PRELIMINARY STUDY OF THE LATE AND POST GLACIAL SEDIMENT HISTORY RECORDED IN A SEDIMENT CORE FROM SUGAR LAKE, PENNSYLVANIA

Sugar Lake is a moraine-dammed lake within the outer margin of the Kent end moraine complex, which marks the maximum extent of Wisconsin glaciation in northwestern Pennsylvania. Sugar Lake contains a continuous record of sedimentation spanning the last 14 kya. Analyses of lithology and magnetic susceptibility (MS) from a 12 meter long sediment core permit interpretations regarding environmental change within the watershed during the late and post-glacial period.

The oldest sediments record an early phase of predominantly clastic, silty sedimentation when glacial ice still existed within the valley. Annual summer/winter cycles (varves) are evident as alternating light grey silt and black organic laminations, respectively. As glaciers retreated northward, varves were gradually replaced by increasingly organic sediments. That trend was terminated by a rapid change to predominantly homogeneous organic sedimentation, which likely marks the transition to an ice-free valley and climatic amelioration at the beginning of the Holocene Epoch. Decreases in MS values suggest that clastic sedimentation generally declined as organic content increased through the early and middle Holocene, although several distinct pulses interrupt that trend, suggesting episodes of landscape instability. Alternation between homogeneous gyttja and burrowed zones containing vivianite suggest changes between eutrophic and oligo- or meso-trophic states in the lake, respectively. The last evidence of non-eutrophic conditions occurred approximately 3 kya. Gyttja dominates the late Holocene record, with a final phase of increased MS likely recording human-induced hillslope erosion over the last 100+ years.