Master of Science, The Ohio State University, 2016, Atmospheric Sciences

The University of Victoria Earth System Climate Model (UVic ESCM) of intermediate complexity was used to simulate the Late Ordovician period (~440 Mya) in order to attempt to recreate the conditions which would be favorable to induce a short-lived glaciation, which is evidenced to have occurred through isotopic and geological analysis of Late Ordovician sediments. This time period featured vastly different geography than that of present day, CO2 concentrations likely ranging from 8x to 20x that of preindustrial levels (PIL), decreased solar luminosity and decreased day length. In addition, life during the time period was limited almost exclusively to the oceans. The end of the Late Ordovician period features one the largest mass extinction events throughout the history of the Earth, in which over three quarters of all marine species became extinct. Multiple simulations were conducted with the UVic ESCM under numerous boundary conditions in order to attempt to replicate the conditions which might lead to glaciation. Primarily these boundary conditions include running simulations at different concentrations of CO2 (from 6x PIL to 12x PIL), and using different orbital configurations designed to yield the hottest or coldest possible summertime temperatures in the southern hemisphere. Attempts were made to reduce the value of solar luminosity in some experiments, but these attempts were unsuccessful due to the model simulations becoming unstable. Literature diverges on what orbital configuration results in the coldest or warmest southern hemisphere summertime temperatures. This study found that the coldest summer temperatures are achieved with an eccentricity of 6.0 x 10-2, an obliquity of 22.0°, and a longitude of perihelion of 90°. The warmest summer temperatures were achieved with an eccentricity of 6.0 x 10-2, an obliquity of 24.5°, and a longitude of perihelion of 270°. Overall, the failure to reduce the solar luminosity resulted in temperatures too warm (open full item for complete abstract)

Committee: Alvaro Montenegro Dr. (Advisor); Bryan Mark Dr. (Committee Member) Subjects: Atmospheric Sciences

Doctor of Philosophy, The Ohio State University, 2014, Geological Sciences

This chemostratigraphic study uses new carbon (d13C) and sulfur (d34S) isotope data measured from Lower–Middle Ordovician carbonate rocks from the Great Basin region, USA. The Pogonip Group was sampled at meter-scale from Shingle Pass (east-central Nevada) and the Ibex area (western Utah) to integrate the stable isotope stratigraphy with a well-studied conodont biostratigraphic framework. The Pogonip Group is a succession of mixed carbonate and siliciclastic rocks that accumulated on a carbonate ramp under normal marine conditions during the Late Cambrian to Middle Ordovician. The d13C trend has four distinct characteristics recognized in both Great Basin sections: 1) a drop in d13C from +1‰ at the base of the Ordovician (Tremadocian) to -0.7‰, 2) a 1–2‰ positive d13C shift during the late Tremadocian, 3) a gradual d13C increase from -2‰ to ca. 0‰ during the end of the Early Ordovician (Floian), and 4) a steady d13C decrease from 0‰ to -4 to -5‰ during Middle Ordovician (Dapingian–Darriwilian). The d34S trend measured from carbonate-associated sulfate (CAS) at Shingle Pass has an overall decrease from +35‰ during the Tremadocian to +20 to +25‰ during the Floian. A 15‰ negative excursion is present near the Dapingian-Darriwilian boundary before d34S values increase up to +35‰ at the top of the section. Corresponding d34S measured from sedimentary pyrite shows an overall similar drop in the Lower Ordovician but pyrite d34S values are more variable. During the early Tremadocian Stage pyrite d34S varies between 0 to +20‰ but makes a major drop of 20‰ during the late Tremadocian to values between -10–0‰ throughout the Floian and Dapingian Stages. Pyrite d34S increases gradually near the Dapingian-Darriwilian boundary to values between +10 to +20‰ at the top of the section. The Lower–Middle Ordovician d13C and d34S trends reported here from the Great Basin are not consistent with a causal mechanism involving sea level change and subsequent migration of isoto (open full item for complete abstract)

Committee: Matthew Saltzman (Advisor); William Ausich (Committee Member); Stig Bergström (Committee Member); Lawrence Krissek (Committee Member) Subjects: Geochemistry; Geology

