Inferences of paleoenvironment from petrographic, chemical and stable-isotope studies of calcretes and fracture calcites

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Past research has indicated a genetic connection between calcite formed in calcretes at the surface of Yucca Mountain, Nevada, and calcites deposited in underlying fractures of the unsaturated zone. This common genesis suggests that paleoenvironmental information, as well as the timing and pathways of past recharge episodes, might be obtained from studies of the deposits in both the calcretes and the unsaturated fractures. Chemical and isotopic modification of calcite-precipitating fluids appears to begin at the surface, largely under the influence of plant roots and their decay products. Chemical characteristics of the deeper calcites are either initiated or largely defined within ... continued below

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9 p.

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Vaniman, D.T. & Whelan, J.F. March 1, 1994.

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Past research has indicated a genetic connection between calcite formed in calcretes at the surface of Yucca Mountain, Nevada, and calcites deposited in underlying fractures of the unsaturated zone. This common genesis suggests that paleoenvironmental information, as well as the timing and pathways of past recharge episodes, might be obtained from studies of the deposits in both the calcretes and the unsaturated fractures. Chemical and isotopic modification of calcite-precipitating fluids appears to begin at the surface, largely under the influence of plant roots and their decay products. Chemical characteristics of the deeper calcites are either initiated or largely defined within the first few meters of fluid migration into the unsaturated tuffs beneath the calcretes. However, petrographic and isotopic data indicate a very unique low-{delta}{sup 13}C microenvironment that is localized at the upper surfaces of the calcretes. These surfaces form an interface in the soil horizon where infiltration may pond above the underlying carbonate ``plug.`` In order to decipher the chemistry and petrology of past recharge events, it is important to first understand microenvironments such as this that contribute to mineral precipitation/dissolution events in the pedogenic environment.

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9 p.

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INIS; OSTI as DE94007559

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  • International high-level radioactive waste management conference, Las Vegas, NV (United States), 22-26 May 1994

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  • Other: DE94007559
  • Report No.: LA-UR--94-640
  • Report No.: CONF-940553--13
  • Grant Number: W-7405-ENG-36
  • Office of Scientific & Technical Information Report Number: 145257
  • Archival Resource Key: ark:/67531/metadc625827

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  • March 1, 1994

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  • June 16, 2015, 7:43 a.m.

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  • Feb. 25, 2016, 7:45 p.m.

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Vaniman, D.T. & Whelan, J.F. Inferences of paleoenvironment from petrographic, chemical and stable-isotope studies of calcretes and fracture calcites, article, March 1, 1994; New Mexico. (digital.library.unt.edu/ark:/67531/metadc625827/: accessed January 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.