The Interplay of Eustasy and Lithospheric Flexure in Forming Stratigraphic Sequences in Foreland Settings: An Example from the Antler Foreland, Nevada and Utah
Katherine A. Giles, William R. Dickinson, 1995. "The Interplay of Eustasy and Lithospheric Flexure in Forming Stratigraphic Sequences in Foreland Settings: An Example from the Antler Foreland, Nevada and Utah", Stratigraphic Evolution of Foreland Basins, Steven L. Dorobek, Gerald M. Ross
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Stratigraphic relationships within the Late Devonian to Early Mississippian Antler foreland of eastern Nevada and westernmost Utah suggest that lithospheric flexure in conjunction with eustasy were important primary controls on accommodation trends. Accommodation trends attributed to lithospheric flexure include: (1) sequence-scale opposing relative sea-level trends in time-equivalent strata and (2) regional-scale inversion of topography.
Loading of the lithosphere by eastward thrust emplacement of the Roberts Mountains allochthon (RMA) over the North American craton from Late Devonian to Early Mississippian time resulted in flexural warping of the craton into an asymmetric downwarp (foreland basin), an upwarp at the cratonward edge of this basin (forebulge), and farther cratonward, a broad, shallow downwarp (back-bulge basin). Stratigraphic sequences formed in conjunction with active flexure of the lithosphere display opposing relative sea-level trends Strata in flexurally subsiding areas reflect increasing trends in accommodation space, and areas of flexural upwarp (forebulge) reflect decreasing trends in accommodation space. During quiescent times, when no new flexural accommodation space was being produced, strata reflect congruous trends in accommodation space predominantly controlled by eustasy.
Eastward migration of the flexural features occurred sporadically in response to eastward transport of the RMA. Migration of the flexural features resulted in regional-scale inversion of topography. Areas formerly occupied by the forebulge were downflexed and incorporated into the foreland basin. Conversely, areas formerly occupied by the back-bulge basin were uplifted as the forebulge migrated cratonward. Stratigraphic evidence of inversion permits delineation of changes in the position and geometry of flexural topography during the transition from a passive to a collisional margin regime.
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Stratigraphic Evolution of Foreland Basins - A strong case can be made that foreland basins are where the casual links between sedimentation and tectonic events were first recognized, as evidenced by the interpretations of geologists working in classic foreland areas. This Special Publication was derived from a Research Symposium entitled ?Stratigraphic Sequences in Foreland Basins ?held at the AAPG-SEPM joint annual meeting on June, 1992, in Calgary, Alberta, Canada. This volume provides a well-balanced perspective of current research on foreland basin stratigraphy and also serves as another element in the evolving framework that comprises our understanding of foreland basins. Given that so many of earth?s resources are found in foreland basins and that foreland basin strata often provide the only preserved record of the tectonic events that led to basin development, the impetus for continued studies of foreland basin strata should remain for many generations of geologists to come.