The regional paleoclimatic and deglacial history of New England isbest constrained along two transects; first along the coast from Cape Codto northern Maine using radiocarbon-dated fossiliferous marine andglaciomarine sediments, and second up the Connecticut Valley using varvedglacial lacustrine sediments (annual rythmites). While radiocarbon datingof these depositional sequences has been instumental in placing a temporalcontext to deglaciation, many questions still persist concerning the datingof the infamous varved lake sequences in the Connecticut Valley due toinherent problems of the natural reworking of organic materials, such astwigs, leaves, etc., into the sediments. Antev's New England varvechronology (1928) has held up to rigorous testing by Verosub (1979 a,1979b) and Ridge and Larson (1990) indicating that the sediments do recordannual sedimentation in a proglacial lake system that can be corrected toother contemporaneous lakes elsewhere in New England. Unresolved, however,is accurately determining when Glacial Lake Hitchcock drained and how thevarve record can be used to determine the rate of regional deglaciation.Such questions have bearing on the history of climate change in NewEngland, the early peopling of New England, and regional isostatic uplifthistory.
At a special session of the Northeast Division of the GeologicalSociety of America (March 20-22, 1995, Cromwell CT), differences of opinionconcerning the lake history were highlighted. Stone and Ashley (1992)maintain that the lake south of the Holyoke Range drained by about 13,500to 14,000 years ago based on radiocarbon age estimates from organics thataccummulated on the ancient lake floor after it drained. On the otherhand, Ridge and Larson (1990) maintain that the proglacial lake drainedlater, about 12,400 years ago based on radiocarbon-dated twigs enclosed inthe varve sequence near Brattleboro, VT. Stone and Ashley (1995) nowsuggest that the lake may have drained sequenially with the southern end ofthe lake draining earlier, followed by the erosion of a sediment dam at theHolyoke Range at 12,400 years before present. Of critical importance tothis work is the accurate dating of the varves in the Amherst region andtheir correlation into the region sequence. Specifically, how manythousands of years of lake sedimentation are recorded here and what is thebest age estimate for the first varve deposited on top of the deglacialtill just as the glaciers retreated from this region.
On Wednesday and Thursday, September 10 and 11, Dr. JulieBrigham-Grette, Dr. Laurie Brown, and graduate student Tammy Rittenour ofthe Geoscience Department, on collaboration with Dr. Don DeGroot from CivilEngineering, will be coring the Amherst varve record west of the MullinsCenter and north of the Amherst Waste Treatment facility. Over two days wehope to recover over 100 feet (33 Meters) of record that may date fromabout 14,500 years to about 12,500 years before present when the region wasoccupied by the lake. When it existed, the lake covered the campus andvalley floor up to about the level of the Faculty Club or about half way upthe Dubois Library Tower. Detailed sedimentological study of the Amherstvarve sequence, coupled with dating via paleomagenetic secular variationand radiocarbon age estimates of organics will contribute criticalinformation concerning the drainage history of Glacial Lake Hitchcock.Accurate logging of varve thickness and systematic counting of the varvesequence will allow us to place the local sediment history into theregional geological framework. In addition, it has been suggested thatwell-sorted sand layers in the Fall season of many varve couplets mayrecord hurricane frequency, and at best may provide us with an index ofpaleostorm history during the time that the lake occupied the valley.This research is currently funded by a UMass Faculty Research Grant toBrigham-Grette and Brown.
