Determining Late Pleistocene to Early Holocene Deglaciation of the Baltic Ice Lake Through Sedimentological and Geochemical Analysis of IODP Site M0064

• Main Author: Kelly, April Lynn
• Format: Text
• Language: unknown
• Published: Montclair State University Digital Commons 2017
• Subjects: Earth Sciences; Environmental Sciences; Ice Sheet
• Online Access: https://digitalcommons.montclair.edu/etd/440; https://digitalcommons.montclair.edu/cgi/viewcontent.cgi?article=1441&context=etd

IODP Site M0064 within the Baltic Sea’s Hanô Bay was drilled to investigate the déglaciation history of the Scandinavian Ice Sheet (SIS) from the Late Pleistocene to the Holocene. This research aims to better understand how déglaciation speed, SIS drainage patterns, and changes in relative sea level influences sediment deposition within the Baltic Ice Lake (BIL) on a high-resolution timescale. Site M0064 contains diamicton at -47 - 9 mbsf, followed by an upward transition to cm-scale grey thinly laminated rhythmites at -8 mbsf, and a sharp 2.5 cm thick dark brown organic layer at -7.87 msbf, transitioning to reddish-brown thinly laminated rhythmites up section. Previous modeling, glacial till, and surface exposure dating studies have suggested ice retreated near the project site -16.7 ka BP, signifying the project site underwent a subglacial to proglacial transition within the SIS’s most recent déglaciation between 20 and 14 ka BP. This research uses particle size analysis to determine the late glacial depositional environment, and ICP-OES, -MS and XRF geochemical analysis to decipher the potential redox changes, Zr/Al ratios to understand meltwater current strength, and Al/Ti ratios to shed light on sediment provenance. Samples were chosen based on high-resolution core images using color and compositional transitions. XRF core scanning of the varve sequence at 1 -cm intervals increased geochemical resolution of all listed elemental ratios. Averaged varve counting provided the time Site M0064 was influenced by annual meltwater fluxes, -72 years. Particle size results yield a subglacial to proglacial shift, however alternating silt and clay layers in the notably colorchanging varve sequence exhibit no grain size variation. Mn/Al ratios show little to no variation in redox sensitivity, and Zr/Al ratios exhibit no meltwater spikes across the color change. Grey varves in Unit Illb display remarkable Th-enrichments, indicating a likely source change from a south central Swedish province, or the Norwegian Oslo igneous province, while the brown organic layer and red varves may originate from the Esrum/Alnarp paleovalley Jurassic red sandstones and coal seams. Based on data collected, the color shift in the varve sequence is not a direct result of the BIL drainage 11,620 ka BP, but potentially an indirect result, causing a provenance change.