Seafloor Weathering and the Middle to Late Ordovician Seawater 87Sr/86Sr Inflection Point Preserved in Conodont Apatite

Seafloor weathering and the Middle to Late Ordovician seawater 87Sr/86Sr inflection point preserved in conodont apatite

Thesis

Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of the Ohio State University

Teresa Daniela Avila, B.S.

Graduate Program in Earth Sciences

The Ohio State University

2019

Thesis Committee

Matthew Saltzman, Adviser

Elizabeth Griffith

John Olesik

Teresa Daniela Avila

2019

Abstract

The strontium isotope ratio (87Sr/86Sr) of global seawater varies through geologic time

and can serve as a proxy for silicate weathering patterns as well as rates of spreading in mid-

ocean ridges. The 87Sr/86Sr value of seawater steadily decreases through the course of the

Ordovician, with an increased rate of change during the Darriwilian to Sandbian (Middle to Late

Ordovician). The precise age of this inflection point has been poorly constrained, making it difficult to ascertain its possible causes and effects. Here, conodont apatite from the Simpson

Group of the Arbuckle Mountains, Oklahoma were analyzed in order to build a higher-resolution

87Sr/86Sr curve. The preparation of conodont samples via leaching in acetic acid is also

investigated. In the case of Oklahoma section conodont elements with low thermal alteration

(i.e., Color Alteration Index; (CAI) ≤ 1), leaching does appear to strip diagenetic Sr, but the

overall effect on 87Sr/86Sr (7.47 x 10-6 ) is smaller than the external analytical error (8.22 x 10-6).

To identify the inflection point in the new data set, a smoothing LOESS curve was used

to produce a gradient curve, a process which has not yet been applied to the Middle to Late

Ordovician. The 87Sr/86Sr inflection point falls in the transition from the Oil Creek to McLish

Formations, within the holodentata conodont zone at 466.4 to 463.8 Mya. The shift in 87Sr/86Sr occurs at the Sauk-Tippecanoe sequence boundary and associated transgression, which may reflect increased spreading rates of mid-ocean ridges. Previous studies have linked the inflection point in 87Sr/86Sr to the Taconic Orogeny at c.a. 465 Mya, which may also play an important role

in the shift of global 87Sr/86Sr but is unlikely to account for the transgression at the base of the

McLish due to asynchronous timing of events.

Dedication

Dedicated to my family and their commitment to education

iii

Vita

May 2010……………………Lafayette High School

2015…………………………B.S. Geological Sciences, University of Missouri

2015…………………………B.S. Science and Agricultural Journalism, University of Missouri

2015 to 2017………………...Laboratory Technician, Department of Earth and Planetary

Sciences, Washington University in St. Louis

2017 to present………………Dean’s Graduate Enrichment Fellow, School of Earth Sciences,

The Ohio State University

Publications

Warren, JW, Schiffbauer, JD, Avila, TD, Broce, JS. (2018). Ecophenotypy, temporal and spatial fidelity, functional morphology, and physiological trade-offs among intertidal bivalves. Paleobiology, 44(3), 530-545.

Fields of Study

Major Field: Earth Sciences

Table of Contents

Abstract……………………………………………………………………………………………ii

Dedication………………………………………………………………………………………...iii

Vita………………………………………………………………………………………………..iv

List of Tables…………………………………………………………………………………..…vi

List of Figures…………………………………………………………………………………....vii

Introduction……………………………………………………………………………………...... 1

Background……………………………………………………………………………………..…5

Method…………………………………………………………………………………………...13

Results…………………………………………………………………………………………....16

Discussion………………………………………………………………………………………..23

Conclusion……………………………………………………………………………………….33

References………………………………………………………………………………………..34

Appendix A: Method Details………..…………………………………………………………...42

Appendix B: Statistics Details…..…..…………………………………………………………...46

Appendix C: Age Model…….…..…..…………………………………………………………...47

Appendix D: Non-Ordovician Samples……..…………………………………………………...48

List of Tables

Table 1. Sr concentration, 87Sr/86Sr, and associated errors of analyzed conodont samples…..16

Table 2. 87Sr/86Sr of leached samples, unleached samples, and leachates……………………18

Table 3. Sr abundance of leached samples and leachates…………………………………….19

List of Figures

Figure 1. Ordovician conodont-based curve………………………………………………………3

Figure 2. Diagenetic alteration of conodont 87Sr/86Sr: A conodont element in vivo, B conodont

element post mortem, C conodont element with low-temperature pore water alteration,

D conodont element with thermal alteration, E conodont element leaching process…..9

Figure 3. Difference between leached samples and leachate in previous studies………………..11

Figure 4. Site location……………………………………………………………………………14

Figure 5. Difference in 87Sr/86Sr of leached samples, unleached samples, leachates…...…….....20

Figure 6. Leached samples vs. unleached samples vs. global LOWESS curve…………………24

Figure 7. Sr mass balance in leached conodont samples……………………………………...…25

Figure 8. SEM images of conodont samples before and after leaching………………………….26

Figure 9. Data plotted against depth……………………………………………………………..27

Figure 10. Data plotted against age, associated gradient curve, whole Ordovician…….……….28

Figure 11. Sr mass balance in leached Pennsylvanian-age conodont samples.………………….50

Figure 12. Difference in 87Sr/86Sr of Silurian leached samples, unleached samples, leachates…51

Figure 13. Data plotted against age, associated gradient curve.………………………………....52

Figure 14. Clear Springs data plotted against depth………….………………………………….53

Figure 15. Antelope Range data plotted against depth……….………………………………….54

Figure 16. Model demonstrating inflection point…………….………………………………….55

vii

Introduction

The Ordovician Period (485 to 444 Mya) is a valuable case study for the various, interconnected

Earth systems that drive and respond to global climate change. The Ordovician climate is

characterized by a roughly 20º C drop in average sea surface temperature—with smaller-scale changes superimposed—that encompassed the extreme warmth of the Early Ordovician (c.a. 42º

C) to the end-Ordovician (Hirnantian) glaciation (c.a. 22º C; Trotter et al., 2008; Albanesi et al.,

2019). This cooling to mild, modern-like sea surface temperatures potentially triggered the Great

Ordovician Biodiversification Event (GOBE), but eventually may have led to the first of the “big five” extinctions: the end-Ordovician mass extinction (Sepkoski, 1996; Trotter et al., 2008).

Multiple factors could have contributed to this cooling, including decreased volcanic degassing

(McKenzie et al., 2016), the appearance of the first land plants in correlation with overall

increased organic carbon burial (Lenton et al., 2012; Algeo et al., 2016), and increased

weathering of calcium-bearing silicates (Swanson-Hysell and Macdonald, 2017; Saltzman, 2017;

Macdonald et al., 2019). Understanding the interplay of these systems and their impact on the

timing and magnitude of cooling steps throughout the Ordovician represents a longstanding

problem.

Previous studies have investigated the Ordovician cooling trend mostly in terms of how

exposure of young, Ca- and Mg- bearing silicates (i.e., basalts) at low latitudes—such as the

island-arc setting of the Ordovician Taconic orogeny in Laurentia—would have increased

weathering rates and the drawdown of CO2 (Shields et al., 2003; Young et al., 2009; Swanson-

Hysell and Macdonald, 2017; Macdonald et al., 2019). An important proxy for basaltic weathering in the geologic record is the trend in global marine 87Sr/86Sr values (McArthur et al.,

2012). However, while the large-scale trend of decreasing 87Sr/86Sr in the Ordovician is fairly well established (Figure 1), uncertainty remains in the timing of a Middle to Late Ordovician

(Darriwilian to Sandbian stages) inflection point in the curve and its correlation with the

Ordovician paleotemperature curve (Trotter et al., 2008; Albanesi et al., 2019). The timing of the inflection point ranges from 458 Mya to 466 Mya, spanning several biostratigraphic zones

(Figure 1; Shields et al., 2003; Young et al., 2009; McArthur et al., 2012; Saltzman et al., 2014;

Swanson-Hysell and Macdonald, 2017). This timing appears problematic for the Taconic weathering hypothesis (Young et al., 2009; Saltzman, 2017), as the late Darriwilian to Sandbian appears to coincide with a slowing of cooling or even a slight warming trend superimposed on long-term cooling (Trotter et al., 2008; Albanesi et al., 2019). A role for Taconic weathering is evidenced by a similarly timed shift in neodymium (Nd) isotopes (Swanson-Hysell and

Macdonald, 2017), but questions persist about the amount of basaltic versus more intermediate composition continental weathering that can be inferred using this proxy (Saltzman, 2017).

Therefore, a more precise understanding of the timing of this 87Sr/86Sr inflection point is critical to evaluate other causal mechanisms that likely played a role distinct from Taconic weathering, namely seafloor spreading rates and associated eustatic changes (e.g., Shields et al., 2003;

Saltzman et al., 2014).

In order to better constrain the timing of the inflection point in the Ordovician 87Sr/86Sr curve, this study focuses on conodont microfossil apatite in the Arbuckle Mountains of

Oklahoma, which contains one of the best-constrained conodont biostratigraphic data sets in the world for the Darriwilian to Sandbian (c.a. 465 to 455 Mya) study interval (Bauer, 1987; Bauer,

Figure 1. Ordovician conodont-based 87Sr/86Sr measurements with Locally Estimated Scatterplot

Smoothing (LOESS) curve with global Locally Weighted Scatterplot Smoothing (LOWESS) curve from McArthur et al. (2012) for comparison. Data from Edwards et al. (2015) and Dwyer

(1996).

