SEDIMENTOLOGICAL MODEL FOR A SMALL LAKE IN THE LAKE MICHIGAN COASTAL DUNE ZONE

Sediments in small lakes within coastal dune complexes are potential sources of information on their geomorphic history. In order to decipher this history, it is important to have a sedimentological model that gives the sources of sediment and the processes distributing these sediments within the lake. Goshorn Lake is on the eastern shore of Lake Michigan north of Saugatuck, Michigan. The western margin of the lake abuts coastal dunes, and a stream enters the lake at the northeastern edge. Before European settlement the lake was surrounded by a mesic oak-maple forest but is now rimmed by cottages. Three vibracores, three Livingstone cores and six Glew cores were collected from different parts of the lake. Smear slides, radiocarbon dating, ¹³⁷Cs analysis, and textural analysis were used to investigate the stratigraphy and sedimentological history of the lake. Near the bottom of the vibracores marls and clays, both containing abundant sponge spicules and diatoms, are interbedded with sand containing sparse sponge spicules and diatoms all of which are overlain by gyttja. This stratigraphy suggests a transition from a stream to marginal wetland to a lake sometime after 5600 cal yr BP, and may mark damming of the stream mouth by the coastal dunes. In the vibracores and Livingstone cores the amount of sand in the gyttja increases toward the dunes, and is variable throughout the core, suggesting that the dunes were the primary source of sand in the lake. Thick sandy layers occur in Glew cores taken from near the shores of the lake away from the dunes. This may suggest pulses of sand stemming from recent cottage development activities around the periphery of the lake.