxygen levels were rising (Lenton et al. 2016; Lu et al. beginning of the Acadian orogeny. Alternatively, it is possible that the clay- 2018), there is evidence for oxygen limitation in the Appalachian Basin. rich layers recorded here are detrital terrestrial clays. The uppermost bed The change from relative sea-level rise to fall is placed at ~75 m, where a occurs in the Mandata at 73.5 m; it is this bed that yielded doubly minor increase in oxygenation is inferred from the change in facies from terminated euhedral zircons (see Online Supplemental File) and is mainly F4b to F4a. therefore considered a confirmed bentonite.

Old Port Formation Shriver Member.—Above the Mandata Member GEOCHEMISTRY is an abrupt transition to the Shriver Member, which consists of micrite with interbedded shales (F1a). Zoophycos feeding traces are prevalent on Micrite samples from this stratigraphic section show an 8.7% increase 13 some bedding planes from ~81 to 87 m. Due to the nature of exposure in in d Ccarb from the base of the section to the upper part of the La Vale the quarry it is difficult to directly observe bedding planes in intervals Member of the Keyser Formation (Fig. 8D, Table 2). Values rise from a higher than ~87 m, though it appears that Zoophycos permeates the minimum of -4.3% in the Tonoloway to a high of þ4.4% in the upper La majority of this unit. The lack of fossils and presence of Zoophycos Vale. A gap in the data through most of the Jersey Shore and the lower part indicate continued deposition under oxygen-limited subtidal below storm of the La Vale reflects the high fossil content through this part of the wave base conditions, though under slightly more oxygenated conditions section, as only samples devoid of visible biotic and sparry components than for underlying deposits (Fig. 6); such conditions would have were sampled. Carbon isotope values then decrease by .5% to a low in prevented the preservation of as much organic matter as observed in the the Mandata Member of the Old Port Formation. 18 Mandata Member black shales. As with the underlying Mandata Member, Oxygen isotope (d Ocarb) values range from -7.3 to -4.1%.Fromthe precipitated pyrite is common in this part of the section, providing further base of the section in the Tonoloway Formation to the base of the data gap support for continued oxygen limitation and likely euxinia. that begins in the Jersey Shore Member of the Keyser Formation, values increase overall from -7.3 to -6.1%. From the middle of the La Vale Member Old Port Formation Ridgeley Member.—The boundary between the of the Keyser to midway through the New Creek-Corriganville Members Shriver and Ridgeley Members is marked by an abrupt increase in fossil (~66 m), values vary between -6.9 and -5.2%. Above this to the top of the content. From ~99 to 106 m, the Ridgeley Member is biomicrite (F2a) in sampled interval in the Shriver Member of the Old Port Formation, values which fossils are less fragmented than in the Keyser Formation. are overall ~1% higher, varying between -6.4 and -4.1%. Argillaceous biomicrite makes up the remainder of the section from Comparison of the oxygen and carbon isotope compositions permits ~106 to 113 m, and the fossils in this unit are dominantly unabraded evaluation of diagenetic overprinting. A plot of carbon versus oxygen gastropods and robust, abraded to unabraded brachiopods. The presence of isotope values for the entire stratigraphic column (Fig. 9) shows little fossils indicates the return of normal-marine, subtidal below fair-weather correlation (R2¼0.01). Most individual facies also show little correlation wave base conditions, likely the result of continued relative sea-level fall. (R2,0.15). Isotope values for facies F1b show some correlation (R2¼0.39), The top of the Winfield Quarry outcrop is in the Ridgeley Member and the but this can be partially explained by two populations of points created by top of the Old Port Formation is not preserved. two different stratigraphic occurrences of this facies. Relatively low isotope values are recorded in the Tonoloway Formation and lower part of the Possible Volcanic Ash Beds.—Seven of the possible volcanic ash beds Keyser Formation; relatively high isotope values are recorded in the lower occur in the Keyser Formation, one in the Jersey Shore Member at 15.3 m part of the Old Port Formation and upper part of the Keyser Formation. and six in the La Vale Member at 38.3, 41.1, 43.6, 47.3, 51.1, and 53.5 m. When trendlines for those intervals are plotted separately, the correlation in No works have thus far documented volcanic ashes in the Keyser the lower part of the section disappears (R2¼0.00) and that in the upper part Formation. If these are in fact volcanic ashes, they may be the oldest in the of the section is substantially reduced (R2¼0.29). Thus, the lack of Devonian of the Appalachian Basin and the earliest indication of the correlation between carbon and oxygen isotope values suggests that the

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13 18 TABLE 2.—d Ccarb and d Ocarb values for stratigraphic section WQ1 micrite samples.

