Synthetic Models of Unconformity Development in Foreland Basins
Christopher Beaumont, David D. Johnson, 1994. "Synthetic Models of Unconformity Development in Foreland Basins", Tectonic and Eustatic Controls on Sedimentary Cycles, John M. Dennison, Frank R. Ettensohn
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Two competing hypotheses can explain distal unconformities in foreland basin stratigraphy: peripheral-bulge migration with stress relaxation in the lithosphere (Quinlan and Beaumont, 1984, Canadian Journal of Earth Sciences, v. 21, p. 973) or orogen tectonics and basin-filling mechanisms (Flemmings and Jordan, 1990, Geology, v. 18, p. 335; Sinclair and others, in review). We investigate synthetically the origin of unconformities using the planform model (Johnson and Beaumont, abstract above). The figure shows an unconformity bounded sequence for one tectonic cycle, on a stress-relaxing lithosphere. I-type erosion occurs when constructive orogenic loading outstrips basin-filling and lithospheric relaxation. F-type erosion occurs when peripheral bulge migration with lithospheric-stress relaxation dominates. I- and F-type unconformities remain distinct when intervening sediments are preserved, otherwise the composite unconformity reflects the superposition of tectonic and relaxation dominated phases that may span several tectonic cycles.
Does synthetic basin stratigraphy provide the evidence to distinguish I- from F-type erosion and to determine which dominates?
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The collected volume begins with a brief perspective by one of the conveners, followed by articles in order of increasing stratigraphic age. Eustatic sea-level changes and tectonic warpings of basins are competing mechanisms for explaining many stratigraphic patterns. The model for sea-level changes should be developed first for a basin, since it is allocyclic and leads to a series of time bands in the strata. The residual effects should then be modeled for tectonic patterns affecting the depositional processes. Doing the reverse limits time constraints on the tectonic warping models and will blur the resolution of detailed time surfaces in the strata. Case histories of situations with both tectonic warping and time surfaces marked by sea-level events will lead to improved interpretations of earth history.