Integrating 40Ar/39Ar, U-Pb, and astronomical clocks in the Cretaceous Niobrara Formation, Western Interior Basin, USA
Bradley B. Sageman et al., Dept. of Earth and Planetary Sciences, Northwestern University, 1850 Campus Drive, Evanston, Illinois 60208, USA. Published online 20 Mar. 2014; http://dx.doi.org/10.1130/B30929.1.
This study by Brad Sageman and colleagues develops and applies new methods for refinement of the geologic time scale to a key Late Turonian through Early Campanian (Late Cretaceous, about 80 to 90 million years ago) succession in the Western Interior Basin of North America. Integration of new high-precision radioisotope dates using both Ar-Ar and U-Pb systems, and floating astrochronologies developed from spectral analysis of the chalk and marl beds of the Niobrara Formation, produce revised estimates for these age boundaries. Sageman and colleagues introduce a new method of estimating uncertainties due to geologic correlation and combines these with astrochronologic uncertainties and those associated with radioisotopic methods to achieve comprehensive total uncertainty estimates for the Stage boundary ages. The co-occurrence of U-Pb and Ar-Ar data from the same ashes allows confirmation of the recently revised age for the Fish Canyon monitor mineral (28.201 million years old) and thereby makes a contribution to the on-going EarthTime initiative, which is working to refine and calibrate deep time geochronometers.
Testing the astronomical time scale for oceanic anoxic event 2, and its extension into Cenomanian strata of the Western Interior Basin (USA)
Chao Ma et al., Departm
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Geological Society of America