2010). Although the section was studied in some detail by Saltzman et al. (2014), visually determining an inflection point from that study’s data is not entirely straightforward. This study examines whether the inflection point can be made clearer. One way to achieve this is adding additional data points in order to better populate the curve, and moreover, adding data points with lower associated uncertainty. The data points from Saltzman et al. (2014) had an average measured uncertainty of 5.2 x 10-4. Here, measured uncertainty is defined as the uncertainty with which the mean 87Sr/86Sr of a sample is known from n independent measurements, as defined by

McArthur et al. (2012). This study examines whether a new generation Triton Thermal

Ionization Mass Spectrometer (TIMS) can decrease the average measured uncertainty. It also examines whether use of leaching methods decreases error (error here meaning the difference between measured and “true” value) and whether this method produces a markedly different

87Sr/86Sr curve. In addition, this study introduces a smoothing LOESS curve and associated gradient curve to this location’s data, allowing for an additional way to visually identify an inflection point (Waltham and Grockë, 2006; McArthur et al., 2012). By better constraining the

Middle to Late Ordovician 87Sr/86Sr inflection point, one can address the question of whether the observed inflection point coincides with a lithologic transition that signals an important geologic

(i.e., eustatic or tectonic) event associated with a change in Sr fluxes.

Background

A. Controls on marine 87Sr/86Sr and link to climate

The Sr residence time in the oceans (5.0 x 106 years) is longer than the ocean mixing time

(1 x 103 years), allowing the ocean to have a homogenous 87Sr/86Sr signal (Taylor and

McLennan, 1985; Palmer and Edmond, 1989). The global marine 87Sr/86Sr value is controlled by three Sr fluxes. The smallest flux is deep sea sediments diagenetically altered by pore water that are then expulsed into the ocean (87Sr/86Sr ~ 0.708); this not considered a significant control on

global 87Sr/86Sr today (Faure and Mensing, 2003). Hydrothermal circulation at ocean spreading

centers (87Sr/86Sr ~ 0.703) is the second largest flux, while riverine Sr from continental

weathering represents the largest flux of Sr to the oceans (Palmer and Edmond, 1989; Davis et

al., 2003; Waltham and Grockë, 2006). To further break down the riverine flux, carbonate

weathering (87Sr/86Sr ~ 0.708) provides a significant source of continental riverine Sr, but its

isotopic input is relatively constant, thus stabilizing marine 87Sr/86Sr rather than causing it to

fluctuate (Veizer, 1989; Faure and Mensing, 2003; Waltham and Gröcke, 2006). Therefore, any

major change in riverine 87Sr/86Sr is likely to come from changes in silicate weathering, i.e.,

granitic (87Sr/86Sr ~ 0.718) versus basaltic (87Sr/86Sr ~ 0.705) weathering (Faure and Mensing,

2003; Waltham and Grockë, 2006). Changes in either silicate weathering patterns or rate of

hydrothermal circulation are therefore the most prominent controls on changes in global 87Sr/86Sr

(Gaillardet et al., 1998; Huh and Edmond, 1998; Taylor and Lasaga, 1999; Dessert et al., 2001;

Faure and Mensing, 2003; Waltham and Gröcke, 2006).

These processes that alter global 87Sr/86Sr can also impact climate. In terms of silicate

weathering, continental basalts weather faster than granites, as they contain more silicate

minerals (Ca-plagioclase and pyroxenes), which are less stable under surface conditions than the

dominant weatherable minerals of granite (Na-plagioclase, K-feldspar, micas; Bowen, 1956;

Meybeck, 1987; Taylor and Lasaga, 1999; Berner, 2004). Combine this with the fact that only

hydrolysis of Ca- and Mg- bearing silicates results in carbon sequestration (Berner, 2004). The

result is that a sudden influx of continental basalts being weathered would boost CO2

sequestration via hydrolysis and simultaneously cause global marine 87Sr/86Sr to decrease.

Basalts, therefore, have the potential to impact global climate on a scale of several million years

(c.a. 1 to 5 My), especially if placed within a zone of high weathering (Taylor and Lasaga, 1998;

Berner, 2004; Waltham and Gröcke, 2006; Swanson-Hysell and Macdonald, 2017).

Hydrothermal weathering, the other major source of Sr to the global cycle, involves the cycling

of seawater through hydrothermal systems off the central axis of mid-ocean ridges, extracting Sr

with a low 87Sr/86Sr value from the young basalt and decreasing the overall global marine

87Sr/86Sr value (87Sr/86Sr ~ 0.703 based on modern measurements; Palmer and Edmond, 1989;

Waltham and Grockë, 2006; Coogan and Dosso, 2015). This process provides a temperature-

dependent feedback on the geologic carbon cycle in the form of carbon sequestration in

secondary carbonate minerals. As atmospheric pCO2 increases and global temperatures rise, the

temperature of bottom waters—and therefore hydrothermal fluid within the oceanic crust— increases as well; the rate of basaltic weathering increases as a result, leading to increased alkalinity within off-axis hydrothermal systems (Coogan and Gillis, 2013; Coogan and Dosso,

2015). Increased alkalinity prompts increased precipitation of secondary carbonate minerals in permeable basalts, sequestering C and ultimately leading to overall cooling, therefore serving as a strong negative feedback on the long-term C cycle (Coogan and Gillis, 2013; Coogan and

Dosso, 2015; Coogan and Gillis, 2018).

B. 87Sr/86Sr in conodonts

Conodonts were a group of marine, eel-like chordates that existed from the Cambrian to

the Triassic periods (Briggs et al., 1983; Donoghue et al., 2000). The only fossilized remains of

these animals are phosphatic proto-teeth referred to as conodont elements. Conodont elements

are common in marine Paleozoic carbonates, geographically widespread, and have a well-

resolved taxonomy, making them an effective tool for biostratigraphy as well as geochemical

studies (Kleffner, 1989; Fordham, 1992; Gradstein, 2012).

The reliability of conodont apatite in Sr isotope studies is equivocal. The general

consensus has been that fossils composed of primary, low-Mg calcite—such as brachiopods or

belemnite guards—are least susceptible to diagenetic alteration and therefore provide the most

reliable 87Sr/86Sr signal (e.g. Brand and Veizer, 1980; Veizer et al., 1982; Brand and Morrison,

1987; Jones et al., 1994; Cummins and Elderfield, 1994; McArthur et al., 2012). McArthur et al.

(2012) constructed global seawater curves based largely on belemnite guards, brachiopods, nanofossil ooze, ammonoid aragonite, and carbonates. However, conodont apatite presents the best alternative for 87Sr/86Sr data in Paleozoic field sites where low-Mg calcite is scarce or

nonexistent and has been shown to be a reliable source of data in the Ordovician (Saltzman et al.,

2014). However, questions remain about the causes of variability in conodont apatite 87Sr/86Sr

and how to assess diagenetic alteration of primary seawater values.

Over the course of the conodont’s life, Sr2+ from the marine environment substitutes for

Ca2+ in the element’s apatite crystal structure, allowing it to act as a record of ancient marine

geochemistry (Bertram et al., 1992; Holmden et al., 1996; Katvala and Henderson, 2012;

Keenan, 2016; Geng et al., 2016). Once the conodont dies, any geochemical alteration that the

element undergoes is referred to as diagenesis, which can be split into two categories: short-term

and long-term. Short-term diagenesis occurs over hundreds to thousands of years and

encompasses the conodont’s decomposition, burial, and the fossilization of elements (Kohn,

2008; Trueman, 2013). During this time, the element recrystallizes and its Sr and REE content

increase rapidly from its interaction with pore fluids that are thought to be derived from marine

sources, therefore buffering the seawater value (Figure 2; Schmitz et al., 1991; Holmden et al.,

1996; Ebneth et al., 1997). It should be noted, however, that short-term diagenesis can still introduce non-seawater values, especially in an argillaceous matrix (Ebneth et al., 1997). Long-

term diagenesis describes geochemical alterations that take place after fossilization, on longer time scales, and is more likely to involve thermal alteration and/or pore fluids that are not derived from the original marine source. Conodont elements that experience thermal alteration— whether through regional, contact, or hydrothermal metamorphism—are blackened via carbon fixation and appear to incorporate more radiogenic Sr via exchange with hydrothermal diagenetic fluids, although the exact reason for this pattern is still unclear among conodont researchers

(Epstein et al., 1977; Rejebian et al., 1987; Bertram et al., 1992; Cummins and Elderfield, 1994).

It is therefore common practice among researchers to select conodont elements with a light color, i.e., a low Color Alteration Index (CAI), preferably around 1 or 2 because this indicates minimal thermal alteration and should result in a less altered 87Sr/86Sr value. Overall, while pore fluids can be either more or less radiogenic than the original marine signal, more radiogenic fluids are more common as a result of the fluid’s interaction with clay minerals (Veizer and Compston,

1974; Jones et al., 1994; Martin and Scher, 2004). Less radiogenic diagenetic fluids, although

Figure 2. A) The marine 87Sr/86Sr is recorded in a conodont element in vivo. B) The Sr concentration increases post-deposition via interaction with seawater-derived porewater, bolstering the marine 87Sr/86Sr. C) Nonseawater-derived porewater interaction leads to 87Sr/86Sr alteration, likely on the outer edge of the element. D) Thermal alteration leads to further diagenesis and darkening of the element. E) Leaching in a weak acid removes the outer edges of the conodont, where the majority of diagenetic Sr is thought to reside.

less common, have been observed and could be attributed to redistribution of Sr within carbonates or the nearby presence of basaltic material, which has a known lower 87Sr/86Sr value

(Jones et al., 1994).

Leaching is a relatively simple procedure aimed at removing outer layers of the conodont that might have been altered from primary seawater values. Elements are placed in weak acetic acid (5% or less) for anywhere from hours to days in order to dissolve away the element’s outer layers (Figure 2). Past studies have concluded that leached elements result in less radiogenic

87Sr/86Sr values (Figure 3; Holmden et al., 1996; Ruppel et al., 1996).

Holmden et al. (1996) is a frequently cited study that provides data in support of leaching’s effectiveness. The researchers placed 1 mg of Panderodus gracilis in 5% unbuffered acetic acid and collected the leachate (i.e., the acetic acid) after 1 hour, 4 hours, and 76 hours.

