Organic matter biomarker analysis as a potential chemostratigraphic tool for Late Pleistocene tills from the Hudson Bay Lowlands, Canada

During the Last Glacial Maximum approximately 22,000 years ago, the Hudson Bay Lowlands (HBL) lay at the center of the 3 km thick Laurentide Ice Sheet. During the course of the last glacial cycle HBL was crossed by ice from the west (the Keewatin sector) and from the east (Labrador sector) but the relative influence of the outflow centers is debateable because of continuing uncertainty surrounding the age and stratigraphic position of lithologically-similar tills in different areas. This study examines the use of organic matter (OM) biomarkers to analyze OM sources in HBL tills. These tills are believed to be of late Wisconsin age (Sachigo, Severn) and an older possibly early Wisconsin deposit (Rocksand Till) and biomarkers may provide insights into source materials and degree of diagenesis. Solvent extraction, base hydrolysis, and cupric oxide oxidation were performed to isolate and quantify free lipids, bound lipids, and lignin-derived phenols respectively. Lipid biomarker patterns indicate higher Sphagnum-derived OM to the Severn and Rocksand tills relative to the Sachigo Till consistent with subglacial reworking and incorporation of peat. OM within the Severn Till is dominated by OM derived from non-woody gymnosperms and non-woody angiosperms whereas Sachigo and Rocksand tills have both woody and non-woody gymnosperms and angiosperms derived OM. Furthermore, the Severn Till contained the most suberin-derived OM, while the Sachigo Till had the least. Acid-to-aldehyde ratios of lignin-derived phenols suggest that the Severn Till has undergone less diagenesis in comparison to Sachigo and Rocksand confirming that it is likely the youngest of the three tills. This study highlights that biomarker analysis is an important chemostratigraphic tool that may distinguish till deposits and provides insight into paleovegetation and paleoclimate in the HBL prior to glacial incorporation of OM into till. This information facilitates paleoenvironmental analyses to be extended into preglacial and interstadial episodes where no stratigraphic record exists.