Accurately reconstructing the rate of movement and extent of eolian dunes over thousands of years is a challenging endeavor. In this paper, we refine the methodology for utilizing lakes and bogs downwind of dune fields as precise recorders of past eolian activity. Sediment cores from two Allegan County lakes and one bog associated with dunes were studied to evaluate the importance of the various sand transport pathways into lakes and bogs. Goshorn Lake's western edge directly abuts a large parabolic dune. Sand concentrations decrease in cores away from the dunes, possibly reflecting avalanching into the lake followed by sediment gravity flows along the lake bottom. Sand input from stream flow was minor. The Allegan Bog core records a fen-emergent bog transition coincident with a decrease in the sand influx. Poorly understood shoreline processes may have contributed sand to the basin's center before the bog's emergence. Sand in Gilligan Lake cores is texturally similar to adjacent dune sand and the eolian activity history derived from this sand is nearly identical to the history derived from the dune's paleosols and optically stimulated luminescence ages. A proposed lake and bog sampling strategy includes choosing sites in the lee of large dunes edged with emergent vegetation and away from steep slopes or stream inlets. The lake's bathymetry should also be considered. Distinguishing between grain fall sedimentary structures and mass movement or sediment gravity flows is important. This strategy provides relatively high resolution, continuous eolian activity histories that can be correlated with paleoenvironmental proxies from the same cores.

ABSTRACT Loess mantles upland summits across much of the Driftless Area of southwestern Wisconsin and its origin and paleoenvironmental significance has been a focus of research since the nineteenth century. Although the Driftless Area was ice free through the many glaciations of the Quaternary, long-term preservation of loess was limited by post-depositional erosion across much if not all of this highly dissected landscape, erosion that was likely accelerated under periglacial conditions during glaciations when ice sheets were nearby. Loess preserved today includes four members of the Kieler Formation and two older loesses known only from one locality. The Peoria Member, the youngest, thickest, and most extensive member of the Kieler Formation, was deposited during and just after the peak of the last glaciation. Its main sources include both the Mississippi River valley and the Iowan Erosion Surface and glacial outwash surfaces farther west in Iowa and Minnesota. More research is needed on the relative contribution from each of these sources to the Peoria Member, and on the sources of older loess units. Eolian sand, often forming dunes, covers extensive low-relief landscapes in the northern Driftless Area, the Mississippi and Wisconsin River valleys, and smaller areas elsewhere in the region, overlying sandstone bedrock, stream terraces, and the former bed of Glacial Lake Wisconsin. These sands are stabilized by vegetation today but were active during and just after the period of Peoria Member deposition. Thus, large areas of eolian sand acted as surfaces of transport where loess did not accumulate but rather was conveyed far downwind of its sources. Colluvium that is a mixture of bedrock-derived sediment and loess covers bedrock slopes throughout the Driftless Area. A variety of geochronologic, geomorphic, and stratigraphic evidence supports the hypothesis that this colluvial mantle formed mainly in the cold, periglacial environment of the last glaciation, with only limited modification during the Holocene. A new research effort, incorporating modern geochemical and geochronological techniques, could provide important insights on the processes that originally produced the colluvial mantle and those that are acting on it today.

Interrelationships among late Holocene climate, the dynamics of coastal dunes and sedimentation in adjacent small lakes along coasts of the upper Great Lakes have been studied for over a decade. Nonetheless, many questions remain as to relationships between climate variability and dune activity. The study site is Oxbow Lake, near Saugatuck, Michigan, which formed as an artificial cutoff of the Kalamazoo River in 1906. Stratigraphic control of the infilled western end of the lake is from ground penetrating radar, and lake sediment from Livingstone and Glew cores with age control from 210 Pb/ 137 Cs/ 7 Be analysis. The climate data used included Lake Michigan water levels and temperature, precipitation, drought and evaporation data from a weather station 30 km to the south and wind data from buoys on Lake Michigan. Episodic peaks of eolian sand in the lake sediment are interpreted to be sourced from adjacent small parabolic dunes along the shoreline and from a foredune west of the lake. Linear regressions of the climate data and weight percent sand resulted in a variety of correlations, some conflicting, and with uncertain meanings. It was found through visual correlation that peaks in sand correspond with both peaks in water levels of Lake Michigan and the winter Palmer drought severity index. The implications of this research are that dune activity is linked to periods of wet conditions and storminess, contrary to typical eolian environments, but consistent with other studies in temperate coastal dunes along the Great Lakes. Results can be used as a modern analogue for coastal dune activity during times of high lake level.

Eolian sands tend to be fine grained and quartz rich. This mineralogical maturation may be attributed to mechanical breakdown of sand-size feldspar grains and their subsequent winnowing from dune fields. During eolian transport, ballistic impacts between saltating grains and stationary grains on the ground are very common. If the impact is sufficiently strong, the collision may be inelastic and part of the kinetic energy of the incident grain may be dissipated through inelastic deformation and subsequent breakdown of the grains involved in the collision. The theoretical calculation presented in this chapter indicate that the mechanical breakdown of feldspar sand grains through ballistic impact can be achieved if wind speed exceeds 10 m·s −1 . Therefore, quartz-rich sand can result from ballistic impacts between sand grains in deserts.