16 Undergraduate Research (Posters)

Monday, 18 May 2020
8:30 AM - 5:30 PM
Lake Superior Ballroom KJ

HEAVY MINERALOGY OF BEDLOAD SEDIMENT IN THE UPPER MISSISSIPPI RIVER AND THE INFLUENCE OF TRIBUTARIES

Paper number: 16-26
Program: Theme Sessions
Time: 8:30 AM – 5:30 PM

Authors

Abstract

The minerals present in the bedload of streams reflect their upstream sources, particularly in the non-quartz fractions. This research was conducted in order to test the hypothesis that the heavy mineral assemblage (the non-quartz fractions) and chemistry in the bedload of large drainage systems vary according to upstream bedrock sources. Five samples were collected: two directly upstream from the confluence of the Wisconsin and Mississippi Rivers, and three locations downstream along a 113-km reach through the Driftless Area. Sediment was collected using a dredge. The 350µm and finer fraction was separated using lithium heteropolytungstate (LST) heavy liquid and was then analyzed using x-ray fluorescence spectroscopy (XRF), scanning electron microscope energy-dispersive x-ray spectroscopy (SEM-EDS), and x-ray mapping. SEM-EDS was repeated ~40 times per sample site to determine the mineralogy. X-ray mapping of sand particles helped discern mineral percentages. Geochemical results from XRF analysis indicate that Fe, Ca, Ti, Si, and Al are remarkably consistent, varying only ~5% in overall composition. In contrast, heavy mineral assemblages, identified using SEM-EDS, show different mineralogy between the Mississippi and Wisconsin Rivers. All samples included: ilmenite, hematite, tschermakite, actinolite, prehnite, chloritoid, and apatite. The Wisconsin River contained significant almandine, which was not found (nor any other garnet variety) in the downstream samples. Other minerals identified exclusively in the Mississippi River included: pumpellyite, staurolite, chamosite, rutile, and edenite. Further research will attempt to identify the bedrock provenance of some of the minerals.

Geological Society of America Abstracts with Programs. Vol. 52, No. 5

doi: 10.1130/abs/2020NC-347898

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