A NEW VARVE RECORD AND 14C DATES FROM THE SOUTHERN BASIN OF GLACIAL LAKE HITCHCOCK

A 13.5 ¹⁴C ka (16.1 cal ka) date from the Matianuck Avenue site in Windsor, CT records the time frame for failure of the Rocky Hill dam that impounded water during high levels and the stable level of glacial Lake Hitchcock (Stone and others, 2005a). This date was obtained from an organic layer in a road-cut exposure of upper lake-bottom deposits. Two meters of varves were exposed beneath the layer containing the dated material, but were not counted or correlated to Antevs' (1922) New England varve chronology (NEVC). In August 2008, continuous core was obtained by drilling at the Matianuck site; the core penetrated 7 m of eolian and lacustrine sand overlying 17 m of varved clay; dense red till was encountered at 24 m depth. Preliminary core analysis reveals the uppermost 3 m of the varved section contains thin (average1.1 cm) gray varves and the lower 9 m contains thicker red varves.

The purpose in obtaining the core is to correlate the varve section with the newly calibrated NEVC (Ridge, 2004) and to the varve record from the former Kelsey-Ferguson (K-F) clay pit across the valley in East Windsor, CT. Jack Ridge recently compiled a sequence of 552 varves from the K-F clay pit and matched them to the Antevs' chronology at NE 3617-4168 (Stone and others, 2005b). Terrestrial plant leaves were found in association with 2 varves, 287 years apart. This material has recently been dated yielding ¹⁴C dates of 14,120 + 80 (GX-32114) from varve 3826 and 13,950 + 90 (GX-32113) from varve 4113. ¹⁴C ages calibrate to 16.84 and 16.62 cal ka, respectively (calib 5.01). NE varve 4168 is overlain by stream terrace deposits, indicating that the uppermost lake-bottom section is missing due to terrace incision at the K-F clay pit locality.

The upper varves in the Matianuck core appear to match the Antevs' record in the missing K-F section above varve year 4168, and provide a record of the last few hundred years (16.5-16.1 cal ka) that glacial Lake Hitchcock existed in the basin south of the Holyoke Range in Massachusetts. The new dates and a potential successful match of the upper 3 m of varves at the Matianuck site to NEVC in the vicinity of NE 4150-4450 further support the interpretation that the southern part of Lake Hitchcock was drained by 13.5 ¹⁴C ka (16.1 cal ka) while the lake to the north continued to exist for at least another 1200 years at slightly lowered levels.