We report on pollen, plant macrofossils, and associated lithostratigraphy of a sediment core extracted from the base of Silver Lake, a kettle lake in northern Lower Michigan, USA, which reveal a complex deglacial scenario for ice block melting and lake formation, and subsequent plant colonization. Complementary multivariate statistical and squared chord distance analyses of the pollen data support these interpretations. The basal radiocarbon age from the core (17 540 cal years BP) is rejected as being anomalously old, based on biostratigraphic anomalies in the core and the date’s incongruity with respect to the accepted regional deglaciation chronology. We reason that this erroneous age estimate resulted from the redeposition of middle-Wisconsin-age fossils by the ice sheet, mixed with the remains of plants that existed as the kettle lake formed at ca. 10 940 cal years BP by ice block ablation. Thereafter, the kettle lake became a reliable repository of Holocene-age fossils, documenting a mature boreal forest that existed until 10 640 cal years BP, followed by a pine-dominated mixed forest, an early variant of the mixed conifer–hardwood forest that persists to the present day. Our study demonstrates that researchers investigating kettle lakes, a common depositional archive for plant fossils in deglaciated landscapes, should exercise caution in interpreting the basal (Late Pleistocene/early Holocene-age) part of lake sediment cores.
Bibliographical noteFunding Information:
We thank Chad Wittkop (now of Minnesota State University) for coring Silver Lake and archiving this sediment core untouched at LacCore, University of Minnesota-Twin Cities campus, USA. We thank Amy Myrbo and Anders Norens of LacCore for sharing photographs they took of the Silver Lake core and for permitting us to sample and analyze the core for this research. We also acknowledge support from the National Science Foundation (NSF) grant GSS-1759528 for this study. Any opinions, findings, and conclusions or recommendations expressed are, however, those of the authors and do not necessarily reflect the views of NSF. Comments by Jim Gardner (associate editor), Michael Lewis, and two anonymous reviewers helped us refine our interpretations and improve the manuscript.
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- Kettle lakes
- Radiocarbon dating
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