Investigation of limestone and dolomite clast alteration in petrocalcic horizons, southern Nevada, USA
| Autor: | Sarah Morgenthaler, Amy L. Brock-Hon |
|---|---|
| Rok vydání: | 2019 |
| Předmět: |
Cobble
Lithology Dolomite Geochemistry Soil Science Petrocalcic Horizon 04 agricultural and veterinary sciences 010501 environmental sciences 01 natural sciences chemistry.chemical_compound Pedogenesis chemistry Clastic rock 040103 agronomy & agriculture 0401 agriculture forestry and fisheries Carbonate Pebble Geology 0105 earth and related environmental sciences |
| Zdroj: | Geoderma. 342:42-54 |
| ISSN: | 0016-7061 |
| Popis: | Petrocalcic horizons formed on Quaternary surfaces in southern Nevada contain altered limestone and dolomite clasts in the enveloping carbonate matrix. Three profiles from two geomorphic surfaces contain pebble to cobble clasts with distinct voids and alteration textures at their tops. Clast and alteration zone characteristics were analyzed with scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, electron microprobe analysis, and with an inductively-coupled plasma spectrophotometer. Limestone and dolomite clasts display considerable top-down alteration marked by vertical tubular voids and an increase in neoformed fibrous clay in the altered regions. Downward percolating soil waters moved through the cemented horizon and contacted the upper clast boundaries as evidenced by selective alteration and void development at the tops of clasts. The preservation of voids indicates that alteration and void development began no earlier than initial petrocalcic formation when soil matrix pore spaces were largely filled with pedogenic carbonate. Undersaturation of soil fluids with respect to primary clast components (Ca and/or Mg) and/or increased pCO2 under conditions enhanced during wetter (pluvial) climates is interpreted to drive dissolution and alteration of clasts in these horizons. Resulting morphological and mineralogical changes in these petrocalcic horizons may mark past climate and geomorphic influence on their development over time. Misinterpretation of parent material provenance as a result of selected removal of individual clast lithologies may occur. |
| Databáze: | OpenAIRE |
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