The Late Cretaceous Eagle Ford Shale of South Texas is a mixed carbonate–siliciclastic succession that serves as both a prolific hydrocarbon source and reservoir. This study integrates chemostratigraphy, mineralogical analysis, and elemental ratio proxies to reconstruct depositional environments and assess controls on detrital influx, paleoproductivity, and redox conditions across multiple cores in Webb and Dimmit counties. Major, trace, and redox-sensitive elements were evaluated alongside Total Organic Content (TOC) and carbonate content to identify stratigraphic trends and environmental shifts.
Results reveal distinct geochemical signatures between the Upper and Lower Eagle Ford Shale, with the Lower Eagle Ford characterized by elevated Al-rich clay fractions, reduced carbonate content, and finer-grained detritus relative to the Upper Eagle Ford. Grain-size–sensitive ratios (Zr/Nb, Si/Al) and carbonate proxies (Ca, Sr) document changes in shoreline proximity, subtle sea-level oscillations, and the transition from carbonate-dominated Austin and Buda units into mixed-sediment deposition. Redox proxies (Mo, U, V) indicate dominantly suboxic to anoxic conditions in the Lower Eagle Ford Shale, with possible abiotic anoxia driven by sediment stratification, while the Upper Eagle Ford Shale is characterized by more oxic to suboxic bottom-water conditions. These findings refine the chemostratigraphic framework for the Eagle Ford Shale in relation to the Western Interior Seaway and provides insights into its depositional dynamics, sediment provenance, and implications for reservoir quality.
","abstract_html":"<p>The Late Cretaceous Eagle Ford Shale of South Texas is a mixed carbonate–siliciclastic succession that serves as both a prolific hydrocarbon source and reservoir. This study integrates chemostratigraphy, mineralogical analysis, and elemental ratio proxies to reconstruct depositional environments and assess controls on detrital influx, paleoproductivity, and redox conditions across multiple cores in Webb and Dimmit counties. Major, trace, and redox-sensitive elements were evaluated alongside Total Organic Content (TOC) and carbonate content to identify stratigraphic trends and environmental shifts.</p> <p>Results reveal distinct geochemical signatures between the Upper and Lower Eagle Ford Shale, with the Lower Eagle Ford characterized by elevated Al-rich clay fractions, reduced carbonate content, and finer-grained detritus relative to the Upper Eagle Ford. Grain-size–sensitive ratios (Zr/Nb, Si/Al) and carbonate proxies (Ca, Sr) document changes in shoreline proximity, subtle sea-level oscillations, and the transition from carbonate-dominated Austin and Buda units into mixed-sediment deposition. Redox proxies (Mo, U, V) indicate dominantly suboxic to anoxic conditions in the Lower Eagle Ford Shale, with possible abiotic anoxia driven by sediment stratification, while the Upper Eagle Ford Shale is characterized by more oxic to suboxic bottom-water conditions. These findings refine the chemostratigraphic framework for the Eagle Ford Shale in relation to the Western Interior Seaway and provides insights into its depositional dynamics, sediment provenance, and implications for reservoir quality.</p>","abstract_has_math":false,"creators":["Girlinghouse, Natalie G"],"institution":null,"degree_name":"Master of Science - Geology","degree_level":"Thesis","degree_discipline":"Geology","degree_department":null,"school":null,"contributors":["Dr. Julie Bloxson","Dr. R. LaRell Nieslon","Dr. Melinda Faulkner"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025-12-01T08:00:00Z","date_published":"2025-12-01T08:00:00Z","updated_at":"2026-07-24T04:30:49Z","subjects":["Petroleum","geochemistry","Eagle Ford Shale","Paleo-redox conditions","Depositional environments","South Texas","Chemistry","Earth Sciences","Geology","Organic Chemistry","Stratigraphy"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://scholarworks.sfasu.edu/etds/658","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Dr. Julie Bloxson","Dr. R. LaRell Nieslon","Dr. Melinda Faulkner"]},{"key":"dc:creator","label":"Author","values":["Girlinghouse, Natalie G"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.available","label":"Dc Date Available","values":["2025-12-12T08:00:00Z"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Geology"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Thesis"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Master of Science - Geology"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Petroleum","geochemistry","Eagle Ford Shale","Paleo-redox conditions","Depositional environments","South Texas","Chemistry","Earth Sciences","Geology","Organic Chemistry","Stratigraphy"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://scholarworks.sfasu.edu/etds/658"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The Late Cretaceous Eagle Ford Shale of South Texas is a mixed carbonate–siliciclastic succession that serves as both a prolific hydrocarbon source and reservoir. This study integrates chemostratigraphy, mineralogical analysis, and elemental ratio proxies to reconstruct depositional environments and assess controls on detrital influx, paleoproductivity, and redox conditions across multiple cores in Webb and Dimmit counties. Major, trace, and redox-sensitive elements were evaluated alongside Total Organic Content (TOC) and carbonate content to identify stratigraphic trends and environmental shifts.
