EXPLORATORY USE OF CHIRP TECHNOLOGY SUB-BOTTOM PROFILER IN SEARCH OF SEDIMENTS AND STRATIGRAPHY IN SOUTHEASTERN LAKE ONTARIO

McKNIGHT, AMY R., and McCLENNEN, Charles E., Dept. of Geology, Colgate University, 13 Oak Drive, Hamilton, NY 13346.
amcknight@center.colgate.edu & cmcclennen@center.colgate.edu

High-resolution sub-bottom seismic reflection profiling (EG&G X- Star) revealed the near surface stratigraphy of Lake Ontario, just east of Little Sodus Bay, Wayne County, New York. Sediment transport pathways, processes, and destination of the fine grained material released from eroding coastal drumlins were the foci of this field study. The fines, which comprise 75-85% of the drumlins, are known to be virtually absent in the beach and nearshore zones (< 27m depth) based on bottom sampling and side scan records. Analysis of the newly acquired sub-bottom records reveals a discontinuous lake bed stratigraphy up to 6km from shore with four distinct reflection patterns: 1) acoustically strong but roughly textured lake bed reflector, 2) acoustically strong and distinctly smoother lake bed reflector, 3) small lens-shaped pods of acoustically stratified sediment 1-3 meters thick constituting topographic highs of the lake bed, which commonly exhibit erosional features, and 4) sediments with parallel sharp reflectors alternating with thin acoustically transparent strata 5-8 meters thick partially filling large channels. Glacial till, exposed as the strong bottom reflectors, also underlies the stratified deposits. Locally there are two superimposed till surfaces. The strongest bottom reflectors are thought to be caused by the cobble and bouldered lag deposits recorded on side san records at the former sites of erosionally truncated drumlins. In the stratified units only the pods show clear evidence of erosion, possibly a result of their position on lake bed topographic highs. The channel fill stratigraphy shows almost exclusively depositional features, indicating a strictly agradational episode(s). It is hypothesized that the subglacial till channels were partially filled by ice and covered by ice-contact or ice-proximal deposits just prior to the final retreat of the glacier and certainly after any local re-advances. No evidence for present day lacustrine sedimentary draping was seen which indicates that the sediments released from contemporary coastal erosion of the drumlins is most likely being deposited further offshore (> 6km) in water depths greater than 120m. This paper presents the detailed analysis and interpretation of the sub-bottom profiles including the Holocene depositional history and sedimentary processes.

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