{"id":{"repo_id":"texas","oai_identifier":"oai:repositories.lib.utexas.edu:2152/116763"},"canonical_url":"https://search.dev.ndltd.org/etd/texas/oai:repositories.lib.utexas.edu:2152/116763","repository":{"repo_id":"texas","name":"University of Texas","base_url":"https://repositories.lib.utexas.edu/server/oai/request"},"display":{"title":"Organic geochemistry of an oil and gas seep in northern Gulf of Mexico sediments","abstract":"During an extensive geochemical and geophysical survey of the outer slope of the northwestern Gulf of Mexico nine piston cores were recovered which had visible liquid organic deposits. In three of the cores deposits were observed concentrated in oblique fracture planes. Other occurrences included large deposits as liquid veins and smaller disseminated pockets in gassy and non-gassy sediments. The benzene soluble material (bitumen) was extracted and chemically and isotopically characterized. Bitumen content ranged as high as 8.6 percent in sediment samples. Gas chromatographic analyses of silica gel fractions showed that both the saturated and aromatic hydrocarbon components are highly biodegraded. The δ¹³C values for the whole oil and fractions were between -26.2 and -26.7 per mil on the PDB scale which closely resembles other Gulf coast oils. The δD values of the oil averaged -104 per mil relative to SMOW. Carbonate nodules found in the oil-rich zones were ¹³C depleted, indicating oxidized organic matter to be the source of the inorganic carbon. Several cores contained natural gas in concentrations high enough to result in large expansion gaps under the reduced ambient pressure at sea level. Hydrocarbon gases from methane through pentanes were sampled in nine cores. Chemical composition and δ¹³C values for methane, ethane, propane, and butanes (-30.5 to -61.9, -28.5, -24.5, -25.7 per mil) indicated that the gas has a major petrogenic component. δD values for methane, ethane, propane and butanes were -172, -101, -104, -101 per mil. Compositional variability of C₂⁺ gases among cores suggests the possible regional influence of gas hydrate formation. Compositional and isotopic variability of methane within and between cores does not conform to a two component mixing model (e.g. biogenic plus petrogenic methane). Instead, highly localized processes, possibly microbial, are implicated","abstract_html":"During an extensive geochemical and geophysical survey of the outer slope of the northwestern Gulf of Mexico nine piston cores were recovered which had visible liquid organic deposits. In three of the cores deposits were observed concentrated in oblique fracture planes. Other occurrences included large deposits as liquid veins and smaller disseminated pockets in gassy and non-gassy sediments. The benzene soluble material (bitumen) was extracted and chemically and isotopically characterized. Bitumen content ranged as high as 8.6 percent in sediment samples. Gas chromatographic analyses of silica gel fractions showed that both the saturated and aromatic hydrocarbon components are highly biodegraded. The δ¹³C values for the whole oil and fractions were between -26.2 and -26.7 per mil on the PDB scale which closely resembles other Gulf coast oils. The δD values of the oil averaged -104 per mil relative to SMOW. Carbonate nodules found in the oil-rich zones were ¹³C depleted, indicating oxidized organic matter to be the source of the inorganic carbon. Several cores contained natural gas in concentrations high enough to result in large expansion gaps under the reduced ambient pressure at sea level. Hydrocarbon gases from methane through pentanes were sampled in nine cores. Chemical composition and δ¹³C values for methane, ethane, propane, and butanes (-30.5 to -61.9, -28.5, -24.5, -25.7 per mil) indicated that the gas has a major petrogenic component. δD values for methane, ethane, propane and butanes were -172, -101, -104, -101 per mil. Compositional variability of C₂⁺ gases among cores suggests the possible regional influence of gas hydrate formation. Compositional and isotopic variability of methane within and between cores does not conform to a two component mixing model (e.g. biogenic plus petrogenic methane). Instead, highly localized processes, possibly microbial, are implicated","abstract_has_math":false,"creators":["Anderson, Richard Kent"],"institution":"University of Texas at Austin","degree_name":"Doctor of Philosophy","degree_level":"Doctoral","degree_discipline":"Chemistry","degree_department":null,"school":null,"contributors":[],"advisors":["Parker, Patrick L."],"committee_chairs":[],"committee_members":[],"year":1984,"date_issued":"1984","date_published":"1984","updated_at":"2026-07-24T05:01:18Z","subjects":["Organic geochemistry","Oil seep","Gas seep","Gulf of Mexico","Sediments","Northwestern Gulf of Mexico","Piston cores"],"languages":["eng"],"rights":["Copyright © is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works."],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://dx.doi.org/10.26153/tsw/43658"],"render_values":[{"text":"http://dx.doi.org/10.26153/tsw/43658","href":"http://dx.doi.org/10.26153/tsw/43658","code":true}]}]},"links":{"outbound_url":"https://hdl.handle.net/2152/116763","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Parker, Patrick L."]