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Abstract

Maghemite, γ-Fe2O3, was identified in soils developed from residuum of Knox Group dolostones (Cambro-Ordovician age) along Chestnut Ridge on the U.S. Department of Energy Oak Ridge Reservation in Oak Ridge, Tennessee. The parent dolostones in the area were free of maghemite and magnetite. Scanning electron micrographs and electron probe analyses indicated that the maghemite replaces oolites, cements siltstones, and occurs as massive to botryoidal material. The most complex replacement by maghemite was displayed by the oolitic material. Oolitic limestone was dolomitized, as revealed by the presence of numerous dolomite rhombohedra, during early diagenesis. During the next stage, dolomite rhombohedra were replaced by chert; much of the remaining oolites and carbonate cements also have been partly replaced by chert. After uplift and erosion brought these oolitic cherts into the upper weathering zone, the cherts were replaced by iron hydroxide. Massive chert and siltstone in all stages of replacement by iron oxides have been observed. The replaced iron phase was converted to maghemite and hematite during a late-stage of paragenesis, possibly a pedogenic process.

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