Rock-magnetic Analyses of Lacustrine Near-shore Sediments to Reconstruct Storm Frequency in Upstate New York, U.S.A

We analyzed several sediment cores from Otsego Lake near Cooperstown, NY (N42.72°, W-74.94°). Cores were obtained near a small delta on the western side of the lake, between 20 and 150 m off-shore. The source rocks in the watershed consist of the Devonian Marcellus shale, which is mantled by glacial deposits. Delta sediments have magnetic susceptibility values between 0.99 × 10^-7 to 2.2 × 10^-7 m³ /kg. Storm events are hypothesized to deliver significant amounts of strongly magnetic terrigenous sediment, which should contrast to the weakly magnetic marls. Lake sediments consist of two units, an upper unit consisting of dark gray (2.5Y 3/1) organic-rich mud which grades into a light gray (10YR 6/1) marl. The mud has magnetic susceptibility values similar to delta sediments (1.4 × 10^-7 to 2.5 × 10^-7 m³/kg), while the underlying marl is much weaker magnetized (0.3 × 10-7 m³/kg). Several susceptibility peaks suggest periods of increased detrital input which can be interpreted as time periods with higher runoff and terrigenous matter deposition. These periods are likely to be caused by large rainfall events.