Constraining the Late Pleistocene history of the Laurentide Ice Sheet by dating the Missinaibi Formation, Hudson Bay Lowlands, Canada

Abstract

Well-dated paleorecords from periods prior to the Last Glacial Maximum (LGM) are important for validating models of ice-sheet build-up and growth. However, owing to glacial erosion, most Late Pleistocene records lie outside of the previously glaciated region, which limits their ability to inform about the dynamics of paleo-ice sheets. Here, we evaluate new and previously published chronology data from the Missinaibi Formation, a Pleistocene-aged deposit in the Hudson Bay Lowlands (HBL), Canada, located near the geographic center of the Laurentide Ice Sheet (LIS). Available radiocarbon (AMS = 44, conventional = 36), amino acid (n = 13), uranium-thorium (U-Th, n = 14), thermoluminescence (TL, n = 15) and optically stimulated luminescence (OSL, n = 5) data suggest that an ice-free HBL may have been possible during parts of Marine Isotope Stage 7 (MIS 7; ca. 243,000 to ca. 190,000 yr BP), MIS 5 (ca. 130,000 to ca. 71,000 yr BP) and MIS 3 (ca. 29,000 to ca. 57,000). While MIS 7 and MIS 5 are 2 well-documented interglacial periods, the development of peat, forest bed and fluvial deposits dating to MIS 3 (n = 20 radiocarbon dates; 4 TL dates, 3 OSL dates), suggests that the LIS retreated and remained beyond, or somewhere within, the boundaries of the HBL during this interstadial. Ice sheet models approximate the margin of the LIS to Southern Ontario during this time, which is 700 km south of the HBL. Therefore, if correct, our data help constrain a significantly different configuration and dynamicity for the LIS than previously modelled. We can find no chronological basis to discount the MIS 3 age assignments. However, since most data originate from radiocarbon dates lying close to the reliable limit of this geochronometer, future work on dating the Missinaibi Formation using other geochronological methods (e.g. U-Th, OSL) is necessary in order to confirm the age estimates and strengthen the boundaries of the LIS during this period.

Sea-level records from the U.S. mid-Atlantic constrain Laurentide Ice Sheet extent during Marine Isotope Stage 3

“…While few field data constrain the evolution of the LIS before the LGM245, a recent field-based study by Dalton et al 34. suggests that large portions of eastern Laurentia were ice-free during MIS 3 (Fig.…”

Deglaciation of the Laurentide Ice Sheet from the Last Glacial Maximum

“…It grew rapidly from its initial inception over the Arctic/sub-Arctic plateaux along the eastern seaboard of Canada and likely attained an MIS 4 maximum around 65-60 ka (Marshall et al, 2000;Stokes et al, 2012). Its extent during MIS 3 is uncertain (Dredge and Thorleifson, 1987;Stokes et al, 2012;Dalton et al, 2016), but it grew rapidly to its Local Last Glacial Maximum, which was attained around 26-25 ka (e.g. Dyke, 2002;Clark et al, 2009), although with some regions advancing much later, such as in the far north-west (Lacelle et al, 2013).…”

“…Kleman et al, 2010) that have survived modification and, in some places, been dated to periods prior to the LGM (e.g. Allard et al, 2012;Dalton et al, 2016).…”

“…Following this event, the general consensus is that there was virtually no ice cover in North America during the peak of the MIS 5 (Sangamonian) interglacial (~125-122 ka), which is primarily based on ages obtained from organic-rich sediments in the Hudson Bay Lowlands (e.g. Allard et al, 2011;Dalton et al, 2016) and a widespread acknowledgement that global sea levels were 6-9 m higher than present during MIS 5e (e.g. Dutton et al, 2015).…”

“…Indeed, the extent of the ice sheet during MIS 3 is very poorly constrained (e.g. see review in Dredge and Thorleifson, 1987), with numerical modelling indicating a relatively large ice sheet that stored up to 30 m of sea level equivalent at 55 ka (Marshall et al, 2000;Stokes et al, 2012), but with a suite of new dates raising the possibility that the Hudson Bay Lowlands, close to the geographic centre of the ice sheet, were completely ice free between ~50 and ~40 ka (see Dalton et al, 2016). Following the MIS 3 minimum, the ice sheet underwent gradual expansion that was punctuated by episodes of successively less recession (e.g.…”