SEDIMENTOLOGY AND CARBON ISOTOPE ( 13C) STRATIGRAPHY … · sedimentology, paleontology, and stratigraphy, and (3) use the chemo-stratigraphic-lithostratigraphic framework to improve

PALAIOS, 2019, v. 34, 405–423

Research Article

DOI: http://dx.doi.org/10.2110/palo.2019.020

SEDIMENTOLOGY AND CARBON ISOTOPE (d13C) STRATIGRAPHY OF SILURIAN–DEVONIAN

BOUNDARY INTERVAL STRATA, APPALACHIAN BASIN (PENNSYLVANIA, USA)

ANYA V. HESS1, 2AND JEFFREY M. TROP1

1Department of Geology and Environmental Geosciences, Bucknell University, Moore Avenue, Lewisburg, Pennsylvania 17837, USA2Department 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 majorperturbation of the carbon cycle, the global Klonk Event, one of the largest carbon isotope excursions during thePhanerozoic. In the Appalachian Basin, these marine strata record the regional buildup to the Acadian Orogeny. Thisstudy reports new sedimentologic, paleontologic, ichnologic, and carbon isotope data from an exceptional quarryexposure in central Pennsylvania, USA, a historically understudied area between better-documented outcrops.500 km away to the southwest (West Virginia, Virginia, Maryland) and northeast (New York). Facies spanning thecontinuous 113-m thick outcrop are dominantly carbonate and fine-grained siliciclastic strata interpreted as beingdeposited in supratidal through subtidal environments, including oxygen-limited environments below storm wavebase. They record parts of three transgressive-regressive cycles, in the (1) upper Silurian Tonoloway Formation,(2) upper Silurian–Lower Devonian Keyser Formation through lower Mandata Member of the Old Port Formation,and (3) Lower Devonian Mandata through Ridgeley Members of the Old Port Formation. Micrite matrix d13Ccarb

analyses exhibit a large, positive d13Ccarb excursion (.5% amplitude). Outcrops of this interval in the AppalachianBasin occur in two belts, between which correlation has been historically challenging. The regional correlationpresented herein is based on carbon-isotope trends and is more consistent with published conodont biostratigraphyand 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 localcontrols (tectonics, sediment supply) rather than global (eustasy) dominated depositional patterns in the Silurian–Devonian boundary interval in the Appalachian Basin.

INTRODUCTION

The Silurian–Devonian transition was a time of major change in the

global biosphere. Vascular land plants had evolved by the late Silurian and

diversified rapidly in the Devonian. In the late Silurian–Early Devonian,

arthropods transitioned to land and impacted soil development (Kenrick et

al. 2012). These changes coincided temporally with an overall increase in

atmospheric oxygen that led to a peak in atmospheric oxygen content

(Lenton et al. 2016; Lu et al. 2018). In the Appalachian Basin, the

Silurian–Devonian boundary interval has recently been the focus of

renewed interest as the advent of modern techniques (uranium-lead

geochronology, carbon isotope chemostratigraphy) allows for more

advanced, quantitative analysis (Kleffner et al. 2009; Husson et al. 2016;

McAdams et al. 2017).

A major perturbation to the carbon cycle, the Klonk Event, is also

recorded at the Silurian–Devonian boundary, as a significant carbon

isotope excursion. Carbon isotope analyses of bulk marine carbonates

(d13Ccarb) document a positive carbon isotope excursion as much as 7% in

amplitude, making it one of the largest such excursions during the

Phanerozoic. The excursion has been documented in sections around the

world: the United States in the Great Basin of Nevada and Utah (3.0%;

Saltzman 2002, 2005) and the Arbuckle Mountains of Oklahoma (3.3%;

Saltzman 2002); the Czech Republic and France (3.8–4.0%; Buggisch and

Mann 2004; Buggisch and Joachimski 2006); and Ukraine (.6%;

Malkowski et al. 2009). The similar shape and magnitude of the d13Ccarb

excursions has led previous workers to argue that it represents a

perturbation to the global carbon cycle, with rising values in d13Ccarb

representing the evolving isotopic composition of global dissolved

inorganic carbon (d13CDIC). Proposed drivers of the Klonk Event include

global regression and the weathering of exposed, isotopically heavy

Silurian carbonate platforms (Saltzman 2002) or enhanced burial of

organic carbon from newly evolved terrestrial biota (Malkowski and Racki

2009). However, coupled chemostratigraphic-sedimentologic studies

spanning Silurian–Devonian strata needed to evaluate these potential

drivers are generally lacking.

The carbon isotope excursion has been of recent interest in the

Appalachian Basin, where it was originally documented in West Virginia

(7%; Saltzman 2002; Husson et al. 2016) and more recently in New York

(Husson et al. 2016). However, there still exists a geographic gap of .500

km between Appalachian Basin sites (Fig. 1). The Silurian–Devonian

boundary interval has been understudied in most of Pennsylvania,

particularly with regards to modern methods, for a number of reasons.

Temporally, the period boundary is a natural stopping point, and many

studies are restricted to either Silurian (e.g., Smosna and Patchen 1978;

Brett et al. 1990; Bell and Smosna 1998; McLaughlin et al. 2012) or

Devonian strata (e.g., Diedrich and Wilkinson 1999; Ver Straeten 2007,

2008; Ver Straeten et al. 2011). Geographically, outcrops occur in two

belts, a northern belt in New York and parts of New Jersey and

northeastern-most Pennsylvania, and a southern belt spanning the Virginia-

West Virginia border, the western tip of Maryland, and southern and central

Pennsylvania (Fig. 1). Outcrops in central Pennsylvania are generally poor

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since they are less resistant to weathering. Many previous studies are

restricted to either the New York-New Jersey part of the northern outcrop

belt (e.g., Epstein et al. 1967; Kleffner et al. 2009) or the Virginia-West

Virginia-southernmost Pennsylvania part of the southern outcrop belt (e.g.,

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, paleontology, 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 deposition. The foreland basin first formed in the

Middle Ordovician, when the Taconic orogeny marked initial closure of the

Iapetus Ocean and collision of an island arc with eastern Laurentia.

Taconic deformation in New England was most intense from ~496 to

~428 Ma, with metamorphism and roughly coincident development of the

foreland basin ranging from ~480 to ~455 Ma in the southern

Appalachians and New England (Hatcher 2010 and references therein).

The Silurian–Devonian transition in the Appalachian Basin was a time

of diminished clastic input that allowed marine organisms to flourish,

resulting in a variety of carbonate facies throughout the basin (e.g., Laporte

FIG. 1.—Map of the eastern United States showing outcrop belts of Silurian–

Devonian boundary interval strata (compiled from King et al. 1974; Denkler and

Harris 1988; Miles 2003; Kleffner et al. 2009). Circles indicate sites of existing

carbon isotope studies from this interval.

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.

A.V. Hess and J.M. Trop406 P A L A I O S


1969; Dorobek and Read 1986). In the central Appalachians, where this

study focuses, the late Silurian through Early Devonian historically has

been considered a time of tectonic quiescence between the Taconic and

Acadian orogenies (Rodgers 1967; Johnson 1971; Dorobek and Read

1986). However, some researchers have suggested that Acadian orogenesis

began as early as the late Silurian and would therefore have coincided with

deposition of the strata discussed herein (Ebert and Matteson 2003; Ver

Straeten 2007).

