SEDIMENTOLOGIC AND STRATIGRAPHIC EVIDENCE OF LATE GLACIAL FLOODS WITHIN LYCOMING CREEK VALLEY, LYCOMING COUNTY, PA

The northern Lycoming Creek Valley occurs just north of the late Wisconsinan glacial maximum on the Appalachian Plateau in Lycoming County, northeastern PA. The majority of the valley slopes are composed of angular sandstone colluvium from the underlying Devonian Catskill Formation that occasionally outcrops. Alluvium of an unknown thickness comprises a 300-500 meters wide plain along the valley floor. Newly completed surficial mapping reveals stream terraces rising to heights of 18 meters along the valley walls.

Sedimentologic analysis of a terrace deposits occurring within a gravel pit near Bodines, PA indicate the terraces are composed of a poorly-sorted, clast supported boulder-gravel consisting of well-rounded and elongated clasts ranging in size from coarse sand to 1.5 m that display imbrication and coarsens upwards. A lack of striations and faceted clasts make it unlikely that the deposits are the result of direct ice contact. Similar terrace-like landforms composed of coarse-grained materials occur episodically through out the valley.

Inversely graded, imbricated, boulder-gravel up to 18 meters thick indicates late glacial floods inundated the Lycoming Valley. Subsequent valley incision led to the formation of stream terraces and erosion of valley fill. Multiple terraces indicate a complex geologic history for the valley and suggest periodic adjustments of base level occurred.