{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/136482"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/136482","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Unraveling Paleoenvironmental Stress in the Late Devonian and Mississippian: Insights into Redox Dynamics and Photosynthetic Adaptations Elucidated Through Geochemical Proxies","abstract":"The Late Devonian and Mississippian Periods (382.7 to 358.9 million years ago) were key moments in the history of our planet. They contain one of the five major mass extinctions of the Phanerozoic which saw profound environmental and ecological disturbances and changed the trajectory of both marine and terrestrial ecosystems. The proliferation of vascular plants on land, major marine transgressions over the continents, and climatic changes also occurred during this time. The mechanisms behind the Late Devonian mass extinctions have been explored by many researchers. One proposed driver, marine deoxygenation, requires further investigation given our current state of understanding. The first two chapters of this dissertation explore the temporal and geographic extent of marine deoxygenation during the Devonian Lower and Upper Kellwasser Events as well as Frasnian-Famennian transition on both the local and global scales. Chapter 1 seeks to evaluate the regional distribution of marine deoxygenation within the Appalachian Basin by using a local redox proxy, Fe speciation, with a focus on the record across the Frasnian-Famennian stage boundary. Based on this data, deoxygenation and anoxia occurred during the Lower Kellwasser Event and persisted in the distal portions of the Appalachian Basin. Chapter 2 builds on the findings of Chapter 1 and applies the thallium isotope redox proxy to track marine deoxygenation on the global scale. Specifically, this proxy is dependent on the global distribution and deposition of Mn oxides and therefore can provide further insight into the role of marine deoxygenation in the Late Devonian mass extinctions. Here we find that global scale deoxygenation occurred across the Frasnian-Famennian transition, however, this deoxygenation post-dates the Lower Kellwasser Event and persists after the second, suggesting a longer time interval of global scale marine deoxygenation. Finally, Chapter 3 shifts the focus to the terrestrial biosphere and explores how environmental stresses such as aridity and low atmospheric CO2 in the Mississippian may have driven evolutionary changes in land plants. Specifically, this study looks for carbon isotope evidence for the emergence of an alternative photosynthetic pathway such as the Crassulacean Acid Metabolism (CAM) in Mississippian arborescent lycopsids. We find that all studied plant fossils had similar carbon isotope compositions. The lack of isotopic difference between the coeval C3 plants and that of lycopsids leaves open three possibilities for the photosynthetic pathway that they employed: 1) the C3 metabolism 2) the aquatic CAM pathway or 3) a facultative CAM pathway. These three chapters reveal the interconnectedness of environmental and evolutionary changes during the Late Devonian and Mississippian. These include the expansion of marine deoxygenation on both the local and global scales and its connection to Frasnian-Famennian extinctions. It also shows what photosynthetic pathways land plants utilized in the context of the environmental changes occurring during the time. More broadly, these findings highlight the connection between life and the environment not only during the Late Devonian and Mississippian, but more broadly over the history of our planet, and reveal how these changes shaped the Earth we see today.","abstract_html":"The Late Devonian and Mississippian Periods (382.7 to 358.9 million years ago) were key moments in the history of our planet. They contain one of the five major mass extinctions of the Phanerozoic which saw profound environmental and ecological disturbances and changed the trajectory of both marine and terrestrial ecosystems. The proliferation of vascular plants on land, major marine transgressions over the continents, and climatic changes also occurred during this time. The mechanisms behind the Late Devonian mass extinctions have been explored by many researchers. One proposed driver, marine deoxygenation, requires further investigation given our current state of understanding. The first two chapters of this dissertation explore the temporal and geographic extent of marine deoxygenation during the Devonian Lower and Upper Kellwasser Events as well as Frasnian-Famennian transition on both the local and global scales. Chapter 1 seeks to evaluate the regional distribution of marine deoxygenation within the Appalachian Basin by using a local redox proxy, Fe speciation, with a focus on the record across the Frasnian-Famennian stage boundary. Based on this data, deoxygenation and anoxia occurred during the Lower Kellwasser Event and persisted in the distal portions of the Appalachian Basin. Chapter 2 builds on the findings of Chapter 1 and applies the thallium isotope redox proxy to track marine deoxygenation on the global scale. Specifically, this proxy is dependent on the global distribution and deposition of Mn oxides and therefore can provide further insight into the role of marine deoxygenation in the Late Devonian mass extinctions. Here we find that global scale deoxygenation occurred across the Frasnian-Famennian transition, however, this deoxygenation post-dates the Lower Kellwasser Event and persists after the second, suggesting a longer time interval of global scale marine deoxygenation. Finally, Chapter 3 shifts the focus to the terrestrial biosphere and explores how environmental stresses