During the Acadian orogeny, a series of terranes collided with the

northern part of the eastern margin of Laurentia. This transpressional,

zippered collision progressed southward through time, affecting areas from

present-day Newfoundland through Georgia. It culminated in the closure of

the Rheic ocean when Baltica (present-day Europe) collided with Laurentia

in the early part of the Mississippian (~345 Ma) (Ver Straeten 2009;

Hatcher 2010 and references therein).

Stratigraphy

The exposure at Winfield Quarry includes the upper Silurian Tonoloway

Formation, upper Silurian to Lower Devonian Keyser Formation, and

Lower Devonian Old Port Formation (Fig. 3). These formation

designations have been adopted from Inners (1997), the most detailed

existing study of upper Silurian–Lower Devonian strata in central

Pennsylvania. The Keyser Formation is divided into the Byers Island,

Jersey Shore, and La Vale Members (Head 1969). The Old Port Formation

is divided into the New Creek-Corriganville, Mandata, and Ridgeley

Members (Inners 1997). Stratigraphic nomenclature used in Pennsylvania

for this interval is broadly similar to that used throughout the southern

outcrop belt but differs significantly from that used in the northern outcrop

belt (Fig. 3).

The Tonoloway Formation consists of evaporitic shelfal carbonates and

is correlative in the subsurface to thick halites and anhydrites in West

Virginia and New York (Smosna et al. 1976; Mount 2014). Strata

immediately overlying the Tonoloway are regionally referred to as the

Helderberg Group, but this can be problematic for correlation as the term

encompasses different formations and members in the southern and

northern outcrop belts (Fig. 3) (e.g., compare Rickard 1962 with Dorobek

and Read 1986), and the term is not used herein.

In West Virginia, Virginia, and Maryland, the contact between the

Keyser and Tonoloway Formations is unconformable at the basin edges

and conformable in the basin center. The Keyser Formation is broken into

three members (Fig. 3). Lowermost is the Byers Island Member, which

consists of fossiliferous, nodular carbonates. The overlying Jersey Shore

Member contains a variety of carbonate facies with diverse fossil

assemblages but is distinguished by its abundant coral-stromatoporoid

buildups along the basin margins. Finally, the La Vale Member is a

laminated, mudcracked carbonate with minor stromatoporoid biostromes

(Head 1969).

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.

SEDIMENTOLOGY AND ISOTOPE STRATIGRAPHY OF SILURIAN–DEVONIAN STRATAP A L A I O S 407


In the southern outcrop belt, the Byers Island Member is termed the

lower Keyser Formation (Fig. 3) and is aggradational open-marine

carbonates with skeletal banks around the basin edges and bioturbated,

nodular carbonates toward the basin center. Skeletal banks consist of coral-

stromatoporoid mud mounds and framestones. The middle part of the

Keyser Formation in West Virginia is regressive Clifton Forge sandstones

on the eastern basin margin and grades basinward into the Big Mountain

shale and correlative skeletal carbonates (Dorobek and Read 1986). These

clastic units do not extend into Pennsylvania (Head 1969) and their

correlation to the carbonate succession there is ambiguous (e.g., compare

Head 1969 and Dorobek and Read 1986). The La Vale Member is

equivalent to the upper Keyser Formation in the southern outcrop belt,

which consists of transgressive skeletal carbonates and contains coral-

stromatoporoid mud mounds and framestones (Dorobek and Read 1986).

The Old Port Formation consists of four members in Pennsylvania, in

stratigraphic order from oldest, the New Creek-Corriganville, Mandata,

Shriver, and Ridgeley Members (Inners 1997) (Fig. 3). The New Creek

Member consists of regressive skeletal banks. The Corriganville Member

is a transgressive cherty carbonate. The Mandata and Shriver Members are

transgressive basinal shales and transgressive-to-regressive cherty carbon-

ates, respectively. The Ridgeley Member is a basin-wide sandstone that

represents the first substantial influx of clastic sediment resulting from the

Acadian Orogeny in the central Appalachian Basin (Dorobek and Read

1986).

Outside of Pennsylvania, the term Old Port Formation is not used and its

members correspond to named formations. In Maryland, the New Creek

Formation interfingers with the uppermost Keyser Formation and is

equivalent to the Elbow Ridge sandstone at the eastern edge of the basin.

The Corriganville Member is equivalent to the Healing Springs sandstone

at the eastern edge of the basin in Virginia. The Mandata and Shriver

Members are equivalent to cherty carbonates of the Licking Creek

Formation nearer the basin margin in the southern outcrop belt. Outside of

central Pennsylvania, the Ridgeley Member is equivalent to the Oriskany

Formation.

The northern outcrop belt is oriented parallel to depositional dip, with

more proximal facies to the west. Facies are time transgressive and timelines

typically span multiple formations or members (Rickard 1962; Laporte

1969; Husson et al. 2016). The Cobleskill Formation (Fig. 3) consists of

massive, fossiliferous carbonates, including stromatoporoids and corals, and

grades westward to less fossiliferous, thin-bedded dolomites. The Rondout

and Manlius Formations represent a transgressive-regressive cycle consist-

ing of shallow-water stromatolites and stromatoporoid-coral biostromes and

bioherms and associated lagoonal facies (Rickard 1962; Laporte 1969;

Belak 1980). The Coeymans, Kalkberg, and New Scotland Formations are

progressively deeper water facies, transitioning to open marine by the

Kalkberg and New Scotland Formations (Laporte 1969).

Regional Stratigraphic Correlations

The units discussed above have been correlated thus far mainly using

lithostratigraphy (Fig. 3). The Keyser Formation is typically correlated in

the northern outcrop belt to portions of the Cobleskill, Rondout, and

Manlius Formations, and the Old Port Formation is typically correlated to

portions of the Manlius, Coeymans, Kalkberg, and New Scotland

Formations (Head 1969; Laporte 1969).

Conodont biostratigraphy, volcanic ashes, and carbon isotope stratigra-

phy have also aided correlation of this complicated stratigraphy. Based on

the first occurrence of the conodont Icriodus woschmidti, the Silurian–

Devonian boundary has been placed in the upper Keyser Formation in

Virginia and West Virginia (Helfrich 1978; Denkler and Harris 1988). In

the northern outcrop belt, it has been variously placed in the Rondout

Formation (Denkler and Harris 1988), the lower Coeymans Formation

(Tucker et al. 1998), and either within the Manlius Formation or between

the Coeymans and Kalkberg Formations (Kleffner et al. 2009, using

combined biostratigraphy and carbon isotope stratigraphy).

Volcanic ashes (bentonites) have been used to correlate the Silurian–

Devonian strata over limited distances (e.g., Rickard 1962; Smith and Way

1988). In the southern outcrop belt, Smith and Way (1988) first described a

set of three ash beds that occur in the Corriganville (Bald Hill Bentonites A

and B) and Mandata (Bald Hill Bentonite C) Members of the Old Port

Formation at the type section near Hollidaysburg, Penn., 84 miles west-

southwest of Winfield Quarry. In the northern outcrop belt, the Kalkberg

Bentonite, an ash bed in the New Scotland Formation, has been dated by

McAdams et al. (2017) using U-Pb analysis of zircons, placing it in the

middle Lochkvian (Early Devonian) at 417.6160.12 Ma. Smith and Way

(1988) correlated this bed to their Bald Hill Bentonite A in the

Corriganville Member of the southern outcrop belt. McAdams et al.

