CGRG Bibliography of Canadian Geomorphology
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Author : Coakley, J.P.
Date : 1985
Title : Evolution of Lake Erie based on the postglacial sedimentary record below the Long Point, Point Pelee and Point-aux-Pins forelands
Publication : Unpublished Ph.D. disseratation. University of Waterloo, waterloo
Issue :
Page(s) :
Abstract
The postglacial geological history of Lake Erie was interpreted primarily on the basis of borehole sedimentary sequences below the major accretionary forelands: Long Point, Point Pelee, and Pointe-aux-Pins. These data were complemented by sedimentary profiles from other boreholes in and around the lake, radiocarbon and pollen-based dating of lake sediments, relict geomorphic features, and stream/lake relationships. Overconsolidated glacial sediments forming the basal portion of the sequences (Unit 1) are overlain disconformably by postglacial silty clays deposited in deep- or quiet-water environments (Unit 2), indicating a rapid increase in water depths. As topographic lows were infilled and water depths decreased, sediment grain size increased, reflected in a rising frequency of sandy laminations (Unit 3). This transitional unit is usually topped by an erosional unconformity, suggesting nondeposition and reworking prior to the deposition of well-sorted, medium sand (Unit 4) at the top of the sequence. Deposition of the top unit began around 5000 years ago, and clearly occurred in an upper shoreface setting. All boreholes show this clear coarsening-upward textural trend, probably associated with lateral migration of higher-energy upper shoreface (spit) facies over lower shoreface and lagoonal facies. When added to the other available data, the sediment interpretation suggests important revisions to earlier concepts of postglacial lake levels in the Erie basin. The lake level curve presented here confirms glacioisostatic rebound of the lake outlet as the major factor in the initial lake level trend, but it also suggests that other processes (such as hydrologic changes, postglacial tectonics, and paleoclimate) could have become important in the later stages. The above data were used in a hypothetical reconstruction of Lake Erie paleogeography, highlighting the three major forelands studied. The reconstruction indicates that these forelands did not result from conventional spit formation processes. Rather, their origin is due primarily to the effectiveness of cross-lake moraines in Lake Erie as sand-accumulation sites. The evolution of the forelands over the past 3000 years is characterized by persistent shoreward transgression under the influence of rising lake levels, in a manner analogous to the ongoing retreat of barrier islands on marine coasts.
Bibliography of Canadian Geomorphology