SPODOSOL-ALFISOL INTERGRADES - BISEQUAL SOILS IN NE MICHIGAN, USA

Twenty three well-drained Boralfs, most of which exhibit bisequal soil morphology, were described and sampled in NE lower Michigan, where th ey occur on landscapes shaped by Greatlakean ice ca 12 ka. Bisequal so ils in Michigan are intergrades between Orthods and Udalfs, with a spo dic-like upper sequum (A-E-Bs) overlying a sequence of E'-Bt-C horizon s. Thus, they frequently occupy a pedogenic ''ecotone''. The purpose o f the study was to characterize these soils, which have been little-st udied, and to determine if parent material homogeneity and texture are correlated with various aspects of their morphology. The soils have f ormed in coarse-loamy and fine-loamy materials, often with a distinct lithologic discontinuity between the two sequa. The lower material, in terpreted as glacial till, is strongly calcareous and slightly coarser -textured, with considerably more dolomitic gravel than the upper mate rial. Water flowing through the material above may ''hang'' at the dis continuity and deposit illuvial clay, Bt horizons are found at or imme diately below the discontinuity. Statistical correlations indicate tha t bisequal sola and their eluvial horizons are thicker when developed in coarser-textured materials. Finer-textured pedons contain more extr actable Fe and Al in the spodic sequum, but have thinner eluvial zones which have not been as completely stripped of metal cations. In the f inest-textured pedons, the E' horizon may be completely lacking.