(2017) note, however, that the number of volcanic ash beds in the Lower

Devonian of the Appalachians makes correlation of individual beds

potentially problematic.

Carbon isotope stratigraphy was recently used by Husson et al. (2016) to

correlate between a section in West Virginia and four sections in New York.

Their correlation shows that facies and the stratigraphic packages based on

them are diachronous across the basin, that the Keyser Formation is

correlative with the Rondout, Manlius, and parts of the Coeymans

Formations of New York, and that the New Creek-Corriganville Members

are correlative with the Kalkberg, New Scotland, and Becraft Formations

of New York. The Winfield Quarry section provides an opportunity to

refine this correlation between the northern and southern outcrop belts.

Field Site

The field site for this study is a quarry approximately 2 km west of

Winfield, Pennsylvania, in Union County (N 40.898168, W 076.893078)

(Fig. 2). It was active a few years prior to the data collection phase,

providing a fresh rockface. It was inactive during the data collection

phase of this project (2007) and has since been reopened; the base of the

original section has been removed. A well-exposed stratigraphic section

(WQ1) was measured on a bed-by-bed basis using a Jacob’s staff at the

west end of the quarry. Refer to Hess (2008) for an additional, less

extensive section spanning only the Old Port Formation. The stratigraphic

section and geochemical data from the western exposure are discussed

herein.

Geochemical Methodology

A total of 63 micrite samples were analyzed from the lower 88 m of the

WQ1 section, spanning the Tonoloway Formation through the Shriver

Member of the Old Port Formation. Only samples devoid of fossil

fragments, fractures, and veins were selected. Rock samples were broken

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-

coated drill bit, while continually monitoring to ensure no material other

than micrite was sampled. Powder was deposited and sealed directly into

glass vials. Between samples, the rock hammer and drill bit were sanitized

using a solution of 10%-diluted hydrochloric acid.

Isotope analyses were conducted in the Stable Isotope Ratios in the

Environment, Analytical Laboratory (SIREAL) in the Department of Earth

and Environmental Science at the University of Rochester. Samples were

pretreated with 30% H2O2 to remove organic material, followed by three

rinses with deionized water and a final rinse with methanol. Analyses were

run on a Thermo Electron Corporation Finnegan Delta plus XP mass

spectrometer in continuous-flow mode via the Thermo Electron Gas Bench

peripheral and a GC-PAL autosampler. Samples were loaded into 4mL tubes

with pierceable, self-healing rubber septa with PTFE liners. Tubes were then

flushed with UHP helium at about 100 mL/minute for 10 minutes.



100% phosphoric acid was injected through the septum manually with a 16-

gauge needle and syringe. All samples were vortexed to insure complete

mixing of the sample and the acid. Tubes were loaded into a block heated to

708C. Samples reacted for at least 45 minutes but never more than 12 hours

before they were analyzed. Carbon dioxide gas evolved from the reaction

with the acid was then drawn into the instrument for analysis. Carbon and

oxygen isotopic results are reported in permil relative to VPDB (Vienna Pee-

Dee Belemnite) and normalized (Coplen 1994) on scales such that the

carbon and oxygen isotopic values of NBS-19 are 1.95 permil and -2.2

permil, respectively, carbon and oxygen isotopic values of NBS-18 are -5.01

permil and -23 permil, respectively, and the carbon isotopic value of

L-SVEC is -46.6 permil. Average precision (1-sigma) is 0.06 and 0.10 for

carbon and oxygen isotopes, respectively. For repeat analyses, the average of

the carbon and oxygen isotope values is discussed herein.

SEDIMENTOLOGY

Facies

Sedimentary facies are defined on the basis of lithology, sedimentary

structures, paleontology, and ichnology, particularly as they relate to the

interpretation of depositional environments. Winfield Quarry strata consist

of four lithologies: micrite, biomicrite and biosparite, sandy intrabiosparite,

and shale. Seven sedimentary facies representative of different depositional

environments are identified on the basis of lithology, sedimentary

structures, ichnofabrics, and fossils (Table 1, Figs. 4, 5). See Hess

(2008) for additional photographs of facies and fossils.

Massive Micrite Facies (F1a).—The massive micrite facies is

characterized by a lack of fossils and physical sedimentary structures,

though some instances contain low-diversity, high-abundance ichnologic

assemblages of Chondrites and Zoophycos trace fossils (Fig. 4A, 4B). The

majority of this facies is interpreted as having been deposited in low-

energy, subtidal environments below storm wave base. The lack of body

fossils indicates an inhospitable environment. Zoophycos has been linked

to low-oxygen, though not entirely anoxic, conditions (Marintsch and

Finks 1978; Bromley and Ekdale 1984), especially when they occur in high

abundance and low diversity, as here. While Chondrites and Zoophycos

traces in more recent deposits occur in deep water, Paleozoic strata with

these traces can have formed in a variety of water depths, from lagoonal to

below storm wave base (Ekdale 1988; Frey et al. 1990). On the basis of its

thickness (~20 m) and association with relatively deep water under- and

overlying units, the package of this facies with Chondrites and Zoophycos

traces is interpreted as having been deposited below storm wave base, in

oxygen-limited conditions (Fig. 6). For micrites lacking trace fossils, their

environmental interpretation is based on the sedimentology and paleon-

tology of interbedded lithofacies, with some units deposited in waters

potentially as shallow as the intertidal zone. Refer to the Inferred

Depositional Setting and Relative Sea-Level Fluctuations section for more

details.

Micrite with Sedimentary Structures Facies (F1b).—The micrite

with sedimentary structures facies is characterized by the presence of

physical and organic sedimentary structures including mudcracks,

evaporites, heterolithic bedding, intraclasts, sparse fenestrae, stromato-

lites, and cryptalgal laminae (Fig. 4C–4F). Stromatolites and cryptalgal

laminae are domal on a millimeter to decimeter scale. In one instance,

stromatolites form a continuous layer of laminated, low-domal mounds.

Laminae thicken toward the crests of mounds (Fig. 4G), a key indicator

of microbial origin (Riding 1999), and these are interpreted as in situ

stromatolite mounds under Riding’s (1999) definition. They are the

‘‘laterally linked hemispheroids’’ type of Logan et al. (1964), which in the

modern of Shark Bay, Australia, form in protected, low-energy, intertidal

settings. A similar environment is inferred for in situ stromatolites at

Winfield Quarry.

This facies contains a low-diversity assemblage of unabraded fossils,

chiefly eurypterids, gastropods, and ostracods. This suite of sedimentary

structures indicates deposition in an environment that was above fair-

weather wave base (symmetrical ripple laminae), within the photic zone

(stromatolites and cryptalgal laminae), within the tidal range (heterolithic

bedding), with intermittent subaerial exposure (mudcracks) and more

extended periods of exposure in the supratidal zone (evaporites). Not all

sedimentary features are present in all instances of this facies, and specific

depositional environments are interpreted for units on a case-by-case basis

(refer to Inferred Depositional Setting and Relative Sea-Level Fluctuations

section).