Stratigraphic level d13C Analysis d18O Analysis Stratigraphic level d13C Analysis d18O Analysis (meters above standard standard (meters above standard standard base of section) d13C deviation d18O deviation base of section) d13C deviation d18O deviation

0.81 -1.7 0.07 -7.3 0.07 63.05 2.6 0.02 -6.3 0.08 2.48 -4.3 0.04 -7.3 0.07 63.37 3.1 0.05 -6.9 0.03 3.10 -4.0 0.05 -7.0 0.03 63.44 1.6 0.03 -6.8 0.06 6.05 -3.0 0.03 -6.4 0.03 65.97 0.7 0.09 -6.9 0.09 6.31 -2.9 0.03 -6.8 0.04 65.97 0.8 0.03 -6.1 0.05 10.71 -2.5 0.03 -6.4 0.05 66.64 1.4 0.06 -5.3 0.09 10.79 -2.9 0.06 -6.3 0.07 66.64 1.4 0.05 -5.8 0.09 10.84 -2.7 0.03 -6.6 0.07 66.81 1.5 0.04 -5.0 0.08 12.86 -0.9 0.02 -6.3 0.08 67.05 1.5 0.02 -5.2 0.06 13.17 -0.9 0.05 -6.3 0.06 67.30 1.5 0.04 -5.2 0.08 13.17 -0.9 0.06 -6.2 0.09 67.30 1.3 0.05 -5.6 0.06 13.31 -1.0 0.04 -6.2 0.06 67.76 1.0 0.03 -5.0 0.03 18.97 -0.5 0.04 -6.1 0.04 67.86 1.5 0.04 -5.5 0.04 44.67 2.7 0.05 -6.3 0.06 68.85 0.5 0.04 -4.7 0.06 44.84 2.2 0.03 -5.9 0.08 68.85 0.4 0.04 -4.3 0.08 45.13 1.4 0.06 -5.2 0.15 68.85 0.4 0.06 -4.4 0.06 47.42 3.4 0.03 -5.8 0.10 71.90 0.6 0.03 -4.8 0.10 47.42 3.3 0.04 -6.3 0.04 71.90 0.6 0.05 -3.9 0.09 48.85 3.4 0.03 -6.1 0.07 71.90 0.7 0.05 -4.9 0.06 48.85 3.3 0.05 -6.3 0.04 72.24 -1.1 0.06 -5.9 0.08 49.81 2.7 0.04 -6.0 0.07 72.24 -1.1 0.06 -5.5 0.06 49.96 2.9 0.03 -6.2 0.06 72.75 0.1 0.05 -5.5 0.04 50.00 3.6 0.05 -5.2 0.05 72.75 0.1 0.06 -5.3 0.10 51.28 2.5 0.05 -5.7 0.05 72.75 0.2 0.06 -5.3 0.06 51.85 2.2 0.06 -5.9 0.07 73.00 0.0 0.03 -7.1 0.09 52.30 2.2 0.05 -6.1 0.08 73.00 -0.2 0.03 -5.3 0.06 52.30 2.1 0.06 -6.0 0.07 73.38 0.4 0.06 -4.9 0.05 54.36 3.2 0.03 -6.9 0.07 73.92 -0.4 0.06 -5.5 0.06 57.91 3.7 0.03 -5.8 0.06 74.19 -0.7 0.05 -4.5 0.09 58.61 3.6 0.05 -5.9 0.07 74.19 -0.7 0.07 -4.2 0.07 59.00 3.6 0.02 -5.7 0.08 74.19 -0.7 0.05 -4.9 0.07 59.41 3.1 0.03 -5.1 0.06 74.49 -4.4 0.02 -4.9 0.07 59.90 3.1 0.04 -5.4 0.04 74.49 -4.0 0.06 -4.0 0.08 59.90 3.2 0.06 -5.3 0.06 75.53 -0.6 0.04 -4.1 0.09 60.90 2.9 0.06 -5.6 0.08 76.30 0.0 0.06 -6.1 0.08 60.90 2.8 0.03 -5.7 0.04 78.10 0.6 0.05 -4.9 0.10 61.86 4.4 0.05 -6.0 0.07 80.24 0.9 0.06 -5.4 0.11 62.00 4.4 0.05 -6.3 0.06 80.92 1.2 0.04 -4.9 0.05 62.00 4.4 0.04 -6.2 0.10 81.30 0.9 0.03 -4.5 0.06 62.37 3.6 0.04 -6.7 0.08 82.01 1.1 0.06 -6.4 0.13 62.49 2.7 0.05 -6.3 0.07 83.88 1.6 0.06 -5.0 0.13 62.82 2.9 0.06 -6.9 0.09 87.96 1.8 0.06 -4.8 0.06

sampled micrite matrix generally provides a faithful record of primary in shallow-marine environments can cause the carbon isotope values of the seawater d13C values. dissolved inorganic carbon in those environments to be lower than those in However, a few anomalously low carbon isotope values in the organic- the open ocean, typically resulting in positive carbon isotope excursions in rich Mandata Member of the Old Port Formation may record early deep-water facies or during rapid transgression (e.g., Patterson and Walter diagenetic cementation. Two carbon isotope values (at 72.24 and 74.49 m 1994; Immenhauser et al. 2003; Saltzman and Edwards 2017). This is above the base of the section) are anomalously low compared to samples opposite of the pattern observed here, with the positive carbon isotope from adjacent strata. It is possible that remineralization of organic matter in excursion recorded in the shallowest-water facies. Nevertheless, caution the sampled shale resulted in an isotopically light early (e.g., should be used when comparing the absolute values of the record presented Weissert et al. 2008). However, carbon isotope values decrease from the here with data from distant locations. peak of the positive carbon isotope excursion