Iron and Manganese Distribution in Nodules from a Young Texas Vertisol
- G. Norman White and
- J. B. Dixon
Iron and Mn distributions in the black nodules from the BCk3 horizon of the microlow position of a Burleson soil, a fine, montmorillonitic, thermic, Udic Haplustert, from a terrace of the Brazos River were mapped with scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) x-ray analysis. Spherical nodules were concentrically banded, and the irregularly shaped nodules lacked well-developed banding of Fe and Mn. More and better expressed banding was found by decreasing pixel size used for mapping and by increasing the count time per pixel for banded nodules. Bands of higher or lower Fe and Mn concentration were not coincident. The Mn/Fe weight ratios of individual nodules analyzed by EDS were between 0.71 to 2.85. Banded nodules had a narrower range of Mn and Fe concentrations and a narrower range in Mn to Fe ratios than unbanded nodules. Barium concentration in the nodules was unusually high, averaging 30 g kg−1, and correlated strongly with Mn concentration. Some interelement correlations (e.g., Fe vs. Mn, r = −0.56; Fe vs. Al, r = −0.58) reflected partitioning into the oxide or silicate minerals of the soil. Fractured nodules revealed the interior to have only a few very small pores. The 30 nodules examined are well developed solid bodies that are expected to persist in the soil environment. They appear to contain unique and important information about the weathering history of the Burleson soil and the landscape in which it occurs. The order and expression of the banding is a relict of the redox history of the nodules, which can be used to induce the redox history of the soil.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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