A Holocene history of high bluffs, strandplains, terraces, and dunes along the southeastern margin of Lake Superior (Michigan, USA) with reference to fluctuating lake levels

The strandplains of the southeast Lake Superior coastline between Au Sable Point and Whitefish Point, Michigan, USA, record a response to Holocene lake-level variation (∼75 m), changing sediment supply, and accommodation space, and are good analogues for future shoreline behaviors associated with water-level changes along lacustrine and marine coastlines. A variety of datasets were used to explore these thick and extensive coastal deposits and to extend further back in time the available relative lake-level curve for the Lake Superior basin. Little is known about the coastal history prior to the Nipissing phase (6−2.8 ka) and what the geomorphic effect was from high rates of water-level rise (∼2−4 cm/yr) during the Nipissing transgression (ca. 8−4.5 ka). Rising and peak water levels eroded into glaciofluvial deposits, which resulted in eastward littoral transport of massive amounts of sediment that led to aggradation and basinward progradation of strandplains during the Nipissing transgression and Nipissing phase. Strandplains developed sequentially eastward as discreet littoral cells ending at the large (∼88 km²) Whitefish Point strandplain complex. High rates of sediment supply drove a shoreline behavior of depositional transgression and depositional regression. In post-Nipissing time, erosion likely continued into glaciofluvial deposits, but falling lake levels likely resulted in decreased sediment supply. With less sediment and less accommodation space, there was an increase in west-to-east longshore sediment transport that contributed to the growth of Whitefish Point during the Algoma (2.8−2.0 ka), Sault (2.0−1.0 ka), and Sub-Sault (1.0 ka to modern) phases. Lake-level rise after 1.0 ka has resulted in retrogradation (erosional transgression) along most of the shoreline between AuSable Point and Whitefish Point.