LATE PLEISTOCENE GLACIAL STRATIGRAPHY OF THE COLD RIVER VALLEY, SOUTH ACWORTH, NEW HAMPSHIRE

Five landslides on the southeastern valley wall of the Cold River, a tributary to the Connecticut River, reveal glacial lacustrine units of at least two ages that seem to correlate with sediments mapped in the Connecticut River valley region as proglacial, sub-till, and postglacial late-Wisconsinan sequences. Bedding thicknesses and attitudes, compositional layering, paleoflow indicators, and deformation were used to define and identify facies in the Cold River valley. Several distinct glacial facies include: 1) plane-bedded sands; 2) sheared east-dipping massive and varved clays with thin .5 - 1 cm interbeds of diamicton; 3) unsheared south-dipping, varved clays with thin diamicton laminae that appear to be sediment flow deposits; 4) extremely compact glacial diamicton with cement like consistency and interpreted to be subglacial till; and 5) interbedded rhythmic sand, silt, and clay of variable thicknesses. Facies are interpreted as fluvial, proglacial lake, subglacial till, and post-glacial lake sediments. Lacustrine units found both above and beneath subglacial till, indicate that the Cold River valley was occupied by glacial lakes both before and after the last glacial advance. Although correlating proglacial lake beds between sections is tempting, differential scouring and preservation of preglacial sediments makes their correlation uncertain.

Because the valley was differentially scoured, there exists the possibility that more than one subglacial till is exposed. Therefore, both fabrics and clast compositions were analyzed. Results were compared with each other, with the orientation of glacial lineations on LiDAR imagery, and the regional bedrock geology. No distinct difference in glacial flow direction was identified in exposures of subglacial till. This is consistent with a 190°-170° flow direction obtained from LiDAR, which presumably reflects a late-Wisconsinan flow pattern.

Our results correlate well with the stratigraphy found down valley along the Cold River and Warren Brook in Alstead and along other Connecticut Valley tributaries including the Little Sugar and Sugar River valleys, and add detail to the glacial history of the region.