beginning ~8 m strati- graphically below the Mandata Member, so the stratigraphic position of the DISCUSSION positive excursion is well constrained. Another possible concern is alteration of the isotopic signature by Parts of three transgression-regression cycles have been identified in meteoric , especially for very shallow-water facies (e.g., at the Winfield Quarry strata (Fig. 8B, 8C). The first is the final portion of a boundary between the Keyser and Old Port Formations). However, the regressive phase in the Tonoloway Formation. The second is a occurrence and similar magnitude of the positive excursion throughout the transgression through the Byers Island and Jersey Shore Members of the Appalachian Basin suggests that any effect is minimal. Finally, restriction Keyser Formation and a regression through the La Vale Member. The third

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includes a transgression through the New Creek-Corriganville Members of Stretching and squeezing of the section during correlation has the Old Port Formation and part of the Mandata Member and a regression implications for relative rates between the WQ1 section through the remainder of the Mandata, Shriver, and Ridgeley Members. and the New York reference section. Stretching implies a lower Transgressive-regressive cycles interpreted elsewhere in the basin by sedimentation rate, periods of nondeposition or erosion, or higher other researchers were added to Figure 8C using correlation based on for the WQ1 section relative to the New York reference lithology (Formation and Member equivalencies; Fig. 3). They do not, for section, and squeezing implies a higher sedimentation rate or lower the most part, coincide with cycles documented here. One exception is the compaction. For the correlation to be viable, the relative sedimentation cycle interpreted for Keyser-equivalent strata in New York, though this rates implied by the stretching and squeezing factors for the WQ1 section correlation, with no intervening outcrop, is uncertain. The relative and the reference section in New York must make sense for their lowstand at the top of the Keyser Formation also roughly coincides with depositional environments (e.g., lower sedimentation rates for shale than that in the New Creek of the southern outcrop belt, as noted by Saltzman for reefal carbonates is reasonable, whereas the reverse is not). (2002). The overall misalignment of transgressive-regressive cycles across The correlation of the lower, biomicrite part of the La Vale Member of the basin could result from lateral facies changes affecting lithologic the Keyser Formation required squeezing of the WQ1 section and implies a correlations, differential tectonic activity affecting accommodation and higher sedimentation rate there than in the New York section. As this part clastic sediment supply, or both. of the Keyser Formation contains significant skeletal material, it is The positive carbon isotope excursion at the Silurian–Devonian reasonable that its sedimentation rate would be higher than that of the boundary is a global event and should peak at the same time in strata thinly bedded, microbialite, lagoonal described by Husson et al. throughout the Appalachian Basin. The stratigraphic peak of the excursion (2016) for the Manlius Formation. Carbon isotope values in the Tonoloway can therefore be used to test whether the lithologic correlations shown in and lower Keyser Formations are more negative than those at the base of Figure 3 in fact correlate time-equivalent strata; if they do, lithologic the section reported by Husson et