Paper No. 7
Presentation Time: 9:30 AM
EOLIAN SAND RECORDS PALEOCLIMATIC FLUCTUATIONS DURING THE MID- TO LATE HOLOCENE IN THE SOUTHERN LAKE MICHIGAN BASIN
Eolian sand deposited in three embayed lakes downwind of coastal dunes along southeastern coastal Lake Michigan, the Grand Mere Lakes in Berrien County, Michigan, record paleoclimatic fluctuations. Sediment cores were sampled at 1-cm intervals, processed to remove all but the sand, and then analyzed for variations in weight percentage of sand with depth. Peaks and troughs in the concentration of eolian sand correspond to Lake Michigan lake-level fluctuations and coastal dune formation since the onset of the Nipissing stage. Radiocarbon dates from wood within basal lake sediments returned an average age of ~6800 cal BP. These and subsequent dates obtained at or near changes in sediment type were used to develop an age-depth model, from which sedimentation rates were derived: Carbonate-rich mud, 0.03 cm/yr; Sapropel, 0.05 cm/yr; and Peat, 0.11 cm/yr. Spectral analyses of the sand data versus age indicate several strong periodicities, including 37–47 yrs; 55–66 yrs; 80–85 yrs; 92–101 yrs; 110–127 yrs; 136–147 yrs; 189–195 yrs; 203–213 yrs; 267–279 yrs; and 1400–1500 yrs. These can be compared to periodicities from other studies, such as the Lake Michigan beach ridge cycle (~33 and ~120–200 yrs); sand signal data from west-central Michigan (~46, ~80–111, and ~160 yrs); geochemical and varve data from Elk Lake, MN (~40–60, ~84, and ~200 yrs); solar variation (~88, ~80–120, and ~150 yrs); historical and beach ridge data from the southwestern Lake Michigan coast (~100–150 yrs); and North Atlantic drift-ice sediment (~1500 yrs). One of the strongest periodicities derived, the 267–279 year cycle, does not closely correspond to any known cycles. The eolian sand peaks and common periodicities between the Grand Mere Lakes sand data and other studies suggest that this new dataset is not random, and is best explained as a record of paleodune mobility. The dataset is a paleorecord of wind or storminess in the southern Lake Michigan basin, from the mid- to late Holocene, and thus may be an effective proxy for paleoclimate in the southern Lake Michigan basin.