A SANDY INTERLOBATE LANDSCAPE WITH SILTY SEDIMENT IN THE BOTTOMS OF DRY KETTLES: EVIDENCE FOR HOLOCENE LOESS

This research examines the paleoenvironmental significance, and possible origins, of anomalous silty deposits in the Evart Upland – a dry, sandy, interlobate landscape in southern Michigan. Here, silty deposits occur in the bottom-centers of dry, sandy kettles. The lens-shaped silty deposits are dominated by fine and medium (10-25 µm) silt; the surrounding interlobate landscape is dominated by medium and fine sands. The abrupt lateral edges of the silty deposits, and their unique textural properties relative to the surrounding landscape, suggest that the silts were not winnowed from kettle backslopes by water. Instead, we propose that the fine sediment originated as loess that was episodically deposited across the Evart Upland and later redeposited into the centers of kettle bottoms by wind and water. Evidence in support of this conclusion includes: (1) the textural characteristics of the sediment, set within an overall sandy landscape, (2) charcoal-rich paleosols, pointing to discrete episodes of loess deposition interspersed with periods of soil formation, and (3) increased silt contents within the upper meter of the sandy soils on nearby geomorphically stable (flat) uplands.

Radiocarbon ages on bulk charcoal samples from nine paleosols within some of these silty deposits range from 960 to 10,930 cal yrs ago; although, most ages fall within the early Holocene. These ages effectively constrain the period of loess deposition/redistribution in the Evart Upland, and provide the first evidence of Holocene loess in the Great Lakes region. Our work also supports other, ongoing research that suggests the nearby Muskegon River floodplain was at least one of the potential loess sources.