Basin-scale cyclostratigraphy of the Green River Formation, Wyoming
W. Aswasereelert et al., Department of Geoscience, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA. Posted online 25 October 2012; http://dx.doi.org/10.1130/B30541.1.
The Green River Formation was deposited by "great lakes" that occupied parts of Wyoming, Colorado, and Utah during the Eocene epoch from about 53 to 44 million years ago. These lakes deposited a richly detailed stratigraphic record of climate change, corresponding to the most geologically recent period of warm climate. Their record may thus provide valuable insights into the behavior of future global warming, provided geoscientists can precisely measure rates and mechanisms of Eocene environmental change. W. Aswasereelert and colleagues present an innovative new way of doing so, by combining previously published radioisotopic dates from volcanic ash that fell into the lakes with a new technique called macrostratigraphy, which rigorously synthesizes outcrop and core data from multiple locations. Unlike previous studies, this approach avoids the need to assume an age model a priori, a practice that can lead to circular reasoning. Based on spectral analysis of macrostratigraphic time series, Aswasereelert and colleagues have discovered a strong 100,000 periodicity in the alternation of lake versus river deposits, which has effectively imprinted a high-resolution "calendar" directly on the rocks. These results suggest that even finer time resolution may be possible and also demonstrate the broader effectiveness of macrostratigraphy in quantifying cyclic sedimentation.
Reactivation of the Archean-Proterozoic suture along the southern margin of Laurentia during the Mazatzal orogeny: Petrogenesis and tectonic implications of ca. 1.63 Ga granite in southeastern Wyoming
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