Origin of drumlins on the floor of Lake Ontario and upper New York State

Upper New York State, USA contains one of the largest drumlin fields (12,600 km2) in North America consisting of some 10,000 drumlins. Drumlin-like bedforms have also been discovered in deep water (∼ 200 m) on the floor of the Rochester Basin in Lake Ontario. Sedimentology of coastal drumlins combined with morphometric analysis of 1487 drumlins, shows that they are the product of subglacial erosion of preexisting sediment. A two-phase subglacial model for drumlin formation is suggested consisting of initial aggradation of extensive till deposits during ice advance followed by erosion and streamlining possibly accompanying stillstand of the ice margin and building of moraines. Offshore streamlined forms have long axes at right angles to the trend of onshore drumlins. These are composed of rock (rock drumlins) and have an orientation structurally controlled by the southwest/northeast strike of a newly identified inlier of Proterozoic (1.1 Ga) Grenville Province metasediments.