Geological Sciences

摘要

We investigated three Allegan County bogs to determine their stratigraphies and geologic histories and to look for regional patterns in these histories. We collected sediment cores in one-meter intervals from the surface down to the lowermost sand layer. We made smear slides every 15 cm along the core and estimated percentages of clastic, authigenic, and biogenic components, organic matter, and aquatic amorphous organic matter to determine the core's composition and to establish where changes in the core's composition occurred. Glacial lake plain sand underlies all three bogs indicating that each bog began as a small, shallow lake formed in shallow depressions left by the retreating glaciers. In two bogs, a rich fen, indicated by the presence of marl, developed. Algal gyttja deposition initially occurred in the third bog and then was followed by marl deposition. The marl deposition was succeeded by the development and accumulation of aquatic peat, probably dominated by sedges. Eventually, enough aquatic peat was deposited to raise part of the mound above water. A Sphagnum-rich bog then developed on this emergent surface, causing the deposition of peat. Currently, these bogs are each dominated by a Sphagnum- and heath-rich bog community.