Seasonally Resolved Î´18O from Pennsylvanian Mollusk Aragonite

Syracuse University SURFACE

Theses - ALL

August 2018

Seasonally resolved δ18O from Pennsylvanian mollusk aragonite

Marie Yerill Jimenez Syracuse University

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Recommended Citation Jimenez, Marie Yerill, "Seasonally resolved δ18O from Pennsylvanian mollusk aragonite" (2018). Theses - ALL. 264. https://surface.syr.edu/thesis/264

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Use of the δ18O thermometer in deep time investigations is complicated by uncertainty in the oxygen isotopic composition of seawater and an increasing potential for diagenetic alteration with age. These concerns are particularly important when considering that δ18O values from

Paleozoic marine carbonates are generally low and show a depletion trend with increasing age.

Competing explanations for this trend include increasing alteration with age, evolution of seawater δ18O through time, and increasing ocean temperatures with age. Demonstrating the preservation of original mineralogy, thus eliminating diagenesis as a factor, is a primary hurdle in deconvolving potential causes. Here, we report data from serially sampled, Middle

Pennsylvanian mollusks from the Appalachian Basin of Kentucky. XRD and SEM analyses indicate an aragonitic mineralogy with retention of primary microtextures, and δ18O data reveal regular cyclic variation over ontogeny, suggesting that original shell carbonate is preserved and records primary environmental (presumably seasonal) conditions over the life history of the animal. However, values are depleted, centering around -4.6‰, and intraannual variation is significant, spanning up to 2.2‰. Recent work on the Carboniferous of the U.S. suggested that negative values reflect a regional salinity trend toward more depleted values with increasing distance from Panthalassa. Our data extend the trend eastward, suggesting significant freshwater input closer to the Allegheny Front. However, the high degree of seasonality differs from published data in the basin, suggesting that mollusks record conditions in nearshore settings that receive seasonally variable contributions of isotopically depleted runoff. Although our data support the primary nature of low δ18O values from brachiopod shells, they also highlight the influence that δ18O values from epicontinental seas may have on the Paleozoic depletion trend.

Seasonally resolved δ18O from Pennsylvanian mollusk aragonite

Marie Y. Jimenez

B.S. University of Rhode Island, 2016

THESIS

Submitted in partial fulfillment of the requirements for the degree of Master of Science in Earth

Sciences

Syracuse University

August 2018

Acknowledgements

Funding for this research comes from student research grants from Paleontological

Society and the Geological Society of America and from the John J. Prucha Field Research Fund at Syracuse University. Part of the specimens for this study were provided by Carnegie Museum of Natural History, Dr. Gordon C. Baird at SUNY Fredonia, and Dr. Joseph G. Carter at UNC

Chapel Hill. I would also like to thank Lindsay R. Moon for assistance in field work done the summer of 2017 to collect more specimens. Thanks to Bruce Barnett at the Keck-NSF

Paleoenvironmental and Environmental Laboratory at Kansas University for performing the stable isotope analyses and to Dr. Edward Berry at SUNY Upstate Medical University for training and access to XRD. Thanks to Dr. Christopher McRoberts at SUNY Cortland for helping me perform SEM analyses.

I want to thank my advisor Dr. Linda Ivany for her continued and unwavering support throughout my two years here. I am extremely grateful for her guidance, feedback, and mentorship which has truly helped me make the best out of my graduate school experience.

Thanks also to the Paleo X extended research group, for providing a sense of community and a venue for weekly scientific discussion; I have learned so much from being a part of this group. I also want to thank Emily Judd for her help with lab work but most importantly for her conversation and mentorship. Being her teaching assistant this past semester has been inspiring.

Thanks to my committee members Dr. Christopher Junium and Dr. Scott Samson who have provided valuable feedback at various stages of this study. Lastly, thanks to the Department of Earth Sciences (faculty, staff, and graduate students) for helping and encouraging me during my time here.

Table of Contents Abstract...... i

Title Page...... ii

Acknowledgements...... iv

Table of Contents...... v

List of Figures...... vi

List of Tables...... vi

Introduction...... 1

Geologic Setting and Taxa Sampled...... 2

Methodology...... 3

Results...... 4

Discussion...... 5

Summary...... 12

Figures...... 13

Supplement...... 17

References...... 31

List of Figures

Main Text

Figure 1. Paleogeography, stratigraphy, and samples...... 13

Figure 2. Oxygen Carbon cross-plot...... 14

Figure 3. Oxygen isotope profiles...... 15

Figure 4. Conceptual model of U.S. epicontinental sea...... 16

Supplement

Figure S1. Trace element cross-plot...... 17

Figure S2. Temperature ranges based on water composition...... 18

List of Tables

Supplement

Table S1. Trace element data...... 19

Table S2. Oxygen and carbon isotope data...... 20

Introduction

The oxygen isotope paleotemperature proxy has been essential in identifying small and large scale environmental change during the relatively recent geologic past (e.g., Emiliani, 1955;

Zachos et al., 2008). However, its application to investigations of paleoenvironmental conditions farther back in time has resulted in controversy over the oxygen isotopic composition of seawater

18 (δ Ow) and sea surface temperatures (SST) through time. These concerns are wrought, in

18 particular, by the oxygen isotope values of Paleozoic marine carbonates (δ Ocarb), which show a general depletion with increasing age (Jaffres et al., 2007; Veizer et al., 1997).

