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 3545 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.