EARLY HOLOCENE EOLIAN ACTIVITY, HURON MOUNTAINS, UPPER MICHIGAN

Multiple lines of evidence document dry climatic conditions in the upper Great Lakes region during the early Holocene (ca. 9 ka), including hydrologic closure of lakes in the Michigan, Huron and Superior basins. The terrestrial response to early Holocene dry climate was recently investigated in eastern Upper Michigan through optical (OSL) dating of eolian sand. Ages from eastern Upper Michigan document dune activity and synchronous reduction in ground cover between 10 and 8 ka (Loope et al., 2012). This project, located within the Huron Mountains in west-central Upper Michigan, aims to extend the potential spatial distribution of terrestrial response to early Holocene dry climate. Data collection included: 1) surficial geological mapping through use of soil survey data and bucket augering, 2) nine ground penetrating radar (GPR) transects totaling three kilometers in length documenting subsurface stratigraphy, 3) high-resolution topographic mapping of a large (10 m high) parabolic dune using a total station, 4) collection of six samples for optical dating of eolian sand from three sites, 5) particle size analysis of eolian and glaciolacustrine sediments. Results from augering, GPR, topographic surveying, and particle size analysis indicate eolian sand (from 0 to >6 m in thickness) overlies coarse-grained (medium sand to pebbles) and fine-grained (fine silt) glaciolacustrine sediment. We interpret the glaciolacustrine sediment as nearshore (coarse-grained) and offshore (fine-grained) deposits of an unnamed glacial lake that stood at ca. 255 m asl in the study area. Based on its altitude and location north of the Yellow Dog Plains (presumed Marquette Stadial ice margin ca. 11,500 cal yr BP), the unnamed glacial lake existed sometime between 11,500 and 10,600 cal yr BP. Optical ages on eolian sand range between 9.6 and 8.6 ka (mean of 9.2 ka), indicating a gap between glacial lake drainage and eolian activity. Optical ages from the Huron Mountains are in alignment with those from eastern Upper Michigan, suggesting a westward extension of dune activity and terrestrial response to early Holocene dry climate.