Extending the western Hudson Bay Lowland Quaternary stratigraphy, in Manitoba Canada, to at least Marine Isotope Stage 10

Quaternary stratigraphy can improve our understanding of glacial dynamics prior to the Last Glacial Maximum. This study uses a hybrid lithostratigraphy–allostratigraphy approach to decipher the stratigraphic record in the Gillam area of the western Hudson Bay Lowland, Manitoba, Canada. The region experienced multiple glaciations, and previous studies were limited to correlating nonglacial “marker beds” amongst numerous till–till contacts. New study of the tills has led to identification of nine glacial (till) units, one pre-Holocene nonglacial (sorted sediment) unit and a paleosol; constrained by radiocarbon and optical age datasets. The composition of most tills in the Gillam area is calcareous-rich and non-distinctive. Nonetheless, our new ice-flow history shows repeated patterns during at least four glacial–interglacial cycles; dominated by ice flowing from the Quebec–Labrador sector of the Laurentide Ice Sheet. The stratigraphic framework, and a quartz optical age estimate, suggest the intertill organic-rich sorted sediments (“Nelson River Sediments”) were deposited during Marine Isotope Stage (MIS) 7 (∼183 ± 21 ka (1σ MAM, sample HBL22-2)). Quantitative analysis of interglacial pollen from the same interval suggests increased annual precipitation (679.3 ± 201.7 mm) and slightly warmer-than-present summer temperatures (14.5 ± 1.6 °C), within a boreal forested environment ( Picea-dominated) with sufficient moisture and nutrients to allow for fen expansion ( Larix and Cyperaceae). This new interpretation pushes the underlying interglacial “Sundance paleosol” to MIS 9 and the tills below to MIS 10 or older. The regional timing and ice-flow history allow for constraints long into the Pleistocene, providing a rare dataset to constrain future modeling efforts.