Abstract

The late Pleistocene sediments of the northern Lake Superior basin consist of a basal reddish till, deposited during the Valders substage, unconformably overlain by a sequence grading upwards from grayish red, silty clay interbedded with thin sand laminae to grayish red and then gray calcareous varves. Holocene sediments consisting of a clay–silt sequence in the topographic lows, or a thin veneer of sands along the lake-shelf area, unconformably overlie the gray varves. The basal contact of the clay–silts or sands with the gray varves marks the time when glacial ice receded from the Lake Superior basin. Radiocarbon dating indicates that this event occurred more than 11 000 years B.P.The best, though fairly low, positive correlations of pairs of elements in the lake-bottom sediments occur between iron and chromium, zinc and nickel, iron and zinc, and iron and nickel. Different upward migration patterns of elements during syndiagenesis probably is the cause of the low correlation between the elements. Strontium shows negative correlations with the elements of the first transition series of the periodic table; however, a strong correlation of strontium with calcium in the Pleistocene gray varved section probably results from isomorphism of strontium for calcium in the precipitated carbonate minerals.

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