Biomicrite to Biosparite Facies (F2a).—The biomicrite to biosparite

facies is characterized by the presence of megascopic fossils or fossil

fragments in a micrite matrix (Fig. 4H, 4I). Fossils are open-marine fauna

consisting of gastropods, brachiopods, bivalves, bryozoans, rugose corals,

crinoids, and sparse ostracods. In many instances, fossils are concentrated

in pods likely formed by bioturbation or winnowing of fines. In some

instances, weathered surfaces appear mottled (Fig. 4H), also possibly

resulting from bioturbation. The varying degrees of abrasion and

orientation of fossils indicate deposition in open marine settings from

subtidal but above fair-weather wave base, for beds with highly abraded

fossils, to lower energy environments between fair-weather and storm wave

base, for beds with abundant unabraded fossils. Some instances contain

symmetrical ripples (Fig. 4J), indicating deposition above fair-weather

wave base.

Some beds contain cm-scale fining-upwards successions, which form

under waning-flow conditions, and could be interpreted as either tidal

channels near to where the fossils were abraded or as turbidity flows

formed below normal wave base and distal to the environment in which the

fossils were abraded. From the association of these beds with relatively

shallow facies and their lack of definitive deep-water indicators, they are

interpreted as tidal-channel deposits (refer to Inferred Depositional Setting

and Relative Sea-Level Fluctuations for more details).

Sponge-Coral-Crinoid Biomicrite to Biosparite Facies (F2b).—The

sponge-coral-crinoid biomicrite to biosparite facies is characterized by the

presence of sponges (stromatoporoids) and(or) corals (Fig. 4K, 4L).

Stromatoporoids are discontinuous, overturned, and abraded, in some

places including oncolites with concentric growth strata (Fig. 4L). These

deposits also contain tabulate and rugose coral, crinoids, and highly

abraded, unidentifiable fossil fragments. These are interpreted as reef-

flank deposits formed in an environment with sufficient wave energy to

rotate oncoids and abrade fossils, above fair-weather wave base and

within the photic zone. Some intervals contain shale partings, which may

indicate slack water suspension fallout associated with tides or lulls in

wave energy. While no framework reefs are present in Winfield Quarry

strata, they have been documented in correlative strata (e.g., Cole et al.

2015).

Sandy Intrabiosparite Facies (F3).—The sandy intrabiosparite facies

consists of coarse-sand- to granule-size quartz and calcareous clasts with

sparse disarticulated brachiopods and crinoid ossicles (Fig. 5A). The lack

of finer grained sediments indicates that wave energy was sufficient to

winnow away mud-sized particles from the depositional environment. This

facies is interpreted as having been deposited in an open marine, above

fair-weather wave base environment.

Shale with Fossils and Ichnofabrics Facies (F4a).—The shale with

fossils and ichnofabrics facies is a medium to dark gray shale and



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te,

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or

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,

intr

acla

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se

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mock

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trae

none

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enot

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ts,

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pte

rids,

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mat

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tes

shal

epar

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shal

es

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pra

tidal

2a:

Bio

mic

rite

to

bio

spar

ite

(spar

se)(

intr

a)bio

mic

rite

to(i

ntr

a)bio

spar

ite

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ked

(intr

a)

bio

mic

rite

,non-

to

ver

yar

gil

lace

ous

thin

toth

ick

tabula

rto

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rpods

and

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conti

nuous

ban

ds

of

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rite

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reev

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tes,

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terb

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none

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te

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le

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ale

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czo

ne

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intr

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upw

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none

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ther

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e

4a:

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ew

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ils

and

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silt

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tes,

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t

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N/A

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ow

storm

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ebas

e,

oxygen

lim

ited

4b:

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ren

shal

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cksh

ale

thin

tabula

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ssil

enone

none

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bra

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rval

N/A

low

ener

gy,

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ther

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ebas

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lim

ited

aD

r.T

ony

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man

ytr

ace

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ils.

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arl

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enti

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man

ym

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oss

ils.

cId

enti

fiab

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ssil

sin

clude

Dis

com

yort

his

,A

crosp

irif

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.m

urc

his

oni,

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uch

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lla

cf.

bra

chyp

rion

,C

ost

elli

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uli

ari

s,L

epto

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lite

s,poss

ibly

Mer

iste

lla

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is,

Pen

tam

erus

cf.

gyp

idula

,an

d

‘‘S

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ort

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na.

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enti

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lefo

ssil

sin

clude

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ira

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hto

ma

,A

ctin

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ria

cf.

com

munis

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ale

gin

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ibly

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all,

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row

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(Ste

norh

ynch

us)

,C

honost

rophie

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ena

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ali

s,

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iculo

idea

cf.

dis

ca,

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rsel

laper

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ans,

and

Dis

com

yort

his

.



siltstone with fossils, including ostracods and very sparse mollusks and

brachiopods, and in many instances intense Chondrites bioturbation (Fig.

5B, lower three-quarters of Fig. 5C). Fossils include Orbiculoidea and

nuculid bivalves, which can indicate an oxygen-limited environment

(Brett et al. 1991). The Chondrites ichnofacies is also common in

oxygen-limited areas, even exceeding Zoophycos in the degree of dysoxia

it can tolerate (Bromley and Ekdale 1984). This facies therefore

represents deposition in an environment below storm wave base in

oxygen-limited waters (Fig. 6).

Barren Shale Facies (F4b).—The barren shale facies is characterized

by dark gray to black shale lacking macrofossils and biogenic and

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)

Evaporite 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.



sedimentary structures (upper quarter of Fig. 5C). The dark color of this

facies is likely due to high concentrations of organic material, and it

may therefore represent oxygen-limited conditions that would have

precluded the presence of bacteria able to break down this organic

matter. The lack of fossils and biogenic structures supports this

interpretation (Bromley and Ekdale 1984), and this facies is interpreted

to represent the most oxygen-deprived environment preserved in the

WQ1 section (Fig. 6). The lack of sedimentary structures indicates

deposition in a low-energy environment. While these conditions can

occur in both lagoonal and offshore settings well below the influence of

fair-weather and storm wave base, regional correlation of the Mandata

Member, in which a large part of the facies occurs, indicates that it is a

deep-water equivalent of sands being shed from the mountains to the

east (Smosna 1988).

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.



Instances of this facies outside of the Mandata Member are thin (,2 m)

and are associated with shallower-water facies. One contains abundant

lingulid brachiopods, which are associated with nearshore dysaerobic

environments (Kammer et al. 1986), and the low-diversity, high-abundance

assemblage indicates a stressed environment, perhaps due to changes in

oxygenation or salinity. These units are interpreted as representing

dysaerobic, below-fair-weather wave base environments, shallower water

than for the bulk of this facies.

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 brachiopod 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.

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.



Possible Volcanic Ash.—In addition to the sedimentary facies, eight

beds of what may be bentonites (altered volcanic ash) are also preserved in

WQ1. They are thin (,10-cm thick), clay-rich (sticky when wetted), and

weather bright orange, often leaching color to underlying beds (Fig. 5D).

The thickest horizon, in the Mandata, was sampled and yielded doubly

terminated euhedral zircons (see Online Supplemental File) indicative of

airfall ash.

