Extent and glacial history of the Cordilleran Ice Sheet in northwest Montana: Using OSL to date glacial sediments from the southeastern Flathead Lobe.

• Main Author: Shukla, Vidhesh
• Format: Thesis
• Language: English
• Subjects: Flathead Lobe; Geochronology; Quaternary Geology; OSL Dating; Geomorphology; Glaciology; Glacial Lake; Mission Valley; Ice Sheet; Alaska
• Online Access: https://hdl.handle.net/2097/43469

Master of Science Department of Geology Joel Q Spencer This thesis investigates glacial sediments in the Flathead Valley, Polson, Montana that were deposited during the last glacial period (~115,000 – 11,700 years ago). Research objectives were to reconstruct the glacial history and timing of the furthest southeasterly extent of the Cordilleran Ice Sheet (CIS) at the Flathead Lobe in northwestern Montana and to assess the viability of luminescence dating of sediments in glacial environments. The advance and retreat of past ice sheets can shed new light on our understanding of the cryosphere. The CIS was one of the major late Quaternary ice sheets. The CIS initially developed in southern Alaska but spread south during the Fraser Glaciation. The maximum extent of the CIS in the west is represented by the Juan de Fuca Lobe (17.5 ka) in Washington and in the east, it is represented by Flathead Lobe in Montana. The Flathead Lobe inhabited the Rocky Mountain Trench and terminated near the north end of the Mission Valley around Polson, Montana. The chronology of the western lobes of the CIS have received much attention, but not the easternmost lobes. There are only a few widely applicable and precise methods to date Quaternary landforms and sediments, and recent developments in optically stimulated luminescence (OSL) dating provide us with an opportunity to date a broad range of late Quaternary sediments. This thesis focused on the sedimentology and stratigraphy of surficial and older glacial sequences in the Flathead Valley and used OSL dating to establish age control for the deposits. Fieldwork for the project was conducted during the summer of 2021, during which time the sites in the vicinity of Flathead Lake and Polson, Montana, representing Quaternary moraine deposits, glacial lake deposits, glacial lake outwash, and glacial till from localities consistent with the position of the furthest extent of the Flathead Lobe were visited, described, and sampled. Updated digital elevation models were created to ...