Introduction
This study conducts a paleoecological analysis of the Late Chesterian Eads Mill Member of the Hinton Formation, dating back to approximately 325 million years ago It examines five key outcrops situated in southern West Virginia and southwestern Virginia, extending from Bluefield, VA, along Route 102 to Princeton, WV, and up to Green Sulfur Springs, WV, along Interstate 64 This strategic selection of outcrops highlights areas rich in marine fossils, providing valuable insights into the paleoecological landscape of the region.
This research aims to identify and analyze the diverse marine invertebrate faunas found in the Eads Mill Member of the Hinton Formation across four outcrops in southern West Virginia and one in Virginia By identifying taxa and employing multivariate techniques, the study constructs a paleoecological interpretation of the data While previous research has focused on other fossil assemblages in Upper Mississippian strata, this study is the first to specifically examine the Eads Mill Member The Hinton Formation, primarily composed of paleosols and non-marine deposits, offers valuable insights into one of the youngest marine faunal assemblages in the Mississippian system of the Appalachian Basin, predating the Pennsylvanian Period.
This research aims to enhance our understanding of the upper Hinton Formation by integrating paleoecological findings with existing data By reconstructing the paleoenvironment of the Eads Mill Member, we can combine these results with studies on eustatic, climatic, and glacial processes from the Late Mississippian This comprehensive approach will provide a deeper insight into the global conditions and depositional processes that shaped the rocks of the Late Chesterian in the Appalachian Basin.
Figure 1 Hinton Formation map illustrating outcrop localities across southern West Virginia and southwestern Virginia Outcrops beginning in the south are: (1) Route 102 VA: UTM 17N 0474845
W 4124495, (2)Christian Fork Lake: UTM 17N 0496405 W 4135323, (3) Bluestone River Bridge: UTM 17N 0493470 W 4147784, (4) Pipestem: UTM 17N 0503534 W 4155548, (5) I-64 above Green Sulfur Springs: UTM 17N 0520041 W 4187292 (Beuthin and Blake, 2004)
Previous Studies
The Hinton Formation, located in southern West Virginia and southwestern Virginia, is a northwest thinning wedge of marine and non-marine rocks Its upper section can reach thicknesses of up to 150 meters and is notable for features such as paleosols, thin impure coal layers, and fluvial facies These non-marine deposits transition upward into thin shales and marine limestones, indicating the maximum extent of marine transgression in the area.
Previous research on the Hinton Formation and similar mid-continent formations has primarily concentrated on interpreting rock strata to develop a climate-influenced depositional model Key areas of investigation have included the significance of paleosols and the increasing abundance of coal, as well as the effects of glacial ice expansion and contraction on incised valley fills during the Late Mississippian However, unlike these earlier studies, this research provides a more comprehensive paleontological assessment, enhancing our understanding of the formations.
The Avis Limestone of West Virginia, identified by Reger (1926) and correlated with the Little Stone Gap Member in Virginia and Kentucky, represents the only marine zone studied within the Hinton Formation As the basal unit of the upper Hinton Formation, the Avis Limestone consists of calcareous mudstones and shales, interspersed with pure limestone This formation is rich in a diverse marine fauna, primarily featuring brachiopods and bryozoans, along with bivalves, corals, and crinoids, suggesting its deposition in a stenohaline, open marine environment.
The marine invertebrate faunas of the Mauch Chunk Group have been extensively studied, particularly in relation to the Bluefield Formation and the Bluestone Formation Research by Kammer and Lake (2001) highlighted the diverse faunas within the Bickett Shale and Reynolds Limestone members of the Bluefield Formation in northern West Virginia The Bickett Shale is characterized by euryhaline taxa, including the gastropod Bellerophon and various bivalve genera such as Ectogrammysia and Phestia, indicating its formation in bays or estuaries during a regression period In contrast, the Reynolds Limestone showcases a stenohaline, open marine fauna, featuring abundant brachiopod genera like Anthracospirifer, Composita, and Diaphragmus, alongside fenestrate bryozoans, crinoids, and solitary rugose corals.
The Bluestone Formation, situated above the Hinton Formation, features two notable marine zones: the Pride Shale Member and the Bramwell Member The Pride Shale, located above the Princeton Sandstone, is characterized by dark gray, silty shale interspersed with siderite nodules, and is rich in plant fossils and bioturbation, alongside fragmented remains of brachiopods, bivalves, cephalopods, and crinoids Meanwhile, the Bramwell Member exhibits stenohaline marine conditions, evidenced by the presence of the bryozoan Fenestella and the brachiopods Orthotetes.
Ovatia (Henry and Gordon, 1992) Many genera of bivalves are also present and many, such as Phestia and Aviculopecten, correspond with those found in the underlying
Figure 2 Mississippian stratigraphic section from nearby Giles Co., VA (McDowell and Schultz,
The Eads Mill Member sits directly below the Princeton Sandstone, forming the upper layer of the Hinton Formation, which features the Avis Limestone bed.
The Mauch Chunk Group and its formations are generally regarded as lacking fossils, with only the most prominent marine units examined for their faunal composition However, findings from the Bluefield and Bluestone Formations reveal a diverse range of invertebrate taxa that thrived during the Chesterian period, influenced by their salinity tolerance in the depositional environment (Kammer and Lake, 2001) Additionally, many of these taxa are also found in the Eads Mill Member of the Hinton Formation, indicating similar preferences for salinity and environmental conditions.
Geologic Setting
During the Late Mississippian (Chesterian) period, the deposition of siliciclastic and carbonate rocks in the Appalachian Basin was influenced by glacio-eustatic sea level fluctuations and the reactivation of tectonism associated with the Alleghanian Orogeny While some researchers have focused on one process over the other to explain sequence formation in the Mauch Chunk Group, this article supports the view that Milankovitch cycles linked to glacio-eustatic changes occurred alongside tectonically driven basin subsidence and isostatic uplift This discussion will explore the hypothesized controls on sedimentation during this period, particularly their impact on the lithofacies of the upper Hinton Formation and the associated faunal assemblages.
During the Late Mississippian period, the Appalachian foreland basin was situated about 10-20 degrees south of the paleoequator As Laurussia gradually moved northward, it played a significant role in the collisional assembly of the supercontinent Pangea.
