The southern part of the Ohio waters of Lake Erie between Conneaut and Marblehead was surveyed in August of 1977 and 1978 to acquire knowledge of the nature, distribution, and geometry of the lake deposits. Primary data consist of 576 kilometers of seismic reflection trackline profiles and 58 vibracores ranging from 0.7 to 6.1 meters long. About 23 percent of Ohio's part of Lake Erie was covered by the survey. Devonian shale overlain by Quaternary glacial tills and postglacial deposits underlies most of the survey area. In general, the shale is exposed nearest the shore and is succeeded offshore by till and postglacial deposits. The shale surface is commonly more irregular than the till and postglacial deposit surfaces; slopes on the lakeward dipping shale surface range from about 5 to 20 meters per kilometer. Pleistocene tills - both basal and flow tills - also underlie most of the survey area with extensive exposures between Fairport Harbor and Avon Lake and off Lorain. Interlaminated silts and clays are interbedded with the flow till in some cores; three cores contain both basal and flow tills. The tills are made up largely of silt and clay-size particles composed of quartz and illite. The till has a flatter and more uniform surface than that of the underlying shale, with lakeward slopes ranging from about 1 to 4 meters per kilometer. The till varies in thickness from 0 to 26 meters and thickens lakeward at about 5 meters per kilometer. Sand, muddy sand, sandy mud, and mud are the four principal postglacial deposits. These deposits commonly lie lakeward and overlie rock and till. In general, the coarser deposits lie nearest the shore. However, the two principal sand deposits at Fairport Harbor and Lorain-Vermilion are well offshore. Also, the finer deposits are found closer to shore and in shallower water west of Cleveland. Combined postglacial deposit thicknesses range from 0 to 22 meters and like the till, the postglacial sediment thickens lakeward. The tills were first deposited on an irregular, erosional shale surface. Till deposition continued intermittently on both shale and previously deposited till until eastward retreat of the last Wisconsinan glacier from the Erie basin. Drainage of the lake ponded west of the glacier then exposed the till to subaerial erosion which led to the formation of stream channels in the till off Lorain and Fairport Harbor. Isostatic rebound of the outlet then led to a rise in lake level with associated erosion and deposition along the expanding lakeshore, which tended to smooth the till surface. The early postglacial (Holocene) deposits, which accumulated during the rise in lake level and cover the underlying till and Shale, were deposited in a complex of fluvial, deltaic, and lacustrine environments. Modern lacustrine muds are now being deposited over these early Holocene deposits.


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    Titel :

    Regional Geology of the Southern Lake Erie (Ohio) Bottom: A Seismic Reflection and Vibracore Study



    Erschienen in:

    Erscheinungsdatum :

    1982


    Format / Umfang :

    22782606


    Medientyp :

    Report


    Format :

    Elektronische Ressource


    Sprache :

    Englisch



    Klassifikation :


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