Results reveal distinct geochemical signatures between the Upper and Lower Eagle Ford Shale, with the Lower Eagle Ford characterized by elevated Al-rich clay fractions, reduced carbonate content, and finer-grained detritus relative to the Upper Eagle Ford. Grain-size–sensitive ratios (Zr/Nb, Si/Al) and carbonate proxies (Ca, Sr) document changes in shoreline proximity, subtle sea-level oscillations, and the transition from carbonate-dominated Austin and Buda units into mixed-sediment deposition. Redox proxies (Mo, U, V) indicate dominantly suboxic to anoxic conditions in the Lower Eagle Ford Shale, with possible abiotic anoxia driven by sediment stratification, while the Upper Eagle Ford Shale is characterized by more oxic to suboxic bottom-water conditions. These findings refine the chemostratigraphic framework for the Eagle Ford Shale in relation to the Western Interior Seaway and provides insights into its depositional dynamics, sediment provenance, and implications for reservoir quality.
"]},{"key":"dc:title","label":"Title","values":["GEOCHEMICAL ANALYSIS OF THE EAGLE FORD SHALE IN WEBB AND DIMMIT COUNTIES, TX"]}]}],"canonical_facts":{"dc:contributor":["Dr. Julie Bloxson","Dr. R. LaRell Nieslon","Dr. Melinda Faulkner"],"dc:creator":["Girlinghouse, Natalie G"],"dc:date.available":["2025-12-12T08:00:00Z"],"dc:description.abstract":["The Late Cretaceous Eagle Ford Shale of South Texas is a mixed carbonate–siliciclastic succession that serves as both a prolific hydrocarbon source and reservoir. This study integrates chemostratigraphy, mineralogical analysis, and elemental ratio proxies to reconstruct depositional environments and assess controls on detrital influx, paleoproductivity, and redox conditions across multiple cores in Webb and Dimmit counties. Major, trace, and redox-sensitive elements were evaluated alongside Total Organic Content (TOC) and carbonate content to identify stratigraphic trends and environmental shifts.
Results reveal distinct geochemical signatures between the Upper and Lower Eagle Ford Shale, with the Lower Eagle Ford characterized by elevated Al-rich clay fractions, reduced carbonate content, and finer-grained detritus relative to the Upper Eagle Ford. Grain-size–sensitive ratios (Zr/Nb, Si/Al) and carbonate proxies (Ca, Sr) document changes in shoreline proximity, subtle sea-level oscillations, and the transition from carbonate-dominated Austin and Buda units into mixed-sediment deposition. Redox proxies (Mo, U, V) indicate dominantly suboxic to anoxic conditions in the Lower Eagle Ford Shale, with possible abiotic anoxia driven by sediment stratification, while the Upper Eagle Ford Shale is characterized by more oxic to suboxic bottom-water conditions. These findings refine the chemostratigraphic framework for the Eagle Ford Shale in relation to the Western Interior Seaway and provides insights into its depositional dynamics, sediment provenance, and implications for reservoir quality.
"],"dc:identifier":["https://scholarworks.sfasu.edu/etds/658"],"dc:subject":["Petroleum","geochemistry","Eagle Ford Shale","Paleo-redox conditions","Depositional environments","South Texas","Chemistry","Earth Sciences","Geology","Organic Chemistry","Stratigraphy"],"dc:title":["GEOCHEMICAL ANALYSIS OF THE EAGLE FORD SHALE IN WEBB AND DIMMIT COUNTIES, TX"],"thesis:degree_discipline":["Geology"],"thesis:degree_level":["Thesis"],"thesis:degree_name":["Master of Science - Geology"]},"updated_at":"2026-07-24T04:30:49Z"}