UPPER SLOPE LANDFORMS IN THE ST. FRANCOIS MOUNTAINS, MISSOURI: A RECONNAISSANCE OF POSSIBLE RELICT PERIGLACIAL FEATURES

Upper slope landforms in the St. Francois Mountains of Missouri were observed and compared to documented relict periglacial landforms in the Appalachian Highlands. The 2500 km2 St. Francois Mountains are the exposed igneous core of the Ozark Plateaus and are within 50 km of the Illinoian glacial boundary in southern Illinois, and within 75 km of the pre-Illinoian glacial boundary in east central Missouri. Erosional landforms at the summits of rhyolitic knobs had the appearance of cryoplantion terraces found in the Appalachians, but were structurally controlled, stratified pyroclastics. No patterned ground landforms were observed at the Missouri summits. A West Virginia summit had stone polygons at the surface. One Missouri rhyolitic summit gave a 36Cl date of 536 ka (pre-Illinoian) at zero erosion. All rhyolitic summits had 30-70 cm of loess over portions of the surface. One granitic summit had the appearance of an exfoliation dome with tors (Elephant Rocks) and had a 36Cl date of 333 ka (pre-Illinoian) at zero erosion. Depositional landforms just off the summits and adjacent to the block source were divided into block fields and block streams of forested, non-sorted, matrix-supported diamicts with large blocks partially buried in loess fines. Appalachian block fields and block streams largely consist of sorted, contiguous blocks with little or no fines and no vegetation. Length, aspect, slope and size of the largest blocks along the length were measured on the Missouri block concentrations and on two typical West Virginia block streams (one 36Cl dated to 143 ka, late Illinoian). The Missouri block concentrations showed no size distribution patterns and were steeper and closer to the block source than the West Virginia block streams and block streams elsewhere in the Appalachians. The Missouri block concentrations appear to be colluvial, block-mantled upper slope terrace remnants and do not have the morphology of documented relict periglacial landforms.