They found that the leachates had greater 87Sr/86Sr values and Sr concentrations from 1 hour to 4 hours, but after 76 hours, the 87Sr/86Sr and Sr concentration had dropped (Figure 3). When compared to the element itself, the leachates consistently had more radiogenic 87Sr/86Sr values and greater Sr concentration. Holmden et al. (1996) concluded that, of the total Sr originally in the conodont element, 11.5% remained in the element after leaching. While other studies (Martin and Macdougall, 1995; Ruppel et al., 1996; Holmden et al., 1996; John et al., 2008; Dudás et al.,

2017) have examined the effect of leaching on 87Sr/86Sr, they do not examine leaching over time, nor do they analyze mass balance. Ruppel et al. (1996) compared leachates’ 87Sr/86Sr values for five samples to the conodont residual material. They leached the elements in 0.5% acetic acid for

12 to 16 hours. Like Holmden et al. (1996), they concluded that the leachates had generally more radiogenic 87Sr/86Sr values, with an average difference of 3.82 x 10-5 (Figure 3). In a recent

Figure 3. Difference in 87Sr/86Sr between leachates and leached conodont elements from

Holmden et al., (1996) and Ruppel et al., (1996). The majority of samples demonstrate that the leachate is more radiogenic than the leached conodont element.

study, Dudás et al. (2017) used three distinct leaching methods. The method that they deemed the most effective leached conodonts for 8 or more hours with the disadvantage that some elements were dissolved completely. The study included multiple stratigraphic sections around the world.

In some sections, the leachates proved more radiogenic than the leached conodont element; in other sections, the opposite proved true. Martin and Macdougall (1995) leached four large elements in 1.5 M acetic acid for approximately 20 minutes. They dissolved the elements in sequential steps and, like Ruppel et al. (1996), found that the 87Sr/86Sr value of the initial leachates were radiogenic relative to the residuum. John et al. (2008) leached elements in 0.5% acetic acid for 12-16 hours. They concluded that the difference that could be accounted for by leaching, 5 x 10-6, was smaller than the minimum error of the samples’ 87Sr/86Sr values. With varying conclusions from multiple past studies, this study aims to collect detailed data on the practical impacts and importance of leaching when analyzing 87Sr/86Sr in conodont apatite.

Method

A. Sample location

The Arbuckle Mts. consist of folded and faulted rocks of Precambrian and Paleozoic age, largely consisting of shallow-marine carbonates with sandstone and shale interbeds (Ham, 1969;

Johnson, 1991). The Oklahoma Basin was formed by an aulacogen, creating a subsiding trough

(Carlucci et al., 2014). The region contains a largely complete Middle to Upper Ordovician succession of strata (Saltzman et al., 2014; Young et al., 2016). Samples for this study were collected from a roughly 600 m interval of the Simpson Group exposed along Interstate 35 N,

from the upper McLish, Tulip Creek, and lower Bromide Formations (Figure 4; Derby et al.,

1991; Saltzman et al., 2014). Overall, the middle to upper Simpson Group’s depositional

environment is characterized by successive fluctuations of sea level in the shallow marine setting

of the Oklahoma Basin, trending toward an overall transgression (Bauer, 1987; Johnson, 1991;

Carlucci et al., 2015).

B. Sample 87Sr/86Sr analysis

Ordovician-age rock samples from the Simpson Group in Arbuckle Mts. were collected and the conodonts extracted by James Bauer as part of his dissertation work at Ohio State

University. Samples were first selected based on their nearness to the perceived inflection point,

then based on the abundance of conodont elements. Conodont elements from this section have a

low color alteration index (CAI ≤ 1) and include an even mix of morphologies, including both

coniform (cones) and ramiform (platform) elements. Approximately 0.2 mg (unleached

duplicates) to 2 mg (leached duplicates) of conodont elements (based on expected Sr

concentration of 5000 to 9000 ppm) were selected from each sample slide. Conodont element

Figure 4. Location of I-35N site in Arbuckle Mts. Figure is modified from Carlucci et al., (2014).

were sonicated in Milli Q deionized water to remove debris. Samples slated for leaching were

placed in 0.5 mL 5% acetic⦁ acid for 72 hours, with collection of acetic acid (i.e., leachate)

occurring after 8 hours, 24 hours, and 72 hours. Elements were then dissolved in 6N HCl and the

Sr separated using Eichrom Industries Sr Spec resin in Teflon microcolumns. Samples were

analyzed for 87Sr/86Sr on a Triton Thermal⦁ Ionization Mass Spectrometry (TIMS) in The Ohio

State University Thermal Ionization Mass Spectrometry Laboratory. SRM 987 was used as a standard with an average measured value of 0.710251 (2SD = 2.01 x 10-5, n = 96). Standard

87Sr/86Sr values were then corrected to 0.710248 (McArthur, 1994) in order to address drift. With

this correction, the average measured value was 0.710248 (2SD = 8.22 x 10-6, n = 96). Here, 8.22

x 10-6 also represents external analytical error, i.e., the error of a given sample’s measured value from one run to the next. 87Rb contamination was accounted for by measuring 85Rb and using the

assumed 87Rb/85Rb value 0.386000 (Steiger and Jäger, 1977). Instrument mass fractionation was

accounted for by normalizing 87Sr/86Sr values to an assumed 88Sr/86Sr ratio of 8.375209 (Steiger

and Jäger, 1977). Additional method details can be found in Appendix A.

C. Elemental abundance analysis

Before samples were processed via Sr Spec resin, a portion was removed for analysis on

either an Inductively Coupled Plasma Optical⦁ Emission Spectrometer (ICP-OES) or Inductively

Coupled Plasma Mass Spectrometer (ICP-MS) in The Ohio State University Trace Element

Research Laboratory. Samples were primarily measured for concentration of Sr in order to 1) determine that enough Sr existed for TIMS analysis, 2) find the overall sample concentration, and 3) determine mass balance of Sr in leached samples and their leachates.

D. SEM analysis

Select samples were analyzed on a Hitachi Tabletop SEM in the Department of Geology at Kent State University. Samples were mounted on Ted Pella stubs using PELCO tabs and analyzed uncoated. Analysis occurred twice on the same samples: once before leaching and once after.

Results

A. 87Sr/86Sr of Arbuckle conodont samples

Table 1. 87Sr/86Sr of unleached samples

Age Internal Sample ID (Mya) Sr ppm 87Sr/86Sr Error (x10-6) 83JD-67A_U 462.35 7530 0.708661 3 83JD-67B_U 462.35 6988 0.708663 3 83JD-80A_U 462.22 7393 0.708645 3 83JD-88A_U 462.14 6834 0.708654 3 83JD-88B_U 462.14 5616 0.708649 3 83JD-115A_U 461.88 6524 0.708614 3 83JD-115B_U 461.88 6837 0.708607 3 83JD-125A_U 461.78 7071 0.708614 3 83JD-125B_U 461.78 5783 0.708609 3 83JD-130A_U 461.73 9625 0.708618 3 83JD-130B_U 461.73 8881 0.708608 2 83JD-166_U 461.38 4030 0.708586 3 83-JD-184_U 460.66 6577 0.708522 3 83JD-191_U 460.21 5568 0.708527 3 83JD-211_U 458.93 4783 0.708535 3 83JE-0_U 458.93 5781 0.708482 3 83JE-0.8_U 458.88 6292 0.708475 3 83JE-5.6_U 458.57 6107 0.708484 3 83JE-13_U 458.10 6524 0.708461 3 83JE-18.5_U 457.75 8987 0.708373 3 83JE-21.8_U 457.54 9495 0.708347 3 83JE-23_U 457.46 8893 0.708349 3 83JE-28_U 457.14 7508 0.708337 3

Eighteen unleached conodont samples from the I-35 N section of the Simpson Group

were analyzed for 87Sr/86Sr, with five of these samples run in duplicate in order to estimate sample heterogeneity (Table 1). Average internal error (i.e., absolute standard error within a

single run) of the samples is 2.84 x 10-6 (2SD 4.60 x 10-7) The standard error within a single run

is calculated automatically from the 200 measurements, or cycles, that make up a single run of a

sample. External error (i.e., error between two different runs) is calculated as the 2SD of multiple

runs of the SRM 987 standard (n = 96) and is found to be 8.22 x 10-6. The average Sr

concentration is 6940 ppm (SD 1436).

The Triton external error of 8.2 x 10-6 is smaller than that of the Finnigan MAT-261A used to measure data from Saltzman et al. (2014), which is 3.2 x 10-5 (n = 80). In addition, data

from this study demonstrates a smaller average measured uncertainty of 4.3 x 10-5 compared to

the average measured uncertainty of Saltzman et al. (2014) data, which is 5.2 x 10-4.

Of the 18 samples, ten were selected to be run again with a leaching preparation method.

Samples were leached for 72 hours in 5% acetic acid (Table 2). The average internal error of

leached samples is 2.77 x 10-6 (2SD 3.47 x 10-7); external error is 8.22 x 10-6, as determined by

the 2SD of SRM 987 measurements (n = 96). Leached samples’ 87Sr/86Sr values are on average

7.47 x 10-6 less radiogenic than the matching unleached samples (2SD 1.88 x 10-5; Table 2;

Figure 6). It is valuable to note that for two samples (83JD-115 and 83JD-130), the leached sample is more radiogenic than the unleached sample (by 7 x 10-6 and 5 x 10-6 respectively),

within external error. In addition, the 87Sr/86Sr of the acetic acid used to leach samples (i.e.,

leachate) was analyzed; the leachate was collected after 8, 24, and 72 hours (Table 2; Figure 5).

