Sediment Source for Sand Dunes in the Green River Lowland
A new publication reports ages for sand dunes in the Green River Lowland, Illinois, and suggests a potential sediment source. The paper by Xiaodong Miao and others is titled "Timing and origin for sand dunes in the Green River Lowland of Illinois, upper Mississippi River Valley, USA" and appears in Quaternary Science Reviews, volume 29, pages 763-773. The reported information provides a better understanding of the dynamic interactions between eolian, glacial, lacustrine, and fluvial processes that shaped the landscapes of the Upper Midwest. The seven coherent optically stimulated luminescence ages (OSL) that were obtained from four sites suggest that major dune construction in the Green River Lowland occurred within a narrow time window around 17,500 years ago. This timeframe implies either enhanced aridity, or an episodic increase of sediment supply at 17,500 years ago, or both. Contrary to previous assertions, dune sand appears to have been sourced from the deflation of the underlying outwash sand deposited when the Lake Michigan lobe retreated from the area. In their article, the authors propose that Green River Lowland dunes sand originated from the Green Bay lobe through the Rock River, a scenario that explains the abrupt dune construction around 17,500 years ago and the lack of later dune activity up to the Pleistocene-Holocene transition.
Both OSL and radiocarbon ages indicate that the dunes were reactivated during the early, middle, and late Holocene Period. Some eolian activation occurred within well-defined dry intervals in the Upper Midwest, suggesting that increased aridity may have been the primary driver in mobilizing sand. However, many ages do not correspond to drier periods. In contrast to the relative coherency shown by the Pleistocene OSL ages from multiple study sites, the Holocene OSL ages do not overlap among sites, suggesting that increased aridity alone cannot explain the multiple phases of dune reactivation during the Holocene. The effects of localized disturbances and greater aridity acted in concert to increase eolian sand activity during the Holocene. These multiple periods of eolian activity during the Holocene suggest a high potential for future sand activation in the region and are informative for environmental prediction and potential future mitigation.