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Book: Soil Color
Published by: Soil Science Society of America


This chapter in SOIL COLOR

  1.  p. 127-159
    SSSA Special Publication 31.
    Soil Color

    J. M. Bigham and E. J. Ciolkosz (ed.)

    ISBN: 978-0-89118-926-8


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The Color of Red Beds—A Geologic Perspective

  1. Robert H. Blodgett,
  2. J.P. Crabaugh and
  3. E.F. McBride
  1. Texas Water Commission, Austin, Texas


Red beds are sediments and sedimentary rocks with hues ranging from 2.5YR to 5R. Reddish pigmentation of these deposits is present in both surface exposures and subsurface well cores. Strata containing red beds commonly exhibit color mottling and may include layers that are not red. The fine-grained hematite (< 2 μm) that pigments red beds can form in the weathering zone and below the zone of soil formation. Many pre-Quaternary red beds contain buried and lithified paleosols that can be identified by micro- and macro-morphologic features such as: specific types of carbonate nodules and pisolitic concretions, smooth curving slickensided surfaces, and fossil roots. Below the zone of soil formation, hematitic pigment forms by diagenetic processes including: oxidation of Fe following the alteration of ferromagnesian minerals and volcanic ash, and oxidation of Fe sulfides. Unresolved problems in the genesis of red beds include the relative importance of inherited pigment, and of time and temperature in hematite formation.

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