Influence of Lake Michigan Holocene Lake Levels on Fluvial Sediments of the Lower Pigeon River, Wisconsin

Thirty-seven vibracores, extending up to 4.86 m, collected along the lower Pigeon River north of Sheboygan, Wisconsin, were used to interpret Holocene lake-level fluctuations of Lake Michigan. The sediments reflect numerous cycles of degradation and aggradation as well as marshland and submergence. The basal unit is till and glaciolacustrine silt and clay. The river cut through these sediments prior to 6,500 14C years BP, probably during the Chippewa Low stand, and deposited the lowest gravel unit in the cores. Between 6,500 and 5,500 14C years BP, yellowish-red fluvial sand and silt were deposited in the northern half of the valley. Aggrading point bar gravel and overbank silt and fine sand throughout the entire valley record the lake rise to the Nipissing level from about 5,500 to 5,000 14C years BP. Subsequent deposition of organic-rich, muddy palustrine sediment indicates that Nipissing water flooded the valley. A lack of sediments with ages between 5,000-2,000 14C years BP suggests lack of aggradation, indicating a lowering lake level until about 2,000 14C years BP. Sandy-silt overbank sediment deposited over the palustrine sediment since 2,000 14C years BP marks the return of floodplain aggradation as lake level stabilized or rose slightly to the modern level. While the river-mouth sediments are not useful for refining Holocene lake-level curves, they do corroborate major events such as the Chippewa Low, the rise to the Nipissing level followed by a period of declining lake level and fluvial erosion, and the small rise to the modern lake level.