The Paleozoic marine oxygen isotope record is predominantly derived from the calcitic shells of brachiopods (Veizer et al., 1997), favored because of their prevalence in the rock record and their resistance to diagenetic alteration (e.g., Carpenter & Lohmann, 1995; Grossman,

2012a). The wide range of values in any given time slice, however, has raised questions about the reliability of these materials (Grossman, 2012b). Eliminating the potential influence of diagenetic alteration is a necessary but not straightforward prerequisite before any interpretation can be made. Screening procedures have resulted in an attenuation in the range of the values, yet these remain contentious (Grossman, 2012b; Jaffres et al., 2007). Oxygen isotope data from aragonite, alternatively, are more likely to be primary because of aragonite’s propensity for neomorphism to the more stable calcite (Lowenstam, 1961; Brand, 1989). While aragonite is exceedingly rare in the Paleozoic record, its potential to clarify the significance of data from coeval calcite is considerable.

Here, we present seasonally resolved stable isotope data from demonstrably primary

Middle Pennsylvanian aragonitic mollusks from the US Appalachian Basin. Isotope values are too low and seasonally variable to reflect precipitation from seawater of normal marine

composition today. We argue that while these values are primary, as likely are those from many other Paleozoic fossils, they do not reflect open marine conditions but rather the often-atypical regional conditions specific to their location in the epicontinental seas in which they are found.

Low Paleozoic oxygen isotope values therefore reflect bias in the rock record, with unaltered sediments preserved only on the craton. Open-ocean-facing shelves, which might have retained a more marine signature, have largely been deformed and altered in subsequent orogenic events.

Geologic Setting and Taxa Sampled

Specimens for this study come from a single outcrop of the Atokan stage Magoffin Shale, in Hazard, KY. During the Pennsylvanian, the U.S. midcontinent was situated at equatorial latitudes and covered by an epeiric sea that extended eastward into the Appalachian Basin

(Figure 1a). The dark gray, calcareous Magoffin Shale, a marine unit of the Breathitt Formation

(Figure 1b), records an interglacial marine transgression (Chesnut, 1981). The unit preserves a diverse shallow-marine assemblage of bivalves, gastropods, cephalopods, and crinoids (Morse,

1931), some of which are reported to retain their original aragonite mineralogy (Brand, 1987).

Here we focus on the mollusks, as they are known to precipitate their shells in isotopic equilibrium with ambient seawater (Grossman & Ku, 1986), and their benthic and relatively sedentary nature reduces the possibility of retrieving oxygen isotope data that reflect lateral migration or vertical movement through the water column. Taxa examined are Bellerophon

(Euphemites) carbonarius and Bellerophon crassus (Monoplacophora), Worthenia tabulata

(Gastropoda), and Septimyalina sp. (Bivalvia) (Figure 1c).

Methodology

Screening for diagenetic alteration

All specimens were screened for diagenetic alteration prior to isotopic analyses. Scanning electron microscopy (SEM) enables evaluation of shell microstructure so as to recognize textures consistent with primary molluscan shell versus dissolution and reprecipitation. Fragments exposing shell cross sections were imaged on the ISI-DS-130C at SUNY Cortland. For initial screening, we chose not only those specimens that appeared most pristine, but also those exhibiting an overt visible range in quality of preservation.

Mineralogy of shell subsamples is confirmed using powder X-Ray diffraction (XRD).

Samples were analyzed using an Xcalibur PX Ultra X-Ray Diffractor and the CrysAlispro data collection program at SUNY Upstate Medical University. Standards for aragonite and calcite were also analyzed for comparison with spectra from fossil specimens. An aragonite mineralogy suggests the preservation of primary shell material and hence suitability for accretionary stable isotope analysis. The same samples used in XRD analyses are also evaluated for their trace element compositions using the quadrupole Elan DRC-e ICP-MS at SUNY College of

Environmental Science and Forestry. Trace-element abundances can help distinguish between biogenic carbonates and diagenetic secondary calcite since their elemental chemistries are dissimilar. In particular, Mn and Fe concentrations are generally elevated with precipitation from anoxic pore waters during diagenesis (Brand & Morrison, 1987).

Stable Isotope Analysis

Sampling for isotopic analysis employed both a hand drill and a Merchantek MicroMill.

Although the MicroMill allows for higher spatial resolution, the hand drill is necessary for

specimens with shell coiling (Figure 1c). Sampling follows growth increments in the outer shell layers of specimens with a spatial resolution of 0.35-0.50 mm in the direction of ontogeny.

Samples span as much of the life history as possible given the condition of the shells. Before sampling, secondary nacre was removed from the surface of bellerophonts where “waterlines” on later whorls suggested that the mantle covered earlier shell growth with aragonite. In addition to ontogenetic trajectories from select specimens, we spot-sampled a number of individuals to reveal the range of values expressed within the assemblage. For comparison with published data, we also spot-sampled two brachiopod specimens from the same location. Stable isotope analyses

18 13 of shell carbonate (δ Ocarb, δ Ccarb) were performed at the Keck-NSF Paleoenvironmental and

Environmental Laboratory at the University of Kansas on a ThermoFinnigan Mat 253 isotope ratio mass spectrometer coupled to a Finnigan Kiel automated preparation device. Precision is

18 13 better than 0.10‰ for both δ Ocarb and δ Ccarb.

Results

Screening for diagenetic alteration reveals both well-preserved and altered specimens.

Specimens with an entirely aragonite mineralogy exhibit microtextures consistent with modern mollusk shells (Carter, 1989) and heavier carbon and oxygen values (Figure 2). Shells with textures generally associated with alteration also show significant calcite peaks and more depleted carbon and oxygen values. Mn and Fe concentrations for the aragonitic shells were within the modern range in values (Milliman, 1974; Morrison & Brand, 1986) whereas the calcitized shells showed elevated concentrations well above the modern range (Figure S1, Table

S1).

18 Magoffin Shale mollusks deemed to be well preserved yield δ Ocarb values that vary cyclically over ontogeny, suggestive of primary environmental variation. Mean values center around -4.6‰ and data range over as much as 2.2‰ within individual shells (Figure 3). Carbon isotope values also show variation over ontogeny, generally exhibiting positive covariance with

δ18O values (Table S2). Mean δ13C values center around 2.6‰ and range over as much as 1.9‰.

