Iron and Manganese Distribution in Nodules from a Young Texas Vertisol

Abstract

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.

Comparison of modern and ancient Vertisols developed on limestone in terms of their geochemistry and parent material

“…10F), and of V, Ni, and Pb (not shown), generally mirrors that of Fe. Complexation and sequestration of trace metals such as Co and Zn (not shown) in various Mn oxides (White and Dixon, 1996) can be similarly interpreted. The trace elements suggest common development of low-Eh conditions in the pedon during times of soil saturation and consequent trace element mobility.…”

Evaluating the use of weathering indices for determining mean annual precipitation in the ancient stratigraphic record

“…Similar Fe or Fe-Mn nodules grow during wet/dry cycles in response to changing redox conditions (e.g., White and Dixon, 1996;Stiles et al, 2001) and are more characteristic of soils that undergo seasonal waterlogging (e.g., Ransom et al, 1987;McKenzie, 1989). Schwertmann and Fanning (1976) found that such nodules increase in abundance and size as soil wetness increases; however they are absent from very poorly drained soils.…”

Microscopic structure of soil Fe-Mn nodules: environmental implication

“…Note the dense and heterogeneous surface coatings of a brown film (I) encasing a black core (M). Occasional occluded quart grains (Q) were also visible described these materials (White and Dixon 1996;Belzile et al 2001;Liu et al 2002). The objectives of this research are to investigate the microscopic characteristics and the distribution of Fe and Mn in nodules from some soils in central Greece using scanning electron microscopy (SEM)/energy dispersive X-ray spectrometer (EDS) analyses supported by element concentration data by atomic absorption spectroscopy (AAS).…”