al. (2016), indicating that the values correlation of sections with carbon isotope data should show coincident likely correlate with a lower part of the section not sampled by Husson et isotope trends, including the stratigraphic placement of the positive al. (2016). Lacking data to correlate to, we applied the squeezing factor excursion at the Silurian–Devonian boundary. This idea was originally put from the upper Keyser Formation to the data gap and the points from the forth by Husson et al. (2016), who used 206Pb/238U dating of volcanic underlying units, which places these points stratigraphically below the ashes to show that carbon isotope stratigraphy can result in a viable Husson et al. (2016) data. Correlation of the upper, micritic part of the La correlation of the Silurian–Devonian boundary interval across the Vale Member of the Keyser Formation required stretching of the WQ1 Appalachian Basin. section relative to the deeper-water (Laporte 1969) Coeymans Formation of The excursion was first documented in the Appalachian Basin by New York. As this part of the section was deposited in very shallow water Saltzman (2002) at Smoke Hole, West Virginia (Fig. 1), where it peaks at depths, accommodation is expected to have been limited, leading to slow ~5% in the upper Keyser Formation. Husson et al. (2016) resampled that sedimentation or even bypass and erosion (Pomar 2001), which would section at higher resolution, confirmed Saltzman’s (2002) trend, and result in a thinner package than the Coeymans. additionally documented the excursion at four sections in New York where A hiatus between the Keyser Formation and the New Creek-Corrigan- it peaks at ~3.5% in the upper Manlius Formation, ~5.3% in the lower ville Members of the Old Port Formation is necessitated by increasingly Coeymans Formation, and ~3.5% in the lower Kalkberg Formation. To negative isotope values in the New Creek-Corriganville. This is consistent test whether lithology-based correlations (Fig. 3) represent timelines, their with the very shallow water depths and limited accommodation for the carbon isotope data from West Virginia was pinned at underlying unit. The New Creek-Corriganville part of the section in WQ1 boundaries and stretched and squeezed uniformly between those was not stretched or squeezed during correlation. The implied similar boundaries (Fig. 8D). This correlation places the West Virginia excursion depositional rates for this unit and the Coeymans Formation in New York about 14 m stratigraphically below its peak in Winfield Quarry (compare are consistent with their similar shallow-shelf depositional environments blue and black d13C data in Fig. 8D). Uncertainty in the lithologic interpreted herein and by Laporte (1969), respectively. Correlation of the correlation between the northern and southern outcrop belts prohibits Mandata Member, an organic-rich shale, required stretching relative to the reliable correlation with the New York data at this level of detail, though New Scotland Formation open-marine carbonates and Becraft sandstones the excursion would peak higher in the section than at Winfield Quarry in the reference section. This stretching is reasonable because, while shelfal (red bar in Fig. 8D). Husson et al. (2016) also noted that a facies-based carbonates, sandstones, and organic-rich shales can have similar correlation results in an apparently diachronous carbon isotope excursion sedimentation rates (e.g., Walker et al. 1983; Stein 1986), shales compact across the basin. They concluded that it is in fact the formation and more (Baldwin and Butler 1985). Data from the