Spot samples from additional specimens retaining aragonite fall within this range for both oxygen and carbon isotope values, while those exhibiting significant calcite are considerably more depleted, with mean values of -10.3‰ and -1.8‰ respectively.

Bulk samples from brachiopod shells (Table S2) reveal slightly more positive oxygen isotope values, averaging around -3.5‰ with less than 0.2‰ variability between specimens.

Aragonite-water fractionation leads to more enriched δ18O values as compared to calcite. We therefore apply a correction of -0.8‰ (Kim et al., 2007) to calcite values, with the result that brachiopod calcite is about 2‰ more positive than co-occurring mollusk aragonite.

Presuming that isotopic variation is seasonal in nature, bellerophonts could record up to four years of growth, Worthenia tabulata two years, and bivalves eight years of growth if annual cycles are extrapolated over unsampled portions of the shells.

Discussion

Preservation is a crucial factor when attempting to apply the oxygen isotope paleothermometer. During diagenesis, the mineralogy, microtextures, and chemistry of skeletal material can all be altered, and if so, the oxygen isotope value of skeletal carbonate may no longer reflect environmental conditions at Earth’s surface at the time of formation. Since the

alteration of aragonite generally results in either dissolution or reprecipitation as calcite

(Bathurst, 1964) its occurrence in ancient sedimentary rocks is, itself, suggestive of an unaltered chemical composition. Past studies (Dennis & Lawrence, 1979; Brand, 1987) have determined that the mollusks of the Magoffin Shale can be preserved as aragonite. In this study, microstructural examinations of molluscan shells by SEM in conjunction with XRD analyses reveal well-oriented textures such as sheeted nacre and crossed lamellar structures (Figure 2;

Carter, 1989), typical of modern aragonitic mollusks, in specimens with an aragonite mineralogy, indicating primary shell preservation. Although shells with varying degrees of calcitization were analyzed for comparison, no secondary growth structures associated with dissolution, reprecipitation, or cementation were detected in any of the shells chosen for serial sampling.

Elemental ratios for Fe and Mn are well within modern molluscan aragonite values (Morrison &

Brand, 1986; Brand, 1989) and there are no observable taxonomic trends associated with these values (Figure S1). Ontogenetic variation in δ18O and δ13C in serially sampled specimens shows regular, cyclical variation along the growth axis, further suggesting the retention of primary isotopic compositions (Ivany & Runnegar, 2010). Therefore, we maintain that these specimens preserve their original chemistry and are therefore suitable for paleoenvironmental analysis.

If we consider molluscan stable oxygen isotope values to reflect temperature alone, we can calculate the temperatures experienced by mollusks in the Magoffin sea using the empirically derived paleotemperature equation of Grossman and Ku (1986), modified by

Dettman et al. (1999):

18 18 T(°C) = 20.6 – 4.34(δ Ocarb - δ Ow + 0.20)

Since samples come from an interglacial interval during a time with a continental ice sheet, conditions broadly similar to today (Crowley et al., 1991), we begin by assuming a seawater

18 composition equivalent to that of today’s global ocean (δ Ow = 0‰). Calculated mean paleotemperatures under these assumptions center around 39 °C and range between ~36 °C and

45 °C, well in excess of mean annual sea surface temperatures (SSTs) in comparable modern equatorial locations and considerably more seasonal (Figure S2). The Java Sea, for example, a shallow, equatorial, semi-enclosed, epicontinental, marine basin, experiences temperatures that vary between 28 °C and 30 °C (Reynolds et al., 2002). While temperatures in excess of 40 °C have been proposed for parts of the Paleozoic (Henkes et al., 2018), these values exceed the thermal tolerances of living members of most animal phyla (Portner, 2002), and so continue to be deliberated. Such observations make clear that Magoffin Shale oxygen isotope values, while primary, are likely to be 1) too low and 2) too seasonal to reflect temperature alone in an equatorial sea with near-modern seawater composition.

Low primary oxygen isotope values from the late Paleozoic Appalachian Basin could be interpreted in two ways. Veizer and Prokoph (2015) posit a secular trend in the δ18O value of the

18 global ocean through the Phanerozoic, yielding baseline δ Ow during the Carboniferous of approximately -1.5‰. In this case, calculated paleotemperatures are more palatable on average

(32 °C) but remain unrealistically seasonal for the tropics (29 – 38 °C). Alternatively, given that

18 the majority of δ Ocarb values for the Paleozoic come from shallow epicontinental settings with proximity to freshwater runoff, Grossman et al. (2008) argue that low values could reflect regional differences in both temperature and salinity within epicontinental seas. A series of studies (Flake, 2011; Joachimski & Lambert, 2015; Roark et al., 2017) investigated this hypothesis by sampling from Carboniferous localities across the U.S. midcontinent. All studies found an enrichment trend in skeletal δ18O from present-day east to west, interpreted to reflect increasing proximity to the Panthalassic Ocean and concomitant reduction of the influence of

18 freshwater mixing on δ Ow. If the observed trend is a product of a salinity gradient across the epicontinental sea, values from the Appalachian Basin should consistently exhibit the most

18 depleted δ Ocarb values for a given time slice. Indeed, Magoffin Shale brachiopod and

18 mineralogy-adjusted mollusk δ Ocarb values from the Appalachian Basin are consistently more depleted than published brachiopod isotope values from the Illinois and Midcontinent basins

(Figure 4; Mii et al., 1999; Grossman et al., 2008).