The average internal error of leachate measurements is 2.83 x 10-6 (2SD 4.78 x 10-7); external

Table 2. 87Sr/86Sr of unleached samples, leached samples, and leachates

Sample ID Unleached Leached 8 hr 24 hr 72 hr 87Sr/86Sr 87Sr/86Sr Leachate Leachate Leachate 87Sr/86Sr 87Sr/86Sr 87Sr/86Sr 83JD-80 0.708645 0.708641 -- 0.708642 0.708628 83JD-88 0.708652 0.708630 0.708670 0.708642 0.708644 83JD-115 0.708610 0.708617 0.708641 0.708636 0.708613 83JD-130 0.708613 0.708618 0.708635 0.708623 0.708611 83JD-184 0.708522 0.708512 0.708555 0.708534 0.708526 83JD-191 0.708527 0.708510 0.708570 0.708519 0.708514 83JD-211 0.708535 0.708523 0.708574 0.708541 0.708524 83JE-13 0.708461 0.708457 0.708501 0.708456 0.708459 83JE-18.5 0.708373 0.708355 0.708421 0.708371 0.708348 83JE-23 0.708349 0.708348 0.708363 0.708361 0.708349

error is 8.22 x 10-6. The 8 hr leachate is on average 3.86 x 10-5 (2SD 3.52 x 10-5) more radiogenic

than the leached sample itself; the 24 hr leachate is on average 1.14 x 10-5 (2SD 1.49 x 10-5) more radiogenic; the 72 hr leachate is on average 3.52 x 10-7 (2SD 1.68 x 10-5) more radiogenic.

It should be noted that one out of the ten samples (83JE-13) has a 24 hr leachate less radiogenic than the leached sample by 1 x 10-6, which is within external error. In addition, four out of the

ten samples (83JD-80, 83JD-115, 83JD-130, 83JE-18.5) have a 72 hr leachate that is less radiogenic than the leached sample, (1.3 x 10-5, 4 x 10-6, 7 x 10-6, 7 x 10-5 respectively; Figure 5).

Of these, samples 83JD-80 and 83JE-18.5 demonstrate differences outside external error.

B. Sr mass balance

All leached samples and their leachates were analyzed for Sr abundance (µg) in order to

determine mass balance (Table 3), i.e., the amount of Sr in each fraction. On average, the Sr that

is removed after 8 hours of leaching represents 8% (SD 3.7%) of the total Sr in the sample; 17%

(SD 7.7%) is removed from 8 to 24 hours of leaching; 24% (SD 6.6%) is removed from 24 to 72 hours of leaching. Overall, 49% (SD 16.9%) of the total Sr is removed from the sample via 72 hours of leaching (Figure 7).

Table 3. Sr abundance for leached samples

Sample ID Leached 8 hr 24 hr 72 hr Element Leachate Leachate Leachate (µg Sr) (µg Sr) (µg Sr) (µg Sr) 83JD-80 11.9 0.9 2.4 4.4 83JD-88 16.7 1.0 1.9 3.0 83JD-115 8.7 1.2 2.3 3.6 83JD-130 3.0 1.6 2.6 3.1 83JD-184 2.1 0.7 1.4 2.1 83JD-191 1.0 0.6 1.6 1.4 83JD-211 9.7 0.6 1.2 1.9 83JE-13 9.3 0.8 2.1 3.3 83JE-18.5 11.1 1.2 2.6 4.7 83JE-23 10.5 1.6 2.9 5.1

Figure 5. Ten samples from the Oklahoma section were split, with one portion left unleached and the other leached. Leached samples were left in 5% acetic acid for 72 hours with leachate collected at 8, 24, and 72 hrs. The unleached and leached portions, and three leachates from each sample are plotted. 83JD-80 (black) did not have a successful 8-hr leachate analysis. See Tables

2 and 3 for a list of samples.

C. SEM analysis of conodont surface

Conodont elements examined under SEM demonstrate physical changes after leaching

for 72 hours, including removal of clay residue, widening of existing cracks and creation of new

cracks, and pitting and “shredding” of the surface fabric (Figure 8). This confirms that leaching does impact conodont elements physically, lending credence to the concept that surficial diagenetic Sr is stripped away through this method. It is valuable to note that the physical effects of leaching do not appear to be homogenous across the conodont element, which could be a result of differing histology or morphology.

D. LOESS curves and inflection point

The data collected for this study is used to constrain the timing of an inflection point. In

Saltzman et al. (2014), the I-35 N section includes 30 data points from samples collected at various intervals along c.a. 600 meters of the Simpson Group. This study introduces 33 new data points, both leached and unleached, including various duplicates of samples run as part of

Saltzman et al. (2014). In addition, Sr data from Saltzman et al. (2014) has been recalibrated to a standard value for SRM 987 of 0.710248 (McArthur, 1994). This has been done following the same data correction method outlined in Appendix A. In addition, one outlier has been eliminated, leaving a total of 62 data points.

Figure 10 plots 87Sr/86Sr data against age (see Appendix C for age model details) along with the smoothing LOESS curve. This smoothing curve demonstrates large trends in the data, and from it, one can plot the rate of change, or gradient, of 87Sr/86Sr over time. An inflection

point is marked by the beginning of an increase in the absolute value of the gradient, which

indicates a shift in the rate of change (see Appendix B for details). The gradient begins to shift

toward a more negative value within the biostratigraphic holodentata zone. The absolute value of the gradient continues to rise until the upper sweeti zone, when it appears to level off.

Discussion

A. Effects of leaching on 87Sr/86Sr

The 87Sr/86Sr value of leachates suggest that leaching does work in the manner that

Holmden et al. (1996) and others suggest. In most samples, the 8-hr leachate is more radiogenic

than the other leachates, unleached samples, and leached samples (Figure 5). The 24-hr leachates are generally more radiogenic than the samples, though oftentimes within analytical error, and the 72-hr leachates have values comparable to the leached samples. This, then, suggests that the majority of Sr coming off the conodont element’s outer edges is indeed more radiogenic and likely diagenetic in origin. However, for these conodont elements, the diagenetic Sr is a comparatively small portion of the overall Sr in the sample, at most 15% but on average 8% of the total Sr, minimizing the overall effect of leaching (Table 3; Figure 7). In addition, most samples show leached samples to be either less radiogenic than or roughly equal to unleached samples, within error (Figure 6).

One can also consider whether leaching samples leads to better constrained data by comparing the error of leached vs. unleached sample duplicates, i.e., the difference between the measured and true values of a sample. The global marine 87Sr/86Sr for a given point in time

cannot be absolutely determined, but the global LOWESS curve as presented by McArthur et al.

(2012) provides the most widely accepted version of “true” primary seawater values. In the case

of the ten unleached duplicates, the measured 87Sr/86Sr has an average error (i.e., average

difference between the measured value and the “true” value predicted by McArthur et al., 2012)

of 7.7 x 10-5 (Figure 6). Leached duplicates have an average error of 8.4 x 10-5. These results

apply to Ordovician-age samples with a CAI ≤ 1, but analysis of Pennsylvanian- and Silurian-

Figure 6. 87Sr/86Sr of leached vs unleached samples (see Figure 5 and Table 2) and the resulting respective LOESS curves. Comparison to the McArthur et al., (2012) LOWESS curve demonstrates that unleached samples are largely more radiogenic than their leached counterparts and are closer to the McArthur curve. Error bars for 87Sr/86Sr are smaller than the data points.

Age error is c.a. 3 My.

17%

51%

24%

8 hr 24 hr 72 hr Leached Sample

Figure 7. Averaged mass balance of Sr in 10 leached conodont samples. On average, 8% of the samples’ total Sr was removed in first 8 hours of leaching, 17% in 8 to 24 hours, and 24% in 24 to 72 hours. On average, samples had 51% of total Sr remaining after 72 hours of leaching. See

Table 3 for Sr mass balance.

age samples with CAI ≤ 3 produce similar results (see Appendix D for details).

B. Middle-Late Ordovician 87Sr/86Sr inflection point

The main shift in the age gradient begins in the holodentata zone (Figure 10). In the depth profile (Figure 9), the holodentata zone correlates with the upper Oil Creek and lower

McLish Formations. The upper Oil Creek is considered to be a highstand systems tract (HST), i.e., a time in which the rise in relative sea level slows, and sedimentation rate becomes relatively larger than accommodation space (Candelaria and Handford, 1995). The Oil Creek Formation contact with the overlying McLish Formation is unconformable, and the lower McLish

Figure 8. Conodont elements from Arbuckle Mt. sample 83JD 80 were imaged before and after leaching. A) before leaching, x600; B) after leaching, x600; C) before leaching, x1.2k; D) after leaching, x1.2k. Leaching appears to remove clay residue, widen and deepen existing cracks, create cracks, and “shred” surface of conodont element.

Figure 9. Data from this study and Saltzman et al. (2014) plotted over depth. Lithologic information and conodont zonation was derived from Bauer (1987, 1990, 1994, 2010) and

Saltzman et al. (2014).

Figure 10. Data from this study and Saltzman et al. (2014), LOESS smoothing curve, and the associated gradient curve plotted over age for the majority of the Ordovician. The LOESS and gradient curves of Edwards et al. (2015) and McArthur et al. (2012) are included for comparison.

This demonstrates the relatively constant rate of 87Sr/86Sr decline in the Early Ordovician and early Middle Ordovician, as well as the point at which the gradient curves begin to shift to a more negative value. This shift in all three curves arguably begins within or very near to the holodentata zone, which has been outlined here.

Formation is considered part of a first- or second-order transgressive systems tract (TST), i.e., a time of rising relative sea level, wherein the accommodation space of the basin is relatively larger than sedimentation rate (Candelaria and Handford, 1995; Carlucci et al., 2014).

This unconformity is correlated with the Sauk-Tippecanoe sequence boundary, the significance of which will be discussed in a later section (Candelaria and Handford, 1995).

In order to place the Arbuckle Mountains data in context and to address concerns of sedimentation rate, these results are compared to two other studies (Figure 10; Figure 13). The global LOWESS curve presented in McArthur et al. (2012) demonstrates a gradual gradient shift starting in the holodentata zone. One can also compare the Arbuckle data points to a collected set of data from across the Appalachian Basin, which contains a greater diversity of locations

(Figure 1; Figure 10; Figure 13; Edwards et al., 2015) and confirms that the prominent gradient shift begins in or very near to the holodentata zone. Placement within this zone, using the current time scale (Cooper and Sadler, 2012) dates the inflection point to c.a. 466 to 464 Mya.