Shriver Member extend member boundaries that are diachronous, as originally suggested by above the part of the section sampled by Husson et al. (2016). In the Rickard (1962) and Laporte (1969), and therefore correlated instead using absence of data to correlate to, they were extended without stretching or carbon isotope stratigraphy. squeezing. The Winfield Quarry section has been added to Husson et al.’s (2016) Note that the correlation presented (Fig. 10) is an interpretation based on carbon-isotope-based correlation by stretching, squeezing, and cutting the the observed carbon isotope trends and that there is some uncertainty isotope curve and accompanying stratigraphic section relative to the inherent in the methodology. have been documented in reference curve in New York (Fig. 10), under the assumption that changes correlative strata, particularly in northern areas (e.g., Ebert and Matteson in d13C occurred at the same time throughout the Appalachian basin. The 2003) and may also complicate interpreted correlations. The Winfield correlation (Fig. 10A) indicates that the Keyser Formation at Winfield Quarry data extend above and below the available data from New York and Quarry is equivalent to the Keyser and Tonoloway Formations in West West Virginia, and correlations in these parts of the section would benefit Virginia and parts of the Rondout, Manlius, and Coeymans Formations in from additional regional data. The peak of the excursion, which occurs New York. The New Creek-Corriganville Members at Winfield Quarry are approximately at the Silurian–Devonian boundary according to Husson et almost entirely equivalent to the New Creek Formation in West Virginia al.’s (2016) preferred interpretation, is better constrained and appears to and parts of the Kalkberg and New Scotland Formations in New York. The correlate well. Mandata Member is equivalent to at least part of the Corriganville Compared to lithostratigraphic correlation, this chemostratigraphic Formation in West Virginia and parts of the Kalkberg, New Scotland, and correlation is more consistent with a conodont biostratigraphy event Becraft Formations in New York. observed by other researchers across the Appalachian Basin. The first

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FIG. 10.—Correlation based on carbon isotope data. Data from this study is in black; New York (red) and West Virginia (blue) data from Husson et al. (2016), except where otherwise specified. Symbols in legend apply to all colors. Vertical scale is normalized stratigraphic position given relative to Husson et al.’s (2016) section H4a, b. A) Stratigraphic sections (lithology) and transgressive-regressive cycles. Lithologies for stratigraphic section WQ1 converted to classification scheme used by Husson et al. (2016) to facilitate combination of these data sets. B) Carbon isotope values on which this correlation is based. Gray shading indicates interpreted oxygen limitation during deposition, with darker shading indicating increasing oxygen limitation. Silurian–Devonian boundary and age data from Husson et al. (2016). FAD I.w.w. is first appearance datum of Icriodus woschmidti woschmidti. LAD O.e.d. is last occurrence datum of elegans detorta. C) Factors by which data in this figure was vertically stretched or squeezed expressed as 1 divided by the stretching or squeezing factor. H1 through H5 refer to Husson et al. (2016) stratigraphic section names. Abbreviations: WV ¼ West Virginia; PA ¼ Pennsylvania; NY ¼ New York; To ¼ Tonoloway; Corr ¼ Corriganville; NC-C ¼ New Creek-Corriganville; Sh ¼ Shriver; Ro ¼ Rondout; Co ¼ Coeymans.