In addition to being depleted, oxygen isotope values from Magoffin Shale mollusks are also quite seasonal, indicating some combination of variation in temperature and/or water composition. If the seasonal range of the temperature observed here (~ 9°) is not likely at the equator, then the dominant influence on the intra-annual variation in shell δ18O is water composition. High-resolution δ18O data from modern low-latitude mollusk shells can show substantial variation due to seasonal changes in freshwater input (Tao et al., 2013). However, the

Magoffin Shale contains a marine assemblage of brachiopods, crinoids, mollusks, and conulariids. Given that crinoids and brachiopods are considered to be stenohaline, salinity should be constrained to a narrow range (~30-35 PSU (EPA, 2006)). Therefore, the δ18O of precipitation would have to be negative enough to lower the δ18O value of local seawater without driving down salinity by more than ~5 PSU. Although equatorial precipitation usually centers around -

3‰ (Bowen & Wilkinson, 2002), significant distillation can be achieved through adiabatic cooling and rainout driven by topography. Precipitation in the northern Andes (latitude: 0-7°S, elevation: > 2000 m), e.g., exhibits a climatological monthly minimum of -10‰ correlated with high precipitation rates (14 mm/day) (Insel et al., 2013). Given that the elevation of the Central

Pangean Mountains (CPMs) most likely reached 3000 m (Zeigler et al., 1985), the δ18O of tropical precipitation could have been similarly, if not more, negative. With a marine endmember

of 0.0‰, fresh water at -10‰, and minimum salinity of 30 PSU, a mixing relationship predicts that the δ18O of local seawater could have been as low as -1.4‰ during the time that stenohaline organisms were present. Using the quadratic approximation of the O’Neil et al. (1969) equation by Hays and Grossman (1991) for calcite material, paleotemperatures derived from brachiopod bulk values could represent mean temperatures as low as ~25 °C (assuming 30 PSU) and up to

32°C (assuming 35 PSU). Given the lack of variability within and among brachiopod shells, albeit data being sparse (Table S2), would suggest that both salinity and temperature remained relatively constant within that range of possibilities. However, in more marginal environments close to the Allegheny Front and the source of isotopically negative fresh water, local seawater could have been even more negative and variable.

That serially-sampled mollusk values are negative and clearly primary further reinforces the validity of the eastward trend toward lower values seen in brachiopod skeletal carbonate.

Nonetheless, while taxon-specific comparisons show agreement within the basin, mollusk aragonite is still somewhat more negative than apparently coeval brachiopod calcite (Brand

1987; this study). In addition, the high degree of seasonality in our study differs from that seen in slightly younger Appalachian Basin brachiopods (Roark et al., 2016). These observations suggest that these Pennsylvanian mollusks could record conditions in more brackish (<30 PSU) and hence variable settings, while brachiopods characterize settings with more stable marine conditions. Many mollusks are tolerant of some degree of reduced or variable salinity, while most brachiopods require more marine and less variable conditions. The proportional abundance of brachiopods in a fauna has even been suggested to reflect the range of salinities experienced by a given assemblage (Lebold & Kammer, 2006). The Magoffin Shale has been described as a mollusk-dominated facies (Brand, 1987), with brachiopods typically concentrated in thin beds

rather than distributed throughout. This suggests that the Magoffin sea typically fluctuated between more and less brackish salinities depending on the intensity of rainfall and runoff and proximity to the shore. Our most depleted δ18O values would then indicate the most reduced salinities of the year. Assuming summer SSTs similar to the Java Sea today (30-31 °C), salinities would have been ~23-24 PSU at the peak of the rainy season. These values agree with the salinities estimated by Brand (1987) for the Kendrick and Magoffin Seas and are consistent with the conceptual models of the epicontinental sea’s circulation (Algeo et al., 2008; Algeo &

Heckel, 2008) which predict the persistence of a halocline at shallow depths (Figure 4). Brief incursions of brachiopods could then be permitted during drier intervals or at times when salinity stratification allowed for a more marine assemblage at depth.

While salinity could have varied on an annual or interannual basis, the general positive cyclic covariation in oxygen and carbon isotope values in these mollusk shells is consistent with seasonal precipitation and runoff of 18O-depleted water containing (isotopically negative) dissolved inorganic carbon derived from the decomposition of terrestrial organic matter.

Seasonality of precipitation at equatorial latitudes is driven mainly by the Intertropical

Convergence Zone (ITCZ), which shifts between the Northern and Southern Hemispheres following the position of highest solar insolation. In the case of an everwet/humid equatorial scenario, the ITCZ is expanded such that seasonal shifts generally do not affect precipitation rates near the equator. Everwet conditions have been posited during Pennsylvanian interglacial intervals, when retreat of the Gondwanan ice sheet allowed for expansion of the ITCZ (Tabor &

Poulsen, 2008). However, our data suggest significant seasonality in precipitation during these times in the Appalachian Basin. Simulations of Pennsylvanian-Permian climate by Peyser and

Poulsen (2008) found that, although seasonal variation is more pronounced during times of

greater ice volume, precipitation is nonetheless monsoonal near the equator even in no-ice scenarios. Higher elevation of the CPM also enhanced seasonality of precipitation in the northern hemisphere due to the blocking effect of equatorial northeast-southwest trending mountains on migration of the ITCZ, but this effect was secondary to the size of the ice sheet (Peyser and

Poulsen, 2008; Otto-Bliesner, 1998). These model results are consistent with the highly depleted and seasonal nature of δ18O values from interglacial mollusks in this study and emphasize the presence of a seasonally varying tropical climate even during interglacial stages.

