Dune formation on late Holocene sandy bay barriers along Lake Michigan's Door Peninsula; the importance of increased sediment supply following the Nipissing and Algoma high lake-level phases

This study focuses on the geomorphology and geochronology of dunes formed on three sandy barrier systems at Clark, Europe and Kangaroo Lakes in Wisconsin's Door Peninsula. The Lake Michigan shoreline in the peninsula contains abundant evidence for fluctuations in lake level with paleo-shoreline features that lie up to approximately 7 m above the present shoreline. Dunes are not very common along the Lake Michigan shoreline in Wisconsin, but the three bay barriers studied contain beach ridges that were buried by varying depths of eolian sand in the form of low relief sandsheets as well as parabolic and transverse dunes that have relief of up to 21 m. The purpose of this study was to document when the barriers formed and when the subsequent eolian activity occurred. The chronology presented here for barrier emplacement and dune development is based on 65 optically stimulated luminescence (OSL) samples which were collected from littoral sediment in the barriers (n = 17) and the overlying eolian sand (n = 48). Sediment samples were collected using bucket augers or a vibracoring device at depths ranging from 0.5 to 4.1 m below the ground surface. The OSL ages show that barriers in each of the study sites were constructed between approximately 5.9 and 3.9 ka, corresponding closely to the Nipissing high lake phase. OSL ages falling between 3.3 and 2.5 ka at the Kangaroo Lake site suggest the portion of the barrier closest to Lake Michigan formed during the Algoma phase. The majority of the eolian ages fall into two primary groups that overlap with or are slightly younger than the ages acquired from the barriers. These results suggest eolian activity ended between 4.5 and 3.7 (n = 20 ages) and 2.5 and 1.8 (n = 11 ages) ka. Both geomorphic and geochronological evidence suggests that dune development occurred rapidly when sand supply increased as lake levels fell following these two transgressive events.