such as aridity and low atmospheric CO2 in the Mississippian may have driven evolutionary changes in land plants. Specifically, this study looks for carbon isotope evidence for the emergence of an alternative photosynthetic pathway such as the Crassulacean Acid Metabolism (CAM) in Mississippian arborescent lycopsids. We find that all studied plant fossils had similar carbon isotope compositions. The lack of isotopic difference between the coeval C3 plants and that of lycopsids leaves open three possibilities for the photosynthetic pathway that they employed: 1) the C3 metabolism 2) the aquatic CAM pathway or 3) a facultative CAM pathway. These three chapters reveal the interconnectedness of environmental and evolutionary changes during the Late Devonian and Mississippian. These include the expansion of marine deoxygenation on both the local and global scales and its connection to Frasnian-Famennian extinctions. It also shows what photosynthetic pathways land plants utilized in the context of the environmental changes occurring during the time. More broadly, these findings highlight the connection between life and the environment not only during the Late Devonian and Mississippian, but more broadly over the history of our planet, and reveal how these changes shaped the Earth we see today.","abstract_has_math":false,"creators":["Putri, Tara Anggita"],"institution":"Virginia Tech","degree_name":"Doctor of Philosophy","degree_level":"doctoral","degree_discipline":"Geosciences","degree_department":"Geosciences","school":null,"contributors":[],"advisors":[],"committee_chairs":["Gill, Benjamin C."],"committee_members":["Reid, Rachel","Romans, Brian W.","Xiao, Shuhai"],"year":2025,"date_issued":"2025-07-15","date_published":"2025-07-15","updated_at":"2026-07-22T22:19:53Z","subjects":["geochemistry","isotopes","thallium","mass extinction","plant fossil","marine","terrestrial"],"languages":["en"],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:44281"],"render_values":[{"text":"vt_gsexam:44281","href":null,"code":true}]}]},"links":{"outbound_url":"https://hdl.handle.net/10919/136482","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["Gill, Benjamin C."]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Reid, Rachel","Romans, Brian W.","Xiao, Shuhai"]},{"key":"dc:contributor.department","label":"Department","values":["Geosciences"]},{"key":"dc:creator","label":"Author","values":["Putri, Tara Anggita"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2025-07-16T08:00:33Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2025-07-16T08:00:33Z"]},{"key":"dc:date.issued","label":"Date","values":["2025-07-15"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Geosciences"]},{"key":"thesis:degree_level","label":"Degree Level","values":["doctoral"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Virginia Polytechnic Institute and State University"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["geochemistry","isotopes","thallium","mass extinction","plant fossil","marine","terrestrial"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["In Copyright"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://rightsstatements.org/vocab/InC/1.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:44281"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/10919/136482"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The Late Devonian and Mississippian Periods (382.7 to 358.9 million years ago) were key moments in the history of our planet. They contain one of the five major mass extinctions of the Phanerozoic which saw profound environmental and ecological disturbances and changed the trajectory of both marine and terrestrial ecosystems. The proliferation of vascular plants on land, major marine transgressions over the continents, and climatic changes also occurred during this time. The mechanisms behind the Late Devonian mass extinctions have been explored by many researchers. One proposed driver, marine deoxygenation, requires further investigation given our current state of understanding. The first two chapters of this dissertation explore the temporal and geographic extent of marine deoxygenation during the Devonian Lower and Upper Kellwasser Events as well as Frasnian-Famennian transition on both the local and global scales. Chapter 1 seeks to evaluate the regional distribution of marine deoxygenation within the Appalachian Basin by using a local redox proxy, Fe speciation, with a focus on the record across the Frasnian-Famennian stage boundary. Based on this data, deoxygenation and anoxia occurred during the Lower Kellwasser Event and persisted in the distal portions of the Appalachian Basin. Chapter 2 builds on the findings of Chapter 1 and applies the thallium isotope redox proxy to track marine deoxygenation on the global scale. Specifically, this proxy is dependent on the global distribution and deposition of Mn oxides and therefore can provide further insight into the role of marine deoxygenation in the Late Devonian mass extinctions. Here we find that global scale deoxygenation occurred across the Frasnian-Famennian transition, however, this deoxygenation post-dates the Lower Kellwasser Event and persists after the second, suggesting a longer time interval of global scale marine deoxygenation. Finally, Chapter 3 shifts the focus to the terrestrial biosphere and explores how environmental stresses such as aridity and low atmospheric CO2 in the Mississippian may have driven evolutionary changes in land plants. Specifically, this study looks for carbon isotope evidence for the emergence of an alternative photosynthetic pathway such as the Crassulacean Acid Metabolism (CAM) in Mississippian arborescent lycopsids. We find that all studied