INTERPRETATIONS OF SPELEOGENESIS AND PALEOCLIMATE FROM SPELEOTHEMS IN DONNEHUE'S CAVE, INDIANA
We provide age and stable isotope data for a set of 9 stalagmites and flowstones from Donnehue’s Cave, located near Bedford, Indiana. Donnehue’s ~ 1.5 km long passages are arranged in two distinct levels – a lower level that corresponds to the presently wet, active part of the cave, and an upper level that corresponds to the presently dry, inactive part of the cave. The location of this cave, within a few kilometers south of both the Illinois and Wisconsin glacial maxima, makes it ideal for studying paleoclimate of the Midwestern US.
Powder samples (~ 10 mg) extracted by microdrilling along speleothem growth layers were dated by U-series (234U/230Th) technique using multi-collector inductively coupled plasma mass spectrometer (MC ICP-MS). Speleothem ages cover a time span of several hundred to about 500,000 years before present (BP), with several of the samples having regions of overlapping age. Sediment from beneath the stalagmites growing in the lower passage was dated by OSL, and its age is 140,000 +/- 9,490 years BP.
A conceptual model for the formation of the cave, its evolution and relationship to glacial and interglacial periods was developed based on the age differences between the spleleothems and sediments in the upper and lower passages. While speleothem ages range between 91,800 to 375,000 years BP in the upper passage, the oldest dated speleothem age in the lower passage is 60,000 years BP. The speleothem ages in the lower passage and the age of the sediment (~ 140,000 years BP) growing beneath the speleothems suggest that the lower passage was developed as a result of the influx of melt waters near the end of the Illinoian stage. Finally, stable isotope data for a stalagmite with good age control from 56,300 years BP to 12,800 years BP provides insight into climatic events and paleovegetation data from the Midwest.