appearance datum (FAD) of I. woschmidti occurs within 2 m of the Similarly, ages from volcanic ashes are more consistent with the Silurian–Devonian boundary and has been used globally to constrain the chemostratigraphic correlation than with lithostratigraphic correlations. An location of that boundary (Denkler and Harris 1988). In the southern ash bed in the Corriganville of West Virginia has been dated as 417.22 Ma, outcrop belt of the Appalachian Basin, this FAD has been documented near and a series of ashes in the uppermost Coeymans and Kalkberg in New the top of the Keyser Formation and in the New Creek Formation (Helfrich York have been dated as 418.42–417.56 Ma (Husson et al. 2016). While 1978; Denkler and Harris 1988). In the northern outcrop belt, it has been documented in the Manlius and Coeymans Formations (Denkler and Harris lithostratigraphic correlation places the New York ashes equivalent to or 1988; Milunich and Ebert 1993; Natel et al. 1996; Kleffner et al. 2009), stratigraphically above the West Virginia ash, chemostratigraphic correla- which lithologic correlation marks as equivalent to units overlying the tion places these ashes in stratigraphic order consistent with their ages Keyser Formation in the southern outcrop belt (Fig. 3). (compare Figs. 3 and 10).

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The transgressive-regressive cycles documented herein record local micrites with mudcracks and tidal bedding, indicating regression and a change in relative sea level from as shallow as supratidal environments to return to an intertidal to supratidal setting; and (3) The New Creek- as deep as below storm wave base. Dorobek and Read (1986) estimated the Corriganville Members of the Old Port Formation are a variety of shallow- water depth of storm wave base at this time in the Appalachian Basin as water facies that, above a basal bed of in situ stromatolites, lack indicators 50–60 m or deeper, on the basis of thicknesses of sedimentary packages of subaerial exposure or tidal influence; this records transgression to a from which they approximated the slope of the Appalachian Basin ramp subtidal, above fair-weather wave base setting. An abrupt shift to mainly (10–15 cm/km). Haq and Schutter (2008) show a maximum of ~80 m of black, barren shales in the lower Mandata Member indicates rapid global sea-level change for third-order fluctuations through the latest deepening to an oxygen-limited environment below storm wave base. Silurian and earliest Devonian (Pridolian and ). Therefore, Upper Mandata Member mainly gray shales with Chondrites traces and a from the local record of relative sea-level change alone, it is possible that limited fossil assemblage and Shriver Member micrites with Zoophycos the transgressive-regressive cycles at WQ1 are the result of eustatic sea- traces were deposited under continued but decreasing levels of oxygen level change. However, if eustasy was the primary driver, relative sea-level limitation, likely related to regression. This trend culminates with a return cycles would be coincident throughout the Appalachian Basin, and the to normal marine conditions, as shown in Ridgeley Member biomicrites chemostratigraphic correlation does not support this scenario (Fig. 10A). deposited below fair-weather wave base. Comparing the transgressive-regressive cycles in light of the chemostrati- The Klonk Event positive carbon isotope excursion is recorded in graphic correlation presented herein, a maximum transgression in the central Pennsylvania as a rise from a minimum of -4.3% in the Tonoloway Keyser Formation was synchronous through at least the southern outcrop Formation to a high of þ4.4% in the upper part of the La Vale Member of belt. Another maximum transgression in the Mandata Member appears to the Keyser Formation, then a drop .5% to a low in the Mandata Member coincide with that in the Kalkberg-New Scotland Formations of New York. of the Old Port Formation. Using trends observed in this globally Otherwise, transgressive-regressive cycles do not appear to correlate across coincident data to correlate regionally, following methodology from the basin. We therefore conclude that local factors such as tectonics and Husson et al. (2016) and incorporating their data, shows that the Keyser sediment supply were the dominant control on depositional patterns in the Formation is equivalent to the Keyser and Tonoloway Formations in West Appalachian Basin at this time. Virginia and parts of the Rondout, Manlius, and Coeymans Formations in A positive carbon isotope excursion requires either addition of 13Cor New York. The New Creek-Corriganville Members at Winfield Quarry are removal of 