plant fossils had similar carbon isotope compositions. The lack of isotopic difference between the coeval C3 plants and that of lycopsids leaves open three possibilities for the photosynthetic pathway that they employed: 1) the C3 metabolism 2) the aquatic CAM pathway or 3) a facultative CAM pathway. These three chapters reveal the interconnectedness of environmental and evolutionary changes during the Late Devonian and Mississippian. These include the expansion of marine deoxygenation on both the local and global scales and its connection to Frasnian-Famennian extinctions. It also shows what photosynthetic pathways land plants utilized in the context of the environmental changes occurring during the time. More broadly, these findings highlight the connection between life and the environment not only during the Late Devonian and Mississippian, but more broadly over the history of our planet, and reveal how these changes shaped the Earth we see today."]},{"key":"dc:description.abstractgeneral","label":"General Abstract","values":["Many changes have occurred to both the environment and life on earth since its formation 4.6 billion years ago. This dissertation is concerned with some of those that happened during the Late Devonian-Mississippian (382.7 to 358.9 million years ago). This time is marked by one of the five major mass extinctions in the history of our planet, but also the proliferation of plants on land. This dissertation explores these events, through the chemical contents of sedimentary rocks and fossils formed during that time. Many factors have been suggested to have caused the mass extinctions in the Late Devonian-Mississippian time. However, the role of loss of oxygen (deoxygenation) from the oceans has yet to be fully explored. Chapters 1 and 2 investigate the extent of marine deoxygenation using the chemistry of shales deposited during this time. In Chapter 1 I use the iron chemistry (Fe speciation) of shales to determine the geographic and temporal extent of deoxygenation in the Appalachian Basin. Based on this data, deoxygenation in the distal portions of the Appalachian Basin and persisted after the extinctions. Chapter 2 presents data on the isotopes of thallium in shales from a site in the Appalachian Basin that suggests that deoxygenation occurred on a global scale with the extinction and that it also persisted globally afterwards. The final chapter of the dissertation is an exploration on how land plants conducted photosynthesis during the Mississippian using the carbon isotopes in plant fossils. There are different chemical reactions for photosynthesis that plants can use that have advantages in different environments. Mississippian plants may have used alternative photosynthetic reactions in response to changes within the atmosphere and climate during that time. The carbon isotope compositions of plant fossils can be used to identify these reactions. We find that all the plants examined likely used the C3 pathway, indicating that these plants did not use an alternative photosynthetic reaction in response to the environment at the time. Alternatively, they may have used other photosynthetic reactions, but they are not reflected in the carbon isotopes of fossils. This dissertation reveals the links between changes in environment and life during the Late Devonian and Mississippian. These include the loss of oxygen from the oceans on both the local and global scales and its connection to extinction during this time. It also shows how plants on land conducted the important process of photosynthesis. More broadly, these findings highlight connectivity between life and the environment not only during the Late Devonian and Mississippian, but more broadly over the history of our planet and reveal how these changes shaped the Earth we see today."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Doctor of Philosophy"]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["ETD"]},{"key":"dc:title","label":"Title","values":["Unraveling Paleoenvironmental Stress in the Late Devonian and Mississippian: Insights into Redox Dynamics and Photosynthetic Adaptations Elucidated Through Geochemical Proxies"]}]}],"canonical_facts":{"dc:contributor.committeechair":["Gill, Benjamin C."],"dc:contributor.committeemember":["Reid, Rachel","Romans, Brian W.","Xiao, Shuhai"],"dc:contributor.department":["Geosciences"],"dc:creator":["Putri, Tara Anggita"],"dc:date.accessioned":["2025-07-16T08:00:33Z"],"dc:date.available":["2025-07-16T08:00:33Z"],"dc:date.issued":["2025-07-15"],"dc:description.abstract":["The Late Devonian and Mississippian Periods (382.7 to 358.9 million years ago) were key moments in the history of our planet. They contain one of the five major mass extinctions of the Phanerozoic which saw profound environmental and ecological disturbances and changed the trajectory of both marine and terrestrial ecosystems. The proliferation of vascular plants on land, major marine transgressions over the continents, and climatic changes also occurred during this time. The mechanisms behind the Late Devonian mass extinctions have been explored by many researchers. One proposed driver, marine deoxygenation, requires further investigation given our current state of understanding. The first two chapters of this dissertation explore the temporal and geographic extent of marine deoxygenation during the Devonian Lower and Upper Kellwasser Events as well as Frasnian-Famennian transition on both the local and global scales. Chapter 1 seeks to evaluate the regional distribution of marine deoxygenation within the Appalachian Basin by using a local redox proxy, Fe speciation, with a focus on the record across the Frasnian-Famennian stage boundary. Based on this