Here, it should be noted that while one can place the inflection point within the holodentata zone, the nature of biostratigraphy creates some uncertainty of the inflection point’s exact numerical age, as it is statistically unlikely that the true “first” and “last” appearance of the species is present in any given section. In this study, the average error in age is c.a. 3 My, based on the length of conodont biostratigraphy zones.

C. Wider context of inflection

The holodentata zone spans from 466.4 to 463.8 Mya (Cooper and Sadler, 2012). Of the global events at that time which could have contributed to decreasing 87Sr/86Sr, the most widely

discussed is a shift in the lithology being weathered combined with uplift and low-latitude paleogeography. The Taconic orogeny, which took place on the Laurentian margin, can be split into three stages. The second stage (Taconic 2) occurred around 488 to 461 Mya and encompassed the Taconic arc system’s leading edge coming into contact with the Laurentian margin, resulting in volcanic degassing in conjunction with uplift of arc magmatism that demonstrates tholeiitic characteristics, i.e., dominated by basaltic lavas (Kearey et al., 2009; van

Staal et al., 2009; van Staal and Barr, 2012; Swanson-Hysell and Macdonald, 2017). The third

stage (Taconic 3) occurred around 461 to 445 Mya and encompassed the closing of the Iapetus

Ocean with arc-arc collision and arc accretion (van Staal and Barr, 2012; Swanson-Hysell and

Macdonald, 2017). In Taconic 3, the closing of the Iapetus and associated arc accretion led to the cessation of arc volcanic activity and the orogenic uplift of young basalts; the collision of two major arcs and the complete closure of the main Iapetus tract occurred c.a. 455 Mya (van Staal and Barr, 2012; Swanson-Hysell and Macdonald, 2017). Swanson-Hysell and Macdonald (2017) found that, with improved paleogeography data, one could place the Taconic orogeny within 10° of the equator: a zone of increased weatherability that would have given the uplifted basalt of the

Taconic arcs a major role in the rate of CO2 drawdown and global cooling in the Middle-Late

Ordovician.

Although the Taconic Orogeny is a plausible scenario for the 87Sr/86Sr inflection point,

questions remain due to the gradual nature of the orogeny (i.e., spanning tens of millions of years) versus the relatively abrupt shift in 87Sr/86Sr (i.e., spanning millions of years). In addition,

the Ordovician sea-surface temperature curve presented by Trotter et al. (2008) shows a slight

warming trend from mid-Darriwilian to mid-Katian, suggesting that basaltic weathering was not

a dominant force, or was accompanied by increased degassing (Young et al., 2009; Saltzman,

2017). Therefore, another possible explanation for the 87Sr/86Sr inflection point is an increase in

the rate of seafloor spreading accompanied by rising sea level—possibly in tandem with the

Taconic orogeny. Haq and Schutter (2008) demonstrate a substantial rise in global sea level in

the upper Darriwilian. In addition, the start of the 87Sr/86Sr inflection point in the holodentata zone of the I-35 N site correlates with the transition from the Oil Creek to McLish Formation,

which has been correlated with the Sauk-Tippecanoe sequence boundary (Candelaria and

Handford, 1995; Carlucci et al., 2014), also dated to the mid-Darriwilian holodentata zone

(Saltzman et al., 2014). Saltzman et al. (2014) speculated that, if a relationship between the

87Sr/86Sr inflection point and Sauk-Tippecanoe supersequence boundary transgression could be

confirmed, this correlation signals a role for increased seafloor spreading in the 87Sr/86Sr

inflection point, as an increase in the rate of seafloor spreading can raise sea level, although at a

rate much slower than glacio-eustasy. If increased seafloor spreading accompanied the

temperature increase due to Taconic volcanism in the mid-Darriwilian (Trotter et al., 2008;

Young et al., 2009; McKenzie et al. 2016), then the dual impact of a greater amount of young,

hot basaltic lava and increased sea bottom temperature would prompt a greater rate of

hydrothermal weathering of seafloor basalts, increasing the flux of unradiogenic Sr. This could

in part explain the inflection point in 87Sr/86Sr. Eventually, when temperature decreased due to

Taconic basaltic weathering (drawdown of C) outpacing volcanic input of carbon (Young et al.,

2009; Swanson-Hysell and Macdonald, 2017), then a decreased flux of unradiogenic Sr into the

ocean due to the cooling of ocean bottom water (i.e., negative feedback of Coogan and Dosso,

2015) during the Katian could explain the turnaround to more radiogenic values heading into the.

Hirnantian and early Silurian

A pattern of increased seafloor spreading leading to a notable drop in 87Sr/86Sr has been discussed and modeled in the Cretaceous (Ingram et al., 1994; Jones and Jenkyns, 2001) as well as the Jurassic (Jones and Jenkyns, 2001). These models support the concept that increased seafloor spreading can have a marked effect on global 87Sr/86Sr. An analogous model can be built for the Middle to Late Ordovician, and is the next step in determining the impact of seafloor spreading rate on marine 87Sr/86Sr.

Conclusion

The global 87Sr/86Sr curve demonstrates an inflection point during the Middle to Late

Ordovician in which the rate of change increases. Using smoothing curves and associated

gradient curves from various data sets, the inflection point can be placed within the holodentata

zone, correlating with the Sauk-Tippecanoe sequence boundary and associated transgression.

This correlation suggests that rising sea level due to increased seafloor spreading was the main

driver of decreasing 87Sr/86Sr in the Darriwilian.

A new generation TIMS did improve the measured uncertainty of data, going from 5.19 x

10-4 to 4.3 x 10-5. In addition, leaching conodont elements in order to remove diagenetic Sr did

result in overall lower 87Sr/86Sr, but not enough to significantly change the pattern of the 87Sr/86Sr

curve. Moreover, leaching did not lead to lower error in 87Sr/86Sr measurements. However,

87Sr/86Sr of leachates demonstrates that leaching does appear to remove radiogenic (i.e., diagenetic) Sr, and that the majority of this Sr is removed between 8 and 24 hours. The diagenetic Sr, however, makes up a small portion of the element’s overall Sr concentration. This is likely due to the low CAI of the conodont elements used (≤ 1); it is still unclear whether elements with a CAI of 4 to 5 would benefit more materially from leaching. On a practical level, researchers using conodont elements for 87Sr/86Sr analysis would be suggested to test leaching’s

effectiveness on a small portion of samples, leaching them for 8 hrs and determining whether the

difference is significant enough to apply to all samples.

References

Albanesi, G.L., Barnes, C.R., Trotter, J.A., Williams, I.S., Bergstrom, S.M. (2019). Comparative Lower-Middle Ordovician conodont oxygen isotope palaeothermometry of the Argentine Precordillera and Laurentian margins. Palaeogeography, Palaeoclimatology, Palaeoecology. Pre-publication.

Allègre, C. J., Louvat, P., Gaillardet, J., Meynadier, L., Rad, S., & Capmas, F. (2010). The fundamental role of island arc weathering in the oceanic Sr isotope budget. Earth and Planetary Science Letters, 292, 51-56.

Algeo, T. J., Marenco, P. J., & Saltzman, M. R. (2016). Co-evolution of oceans, climate, and the biosphere during the ‘Ordovician Revolution’: A review. Palaeogeography, Palaeoclimatology, Palaeoecology, 458, 1-11.

Armstrong, H. A., Pearson, D. G., & Griselin, M. (2001). Thermal effects on rare earth element and strontium isotope chemistry in single conodont elements. Geochimica et Cosmochimica Acts, 65(3), 435-441.

Banner, J., & Hanson, G. (1990). Calculation of simultaneous isotopic and trace element variations during water-rock interaction with applications to carbonate diagenesis. Geochemica et Cosmochimica Acta, 54, 3123-3137.

Bauer, J. A. (1987). Conodont biostratigraphy, correlation, and depositional environments of Middle Ordovician rocks in Oklahoma. [Ph.D. dissertation]. Columbus, Ohio. Ohio State University.

Bauer, J. A. (1989). Conodont biostratigraphy and paleoecology of Middle Ordovician rocks in eastern Oklahoma. Journal of Paleontology, 63(1), 92–107.

Bauer, J.A. (1990). Early to Middle Paleozoic Conodont Biostratigraphy of the Arbuckle Mountains Southern Oklahoma. Oklahoma Geologic Survey, Guidebook 27.

Bauer, J. A. (1994). Conodonts from the Bromide Formation (Middle Ordovician), south- central Oklahoma. Journal of Paleontology, 68(2), 358-376.

Bauer, J. A. (2010). Conodonts and Conodont Biostratigraphy of the Joins and Oil Creek Formations. Oklahoma Geological Survey, Bulletin 150.

Berner, R. A., & Ryem D. M. (1992). Calculation of the Phanerozoic Strontium Isotope Record of the Oceans from a Carbon Cycle Model. American Journal of Science, 292, 136-148.

Berner, R. A. (2004). A model for calcium, magnesium and sulfate in seawater over Phanerozoic time. American Journal of Science, 304(5), 438–453. 34

Bertram, C. J., Elderfield, H., Aldridge, R. J., & Morris, S. C. (1992). 87Sr/86Sr, 143Nd/144Nd and REEs in Silurian phosphatic fossils. Earth and Planetary Science Letters, 113, 239–249.

Bowen, N.L. (1956). The evolution of the igneous rocks. Princeton University Press.

Brand, U., & Veizer, J. (1980). Chemical Diagenesis of a Multicomponent Carbonate System--1: Trace Elements. SEPM Journal of Sedimentary Research, 50(4), 1219-1236.

Brand, U., Morrison, J. O., Brand, N., & Brand, E. (1987). Isotopic variation in the shells of recent marine invertebrates from the Canadian pacific coast. Chemical Geology: Isotope Geoscience Section, 65, 137-145.