We suggest that low and seasonal stable isotope data from exceptionally preserved aragonitic mollusks in the Appalachian Basin reflect the most proximal (eastward) end of a salinity gradient across the North American epicontinental sea extending from Panthalassa to the west. The demonstrably primary nature of these shell data reinforces the primary nature of low

δ18O values from more widely available brachiopod carbonate of the epicraton. Further, strong seasonality in tropical mollusk δ18O values demands a departure from normal marine salinity/water composition. Published Paleozoic data are broadly similar to North American data in that they necessarily come from epicontinental seas, and therefore likely also experienced

18 δ Owater values that did not reflect the open ocean. The non-normal-marine nature of epicontinental environments has been noted in the paleontological literature as well with the observation that the number of unfossiliferous units per unit time was higher in the Paleozoic than in the Meso-Cenozoic and correlates with the degree of continental flooding (Peters, 2007).

That many more Paleozoic sedimentary units than expected are depauperate or barren suggests that some combination of hypoxia and salinity stress in epicontinental seas may have limited macrofaunal diversity (Peters, 2007). The generally more negative δ18O values from Paleozoic skeletal carbonates may reflect the same bias against normal marine conditions, as δ18O values

from the Paleozoic generally come from epicontinental settings. We therefore follow Grossman

18 et al. (2008) in arguing for δ Owater values that do not reflect the global open ocean, with the consequence that reliable paleotemperatures cannot be calculated from Paleozoic shell δ18O values simply by assuming a standard open-marine water composition. High-resolution sampling of molluscan carbonates from other regions (such as the Russian Platform), should they become available, could further test this hypothesis and help to constrain bias. While muting concerns about a systematic preservation bias with age (Land and Lynch, 1996), seasonally resolved data from molluscan aragonite simultaneously emphasize that δ18O values from the Paleozoic should not be used at face value to make deductions about the oxygen isotopic composition or temperature of the global oceans through time.

Summary

Multiple lines of evidence demonstrate that the fossils of the Magoffin Shale preserve their original chemistry. Depleted δ18O values are consistent with the influence of freshwater influx closer to the Allegheny Front. The high range of seasonal variation suggests a seasonal precipitation regime driven by the migration of the ITCZ. Published brachiopod data are increasingly positive to the west, consistent with a salinity gradient across the epicontinental sea toward the open ocean. The majority of Paleozoic isotope data come from epicontinental seaways, raising the question of whether they can reflect fully marine chemistries and therefore global temperature trends. Future work should focus on finding and sampling rare accretionary aragonite from other locations so as to evaluate the potential influence of reduced salinity more generally on the Paleozoic oxygen isotope record, and on climate model predictions for how salinity and water composition may have varied across Paleozoic epicontinental seas

Figures

Figure 1 (A) Paleogeography of the Pennsylvanian mid-continental sea of North America (After Blakey, 2006). Red star marks the location where specimens for this study were collected. (B) Stratigraphic column of the Pennsylvanian section in Kentucky, showing the position of the Magoffin Shale. C) Fossil mollusks sampled for this study: Bellerophon (Euphemites) carbonarius (1-2), Worthenia tabulata (3-4), Septimyalina sp. (5-6). Scale bars = 10 mm.

Figure 2. Oxygen versus carbon stable isotope cross-plot comparing data from well-preserved shells versus values from altered material. Filled symbols belong to serial samples and unfilled symbols are spot samples. SEM images confirm the retention of molluscan shell microtextures in specimens that also retain an aragonite composition. Specimens with textural evidence for dissolution and reprecipitation also contain significant calcite.

Figure 3. Stable oxygen isotope profiles for all specimens. Colored bars along bivalve profiles indicate physical location of growth bands. Regular variation along the growth axis suggests seasonal variation and retention of primary mineralogy.

Figure 4. A schematic cross section (adapted from Algeo et al., 2008) of the epicontinental sea from the Midcontinental Shelf to the Appalachian Basin showing how proximity to the Central Pangean Mountains could affect the isotopic composition of seawater. Various studies have postulated the persistence of a halocline within the sea as a result of everwet conditions. Assuming a seasonal variation in intensity of rain and runoff, the fauna of the Magoffin could have been subjected to brackish and variable conditions. Superimposed data are oxygen isotope values from brachiopods of Middle Pennsylvanian Age. white circles represent values from published studies (Mii et al., 1999; Grossman et al., 2008). Red circles are values from this study used for comparison with our mollusk data. Middle Pennsylvanian data exhibit a depletion trend eastward further suggesting a salinity gradient and reduced salinity in the Appalachian Basin.

Supplement

Figure S1. Cross-plot of Mn and Fe concentrations in specimen shells. Upper limits of observed concentrations in modern molluscan aragonite are delineated by the dashed lines (Milliman, 1974; Morrison & Brand, 1986). Concentrations in specimens that retain their aragonite mineralogy fall within modern values whereas calcitized shells exhibit highly enriched concentrations.

18 Figure S2. Temperature possibilities for range of mean δ Ocarb values from well preserved 18 18 shells given constant δ Ow compositions (dashed lines). If we assume a δ Ow composition similar to today (0.0‰) temperatures would be above what is considered the upper thermal limit to metazoan life (Portner, 2002). In order for temperatures to be comparable to conditions in a 18 similar setting today, such as the Java Sea, δ Ow compositions would have to be more depleted and vary inter- and/or intra-annually. Java Sea range of temperatures from Reynolds et al. (2002).

Tables

Table S1. Geochemistry data for specimens sampled. All elemental concentrations reported in ppm. A = aragonite C = calcite.

