A CONTINUED ANALYSIS OF THE GLACIAL LAKE WARRENSBURG VARVE CHRONOLOGY

Glacial Lake Warrensburg was formed approximately 12.6-11.9 kya as the Laurentide Ice Sheet retreated through the Hudson River Valley near Warrensburg, NY (Ehlers and Gibbard 2008). Pinkey-Drobnis et al. (2011) examined two overlapping cores from Glacial Lake Warrensburg sediments containing 0.9 meters of ice proximal glacial varves deposited over an eight year period. In a continuation of this study, we collected two varve cores from the top and bottom of the same field location using a standard Ridge-style percussion varve coring device. The transect exposes approximately 15 meters of varve outcrop overlain by a well-sorted sand unit in the Hudson River Special Management Area along the Buttermilk Trail and an unnamed perennial streambed. Varves were also observed stratigraphically below this site in the Hudson River both in and below the riverbed, as well as along the banks. The newly collected varve core tubes were cut and the cores were split in half with one half devoted as a working core and the other archived.

A varve chronology was measured for each core by counting and measuring annual couplets of summer and winter layers. The 0.60 meter varve core collected at the top of the varve unit contains approximately 22 varves with an average annual thickness of 0.5 cm. The 0.37 meter bottom core contains approximately 21 years with variable annual thickness: Near the top of the core the layers are thinnest (0.3-0.6 cm/yr), some of the middle annual layers are as thick as 4 cm, and the verves near the bottom of the core had an average thickness of 2 cm/yr. Neither of the new cores contained ice proximal varves, suggesting that the ice retreat in this area included at least one significant readvance during the late Allerod interstadial. The varves collected throughout the transect at this site represent at least 50 years of glacially deposited sediment during an inferred ~700 yr period of lake existence. Further research could include additional coring to complete the transect at this site, radiocarbon sample collection, and collecting cores from new sites within the extensive Glacial Lake Warrensburg basin in order to characterize the patterns of glacial retreat in the northern Hudson River Basin.