PROVENANCE OF MODERN LACUSTRINE SEDIMENT, MOUNTAIN LAKE, SW VIRGINIA

Mountain Lake, located in Giles County, SW Virginia, is one of only two natural lakes in Virginia, and is interpreted by some to have formed when a landslide dammed the stream known today as Pond Drain. Mountain Lake periodically drains and refills, lending itself to an unparalleled opportunity for research of modern lake sediments. In 2011 the water dropped to nearly its lowest level in many years, allowing Radford University students to extract several sediment cores for study. Five cores were taken from the lakebed at different locations along its length. For each of the cores, students created a core log, performed sieve analysis, and collected geochemical data using a handheld XRF. We have compiled the data from all five cores in order to assess variations in sediment characteristics and source across the lakebed. Mountain Lake is underlain by four distinct rock units of Ordovician and Silurian age: limestone and calcareous shale of the Martinsburg Fm., red sandstone and shale of the Juniata Fm., quartz arenite of the Tuscarora Sandstone, and hematite-cemented sandstone of the Rose Hill Fm. The variation of major and minor elements within and between the cores should reflect the relative contribution of these potential sources to the lake sediment. We found Fe, K, Ca, Ti, Zr, Pb, and Zn to show the most significant differences in the cores. For example, the generally low abundance of Ca throughout the cores indicates a minor contribution from the Martinsburg Fm., whereas fluctuations in the amount of Fe point toward varying input from the Juniata or Rose Hill Formations.