Holocene, silty-sand loess downwind of dunes in Northern Michigan, USA

Abstract

ABSTRACT In Michigan’s Upper Peninsula, sand dunes are widespread on the sandy floor of former Glacial Lake Algonquin, and many of the nearby uplands also have thin mantles of loess. Previous work concluded that these dunes formed during the early Holocene, long after the lake had drained. Where these dunes have migrated against bedrock uplands, many have accreted into larger dune complexes. South and east of these complexes, uplands are mantled with well-sorted sediment, comparatively rich in finer sands and much like the thin, locally sourced loess deposits in Wisconsin and Michigan. Near the dunes, this loess is typically 50–75 cm thick, and rich in very fine sands; presumably much of this sand was deposited as short-range “blow-over” while the dunes were forming. The loess thins to ≈45 cm and becomes siltier on sites farther downwind, to the southeast. Because the dune complexes contain almost no silt, the silt in the loess was likely generated by deflation of saltating sands on the lake plain, transported in suspension, and deposited generally uniformly across the forested uplands, as indicated by spatial trends in silt contents. Periodic Holocene drought may have thinned the forest and helped to intermittently facilitate this type of eolian activity.