Evidence for Loess in Northwest Lower Michigan: the Silty Mantle on the Buckley Flats Outwash Plain
Randall J. Schaetzl and James Hook
We report on a silt-rich mantle, generally 35–45 cm thick, on a section of the Outer Port Huron outwash plain in northwest Lower Michigan, known locally as the Buckley Flats. Below the mantle (cap) are coarse, sandy outwash sediments. The study examines various hypotheses on the origin of the silt-rich sediment. The silty cap was sampled at 67 sites across the Buckley Flats; data derived from these sites were kriged to create smoothed surfaces of cap thickness and various textural attributes. The silty cap thins progressively from south to north, away from the Manistee River valley. The cap also becomes progressively siltier and finer-textured, and contents of medium and coarser sands diminish, toward the north, away from the presumed source. We suggest that, during the latter phases of the Port Huron advance, while the Manistee River was carrying glacial meltwater, the Buckley Flats would have been a high, dry, stable landscape, relatively near to the river. Silty sediment probably was transported by wind, out of the Manistee floodplain, just as it was with larger meltwater rivers in the Midwest, and deposited on nearby uplands. Eolian sediment deposited on the Buckley Flats, however, was more likely to have been preserved than was sediment on nearby, less stable landscapes, or on landscapes much farther away. Thus, we conclude that the silty mantle on the Buckley Flats is loess, making our study the first to document and characterize an extensive loess sheet in Lower Michigan.