August 1, 2013.
The landforms and geologic layers of Southeastern Washington record fascinating, unique geologic events, including repeated catastrophic flooding that occurred during the last Ice Age. These floods left behind many distinctive features, and a variety of fossils. After discovery of mammoth-sized bones in 1999, and confirmation that more bones were still in place in 2008, the Coyote Canyon Mammoth Site near Kennewick, Washington was secured for research, and formal excavation began in 2010.
Previous research suggests that the remains are buried in Ice Age flood deposits, which are overlain by eolian sediments, and those in turn overlain by slope wash. We hypothesize that the flood deposits will have a higher percentage of granitic grains, because the flood debris has a non-local source, whereas locally-sourced deposits would have a high basalt content because of the local abundance of basalt.
The research presented here was conducted to further test this hypothesis, by examining differences in the sediment composition of 23 layers of sediment from the site, each layer representing 10 cm of the outcrop. Point count analysis was conducted on the 1-2mm sand fraction from these sediments, using a 2-gram aliquot of sand. These sand grains were visually separated into seven clast types (basaltic, caliche, granitic, light-colored translucent, light-colored opaque, organics, and other).
By far, the majority of the grains were basalt, representing 44 to 82% of the grains. Caliche clasts made up 5 to 26%, and granitics, 4 to 18%. The data was highly variable with depth, however, some data (such as the ratio between basaltic clasts and granitic clasts) appear to correlate well with the previously interpreted stratigraphic contacts.
Geology | Geomorphology | Glaciology | Paleontology | Sedimentology | Soil Science | Stratigraphy
George V. Last
Pacific Northwest National Laboratory (PNNL)
This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation. This project has also been made possible with support of the National Marine Sanctuary Foundation. The STAR program is administered by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the California State University (CSU).