Geological Tests of the Varve and Radiocarbon Chronologies

The time since the Valders glacial maximum at Milwaukee is estimated on stages, features, and sediments of the glacial Great Lakes, on the ice-border movements at Lake Simcoe, on the regressions and transgressions of the marine shore line in the Ottawa region, and on other geological events and features. The principal time estimates are as follows: the post-Nipissing age, 3,500 years; the post-North Bay drainage or post-Pembroke age, 14,500; and the post-Valders age, 18,000 or 19,000 years. In appraising radiocarbon dates, it is essential to keep in mind that the C¹⁴ content in an organic layer such as the Two Creeks forest bed can be expected to have undergone about equal extra changes, so that several analyses check only one another but not the actual age of the sample. Several determinations do not certify the age merely because of agreement. Each geological C¹⁴ date should be checked for general reasonableness and weighed against the geological knowledge. C¹⁴ dates are not absolutes to be accepted blindly. The time estimates here made generally support the varve chronology. They also suggest that the C¹⁴ dates for the Nipissing Great Lakes are of the right magnitude but that most older dates become progressively too young as the age increases, so that the date for the Two Creeks forest bed is several thousand years too young. One reason for this may be that contamination of the material becomes increasingly effective, as the original radiocarbon is being reduced by the natural decay. The C¹⁴ chronology and its correlation with Europe have unreasonable geologic and climatic implications, whereas the varve chronology synchronizes the major temperature ages in North America and Europe.