Inferred Depositional Setting and Relative Sea-Level Fluctuations

This section summarizes the stratigraphic distribution of the facies

documented in the previous section (Fig. 7) and relative sea-level

fluctuations inferred from the upsection facies changes (Fig. 8A–8C).

Tonoloway Formation.—The base of WQl consists of ~7 m of

Tonoloway Formation laminated micrite (F1b; Fig. 7). Laminae show the

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



FIG. 8.—Stratigraphy, relative sea level, transgressive-regressive cycles, and geochemistry 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



convex geometry of cryptalgal laminae and stromatolites, evaporites, and

mudcracks are also abundant. Laminae are lacking in some portions of this

stratigraphic package. Identifiable fossils are for the most part limited to

sparse ostracods, with unidentifiable fossil fragments also present. These

strata are interpreted to represent deposition in shallow-water intertidal to

supratidal environments, including carbonate tidal flats (Fig. 8B).

An exposure ~580 m along strike from the base of section WQ1 along

the north wall of Winfield Quarry contains an exceptionally well-preserved

eurypterid Lagerstatte ~2 m below the top of the Tonoloway Formation

(Vrazo et al. 2014). The exceptional exposure in the quarry allowed for

physical tracing of this bed to the WQ1 section. Upon close inspection, two

partial eurypterid fossils of the taxa noted by Vrazo et al. (2014;

Eurypterus cf. remipes) were found in the Tonoloway Formation of WQ1

and it is likely that the 3.2-m-thick covered section 2 m below the contact

between the Tonoloway and Keyser Formations correlates to the Lager-

statte exposed along strike within Winfield Quarry.

In the uppermost 1.5 m of the Tonoloway Formation, sedimentary

structures are lacking and the concentration of evaporites gradually

decreases. The boundary between the Tonoloway and the Byers Island

Member of the Keyser Formation is marked by an increase in fossil

abundance and diversity from sparse ostracods in the Tonoloway to

bryozoans, brachiopods, bivalves, gastropods, ostracods, and rugose

corals typical of F2a in the Keyser. This transition is gradational from 5.9

to 7.6 m and the formation boundary is picked at 7.6 m in WQ1, the point

where the rate of increase in fossil abundance slows. The loss of

evaporites and mudcracks and the increasing fossil abundance and

diversity indicate freshening and minor relative sea-level rise across the

contact between the Tonoloway and Keyser Formations.

Keyser Formation Byers Island Member.—The Byers Island

Member is distinguished by the nodularity of its beds (Head 1969). It is

biomicrite (F2a) with normal marine fauna and is interpreted to represent

deepening to a subtidal above fair-weather wave base environment. The

upper contact of this member is chosen at 12.8 m, where consistently

nodular strata become more sporadically nodular.

Keyser Formation Jersey Shore Member.—Fossils in the nodular

biomicrite (F2a) of the Jersey Shore Member are fragmented and randomly

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).

Two stromatoporoid-bearing units (F2b) are at 17–18 m and 26–31 m, and

the lower contains oncoids while the upper contains fragmented fossils that

become increasingly abundant and diverse upsection. The covered section

at 23–26 m is exposed in nearby parts of the quarry, where it contains

stromatoporoids, Favosites corals, and abundant crinoid ossicles; it is

inferred to also be facies F2b. The presence of oncoids and stromatop-

oroids indicate that these formed in a high-energy environment within the

photic zone during continued relative sea-level rise. As the corals and

stromatoporoids are mainly not in life position, these units are interpreted

as reef-margin deposits that would have formed adjacent to reefs. Above

the covered section in WQ1, stromatoporoids are present up to 31 m and

other fossils are fragmented and increasingly abundant and diverse. The

top of the stromatoporoid-bearing strata at 31 m was chosen as the

boundary between the Jersey Shore and overlying La Vale Member.

Keyser Formation La Vale Member.—The La Vale Member is

biomicrite, biosparite, and argillacous biomicrite (F2a). A return to non-

reef margin biomicrites stratigraphically above the reef margin unit may

indicate a relative sea-level fall and a return to environments similar to

those inferred from strata below the reef-margin package. Alternatively, sea

level may have continued to rise, as depositional environments would have

been broadly similar both landward and seaward of the reef. Starting at

~45 m, fossils are gradually more abraded upsection and cm-scale fining-

upwards successions are noted at ~50 m. Based on the stratigraphic

context and lack of definitive deep-water features, they are interpreted as

having formed by waning flow in tidal channels and bars, indicating that by

this point relative sea level had begun to fall. Upsection, strata grade into

laminated micrite (F1b), argillaceous micrite (F1a), and finally a package

of micrite and interbedded shales from ~61 to 64 m in which the micrites

exhibit mudcracks, cm-scale cut-and-fill structures, sparse fenestrae, and

heterolithic bedding with silt-sized particles showing ripple-scale multidi-

rectional planar crossbedding (F1b). The variations observed in the La Vale

Member are consistent with tidally influenced nearshore environments and

indicate an overall regressive trend culminating with interbedded micrites

and shales at the top of the unit deposited in an intertidal environment

frequently subject to subaerial exposure and tidal influence.

Old Port Formation New Creek and Corriganville Members.—A

distinct contact separates the Keyser and Old Port Formations at 64 m

above the base of the section. Interbedded micrites and shales of the

uppermost Keyser Formation occur below ~l m of in situ mounded

stromatolites (F1b) of the New Creek-Corriganville Members of the Old

Port Formation. It is an apparently conformable contact with shallow

marine facies above and below and no evidence of erosion or prolonged

exposure. In situ stromatolites are interpreted to have formed in a protected

intertidal environment.

Above the in situ stromatolites is a ~1-m-thick cross-bedded, sandy

intrabiosparite (F3) representing siliciclastic input into the basin and

similar to that described by Inners (1981) ~1 m above the contact in the

Bloomsburg and Mifflinville Quadrangles ~15 km to the east. The sandy

unit is overlain by a series of biosparite, micrite, and biomicrite strata with

moderate to sparse, dominantly abraded fossils, which indicate a deepening

to a shallow subtidal environment above fair-weather wave base.

Old Port Formation Mandata Member.—An abrupt transition to

shale and siltstone at ~71 m marks the contact between the New Creek-

Corriganville and Mandata Members. Packages of dark gray bioturbated

shale with sparse fossils (F4a) and black, barren shale (F4b) are punctuated

by tens-of-centimeter-thick beds of nodular micrite and biomicrite.

Together, these facies indicate deposition in a subtidal environment below

storm wave base following a rapid relative sea-level rise at the base of the

Mandata Member. Black shales are interpreted to represent times when

bottom waters were the most inhospitable to normal marine fauna, oxygen

limited, and conducive to preservation of organic material. Micrite,

biomicrite, and fossiliferous shale with Chondrites bioturbation are

interpreted to represent times of oxygen limitation, but to a lesser degree

than during deposition of facies F4a (Fig. 6). Precipitated pyrite is common

throughout this member, further supporting the interpretation of oxygen-

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.¼Member, FWWB¼ fair-weather wave base; SWB¼ storm wave base; VA¼Virginia; WV¼West Virginia; MD¼Maryland; PA¼Pennsylvania; NY ¼ New York.



surface-water oxygen levels were rising (Lenton et al. 2016; Lu et al.