Around 2000, the climate transitioned from semi-arid conditions, characterized by the development of numerous paleosols in the lower Hinton Formation, to the more humid conditions observed during the Early Pennsylvanian period (Cecil, 1990).
Paleogeographic maps illustrate the oceanic current trends and the positioning of the Appalachian Basin, highlighting two significant climatic phases Initially, free-flowing ocean currents promoted open climatic circulation, resulting in humid conditions across the North American plate Subsequently, the closure of the intercontinental seaway redirected ocean flow around Gondwana, leading to the onset of glacial formation in the Southern Hemisphere.
Closing of the intercontinental seaway separating Laurussia and Gondwana significantly affected oceanic and atmospheric circulation patterns, as illustrated in
The reduced circulation led to the periodic formation of continental glaciers in the southern hemisphere on Gondwana, resulting in high-frequency eustatic sea level fluctuations Simultaneously, the Appalachian Basin underwent isostatic rebound as the tectonic highlands responded to unloading during the Middle Chesterian period.
(Ettensohn et al., 2002) Sediments filling the basin were sourced from the nearby
Appalachian tectonic highlands, which experienced a rapid increase in source area size caused by the initiation of isostatic uplift (Brezinski, 1989)
The Mauch Chunk siliciclastic wedge was formed by the combined influences of climate and isostatic uplift following the Acadian Orogeny Located in southern West Virginia, this wedge, primarily composed of clastic rocks, tapers westward and attains a maximum thickness of 900 meters (Maynard et al.).
The Mauch Chunk Group, which includes the Bluefield, Hinton, Princeton, and Bluestone Formations, features terrestrial facies like paleosols and fluvial deposits found in incised valleys.
2001), and a lesser number of thin coal beds (Englund et al., 1986) These lithologies confirm a semi-arid climate with periodically seasonally wet conditions (Cecil, 1990; Beuthin and Blake, 2002)
The upper Hinton Formation as defined by Beuthin and Blake (2004), extends from the top of the Avis Limestone of Reger (1926) to the base of the Princeton
The upper Hinton Formation, particularly the Eads Mill member, reaches a maximum thickness of 150 meters near Bluefield, VA, and progressively thins toward northern West Virginia This formation is characterized by nearshore deposits, including fossiliferous shales, limestones, paleosols, fluvial sandstones, and thin impure coals, indicating a marginal marine depositional environment with estuarine, lagoonal, shoreface, and tidal facies The climatic conditions during its formation were primarily dry and semi-arid, as evidenced by terrestrial calcareous red beds, although some studies suggest the presence of leached paleosols and thin coals indicates more humid conditions However, these features are likely the result of deposition in waterlogged areas near the coastline Overall, the upper Hinton Formation showcases a diverse range of facies reflective of dynamic nearshore and coastal environments.
The Eads Mill Member, the highest unit of the Hinton Formation, is characterized as a distinct marine layer that is sometimes directly topped by the Princeton Sandstone It is separated from the underlying Fivemile Member by over 25 meters of terrestrial deposits, including fluvial sandstones, shales, and rooted paleosols The base of the Eads Mill Member features a sudden shift from rooted paleosols to fissile marine shales and argillaceous bioclastic limestones, offering a valuable opportunity to examine a fully marine biotic assemblage in the upper geological strata.
The Hinton Formation provides valuable insights that enhance our understanding of the faunas found in the underlying Bluefield Formation and Avis Limestone, as well as the younger Pride Shale of the Bluestone Formation This information helps to construct a clearer picture of the paleoecological conditions that existed in the Appalachian Basin during the Late Mississippian period.
Figure 4 Stratigraphic chart illustrating previous and current nomenclature for the upper Hinton Formation in southern West Virginia (Beuthin and Blake, 2004)
Methods
Field Methods
In early November 2005, a preliminary trip was conducted to examine outcrops containing the Fivemile and Eads Mill lithologic sections, spanning from Bluefield, VA to north of Green Sulfur Springs, WV This trip aimed to familiarize researchers with these locations and involved brief sampling of fossiliferous intervals to assess taxonomic richness and diversity The collected samples were analyzed in the lab, identified to the genus level, and categorized by outcrop This effort led to the identification of five productive outcrops, notable for their multiple fossil-rich horizons, forming a northeast/southwest transect along the ancient coastal plain The selected outcrops, from south to north, include Route 102 VA, Christian Fork Lake, Bluestone River Bridge, Pipestem, and I-64 north of Green Sulfur Springs.
Data collection commenced on May 7, 2006, at Camp Creek State Park near Princeton, WV, focusing on outcrops from south to north, starting with Route 102 VA, which featured the thickest Eads Mill section and the Fivemile Member Specimens were collected both loose, weathered from the outcrop, and in situ using rock hammers and chisels Each sample was meticulously placed in labeled collection bags that indicated the outcrop locality, date, and specific stratigraphic position, referencing the measured sections compiled by Jack Beuthin and Mitch Blake in their 2004 study To prevent mixing from different stratigraphic zones, loose surface samples and in-place samples were kept separate Additionally, bulk samples containing numerous fossils were collected and labeled similarly to individual specimens, later disaggregated in the lab for fossil content analysis.
Throughout the week, a comprehensive fossil collection was conducted at each outcrop, assisted by Tom Cawthern, who helped gather multiple sample bags from various fossiliferous lithologic zones Although the goal of collecting 300 or more specimens from each unit was not fully achieved, a sufficient number of fossils was obtained to represent the taxonomic diversity of each outcrop By Saturday, May 13, the collection from all five outcrops was completed, and the samples were transported back to 303 White Hall for preparation and identification.
Laboratory Methods
In June 2006, the laboratory identification process for collected fossils commenced, involving the washing and drying of muddy specimens Bulk samples were disaggregated, and derived specimens were organized into labeled collection bags Using microscopes, hand lenses, and reference materials, fossils were identified to the genus level for each outcrop Key references for identification included works on cephalopods, brachiopods, bivalves, gastropods, bryozoans, and trilobites Each identified specimen was placed in a labeled collection tray, detailing the genus name, sample age, location, collection date, and collector's name All genera from each sampled unit were stored in cabinets marked with the outcrop location and unit designation.
