Mineral Composition, Sr/Sr Ratios, and Concentrations of Strontium and Rubidium in Late Wisconsin Till of Ohio
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Date
1979-07
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Abstract
Samples of Late Wisconsin till from the Powell-Union City Moraine of Ohio have bimodal grainsize distributions and concentrations of carbonate minerals, illite, and kaolinite-chlorite that are primarily the result of grinding of clasts derived from local bedrock. Quartz and feldspar have unimodal grainsize distributions that suggest their derivation from distant sources on the Precambrian Shield of Canada. The carbonate content of the silt and clay fractions (<62.5jum) of 13 till samples collected along the Powell-Union City Moraine increases from less than 10% in the east to about 35% in western Ohio. The change in carbonate content is compatible with bedrock lithology and a southwesterly iceflow direction. The silt and clay fractions (non-carbonate) contain Rb= 154.7=*= 13.5 ppm, Sr= 104.8 ±11.0 ppm, Rb/Sr = 1.49±0.21, 87Sr/86Sr = 0.7345±0.0041. The average 87Sr/86Sr ratio of these till samples is similar to results obtained elsewhere for strontium of the continental crust and supports previous suggestions that the average 87Sr/86Sr ratio of the continental crust is 0.730±0.010. The ratio of radiogenic 87Sr/87Rb increases from about 0.0060 in the east to 0.0075 in western Ohio. The low magnitude of this ratio is due to the predominance of locally derived sediment of Palezoic age in the silt and clay fractions of till. The westerly increase is probably the result of several factors, including: 1) Increasing age of the Precambrian component (feldspar); 2) Increasing abundance of the Precambrian component; 3) Increasing age of the local bedrock from Mississippian in the east to Silurian in western Ohio.
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Author Institution: Institute of Polar Studies, Department of Geology and Mineralogy, Ohio State University
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The Ohio Journal of Science. v79, n4 (July, 1979), 149-159