T195 The Critical Zone As Heterogeneous Media: Implications for Physical, Chemical, and Biological Processes

Tuesday, 24 October 2017
8:00 AM - 12:00 PM
Room 618/619/620

GEOCHEMICAL ANALYSIS OF FE-ENRICHED SOIL OF MEHERRIN, VIRGINIA

Paper number: T195-13
Program: Technical Sessions
Time: 11:00 AM – 11:15 AM

Authors

Abstract

The red soil of Meherrin is an attractive part of the Southern Piedmont region due to its unique features. Consisting of Ultisols of the Georgeville Series, it has a high amount of clay (27%) in comparison with the rest of the georgeville series. Several sites in Meherrin have been assessed, with respect to their soil characteristics, in order to understand the cause of color and special properties. Texture and elemental composition have been analysed at three different locations, respectively. The samples, at each site, were collected by core sampling at 6-inch intervals. For this study, sites were coded as MA, MB, and MC and located within 1 mile of each other. MA and MB differ considerably in their color; site MA has a color of red (10R 4/8) while MB has a color of green (10Y 5/2). Samples were size partitioned by wet sieving. The sample fractions, less than 63 microns and greater than 63 microns were analysed by an X-Ray Fluorescence (XRF) spectrophotometer to understand elemental composition, soil color, and properties. After thoroughly washing and drying of the greater than 63-micron fractions, magnetic particles were manually separated by a strong hand magnet and composition was studied with XRF. X-Ray Diffraction (XRD) analysis of separated magnetic particles was conducted by an Olympus transmitted XRD instrument, using the Cobalt anode x-ray tube. Furthermore, morphological and elemental analysis was carried out by Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectrum (EDS). The Fe₂O₃ content in bulk samples is relatively high, varying between 10% and 30%. Concentration of Fe₂O₃ increases with depth in samples for location MA, yet, the highest concentration is observed in the most shallow samples. In all locations, the distribution of alkali metals does not show a trend. Results of the elemental analysis for separated magnetic particles reveal the presence of well-preserved euhedral crystals of magnetite, hematite, and potentially wusite (cubic FeO). Furthermore, the SEM analysis revealed magnetic spherules and relic grains with apparent widmanstӓtten patterns. Such patterns may indicate an extra-terrestrial or volcanic source of Fe-the enriched mineral phases, accountable for the special characteristics of Meherrin soil.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-302664

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