Present address: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964-8000, USA (E-mail: firstname.lastname@example.org).
Petrographic and trace element analysis of uranium-rich tufa calcite, middle Miocene Barstow Formation, California, USA
Article first published online: 30 APR 2004
Volume 51, Issue 3, pages 433–453, June 2004
How to Cite
Cole, J. M., Rasbury, E. T., Montañez, I. P., Pedone, V. A., Lanzirotti, A. and Hanson, G. N. (2004), Petrographic and trace element analysis of uranium-rich tufa calcite, middle Miocene Barstow Formation, California, USA. Sedimentology, 51: 433–453. doi: 10.1111/j.1365-3091.2004.00631.x
- Issue published online: 21 MAY 2004
- Article first published online: 30 APR 2004
- Manuscript received 9 September 2003; revision accepted 18 November 2003.
- synchrotron XRF;
- trace elements;
An integrated petrographic and spectroscopic (X-ray diffraction, phosphor imaging and synchrotron X-ray absorption spectroscopy) study of tufas from the Miocene Barstow Formation, California, relates sample morphology, mineralogy and geochemical composition. The tufas, composed mainly of calcite that formed at the interface between an ancient alkaline lake and ground or spring waters, have textures similar to those of microbially mediated terrestrial stromatolites and travertines. The tufas have elevated concentrations of a number of trace elements including Mn, Fe, Sr and U. Synchrotron X-ray fluorescence analyses show that U concentrations can exceed 500 p.p.m. X-ray absorption spectroscopy indicates that the U in these samples is incorporated as U(IV). It is suggested here that alkaline lake waters had a high U/Ca ratio and tufa calcite formed where groundwater or (possibly epithermal) springs brought in Ca and trace elements such as Sr. The rapid, and possibly microbially mediated, precipitation of calcite allowed for incorporation of high concentrations of trace metals as either structural substitutes or extremely fine-scale inclusions.