Brand, U. (1989). Biogeochemistry of Late Paleozoic North American brachiopods and secular variation of seawater composition. Biogeochemistry, 7, 159-193.

Brand, U. (1991). Strontium isotope diagenesis of biogenic aragonite and low-Mg calcite. Geochimica et Cosmochimica Acta, 55, 505-513.

Briggs, D.E.G., Clarkson, E.N.K., & Aldridge, R.J. (1983). The conodont animal. Lethaia, 16, 1- 14.

Bruhn, F., Korte, C., Meijer, J., Stephan, A., & Veizer, J. (1997). Trace element concentrations in conodonts measured by the Bochum proton microprobe. Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, 130, 636-640.

Burke, W. H., Denison, R. E., Hetherington, E. A., Koepnick, R. B., Nelson, H. F., & Otto, J. B. (1982). Variation of seawater Sr throughout Phanerozoic time, 10, 516-519.

Carlucci, J. R., Westrop, S. R., Brett, C. E., & Burkhalter, R. (2014). Facies architecture and sequence stratigraphy of the Ordovician Bromide Formation (Oklahoma): a new perspective on a mixed carbonate-siliciclastic ramp. Facies, 60(4), 987–1012.

Carlucci, J. R., Goldman, D., Brett, C. E., Westrop, S. R., Leslie, S. A. (2015). Katian GSSP and Carbonates of the Simpson and Arbuckle Groups in Oklahoma.

Carpenter, S. J., & Lohmann, K. C. (1992). Sr Mg ratios of modern marine calcite: Empirical indicators of ocean chemistry and precipitation rate. Geochimica et Cosmochimica Acta, 56, 1837-1849.

Coogan, L. A., & Dosso, S. E. (2015). Alteration of ocean crust provides a strong temperature dependent feedback on the geological carbon cycle and is a primary driver of the Sr-isotopic composition of seawater. Earth and Planetary Science Letters, 415, 38–46.

Cooper, R. A., & Sadler, P. (2012). The Ordovician period. A Geologic Time Scale. 2012.

Cummins, D., & Elderfield, H. (1994). The strontium isotopic composition of Brigantian (late Dinantian) seawater. Chemical Geology, 118, 255–270.

Davis, A. C., Bickle, M. J., & Teagle, D. A. H. (2003). Imbalance in the oceanic strontium budget. Earth and Planetary Science Letters, 211, 173-187.

Derby, J.R., Bauer, J.A., Creath, W.B., Dresbach, R.I., Ethington R.L., Loch, J.D., Stitt, J.H., Mchargue, T.R., Miller, J.F., Miller, M.A., Repetski, J.E., Sweet, W.C., Taylor, J.F., and Williams, M., (1991). Biostratigraphy of the Timbered Hills, Arbuckle, and Simpson Groups, Cambrian and Ordovician, Oklahoma: A review of correlation tools and techniques available to the explorationist: Oklahoma Geological Survey Circular 92, 15–41.

Dessert, C. (2001). Erosion of Deccan Traps determined by river geochemistry: impact on the global climate and the 87Sr/86Sr ratio of seawater. Earth and Planetary Science Letters, 188, 459-474.

Diener, A., Ebneth, S., Veizer, J., & Buhl, D. (1996). Strontium isotope stratigraphy of the Middle Devonian: Brachiopods and conodonts. Geochimica et Cosmochimica Acta, 60(4), 639-652.

Donoghue, P. C. J., Forey, P. L., & Aldridge, R. J. (2018). Conodont affinity and chordate phylogeny. Biol. Rev, 75, 191–251.

Dudas, F., Yuan, D. X., Shen, S. Z., & Bowring, S. A. (2017). A conodont-based revision of the 87Sr/86Sr seawater curve across the Permian-Triassic boundary. Palaeogeography, Palaeoclimatology, Palaeoecology, 470, 40-53.

Ebneth, S., Diener, A., Buhl, D., & Veizer, J. (1997). Strontium isotope systematics of conodonts: Middle Devonian, Eifel Mountains, Germany. Palaeogeography, Palaeoclimatology, Palaeoecology, 132, 79-96.

Ebneth, S., Shields, G. A., Veizer, J., Miller, J. F., & Shergold, J. H. (2001). High-resolution strontium isotope stratigraphy across the Cambrian-Ordovician transition. Geochimica et Cosmochimica Acta, 65(14), 2273–2292.

Edwards, C. T., Saltzman, M. R., Leslie, S. A., Bergström, S. M., Sedlacek, A. R. C., Howard, A., Young, S. A. (2015). Strontium isotope (87Sr/86Sr) stratigraphy of Ordovician bulk carbonate: Implications for preservation of primary seawater values. Bulletin of the Geological Society of America, 127(9–10), 1275–1289.

Elderfield, H. (1986). Strontium isotope stratigraphy. Palaeogeography, Palaeoclimatology, Palaeoecology, 57, 71-90.

Epstein, A. G., Epstein, J. B., Harris, L. D., & Mckelvey, V. E. (1977). Conodont Color Alteration- an Index to Organic Metamorphism. Geological Survey Professional Paper 995.

Faure, G., Crocket, & Hurley. (1967). Some aspects of the geochemistry of strontium and calcium in the Hudson Bay and the Great Lakes. Geochimica et Cosmochimica Acta, 31, 451-461.

Faure, G, & Mensing, T.M. (2003). Isotopes: Principles and Applications.

Ferretti, A., Malferrari, D., Medici, L., & Savioli, M. (2017). Diagenesis does not invent anything new: Precise replication of conodont structures by secondary apatite. Scientific Reports, 7(1), 1–9.

Fordham, B. G. (1992). Chronometric calibration of mid-Ordovician to Tournaisian conodont zones: A compilation from recent graphic-correlation and isotope studies. Geological Magazine, 129(6), 709-721.

Gaillardet, J., Dupre, B., Louvat, P., & Allegre, C. J. (1999). Global silicate weathering and CO consumption rates deduced 2 from the chemistry of large rivers. Chemical Geology, 159, 3– 30.

Gradstein, F. M. (2012). Biochronology. The Geologic Time Scale 2012.

Ham, W. (1969). Regional Geology of the Arbuckle Mountains, Oklahoma. Geological Society of American Bulletin. Guidebook.

Haq, B. U., & Schutter, S. R. (2008). A Chronology of Paleozoic Sea-Level Changes. Science, 322(5898), 64-68.

Holmden, C., Creaser, R. A., Muehlenbachs, K., Bergstrom, S. M., & Leslie ’, S. A. (1996). Isotopic and elemental systematics of Sr and Nd in 454 Ma biogenic apatites: implications for paleoseawater studies. Earth and Planetary Science Letters, 142, 425–437.

Huh, Y., & Edmond, J. M. (1998). On the interpretation of the oceanic variations in 87Sr/86Sr as recorded in marine limestones. Proceedings of the Indian Academy of Sciences, Earth and Planetary Sciences, 107(4), 293-305.

Ingram, B. L., Coccioni, R., Montanari, A., Richter, F.M. (1994). Strontium isotopic composition of mid-Cretaceous seawater. Science, 264, 546-549.

John, E. H., Cliff, R., & Wignall, P. B. (2008). A positive trend in seawater 87Sr/86Sr values over the Early-Middle Frasnian boundary (Late Devonian) recorded in well-preserved conodont elements from the Holy Cross Mountains, Poland. Palaeogeography, Palaeoclimatology, Palaeoecology, 269, 166-175. 37

Johnson, K. S. (2008), Geologic history of Oklahoma, Oklahoma Geological Survey Educational Publication 9.

Jones, C. E., Jenkyns, H. C., Hesselbo, S. P. (1994). Strontium isotopes in Early Jurassic seawater. Geochimica et Cosmochimica Acta, 58(4), 1285-1301.

Jones, C.E., Jenkyns, H.C. (2001). Seawater strontium isotopes, ocean anoxic events, and seafloor hydrothermal activity in the Jurassic and Cretaceous. American Journal of Science, 301, 112-149.

Katvala, E. C., & Henderson, C. M. (2012). Chemical element distributions within conodont elements and their functional implications. Paleobiology. 38(3), 447-458.

Kearey, P., Klepeis, K.A., Vine, F.J. (2009). Global Tectonics.

Keenan, S. W., Engel, A. S., Roy, A., & Lisa Bovenkamp-Langlois, G. (2015). Evaluating the consequences of diagenesis and fossilization on bioapatite lattice structure and composition. Chemical Geology, 413, 18–27.

Keenan, S. W. (2016). From bone to fossil: A review of the diagenesis of bioapatite. American Mineralogist, 101(9), 1943–1951.

Kohn, M. J. (2008). Models of diffusion-limited uptake of trace elements in fossils and rates of fossilization. Geochimica et Cosmochimica Acta, 72(15), 3758–3770.

Lenton, T. M., Crouch, M., Johnson, M., Pires, N., & Dolan, L. (2012). First plants cooled the Ordovician. Nature Geoscience, 5, 86-89.

Lightfoot, P., & Hawkesworth, C. (1988). Origin of Deccan Trap lavas: evidence from combined trace element and Sr-, Nd- and Pb-isotope studies. Earth and Planetary Science Letters, 91, 89-104.

Macdonald, F. A., Swanson-Hysell, N. L., Park, Y., Lisiecki, L., & Jagoutz, O. (2019). Arc- continent collisions in the tropics set Earth’s climate state. Science, 364(6436), 181–184.

Martin, E. E., & Macdougall, J. D. (1995). Sr and Nd isotopes at the Permian/Triassic boundary: A record of climate change. Chemical Geology, 125, 73–99.

Martin, E. E., & Scher, H. D. (2004). Preservation of seawater Sr and Nd isotopes in fossil fish teeth: Bad news and good news. Earth and Planetary Science Letters, 220, 25–39.

McArthur, J.M. (1994). Recent trends in strontium isotope stratigraphy. Terra Nova, 6, 331-358.