MS, University of Cincinnati, 2003, Arts and Sciences : Geology

The Late Ordovician mass extinction is one of the most extensive faunal events in earth history. However, there have been few local analyses on the faunal turnover at this boundary. In addition, it has been suggested that this boundary does not exhibit marked ecologic change. The purpose of this study is to compare faunal distribution from the Upper Ordovician to the Lower Silurian in terms of faunal turnover, ecologic structure, and genus richness. Samples were collected from strata that represent comparable depositional environments, including the Drakes and Brassfield Formations of Ohio, and the Georgian Bay and Cabot Head Formations of Ontario. Multivariate techniques suggest a change in the composition and abundance ratios of taxa across the boundary in the study region. There is no evidence of significant ecologic restructuring across the Ordovician-Silurian boundary and the distribution of some rarefied samples suggests slightly elevated richness in the Silurian.

Committee: Dr. Carlton Brett (Committee Co-Chair); Dr. Arnold Miller (Committee Co-Chair) Subjects: Geology; Paleontology

PhD, University of Cincinnati, 2024, Arts and Sciences: Geology

The following dissertation explores the strata that surround the current Ordovician and Silurian boundary in eastern North America through the examination, dating, and correlation of stratigraphic units. Tools and techniques of chemostratigraphy, biostratigraphy and sequence stratigraphy helped to further constrain the geochronology of events during the latest Ordovician and earliest Silurian. With the detailed stratigraphic framework established, it was possible to document patterns of glacioeustacy and faunal change. Chapter one investigates whether the Manitoulin and Whirlpool formations of southern Ontario and western New York record late Hirnantian time. Detailed outcrop examinations and d13Ccarb analysis revealed the presence of the Hirnantian Isotopic Carbon Excursion (HICE) in these formations, supporting their late Hirnantian age assignment. Additionally, the chapter examines significant unconformities in the Late Ordovician and early Silurian strata of southern Ontario, correlating them with sections of comparable age in other parts of eastern North America. Chapter two focuses on the greater Cincinnati region, particularly the late Hirnantian Whippoorwill Formation. Evidence from lithostratigraphic, biostratigraphic, and chemostratigraphic analyses suggests the presence of the upper part of the HICE in the Whippoorwill Formation, along with the globally recognized Edgewood-Cathay fauna, advocating for a late Hirnantian age. Sequence stratigraphy of the interval revealed depositional patterns influenced by glacial eustasy during the late Hirnantian and Rhuddanian periods, offering improved constraints on the Ordovician-Silurian Boundary. Chapter three explores the paleontology of the Whippoorwill Formation, particularly the Edgewood-Cathay Fauna. This study expanded on previous collections, revealing new species, and showcasing the fauna's similarity to Silurian assemblages. The well-preserved taxa provide insight into a recovering late Hirnantian (open full item for complete abstract)

Committee: Carlton Brett Ph.D. (Committee Chair); Daniel Sturmer Ph.D. (Committee Member); Warren Huff Ph.D. (Committee Member); Ben Dattilo Ph.D M.A B.A. (Committee Member); Thomas Algeo Ph.D. (Committee Member) Subjects: Geology

PhD, University of Cincinnati, 2023, Arts and Sciences: Geology

Integration of event-stratigraphy, biostratigraphy, chemostratigraphy, and allostratigraphic methodology yields high-resolution correlations and helps to elucidate processes in the ancient past. This study presents an integrated stratigraphic approach applied to a Late Ordovician (Sandbian - Katian) mixed carbonate platform, cratonic basin system in Kentucky and Ohio. Identification of four widespread carbon isotope excursions (Logana, Macedonia, Brannon, and Bromley) enhanced regional chronostratigraphic correlations. Further, event beds (faunal epiboles, ash beds, deformed horizons) differentiated non-unique signatures in the stratigraphy and corroborated correlations. Numerous stratigraphic sections of the Lexington Platform (outcrops and core throughout) were studied to improve the existing stratigraphic framework and revisions to the regional correlation and nomenclature are documented. Key basin and basin margin reference sections (Cadiz Core, Middletown Core and others) were analyzed for stratigraphic patterns and whole rock carbon isotopes (d13Ccarb), percent total organic carbon, and elemental abundance (pXRF) in addition to detailed (bed scale) lithostratigraphic study. The Point Pleasant Basin (east-central Ohio) underwent differential subsidence relative to the Lexington Platform (central Kentucky) in three distinctive phases. Despite the progressive differentiation of the two depositional environments, integrative stratigraphy (especially faunal epiboles and d13Ccarb excursions) permits direct comparison. Widespread soft-sediment deformation (seismites) and increased occurrence of ash beds (k-bentonites) are coincident with the onset of increased differentiation of the Lexington Platform from the Point Pleasant Basin supporting a tectonic driver. However, small-scale sequences are recognizable across significant facies changes, supporting an overall eustatic origin of cyclicity. Carbon isotopic trends across much of the Laurentian Craton, plat (open full item for complete abstract)