Multivariate Techniques
An Excel dataset was created to compile all sampled units and identified genera, utilizing four multivariate analysis techniques for interpretation The original spreadsheet featured binary presence/absence data for each genus across the sampled units, eliminating the need for taxonomic abundance counts This approach is justified, as binary data can yield results comparable to abundance data when a strong paleoecologic signal is present (Kammer and Lake, 2001) Notably, the data from Eads Mill revealed robust patterns through multivariate analysis, further supporting the decision to forgo taxon counts.
The initial multivariate techniques employed for data interpretation included cluster analysis, non-metric multi-dimensional scaling (MDS), and correspondence analysis Cluster analysis generates a dendrogram that groups taxa or samples based on their ecological similarities, although it does not reveal data gradients In contrast, non-metric MDS positions these groups within a low-dimensional Euclidean space, allowing the distance between points to reflect their degree of similarity, thus highlighting gradients in the data Lastly, correspondence analysis visualizes the relationship between samples and taxa by plotting both Q-mode and R-mode, illustrating how closely individual taxa relate to specific samples All multivariate analyses were conducted using the PAST software (Hammer et al., 2007).
Data
Outcrop Descriptions
The first sampling location is along the west side of Rt 102, just outside of
In Bluefield, VA, two ripple bedded sandstones, previously identified as the Falls Mill Sandstone, exhibit unique geological features such as dewatering escape structures and shale rip-up clasts, indicating a tidally influenced estuarine environment Above these sandstones lies a fossil-rich limestone unit, home to stenotropic taxa like brachiopods and crinoids, followed by a thick dark gray shale that contains scarce gastropods and poorly preserved bivalves Additional argillaceous limestones above demonstrate open marine conditions, while another dark gray shale unit features bioclastic limestones rich in Phestia bivalves and rare cephalopods The sequence culminates in a gray sandstone with flaser bedding and evidence of bidirectional paleocurrents, ultimately capped by a rooted mudstone, highlighting the area's diverse paleoenvironments and fossil record.
100) with a thin (2 cm) impure coal at the top
The Stigmaria plant fossil, discovered in Sample 99 sandstone along Rt 102 in Virginia, is indicative of a seasonally wet coastal environment These fossils are frequently found in Upper Mississippian and Pennsylvanian strata, highlighting the region's ancient ecological conditions (Gillespie et al., 1978).
The stratigraphic column of the Rt 102 Virginia outcrop reveals a significant transition from terrestrial to marine conditions, indicated by the tidal sandstones at the base (Samples 89, 90) During the deposition of the middle shales and limestones, water depth experienced fluctuations, ultimately regressing to terrestrial conditions, as evidenced by the uppermost sandstone and thin coal layers (Samples 99 and 100) The sampling units for all five Eads Mill Member outcrops align with those described by Jack Beuthin and Mitch Blake, with constituent fossil images provided by Jack Beuthin.
The second outcrop, located on a hillside near Christian Fork Lake east of Princeton, WV, along Rt 460, is the shortest of five examined and consists of three stratigraphic units The base features a gray, unfossiliferous shale (unit 1), supporting large blocks from the overlying shale Above this is a nearly one-meter-thick bioclastic limestone (unit 2), which contains biotic remains, though many are highly abraded and embedded within the crystalline limestone, complicating identification The uppermost unit is a rich, fossiliferous gray-green shale (unit 3) that hosts a diverse stenohaline fauna, including brachiopods, bivalves, crinoids, fenestrate bryozoans, and solitary rugose corals, with specimens easily weathering out for extensive sampling.
The stratigraphic column of the Christian Fork Lake outcrop reveals distinct lithological features and fossil taxa The middle sample (2) consists of a highly abraded bioclastic limestone, which hindered the collection and identification of fossils In contrast, sample 3 is rich in fossils and can be easily disaggregated for analysis.
5.1.3 Bluestone River Bridge along Eads Mill Road
The Eads Mill Member, as defined by Beuthin and Blake (2004), is located along Mercer County Route 3 (Eads Mill Road) and extends beneath the I-77 bridge over the Bluestone River Gorge The lower sections consist of gray mudstones and shales rich in fossils, including brachiopods, bivalves, gastropods, and occasional cephalopods, with diversity increasing upward These are topped by 1.5 meters of limestone, which features brachiopods, solitary rugose corals, and fenestrate bryozoans, notably dominated by the tethered brachiopod Composita Above the limestone lies an 11.4-meter thick layer of fissile, unfossiliferous olive gray shale The uppermost units comprise interbedded fossiliferous shales and limestones, where the shales weather easily for sampling, and the limestones exhibit distinctive "toadstool" weathering, being bioclastic and crystalline Similar to the underlying limestones, these upper units are primarily characterized by brachiopods and include stenohaline taxa such as fenestrate bryozoans, crinoids, and solitary rugose corals The Princeton Sandstone erodes into the units located five meters above the Eads Mill.
Figure 8 Characteristic “toadstool” weathering of the Sample 11 limestone underneath the Bluestone River Bridge The highly fossiliferous Sample 12 shale crops out above the toadstool limestone
Figure 9 Stratigraphic column of the Bluestone River Bridge outcrop showing lithology and taxa Limestones were crystalline and difficult to sample Shale units were abundantly fossiliferous and easily disaggregated
The highly fossiliferous Sample 12 shale, observed at the Bluestone River Bridge, closely resembles Sample 3 shale from Christian Fork Lake, as both exhibit identical coloration and a rich taxonomic diversity.
The outcrop along WV Rt 20, near Pipestem Creek, features a crystalline bioclastic limestone (unit 63) at its base, which contains the brachiopod genus Anthracospirifer Above this limestone, two gray shales (units 64, 66) are present, with a concealed unit in between The upper shale hosts several bivalve genera near its base and transitions into a calcareous mudstone (unit 67) and an argillaceous limestone (unit 68), both rich in brachiopod taxa, Bellerophon gastropods, and fenestrate bryozoans The mudstone also contains stenohaline taxa, including crinoids and solitary rugose corals, while the limestone features a resurgence of bivalves alongside brachiopods Above three meters of unfossiliferous shale and siltstone (units 69, 70), a shale with brachiopods and fenestrate bryozoans (unit 71) is found The uppermost olive gray shale contains thin sandstone lenses (unit 72), which, despite lacking body fossils, exhibit feeding trace bioturbation The Princeton Sandstone cuts into this uppermost unit.
