Cretaceous shales from the western interior of North America: Sulfur/carbon ratios and sulfur-isotope composition

Research Article| March 01, 1986 Cretaceous shales from the western interior of North America: Sulfur/carbon ratios and sulfur-isotope composition Donald L Gautier Donald L Gautier 1U.S. Geological Survey, M.S. 940, Box 25046, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information Donald L Gautier 1U.S. Geological Survey, M.S. 940, Box 25046, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1986) 14 (3): 225–228. https://doi.org/10.1130/0091-7613(1986)14<225:CSFTWI>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Donald L Gautier; Cretaceous shales from the western interior of North America: Sulfur/carbon ratios and sulfur-isotope composition. Geology 1986;; 14 (3): 225–228. doi: https://doi.org/10.1130/0091-7613(1986)14<225:CSFTWI>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Carbon and sulfur abundance and δ34S of pyrite sulfur were studied in cores of selected Cretaceous marine shales from the western interior of North America. Sulfur/carbon ratios average 0.67, a value greater than that observed in recent marine sediments and much higher than global values calculated for the Cretaceous. Increased S/C ratios probably result from generally low levels of bioturbation and enhanced efficiency of sulfate reduction due to low oxygen levels in the Cretaceous seaway. Isotopic compositions of pyrite sulfur vary systematically with the level of oxygenation of the depositional environment and therefore with organic carbon abundance and type of organic matter. Samples with organic carbon in excess of 4 wt% contain disseminated pyrite that is extremely depleted in 34S (mean δ34S = −31‰); these samples are laminated clay shales that contain hydrogen-rich (type II) organic matter. Samples containing less than 1.5% organic carbon display relatively “heavy” but wide ranging δ34S values (δ34S = −34.6‰ to +16.8‰; mean δ34S = −12.4‰); these samples are highly bioturbated and contain only type III, hydrogen-poor organic matter. Samples containing intermediate amounts of organic carbon contain pyrite with δ34S values averaging −25.9‰ and contain mixed type II and type III organic matter. The higher organic carbon content and the preservation of hydrogen-rich organic matter generally correlate with slow sedimentation. Samples rich in organic carbon and containing isotopically “light” sulfide sulfur accumulated beneath anoxic and perhaps sulfidic bottom waters. Samples with intermediate organic matter content and intermediate sulfur isotopic compositions accumulated under mainly dysaerobic bottom waters. Samples with relatively low amounts of organic carbon and wide-ranging but less negative sulfur isotopic values were deposited beneath oxygenated bottom waters. Sulfur-isotope data are apparently a sensitive indicator of diagenetic or depositional facies of fine-grained Cretaceous rocks in the western interior. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.