Committee: Carlton Brett Ph.D. (Committee Chair); Thomas Algeo Ph.D. (Committee Member); Daniel Sturmer (Committee Member); Patrick McLaughlin Ph.D. (Committee Member); Peter Holterhoff Ph.D. (Committee Member) Subjects: Geology

MS, University of Cincinnati, 2023, Arts and Sciences: Geology

Species invasions are a major interest for their causes and potentially detrimental impact on native communities. However, modern ecologists work within the very limited timeframe of a few decades, at most. To examine longer-term patterns of biotic invasions, we must turn to the geologic record, which permits study of these events over scales of 10^3 to 10^4 years. The Cincinnati Arch region of Ohio, Indiana and northern Kentucky is world-renown for its detailed preservation of marine communities of the Late Ordovician Period . Within the Richmondian Stage strata (~447.5 to 445 Ma), a suite of more than 70 genera of mostly warm water marine invertebrates, including brachiopods, bryozoans, and corals, immigrated into the Cincinnati Arch region. Previous studies have examined this so-called “Richmondian invasion” at a coarse scale and tentatively concluded strong effects of invaders on incumbent communities, but many questions remain regarding the success of invading taxa, the conditions in which invading taxa are favored, the persistence and dominance of invading taxa, the effects on native (incumbent) taxa, and the abundance of incumbents and invaders post-invasion. To examine these questions, this study utilized a two-pronged approach to examine patterns within a recently revised stratigraphic framework. First, it employed an extensive presence/absence dataset, of 187 genera distributed in 128 samples through seven intervals, spanning the Richmondian, to study aspects of the diversity of incumbents (total 111 genera) and invaders (76 genera) and patterns of appearance and persistence. Second, we used a series of 125 bulk samples of all fossiliferous beds of a critical ~20 m interval to quantify patterns of relative abundance of incumbents and invaders. Using the historical dataset, we found that the richness of invaders and incumbents has no correlation. A large majority of incumbents span the entire 2.5-to-3-million-year interval, with only a single extinction, de (open full item for complete abstract)

Committee: Carlton Brett Ph.D. (Committee Chair); Daniel Sturmer Ph.D. (Committee Member); Joshua Miller Ph.D. (Committee Member) Subjects: Paleoecology

Doctor of Philosophy, The Ohio State University, 2023, Earth Sciences

One of the most important features of our planet is its ability to sustain life in multi million year timescales. This ability largely depends on Earth's internal system in regulating the global carbon cycle. One of the key processes that regulates the global carbon cycle is weathering of silicate rocks. As such, a refined understanding of the silicate weathering system and its role in regulating the global carbon cycle in multi million year timescales is essential in predicting the fate of our planet amid the current and future increase in anthropogenic atmospheric CO2 concentrations. However, characterizing and identifying the direct or indirect evidence of changes in the global carbon cycle in the rock record is not trivial. First, the signals preserved in the rock record are prone to secondary alteration. Second, the traditional geochemical proxies can produce non-unique interpretations. My research is, therefore, aimed at addressing these issues by investigating and constraining the extent of diagenetic processes and elucidating possible links between tectonics and changes in silicate weathering during the Ordovician Period using novel geochemical techniques and numerical modeling. This research is broken down into three separate projects and presented in Chapter 2 through Chapter 4 of this dissertation. The study presented in Chapter 2 uses bulk carbonate measurements of calcium isotopes (δ44/40Ca) and trace element concentrations to constrain the extent of diagenetic processes affecting the δ13C record from the Middle Ordovician. The data and numerical models presented in this study suggest that variations in Sr/Ca and δ44/40Ca from Meiklejohn Peak correspond to changes in the dominant carbonate primary mineralogy and early marine diagenesis. However, the δ13C seem to reflect a primary change in the dissolved inorganic carbon (DIC). The positive shift recorded as the MDICE (Middle Darriwilian Carbon Isotope Excursion) likely represents a transient increas (open full item for complete abstract)