Figure 11 Stratigraphic column of the Pipestem Creek outcrop showing lithology and taxa Samples
Samples 67 and 68 featured the richest and most diverse fossil assemblage, making them the most accessible units for sampling Notably, the fluvial Princeton Sandstone is observed to truncate the top of Sample 72, as illustrated in Figure 12.
The Eads Mill Member outcrop, located along the western side of WV Rt 20 near Pipestem Creek, showcases a resistant ledge formed by the Princeton Sandstone, which unconformably incises into the top of the Eads Mill Member Key lithologic unit sample numbers corresponding to Figure 11 are indicated in the photograph.
The northernmost outcrop of the Eads Mill formation is located approximately 2.2 miles east of Exit 143 along the north side of I-64, near Green Sulfur Springs, WV This geological transition features a shift from red rooted mudstone to a strongly calcareous gray shale (unit 56), characterized by thin dark gray laminations that include Modiolus and Septimyalina bivalves Additionally, the formation comprises a mudstone (unit 57), impure limestone (unit 58), and shale.
59) overlie the basal unit The impure limestone (unit 58) correlates to the lower limestones found in the other three complete Eads Mill Member sections (Figure 14) No identifiable body fossils were noted but the shale contained thin, bivalve shell hash layers that were heavily abraded Above the shale, a ripple cross-laminated sandstone (unit 60) grades upward into a half-meter thick immature paleosol with poorly developed slickensides (unit 61) Above the paleosol are two medium gray shales (units 62, 63), both of which have centimeter thick bands of siderite and contain euryhaline taxonomic assemblages The lower shale represents a restricted fauna with Septimyalina and the only occurrence of the brachiopod Lingula, which can regulate its body’s ionic concentration and thus can survive in a wide range of ecologic conditions (Kammer and Lake, 2001) The upper shale contains an abundance of bivalves, gastropods, and occasional straight shelled cephalopods, all of which are most easily retrieved from above the runaway truck ramp as they weather out free from the top of the unit Atop the shales is a bioclastic limestone (unit 64), which contains the only occurrence of crinoids and fenestrate bryozoans at this outcrop In the limestone all bivalves from the underlying shale have been displaced by brachiopods, which also occurred in the lower limestone units (7,8) from the Bluestone River Bridge outcrop (Figure 9) On top of the limestone is a thick (11.3 m), medium gray shale (unit 65) that also contains numerous siderite bands like those previously described Above it is a small (.2 m) bioclastic limestone (unit 66) that holds numerous straight shelled cephalopods The uppermost units begin with a shale (unit 67) that grades into a mudstone (unit 68) and finally a thin (0.1 m) limestone (unit 69), all of which are unfossiliferous
Figure 13 Stratigraphic column of the I-64 outcrop showing lithology and taxa The most abundantly fossiliferous samples (63, 64) were located above the runaway truck ramp
The correlation diagram illustrates the five sections of the Eads Mill Member, highlighting the top and bottom boundaries with solid lines At both the Bluestone River Bridge and Pipestem Creek locations, the Princeton Sandstone is found unconformably overlying the Eads Mill Member Dashed lines indicate the correlation of the Pluto and Terry Limestones from Reger's 1926 study, which mark the two maximum transgressive surfaces within the Eads Mill Member Additionally, the lithology and taxa of the Christian Fork Lake middle limestone and upper shale are consistent with those found in the upper Bluestone River Bridge samples The stratigraphic columns are arranged from south to north, with no horizontal scale indicated.
Invertebrate Fossils
The most abundant fossil taxa in the Eads Mill Member were brachiopods (Figure
The study identified 13 different genera, with all but Lingula being stenohaline (Kammer and Lake, 2001; Lebold and Kammer, 2006) Brachiopods were present in 17 out of 23 sampled intervals, while bivalves, which had the second highest generic abundance in the Eads Mill Member with 10 genera, were found in 14 samples Notably, both brachiopods and bivalves coexisted in nine samples, suggesting that bivalves thrived in stenotropic conditions.
The analysis reveals that 13 genera exhibit significant associations with either brachiopods or bivalves Notably, brachiopods are linked with eight samples featuring characteristic stenotropic taxa, including bryozoans, crinoids, and rugose corals In contrast, six out of nine samples containing gastropods and all six samples with the cephalopod Reticycloceras are associated with bivalves Additionally, the sole occurrence of ostracods was also found with bivalves, while the only other genera accompanying the single sample of Paraconularia were brachiopods Trilobites appeared in two of the nine samples that included both brachiopods and bivalves Overall, brachiopods and typical stenotropic taxa are closely intertwined, whereas bivalves tend to associate with eurytropic taxa, although they can also thrive in stenotropic environments.
Table 1 Complete list of all 36 Eads Mill Member genera and 10 taxonomic types
Brachiopods Anthracospirifer, Cleiothyridina, Composita, Diaphragmus,
Eumetria, Flexaria, Fluctuaria, Inflatia, Lingula, Orthotetes, Ovatia, Punctospirifer, Torynifer
Aviculopecten, Cardiomorpha, Edmondia, Ectogrammysia, Modiolus, Nuculopsis, Paleyoldia, Phestia, Schizodus, Septimyalina,
Gastropods Bellerophon, Euphemites, Ianthinopsis, Knightites, Naticopsis
The bivalve Ectogrammysia is characterized by its distinct coarse concentric growth lines radiating from the hinge This species was discovered in at least one sampled interval across each outcrop, highlighting its widespread presence The scale bar provided measures in centimeters.
Figure 16 The straight shelled nautiloid Reticycloceras has relatively parallel septa that are closely spaced together It was commonly identified with the other euryhaline taxa Scale bar is in centimeters
Solitary rugose corals were discovered alongside crinoids, bryozoans, and various genera of brachiopods, indicating a diverse marine ecosystem These corals, similar to bryozoans and crinoids, exhibit a limited tolerance to changes in salinity, making their presence a key indicator of open marine, stenohaline conditions in the depositional environment (Kammer and Lake, 2001) The scale bar in the accompanying image is measured in centimeters.
Figure 18 One of the most common taxa in all samples, the productid brachiopod Ovatia has very fine ribs closely spaced together on its pedicle valve.
