IDENTIFICATION OF PALEOCLIMATIC CYCLES DURING THE HOLOCENE USING GRAIN SIZE ANALYSIS OF SEDIMENTS CORED FROM LAKE MOREY IN FAIRLEE, VT

Since the final retreat of the Laurentide ice sheet (~14,000 cal 14C), sediments have been deposited in glacially formed lakes across New England. Analyses of the stratigraphy and physical properties of these sediments can be used to determine when storms happened in the past and whether or not such storms were grouped in space and time or whether they occurred as random one time, high-energy events. Previous analyses (loss-on-ignition, magnetic susceptibility, and X-radiography) of the sediments cored from Lake Morey suggest that the storms happen in a cyclical manner, separated by long periods of relatively quiet, low-energy depositional environments.

The continuous sediment core taken from Lake Morey reaches down to ~12,800 year old (calendar years) sediments. A Coulter Laser Diffraction unit (LS230) has been used to determine the grain size of several consecutive samples at 1 cm intervals starting at the top of the core. Inorganic grain size is a physical characteristic directly related to the energy of the incoming flow at a given point in time (determined by radiocarbon dating). Using these data, I have found that suspected periods of greater storminess exhibit larger, better sorted grains, whereas intervals between storms have smaller, less well sorted grains.

Together with other core analysis techniques, grain size analysis is an important tool for elucidating the intensity of past storm events. Its correlation with other data suggests that it should be considered as another useful method of paleostorm detection in sediment cores.