Evidence, from microstructures, of deformable bed conditions within drumlins, Chimney bluffs, New York State

Discussion on the process of drumlin formation has been ongoing for over a century. At present, two dominant schools of thought prevail, viz, formation by (a) subglacial hydraulic mechanisms, and (b) due to subglacial sediment deformation. The latter mechanism depends on the existence of a subglacial deformable bed. Evidence from part of the large central New York drumlin field reveals evidence of syn-depositional deformation during the emplacement of diamictons that constitute the major portion of drumlins exposed along shore bluffs in Chimney Bluffs State Park. These diamictons cannot be lodgement till facies members but appear to comprise facies indicative of melange-style deposition under subglacial deformable bed conditions. The evidence obtained from microstructures and plasma fabric within these diamictons supports the existence of a deformable bed during diamicton emplacement. It is likely that formation of the drumlins occurred under these same subglacial bed conditions.