20 



ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 496 



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10 



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5 50 



« 60 



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£ 70 



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80 

 90 

 100 

 I 10 

 120 



0.49 mm/yr 

 Ambrosia 

 Core I00I-3A 



2770 ± 230 (ISGS-159) 



3050 ± 120 (ISGS-153) 



3390 ± 150 (ISGS-158) 



3890 ± 120 (ISGS-152) 



7460 ± 150 

 (ISGS-155) 



2 3 



Radiocarbon years 



thousands) 



Fig. 9 - Sedimentation rates from central Lake Michigan. A. Plot of the 



depth of the Ambrosia increase in core 1001-3A; B. Plot of the radio- 

 carbon dates from core 800-5. Rates are determined from the slopes 

 of the lines and are given in mm/yr. 



Late Holocene sedimentation rates calculated for the other Great Lakes 

 show a range of values similar to that found for Lake Michigan. In western Lake 

 Superior, Maher (1975) reported rates of . 1 to . 8 mm/yr. The highest rate was 

 in water 100 m deep where there was an influx of river sediments. Postsettlement 

 rates in western Lake Superior were as much as 10 times greater than the presettle- 

 ment rates (Maher, 1975). In Lake Ontario, the beginning of the Ambrosia increase 

 was found at a depth of 15 to 20 cm in the central basin, an indication of rates 

 of 1.3 to 1.7 mm/yr, which are significantly greater than the presettlement rates 

 (McAndrews, 1972). Data presented by Kemp et al. (1974) indicate sedimentation 

 rates of 2.3 mm/yr for Lake Ontario, 5 . 8 to 15 mm/yr for Lake Erie, and 1.2 mm/yr 

 for Lake Huron. 



The radiocarbon dates from core 1 000-3 C plot nearly a straight line with 

 depth (fig. 8) and suggest a sedimentation rate of 0.65 mm/yr between 25 cm and 

 95 cm. This regression line intersects the zero-depth line at about 3700 radio- 

 carbon years B.P. The wood date of 910 ±140 radiocarbon years B.P. (ISGS-100) 

 from core 836-5 indicates a sedimentation rate of 0.90 mm/yr. These rates are 

 about the same as, or slightly lower than, the rate since 1840. Working with 

 210 Pb, Edgington and Robbins (1976) report sedimentation rates in the same range 

 for southern Lake Michigan. 



