CGRG Bibliography of Canadian Geomorphology
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Author : Blasco, S.M.; McCarthy, F.M.G.; and McAndrews, J.H.
Date : 2004.
Title : The stratigraphic record of large lakes- far from layer-cake!
Publication : 49th Annual Meeting of the Geological Association and the Mineralogical Association of Canada. May 12-14, 2004. Brock University, St. Catharines, Ontario.
Issue :
Page(s) :
Abstract
Lakes in Canada are generally assumed to be quiescent areas of undisturbed sediment accumulation with a continuous record of deposition since deglaciation. However, some large lake basins like Georgian Bay contain a spatially and temporally discontinuous sediment infill since ice retreat. Shallow seismic and subbottom profile data collected on a regional lake-wide grid together with a sediment chronology (obtained by correlating the lake pollen record with the regional pollen zonation) revealed a discontinuous sedimentation history. Holocene sediment thickness does not always conform to bathymetry with the thickest sequences in the deepest depressions. The relatively shallow Severn Sound at the southeast end of Georgian Bay, for instance, contains thicker sequences of Holocene sediments than the very deep western Georgian Bay Flowerpot basin. Holocene sediment thickness varies from more than 6 m to absent across the basin and deposition was not continuous over time. Little sediment accumulated over the last 4000 years. Glaciolacustrine and postglacial sediments outcrop on the lakebed even in deep water over much of the basin. This discontinuous distribution pattern suggests that sedimentation is controlled by waves and currents and sediment supply linked to major lake level fluctuations before the mid Holocene. Thick sediment sequences are associated with dynamic periods when lake levels were rising. Non-deposition and unconformities are associated with lake level still-stands with less dynamic conditions and sediment-starved environments. This discontinuous record of deposition demonstrates the importance of understanding geologic and taphonomic conditions when interpreting paleoenvironmental proxy records. Such records are not ideal for paleoclimatic reconstruction, however an understanding of basin depositional dynamics coupled with the selective sampling of seismostratigraphic units will allow for the reconstruction of a discontinuous paleoclimatic and paleohydrologic record.
Bibliography of Canadian Geomorphology