Radiocarbon Dates of Pre-Mankato Events inEastern and Central North America

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Science  06 May 1955:
Vol. 121, Issue 3149, pp. 649-658
DOI: 10.1126/science.121.3149.649


1) A group of samples from horizons previouslycorrelated with the upper part of the Cary substageconfirms the correlation as reasonable and is consistently related in time to the dates of the peat layerat Two Creeks and subsequent Mankato events.

2) A major glaciation affected the Great Lakes region beginning 25,000 or more yr ago and reachingits maximum extent about 18,000 yr ago. It is represented by drift correlated in Ohio with the Cary substage and, at least in part, with the Tazewell substage; in Illinois and adjacent states it is correlatedwith most of the Tazewell substage and with theFarmdale loess.

3) The ecology and other associations implied bythe dated samples are more consistent with glacialthan with nonglacial conditions.

4) The lower till at Sidney, Ohio (W-188), onwhich is developed a soil considered a correlative ofthe Fox series soil on gravels and also buried by tillof the major glaciation of 25,000 to 18,000 yr ago, indicates an earlier glaciation extensively exposed inOhio and believed to be an early Wisconsin event.

Table 2. List of samples and dates arranged by agegroups.

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5) An earlier glaciation, or glaciations, is impliedat several localities by peat, gyttja, or wood morethan 30,000 yr old, overlain by till.

6) The time interval between the middle group andthe old group of samples, which has been determinedwithin conservative radiocarbon limits to be greaterthan 3000 yr, is possibly of the order of 16,000 yr,as suggested by the depth of leaching at Sidney, Ohio.(The ages of all the samples discussed are listed inTable 2.)

7) An attempt should now be made to fix moreclosely the dates of the old samples and to reexaminein the field the stratigraphic sequence in the light ofthe radiocarbon dates discussed.