T28 Core Analysis of Lake Sediments (Posters)

Sunday, 22 October 2006
8:00 AM - 12:00 PM

A RECORD OF STORMY WEATHER IN CANANDAIGUA LAKE, NY DURING THE HOLOCENE

Paper number: T28-5
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

Analysis of a 4.71 m-long sediment core retrieved from the middle of Canandaigua Lake, NY reveals a detailed record of extreme hydrologic events in the watershed throughout the Holocene. We used four techniques to identify discrete intervals of deposition of terrigenous sediment: magnetic susceptibility (MS), visual logging, grain size analysis by laser diffraction, and petrography. Two accelerator mass spectrometer radiocarbon dates on terrestrial plant macrofossils were calibrated to calendar years. Assuming a zero time frame for the top of the core and 13,900 years for the bottom of the core, and using these two radiocarbon ages, linear sedimentation rates were calculated to identify the timing of the significant depositional events.

The core is composed of very weakly to well laminated dark olive gray (5Y 3/2) and black (N1) mud. The entire core is punctuated by thin (<1 cm thick) intervals of increased sand content (>1%), greater than average mean grain size of silicilastic material, and average to high MS values. Based on petrographic examination of thin sections, the composition of these layers is a mixture of quartz sand and fragmented organic matter, either terrestrial material (twigs, leaves, needles) or aquatic vegetation. These intervals are interpreted to be storm deposits. Using our age model, we infer that the most intense storms occurred at approximately 780, 2800, 4700, 9000, and 11900 cal yrs BP. The timing of these millennial-scale events is similar to those reported for Vermont and eastern New York over the past ~13,200 cal yrs BP.