},{"key":"dc:creator","label":"Author","values":["Anderson, Richard Kent"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2022-11-21T20:18:37Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2022-11-21T20:18:37Z"]},{"key":"dc:date.issued","label":"Date","values":["1984"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Chemistry"]},{"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":["University of Texas at Austin"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Organic geochemistry","Oil seep","Gas seep","Gulf of Mexico","Sediments","Northwestern Gulf of Mexico","Piston cores"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright © is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works."]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/2152/116763","http://dx.doi.org/10.26153/tsw/43658"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["During an extensive geochemical and geophysical survey of the outer slope of the northwestern Gulf of Mexico nine piston cores were recovered which had visible liquid organic deposits. In three of the cores deposits were observed concentrated in oblique fracture planes. Other occurrences included large deposits as liquid veins and smaller disseminated pockets in gassy and non-gassy sediments. The benzene soluble material (bitumen) was extracted and chemically and isotopically characterized. Bitumen content ranged as high as 8.6 percent in sediment samples. Gas chromatographic analyses of silica gel fractions showed that both the saturated and aromatic hydrocarbon components are highly biodegraded. The δ¹³C values for the whole oil and fractions were between -26.2 and -26.7 per mil on the PDB scale which closely resembles other Gulf coast oils. The δD values of the oil averaged -104 per mil relative to SMOW. Carbonate nodules found in the oil-rich zones were ¹³C depleted, indicating oxidized organic matter to be the source of the inorganic carbon. Several cores contained natural gas in concentrations high enough to result in large expansion gaps under the reduced ambient pressure at sea level. Hydrocarbon gases from methane through pentanes were sampled in nine cores. Chemical composition and δ¹³C values for methane, ethane, propane, and butanes (-30.5 to -61.9, -28.5, -24.5, -25.7 per mil) indicated that the gas has a major petrogenic component. δD values for methane, ethane, propane and butanes were -172, -101, -104, -101 per mil. Compositional variability of C₂⁺ gases among cores suggests the possible regional influence of gas hydrate formation. Compositional and isotopic variability of methane within and between cores does not conform to a two component mixing model (e.g. biogenic plus petrogenic methane). Instead, highly localized processes, possibly microbial, are implicated"]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["electronic"]},{"key":"dc:title","label":"Title","values":["Organic geochemistry of an oil and gas seep in northern Gulf of Mexico sediments"]}]}],"canonical_facts":{"dc:contributor.advisor":["Parker, Patrick L."],"dc:creator":["Anderson, Richard Kent"],"dc:date.accessioned":["2022-11-21T20:18:37Z"],"dc:date.available":["2022-11-21T20:18:37Z"],"dc:date.issued":["1984"],"dc:description.abstract":["During an extensive geochemical and geophysical survey of the outer slope of the northwestern Gulf of Mexico nine piston cores were recovered which had visible liquid organic deposits. In three of the cores deposits were observed concentrated in oblique fracture planes. Other occurrences included large deposits as liquid veins and smaller disseminated pockets in gassy and non-gassy sediments. The benzene soluble material (bitumen) was extracted and chemically and isotopically characterized. Bitumen content ranged as high as 8.6 percent in sediment samples. Gas chromatographic analyses of silica gel fractions showed that both the saturated and aromatic hydrocarbon components are highly biodegraded. The δ¹³C values for the whole oil and fractions were between -26.2 and -26.7 per mil on the PDB scale which closely resembles other Gulf coast oils. The δD values of the oil averaged -104 per mil relative to SMOW. Carbonate nodules found in the oil-rich zones were ¹³C depleted, indicating oxidized organic matter to be the source of the inorganic carbon. Several cores contained natural gas in concentrations high enough to result in large expansion gaps under the reduced ambient pressure at sea level. Hydrocarbon gases from methane through pentanes were sampled in nine cores. Chemical composition and δ¹³C values for methane, ethane, propane, and butanes (-30.5 to -61.9, -28.5, -24.5, -25.7 per mil) indicated that the gas has a major petrogenic component. δD values for methane, ethane, propane and butanes were -172, -101, -104, -101 per mil. Compositional variability of C₂⁺ gases among cores suggests the possible regional influence of gas hydrate formation. Compositional and isotopic variability of methane within and between cores does not conform to a two component mixing model (e.g. biogenic plus petrogenic methane). Instead, highly localized processes, possibly microbial, are implicated"],"dc:format.medium":["electronic"],"dc:identifier.uri":["https://hdl.handle.net/2152/116763","http://dx.doi.org/10.26153/tsw/43658"],"dc:language.iso":["eng"],"dc:rights":["Copyright © is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works."],"dc:subject":["Organic geochemistry","Oil seep","Gas seep","Gulf of Mexico","Sediments","Northwestern Gulf of Mexico","Piston cores"],"dc:title":["Organic geochemistry of an oil and gas seep in northern Gulf of Mexico sediments"],"dc:type":["Thesis"],"thesis:degree_discipline":["Chemistry"],"thesis:degree_level":["Doctoral"],"thesis:degree_name":["Doctor of Philosophy"],"thesis:institution_name":["University of Texas at Austin"]},"updated_at":"2026-07-24T05:01:18Z"}