Multivariate Matrices and Analyses
After completing laboratory identification, all generic and sample data were organized into an Excel spreadsheet, comprising 23 samples and 36 identified genera Multivariate analysis revealed subtle trends within the original binary data; however, high stress values indicated excessive noise, complicating pattern recognition Stress values, which range from 0 to 1, assess the data's fit to a linear curve, with values above 0.40 signifying poor fit To enhance clarity, taxa with a single occurrence and samples containing only one genus were removed, resulting in improved stress values of 0.15-0.20 for both Q and R-mode data, thereby revealing more distinct patterns.
To streamline the diverse range of taxa, seven distinct guilds were established to minimize the number of variables in the dataset Each guild comprised members with similar morphology, food source preferences, and life habits, allowing them to function as a unified proxy for the various genera included within each group (Bambach, 1983; Kammer and Lake).
In this study, taxa were categorized into seven distinct guilds based on their characteristics, as outlined by Kammer and Lake (2001) and Lebold and Kammer (2006) The identified guilds include osmo-conformers (encompassing crinoids, bryozoans, and corals), tethered brachiopods, productid brachiopods, infaunal bivalves, epifaunal bivalves, gastropods, and cephalopods To ensure data integrity, taxa with two or fewer occurrences and samples with two or fewer genera were excluded The analysis resulted in a streamlined dataset, reducing the original R-mode data from 36 variables to seven and the Q-mode data from 23 samples to 18, which minimized noise and stress while enhancing the paleoecological signal.
Binary data from seven guilds was analyzed using PAST software, conducting three multivariate analyses with both Q-mode (sample) and R-mode (guild) data to uncover common trends Cluster analysis revealed groupings categorized into marginal and open marine conditions, with marginal marine salinity ranging from 5-30‰ and open marine conditions stabilizing around 35‰ Additionally, non-metric MDS plots for both Q-mode and R-mode data further distinguished samples and guilds into these marine groupings A correspondence analysis that integrated both data modes illustrated a clear trend of increasing salinity stability as samples and guilds transitioned from marginal to open marine environments.
Table 2 presents a binary dataset of all identified fossil genera along with their respective sampling intervals The samples are organized by outcrop locality, with each number corresponding to a sampled unit on the associated stratigraphic column A value of 1 signifies the presence of the genus in the sample, whereas a value of 0 indicates its absence.
Anthracospirifer Cleiothyridina Composita Diaphragmus Eumetria Flexaria Fluctuaria Inflatia Lingula
Orthotetes Ovatia Punctospirifer Torynifer Aviculopecten Cardiomorpha Edmondia Ectogrammysia Modiolus
Nuculopsis Paleyoldia Phestia Schizodus Septimyalina Bellerophon Euphemites Ianthinopsis Knightites
Naticopsis Reticycloceras Paladin Fenestrate Encrusting Paraconularia Crinoids Rugose Corals Ostracods
Table 3 Constituent taxa of 7 constructed guilds Taxa with two or fewer total occurrences were removed from the data to reduce the noise and enhance the underlying paleoecologic signal
Brachiopods Anthracospirifer Fluctuaria Composita Eumetria
Infaunal Bivalves Ectogrammysia Edmondia Schizodus Phestia
Osmo-conformers Rugose Corals Crinoids Archimedes
Table 4 Taxa with two or fewer occurrences that were removed from the data set during the construction of guilds
Infaunal Bivalves Paleyoldia Nuculopsis Cardiomorpha
Table 5 presents outcrop samples and the formation of seven guilds based on binary count data Following the compilation of presence/absence data for all genera, the counts of constituent members within each guild were organized for every sampling interval Additionally, the sample lithology is documented, with the following abbreviations used: SH for Shale, LS for Limestone, and MS for Mudstone.
Lithology T.BRACH PROD.BRACH IN.BIV EPI.BIV OSMO GASTRO CEPHALO
Cluster analysis of Eads Mill Member samples, which include three or more taxa, utilizes the cosine theta coefficient to categorize different marine environments The analysis reveals that marginal marine samples represent both transitional and brackish conditions, while open marine samples indicate stenohaline environments Locality abbreviations include RTVA for Rt 102, VA; CFL for Christian Fork Lake; BRB for Bluestone River Bridge; PIPE for Pipestem Creek; and INT for Interstate 64, with numbers next to each abbreviation denoting specific sampling units on the stratigraphic column for each location.
Q M o de C lus te r A nal ys is (C o sine) 0 0 12 0 24 0 36 0 48 0 72 0 84 0 96 0 6
R M o de C lus te r A n a ly s is (C o rrelat io n ) -1 -0 7 5 -0 5 -0 2 5 0 0 25 0 5 0 75
Figure 20 Cluster analysis illustrating similarities between guilds based on their salinity tolerances, using the correlation coefficient
Marginal Marine Samples Open Marine Samples
Non-metric MDS analysis reveals clear separation of samples based on salinity tolerance, with both marginal marine and open marine samples exhibiting similar groupings Open marine samples are closely clustered, while marginal marine samples form a tight grouping of four units Additionally, sample INT66, although marginal, shows a looser association with the other samples.
The non-metric multidimensional scaling (MDS) analysis reveals a distinct separation of marine guilds into open marine and marginal marine categories based on their salinity tolerances This classification aligns with the groupings identified in Figure 20 through cluster analysis, demonstrating consistent patterns in the ecological organization of these marine communities.
The correspondence analysis of Eads Mill samples reveals strong associations among open marine taxa, as indicated by the Q-mode cluster analysis In contrast, fewer samples representing marginal marine conditions, primarily dominated by bivalves, show more widespread distribution As the environment transitions from marginal marine to open marine conditions, salinity stability increases due to reduced freshwater influx and mixing further offshore.
Results and Discussion
Stratigraphic Analysis
The Eads Mill Member was formed during a cycle of transgression and regression influenced by eustatic sea level changes, with some variations observed in certain outcrops It is characterized by a transition from non-marine shales and paleosols to marine shales or sandstones, often indicated by the presence of bivalves in complete sections A significant thick marine shale was deposited during the transgression, with some layers featuring thin interbedded limestones Notably, generic diversity peaked at the top of the shale and into the lower limestone, which is consistently mappable across all complete outcrops This limestone represents the maximum transgressive surface of the initial sea level rise.