McArthur, J. M., Howarth, R. J., & Shields, G. A. (2012). Strontium Isotope Stratigraphy. The Geologic Time Scale, 127–144.

McKenzie, R. N., Horton, B. K., Loomis, S. M., Stockli, D. F., Planavsky, N. J., & Lee, C.-T. A. (2016). Continental arc volcanism as the principal driver of icehouse-greenhouse variability. Science, 352(6284), 444-447.

Meybeck, M. (1987). Global chemical weathering of surficial rocks estimated from river dissolved loads. American Journal of Science, 287, 401-428.

Morrison, J. O., & Brand, U. (1988). An evaluation of diagenesis and chemostratigraphy of upper cretaceous molluscs from the Canadian Interior Seaway. Chemical Geology: Isotope Geoscience Section, 72, 235-248.

Palmer, M. R., & Edmond, J. M. (1989). The strontium isotope budget of the modern ocean. Earth and Planetary Science Letters, 92, 11-26.

Pietzner, Horst; Vahl, Johanna; Werner, Hans; Ziegler, Willi. (1968). Palaeontographica Abteilung A Band A128 Lieferung 4-6, 115-152.

Pope, M., & Read, J. F. (1997). High-Resolution Surface and Subsurface Sequence Stratigraphy of Late Middle to Late Ordovician (Late Mohawkian-Cincinnatian) Foreland Basin Rocks, Kentucky and Virginia. AAPG Bulletin, 81(11), 1866-1893.

Quinton, P. C., Leslie, S. A., Herrmann, A. D., & MacLeod, K. G. (2016). Effects of extraction protocols on the oxygen isotope composition of conodont elements. Chemical Geology, 431, 36-43.

Rejebian, V. A., Harris, A. G., & Huebner, J. S. (1987). Conodont Color and Textural Alteration: An Index to Regional Metamorphism, Contact Metamorphism, and Hydrothermal Alteration. Bulletin of the Geological Society of America, 99, 471-479.

Ruppel, S. C., James, E. W., Barrick, J. E., & Nowlan, G. (1996). High-resolution Sr chemostratigraphy of the Silurian: Implications for event correlation and strontium flux. Geology, 24(9), 831-834.

Saltzman, M. R., Edwards, C. T., Leslie, S. A., Dwyer, G. S., Bauer, J. A., Repetski, J. E., Bergström, S. M. (2014). Calibration of a conodont apatite-based Ordovician 87Sr/86Sr curve to biostratigraphy and geochronology: Implications for stratigraphic resolution. Bulletin of the Geological Society of America. 126(11-12), 1551-1568.

Saltzman, M. (2017). Silicate weathering, volcanic degassing, and the climate tug of war. Geology, 45(8), 763–764. 39

Schmitz, B., Aberg, G., Werdelin, L., Forey, P., & Bendix-Almgreen, S. E. (n.d.). 87Sr/86Sr, Na, F, Sr, and La in skeletal fish debris as a measure of the paleosalinity of fossil-fish habitats. Geological Society of American Bulletin, 103, 786-794. 38 Shields, G. A., Carden, G. A. F., Veizer, J., Meidla, T., Rong, J. Y., & Li, R. Y. (2003). Sr, C, and O isotope geochemistry of Ordovician brachiopods: A major isotopic event around the Middle-Late Ordovician transition. Geochimica et Cosmochimica Acta, 67(11), 2005-2025.

Steiger, R.H., Jäger, E. (1977). Subcommission on geochronology: convention on the use of decay constants in geo- and cosmochronology. Earth and Planetary Science Letters, 36, 359-362.

Swanson-Hysell, N. L., & Macdonald, F. A. (2017). Tropical weathering of the Taconic orogeny as a driver for Ordovician cooling. Geology, 45(8), 719-722.

Taylor, A. S., Lasaga, A. C. (1999). The role of basalt weathering in the Sr isotope budget of the oceans. Chemical Geology, 161, 199-214.

Trotter, J. A., Korsch, M. J., Nicoll, R. S., & Whitford, D. J. (1998). Sr isotopic variation in single conodont elements: implications for defining the Sr seawater curve. Bollettino Della Societa Paleontologica Italiana, 37(2–3), 507–514.

Trotter, J. A., & Eggins, S. M. (2006). Chemical systematics of conodont apatite determined by laser ablation ICPMS. Chemical Geology, 233, 196-216.

Trotter, J. A., Fitz Gerald, J. D., Kokkonen, H., & Barnes, C. R. (2007). New insights into the ultrastructure, permeability, and integrity of conodont apatite determined by transmission electron microscopy. Lethaia.

Trotter, J. A., Williams, I. S., Barnes, C. R., Lecuyer, C., & Nicoll, R. S. (2008). Did Cooling Oceans Trigger Ordovician Biodiversification? Evidence from Conodont Thermometry. Science, 321, 550-554.

Trotter, J. A., Barnes, C. R., & McCracken, A. D. (2016). Rare earth elements in conodont apatite: Seawater or pore-water signatures? Palaeogeography, Palaeoclimatology, Palaeoecology, 462, 92-100.

Trueman, C. N. (2013). Chemical taphonomy of biomineralized tissues. Palaeontology, 56(3), 475–486. van Staal, C. R., Whalen, J. B., Valverde-Vaquero, P., Zagorevski, A., & Rogers, N. (2009). Pre- Carboniferous, episodic accretion-related, orogenesis along the Laurentian margin of the northern Appalachians. Geological Society, London, Special Publications, 327(1), 271–316. 40

van Staal, C. R., Barr, S. M., & Murphy, J. B. (2012). Provenance and tectonic evolution of Ganderia: Constraints on the evolution of the Iapetus and Rheic oceans. Geology, 40(11), 987–990.

Veizer, J., & Compston, W. (1974). 87Sr/86Sr composition of seawater during the Phanerozoic. Geochimica et Cosmochimica Acta, 38, 1461-1484.

Veizer, J., Compston, W., Hoefs, J., & Nielsen, H. (1982). Mantle buffering of the early oceans. Naturwissenschaften, 69, 173-180.

Veizer, J., Compston, W., Clauer, N., & Schidlowski, M. (1983). 87Sr/86Sr in Late Proterozoic carbonates: evidence for a “mantle” event at ~900 Ma ago. Geochimica et Cosmochimica Acta, 47, 295-302.

Veizer, J. (1989). Strontium Isotopes in Seawater through Time. Annual Review of Earth and Planetary Sciences, 17, 141-167.

Veizer, J., & Prokoph, A. (2015). Temperatures and oxygen isotopic composition of Phanerozoic oceans. Earth-Science Reviews, 146, 92-104.

Waltham, D., & Gröcke, D. R. (2006). Non-uniqueness and interpretation of the seawater 87Sr/86Sr curve. Geochimica et Cosmochimica Acta, 70, 384-394.

Young, S. A., Saltzman, M. R., Foland, K. A., Linder, J. S., & Kump, L. R. (2009). A major drop in seawater 87Sr/86Sr during the Middle Ordovician (Darriwilian): Links to volcanism and climate? Geology, 37(10), 951-954.

Young, S. A., Gill, B. C., Edwards, C. T., Saltzman, M. R., & Leslie, S. A. (2016). Middle–Late Ordovician (Darriwilian–Sandbian) decoupling of global sulfur and carbon cycles: Isotopic evidence from eastern and southern Laurentia. Palaeogeography, Palaeoclimatology, Palaeoecology, 146, 92-104.

Appendix A: Method Details

A.1 Conodont Processing

Conodont element samples had been previously extracted by James Bauer and were

selected from labelled slides. The selected elements had a low color alteration index (CAI ≤ 1)

and included an even mix of morphologies, including both coniform (cones) and ramiform

(platform) elements. In the case of Ordovician-age samples, approximately 0.2 g of conodont elements with an average Sr concentration of 6000 ppm were selected. In the case of

Pennsylvanian-age samples, approximately 1.0 g of conodont elements with an average Sr

concentration of 1000 ppm were selected. All elements were weighed and placed in microtubes

and sonicated in Milli Q deionized water for 15 minutes; this was done three times. Elements

were then placed in trace⦁ -metal grade, distilled 6N HCl, agitated for 30 seconds, and centrifuged

for 3 minutes. The elements were left to dissolve overnight. The next day, the solutions were

once again agitated and centrifuged. The solutions were transferred to Teflon vials and sonicated

for 40 minutes. These steps ensured that the elements were completely dissolved. The samples

were placed on a hot plate in a laminar flow hood and allowed to dry.

A.2 Leaching

If the conodont elements were leached, leaching occurred after sonication in deionized

water and before dissolution in trace-metal grade, distilled 6N HCl. Elements were placed in 0.5

mL 5% acetic acid. Under normal circumstances, conodont elements would be left in the same

acetic acid for anywhere from 1 to 3 days. However, the purpose of this project was to determine

the amount and isotopic value of Sr leached over time. At various time intervals, 5% acetic acid

was collected, conodont samples were rinsed three times with deionized water, and fresh 5% acetic acid was added to the sample. Collected acetic acid samples were placed on a hot plate in a laminar flow hood and allowed to dry. They were subsequently processed the same way as conodont samples.

A.3 Determining Sr Concentration

Once dry, the concentration of Sr in each sample was determined. To do this, a fraction of each sample was collected. In the case of conodont samples, each sample was brought up in 2 ml of trace-metal grade, distilled 50% HNO3; 0.2 ml of the HNO3 solution was removed, ideally

collecting approximately 10% of the total Sr in the sample. The 0.2 ml of HNO3 solution was

transferred to a 15 ml polyethene tube (Fisher Scientific Falcon) and brought up to 5 ml of HNO3

total. In the case of acetic acid samples, a much lower concentration of Sr was assumed.

Therefore, these samples were brought up in 6 mL of 50% HNO3 before 0.2 mL of solution were

removed.

The Sr concentration of the 5 ml HNO3 solution were analyzed using an Inductively

Coupled Plasma Optical Emission Spectrometer (ICP-OES) in The Ohio State University Trace

Element Research Laboratory. That concentration was used to back-calculate the amount of Sr left in the sample and the Sr concentration of the conodont elements.

