Th230-U234 dating of pedogenic carbonates in gravelly desert soils of Vidal Valley, southeastern California

Research Article| November 01, 1979 Th230-U234 dating of pedogenic carbonates in gravelly desert soils of Vidal Valley, southeastern California TEH-LUNG KU; TEH-LUNG KU 1Department of Geological Sciences, University of Southern California, Los Angeles, California 90007 Search for other works by this author on: GSW Google Scholar WILLIAM B. BULL; WILLIAM B. BULL 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar S. THOMAS FREEMAN; S. THOMAS FREEMAN 3Woodward-Clyde Consultants, 4000 W, Chapman Avenue, Orange, California 92668 Search for other works by this author on: GSW Google Scholar KEVIN G. KNAUSS KEVIN G. KNAUSS 4Lawrence Livermore Laboratory, University of California, Livermore, California 94550 Search for other works by this author on: GSW Google Scholar Author and Article Information TEH-LUNG KU 1Department of Geological Sciences, University of Southern California, Los Angeles, California 90007 WILLIAM B. BULL 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721 S. THOMAS FREEMAN 3Woodward-Clyde Consultants, 4000 W, Chapman Avenue, Orange, California 92668 KEVIN G. KNAUSS 4Lawrence Livermore Laboratory, University of California, Livermore, California 94550 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1979) 90 (11): 1063–1073. https://doi.org/10.1130/0016-7606(1979)90<1063:TDOPCI>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 Email Permissions Search Site Citation TEH-LUNG KU, WILLIAM B. BULL, S. THOMAS FREEMAN, KEVIN G. KNAUSS; Th230-U234 dating of pedogenic carbonates in gravelly desert soils of Vidal Valley, southeastern California. GSA Bulletin 1979;; 90 (11): 1063–1073. doi: https://doi.org/10.1130/0016-7606(1979)90<1063:TDOPCI>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 SocietyGSA Bulletin Search Advanced Search Abstract Radioactive disequilibrium relationships among Th230, U234, and U238 can be used to date pedogenic carbonates formed in regions of arid to semiarid climate. Samples suitable for dating consist of dense carbonate rinds around pebbles from the Cca soil horizon. Analytically, the method involves leaching the samples with dilute hydrochloric acid and measuring U238, U234, Th230, and Th232 in both the leachate and residue fractions. As the soil carbonate commonly incorporates silicate mineral-bearing detritus, corrections are made to account for possible introduction of detrital Th230 and U234 into the acid leachate. The corrections are based on the assumptions that (1) the carbonate initially contains negligible amounts of Th232 and Th230, or has a Th230/Th232 ratio similar to that in detrital minerals, (2) U238, U234, and Th230 in the detrital silicate phase are in secular equilibrium with each other, and (3) the thorium isotopes in the detrital phase are not fractionated by the acid leaching. Application of the method to calcareous soils developed on upper Quaternary alluvial deposits of the eastern Mojave Desert in southern California gives ages that are internally consistent and that agree with the geomorphic and stratigraphic relative age relationships. Fourteen samples from an upper Pleistocene geomorphic surface, Q2b, yielded an average age of 83,000 ± 10,000 yr. This age is confirmed by a different assessment of the data independent of the aforementioned assumptions. On one specimen two different layers of a pebble coating were dated, and a carbonate accumulation rate of about 1 mm/8,000 yr was obtained. It is hoped that this study will serve as a basis for further research into the absolute dating of various types of impure carbonates of late Quaternary origin. 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.