DECIPHERING THE EXCEPTIONAL QUATERNARY STRATIGRAPHIC RECORD OF SOUTHWEST HUDSON BAY, CANADA

The Hudson Bay Lowland (HBL) contains some of the most extensive depositional records of glacial and nonglacial events from inside the limits of the Laurentide Ice Sheet, including at least the last 3 glacial cycles (MIS 2 to MIS 7). The Quaternary stratigraphy in southwestern Hudson Bay has nonglacial units which have been assigned to either ‘the last interglacial’ or the ‘pre-last interglacial’. There is a lack of reliable chronological constraints on both the glacial (typically till) and nonglacial units, leading to correlations based on elevation and relative stratigraphy and the stratigraphic record is also fragmented due to spatio-temporal changes in subglacial conditions controlling erosion/deposition. Here we present new observations from one area, which indicate there are at least twelve stratigraphic units. These units are based on the correlation of tills using multiple proxies (sedimentology, clast fabrics and composition) and the stratigraphic relationships between glacial and nonglacial units. Three nonglacial units, and possibly a fourth, are recognized. This includes a rare record of three nonglacial units at one section. In particular, intertill organic-bearing units at two previously-studied sections (Flamborough and Port Nelson, just 9 km apart) are now correlated as two separate nonglacial events. A new infinite (>55 000 ¹⁴C yr) radiocarbon age on wood from the Flamborough nonglacial sediments contradicts previous MIS 3 TL ages at both sections. The Flamborough intertill sediments (MIS 5e?) are younger than the Port Nelson intertill sediments (MIS 7?) based on the revised stratigraphy of the study area. This study affirms that intertill organic-bearing units should only be correlated with supporting stratigraphic evidence since there are multiple nonglacial units and that additional chronologic constraints are needed in the HBL. This work highlights the importance of using multiple proxies and results have implications for paleo-ice sheet reconstruction and characterization of the paleoenvironmental conditions during nonglacial periods from MIS 7(?) to 2.