Cyclic variations of uranium concentrations and oxygen isotopes in tufa from the middle Miocene Barstow Formation, Mojave Desert, California

Abstract

Research Article| February 01, 2001 Cyclic variations of uranium concentrations and oxygen isotopes in tufa from the middle Miocene Barstow Formation, Mojave Desert, California Mona L. Becker; Mona L. Becker 1Department of Geosciences, State University of New York, Stony Brook, New York 11794-2100, USA Search for other works by this author on: GSW Google Scholar Jennifer M. Cole; Jennifer M. Cole 2Interdepartmental Doctoral Program in Anthropological Sciences, State University of New York, Stony Brook, New York 11794-4364, USA Search for other works by this author on: GSW Google Scholar E. Troy Rasbury; E. Troy Rasbury 3Department of Geosciences, State University of New York, Stony Brook, New York 11794-2100, USA Search for other works by this author on: GSW Google Scholar Vicki A. Pedone; Vicki A. Pedone 4Department of Geological Sciences, California State University, Northridge, California 91330-8266, USA Search for other works by this author on: GSW Google Scholar Isabel P. Montañez; Isabel P. Montañez 5Department of Geology, University of California, Davis, California 95616-8605, USA Search for other works by this author on: GSW Google Scholar Gilbert N. Hanson Gilbert N. Hanson 6Department of Geosciences, State University of New York, Stony Brook, New York 11794-2100, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Mona L. Becker 1Department of Geosciences, State University of New York, Stony Brook, New York 11794-2100, USA Jennifer M. Cole 2Interdepartmental Doctoral Program in Anthropological Sciences, State University of New York, Stony Brook, New York 11794-4364, USA E. Troy Rasbury 3Department of Geosciences, State University of New York, Stony Brook, New York 11794-2100, USA Vicki A. Pedone 4Department of Geological Sciences, California State University, Northridge, California 91330-8266, USA Isabel P. Montañez 5Department of Geology, University of California, Davis, California 95616-8605, USA Gilbert N. Hanson 6Department of Geosciences, State University of New York, Stony Brook, New York 11794-2100, USA Publisher: Geological Society of America Received: 30 May 2000 Revision Received: 02 Nov 2000 Accepted: 05 Nov 2000 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2001) 29 (2): 139–142. https://doi.org/10.1130/0091-7613(2001)029<0139:CVOUCA>2.0.CO;2 Article history Received: 30 May 2000 Revision Received: 02 Nov 2000 Accepted: 05 Nov 2000 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Mona L. Becker, Jennifer M. Cole, E. Troy Rasbury, Vicki A. Pedone, Isabel P. Montañez, Gilbert N. Hanson; Cyclic variations of uranium concentrations and oxygen isotopes in tufa from the middle Miocene Barstow Formation, Mojave Desert, California. Geology 2001;; 29 (2): 139–142. doi: https://doi.org/10.1130/0091-7613(2001)029<0139:CVOUCA>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 Uranium concentrations of 42 to 169 ppm in fibrous calcite from spring-deposited tufa in the middle Miocene Barstow Formation, California, are among the highest reported for calcite. Fission-track maps of multiple bands of uniformly dull-luminescent fibrous calcite show that the concentration of U increases in the outward growth direction of the calcite of each individual band. Homogeneous dull luminescence in the fibrous calcite indicates no change in redox conditions of the fluid from which the calcite was precipitated. It is proposed that the cyclic pattern of increase in U concentration reflects a cyclical change in the U/Ca ratio in the fluid. Episodic mixing between Ca-rich spring water with a low U/Ca ratio and Ca-poor saline alkaline lake water with a high U/Ca ratio could produce the episodes of formation of fibrous calcite with increasing U concentrations. The spring water supplies the Ca for calcite precipitation, and the U concentrations increase with the decreasing fraction of spring water and increasing fraction of lake water. These cycles reflect a variable recharge of groundwater into the lake by springs. The large variation in U concentrations suggests mixing of 0% to 45% spring water with the lake, while the narrow range in δ18O of −6.37‰ to −6.87‰ limits the variation of the proportions of spring and lake water to 5%. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.