Comparison of varve and 14C chronologies from Steel Lake, Minnesota, USA

Annually laminated sediments (varves) offer an effective means of acquiring high-quality palaeoenvironmental records. However, the strength of a varve chronology can be compromised by a number of factors, such as missing varves, ambiguous laminations and human counting error. We assess the quality of a varve chronology for the last three millennia from Steel Lake, Minnesota. through comparisons with nine AMS C-14 dates on terrestrial plant macrofossils from the same core. These comparisons revealed an overall 8.4% discrepancy, primarily because of missing/uncountable varves within two stratigraphic intervals characterized by low carbonate concentrations and obscure laminations. Application of appropriate correction factors to these two intervals results in excellent agreement between the varve and C-14 chronologies. These results, together with other varve studies, demonstrate that an independent age-determination method, such as C-14 dating, is usually necessary to verify, and potentially correct, varve chronologies.