Geodynamic significance of localized spasmodic rapid-subsidence rates within the Cretaceous of central North America |
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| Authors: | EHT Whitten |
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| Institution: | Department of Geological Sciences, Northwestern University, Evanston, Illinois 60201, USA |
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| Abstract: | On the basis of spatial-time analyses, rates of subsidence within 5 Ma intervals in Montana, Wyoming, and adjacent areas, are mapped on the basis of thicknesses of the dominantly shallow-water sedimentary rocks; this is possible by using (a) existing detailed radiometric (mainly for abundant bentonites) and biostratigraphic chronology, and (b) published details of several hundred well logs and measured outcrop sections. Nine 5 Ma-interval maps for Montana and Wyoming show that, in general, as in eastern U.S.A. and eastern Brazil, subsidence rates tend to be low (< 50 m/Ma and commonly < 25 m/Ma) and monotonous in space and time. However, a few localized domains are characterized by significantly higher sedimentation and subsidence rates (> 100 m/Ma and very locally > 200 m/Ma or even > 300 m/Ma); these domains are sharply defined in both space and time. Domains of very high rates sometimes partially overlap areally in successive 5 Ma intervals, but they do not do so in all cases.The well-documented Cretaceous global marine transgressions are complicated by these differential-downwarp events of the “basement”. The broadly analogous patterns documented in the Western Interior Basin, eastern U.S.A., and eastern Brazil militate against special localized explanations (e.g. a shallowly subducted plate). Analogies with major cratonic basins and geodynamic implications are reviewed briefly. |
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| Keywords: | Montana Wyoming Cretaceous sedimentation rates Subsidence rates Sea-level change Western Interior Basin |
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