Committee: Matthew Saltzman (Advisor); John Olesik (Committee Member); Derek Sawyer (Committee Member); Elizabeth Griffith (Committee Member) Subjects: Earth; Geology

Doctor of Philosophy, The Ohio State University, 2023, Earth Sciences

The study of ancient climate change on multimillion-year time scales is a key part of understanding how planetary climate systems operate. Silicate chemical weathering is a geochemical process that acts as a carbon sink; it operates as a major driver of the global carbon cycle and therefore global climate. The rate and pattern of silicate weathering has fluctuated throughout Earth's history, driven by a series of interacting factors such as seafloor production rate, orogenic uplift, ophiolite obduction, paleogeography, and terrestrial plant activity. Strontium (Sr) isotopic ratio (87Sr/86Sr) is a geochemical proxy used to track these fluctuations in silicate weathering patterns. However, while 87Sr/86Sr has long been used to inform and provide context for observed shifts in global climate, the nuances of how silicate weathering drives climate—or how climate drives silicate weathering—require deeper study. In this dissertation, I present three case studies of periods in the Paleozoic when silicate weathering and climate have appeared to change together: rapid cooling in the Middle to Late Ordovician, a shift from warming to cooling in the late Silurian and Early Devonian, and a shift from cooling to warming in the Middle and Late Devonian. In each case study, I compared the 87Sr/86Sr and δ18O (i.e., paleoclimate proxy) data of the same set of conodont apatite samples, which allowed me to directly compare shifts in each of these proxies and create informed interpretations of how silicate weathering and climate interacted. I concluded that silicate weathering drove cooling in the Middle to Late Ordovician, some combination of silicate weathering and terrestrial plant evolution drove cooling in the late Silurian to Early Devonian, and warming drove silicate weathering in the Middle to Late Devonian. Overall, silicate weathering is just one major driver of multimillion-year climate change in the Paleozoic, and moreover, does not produce the same climatic results in all s (open full item for complete abstract)

Committee: Matthew Saltzman (Advisor); John Olesik (Committee Member); Elizabeth Griffith (Committee Member); Loren Babcock (Committee Member) Subjects: Earth; Geology

Doctor of Philosophy, The Ohio State University, 2023, Earth Sciences

Our understanding of the Earth's multimillion-year carbon cycle, with primary implications for the evolution of life, depends on our ability to decipher information encoded in chemical signals of shallow marine sediments. This dissertation attempts to develop our knowledge of two main topics: (1) the causes of multimillion-year global climate change in terms of changes in the sources and sinks of atmospheric carbon dioxide (CO2), and (2) the causes and meaning of post-depositional alteration of shallow marine sediments with respect to chemical proxy records of the evolution of global (and/or local) Earth processes. To this end, this work applies radiogenic strontium and neodymium (87Sr/86Sr, εNd(t)) and stable calcium (δ44/40Ca) isotopic records in bulk carbonate rocks and conodont apatite from Middle–Late Ordovician (Darriwilian–Katian stages; ~470–450 million years ago, abbrev. Ma) sections in the Antelope Range, central Nevada; Clear Spring, Maryland; and the Fjacka and Kargarde sections of the Siljan district, Dalarna province, central Sweden. Bulk rock samples from the tropical Middle–Late Ordovician setting of the Antelope Range, Nevada were analyzed for proxy records of regional and global continental weathering source lithology (87Sr/86Sr and εNd(t)) which were paired with published paleotemperature proxy measurements (δ18O) of conodont apatite from the same section. This paired suite of proxy records is used to test the hypothesis that low-latitude island arc accretion during the Middle–Late Ordovician Taconic Orogeny enhanced the weatherability of Earth's crust, increasing the rate of CO2 removal by the weathering of mafic silicate minerals and producing the global cooling observed in the Middle–Late Ordovician paleotemperature record. These records show coeval inflections in 87Sr/86Sr and εNd(t) values at ~463 Ma that reveal the influence of tectonic uplift and enhanced weathering of mafic ophiolite provinces on the Taconic margin. This change in weather (open full item for complete abstract)

Committee: Matthew Saltzman (Advisor); Audrey Sawyer (Committee Member); Elizabeth Griffith (Committee Member); William Ausich (Committee Member) Subjects: Chemistry; Earth; Geochemistry; Geology

