| Abstract | Lake Erie today is fourth in the chain of Laurentian Great Lakes that overflow and drain by connecting rivers to the St. Lawrence River and Atlantic Ocean. Ninety percent of the water supply of Lake
Erie comes by overflow from upstream Lake Huron. This supply was diverted from the Erie basin when the Huron basin drained directly to the Ontario basin about 12,500 to 11,000 14C (14,640 to 12,920 cal) years BP, and later, when it drained to the
Ottawa River valley from 10,500 to 5500 14C (12,510 to 6320 cal) BP. Thus low water levels are expected to have existed in Erie basin during these periods of reduced inflow, in combination with an early Holocene drier-than-present climate. Evidence
of low water levels was revealed by acoustic profile and sediment core data in the form of a beach and erosional shoreface 21 m below eastern Lake Erie 10 km south of Nanticoke, Ontario. Similarly, an erosion surface, interpreted as a wave-cut
platform, extends southward from Rondeau, Ontario, and along the whole northern shore of the central Erie basin beneath postglacial lacustrine mud to depths of 30 m below present lake level. Cores dated by pollen- and PSV (paleomagnetic secular
variation)-correlation to radiocarbon-dated onshore organic sediment sequences show that mud accumulation over the wave-eroded surface only began after 7600 14C (8400 cal) BP while a significant reduction in the mud accumulation rate occurred
offshore from 10,500 to 7500 14C (12,510 to 8300 cal) BP. In the relatively shallow western Erie basin, sediment sequences contain plant detritus concentrations indicative of marsh environments between 12,500 and 11,000 14C (14,640 and 12,920) BP,
and after 10,400 14C (12,270 cal) BP. After removing the effects of ongoing differential glacio-isostatic crustal warping, the above data revealed that lake levels were low (below the basin overflow outlet) when Huron basin drainage was diverted from
the Erie basin. Throughout the early Holocene, the lake in the central and eastern Erie basins was hydrologically closed below the overflow sill, as indicated by the Nanticoke and Rondeau paleo-shore zones. After 7600 14C (8400 cal) BP the lake level
rose about 7 m, then more slowly, still in hydrological closure, while geomorphic coastal zone indicators formed throughout the basin, identified by Holcombe et al. (2003; J. Great Lakes Research 29, 681-704). Finally, the lake level rose to overflow
the Niagara River sills about 5,500 14C (6320 cal) BP with the resumption of Huron basin overflow, as at present. |