USING SOILS AND SEDIMENTOLOGY FOR DECIPHERING THE ORIGINS OF GEOMORPHIC SURFACES NEAR MASSANUTTEN MOUNTAIN, CENTRAL SHENANDOAH VALLEY, VIRGINIA

Our research investigates the origins of a series of landforms located between the Massanutten Mountain Range and the South Fork of the Shenandoah River in the central Shenandoah Valley of Virginia. The morphology and position of these landforms led to a hypothesis that their formation was a combination of alluvial and colluvial processes. The work compared the pedogenesis, mineralogy and sedimentology of these surfaces to data collected from a control group of debris flows originating from the Massanutten, and floodplain deposits of the South Fork. Four of these landform surfaces were examined in detail in 2008 from soil pits that ranged in depth from 1.5 to 2 m. Laboratory techniques conducted included grain size analyses, shape factor analyses of sphericity and roundness, and sand grain mineralogy for samples originating from the landforms of unknown origin and the control groups. Grain size data plotted on cumulative frequency curves show high uniformity coefficient values, indicating that the in-situ sediments of the surfaces are all poorly sorted, which is similar to the debris flow control sample. Mineralogy and shape analysis conducted on grains of 1 mm show the dominating mineralogy of the samples being quartz, which indicates its source originating from the Massanutten Mountain Range, as well as the South Fork. Depending on the proximity of each pit to the river or the Massanutten Ridge and the depth of each sample, the sediments show a wide degree of angularity of particle shape, which indicates a combination of processes that formed the landforms of interest. One surface showed a mixture sand grains and cobbles that represented origins from both the Massanutten Range and the South Fork. The samples from the different depths and soil horizons show that each pit did not have one unique source and process; instead some pits contain material that originated from both the Massanutten and the Blue Ridge that was deposited at different intervals. From these findings, we suggest that these specific landforms situated between the Massanutten Ridge and the South Fork of the Shenandoah River are composite features of relict debris fans and alluvial terraces.