ID Taxa Min. Ca Fe Mg Mn Ba Sr BPHK-01-b Bellerophon A 366783 282 147 26 234 3237 BPHK-01-c Bellerophon A 406165 263 160 54 192 3891 BPHK-02-b Worthenia A 386827 443 308 96 68 2461 BPHK-03-a Septimyalina A 380214 481 280 86 66 1804 BPHK-04-a Septimyalina A 369645 1267 441 234 140 1703 BPHK-05-a Bellerophon C 375371 10349 5557 1208 184 1609 BPHK-05-b Bellerophon C 388837 7763 3168 1182 110 2779 BPHK-06-a Bellerophon A 395305 980 445 242 1043 3254 BPHK-07-a Spirifer C 374826 173 866 59 9 715 BPHK-11-a Worthenia A 380014 511 383 184 38 2462 BPHK-JC1-a Bellerophon A 214071 190 115 29 5192 4160 BPAM-01-a Bellerophon C 369555 11929 4357 2903 2858 2104 BPAM-02-a Bellerophon C 349293 12812 4192 2946 9462 1879 BPAM-03-a Bellerophon C 366930 12175 4455 2796 3033 1991

Table S2. Oxygen and Carbon isotope data from specimens sampled. All values reported in per mille (‰). * = spot samples from aragonitic shells. # = spot samples from calcitized shells. + = spot samples from brachiopods.

ID δ13C δ18O ID δ13C δ18O ID δ13C δ18O BPHK-01 BPHK-01-37 0.79 -5.05 BPHK-01-73 1.64 -5.07 BPHK-01-01 0.98 -5.08 BPHK-01-38 0.99 -4.94 BPHK-01-74 1.56 -5.36 BPHK-01-02 1.44 -5.56 BPHK-01-39 1.42 -4.8 BPHK-01-75 1.47 -5.42 BPHK-01-03 1.12 -5.11 BPHK-01-40 1.31 -4.8 BPHK-01-77 1.35 -5.54 BPHK-01-05 1.07 -4.93 BPHK-01-41 1.61 -4.71 BPHK-01-78 1.19 -5.75 BPHK-01-06 0.91 -5.94 BPHK-01-42 1.62 -4.75 BPHK-01-79 1.19 -5.54 BPHK-01-07 0.86 -5.12 BPHK-01-43 1.7 -4.74 BPHK-01-80 1.24 -5.52 BPHK-01-08 0.31 -5.22 BPHK-01-44 1.59 -4.77 BPHK-01-81 1.19 -5.57 BPHK-01-11 0.65 -5.25 BPHK-01-45 1.58 -4.73 BPHK-01-82 1.26 -5.52 BPHK-01-12 0.56 -5.04 BPHK-01-46 1.45 -4.77 BPHK-01-83 1.1 -5.6 BPHK-01-13 0.72 -4.7 BPHK-01-47 1.47 -4.45 BPHK-01-84 1.31 -5.38 BPHK-01-14 0.47 -4.75 BPHK-01-48 1.3 -4.56 BPHK-01-85 1.28 -5.44 BPHK-01-15 0.24 -4.47 BPHK-01-49 1.61 -4.47 BPHK-01-86 1.3 -5.48 BPHK-01-16 0.66 -4.74 BPHK-01-50 1.48 -4.5 BPHK-01-87 1.29 -5.44 BPHK-01-20 0.52 -4.73 BPHK-01-52 1.28 -4.49 BPHK-01-88 1.44 -5.07 BPHK-01-21 0.55 -5.01 BPHK-01-53 1.4 -4.51 BPHK-01-89 1.52 -4.97 BPHK-01-23 0.21 -4.83 BPHK-01-54 1.19 -4.48 BPHK-01-90 1.53 -4.73 BPHK-01-24 0.55 -4.79 BPHK-01-55 1.13 -4.25 BPHK-01-91 1.51 -4.81 BPHK-01-25 0.72 -4.86 BPHK-01-60 0.67 -4.65 BPHK-01-92 1.46 -4.64 BPHK-01-26 0.93 -4.77 BPHK-01-61 0.63 -4.57 BPHK-01-93 1.37 -4.51 BPHK-01-27 0.84 -4.94 BPHK-01-62 0.6 -4.62 BPHK-01-94 1.22 -4.61 BPHK-01-28 0.75 -5.29 BPHK-01-63 0.9 -4.37 BPHK-01-95 1.03 -4.61 BPHK-01-29 0.81 -5.2 BPHK-01-65 0.8 -4.61 BPHK-01-96 0.92 -4.58 BPHK-01-30 0.56 -5.58 BPHK-01-66 0.71 -4.88 BPHK-01-97 1.08 -4.7 BPHK-01-31 0.6 -5.26 BPHK-01-67 0.75 -4.68 BPHK-01-98 1.28 -4.61 BPHK-01-32 0.72 -5.36 BPHK-01-68 0.73 -4.77 BPHK-01-100 1.47 -4.57 BPHK-01-33 0.78 -5.4 BPHK-01-69 0.97 -4.45 BPHK-01-101 1.37 -4.54 BPHK-01-34 0.61 -5.36 BPHK-01-70 1.31 -4.69 BPHK-01-102 1.3 -4.42 BPHK-01-35 0.84 -5.22 BPHK-01-71 1.68 -4.64 BPHK-01-103 1.24 -4.52 BPHK-01-36 0.8 -5.19 BPHK-01-72 1.69 -4.94 BPHK-01-104 1.26 -4.45

