Geomorphologic activity in Grinnell valley from lower Grinnell Lake: mineralogical and chemical composition tracer reflections of Mesoproterozoic Belt-Purcell Supergroup formations from Grinnell valley, Glacier National Park, Montana

Event Center A & B

During the summer 2014, sediment cores were collected from Swiftcurrent Lake and Lake Josephine in Glacier National Park. Over 70 meters of core were collected on this excursion. In 2010 LacCore also collected the lower Grinnell Lake cores (LGRIN10-1B-1P-1 and LGRIN10-1C-2B-1) that are studied for this project. Sampling of 4 cubic centimeters (cc) at 1 cm intervals, with a total of 127 samples were collected at LacCore for analysis. X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) were used to determine whether the mineralogical and chemical composition of lake sediment tracers could reflect those of the Mesoproterozoic Belt-Purcell Supergroup rocks that surround Grinnell Valley. Previous mineralogical analyses from two lakes down valley of lower Grinnell Lake demonstrate that quartz, phyllosilicate minerals such as illite (clay), chlorite (mica), and occasionally dolomite are found in varying amounts through the section. Previous XRD and percent total inorganic carbon (%TIC) data showed that during times of glacial advance, there are greater amounts of dolomite found in lake sediments. This suggests the amount of dolomite in the sediments is a proxy for glacier volume due to: (1) the glacier being more erosive, producing fine-grained dolomite, (2) subglacial transport from the cirque to the glacier toe is more efficient, and (3) by advancing over the lake, a more extensive glacier will scour the lake bed and remove lake sediment from the system.