2018), there is evidence for oxygen limitation in the Appalachian Basin.

The change from relative sea-level rise to fall is placed at ~75 m, where a

minor increase in oxygenation is inferred from the change in facies from

mainly F4b to F4a.

Old Port Formation Shriver Member.—Above the Mandata Member

is an abrupt transition to the Shriver Member, which consists of micrite

with interbedded shales (F1a). Zoophycos feeding traces are prevalent on

some bedding planes from ~81 to 87 m. Due to the nature of exposure in

the quarry it is difficult to directly observe bedding planes in intervals

higher than ~87 m, though it appears that Zoophycos permeates the

majority of this unit. The lack of fossils and presence of Zoophycos

indicate continued deposition under oxygen-limited subtidal below storm

wave base conditions, though under slightly more oxygenated conditions

than for underlying deposits (Fig. 6); such conditions would have

prevented the preservation of as much organic matter as observed in the

Mandata Member black shales. As with the underlying Mandata Member,

precipitated pyrite is common in this part of the section, providing further

support for continued oxygen limitation and likely euxinia.

Old Port Formation Ridgeley Member.—The boundary between the

Shriver and Ridgeley Members is marked by an abrupt increase in fossil

content. From ~99 to 106 m, the Ridgeley Member is biomicrite (F2a) in

which fossils are less fragmented than in the Keyser Formation.

Argillaceous biomicrite makes up the remainder of the section from

~106 to 113 m, and the fossils in this unit are dominantly unabraded

gastropods and robust, abraded to unabraded brachiopods. The presence of

fossils indicates the return of normal-marine, subtidal below fair-weather

wave base conditions, likely the result of continued relative sea-level fall.

The top of the Winfield Quarry outcrop is in the Ridgeley Member and the

top of the Old Port Formation is not preserved.

Possible Volcanic Ash Beds.—Seven of the possible volcanic ash beds

occur in the Keyser Formation, one in the Jersey Shore Member at 15.3 m

and six in the La Vale Member at 38.3, 41.1, 43.6, 47.3, 51.1, and 53.5 m.

No works have thus far documented volcanic ashes in the Keyser

Formation. If these are in fact volcanic ashes, they may be the oldest in the

Devonian of the Appalachian Basin and the earliest indication of the

beginning of the Acadian orogeny. Alternatively, it is possible that the clay-

rich layers recorded here are detrital terrestrial clays. The uppermost bed

occurs in the Mandata at 73.5 m; it is this bed that yielded doubly

terminated euhedral zircons (see Online Supplemental File) and is

therefore considered a confirmed bentonite.

GEOCHEMISTRY

Micrite samples from this stratigraphic section show an 8.7% increase

in d13Ccarb from the base of the section to the upper part of the La Vale

Member of the Keyser Formation (Fig. 8D, Table 2). Values rise from a

minimum of -4.3% in the Tonoloway to a high ofþ4.4% in the upper La

Vale. A gap in the data through most of the Jersey Shore and the lower part

of the La Vale reflects the high fossil content through this part of the

section, as only samples devoid of visible biotic and sparry components

were sampled. Carbon isotope values then decrease by .5% to a low in

the Mandata Member of the Old Port Formation.

Oxygen isotope (d18Ocarb) values range from -7.3 to -4.1%. From the

base of the section in the Tonoloway Formation to the base of the data gap

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

of the Keyser to midway through the New Creek-Corriganville Members

(~66 m), values vary between -6.9 and -5.2%. Above this to the top of the

sampled interval in the Shriver Member of the Old Port Formation, values

are overall ~1% higher, varying between -6.4 and -4.1%.

Comparison of the oxygen and carbon isotope compositions permits

evaluation of diagenetic overprinting. A plot of carbon versus oxygen

isotope values for the entire stratigraphic column (Fig. 9) shows little

correlation (R2¼0.01). Most individual facies also show little correlation

(R2,0.15). Isotope values for facies F1b show some correlation (R2¼0.39),

but this can be partially explained by two populations of points created by

two different stratigraphic occurrences of this facies. Relatively low isotope

values are recorded in the Tonoloway Formation and lower part of the

Keyser Formation; relatively high isotope values are recorded in the lower

part of the Old Port Formation and upper part of the Keyser Formation.

When trendlines for those intervals are plotted separately, the correlation in

the lower part of the section disappears (R2¼0.00) and that in the upper part

of the section is substantially reduced (R2¼0.29). Thus, the lack of

correlation between carbon and oxygen isotope values suggests that the

FIG. 9.—Carbon versus oxygen isotope values with trendlines and R2 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.



sampled micrite matrix generally provides a faithful record of primary

seawater d13C values.

However, a few anomalously low carbon isotope values in the organic-

rich Mandata Member of the Old Port Formation may record early

diagenetic cementation. Two carbon isotope values (at 72.24 and 74.49 m

above the base of the section) are anomalously low compared to samples

from adjacent strata. It is possible that remineralization of organic matter in

the sampled shale resulted in an isotopically light early cement (e.g.,

Weissert et al. 2008). However, carbon isotope values decrease from the

peak of the positive carbon isotope excursion beginning ~8 m strati-

graphically below the Mandata Member, so the stratigraphic position of the

positive excursion is well constrained.

Another possible concern is alteration of the isotopic signature by

meteoric diagenesis, especially for very shallow-water facies (e.g., at the

boundary between the Keyser and Old Port Formations). However, the

occurrence and similar magnitude of the positive excursion throughout the

Appalachian Basin suggests that any effect is minimal. Finally, restriction

in shallow-marine environments can cause the carbon isotope values of the

dissolved inorganic carbon in those environments to be lower than those in

the open ocean, typically resulting in positive carbon isotope excursions in

deep-water facies or during rapid transgression (e.g., Patterson and Walter

1994; Immenhauser et al. 2003; Saltzman and Edwards 2017). This is

opposite of the pattern observed here, with the positive carbon isotope

excursion recorded in the shallowest-water facies. Nevertheless, caution

should be used when comparing the absolute values of the record presented

here with data from distant locations.

DISCUSSION

Parts of three transgression-regression cycles have been identified in

Winfield Quarry strata (Fig. 8B, 8C). The first is the final portion of a

regressive phase in the Tonoloway Formation. The second is a

transgression through the Byers Island and Jersey Shore Members of the

Keyser Formation and a regression through the La Vale Member. The third

TABLE 2.—d13Ccarb and d18Ocarb values for stratigraphic section WQ1 micrite samples.

Stratigraphic level

(meters above

base of section) d13C

d13C Analysis

standard

deviation d18O

d18O Analysis

standard

deviation

Stratigraphic level

(meters above

base of section) d13C

d13C Analysis

standard

deviation d18O

d18O Analysis

standard

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



includes a transgression through the New Creek-Corriganville Members of

the Old Port Formation and part of the Mandata Member and a regression

through the remainder of the Mandata, Shriver, and Ridgeley Members.

Transgressive-regressive cycles interpreted elsewhere in the basin by

other researchers were added to Figure 8C using correlation based on

lithology (Formation and Member equivalencies; Fig. 3). They do not, for

the most part, coincide with cycles documented here. One exception is the

cycle interpreted for Keyser-equivalent strata in New York, though this

correlation, with no intervening outcrop, is uncertain. The relative

lowstand at the top of the Keyser Formation also roughly coincides with

that in the New Creek of the southern outcrop belt, as noted by Saltzman

(2002). The overall misalignment of transgressive-regressive cycles across

the basin could result from lateral facies changes affecting lithologic

correlations, differential tectonic activity affecting accommodation and

clastic sediment supply, or both.