A regression led to a renewed clastic influx, resulting in a thick shale layer deposited over the lower limestone Subsequently, a transgression deposited a second extensive limestone layer atop the shale, indicating the maximum transgressive surface and the furthest deposition from clastic influx at the paleoshoreline Another regression above this upper limestone resulted in the deposition of another thick shale across the region, particularly observed at Bluestone River Bridge.
The presence of thinner limestones interbedded near the top of the shale suggests periods of local sediment starvation This regression at the top of the Eads Mill Member marked a transition back to coastal facies, characterized by the deposition of channel sandstones, shales, and thin impure coals, signifying the conclusion of the Eads Mill Member deposition Additionally, the conglomeratic Princeton Sandstone unconformably truncates the underlying deposits, establishing the upper contact of the Eads Mill Member at Pipestem Creek.
Sandstone, which forms an unconformable sequence boundary between itself and the Hinton Formation, indicates continued regression after the Eads Mill Member transgressive event (Englund et al., 1986).
Multivariate Analysis
Cluster analysis of Q and R-mode data revealed two distinct groupings, attributed to variations in salinity The results indicate that marginal marine samples and euryhaline guilds are closely clustered, while open marine samples and stenohaline guilds are similarly grouped This differentiation aligns with the known salinity tolerances and life habits of the taxa within each guild, as supported by previous studies (Fursich, 1993; Hudson et al., 1995; Kammer and Lake, 2001; Lebold and Kammer).
The non-metric MDS charts reveal a significant dichotomy in the data, supporting the findings from the cluster analysis The combined correspondence analysis plot demonstrates a clear trend across all charts, highlighting the strong impact of salinity on the distribution of guild and sample data All three multivariate techniques consistently show the same grouping pattern in both Q and R-mode data, indicating a robust paleoecological signal affecting the Eads Mill Member Notably, many taxa within each guild are present across various lithofacies in each outcrop, such as brachiopods found in limestone, mudstone, and shale at the Bluestone River Bridge outcrop.
Reticycloceras in a shale and limestone at both the I-64 and Rt 102 VA outcrops)
Substrate preferences and the abundance of clastic material did not influence the taxonomic distribution of Eads Mill faunas, as noted by Fursich (1993) Additionally, oxygen availability was not a significant factor, evidenced by the scarcity of pyritized specimens and the absence of stunted taxa Consequently, the primary control on the faunal assemblages is believed to be the salinity tolerances of the taxa within each guild.
Eads Mill Member Paleoecology
The Eads Mill Member signifies a significant marine transgression within the upper Hinton Formation, characterized by the deposition of nearshore sandstones and shales over terrestrial paleosols during early sea level rise This environment led to brackish conditions resulting from the mingling of saline marine water and freshwater from land, allowing only bivalves, gastropods, and cephalopods to thrive in the fluctuating salinities of the shallow, nearshore habitat.
As transgression progressed, the influx of freshwater to the depositional area diminished, allowing stenohaline taxa such as brachiopods, fenestrate bryozoans, and crinoids to thrive in the newly established normal marine conditions during the deposition of the lower (Pluto) limestone These organisms, adapted to typical marine salinities, emerged as the dominant species in the ecosystem.
After the maximum transgressive surface was reached, clastic influx was renewed and mud began to fill the basin depositing a thick gray shale above the lower limestone
The shale contains a limited variety of genera, including bivalves, gastropods, cephalopods, and a rare instance of the brachiopod Lingula The presence of siderite bands at I-64 suggests that the shale was deposited in either a freshwater bay or a restricted nearshore environment characterized by low sulfate levels in the sediment.
The upper (Terry) limestone, situated above the shale, represents the second maximum transgressive surface and is characterized by predominantly stenohaline taxa across all five outcrops Similar to the lower RTVA92 limestone, this layer is rich in brachiopods, fenestrate bryozoans, and crinoids, alongside the first appearance of rugose corals, showcasing the highest taxonomic diversity among the samples It includes representatives from all seven guilds and features the only two trilobite specimens discovered in the Eads Mill While some euryhaline genera persisted in this stenohaline environment, their abundance significantly declined, with 100% of taxa in the RTVA97 mudstone being euryhaline compared to just 35% in the more diverse RTVA96 limestone At Pipestem Creek, euryhaline taxa constituted only 9% in the presence of rugose corals and crinoids in PIPE67, but rose to 50% in PIPE68 when these taxa were absent This suggests that stenohaline genera thrived in open marine conditions, outcompeting euryhaline genera for resources.
After the deposition of the upper limestone unit, the shoreline receded, leading to the accumulation of fine clastic sediments in the basin Similar to previous conditions, the fauna was primarily composed of euryhaline species, with only a few rare occurrences of brachiopods Additionally, the presence of siderite was noted in the sediment.
Outcrops along Rt 102 and I-64 reveal that the shale in these areas was formed under brackish nearshore conditions Throughout the Eads Mill Member, the shoreline receded, resulting in euryhaline marginal marine environments at Rt 102, Pipestem Creek, and I-64 In contrast, open marine conditions were sustained longer at the Bluestone River Bridge and Christian Fork Lake, likely due to their greater distance from freshwater sources, as evidenced by the presence of stenohaline open marine taxa at the top of these outcrops This regression continued until terrestrial facies were deposited, as indicated by the thin impure coal found at the top of the Rt 102 VA section.
A fourth multivariate technique utilizing guild binary data highlights the transgressive/regressive cycle responsible for the deposition of the Eads Mill Member Detrended correspondence analysis (DCA), which eliminates the arch effect present in traditional correspondence analysis, has been previously applied by researchers Scarponi and Kowalewski.
(2004) to determine sea level fluctuations based on estimated water depth Figures 25 and
The Eads Mill Member's deposition reflects a transgressive-regressive cycle characterized by a shift from nearshore, marginal marine facies to open marine conditions as water depth and salinity increased Initially, the base was laid during the transgression, transitioning from brackish to open marine environments as indicated by lower DCA Axis 1 values The first maximum transgressive surface is identified by the lower limestone, followed by the deposition of thick shale and the upper limestone, marking the second maximum Regression occurred post-upper limestone deposition, with the re-establishment of marginal marine conditions and terrestrial facies, evidenced by channel sandstone and coal deposits Notably, the Bluestone River Bridge and Christian Fork Lake outcrops represent the most stable marine environments, showcasing complete open marine deposition with the lowest DCA1 values, indicating prolonged open marine conditions, supporting their deposition farthest from the paleoshoreline.
