Two hydrosequences in central Michigan were investigated to evaluate the degree of Bt horizon expression as influenced by the depth and duration of soil saturation. Each hydrosequence was sampled in duplicate and consisted of well or moderately well, somewhat poorly, and poorly drained soils. Total clay ratios, I/E indices (fine clay/total clay of the illuvial zone divided the fine clay/total clay of the eluvial zone), and argillan development were greatest in the well‐drained soils and decreased with decreasing depth to and increasing duration of soil saturation. One of the poorly drained soils lacked Bt horizons while one had Bt horizon expression similar to that of the somewhat poorly drained soils. The water table regimes of all poorly drained soils were similar. The poorly drained soils with Bt horizons contained relatively large amounts of smectite, particularly in the clay films, while those lacking Bt horizons contained virtually no smectite. The Bt horizons developed to a greater degree where moisture fronts penetrated the solum the greater period of the year. Where penetration was retarded by soil saturation, mineralogy contributed to the degree of Bt horizon development.

Cotiga Mound, an Early Woodland mortuary mound constructed 2100 YBP, was sampled to evaluate diagnostic horizon development during a well‐defined, relatively short period of time. Five columns (profiles), three of which extended into the submound terrace soil, and one Giddings core of the terrace soil were sampled for particle‐size, pH, organic C, and micromorphology analysis. Six additional cores were collected to characterize the terrace soil. The mound was constructed of acid, silty material, in a manner that resulted in basketloading macrofabric consisting of long, sinuous, thin layers contrasting in color and texture. Pedogenesis destroyed the macrofabric and formed a solum in the upper 0.75 to 1.0 m of the mound. The solum consisted of a thin, dark A horizon; and intermittent, thin E horizon; and a variable B horizon. The B horizon was thickest at the mound crest, contained clay films on ped surfaces, and was designated Bt. On side slopes, the B horizon was thinner, lacked clay films, and was designated Bw. No B horizon was formed at the mound periphery. Clay distribution indices indicated that the Bt horizon was borderline cambic‐argillic, consistent with those typical of 2000‐yr‐old mid‐Atlantic alluvial soils. Clay films were sparsely distributed throughout the mound, indicating that clay accumulation mechanisms were largely inefficient in the 2100 yr. Mound soils were classified as Typic Dystrochrepts grading to Typic Hapludults at the mound crest. These soils are similar to floodplain soils mapped nearby. Submound terrace soils and adjacent terrace soils were classified as Humic Hapludults.

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Abstract. Relationships between soil colour patterns and depth and duration of water tables were studied using piezometers in three soil hydrosequences. A colour index was developed to quantify matrix colour, size and colour of mottles, and continuity and colour of clay films. It correlated well with duration of saturation when above 5°C (r= 0.88) and with duration of total saturation (r= 0.87). The colour index is useful to evaluate soils for various land uses.

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