ID δ13C δ18O ID δ13C δ18O ID δ13C δ18O BPHK-02 BPHK-02-94 2.34 -4.01 BPHK-02-58 2.72 -3.2 BPHK-02-124 2.64 -3.74 BPHK-02-93 2.15 -4.19 BPHK-02-56 2.75 -3.21 BPHK-02-122 2.23 -3.8 BPHK-02-92 2.19 -4.26 BPHK-02-54 2.94 -3.15 BPHK-02-121 2.09 -4.19 BPHK-02-91 2.3 -3.92 BPHK-02-52 2.8 -3.26 BPHK-02-120 2.4 -3.92 BPHK-02-90 2.59 -3.7 BPHK-02-50 2.74 -3.11 BPHK-02-119 2.53 -3.89 BPHK-02-89 2.84 -3.72 BPHK-02-48 2.81 -3.28 BPHK-02-118 2.62 -3.85 BPHK-02-88 2.76 -3.61 BPHK-02-46 2.74 -3.26 BPHK-02-117 2.66 -4.04 BPHK-02-87 2.82 -3.46 BPHK-02-44 2.89 -3.3 BPHK-02-116 2.02 -4.23 BPHK-02-86 2.8 -3.37 BPHK-02-42 2.73 -3.32 BPHK-02-115 2.23 -3.91 BPHK-02-85 2.93 -3.39 BPHK-02-40 2.72 -3.48 BPHK-02-114 2.4 -3.62 BPHK-02-83 2.83 -3.45 BPHK-02-39 3.02 -3.37 BPHK-02-113 2.69 -3.8 BPHK-02-82 2.86 -3.14 BPHK-02-37 2.67 -3.38 BPHK-02-112 2.55 -3.68 BPHK-02-81 2.79 -3.54 BPHK-02-35 2.71 -3.28 BPHK-02-111 2.28 -3.83 BPHK-02-80 3.04 -3.22 BPHK-02-33 2.66 -3.22 BPHK-02-110 2.39 -3.74 BPHK-02-79 3.09 -3.24 BPHK-02-31 2.82 -3.22 BPHK-02-109 2.3 -4.18 BPHK-02-78 2.98 -3.74 BPHK-02-30 3.23 -3.42 BPHK-02-108 2.14 -4.32 BPHK-02-77 3.12 -3.3 BPHK-02-29 3.19 -3.47 BPHK-02-107 2.31 -4.16 BPHK-02-76 3.11 -3.35 BPHK-02-27 3.37 -3.38 BPHK-02-106 2.53 -4.06 BPHK-02-75 2.99 -3.31 BPHK-02-25 3.53 -3.38 BPHK-02-105 2.54 -4.11 BPHK-02-74 3 -3.36 BPHK-02-23 3.48 -3.43 BPHK-02-104 2.31 -4.45 BPHK-02-73 3.03 -3.38 BPHK-02-21 3.6 -3.36 BPHK-02-103 2.01 -4.85 BPHK-02-72 3.03 -3.44 BPHK-02-19 3.67 -3.26 BPHK-02-102 2.05 -4.62 BPHK-02-71 3.13 -3.26 BPHK-02-17 3.58 -3.14 BPHK-02-101 1.87 -4.85 BPHK-02-70 2.83 -3.31 BPHK-02-15 3.77 -3.21 BPHK-02-100 2.14 -4.63 BPHK-02-69 2.89 -3.23 BPHK-02-13 3.77 -3.1 BPHK-02-99 2.35 -4.45 BPHK-02-68 2.81 -3.34 BPHK-02-10 3.58 -3.15 BPHK-02-98 2.24 -4.62 BPHK-02-66 2.89 -3.3 BPHK-02-09 3.63 -3.17 BPHK-02-97 2.41 -4.45 BPHK-02-64 3.19 -3.32 BPHK-02-07 3.7 -3.14 BPHK-02-96 2.04 -5.28 BPHK-02-62 2.59 -3.29 BPHK-02-05 3.69 -3.23 BPHK-02-95 2.22 -4.46 BPHK-02-60 2.62 -3.27 BPHK-02-03 3.7 -3.21 BPHK-02-01 3.74 -3.26

ID δ13C δ18O ID δ13C δ18O ID δ13C δ18O BPHK-03 BPHK-04 BPHK-06 BPHK-03-01 4.66 -3.81 BPHK-04-02b 4.15 -5.22 BPHK-06-01 0.68 -5 BPHK-03-02 4.54 -4.32 BPHK-04-03c 4.24 -5.29 BPHK-06-02 0.8 -4.84 BPHK-03-03b 4.66 -3.78 BPHK-04-04b 4.01 -5.15 BPHK-06-03 0.83 -4.83 BPHK-03-04b 4.41 -3.84 BPHK-04-04c 4.17 -4.91 BPHK-06-04 0.98 -4.77 BPHK-03-05 4.53 -3.99 BPHK-04-05 5.18 -3.91 BPHK-06-05 0.63 -4.85 BPHK-03-06b 4.61 -3.98 BPHK-04-06 4.73 -4.15 BPHK-06-06 0.3 -4.7 BPHK-03-06c 3.97 -5.06 BPHK-04-07 4.41 -3.83 BPHK-06-07 0.41 -4.73 BPHK-03-06d 4.57 -6.06 BPHK-04-08 4.51 -4.23 BPHK-06-08 0.71 -4.67 BPHK-03-06e 4.45 -6.00 BPHK-04-09 5.17 -3.81 BPHK-06-09 0.83 -4.65 BPHK-03-06f 4.40 -4.66 BPHK-04-10 5.38 -3.79 BPHK-06-10 1.09 -4.75 BPHK-03-06g 4.52 -3.75 BPHK-04-11 4.9 -4.15 BPHK-06-11 1.18 -4.81 BPHK-03-07 4.63 -3.8 BPHK-04-12 4.99 -4.24 BPHK-06-12 1.1 -4.97 BPHK-03-08 4.77 -3.88 BPHK-04-13 4.91 -4.13 BPHK-06-13 1.04 -4.96 BPHK-03-09 4.9 -3.74 BPHK-04-14 4.96 -4.1 BPHK-06-14 1.12 -4.91 BPHK-03-10b 4.86 -4.80 BPHK-04-15 4.74 -4.13 BPHK-06-15 1.11 -4.95 BPHK-03-11 4.48 -4.66 BPHK-04-16 4.54 -3.97 BPHK-06-16 0.99 -4.97 BPHK-03-12 4.6 -3.8 BPHK-04-17 4.4 -4.13 BPHK-06-17 0.83 -5.23 BPHK-03-13 4.71 -3.71 BPHK-04-17b 4.17 -4.10 BPHK-06-18 0.79 -4.87 BPHK-03-14 4.94 -3.48 BPHK-04-18b 4.71 -5.30 BPHK-06-19 0.91 -4.97 BPHK-03-15 5.25 -3.41 BPHK-04-19 4.62 -4.04 BPHK-06-20 1.08 -4.88 BPHK-03-16 5.22 -3.29 BPHK-04-20 4.85 -3.82 BPHK-06-21 1.16 -4.84 BPHK-03-17 5.06 -3.3 BPHK-04-21 4.51 -4.28 BPHK-06-22 1.04 -5.01 BPHK-03-18 4.87 -3.35 BPHK-04-22 4.46 -4.24 BPHK-06-23 1.04 -5.11 BPHK-03-19b 3.85 -3.86 BPHK-04-23 4.68 -3.87 BPHK-06-24 0.99 -5.07 BPHK-03-20 4.23 -3.55 BPHK-04-24 4.49 -4.01 BPHK-06-25 0.89 -5.07 BPHK-03-21b 5.20 -3.55 BPHK-04-25 4.51 -3.77 BPHK-06-26 0.74 -5.07 BPHK-03-22 5.06 -3.59 BPHK-04-26 4.92 -3.86 BPHK-06-27 0.72 -5.09 BPHK-03-23 5.22 -3.43 BPHK-04-27 4.92 -3.98 BPHK-06-28 0.92 -5.03 BPHK-03-23b 5.07 -3.83 BPHK-04-28 4.67 -4.33 BPHK-06-29 0.88 -5.14 BPHK-03-24 4.9 -3.78 BPHK-04-29 4.46 -4.46 BPHK-06-30 0.83 -5.24 BPHK-03-25 4.71 -3.55 BPHK-04-30 4.36 -4.53 BPHK-06-31 0.63 -5.29 BPHK-03-26 4.40 -3.61 BPHK-06-32 0.62 -5.21 BPHK-03-27 4.28 -3.88 BPHK-06-33 0.75 -5.04 BPHK-03-28 4.19 -4.11 BPHK-06-34 0.62 -5.33 BPHK-06-35 0.61 -5.41

