Abstract

Southeastern Minnesota contains an extensive karst, developed in limestones and dolomites ranging in age from Early Ordovician to Middle Devonian. Preliminary results from U-series dated speleothems from caves within the karst show cyclic deposition of secondary calcium carbonate that coincides with cycles of late Pleistocene glaciation. Peak intervals of deposition, which broadly correlate with interglacial or interstadial climates, occur from the present to 13,000 yr B.P., from 35,000 to 70,000 yr B.P., from 90,000 to 170,000 yr B.P., and an undivided interval from 170,000 to 350,000 yr B.P. Intervals of little or no deposition are thought to reflect glacial climates. The youngest growth intervals can be interpreted in terms of known glacial records in the Midwest, but for the older intervals, where the glacial record is not well defined and beyond the range of radioactive dating, it becomes more difficult to correlate speleothem deposition to glacial cycles. Although the groups of ages are in general agreement with sea-level curves, the correlation is not exact. Local climatic conditions seem to have had as much importance in determining when deposition occurred as did the major climatic cycles recorded in the marine record.

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