Oxygen isotope records of goethite from ferricrete deposits indicate regionally varying Holocene climate change in the Rocky Mountain region, U.S.A. |
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| Authors: | Derek J Sjostrom Michael T Hren |
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| Institution: | a Department of Geology, The University of Montana, Missoula, MT 59812, USA
b Department of Earth and Environmental Sciences, Stanford University, Stanford, CA 94305, USA |
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| Abstract: | Oxygen isotopes of goethite from ferricrete deposits were measured from both northern and southern Rocky Mountain localities to assess geographic variability in regional Holocene paleoclimate change. A ∼3.7‰ increase in oxygen isotope values of 14C-dated goethites in the northern Rocky Mountains suggests a regional-scale relative increase in amounts of isotopically heavy summer precipitation since the early Holocene. In contrast, oxygen isotope values from the southern Rocky Mountains increase abruptly ∼2.1‰ at ∼6200 14C yr B.P., then decrease ∼2.4‰ between ∼2000 14C yr B.P. and the present. We interpret this period of relatively high δ18O values as evidence for a middle Holocene warm period combined with a relatively strong summer monsoon. These variable climate records suggest that the Rocky Mountains of the western United States have had a spatially heterogeneous Holocene climate history. |
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| Keywords: | Oxygen isotopes Goethite Ferricrete Holocene Paleoclimate Rocky Mountains |
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