Fine Clay Mineralogy of Soil Matrices and Clay Films in Two Michigan Hydrosequences

Fine clays (<0.2 µm) from the matrices and clay films of soils from two Michigan hydrosequences were analyzed by x‐ray diffraction to determine depth distributions and relationships to weathering and translocation processes associated with position in the hydrosequence. Illite contents of matrices generally increased, whereas vermiculite decreased with depth. This depth function was most prominent in the well and moderately well drained soils and diminished with decreasing natural drainage. Vermiculite content was negligible in both, and smectite was found in only one of the two poorly drained soils. Clay films from the well and moderately well drained soils had a mixed mineralogy of illite, kaolinite, and vermiculite, whereas those from the somewhat‐poorly drained soils were primarily illitic. Where present, clay films from the poorly drained soils contained smectite in addition to illite and kaolinite. Depth distributions of matrix clay minerals in the better drained soils suggested that illite had weathered to vermiculite and hydroxy‐interlayered vermiculite. Prolonged saturation and associated higher pH values may have favored illite‐smectite transformations in the poorly drained positions. We suggest that hydrosequence differences in moisture content of the eluvial zones resulted in a differential dispersion of clay minerals upon wetting. This may have led to selective translocation and the observed differences in clay film mineralogy.