12C. As a possible cause of the Klonk excursion, Malkowski mostly equivalent to the New Creek Formation in West Virginia and parts and Racki (2009) suggested that the expansion of land plants resulted in of the Kalkberg and New Scotland Formations in New York. The Mandata burial of organic matter rich in 12C in epicontinental seas. The Winfield Member is equivalent to at least part of the Corriganville Formation in section records oxygen limitation and enhanced burial of organic matter in West Virginia and parts of the Kalkberg, New Scotland, and Becraft the Mandata Member. However, that unit is 9 m above the peak of the Formations in New York. This new correlation is more consistent with positive isotope excursion, having been deposited after rather than before other time-correlative markers, including conodont biostratigraphy and or during the excursion as would be expected for organic-rich units that volcanic-ash chronostratigraphy. could have contributed to the positive excursion. Saltzman (2002) noted Interpreted transgressive-regressive trends do not match between West that the carbon isotope excursion in West Virginia coincides with a relative Virginia, Pennsylvania, and New York when correlated using existing sea-level lowstand and suggested that the lowered sea level could have lithostratigraphic correlation or the carbon-isotope correlation presented exposed and caused increased erosion of 13C-rich Silurian carbonate strata. here incorporating data from Pennsylvania. It is inferred that local The correlation presented herein using carbon isotope data does not show a (tectonics, sediment supply) rather than global (eustatic) controls synchronous lowstand throughout the Appalachian Basin (Fig. 10A). dominated depositional patterns in the Silurian–Devonian boundary However, because transgressive-regressive cycles appear to reflect local interval in the Appalachian Basin. rather than regional or global sea-level changes, a finer scale than the forces that would have governed global carbon isotope trends, this does not ACKNOWLEDGMENTS disprove Saltzman’s (2002) hypothesis. Additional stratigraphic studies reporting high-resolution isotopic, geochronologic, and lithologic data Thank you to Eastern Industries for allowing access to their quarry, without from late Silurian–Early Devonian sections are needed to fully characterize which this project would not have been possible, and especially Albert Mabus and interpret the Klonk excursion. who facilitated that access daily. Many thanks to Dr. Patrick McLaughlin for his important scientific contributions and guidance. Drs. Carmala Garzione and Penny Higgins at the University of Rochester generously provided time and CONCLUSIONS guidance during geochemical analyses. The Geological Society of America At a time when global atmospheric and surface-water oxygen levels provided financial support for analyses. Dr. Tony Ekdale helped classify trace were rising, there is evidence for oxygen limitation in the Appalachian fossils, and Dr. Carl Brett helped classify macrofossils. Special thanks to Eric Lynch for his numerous contributions in the field and lab. Thank you also to Dr. Basin. Strata at Winfield Quarry are interpreted to document a range of Matthew Saltzman and an anonymous reviewer for their thoughtful reviews of depositional oxygenation conditions. Normal marine conditions are this manuscript. interpreted for biomicrite with abundant, diverse fauna. Progressively lower oxygenation is interpreted for facies from gray micrite with Zoophycos burrows to gray shale with Chondrites burrows and limited, SUPPLEMENTAL MATERIAL sparse fauna to black, barren shale. Data are available from the PALAIOS Data Archive: Facies distribution in the stratigraphic section reveals parts of three https://www.sepm.org/supplemental-materials. transgressive-regressive cycles: (1) The Tonoloway Formation with intertidal to supratidal laminated, mudcracked, evaporitic micrites REFERENCES represents the tail end of a regression; (2) The Byers Island and Jersey Shore Members of the Keyser Formation are biomicrites with sponge- BALDWIN,B.AND BUTLER, C.O., 1985, Compaction curves: American Association of coral-crinoid biostromes that indicate a return to normal marine conditions Bulletin, v. 69, p. 622–626. BELAK, R., 1980, The Cobleskill and Akron Members of the Rondout Formation: late and overall transgression. The La Vale Member of the Keyser Formation Silurian carbonate shelf sedimentation in the Appalachian Basin, New York State: contains fossils that are increasingly abraded upsection and culminates in Journal of Sedimentary , v. 50, p. 1187–1204.

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