SURFICIAL GEOLOGICAL MAPPING IN MUSKEGON COUNTY, MICHIGAN USA: LATE WISCONSIN LANDFORMS AND STRATIGRAPHY OF THE LAKE MICHIGAN LOBE

Surficial geologic mapping in Muskegon County, Michigan provides insight into sediments, landforms, and stratigraphy formed by the Lake Michigan lobe (LML) during at least two glaciations. The maximum extent of the late Wisconsin LML is marked by the Valparaiso moraine complex, composed of interbedded sand, gravel, and diamicton that formed as an ice margin, outwash fans, and meltwater channels sloping southward. The Lake Border moraine trends NW-SE, in two ridges in the southeastern Muskegon County, and buried beneath pitted outwash and glaciolacustrine sediment (slightly gravelly sand to gravelly sand) in the northwest. In northwest Muskegon County, the Whitehall-Montague moraine complex consists of two ridges of diamicton and glaciolacustrine fines, with areas of glaciolacustrine and outwash in front of and between the ridges. In the southwest these ridges are buried by glaciolacustrine sediment of Glacial Lake Chicago (GLC). Extensive areas of the county are covered with organic sediment, legacy sediment-alluvium, and coastal and inland eolian dune sediment (sand).

The surface diamicton within the Whitehall-Montague (Montague till) is reddish-brown to gray in color, fine-grained, and was likely deposited during the Port Huron Phase (~15,000 cal yr BP). Results from cores confirm that the Saugatuck till (gray to dark gray diamicton with a fine-grained to sandy matrix) is the surface till in the Valparaiso and Lake Border moraines. GLC sediments occur at elevations >207 m (>680 ft) in central/western Muskegon County and are up to 68 m thick (223 ft). Maximum GLC levels likely occurred after the advance to the Lake Border position during the Glenwood phase. Below the Saugatuck till and surface sediments is a up to 45 m thick (~150 ft), package of sandy to fine-grained glaciolacustrine sediment of Glacial Lake Milwaukee (GLM). GLM existed before the advance to the Kalamazoo moraine during the Crown Point Phase. The Ganges till (late Wisconsin) and Glen Shores till (Pre-Illinoian) occur in the subsurface below GLM sediments. In 3 of 7 cores, we found organic sediments that are likely correlate to the Port Sheldon Formation. Buried organics, both in-situ and detrital produced non-finite radiocarbon ages of >47,000 cal yr BP and likely were deposited during MIS-5 to MIS-3 before the last Late Wisconsin Glaciation (MIS-2).