Master of Science (MS), Ohio University, 2023, Geological Sciences

The Great Ordovician Biodiversification Event (GOBE) records a global increase in marine biodiversity, which peaked during the Middle Ordovician, and established the foundation of modern marine ecosystems. Prior studies have compiled brachiopod occurrence data in order to quantify diversity trajectories during the GOBE; however, these studies often fail to fully consider how local environmental change influences species diversity. In this study, stratigraphically constrained field-based data from the Middle Ordovician Simpson Group of Oklahoma were collected to relate changes in brachiopod volume with associated environmental change in a temporal context. This analysis focused on Simpson Group rocks aged before, during, and after the main GOBE biodiversification pulse, which occurred locally during the Darriwilian Stage. Detailed morphological measurements based on anteroposterior–transverse (AT) volume estimations were collected from brachiopods during fieldwork from each stratigraphic unit at a bedding plane level of resolution. A time series analysis was used to establish temporal trends in brachiopod volume. Volume data were then analyzed alongside paired δ18O, Δ13C, 87Sr/86Sr, taxonomic diversity, and lithologic data using a boosted regression Analysis to identify the influence of these factors on volume through time. Results of these analyses indicate that a rapid pulse of brachiopod volume increase occurred across the main GOBE pulse in Simpson Group Strata which was not coupled with an increase in brachiopod size variance. This pulse was primarily driven by global-scale factors such as temporal progression, δ18O, 87Sr/86Sr, and taxonomic diversity trends; whereas local-scale factors of Δ13C and lithologic trends had a limited influence over local volume trends. Notably, all factors had a non-zero influence over brachiopod volume, indicating that locally, GOBE diversification was driven by multifaceted interactions among abiotic and biotic controls. These res (open full item for complete abstract)

Committee: Gregory Springer (Advisor); Eung Lee (Committee Member); Alycia Stigall (Committee Member) Subjects: Geology; Paleontology

Master of Science (MS), Ohio University, 2022, Geological Sciences

Type Cincinnatian strata are among the best preserved Upper Ordovician deposits in the world and record a range of depositional environments as well as various biotic and abiotic changes, making them an ideal natural laboratory in which to study biotic and abiotic processes. The most substantial biotic change in the Type Cincinnatian Series is a biotic invasion known as the Richmondian Invasion. The first pulse of the Richmondian Invasion is referred to as the Clarksville Phase (Aucoin and Brett, 2016) and is the focal point of this study which quantifies the impact the Clarksville Phase had on the ecology and diversity of the fauna of the Cincinnati basin. A suite of methods were employed to quantify the invader impact including detrended correspondence analysis, cluster analysis, rarefaction, Simpson's index of dominance, guild analysis, and comparison of environmental preferences and tolerances through time. Results indicate the Clarksville Phase had numerous impacts on the fauna of the Cincinnati Sea including modification of occupied habitat, ecospace utilization, gradient structure, community structure, community composition, and biodiversity. Habitat occupation changed considerably following the introduction of the invaders with taxa shifting both their environmental tolerances and preferences. Ecospace utilization shifted as previously low diversity guilds were filled out with novel taxa. Faunal differentiation across the depth gradient increased with the introduction of the invaders. Generic richness increased within the basin, generic evenness decreased, and community composition became more complex. The results of this study contribute to our understanding of the Richmondian Invasion and our general understanding of earth history as well as provide new insights about the potential long term ecological and biodiversity impacts of biotic invasions today.

Committee: Alycia Stigall (Advisor); Gregory Springer (Committee Member); Katherine Fornash (Committee Member) Subjects: Ecology; Geobiology; Paleoecology; Paleontology