A.4 Sr Column Chemistry

If the sample had at least 1 µg of Sr remaining, the Sr was extracted using Teflon microcolumns with 125 µL volume stems. The microcolumns were filled with 0.125 mL

Eichrom Industries Sr Spec resin in 0.005 N HNO3. The resin was then washed with 600 µL of

0.005 N HNO3 and conditioned⦁ with 200 µL of 8 N HNO3. The sample was brought up in 100

µL of trace-metal grade, distilled 8 N HNO3 and added to the resin. The resin was washed with 2 mL of 8 N HNO3, and the sample was collected via elution with 1 mL of in 0.005 N HNO3. The

sample was collected in Teflon vials and dried down on a hotplate in a laminar flow hood.

A.5 TIMS Processing

Samples were analyzed for 87Sr/86Sr on a Triton Thermal Ionization Mass Spectrometry

(TIMS) in The Ohio State University Thermal Ionization Mass Spectrometry Laboratory.

Samples were loaded on rhenium ribbon on single-filament posts using the “sandwich method”:

0.5 µL of activator was placed on the ribbon followed by 1 µL of sample dissolved in 2 N HNO3

followed by another 0.5 µL of activator. This was done with a current of 0.6 A running through

the posts. After the sample and activator were loaded, the current was brought up to 1.8 A for 1

minute. The current was then slowly increased until the filaments glowed a dull red; the current

was then turned off. Samples were loaded onto a wheel, along with at least three SRM 987

standards, and placed in the TIMS to be run.

For each sample, before the analyzer gate was opened, the filament was slowly heated

with 2000 mA of current. The analyzer gate was then opened to allow the signal to reach the

Faraday cups. Five Faraday cups were used for this analysis. 84Sr was measured in Cup 4 (L1),

85Rb in Cup 5 (center cup), 86Sr in Cup 6 (H1), 87Sr in Cup 7 (H2), and 88Sr in Cup 8 (H3). The

current was increased stepwise and the signal intermittently tuned until the Faraday cups

received a signal intensity of c.a. 4 V. During data collection, the current was automatically

adjusted in order to maintain this intensity. Corrections for 87Rb contamination were accounted

for by measuring 85Rb and using the assumed 87Rb/85Rb value 0.386000 (Steiger and Jäger,

1977). Mass fractionation correction was completed by measuring 88Sr and 86Sr and using an

assumed 88Sr/86Sr ratio of 8.375209 (Steiger and Jäger, 1977). These corrections were done

automatically. For each sample, 200 preliminary measurements were taken, referred to as cycles.

These cycles were grouped into 10 blocks, with 20 cycles within a block. For corrected 87Sr/86Sr values, a 2 Sigma outlier test was conducted over all 200 cycles, the outliers identified, and all non-outliers used to calculate the average of the 200 cycles, which was used as the final 87Sr/86Sr

measured value.

A.6 Manual Data Correction

Each wheel of samples contained at least three SRM 987 standards. These standards were

averaged. The correct SRM 987 value was determined to be 0.710248 (McArthur, 1994); this

correct value was divided by the averaged SRM 987 value from the wheel, creating a correction

value. Each measured sample was then multiplied by this correction value to produce a corrected

sample value.

Appendix B: Statistics Details

All LOESS smoothing curves were formed using R. In the case of the Arbuckle

Mountains curve, while there were 62 total data points, several conodont samples had been run in duplicate to produce multiple data points. These were averaged to give each sample a single

87Sr/86Sr value. This produced a set of 38 data points with which to create a LOESS curve. While producing the Arbuckle Mountains LOESS curve, the span was set to 0.7 and degree set to 1

(i.e., using best fit lines rather than best fit parabola for each set of data points). The large span was selected to avoid statistical noise. The Antelope Range (Figure 14) and Clear Springs

(Figure 15) LOESS curves were formed using the same method and parameters.

In the case of Edwards et al. (2015) the LOESS curve was produced from 133 averaged data points, with a span of 0.33 and degree set to 1. The greater number of data points allowed for less statistical noise and a smaller span.

The McArthur et al. (2012) LOWESS curve was created by that group of authors, and the details of its creation are unknown.

The gradient curves were formed by dR/dt (i.e., change in 87Sr/86Sr over change in time or depth). An inflection point is marked by where the gradient value begins to shift in absolute value (Figure 16).

Appendix C: Age Model

The age model used for this study was built from conodont biostratigraphy of the I-35 N section of the Arbuckle Mts, using Bauer (1987, 1990, 1994, 2010). The “first” and “last” appearance of each zone species was determined and plotted against depth of the section. Ages of conodont zones were then taken from Cooper and Sadler (2012) and applied to the section.

The age of data points was calculated by first determining which conodont zone a point fell into and then using linear interpolation to correlate its placement within that zone to an age. This assumes constant sedimentation rate within each conodont zone. Age error can be determined by

the age width of each conodont zone. On average, the age error is 3 My; the error of the

holodentata zone is 2.6 My. This does not impact the conclusion that the inflection point falls

within the holodentata zone, though it does impact the numerical age one would assign to the

inflection point.

Appendix D: Non-Ordovician Samples

While Ordovician-age samples from the I-35 N section of the Simpson Group represent

the focus of this study, additional samples from other periods also underwent analysis. This was

aimed at supplementing the leaching portion of the study by testing whether patterns observed in

a fairly specific set of conodont samples could be reproduced in other time periods from other

locations. In addition, several Ordovician-age samples were size limited; non-Ordovician

samples allowed one to test methods and establish broad patterns without wasting Ordovician

sample.

D.1 Pennsylvanian samples

Three Pennsylvanian-age samples (G001, G007, and G0011) were leached, with the leached sample and three to four leachates analyzed for Sr concentration as well as 87Sr/86Sr.

Sample G001 is species Idioprioniodus sp extracted from Hushpickney Shale; G007 is species

Idiognathodus sp extracted from Stark Shale; G0011 is species Idiognathodus sp extracted from

Quivira Shale. All samples have a CAI of 1 to 2 and an average Sr concentration of 1000 ppm.

These Pennsylvanian samples were used to test methods and determine the best time intervals to collect leachate.

All three samples were leached and analyzed in duplicate. In the first duplicate, samples were leached for 72 hours with leachate collected at 4 hrs, 24 hrs, and 72 hrs. In the second duplicate, leachates were collected at 1 hr, 4 hrs, 24 hrs, and 72 hrs. Sr concentration of the leached samples and their leachates were analyzed. None of the leachates had enough Sr to conduct 87Sr/86Sr analysis; these samples were only used to determine Sr mass balance. A

summary of this analysis can be found in Figure 11. On average, 3% of the samples’ total Sr

was removed after 1 hour of leaching, 3% between 1 and 4 hours, 10% between 4 and 24 hours,

and 14% between 24 and 72 hours. On average, 73% of the total Sr was left in in the sample after

leaching.

Overall, the Pennsylvanian samples helped to establish how much of a sample’s total Sr

was likely to be leached over time and, moreover, that 1 and 4 hr leachates would likely not have

enough Sr for isotopic analysis. For Ordovician-age samples, the first leachate was collected at 8

hrs instead.

D.2 Silurian samples

Two Silurian-age samples with CAI 2 to 3 were run in duplicate, one left unleached and

one leached for 8 hours. The unleached and leached samples, as well as the 8 hr leachate, were

run for 87Sr/86Sr (Figure 12). In the case of sample M6, the leached sample was 2.4 x 10-5 more

radiogenic than the unleached sample, while the 8 hr leachate was 4.6 x 10-4 more radiogenic than the leached sample itself. In the case of sample M7, the leached sample was 1.7 x 10-5 less

radiogenic than the unleached sample, while the 8 hr leachate was 1.0 x 10-4 more radiogenic

than the leached sample itself. This broadly follows patterns seen in the Ordovician-age samples,

wherein the 8 hr leachate is significantly more radiogenic, suggesting that it does remove

diagenetic Sr, but the overall effect on leached samples is small and equivocal. It is notable that

the difference between the 8 hr leachates and leached samples in the Silurian samples is greater

(i.e., a difference in the fourth place) than in the case of the Ordovician samples (a difference in the fifth place). This could be due to higher CAI, which suggests that even in less well-preserved samples, the relative amount of diagenetic Sr is small.

3% 3% 10%

14%

73%

1 hr 4 hr 24 hr 72 hr Leached Sample

Figure 11. Average Sr mass balance of six Pennsylvanian samples, CAI = 1 to 2. Samples were leached for 72 hours with leachates collected after 1, 4, 24, and 72 hours. Mass balance pattern is similar to that of Ordovician-age samples, with 6% of the total Sr leached within the first 4 hours.

Figure 12. Results of leaching of two Silurian samples, CAI = 2 to 3. Samples were leached for 8 hours. Patterns are similar to those of Ordovician-age samples with CAI < 1, with the 8 hr leachate significantly more radiogenic and the leached and unleached samples close in value.

Figure 13. Data from this study and Saltzman et al. (2014), LOESS smoothing curve, and the associated gradient curve plotted over age. The LOESS curve of Edwards et al. (2015) and

LOWESS curve of McArthur et al. (2012) are included for comparison, along with their respective gradient curves. All three gradient curves demonstrate a spike beginning in the holodentata zone, which has been outlined.

Figure 14. Data, LOESS, and gradient curves of conodonts from Clear Springs, MD. The inflection point appears to fall within the holodentata zone in the upper Pinesburg Station

Dolomite. Data from Saltzman et al. (2014).

Figure 15. Data, LOESS, and gradient curves of conodonts from the Hill 8308 site, Antelope

Range, NV. The inflection point appears to fall within the friendsvillensis zone in the upper

Antelope Valley Limestone. Data from Saltzman et al. (2014).

Figure 16. Idealized model of inflection point in a given value over time. The gradient curve can demonstrate where the rate of change shifts.