No abstract

Outcrops of buried soils on lake-plains and glacial headlands along Lake Michigan's eastern shore suggest that periodic dune-building has occurred there after relatively long (≥100 yr) periods of low sand supply. We located, described, and radiocarbon dated 75 such buried soils that crop out in 32 coastal dune fields beside the lake. We assume that peaks in probability distributions of calibrated 14C ages obtained from wood, charcoal, and other organic matter from buried A horizons approximate the time of soil burial by dunes. Plotted against a late Holocene lake-level curve for Lake Michigan, these peaks are closely associated with many ∼150-yr lake highstands previously inferred from beach ridge studies. Intervening periods of lower lake levels and relative sand starvation apparently permitted forestation and soil development at the sites we studied. While late Holocene lake-level change led to development and preservation of prominent foredunes along the southern and southwestern shores of Lake Michigan, the modern dune landscape of the eastern shore is dominated by perched dunes formed during ∼150-yr lake highstands over the past 1500 yr.

No abstract

The central Great Plains is an excellent place to study late-Quaternary geomorphic responses to climatic fluctuations because the landscape is easily disturbed and deposits contain abundant paleoenvironmental information. Although much research has already been conducted, studies are needed that correlate a variety of geomorphic responses to environmental change at specific sites. This paper presents a paleoenvironmental and geomorphic reconstruction for the Great Bend Sand Prairie, a mosaic of sand sheets and dune fields in south-central Kansas. Results indicate that two stratigraphic units dominate the upland geology. Late-Wisconsin deposits consist of poorly sorted sand, silt, and clay that probably accumulated in a low-energy fluvial environment. Eolian deposition of loess also occurred, but most silt was integrated with the alluvium. Intact deposits of loess are widely scattered. All sediments contain well developed soils, indicating extended surface stability. Macrofossil and isotopic (δ 13 C) evidence suggest a mesic environment. Where eolian sedimentation did occur, northwest winds were responsible for mobilization. Although late-Wisconsin strata crop out intermittently, eolian sand is the common surficial deposit. Radiocarbon dating indicates that most dunes are Holocene landforms. In comparison to late-Wisconsin deposits, dune sands are well sorted, δ 13 C values infer a relatively warm climate, and the orientation of parabolic dunes indicate mobilizing southwesterly winds. Dunes usually contain one or two weakly developed buried soils, indicating episodic mobilization of eolian sand in the latest Holocene. Surface soils are generally poorly developed, suggesting that dunes can easily be mobilized if vegetation is reduced, perhaps due to C02 warming.

No abstract