ABSTRACT: Cyclic Post-Glacial Sequences in the Finger Lakes: Response to Climatically Driven Lake Level Fluctuations?

WELLNER, ROBERT W., and HENRY T. MULLINS, Syracuse University, Syracuse, NY

A cyclic sequence of peats and gray clays has been recovered in the upper 12 m of a 119 m drillcore and a 13 m drillcore from the dry valley just south of Canandaigua Lake, New York. Nine radiocarbon dates document the age of these cyclic deposits as less than 13,600 +/- 200 years B.P., as well as a linear accumulation rate of 0.88 m/1000 years. Magnetic peleoinclination measurements correlated with the master curve from the Great Lakes provide further detailed chronologic control.

The peats are interpreted as freshwater marsh deposits analogous to nearby modern wetlands, and the gray clays are interpreted as more open (i.e., deep water) lacustrine sequences. The gross stratigraphy of these deposits argues for a long-term, post-glacial rise of lake level on the order of 12 m; whereas the detailed cyclic stratigraphy argues for a shorter-term oscillation. We have identified six peat-clay cycles that appear to have periodicities on the order of 2000-2500 years.

The long-term rise of lake level may be a response to differential isostatic uplift since the final retreat of the Laurentide ice sheet. However, the shorter-term oscillations may be responding to high-frequency fluctuations. Non-Milankovitch climatic cycles with periodicities of 2-3 Ka have recently been recognized from the global Holocene record as well as in the rock record as far back as the Paleozoic.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)