The positive carbon isotope excursion at the Silurian–Devonian

boundary is a global event and should peak at the same time in strata

throughout the Appalachian Basin. The stratigraphic peak of the excursion

can therefore be used to test whether the lithologic correlations shown in

Figure 3 in fact correlate time-equivalent strata; if they do, lithologic

correlation of sections with carbon isotope data should show coincident

isotope trends, including the stratigraphic placement of the positive

excursion at the Silurian–Devonian boundary. This idea was originally put

forth by Husson et al. (2016), who used 206Pb/238U dating of volcanic

ashes to show that carbon isotope stratigraphy can result in a viable

correlation of the Silurian–Devonian boundary interval across the

Appalachian Basin.

The excursion was first documented in the Appalachian Basin by

Saltzman (2002) at Smoke Hole, West Virginia (Fig. 1), where it peaks at

~5% in the upper Keyser Formation. Husson et al. (2016) resampled that

section at higher resolution, confirmed Saltzman’s (2002) trend, and

additionally documented the excursion at four sections in New York where

it peaks at ~3.5% in the upper Manlius Formation, ~5.3% in the lower

Coeymans Formation, and ~3.5% in the lower Kalkberg Formation. To

test whether lithology-based correlations (Fig. 3) represent timelines, their

carbon isotope data from West Virginia was pinned at stratigraphic unit

boundaries and stretched and squeezed uniformly between those

boundaries (Fig. 8D). This correlation places the West Virginia excursion

about 14 m stratigraphically below its peak in Winfield Quarry (compare

blue and black d13C data in Fig. 8D). Uncertainty in the lithologic

correlation between the northern and southern outcrop belts prohibits

reliable correlation with the New York data at this level of detail, though

the excursion would peak higher in the section than at Winfield Quarry

(red bar in Fig. 8D). Husson et al. (2016) also noted that a facies-based

correlation results in an apparently diachronous carbon isotope excursion

across the basin. They concluded that it is in fact the formation and

member boundaries that are diachronous, as originally suggested by

Rickard (1962) and Laporte (1969), and therefore correlated instead using

carbon isotope stratigraphy.

The Winfield Quarry section has been added to Husson et al.’s (2016)

carbon-isotope-based correlation by stretching, squeezing, and cutting the

isotope curve and accompanying stratigraphic section relative to the

reference curve in New York (Fig. 10), under the assumption that changes

in d13C occurred at the same time throughout the Appalachian basin. The

correlation (Fig. 10A) indicates that the Keyser Formation at Winfield

Quarry is equivalent to the Keyser and Tonoloway Formations in West

Virginia and parts of the Rondout, Manlius, and Coeymans Formations in

New York. The New Creek-Corriganville Members at Winfield Quarry are

almost entirely equivalent to the New Creek Formation in West Virginia

and parts of the Kalkberg and New Scotland Formations in New York. The

Mandata Member is equivalent to at least part of the Corriganville

Formation in West Virginia and parts of the Kalkberg, New Scotland, and

Becraft Formations in New York.

Stretching and squeezing of the section during correlation has

implications for relative sedimentation rates between the WQ1 section

and the New York reference section. Stretching implies a lower

sedimentation rate, periods of nondeposition or erosion, or higher

compaction for the WQ1 section relative to the New York reference

section, and squeezing implies a higher sedimentation rate or lower

compaction. For the correlation to be viable, the relative sedimentation

rates implied by the stretching and squeezing factors for the WQ1 section

and the reference section in New York must make sense for their

depositional environments (e.g., lower sedimentation rates for shale than

for reefal carbonates is reasonable, whereas the reverse is not).

The correlation of the lower, biomicrite part of the La Vale Member of

the Keyser Formation required squeezing of the WQ1 section and implies a

higher sedimentation rate there than in the New York section. As this part

of the Keyser Formation contains significant skeletal material, it is

reasonable that its sedimentation rate would be higher than that of the

thinly bedded, microbialite, lagoonal limestones described by Husson et al.

(2016) for the Manlius Formation. Carbon isotope values in the Tonoloway

and lower Keyser Formations are more negative than those at the base of

the section reported by Husson et al. (2016), indicating that the values

likely correlate with a lower part of the section not sampled by Husson et

al. (2016). Lacking data to correlate to, we applied the squeezing factor

from the upper Keyser Formation to the data gap and the points from the

underlying units, which places these points stratigraphically below the

Husson et al. (2016) data. Correlation of the upper, micritic part of the La

Vale Member of the Keyser Formation required stretching of the WQ1

section relative to the deeper-water (Laporte 1969) Coeymans Formation of

New York. As this part of the section was deposited in very shallow water

depths, accommodation is expected to have been limited, leading to slow

sedimentation or even bypass and erosion (Pomar 2001), which would

result in a thinner package than the Coeymans.

A hiatus between the Keyser Formation and the New Creek-Corrigan-

ville Members of the Old Port Formation is necessitated by increasingly

negative isotope values in the New Creek-Corriganville. This is consistent

with the very shallow water depths and limited accommodation for the

underlying unit. The New Creek-Corriganville part of the section in WQ1

was not stretched or squeezed during correlation. The implied similar

depositional rates for this unit and the Coeymans Formation in New York

are consistent with their similar shallow-shelf depositional environments

interpreted herein and by Laporte (1969), respectively. Correlation of the

Mandata Member, an organic-rich shale, required stretching relative to the

New Scotland Formation open-marine carbonates and Becraft sandstones

in the reference section. This stretching is reasonable because, while shelfal

carbonates, sandstones, and organic-rich shales can have similar

sedimentation rates (e.g., Walker et al. 1983; Stein 1986), shales compact

more (Baldwin and Butler 1985). Data from the Shriver Member extend

above the part of the section sampled by Husson et al. (2016). In the

absence of data to correlate to, they were extended without stretching or

squeezing.

Note that the correlation presented (Fig. 10) is an interpretation based on

the observed carbon isotope trends and that there is some uncertainty

inherent in the methodology. Unconformities have been documented in

correlative strata, particularly in northern areas (e.g., Ebert and Matteson

2003) and may also complicate interpreted correlations. The Winfield

Quarry data extend above and below the available data from New York and

West Virginia, and correlations in these parts of the section would benefit

from additional regional data. The peak of the excursion, which occurs

approximately at the Silurian–Devonian boundary according to Husson et

al.’s (2016) preferred interpretation, is better constrained and appears to

correlate well.

Compared to lithostratigraphic correlation, this chemostratigraphic

correlation is more consistent with a conodont biostratigraphy event

observed by other researchers across the Appalachian Basin. The first



appearance datum (FAD) of I. woschmidti occurs within 2 m of the

Silurian–Devonian boundary and has been used globally to constrain the

location of that boundary (Denkler and Harris 1988). In the southern

outcrop belt of the Appalachian Basin, this FAD has been documented near

the top of the Keyser Formation and in the New Creek Formation (Helfrich

1978; Denkler and Harris 1988). In the northern outcrop belt, it has been

documented in the Manlius and Coeymans Formations (Denkler and Harris

1988; Milunich and Ebert 1993; Natel et al. 1996; Kleffner et al. 2009),

which lithologic correlation marks as equivalent to units overlying the

Keyser Formation in the southern outcrop belt (Fig. 3).