The detrended correspondence analysis (DCA1) of the Eads Mill Member’s Q-mode data reveals that this geological formation is primarily characterized by open marine samples, with a limited presence of transitional and brackish marine units This finding suggests that the transgressions responsible for the formation of the Eads Mill Member were extensive, resulting in predominantly open marine conditions throughout most of its deposition period.
M e te r s ab ove b as e of E ad s M il l M e m b e r
M e te r s ab ove b a se of E a d s M il l M e m b e r
M e te r s ab ove b a se of
The stratigraphic patterns illustrated in Figure 25 showcase DCA1 scores for the Eads Mill Member outcrops, with the base and top of the member clearly marked Sample numbers within the columns correspond to specific stratigraphic units, indicating that values above 2 reflect increasingly brackish marine conditions, while values below 2 suggest more open marine environments Additionally, the dashed line represents the Terry Limestone, which signifies the highest transgressive surface A regression above the Terry Limestone indicates a shift back towards brackish marine conditions.
The combined detrended correspondence analysis (DCA1) sample score graphs for the Eads Mill Member reveal a transgressive sequence at each outcrop, transitioning from transitional to brackish conditions at the base, reaching open marine conditions in the middle, and regressing back to brackish conditions at the top Notably, the Bluestone River Bridge locality exhibits the most extensive open marine conditions among all outcrops, suggesting it was deposited the farthest from the paleoshoreline.
Eads Mill Member Combined DCA1 Sample Scores
M ete rs a b o v e b a se o f E a d s M ill M em b er
Rt 102 Virginia Bluestone River Bridge Pipestem Creek Interstate 64
The Eads Mill Member reflects a transition from marginal to open marine conditions during the deposition of the upper Hinton Formation, with fossil distribution influenced by proximity to the paleoshoreline and varying water salinity Samples near the shore reveal a rich assemblage of euryhaline taxa, including bivalves, gastropods, and cephalopods, thriving in environments where freshwater mixed with saline seawater Only taxa capable of regulating salt levels could survive the fluctuating salinity As the shoreline retreated, the mixing zone diminished, allowing stenohaline taxa, which prefer stable marine salinities, to dominate the seafloor, thereby enhancing overall taxonomic diversity This indicates that euryhaline species are generalists adaptable to various salinity levels, while stenohaline species are specialists requiring consistent open marine conditions Consequently, salinity emerges as the most significant environmental factor, clearly reflected in the presence and absence of genera and supported by multivariate analyses in this study.
6.4 Upper Hinton Formation Marine Paleoecology
Data from this and a concurrent study of the underlying Fivemile Member of the upper Hinton Formation (Figure 4) conducted by my fellow graduate student Tom
The analysis of combined Cawthern samples aimed to identify overall depositional patterns across two members, incorporating data from samples with multiple taxa This led to the construction of twelve distinct guilds, including three new guilds specifically for ostracods, trilobites, and the brachiopod Lingula Additionally, taxa such as rugose corals, crinoids, and bryozoans were separated from the previously combined osmo-conformer guild of the Eads Mill.
The analysis of the Eads Mill Member involved Q and R-mode data examined through cluster analysis, non-metric MDS, and DCA1 techniques Samples and guilds were categorized based on paleosalinity into brackish marine (5-30‰), transitional marine (30‰), and open marine conditions (35‰) Visual representations, including a bar graph of the twelve guilds' DCA1 values and a combined DCA1 sample score graph for both the Fivemile and Eads Mill Member, were created These findings underscore that proximity to the shoreline and salinity levels were the key factors influencing the distribution of taxa in the marine zones of the upper Hinton Formation.
Table 6 presents binary guild data for the Eads Mill Member and the Fivemile Member, with total abundance calculated at the bottom and total guild richness displayed along the side for each sample Additionally, the combined guild abundance for both members is summarized at the bottom of the second half of the table.
Locality and sample number Guild Sum
T- Brachs Lingula P-Brachs Epi-Biv In-Biv Gastropods Nautiloid Trilobote Bryozoans Crinoids
Locality and sample number Guild Sum
In- Biv Gastropods Nautiloid Trilobote Bryozoans Crinoids
Q M o de Cl us te r A nal ys is (J ac ca rd ) 0 0 12 0 24 0 36 0 48 0 6 0 72 0 84 0 96
Synthesis
The paleoecology of the Fivemile and Eads Mill members is influenced by their proximity to the shoreline, affecting water depth, salinity, and turbidity Each member contains taxa that reflect the paleosalinity of their depositional environments While they share 20 of the 36 identified genera, the Fivemile Member is characterized by brackish marine taxa, indicating a transitional environment, whereas the Eads Mill Member is dominated by open marine taxa, with transitional and brackish conditions present during specific phases of transgression and regression Thus, despite sharing several taxa, these two marine members represent distinct depositional environments with differing taxonomic compositions linked to their paleosalinity.
Salinity and proximity to shoreline were the principal environmental factors controlling the taxonomic composition of each sampled unit within the Eads Mill
The Eads Mill Member features brackish and transitional marine taxa that indicate the onset of transgression and the conclusion of regression, characterized by lower salinity due to the influx of freshwater from local rivers Although turbidity and clastic material were more prevalent in the marginal marine environment, their impact on taxonomic composition was overshadowed by salinity levels The presence of brachiopods and stenohaline taxa in two limestones within the Eads Mill Member suggests that transgression progressed until open marine conditions with normal salinity were achieved These two limestone formations represent maximum transgressive surfaces, indicating a transition to open marine conditions and a reduction in clastic influx in the middle sections of the Eads Mill Member.
Member outrops Thus the salinity tolerance of each guild identified within the Eads Mill Member controlled its occurrence within the stratigraphic sequence
Taxa from the Eads Mill Member of the upper Hinton Formation exhibit significant similarities to those found in the Reynolds Limestone of the Bluefield Formation, as noted by Kammer and Lake (2001), as well as the Avis Limestone of the Hinton Formation, highlighted by Henry and Gordon (1992).
