NEWLY DISCOVERED SPELEOTHEM GROWTH PHASES IN OREGON CAVES (SW OREGON)

Oregon Caves is located in the Siskiyou Mountains of southwestern Oregon (USA). The growth of carbonate speleothems in the marble cave is sensitive to temperature, precipitation, and environmental conditions at the surface. Previous work at Oregon Caves revealed intermittent growth phases over the last 380,000 years, with a majority of speleothem growth occurring during interglacial periods (Ersek et al., 2009). For this study, we drilled 8 small-diameter calcite cores from 6 previously unstudied intact stalagmites in Oregon Caves. In addition, calcite chips were collected from 2 broken stalagmites using a small chisel. The age of calcite sampled was determined using uranium-thorium (U-Th) dating at the University of Minnesota. U-Th results reveal growth phases at 7.7 thousand years before present (ka), 40 ka, 132-123 ka, 216 ka, 218 ka, 385 ka, and 522-513 ka. 2σ relative age uncertainties average 2%. One stalagmite is older than the limit of U-Th dating (>600 ka) and is currently the oldest known stalagmite in Oregon Caves. Similarly aged stalagmites are clustered together within the cave. Upper Banana Grove chamber (~100 ft below surface) contains the oldest stalagmites (>500 ka). Consistent with Ersek et al. (2009), nearly all sampled stalagmites grew during interglacial periods, specifically Marine Isotope Stage (MIS) 1, 5e, 7c, 11 and 13. Our preliminary results are part of an ongoing investigation into the climate history of SW Oregon during previous interglacial periods.

Ersek, V., Hostetler, S. W., Cheng, H., Clark, P. U., Anslow, F. S., Mix, A. C., & Edwards, R. L. (2009). Earth and Planetary Science Letters, 279(3-4), 316-325