Paper No. 17
Presentation Time: 9:00 AM-6:00 PM

AN EXTENDED ASTRONOMICAL TIME SCALE FOR THE CENOMANIAN/TURONIAN BOUNDARY INTERVAL, CRETACEOUS WESTERN INTERIOR BASIN (USA)


MA, Chao, Department of Geosience, University of Wisconsin Madison, Weeks Hall, 1215 W Dayton St, Madison, WI 53706, MEYERS, Stephen R., Department of Geoscience, University of Wisconsin, 1215 West Dayton St, Madison, WI 53076, SAGEMAN, Bradley B., Earth and Planetary Sciences, Northwestern University, 1850 Campus Drive, Evanston, IL 60208, SINGER, Brad S., Geoscience, University of Wisconsin-Madison, 1215 W. Dayton St, Madison, WI 53076, JICHA, Brian R., Department of Geoscience, University of Wisconsin-Madison, 1215 W. Dayton St, Madison, WI 53706 and JOO, Young Ji, Department of Earth and Planetary Sciences, Northwestern University, 1850 Campus Drive, Evanston, IL 60208-2150, mchao4@wisc.edu

In this study, X-ray fluorescence (XRF) core scanning is utilized to develop a new elemental dataset for cyclostratigraphic investigation of Cenomanian/Turonian strata in the Western Interior Basin (WIB), using material from the Aristocrat Angus core (north central Colorado). The new XRF data set provides the first continuous 5 mm resolution analysis of a wide suite of paleoenvironmental proxies through the Hartland Shale Member and Bridge Creek Limestone Member, including Oceanic Anoxic Event 2 (OAE 2), allowing assessment of climate-sensitive lithogenic (Al, Si, K), biogenic (Ca), and authigenic (S, Fe/Al, Mn) processes. 40Ar/39Ar radioisotopic ages from three biozones, including a new age from the Dunveganoceras pondi biozone (uppermost Lincoln Limestone Member), provide geochronologic constraints for our cyclostratigraphic assessment. Application of average spectral misfit analysis to evaluate the XRF data yields strong evidence for orbital influence on climate and sedimentation during deposition of both members. The new results from the Bridge Creek Limestone Member are consistent with the published astrochronology from the USGS #1 Portland Core (Meyers et al., 2001), and identification of an orbital signal in the underlying Hartland Shale Member now allows extension of the WIB astrochronology into the earlier Cenomanian, prior to OAE 2.