A DEEP GLACIAL VARVE RECORD FROM THE HADLEY BASIN, GLACIAL LAKE HITCHCOCK, SUNDERLAND, MASSACHUSETTS

Three new stratigraphic core holes from the Hadley basin of glacial Lake Hitchcock penetrated 13.5 m of either terrace or lake sand, 62.5 m of varved sediments, and 3 m of red sandy till at the base. The holes are 2.5 km WSW of the Sunderland delta, and 5 km NW of the UMASS core hole (Rittenour, 1999). The drill sites are located above a closed bedrock depression where the lake basin was deepest and the varve section is thickest.

Where core analysis has been completed, varves match well with the UMASS core and the New England varve chronology (NEVC). Three distinct stratigraphic zones are recognized. A basal zone at 70-58 m depth contains red sandy varves that average 10-20 cm in thickness and may number 50-100 over the interval. A gray and red, silty varve zone at 58-45 m depth exhibits four-part varves having 1) basal red clayey silt, 2) a single lamination of fine white sand, 3) gray micro-laminated silt, 4) a normally graded gray clay top layer. These varves average 8 cm in thickness and were sourced from sediment interflows carrying red fine sediment that composes each basal silt layer. A zone of thin gray silty varves at 46-14 m depth contains varves with lower gray micro-laminated silt, locally interrupted by laminae of white very fine sand, passing upward into normally graded gray clay. Above 27 m depth, these varves thin upward from an average thickness of 3 cm to 2 cm. Derived from tributary rivers mixed with meltwater from the north, cycles of these varves dominate the climate record of the basin. A section of thicker, sandy varves at 40-36.5 m depth in the gray varve zone records a series of increased discharge events. In the uppermost 6 m of the lake section (core 2) gray varves thicken to an average couplet thickness of >3 cm.

The combined section contains a continuous record of ~1400 varves in the range of varve years 4450-5900 NEVC. The varves correlate well with the UMASS core despite the 2X thickness of the section. These thicker varves indicate focusing of sedimentation by interflows to the bottom of the central lake basin. The higher discharge events recorded by thicker varves at 4879-4940 NEVC in the UMASS and Sunderland cores, by their location and age, cannot record a glacial readvance at the Camp Meeting cutting in Northampton. Instead, they signify a 60-year period of increased, probable meltwater flows aligned along the axis of the Hadley basin.