ALLOSTRATIGRAPHY OF HOLOCENE ALLUVIUM IN GLACIATED REACHES OF THE SUSQUEHANNA RIVER VALLEY, PENNSYLVANIA, U.S.A

Steeply sloping bouldery diamicton upstream of Berwick, Pennsylvania marks the maximum extent of the late Wisconsinan glacial advance in the North Branch of the Susquehanna River valley. Sand and gravel deposited by meltwater floods stand at elevations of over 30 m through a 250 km long field area, while discontinuous alluvial terrace remnants are all less than 7 m above mean low water. The bedrock valley twists and turns between folded and thrust-faulted Paleozoic sedimentary rocks of the Ridge and Valley, and the discontinuous distribution of alluvium manifests downstream changes in flow turbulence and velocity as well as postdepositional scour. Stratified archaeological sites provide definitive evidence of Holocene alluvium in locations previously mapped as "periglacial" or outwash terraces, while a database of over 140 radiocarbon dates facilitates correlation between discontinuous exposures. Three "alloformations" are proposed based on buried soils and sedimentological features which are consistent in terms of age and stratigraphic position. The buried soils are characterized with thin sections as well as bulk sample textural and chemical analyses.