Similarly, ages from volcanic ashes are more consistent with the

chemostratigraphic correlation than with lithostratigraphic correlations. An

ash bed in the Corriganville of West Virginia has been dated as 417.22 Ma,

and a series of ashes in the uppermost Coeymans and Kalkberg in New

York have been dated as 418.42–417.56 Ma (Husson et al. 2016). While

lithostratigraphic correlation places the New York ashes equivalent to or

stratigraphically above the West Virginia ash, chemostratigraphic correla-

tion places these ashes in stratigraphic order consistent with their ages

(compare Figs. 3 and 10).

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 Oulodus 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: WV¼West

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; Co¼ Coeymans.



The transgressive-regressive cycles documented herein record local

change in relative sea level from as shallow as supratidal environments to

as deep as below storm wave base. Dorobek and Read (1986) estimated the

water depth of storm wave base at this time in the Appalachian Basin as

50–60 m or deeper, on the basis of thicknesses of sedimentary packages

from which they approximated the slope of the Appalachian Basin ramp

(10–15 cm/km). Haq and Schutter (2008) show a maximum of ~80 m of

global sea-level change for third-order fluctuations through the latest

Silurian and earliest Devonian (Pridolian and Lochkovian). Therefore,

from the local record of relative sea-level change alone, it is possible that

the transgressive-regressive cycles at WQ1 are the result of eustatic sea-

level change. However, if eustasy was the primary driver, relative sea-level

cycles would be coincident throughout the Appalachian Basin, and the

chemostratigraphic correlation does not support this scenario (Fig. 10A).

Comparing the transgressive-regressive cycles in light of the chemostrati-

graphic correlation presented herein, a maximum transgression in the

Keyser Formation was synchronous through at least the southern outcrop

belt. Another maximum transgression in the Mandata Member appears to

coincide with that in the Kalkberg-New Scotland Formations of New York.

Otherwise, transgressive-regressive cycles do not appear to correlate across

the basin. We therefore conclude that local factors such as tectonics and

sediment supply were the dominant control on depositional patterns in the

Appalachian Basin at this time.

A positive carbon isotope excursion requires either addition of 13C or

removal of 12C. As a possible cause of the Klonk excursion, Malkowski

and Racki (2009) suggested that the expansion of land plants resulted in

burial of organic matter rich in 12C in epicontinental seas. The Winfield

section records oxygen limitation and enhanced burial of organic matter in

the Mandata Member. However, that unit is 9 m above the peak of the

positive isotope excursion, having been deposited after rather than before

or during the excursion as would be expected for organic-rich units that

could have contributed to the positive excursion. Saltzman (2002) noted

that the carbon isotope excursion in West Virginia coincides with a relative

sea-level lowstand and suggested that the lowered sea level could have

exposed and caused increased erosion of 13C-rich Silurian carbonate strata.

The correlation presented herein using carbon isotope data does not show a

synchronous lowstand throughout the Appalachian Basin (Fig. 10A).

However, because transgressive-regressive cycles appear to reflect local

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

disprove Saltzman’s (2002) hypothesis. Additional stratigraphic studies

reporting high-resolution isotopic, geochronologic, and lithologic data

from late Silurian–Early Devonian sections are needed to fully characterize

and interpret the Klonk excursion.

CONCLUSIONS

At a time when global atmospheric and surface-water oxygen levels

were rising, there is evidence for oxygen limitation in the Appalachian

Basin. Strata at Winfield Quarry are interpreted to document a range of

depositional oxygenation conditions. Normal marine conditions are

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,

sparse fauna to black, barren shale.

Facies distribution in the stratigraphic section reveals parts of three

transgressive-regressive cycles: (1) The Tonoloway Formation with

intertidal to supratidal laminated, mudcracked, evaporitic micrites

represents the tail end of a regression; (2) The Byers Island and Jersey

Shore Members of the Keyser Formation are biomicrites with sponge-

coral-crinoid biostromes that indicate a return to normal marine conditions

and overall transgression. The La Vale Member of the Keyser Formation

contains fossils that are increasingly abraded upsection and culminates in

micrites with mudcracks and tidal bedding, indicating regression and a

return to an intertidal to supratidal setting; and (3) The New Creek-

Corriganville Members of the Old Port Formation are a variety of shallow-

water facies that, above a basal bed of in situ stromatolites, lack indicators

of subaerial exposure or tidal influence; this records transgression to a

subtidal, above fair-weather wave base setting. An abrupt shift to mainly

black, barren shales in the lower Mandata Member indicates rapid

deepening to an oxygen-limited environment below storm wave base.

Upper Mandata Member mainly gray shales with Chondrites traces and a

limited fossil assemblage and Shriver Member micrites with Zoophycos

traces were deposited under continued but decreasing levels of oxygen

limitation, likely related to regression. This trend culminates with a return

to normal marine conditions, as shown in Ridgeley Member biomicrites

deposited below fair-weather wave base.

The Klonk Event positive carbon isotope excursion is recorded in

central Pennsylvania as a rise from a minimum of -4.3% in the Tonoloway

Formation to a high ofþ4.4% in the upper part of the La Vale Member of

the Keyser Formation, then a drop .5% to a low in the Mandata Member

of the Old Port Formation. Using trends observed in this globally

coincident data to correlate regionally, following methodology from

Husson et al. (2016) and incorporating their data, shows that the Keyser

Formation is equivalent to the Keyser and Tonoloway Formations in West

Virginia and parts of the Rondout, Manlius, and Coeymans Formations in

New York. The New Creek-Corriganville Members at Winfield Quarry are

mostly equivalent to the New Creek Formation in West Virginia and parts

of the Kalkberg and New Scotland Formations in New York. The Mandata

Member is equivalent to at least part of the Corriganville Formation in

West Virginia and parts of the Kalkberg, New Scotland, and Becraft

Formations in New York. This new correlation is more consistent with

other time-correlative markers, including conodont biostratigraphy and

volcanic-ash chronostratigraphy.

Interpreted transgressive-regressive trends do not match between West

Virginia, Pennsylvania, and New York when correlated using existing

lithostratigraphic correlation or the carbon-isotope correlation presented

here incorporating data from Pennsylvania. It is inferred that local

(tectonics, sediment supply) rather than global (eustatic) controls

dominated depositional patterns in the Silurian–Devonian boundary

interval in the Appalachian Basin.

ACKNOWLEDGMENTS

Thank you to Eastern Industries for allowing access to their quarry, without

which this project would not have been possible, and especially Albert Mabus

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

guidance during geochemical analyses. The Geological Society of America

provided financial support for analyses. Dr. Tony Ekdale helped classify trace

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.

Matthew Saltzman and an anonymous reviewer for their thoughtful reviews of

this manuscript.

SUPPLEMENTAL MATERIAL

Data are available from the PALAIOS Data Archive:

https://www.sepm.org/supplemental-materials.

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Received 17 February 2019; accepted 10 August 2019.



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