BPHK-06-36 0.33 -5.42 BPHK-06-37 0.41 -5.16

BPHK-06-38 0.58 -4.93

BPHK-06-39 0.68 -4.84 BPHK-06-40 0.69 -4.58 BPHK-06-41 0.76 -4.51 BPHK-06-42 0.95 -4.74

ID δ13C δ18O ID δ13C δ18O BPHK-06-43 0.98 -4.69 BPHK-JC1* BPHK-06-44 1.04 -4.88 BPHK-JC1-01 2.26 -4.88 BPHK-06-45 1.16 -5.16 BPHK-JC1-02 2.21 -4.86 BPHK-06-47 1.47 -4.99 BPHK-JC1-03 2.20 -4.89 BPHK-06-49 1.55 -5.24 BPHK-JC1-04 2.14 -4.84 BPHK-06-50 1.48 -4.99 BPHK-JC3* BPHK-06-51 1.6 -4.92 BPHK-JC3-01 0.85 -4.75 BPHK-06-53 1.79 -4.85 BPHK-JC3-02 0.67 -4.84 BPHK-06-54 1.7 -5.36 BPAM-01# BPHK-06-55 1.84 -4.8 BPAM-01-03 -2.62 -9.44 BPHK-06-56 2.05 -4.64 BPAM-02# BPHK-06-57 1.94 -4.88 BPAM-02-01 -3.14 -10.66 BPHK-06-58 1.84 -4.89 BPAM-02-02 -2.84 -10.58 BPHK-06-59 1.88 -4.74 BPAM-02-03 -2.3 -10.24 BPHK-06-60 1.68 -4.76 BPAM-02-04 -2.89 -10.83 BPHK-06-61 1.61 -4.76 BPAM-03# BPHK-06-62 1.65 -4.64 BPAM-03-02 -2.18 -8.5 BPHK-06-63 1.62 -4.66 BPAM-03-03 -2.75 -9.92 BPHK-06-64 1.72 -4.72 BPAM-03-04 -2.73 -9.28 BPHK-06-65 1.62 -4.63 BPHK-05# BPHK-06-66 1.59 -4.75 BPHK-05-01 -1.12 -9.71 BPHK-06-67 1.47 -4.75 BPHK-05-02 2.3 -11.08 BPHK-06-68 1.44 -4.63 BPHK-05-03 0.93 -11.79 BPHK-06-69 1.41 -4.64 BPHK-05-04 -1.59 -11.25 BPHK-06-70 1.07 -5.29 BPHK-05-05 -0.57 -10.56 BPHK-06-71 1.25 -4.6 BPHK-07+ BPHK-06-72 1.16 -4.46 BPHK-07-01 2.82 -3.55 BPHK-06-73 1.17 -4.49 BPHK-07-02 3.32 -3.48 BPHK-10* BPHK-08+ BPHK-10-01 3.37 -5.79 BPHK-08-01 2.60 -3.47 BPHK-10-02 3.93 -5.61 BPHK-08-02 2.97 -3.40 BPHK-10-03 2.79 -6.19 BPHK-10-04 3.41 -5.68 BPHK-11* BPHK-11-01 3.44 -3.82 BPHK-11-02 3 -4.04 BPHK-11-03 2.81 -4.36 BPHK-11-04 2.79 -4.77 BPHK-JC2* BPHK-JC2-01 2.12 -4.39 BPHK-JC2-02 2.21 -4.36 BPHK-JC2-03 1.94 -4.95 BPHK-JC2-04 1.75 -4.61

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Vita

Name of Author: Marie Y. Jimenez

Date of Birth: September 7, 1992

Place of Birth: Espaillat, Dominican Republic

Degrees Awarded: Bachelor of Science, 2016, University of Rhode Island