A 10BE BASED CHRONOLOGY FOR THE ARNOTT MORAINE OF THE LAURENTIDE ICE SHEET, CENTRAL WISCONSIN

Our understanding of the Laurentide Ice Sheet prior to Marine Isotope Stage (MIS) 2 phase is limited, stemming from a lack of terrestrial paleoclimatic archives. Evidence of pre-MIS 2 glaciations is primarily from marine sediment cores, which provide an integrated spatiotemporal signal of glaciation based on oxygen isotopes from benthic foraminifera (Raymo, 1994). These records lack the ability to provide information about specific ice sheets or lobes within an ice sheet. Apart from a small number ages on the maximum-extent (Balco and Rovey, 2010), numerical constraints are lacking on pre- MIS 2 landforms for the Laurentide Ice Sheet (LIS). Determining the timing of past ice-sheet extents during pre-MIS 2 glaciations is important for constraining past sea level changes and the specific ice-sheet contribution (e.g. Mitrovica et al., 2009) as well as providing boundary conditions for constraining paleoclimate model simulations (Kleman et al., 2013; Abe-Ouchi et al., 2015).

Despite long-standing age estimates of pre-MIS 2 glacial landforms in Wisconsin (Weidman, 1907; Clayton, 1986; Attig and Muldoon, 1989), no direct age estimate to constrain the timing of their deposition. The Arnott Moraine in central Wisconsin is a 19 km-long sinuous ridge containing erratic boulders, located ~4 km beyond of the MIS-2 aged Hancock and Almond Moraines. The moraine represents a stand-still of the Green Bay Lobe of the LIS that predates the MIS 2, and based on its degree of weathering, subdued topography, is estimated to date from the Pliocene to late Pleistocene (Weidman, 1907; Clayton, 1986; Attig and Muldoon, 1989). Because of a lack of precise age control on the moraine, we have collected ~30 samples from quartz-bearing boulders located on the crest of the moraine for cosmogenic surface exposure dating. These new exposure ages will provide the first age constraints of this pre-MIS 2 moraine and provide new information about moraine construction and past climate conditions. At the meeting, we will present our newest ages (currently awaiting measurement) and our ongoing work related to the study.