Master of Science, The Ohio State University, 2021, Earth Sciences

Most of the fossil record consists of "ordinary" deposits, those where only biomineralized parts such as teeth, shells, and bones are preserved. Rarely, when the proper conditions are met, nonbiomineralized tissues such as guts and muscles also can be preserved. These deposits can reveal new insights into the biology, ecology, and taphonomy of ancient organisms, so identifying and understanding them is critical to paleontology. Anoxia is one of the conditions thought to be necessary for exceptional preservation. Because of this, "ordinary" deposits from predominantly aerobic depositional settings have been largely disregarded as potential sites for exceptional preservation. The discovery of pyritized nonbiomineralized tissues in the Silica Shale (Devonian) of Ohio, Michigan, and Indiana seems to contradict historical assumptions about environments conducive to exceptional preservation. This study characterizes the extent of exceptional preservation in the Silica Shale, and provides a comparison with another similar "ordinary" deposit for exceptional preservation, the Cincinnatian (or 'Cincinnati Group'; Ordovician) of Ohio, Kentucky, and Indiana. Comparing these two occurrences provides insight into the mechanism for exceptional preservation in these deposits. Fossil specimens were examined using X-ray Computed Tomography (XCT) to non-destructively view internal structures. In total, 247 specimens from the Silica Shale and 102 specimens from the Cincinnatian were examined. They represent a variety of taxa including brachiopods, trilobites, corals, cephalopods, gastropods, bivalves, and echinoderms. More than 60% of Silica Shale specimens and 20% of Cincinnatian specimens contained pyritized nonbiomineralized tissues. XCT analysis reveals that one brachiopod specimen from the Silica Shale, assigned to Paraspirifer bownockeri, lived with situs ambiguous. In both the Silica Shale and the Cincinnatian, rapid burial during storm events likely created local, tempora (open full item for complete abstract)

Committee: Loren Babcock (Advisor); Jill Leonard-Pingel (Committee Member); Ann Cook (Committee Member) Subjects: Earth; Geology; Paleoecology; Paleontology

PhD, University of Cincinnati, 2021, Arts and Sciences: Geology

The Upper Ordovician (Katian, Richmondian) Waynesville-Liberty Formations are an important interval in geologic history. The Upper Ordovician, Katian, superbly exposed in the Cincinnati Arch records the transition stage between the rapid biological diversification initiated in the Early Ordovician and the terminal–Ordovician extinction in the Hirnantian. During this interval, we see the biotic turnover of the Richmondian Invasion, perturbations in the carbon cycle represented by the Arnheim isotopic carbon excursion (ICE) low, the Waynesville ICE, the Liberty Low and the Whitewater ICE and unique time specific facies. The Richmondian Biotic Invasion was characterized by the incursion of exotic taxa into the Cincinnati Arch region from other paleobasins. The Waynesville Formation is also host to unique time specific facies including trilobite butter shale Lagerstatten, nearshore verdine facies and unusual relict preservation of molluscan shell structure. In this dissertation, I employ carbon isotope chemostratigraphy, cathodoluminescence, scanning electron microscopy and other techniques to understand how these biotic, chemical and taphonomic events relate not only locally in the Cincinnati Arch, but across other paleobasins.

Committee: Carlton Brett Ph.D. (Committee Chair); Ben Dattilo Ph.D. (Committee Member); Daniel Sturmer (Committee Member); Arnold Miller Ph.D. (Committee Member); Warren Huff Ph.D. (Committee Member) Subjects: Geology

Master of Science (MS), Ohio University, 2021, Geological Sciences

The Ordovician Period is characterized by dramatic abiotic and biotic environmental alterations, particularly during the Late Ordovician epoch. Climatic shifts and sea level change were common throughout the Late Ordovician, and the Taconic Orogeny locally deformed the eastern margin of Laurentia and altered sedimentation regimes. This interval is also characterized by changes in diversity and dispersal among marine faunas. Towards the end of the Late Ordovician, the Richmondian Invasion, a regional species invasion, introduced new competitive biotic interactions among shallow marine species. These environmental alterations impacted the taxa present at the time by affecting the habitat structure. The distribution of ancient and modern taxa alike are either directly or indirectly influenced by the environmental variables around them, and their occupation of this ecospace, or niche, is classically interpreted to reflect this relationship. Modern ecological studies that utilize niche concepts, including conservation ecology, are frequently based on the assumption that species will maintain their niche, referred to as niche stability. However, modern studies lack the long-term record necessary to assess this assumption. In this study, I investigated brachiopod niche occupation through the Late Ordovician (Sandbian-Katian) to determine how environmental change influenced niche stability within brachiopods, a clade of benthic marine invertebrates. Ecological niche models (ENMs) were created using Maxent, a well-supported algorithm for paleontological niche modeling investigations to investigate primary environmental controls on niche space, to determine the validity of modeling niche space using environmental proxies and fossil occurrence information. Generic niche overlap between time slices was then compared within a two-dimensional environmental grid space. Comparisons of niche overlap assess the presence of niche equivalency and similarity over time, as well as spe (open full item for complete abstract)

