Compositional changes in deglacial red mud event beds off the Laurentian Channel reveal source mixing, grain-size partitioning and ice retreat

• Published in: Quaternary Science Reviews
• Main Authors: Leng, Wei, Dobeneck, Tilo von, Just, Janna, Govin, Aline, St-Onge, Guillaume, Piper, David J.W.
• Format: Article in Journal/Newspaper
• Language: French
• Published: 2019
• Subjects: Ice Sheet; Newfoundland; North Atlantic
• Online Access: https://semaphore.uqar.ca/id/eprint/1817/; https://semaphore.uqar.ca/id/eprint/1817/1/Wei_Leng_et_al_mai2019.pdf; https://doi.org/10.1016/j.quascirev.2019.04.031

Between 22 and 17 cal ka BP, five large meltwater events from within the Laurentian Channel Ice Stream deposited mud beds meters thick across a large area of the Laurentian Fan and adjacent continental slopes. This study determines the sources of these event beds and relates them to the glaciological evolution of the retreating Laurentian Ice Stream. We analyzed major element and magnetic mineral contents of these event beds and compare them with a new collection of 80 source reference samples from the Gulf of St. Lawrence area. Element ratios suggest a steady compositional change from older to younger outburst event beds, while element-specific offsets from reference sample compositions indicate grain-size and mineral/element partitioning during suspension transport. Their magnetic properties place event beds on the source mixing trend of four reference samples groups, which represent two magnetite-rich sources (Canadian Shield and/or Southern Newfoundland) and two hematite-rich sources (Appalachian red beds). Using a deterministic linear source mixing model based on IRM100mT, HIRM and Ca%, we find that the earlier two outburst events had higher contributions from granitic and calcareous sources than the later three events. Combining materials, timing and scenarios of the outburst events with ice-sheet retreat and ice-stream dynamics, we argue that the subglacial sediment depocenter of the earlier two event beds was located in the lower Laurentian Channel while that of the later three events was upstream from Cabot Strait. -- Keywords : Quaternary Paleoceanography North Atlantic Sedimentology-marine cores Gulf of St. Lawrence Laurentian Channel Ice Stream Subglacial outburst floods Environmental Magnetism Major element analysis Provenance study.