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Division S-5—Pedology

Range of Fragipan Expression in Some Michigan Soils

I. Morphological, Micromorphological, and Pedogenic Characterization

Dep. of Geography, 314 Natural Science Building, Michigan State Univ., East Lansing, MI 48824-1115

^* Corresponding author (weisenbo{at}msu.edu).

Many of Michigan's loamy soils exhibit varying degrees of fragipan expression, which may be variously influenced by their parent materials. We examined three soils in northern Michigan with varying degrees of fragipan expression to assess development of fragipans formed in acidic and calcareous glacial drift. To accomplish this, soil characterizations were made through field, physical, chemical, and micromorphological observations and analyses. The soils have bisequal horizonation: an upper sequum associated with podzolization processes and lower sequum associated with lessivage. Protofragipans and fragipans are found only in the lower sequum. The soils experience periodic episaturation and contain at least one lithologic discontinuity, often near the protofragipan or fragipan. The protofragipan and fragipans have loamy sand to loam textures, weak platy to subangular blocky structure, higher bulk densities (1.5–1.9 g cm^–3) and lower pH values (4.8–6.8) than adjacent horizons, brittle failure, and fine vesicular pores. Eluvial protofragipan and fragipan horizons contain albic materials that tongue into underlying argillic horizons. Illuvial fragipans exhibit clay coats, flows, and bridging. Thin-section characterizations confirm the presence of closely packed fabrics, intergrain bridging by clays, and void pedofeatures. Scanning electron microscopy (SEM) provides evidence of eluviation, reorganization of silt and clay, fluctuating redox conditions, degraded void pedofeatures, and the presence of surficially amorphous (bonding) materials in the protofragipan and fragipans. Soil extraction data do not preclude the presence of a fragic-property (brittleness) agent. Results, therefore, indicate that these protofragipans and fragipans are pedogenic and can form, with variable expression, in both acidic and calcareous glacial parent materials.

Abbreviations: AAO, acid ammonium-oxalate • CD, sodium citrate-dithionite • RDP, related distribution pattern • SEM, scanning electron microscopy