THE ANTIGO LOESS SHEET IN NORTHEASTERN WISCONSIN

The Antigo loess sheet covers much of the Late Wisconsin-aged outwash plain centered on Langlade County, Wisconsin. This area, known as the “Antigo Flats,” contains many hectares of soils formed in 50-100+ cm of loess over outwash sand and gravel; it lies in the rectangularly shaped re-entrant between the Harrison, Parrish and Hancock moraines. The Antigo Flats have had such longstanding popularity that the state soil of Wisconsin – the Antigo Silt Loam – is named for this locality. In this poster, we present spatial characteristics of the thickness and textural properties of the loess cover on the Antigo Flats, based on >100 samples. These data are used to ascertain the possible source area(s) for the loess. Because loess commonly exhibits strong spatial trends relative to its source area, this approach was deemed appropriate for ascertaining the likely source of the loess on the Antigo Flats. Additionally, we report on the first OSL age from this loess sheet, from a site in thick loess very near the Hancock moraine. Textural data show that the Antigo loess coarsens markedly at the edge of the loess sheet - nearer to the three fringing moraines - particularly in the 35-75 um fraction. This would support the hypothesis that the moraines themselves, which have an abundance of fine sand drift, and also have numerous ice-walled lake plains with silty lake floor deposits, are the main sources of the loess. The OSL age on the loess - 13.2 ka - suggests that loess was being deposited onto the Antigo Flats for several millennia after the main glacial advance, perhaps because of the slow meltout of permafrost in the moraines and the concomitant degradation and draining of the ice-walled lake plains. Lastly, soil pits in the thick loess near the moraines suggest that loess deposition in these proximal areas may have been interspersed with, or contemporaneous with, outwash deposition, while at sites farther from the ice front the landscape was drier and loess was accumulating mainly onto previous deposits of loess.