Interpretations of Paleoclimate and Speleogenesis from Speleothems in Donnehue's Cave, Indiana

A detailed understanding of the climate of the Pleistocene (1,800,000 years ago to 10,000 years ago) is crucial for constructing predictive models of future climate trends. Researchers studying past climate (paleoclimate) records from different parts of the world are beginning to piece together an increasingly detailed picture of past climatic patterns on a global scale. Some of the most reliable resources for investigating continental paleoclimatic conditions are cave deposits, especially speleothems (stalagmites and flowstones). \nA major obstacle in the overall understanding of continental climatic fluctuations in the Midwest is the scarcity of the well-dated paleoclimate records. This investigation provides additional data from the midcontinental US and puts forth a conceptual model of the development of a cave in an area proximal to past glacial margins. Donnehue’s Cave is located near Bedford, Indiana, within a few kilometers of both the Illinois and Wisconsin glacial maxima. Speleothems from Donnehue’s cave were dated using the U-series (234U/230Th) technique that covers a time span of several hundred to ca. 500,000 years before present (BP). The ages of these speleothems are exceptionally continuous over the past ca. 400,000 years, the time during which major glacial and interglacial episodes affected most of the Midwestern US, as well as the rest of the globe. By investigating stalagmite and flowstone ages in both the lower and upper passage of Donnehue’s Cave, it was possible to develop a conceptual model for its formation, evolution and relationships to glacial and interglacial periods. Further, stable isotope data for a stalagmite with ages corresponding to known climatic events were collected and compared with the paleovegetation data from other proxies. This step was necessary for accurate modeling of the climatic trends in the study area for the period from 56,300 years BP to 12,800 years BP.