GEODER&4 Geoderma 74 ( 1996) 23-47 Spodosol-Alfisol intergrades: bisequal soils in NE Michigan, USA Randall J. Schaetzl ’ Department of Geography, Michigan State UnirersiQ, East Lansing. MI 48824-l 115, USA Received 24 October 1995; accepted 16 July 1996 Abstract Twenty three well-drained Boralfs, most of which exhibit bisequal soil morphology, were described and sampled in NE lower Michigan, where they occur on landscapes shaped by Greatlakean ice ca 12 ka. Bisequal soils in Michigan are intergrades between Orthods and Udalfs, with a spodic-like upper sequum (A-E-Bs) overlying a sequence of E’-Bt-C horizons. Thus, they frequently occupy a pedogenic “ecotone”. The purpose of the study was to characterize these soils, which have been little-studied, and to determine if parent material homogeneity and texture are correlated with various aspects of their morphology. The soils have formed in coarse-loamy and fine-loamy materials, often with a distinct lithologic discontinuity between the two sequa. The lower material, interpreted as glacial till, is strongly calcareous and slightly coarser-textured, with considerably more dolomitic gravel than the upper material. Water flowing through the material above may “hang” at the discontinuity and deposit illuvial clay; Bt horizons are found at or immediately below the discontinuity. Statistical correlations indicate that bisequal sola and their eluvial horizons are thicker when developed in coarser-textured materials. Finer-textured pedons contain more extractable Fe and Al in the spodic sequum, but have thinner eluvial zones which have not been as completely stripped of metal cations. In the finest-textured pedons, the E’ horizon may be completely lacking. Keywords: podzolization; eluviation; pedogenesis: factor analysis; discontinuities 1. Introduction Bisequal soils contain two eluvial-illuvial sequa, typically an E-Bs sequum overly- ing an E’-Bt sequum (Anonymous, 1987), although by definition the lower sequum may contain a fragipan (i.e., Ex-Bx or Ex-Btx) (Yassoglou and Whiteside, 1960). These ’ Phone: + 1(517)3537726, Fax: + 1(517)432 1671, E-mail: [email protected] 0016-7061/96/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved. PII SO0 16-706 I (96)00060-Z24 R. J. Schaet;l/ Geoderrna 74 (I YY6I 23-47 soils have characteristics of Spodosols in their upper solum, and an Alfisol- or Ultisol-like sequum below, and thus are often found at the interfaces between areas of Spodosols and areas of Alfisols (Stobbe, 1952; Allen and Whiteside, 1954; Beaver, 1966) or Ultisols (Markewich and Pavich, 1991). As a result, they are positioned in an “ecotonal” area, such that their study may shed light on podzolization and the lessivage processes, both of which are active in these soils. In bisequal soils, therefore, lessivage and podzolization may be studied simultaneously. Most bisequal soils in the Great Lakes area, USA, and in southern Ontario classify as Boralfs in Soil Taxonomy (Soil Survey Staff, 1975). If they contain a glossic (E/Bt) horizon, they key out as Glossic Eutroboralfs or Mollic Paleoboralfs; otherwise these soils are usually Typic Eutroboralfs. If the upper Bs or Bh horizon is strongly-developed and therefore classifies as a spodic horizon, they are Alfic Haplorthods. Using old terminology, they would be intergrades between Podzols and Brown Podzolic soils. Most are in the frigid soil temperature regime (MAST < 8°C with marked seasonality) (Soil Survey Staff, 1994). Soils with bisequal profiles were initially documented early in the 20th century by Veatch and Millar (1934). Most studies of bisequal soils, however, date from the mid-20th century, with little work in the past 30 years. Characterization studies of a few, select bisequal profiles and their morphological associates were accomplished in the 1940’s and 1950’s. Often, the purpose of these studies was to place these pedologic anomalies within a developmental and/or morpho-sequence of soils, with more zonal soils as the end members: those dominated by lessivage and clay translocation (the Gray-Brown Podzolic or Red-Yellow Podzolic soils) and those dominated by podzoliza- tion (the Podzols) (e.g., Cline, 1949; Frei and Cline, 1949; Gardner and Whiteside, 1952; Stobbe, 1952; Cline, 1953; Allen and Whiteside, 1954; Holt and McMiller, 1956; Markewich and Pavich, 1991). The purpose of this study was (1) to provide data on bisequal soils, given that a wide range of pedons (23 in all) were examined across a range of parent materials, and thus to (2) determine the effects of parent material, its texture, relative homogeneity (i.e., presence or absence of lithologic discontinuities) and carbonate content, and landform slope, on the morphology of these soils. Soils with this type of profile have not been studied extensively in nearly three decades. By examining the relationships between parent material characteristics and soil morphology, insight into the genesis of these profiles can be ascertained, .yen~u Schaetzl (1992). In soil studies where a large sample size exists, such as this study and a few others (e.g., Litaor et al., 1989; Delgado et al., 1994; Alexander, 1995), statistical analyses of relationships among various morphologic attributes can be performed. The statistical relationships discerned for the 23 pedons studied here were interpreted in light of pedogenic theory. 2. Theory of formation Bisequal soils usually have horizon E-Bs horizon sequences above and E-Bt sequum, although E-Bt above E-Bh horizon sequences have been described for soils in thermic soil temperature regimes (Daniels et al., 1975). In this study, E-Bs-E’-Bt horizon sequences in soils of frigid soil temperature regimes are the