Early-Middle Ordovician lithostratigraphy, biostratigraphy, and depositional environments of the Illinois Basin.
Item
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Title
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Early-Middle Ordovician lithostratigraphy, biostratigraphy, and depositional environments of the Illinois Basin.
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Identifier
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AAI9924851
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identifier
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9924851
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Creator
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Shaw, Thomas Howard.
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Contributor
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Adviser: B. Charlotte Schreiber
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Date
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1999
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Language
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English
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Publisher
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City University of New York.
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Subject
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Geology
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Abstract
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Biostratigraphic and sedimentological data from the early-Middle Ordovician of the Illinois Basin allows for identification of four genetic depositional sequences made up of a complex mosaic of time-transgressive, clastics, carbonates and evaporites. The synchroneity of these sequences with those of the Taconic foreland, eastern North America, and Arbuckle region, southern Midcontinent, strongly implies a common control, either tectonic and/or eustatic, for the creation of accommodation space. Lithostratigraphic units are mostly time-transgressive lithotopes indicative of specific inner shelf, restricted marine depositional subenvironments.;Examining the interaction of the Taconic foreland and Illinois Basin during the early-Middle Ordovician is hampered by the insufficient resolution of age determinations for the Ancell Group, and its regional equivalents, due to four factors. (1) Total stratigraphic ranges for the component faunas of the peritidal lower Ancell Group are still to poorly-known to be usable for graphic correlation. (2) Given the absence of biostratigraphic datum's within this peritidal interval, graphic age determination requires the assumption of constant net rock accumulation. This assumption is questionable based on evidence for the development of condensed interval(s), differential compaction and post-burial evaporite dissolution. (3) Higher resolution sampling is required in some sections to more adequately establish biostratigraphic control for parts of the basin. And, (4) formation contacts defined for outcrop-based stratigraphic units are difficult to identify in the subsurface and units widely recognized in the subsurface have not been tied in detail with their correlative surface exposures.;A key finding of this study is recognition of wide-spread, early-Middle Ordovician evaporite depositional which has been unappreciated due to the lack of sedimentological study of the St. Peter Sandstone in the subsurface, and the apparent dissolution of many of the soluble phases by meteoric groundwater. The presence of evaporites has important implications for the sourcing of brines and for subsidence modeling of the basin. Previously, mass balance required deep basinal sources for sulfur, and other ions, for mineralizing brines. Evaporite dissolution offers an alternative source at a shallower level within the basin, but complicates subsidence modeling in that back-stripping using simple compactional functions does not account for this loss of rock volume.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