Committee: Alycia Stigall Dr. (Advisor); Daniel Hembree Dr. (Committee Member); Greg Springer Dr. (Committee Member) Subjects: Geology; Paleoecology; Paleontology

Master of Science (MS), Ohio University, 2020, Geological Sciences

The evolution and biogeographic changes of three Ordovician brachiopod genera were examined using species-level phylogenetic analyses and phylogenetic biogeographic analyses in order to examine geological drivers of biogeographic evolution during the Great Ordovician Biodiversification Event (GOBE). Species-level phylogenetic hypotheses are reconstructed for Laurentian species of Hesperorthis Schuchert and Cooper 1931, Mimella Cooper, 1931, and Oepikina Salmon, 1942 using Bayesian inference. The reconstructed phylogenetic relationships were then used to investigate biogeographic patterns within the speciation of each lineage in order to evaluate how speciation occurred during the GOBE. Results indicate that alternating dispersal and vicariance events throughout the lineages of Hesperorthis, Mimella and Oepikina contributed to their increase in diversification during the Middle Ordovician which conforms to the BIME model of diversification. The oscillations of dispersal and vicariance events were related to fluctuating sea-level changes observed during the Middle to Late Ordovician.

Committee: Alycia Stigall Dr. (Advisor) Subjects: Geology; Paleontology

Master of Science, The Ohio State University, 2019, Earth Sciences

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 midocean 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.

Committee: Matthew Saltzman (Advisor); Elizabeth Griffith (Committee Member); John Olesik (Committee Member) Subjects: Earth; Geochemistry; Geological; Geology; Paleoclimate Science

Master of Science, The Ohio State University, 2019, Earth Sciences

A step-change in atmospheric oxygen (O2) levels in the Ordovician has been attributed to the emergence of land plants. This phenomenon is tied to a major baseline shift in the stable carbon isotope (δ13C) curve consistent with an increase in nutrient delivery and enhanced primary productivity in the ocean and land, leading to high organic carbon burial. The timing and magnitude of this baseline shift, however, is still elusive in part because of the lack of high resolution δ13C data from this period. Much of the existing Ordovician 13C literature is focused on isotopic excursions with less emphasis on identifying long term shifts in baseline (pre- and post-excursion) values. This study presents new 13C curves from stratigraphic sections at Germany Valley (West Virginia) and Union Furnace (Pennsylvania) in the Central Appalachian Basin. These sections span the Upper Ordovician Sandbian Stage (~ 458.4 to 453.0 Ma) and cross into the Lower Katian Stage. The curves from both sections are characterized by relative stability and light (< 0‰) carbon isotope values in the Early Sandbian, followed by a shift toward positive values (> 0‰) in the Late Sandbian. I propose that the positive shift represents a long-term global shift in the δ13C baseline. A temporal relationship between this positive shift and diversification of liverworts clade and a clade that letter became mosses, hornworts, and vascular plants from their common ancestor in terrestrial plants suggests an organic carbon burial (net release of oxygen) mechanism for the stepwise oxygenation of the atmosphere in the Late Ordovician.

Committee: Matthew Saltzman (Advisor); Elizabeth Griffith (Committee Member); Thomas Darrah (Committee Member) Subjects: Earth; Geology; Sedimentary Geology

Master of Science, Miami University, 2018, Geology and Environmental Earth Science

The fossil record contains ecosystem changes, and can provide insights into ecological conditions over evolutionary timescales, particularly factors affecting community structure before and after disturbance. Our current understanding of these effects is based on changes in biodiversity, which cannot capture interactions between organisms. Food webs provide an alternative approach, representing interactions within a community. Food webs present unique challenges as they require assembling paleocommunity data for species across trophic levels. Numerous sources may be used to determine the species present in a paleocommunity. However, the potential effects of differences between data derived from museum collections and data compilations have not yet been tested. Here we examined differences between food web models of Late Ordovician marine communities assembled using two types of data: museum collections and field work; and the PBDB. To determine whether both data types produced consistent outcomes, paleocommunities were compared before and after the Richmondian Invasion. Relative differences in model outcomes across the invasion did not vary between data types. Differences in structure were consistent between the datatypes, with similar changes across the invasion. These findings suggest that both data types may be suitable for studies examining differences in resistance.

