Comparison of Rb-Sr and K-Ar dates of middle Eocene bentonite and glauconite, southeastern Atlantic Coastal Plain

Abstract

Research Article| April 01, 1989 Comparison of Rb-Sr and K-Ar dates of middle Eocene bentonite and glauconite, southeastern Atlantic Coastal Plain W. BURLEIGH HARRIS; W. BURLEIGH HARRIS 1Department of Earth Sciences, University of North Carolina at Wilmington, Wilmington, North Carolina 28403 Search for other works by this author on: GSW Google Scholar PAUL D. FULLAGAR PAUL D. FULLAGAR 2Department of Geology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3315 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1989) 101 (4): 573–577. https://doi.org/10.1130/0016-7606(1989)101<0573:CORSAK>2.3.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 W. BURLEIGH HARRIS, PAUL D. FULLAGAR; Comparison of Rb-Sr and K-Ar dates of middle Eocene bentonite and glauconite, southeastern Atlantic Coastal Plain. GSA Bulletin 1989;; 101 (4): 573–577. doi: https://doi.org/10.1130/0016-7606(1989)101<0573:CORSAK>2.3.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 SocietyGSA Bulletin Search Advanced Search Abstract Rb-Sr and K-Ar dates for euhedral biotite from high-Mg, Chetotype smectitic bentonite in glaucony-bearing beds of the middle Eocene (Lutetian) Castle Hayne Limestone indicate deposition of volcanic ash in the North Carolina Coastal Plain at 46 Ma. Five evolved (high-potassium) glauconitic micas from 30-35 cm below the bentonite yield a Rb-Sr isochron date of 45.3 ± 0.3 Ma and an initial 87Sr/86Sr ratio of 0.70764 ± 0.00015; a single split yields a conventional K-Ar date of 46.7 ± 1.8 Ma. Six evolved (high-potassium) glauconitic micas from 25-30 cm above the bentonite yield a Rb-Sr date of 43.1 ± 1.2 Ma and an initial 87Sr/86Sr ratio of 0.7079 ± 0.00011; a single split yields a conventional K-Ar date of 44.5 ± 1.7 Ma.Agreement of Rb-Sr and K-Ar biotite dates in the bentonite with Rb-Sr and K-Ar glauconitic mica dates in the underlying and overlying carbonate suggests that carefully selected, evolved glauconitic mica that has neither been deeply buried nor experienced cation exchange with ground water can provide reliable isotopic ages and constraints for the standard geologic time scale. 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.