Mineral distribution in soils formed in the Indiana Dunes, usa

Abstract

The distribution of minerals and major elements in five soils developed on sand dunes ranging in age from Recent to 12,000 yr BP was studied with respect to particle-size fractions, soil depth, and soil age. The mineralogy in the sand, silt, and clay fractions was determined by XRD and SEM/EDAX, and element concentrations in the same fractions were determined by AA and XRF. Physical weathering has had a significant influence on the mineral distribution in the silt and clay fractions. Consequently, in these soils mineral weathering cannot be studied based on these fractions alone. The distribution of plagioclase a chlorite appears to be most affected by physical weathering of the coarse fragments. An irregular distribution with depth of shale fragments in the coarse sand fraction has resulted in a similar distribution of chlorite in the clay fraction and, for two of the profiles, a similar distribution of soil pH. In both the silt and clay fractions, chlorite appears more stable than mica due to a higher input rate of chlorite from coarser fractions. Rapid weathering of the clay fraction and comminution of coarser particles have resulted in a similar clay mineralogy across soil age within the A, E, and B horizons. Mica weathers to vermiculite with maximum Al-hydroxy interlayers in the B horizon and minimum in the A horizon. Reduced drainage seems to impede the formation of Al-hydroxy interlayers. Chlorite dissolves either directly or via a vermiculite phase. Carbonates have been dissolved below rooting depth (∼80 cm) within a few hundred years after stabilization of the dunes.