GROUND-PENETRATING RADAR EXAMINATION OF DRUMLINS IN SOUTHERN MAINE

Long axes of streamlined hills in southern Maine parallel striations from late Wisconsinan glaciation flowing SE. Some hills are complex, with secondary southern axes parallel to an earlier southerly glacial flow. Hills may be composed of bedrock (large roches moutonées), bedrock plus till (crag and tail), or predominately of till (drumlins). Ground-penetrating radar (GPR) was used to evaluate the composition of these streamlined features, and to test a hypothesis of two-stages of emplacement and/or modification of glacial sediments. GPR profiles show prograding clinoforms in the mixed-till zone, where Late Wisconsinan till overlies older till, to approximately 10 meters depth. Below 10 m the over-consolidated, over-ridden older till causes complete attenuation of the 100 MHz signal. The flanks of drumlins preserve evidence of wave-cut terraces lower than the inland marine limit (52m) widely recorded in the region by deltas and beach deposits. At Marsh Hill, a distinct notch at 24 m elevation is overlain by gently inclined parallel strata, interpreted as a marine terrace. The local relative sea-level curve places this event during deglacial fall of sea-level due to rapid isostatic rebound, roughly 11,000 BP. A GIS map reconstruction of the landscape surrounding Marsh Hill was modeled at a +24 m sea-level. This model isolates several elongate valleys, interpreted as meltwater channels. In addition, one elongate valley would have connected to the sea in a fjard. This sea-level isolated the streamlined hills into separate islands, which made them also susceptible to wave-action. Further topographic and geophysical study will seek similar shoreline deposits at this level. In addition, the former fjard may preserve sediments with datable materials that can tie this regressive record into the Maine sea-level curve and deglacial history.