data, deoxygenation and anoxia occurred during the Lower Kellwasser Event and persisted in the distal portions of the Appalachian Basin. Chapter 2 builds on the findings of Chapter 1 and applies the thallium isotope redox proxy to track marine deoxygenation on the global scale. Specifically, this proxy is dependent on the global distribution and deposition of Mn oxides and therefore can provide further insight into the role of marine deoxygenation in the Late Devonian mass extinctions. Here we find that global scale deoxygenation occurred across the Frasnian-Famennian transition, however, this deoxygenation post-dates the Lower Kellwasser Event and persists after the second, suggesting a longer time interval of global scale marine deoxygenation. Finally, Chapter 3 shifts the focus to the terrestrial biosphere and explores how environmental stresses such as aridity and low atmospheric CO2 in the Mississippian may have driven evolutionary changes in land plants. Specifically, this study looks for carbon isotope evidence for the emergence of an alternative photosynthetic pathway such as the Crassulacean Acid Metabolism (CAM) in Mississippian arborescent lycopsids. We find that all studied plant fossils had similar carbon isotope compositions. The lack of isotopic difference between the coeval C3 plants and that of lycopsids leaves open three possibilities for the photosynthetic pathway that they employed: 1) the C3 metabolism 2) the aquatic CAM pathway or 3) a facultative CAM pathway. These three chapters reveal the interconnectedness of environmental and evolutionary changes during the Late Devonian and Mississippian. These include the expansion of marine deoxygenation on both the local and global scales and its connection to Frasnian-Famennian extinctions. It also shows what photosynthetic pathways land plants utilized in the context of the environmental changes occurring during the time. More broadly, these findings highlight the connection between life and the environment not only during the Late Devonian and Mississippian, but more broadly over the history of our planet, and reveal how these changes shaped the Earth we see today."],"dc:description.abstractgeneral":["Many changes have occurred to both the environment and life on earth since its formation 4.6 billion years ago. This dissertation is concerned with some of those that happened during the Late Devonian-Mississippian (382.7 to 358.9 million years ago). This time is marked by one of the five major mass extinctions in the history of our planet, but also the proliferation of plants on land. This dissertation explores these events, through the chemical contents of sedimentary rocks and fossils formed during that time. Many factors have been suggested to have caused the mass extinctions in the Late Devonian-Mississippian time. However, the role of loss of oxygen (deoxygenation) from the oceans has yet to be fully explored. Chapters 1 and 2 investigate the extent of marine deoxygenation using the chemistry of shales deposited during this time. In Chapter 1 I use the iron chemistry (Fe speciation) of shales to determine the geographic and temporal extent of deoxygenation in the Appalachian Basin. Based on this data, deoxygenation in the distal portions of the Appalachian Basin and persisted after the extinctions. Chapter 2 presents data on the isotopes of thallium in shales from a site in the Appalachian Basin that suggests that deoxygenation occurred on a global scale with the extinction and that it also persisted globally afterwards. The final chapter of the dissertation is an exploration on how land plants conducted photosynthesis during the Mississippian using the carbon isotopes in plant fossils. There are different chemical reactions for photosynthesis that plants can use that have advantages in different environments. Mississippian plants may have used alternative photosynthetic reactions in response to changes within the atmosphere and climate during that time. The carbon isotope compositions of plant fossils can be used to identify these reactions. We find that all the plants examined likely used the C3 pathway, indicating that these plants did not use an alternative photosynthetic reaction in response to the environment at the time. Alternatively, they may have used other photosynthetic reactions, but they are not reflected in the carbon isotopes of fossils. This dissertation reveals the links between changes in environment and life during the Late Devonian and Mississippian. These include the loss of oxygen from the oceans on both the local and global scales and its connection to extinction during this time. It also shows how plants on land conducted the important process of photosynthesis. More broadly, these findings highlight connectivity between life and the environment not only during the Late Devonian and Mississippian, but more broadly over the history of our planet and reveal how these changes shaped the Earth we see today."],"dc:description.degree":["Doctor of Philosophy"],"dc:format.medium":["ETD"],"dc:identifier.other":["vt_gsexam:44281"],"dc:identifier.uri":["https://hdl.handle.net/10919/136482"],"dc:language.iso":["en"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:subject":["geochemistry","isotopes","thallium","mass extinction","plant fossil","marine","terrestrial"],"dc:title":["Unraveling Paleoenvironmental Stress in the Late Devonian and Mississippian: Insights into Redox Dynamics and Photosynthetic Adaptations Elucidated Through Geochemical Proxies"],"dc:type":["Dissertation"],"thesis:degree_discipline":["Geosciences"],"thesis:degree_level":["doctoral"],"thesis:degree_name":["Doctor of Philosophy"],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:19:53Z"}