The Greenbrier Limestone Group, as identified by Carney and Smosna (1989) and Wynn (2005), is part of the Upper Mississippian in the Appalachian Basin and features four units rich in open marine taxa This diverse assemblage is primarily composed of brachiopods, crinoids, fenestrate bryozoans, and some rugose corals In contrast, the taxonomic composition of the Fivemile Member from the upper Hinton Formation closely resembles that of the Bickett Shale found in the Bluefield Formation.
Kammer and Lake (2001) indicate that both deposits were formed in brackish marine environments and feature a variety of euryhaline taxa, including bivalves and gastropods The tolerance to salinity is understood to play a crucial role in determining the distribution of invertebrate fauna within the Upper region.
Mississippian strata in the Appalachian Basin
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WVGS Fieldbook Numbers for Eads Mill Member Sections
Taxa Characteristics Used in Identification
Brachiopods: Page numbers from Moore (1965) listed in parentheses
Anthracospirifer (H 704) - Its hinge line is transverse and nearly equal to maximum width, and it has a moderate number of bifurcating lateral plications The fold and sulcus is distinct
Cleiothyridina (H 662) – It has a transversely sub-oval shell that is nearly biconvex Distinct fold and sulcus are developed anteriorly
Composita (H 662) – Has a characteristically smooth, biconvex shell with well developed fold and sulcus Growth lines are nearly perpendicular to the hinge
Diaphragmus (H 484) – Is medium sized with medium to thick costellae extending the length of the pedicle valve A few scattered spine bases noted on some specimens
Eumetria (H 651) – Has slightly oval to elongated costate shells No fold or sulcus noted
Flexaria (H 490) – Shell is a rounded triangle in outline Pedicle valve has irregular to elongate costae with short overlapping spine ridges
Fluctuaria (H 501) – Is a small shell that is sub-circular in outline and is broadest anteriorly Pedicle valve has fine costellae and is strongly rugose over the entire valve
Inflatia (H 482) – Is a medium sized specimen with highly convex pedicle valve that contains small, rounded costae that converge at the sulcus
Lingula (H 263) – Has an elongated oval outline with slightly convex valves
Concentric growth lines are sub-parallel to hinge and extend anteriorly
Orthotetes (H 409) – Medium to large size with a sub-rounded outline whose hinge extends nearly its entire width Has numerous fine costellae that radiate from its umbo
Ovatia (H 503) – Has an elongate shell with highly convex pedicle valve It contains numerous fine costellae extending the length of the pedicle valve
Punctospirifer (H 714) – Is small to medium sized similar to Anthracospirifer
Has strong lateral plications, imbricate growth lamellae, and is punctuate, from which it derives its name
Torynifer (H 724) – A small, sub-rounded shell with a prominent umbo No distinct fold and sulcus noted, and both valves lack ornamentation
Bivalves: Page numbers from Moore & Teichert (1969) listed in parentheses
Aviculopecten (N 336) – Has fine radial ornamentation propagating from its beak
Its hinge extends nearly the width of the shell, below which is a deep byssal notch
Cardiomorpha (N 818) – Similar in shape to Edmondia, but with a much more prominent beak and umbo It has a smooth exterior with very fine growth lines
Edmondia (N 818) – Ovoid to elliptically elongate shell, with a small beak located one-third behind its anterior margin Its exterior has irregular concentric growth lines
Ectogrammysia (N 819) – Has an ovoid shell with thick radial ribs
Modiolus (N 278) – An oval, elongated shell with the beak behind the anterior end The exterior is smooth with fine concentric growth lines
Nuculopsis (N 231) – It is a very inequilateral shell with fine concentric growth lines and a curved beak
Paleyoldia (N 237) – Has a compressed, trigonally rounded shell with numerous fine concentric growth lines
Phestia (N 238) – It has a compressed anteriorly oblique shell with numerous fine concentric growth lines Inside, the hinge contains chevron shaped tooth and socket holes
Schizodus (N 475) – Has an inequilateral, trigonally ovate shell with a pronounced beak and fine concentric growth lines
Septimyalina (N 291) – It has a slender elongated shell with and extended beak and a smooth exterior A distinct linear ridge extends along one edge of the shell and disappears near its anterior end
Gastropods: Page numbers from Moore & Pitrat (1960) listed in parentheses
Bellerophon (I 182) is a young specimen characterized by a tightly whorled shape that flattens as it matures It features a convexly elevated selenizone that accounts for approximately 10 percent of its width The growth lines, which become increasingly prominent near the aperture, are closely spaced and sharply curved towards the selenizone.
Euphemites (I 178) – Whorl profile is evenly rounded in young specimens
Selenizone comprises 25 percent of the width Evenly spaced lirae are continuous along the length of the whorl to the shell aperture
Ianthinopsis (I 320) – It has a wide, globular form with a small pointed apex
Some faint spiral ridges may be noted on an otherwise plain exterior
Knightites (I 184) exhibit a sub-triangular whorl profile at maturity, transitioning to a more rounded shape The shell features a prominent selenizone, which constitutes 25 percent of its width and is convexly elevated, resembling a keel near the aperture in mature specimens Additionally, closely spaced growth lines curve toward the selenizone and are intersected nearly perpendicularly by fine lirae.
Naticopsis (I 276) – Has an extremely wide body whorl with a slightly elevated spire Its body whorl is relatively well rounded
Cephalopods: Page numbers from Moore (1964) listed in parentheses
Reticycloceras (K 250) – A straight shelled nautiloid with coarse, evenly spaced transverse ribbing extending the length of the shell The siphuncle is centrally located
Trilobites: Page numbers from Moore (1959) listed in parentheses
Paladin (O 401) – Its glabella is nearly parallel sided, and its eyes are large in size and are posteriorly located The pygidium has a well defined border
Archimedes – A fenestrate with fans the spread outward from a central screw- shaped spiral The fans have a fine cross-crossed mesh pattern in which the individual organisms lived
Encrusting – A homogenous pattern of very fine (< 1mm) pits or borings on the exterior of shell material
Paraconularia – A cnidarian with coarse, wavy ribs that extend transversely across its body It is narrow where it attaches to the substrate, and forms a widening taper upwards.