The origin and dynamics of coastal processes at Sand Point, Pictured Rocks National Lakeshore, Michigan, USA

Castaneda, Mario

AMS (accelerator mass spectrometer) ages from basal paludal sediment collected from three ponds on Sand Point were integrated and analyzed with geomorphic mapping, OSL (optically stimulated luminescence) dating from beach ridges, topographic survey, inland and offshore GPR (ground penetrating radar) surveys and a seismic survey of the Grand Island Harbor Basin to understand the age and evolution of Sand Point, Pictured Rocks National Lakeshore. GPR and seismic analysis define Sand Point as an emergent cuspate foreland or spit. The evolution of Sand Point likely began at deglaciation and the rate increased shortly before and after the peak Nipissing level. According to radiocarbon dating, Sand Point did not emerge from wave base until approximately 1200 years ago. The origin and age of Sand Point was hypothesized to “represent a composite feature, emplaced during the peak of the Nipissing Transgression 6500-4500 cal BP, and was modified and eroded by wave action 4500-1500 cal BP, and augmented by sand nourishment from friable sandstone bedrock during the transgression of Lake Superior 1500 cal BP to the present”.