TIDAL? RHYTHMITES OF THE LATE WISCONSINAN CHAMPLAIN SEA

Following the late Wisconsinan deglaciation, the short-lived, postglacial Champlain Sea occupied the upper reaches of the modern St. Lawrence Lowlands and Champlain Valley from roughly 12,000 to 9,500 ka. This large body of water developed a variety of fresh, brackish and marine facies, some of which appear to record a tidal influence that is preserved in various marginal facies. It is likely that portions of the basin may have been subjected to micro- to mesotidal conditions, much as inland (up-stream) portions of the modern St. Lawrence River System experience a tidal range of over a meter.

Numerous preserved basin marginal facies of the Champlain Sea have been identified throughout northwestern Vermont, northeastern New York and eastern Ontario, which are primarily represented by well-preserved littoral facies, including frequent topset delta facies. The study of these various sedimentary facies aims to identify the tidal signature that may be preserved within characteristic rhythmic bedding expressed at these many localities. Analysis of these tidal signals allows for characterization of the local tidal regime as well as the determination of the sediment accumulation rates of these various littoral basin-fill sediments.