Committee: Carrie Tyler PhD (Advisor); Hailiang Dong PhD (Committee Member); Michael Brudzinski PhD (Committee Member); Peter Roopnarine PhD (Committee Member) Subjects: Geology; Paleoecology; Paleontology

MS, University of Cincinnati, 2017, Arts and Sciences: Geology

The Late Ordovician was a period of exceptionally widespread hardground development. In carbonate settings, these synsedimentarily lithified seafloors occurred during conditions of rapid sea level rise, low net sedimentation, and periodic submarine scour. Abundant hardgrounds in the Ordovician provided key hard substrates for attachment by a variety of organisms, and hardground proliferation and diversification co-occurred with an evolutionary radiation of sclerobionts coincident with the Great Ordovician Biodiversification Event. These organisms developed novel methods for attachment, cementation, and boring of this extensive benthic habitat, and their traces are often the diagnostic characteristic of hardgrounds. The Upper Ordovician carbonate sedimentary rocks of the eastern Unites States record a predominantly shallow, subtropical carbonate bank with abundant fossils. From the Sandbian to the Katian, TSTs and early HSTs of 4th order eustatic sequences commonly preserve hardgrounds with diverse encrusting communities. Most striking among these are hardgrounds which exhibit dramatic surface relief in the form of hardground clasts, hummocky or dimpled surface relief, and high-relief mounds. Heterogeneous hardground surface relief is a product of an array of biological, geochemical, and environmental processes which shape these surfaces in characteristic fashions. An Upper Ordovician (Katian, Mohawkian) mounded hardground from the Kirkfield Formation of southern Ontario is here documented, described, and placed in a stratigraphic context. The research herein aims to characterize the processes of genesis, development, and modification of mounded hardgrounds and examine the effect these surfaces have on local encrusting communities. Specifically, this study seeks to: 1) revise and refine the stratigraph of the lower Simcoe Group of southern Ontario using an integrated approach; 2) determine hardground distributions in a sequence stratigraphic framework; 3) describe (open full item for complete abstract)

Committee: Carlton Brett Ph.D. (Committee Chair); Warren Huff Ph.D. (Committee Member); Joshua Miller Ph.D. (Committee Member) Subjects: Geology

Doctor of Philosophy, The Ohio State University, 2017, Atmospheric Sciences

One of the largest ecosystem controls in the oceans is the presence of dissolved oxygen. As oxygen levels fall, both micro- and macroorganisms face shrinking habitats and potential mortality. There have been several periods in Earth history where oxygen levels have fallen to anoxic (dissolved O2 concentration < 10 µmol L-1) or hypoxic (< 60 µmol L-1) levels in certain ocean basins or within inland seas and some of these events could potentially be linked to mass extinction events. Several hypotheses exist regarding the depletion of oxygen, the spread of hypoxia-anoxia, and why the low oxygen events occur at certain points in the geologic record, including rapid climate warming, enhanced nutrient inputs, and modifications to the surface biological pump. Unfortunately, there is little agreement on which of these potential hypotheses caused individual events and what might impact the oxygenation of our oceans in the future. This dissertation will test hypotheses related to deep ocean oxygen using the University of Victoria Earth System Climate Model. The first set of experiments feature Late Ordovician winds and paleogeography and test the impacts of atmospheric CO2 and O2, ocean bottom topography, and nutrient loadings on deep ocean oxygen concentrations. The second set of experiments is also within the Late Ordovician, but tests the impacts of remineralization rates, detrital sinking velocities, and ocean surface albedo on ocean oxygenation. The final set of experiments tests the impacts of a warming climate on the oxygenation of near-future oceans, in addition to the impacts of detrital sinking velocities and ocean surface albedo. For the Late Ordovician, the factors most favorable for the spread of anoxia are reduced atmospheric O2, increased loadings of nitrate, and a reduction in ocean surface albedo. Climatic factors (namely, increased CO2) played little role in the spread of anoxia or the depletion of oxygen in these experiments. Similarly, phosphate, enhanc (open full item for complete abstract)

Committee: Alvaro Montenegro (Advisor); Bryan Mark (Committee Member); Michael Melchin (Committee Member); Ellen Mosley-Thompson (Committee Member) Subjects: Atmospheric Sciences; Biogeochemistry; Climate Change; Oceanography; Paleoclimate Science