Mineralogy and Distribution of Fine-Grained Sediments in Little Traverse Bay, Lake Michigan

Abstract

Little Traverse Bay, northeastern Lake Michigan, contains sediments ranging in mean grain size from about 1.5ϕ around the bay margins to 7ϕ in the central portion. Mineralogy of the fine-grained fraction of these sediments show the four main mineral groups, quartz, feldspars, clays, and carbonates to have decidedly different distributions within the bay. Quartz and feldspar reach maxima near the center of the bay, while carbonates are highest around the edge. Clay mineral abundance reaches three separate maxima in regions characterized by very poorly sorted sediment. There are two important sources of these sediments, extensive outcrops of Devonian limestones and dolomites along the south shore of the bay and bluffs of reddish glacial till along the northwestern shoreline. Materials from these areas are transported eastward to the bay head by longshore transport incurred by the prevailing westerly winds and then return westward along the deep central trough of the bay as the wind-induced setup is relieved. Essentially all of the calcite and much of the dolomite entering Little Traverse Bay undergoes dissolution during transport resulting in the carbonate-poor sediments of the bay floor.