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Book: Acid Sulfate Weathering
Published by: Soil Science Society of America



  1.  p. 127-146
    SSSA Special Publication 10.
    Acid Sulfate Weathering

    J.A. Kittrick, D.S. Fanning and L.R. Hossner (ed.)

    ISBN: 978-0-89118-905-3


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Alfisols and Ultisols with Acid Sulfate Weathering Features in Texas1

  1. C. D. Carson,
  2. D. S. Fanning and
  3. J. B. Dixon2


Jarosite has been identified in soils classified as Ultisols (e.g., Aubrey soil series) and/or Alfisols (e.g., Lufkin soil series) developed on the Woodbine, Cata-houla, and Yegua geologic formations in Texas. The Woodbine is Upper Cretaceous, the Catahoula is Oligocene, and the Yegua is Eocene. The extent of these geologic formations suggests that there may be many other upland soils that contain jarosite. Jarosite has been identified in very acid soil horizons and in other soil horizons with near neutral pH. Some horizons containing jarosite have as much as 8.1 meq/100 g exchangeable aluminum (Al) and 23.8 meq/100 g nonexchangeable titratable acidity. Appreciable amounts of acidity determined in soils with a near neutral pH may reflect an earlier acid sulfate weathering regime. None of these upland soils have pH values low enough to have any horizons that qualify as sulfuric horizons today, but the presence of jarosite is interpreted as indicating that these soils underwent active sulfuricization at some time in the past.

Jarosite has been identified in these soils by noting mottles with yellow (5Y) hues and with verification in the laboratory by X-ray diffraction or differential thermal analysis on relatively pure hand picked specimens. Barite, gypsum, and calcite have been identified in some horizons that contain jarosite by employing a similar combination of field and laboratory techniques. The mineralogy of the matrix soil materials associated with the presence of jarosite is usually mixed in the Woodbine derived soils and smectitic in the Yegua and Catahoula derived soils. Pyrite weathering has apparently been the source of sulfate ions and acidity necessary for jarosite formation. Jarosite seems to be preserved in some Claypan soils due in part to their dense clayey subsoil.

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