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Abstract

Holocene sediments from three deep boreholes from Long Point, a 35-km-long sandy foreland on the Canadian side of eastern Lake Erie, display a consistent coarsening-upward trend from sheltered-water clays and silts to well-sorted shoreface sands. This trend persists in spite of the documented record of lake-level rise, due primarily to postglacial isostatic rebound of the Niagara River outlet. To resolve this contradiction within the context of shoreline evolutionary trends in eastern Lake Erie, sediment data from the boreholes are analyzed in combination with data from other sources. The analysis suggests that the sedimentary sequence is linked to the history of the Long Point foreland and its precursors. The resulting evolutionary model, supported by relict shore features, postulates that Long Point began as a north-south-trending cuspate peninsula, once linked to the ancestral Presque Isle spit on the United States side. The location of the feature was controlled by the Norfolk moraine, a cross-lake ridge of glacial origin. As lake levels rose, the foreland retreated northward with the shoreline as a whole, becoming smaller and more rounded but with well-developed recurves extending northeast. Around 5 to 4 ka, an abrupt rise in lake levels, related to resumption of drainage from the Nipissing Phase in the Upper Great Lakes into the Erie basin, resulted in inundation of most of the ancestral foreland. When the lake later fell to previous levels, presumably due to widening of the Niagara River outlet, the foreland commenced its present east-west orientation. At present, the distal portions of the spit are prograding southward, while the proximal areas are still retreating northward; in other words, the feature is slowly rotating clockwise. The pattern of landward retreat of parts of the foreland over sheltered (lagoonal) deposits and the rotation of the distal portions are also noted in the two other north-shore forelands. Point Pelee and Pointe-aux-Pins, and comparison is made with the transgressive marine barrier islands of the United States east coast.

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