TIDAL RECORD PRESERVED IN MARGINAL SEDIMENTS OF THE LATE WISCONSINAN CHAMPLAIN SEA

Numerous preserved basin marginal facies of the Late Wisconsinan Lakes Vermont and Candona and the subsequent Champlain Sea have been identified throughout northwestern Vermont, northeastern New York and eastern Ontario. These are primarily represented by well-preserved littoral facies, including a frequent fine sandy parallel-laminated facies. We investigated this late Pleistocene littoral sedimentary record for evidence of micro- or mesotidal conditions. This approach is suggested by the fact that modern inland (up-stream) portions of the St. Lawrence River System presently experience a tidal range of over a meter. Facies at two Champlain Sea localities preserve rhythmically laminated sediments with variations in thickness at periodicities that we find to be consistent with tidal cycling - both the synodic spring-neap cycle and the semidiurnal inequality varying with the tropical month.

Once identified, analysis of these tidal signals allows for characterization of the local tidal regime as well as the determination of site specific sediment accumulation rates of these various littoral basin-margin sediments. The sedimentary character of these facies implies the formation of tidal rhythmites in a system with a minimum tidal range of roughly one meter. This is on the lower limit of a mesotidal range, but again similar to that of the modern St. Lawrence River. This record may indicate that the Champlain Sea actually had a larger tidal range, implying a true, rather than borderline, mesotidal setting. Although the more ancestral Lakes Vermont and Candona were large lacustrine water bodies, similar facies associated with them do not appear to demonstrate a tidal signal.