Range of Fragipan Expression in Some Michigan Soils:
I. Morphological, Micromorphological, and Pedogenic Characterization
Beth N. Weisenborn and Randall J. Schaetzl
Little research exists on Michigan’s fragipan soils and, as a result, they are poorly characterized and their genesis is unclear. We examined three soils in northern Michigan with varying degrees of fragipan expression, to elucidate their possible pedogenic pathways. To accomplish this, physical, chemical, and micromorphological properties were first characterized and evaluated. The soils have bisequal horizonation: an upper sequum associated with podzolization processes and lower sequum associated with lessivage. Protofragipans (having fragic soil properties but not meeting diagnostic criteria) and fragipans are found only in the lower sequum. These soils probably experience periodic episaturation and all contain at least one lithologic discontinuity near the protofragipan or fragipan. The protofragipans and fragipans have loamy textures, subangular blocky structure, higher bulk densities and lower pH values than adjacent horizons, as well as brittle failure and many 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, while scanning electron microscopy provides additional 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. Although fragic properties do not appear to be associated with extractable forms of Fe, Al, or Si, our data do not preclude these elements acting in combination. Results, therefore, indicate that the protofragipans and fragipans are pedogenic; data presented here are subsequently used in a companion paper to evaluate and model fragipan evolution.