2000 GSA Annual Meeting -- Reno, Nevada
2000 GSA Annual Meeting -- Reno, Nevada
Author(s): MEYERS, Stephen R., SAGEMAN, Bradley B., Department of Geological Sciences, Northwestern University, Evanston, IL 60208, meyers@earth.nwu.edu
Keywords: Milankovitch, OAE-II, KWIS, Bridge Creek
Late Cenomanian-Early Turonian hemipelagic deposits of the Cretaceous Western Interior (North America) are characterized by laterally extensive lithologic couplets traceable over 1000's of kilometers within the basin. Previous cyclostratigraphic analysis of the deposits in the central portion of the basin (Colorado, USA) have confirmed the presence of statistically significant Milankovitch orbital components. The diagnostic orbital components were identified through the application of spectral analysis techniques to stratigraphic data series which contain numerous radiometrically dated bentonites. This preserved orbital signal provides an internal stratigraphic chronometer that far exceeds the resolution of other absolute or relative dating methods applicable to pre-Pleistocene deposits. Using advanced time series analysis techniques, the orbital chronometer recorded in these deposits can be utilized to identify hiatuses, as well as to reconstruct high-resolution bulk sedimentation rates in the study interval. In this study we report initial results from a quantitative cyclostratigraphic analysis of late Cenomanian-early Turonian sedimentation patterns across latitude in the Western Interior basin. These results are based on the analysis of new core data from the northern part of the basin (Saskatchewan, Canada), in addition to an analysis of new data from the previously studied central basin core (Colorado, USA). Geochemical data from these cores is used to constrain sediment source and depositional conditions during the late Cenomanian-early Turonian. The major contributions resulting from the study include: 1) refinement of relative sea-level reconstructions, 2) an improved test of hypotheses for climatic and oceanographic change during the late Cenomanian-early Turonian (Ocean Anoxic Event II), and 3) quantification of the meridional expression of orbital cyclicity during the Mid-Cretaceous greenhouse climate (i.e., how do frequencies recorded by strata change across latitude in terms of compositional variation and dominant frequency content).
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