Evidence for Periodic, Holocene Loess Deposition in Kettles in a Sandy Interlobate Landscape, Michigan, USA

Trevor Hobbs, Randall J. Schaetzl and Michael D. Luehmann

Loess deposits are common in mid-continental North America, but are rare in Michigan, and most loess found in this region is of last-glacial age. We report on evidence for Holocene-age, silt-dominated deposits found in kettle bottoms, which we interpret as loess. These silty deposits contrast with the broader interlobate landscape, which is composed of glaciofluvial materials dominated by medium and fine sands (125–500 lm). The abrupt lateral edges of the silty deposits, and their unique textural properties relative to the surrounding landscape, suggest that the silts were not washed from kettle backslopes. Rather, we suggest that the silts originated as loess that was episodically deposited in kettle bottoms across the Upland. Later, loess that may have been deposited on backslopes was occasionally redeposited into the centers of vegetated kettles, along with some background sands, by wind and water. Evidence in support of our conclusions includes (1) the fine-silty textural characteristics of the sediments, set within an otherwise sand-dominated landscape, (2) depositional sequences of charcoal-rich paleosols, intercalated within the otherwise ‘‘clean’’ kettle bottom silts, pointing to episodes of loess deposition interspersed with periods of slope stability and pedogenesis, and (3) increased silt contents within the upper meter of sandy soils on nearby stable uplands. Radiocarbon ages on bulk charcoal from nine paleosols within the kettle-bottom silt deposits fall mainly within the early Holocene. These deposits and 14 C ages provide the first evidence of Holocene loess in the Great Lakes region, some of which probably originated from the nearby Muskegon River floodplain.