Soil-Saprolite Profiles Derived from Mafic Rocks in the North Carolina Piedmont: I. Chemical, Morphological, and Mineralogical Characteristics and Transformations

摘要

The chemical, morphological and mineralogical properties of two Enon sandy loam (fine, mixed, thermic Ultic Hapludalfs) soilsaprolite profiles, one formed on gabbro and the other on metagabbro, are compared. Clay skins are scarce and stress cutans common in the argillic horizons of these soils. Iron-manganese concretions are concentrated in soil horizons immediately above the argillic horizons. The high shrink-swell capacities and slow permeabilities of the argillic horizons result in relatively shallow depths to paralithic contact with saprolite. The parent rock from the Enon profile near Albemarle, Stanly County, North Carolina is a medium-grained metagabbro with chlorite, hornblende, quartz, and calcic plagioclase feldspar as the dominant primary minerals. Chlorite weathers to regularly interstratified chlorite-vermiculite, which alters to randomly interstratified chlorite-vermiculite and smectite. Particle size decreases with each mineral alteration. Hornblende weathers to smectite and goethite. Calcic plagioclase feldspar transforms to kaolinite in the saprolite and soil horizons. Quartz is relatively resistant to chemical weathering. The parent rock of the Enon profile near Concord, Cabarrus County, North Carolina is a coarse-grained gabbro with hornblende and calcic plagioclase feldspar as the dominant primary minerals. Hornblende transforms to smectite and goethite. Calcic plagioclase feldspar alters to kaolinite in the saprolite and soil horizons