THE BUCKLEY LOESS SHEET IN NW LOWER MICHIGAN: EVIDENCE FOR A MANISTEE RIVER OUTWASH SOURCE

The soils near Buckley, Michigan have long been considered anomalies. Unlike the dry sandy soils that dominate most of northern Lower Michigan, the soils on the “Buckley Flats” are silty, with sand and gravel present only at depth. The Flats are geomorphically part of the Outer Port Huron moraine, which in this part of Michigan is a series of broad, flat, outwash fans. The Buckley Flats are, therefore, the highest (and flattest) part of the Outer Port Huron outwash fan. Meltwater from the Outer Port Huron advance drained into the Manistee River, which forms the southern boundary of the Flats, and thence (tortuously) to ancestral Lake Michigan. The silt cap on the Buckley Flats is typically about 30-35 cm thick (70 cm max), above gravelly sand and coarse sand outwash. The silt and clay contents of the cap average 23.0% and 7.4%, respectively. Most commonly, the cap is sandy loam in texture.

In this research, I sought to explain the origin of this silty “cap” and hypothesized that it was either (1) a silty lacustrine sediment, formed as the Manistee River was dammed and backup up, onto the Flats, (2) the last of a series of fining-upward outwash facies, or (3) loess. To this end, detailed particle size data were determined for over 90 sites across the Buckley Flats, and mapped. In every case, the data for the silty cap show spatial trends that are consistent with a loessial origin, with the Manistee River as its source. For example, the mean particle size of the silt cap exhibits a clear spatial trend – the cap is coarsest in the SE (near the Manistee River) and gets finer to the north. This type of spatial trend is typical of loess, which gets finer with distance away from its source area. Like most loess deposits, which become more texturally uniform with distance from the source, the silt cap here is most uniform near the northern end of the Buckley Flats, far from the presumed source - the Manistee River. Silt and clay contents also increase to the north, away from the Manistee River, while the various sand components of the cap sediments decrease along the same transect. All these data point to a Manistee River source, despite the fact that it carried meltwater for only several decades or more. The work, therefore, is the first to identify a loess sheet in Lower Michigan, and illustrates that a significant amount of loess can be generated from medium-sized meltwater streams, even if they carried meltwater for only a short period of time.