Spheroidal Dolomite, Mg-Kutnohorite, and a New Mineral Occurrence of Boracite in Death Valley CA, USA: Implications for Genesis and Paleoenvironmental Interpretations. (4535) Authors: B.J. Buck* - Univ. Nevada Las Vegas S. Mrozek - Univ. Nevada Las Vegas D. Merkler - NRCS Las Vegas NV B. Harrison - New Mexico Tech Univ. Socorro NM L. Lato - NRCS Las Vegas NV Abstract: Spheroidal dolomite has been interpreted to form in numerous depositional environments including: (1) the oxidation of surface hydrocarbon seepages combined with bacterial activity and groundwater flow, (2) precipitation in ponds and peritidal depositional environments, (3) precipitation from hypersaline water and mixed saline-fresh water, and (4) phreatic precipitation. In this study, we find spheroidal forms of dolomite, calcite, Mg-calcite, and Mg- kutnahorite (sometimes spelled kutnohorite) in pedogenic pendants in an aridic, hyperthermic soil in Death Valley, California. Pedogenic minerals present include calcite, calcite/Mg-calcite, Mg-calcite, dolomite, Mg-kutnahorite, ankerite, boracite, gypsum, aragonite, halite, anhydrite, and sepiolite/palygorskite. This is the first documentation of the pedogenic formation of boracite, ankerite, and kutnahorite in a modern soil. Spheroids are 5-50 microns, (rarely up to 400 microns) in size, contain split growth, and are commonly hollow. No evidence of a water table is present within the soil profile; the extreme aridity of the study area, coupled with topographic position of the geomorphic surface, makes it extremely unlikely that this site had a high water table in the past. The results of this study support a pedogenic (and probably bacterial) origin for spheroidal dolomite, calcite/Mg-calcite, and Mg-kutnohorite in these arid soils. Speaker Information: Brenda Buck, Univ. Nevada Las Vegas, Department of GeoscienceUniversity of Nevada Las Vegas4505 Maryland Parkway, Las Vegas, NV 89154; Phone: 702-895-1694; E-mail: [email protected] Session Information: Tuesday, November 2, 2004, 2:00 PM-4:00 PM Presentation Start: 2:00 PM (Poster Board Number: 1750) Keywords: Dolomite; Pendants; Arid; Carbonate.