Glacio-Eustatic Origin of Permo-Carboniferous Stratigraphic Cycles: Evidence from the Southern Cordilleran Foreland Region
William R. Dickinson, Gerilyn S. Soreghan, Katherine A. Giles, 1994. "Glacio-Eustatic Origin of Permo-Carboniferous Stratigraphic Cycles: Evidence from the Southern Cordilleran Foreland Region", Tectonic and Eustatic Controls on Sedimentary Cycles, John M. Dennison, Frank R. Ettensohn
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Shallow-marine and marginal-marine depositional systems of foreland regions between cratons and orogens are sensitive to all the potential influences thought to control stratigraphic cyclicity: autogenic, climatic, tectonic, tectono-eustatic, and glacio-eustatic. In foreland settings, both clastic and carbonate depositional systems of shelf or epeiric seas and adjacent coastal plains are responsive to (a) shifts in shoreline position caused by local or regional variations in sediment supply, and (b) fluctuations in accommodation space controlled by either global eustasy or tectonic flexure that changes relative sea level. For half a century, many have attributed development of prominent Permo-Carboniferous foreland cyclothems to glacio-eustasy in response to Gondwanan glaciations, but dominance of other controls is not easy to exclude. Stratigraphic analysis of key sequences in the southern Cordilleran region supports a primarily glacio-eustatic origin for Permo-Carboniferous cyclothems. This is based on the following observations difficult to reconcile jointly with dominance of other controls: (a) ubiquitous development of stacked cyclothems in both the Permo-Carboniferous foreland of the Ouachita-Marathon orogenic system and in correlative non-foreland settings of Nevada and Utah; (b) absence of comparable cyclicity in older Antler and younger Sevier foreland successions; (c) distinctly diachronous stratigraphic records produced by foreland tectonic flexure and associated migratory forebulges; (d) basinwide distribution of multiple intrabasinal cyclothems in selected Ancestral Rockies basins; (e) provisional interbasinal correlation of individual cyclothems from the midcontinent region through the Ouachita-Marathon foreland; and (f) apparent cyclothem duration within the Milankovitch time band.
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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.