Carbonate Microfacies and Depositional Environments of the Joachim Dolomite (Middle Ordovician), Southeast Missouri and Southern Illinois, u.s.a
Okhravi, Rasool
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https://hdl.handle.net/2142/71126
Description
Title
Carbonate Microfacies and Depositional Environments of the Joachim Dolomite (Middle Ordovician), Southeast Missouri and Southern Illinois, u.s.a
Author(s)
Okhravi, Rasool
Issue Date
1983
Department of Study
Geology
Discipline
Geology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Geodesy
Abstract
A total of 1120 vertically-oriented carbonates samples were collected from eleven stratigraphic sections of the Joachim Dolomite located in southeast Missouri and southern Illinois.
Microfacies studies revealed eleven distinct microfacies. From the superposition of the microfacies which form an ideal shallowing-upward sequence, a depositional-diagenetic model was constructed and confirmed by a bivariate correlation analysis between microfacies. The depositional environments were interpreted as follows: dolomitized pelletoidal calcilutite to calcisiltite (offshore); dolomitized mud-supported intraclastic calcarenite to calcirudite (shoreface); dolomitized grain-supported intraclastic calcarenite with interstitial pelletoidal calcisiltite matrix and poikilotopic sparite cement (intra-bioclastic bar); dolomitized mud-supported to grain-supported intraclastic pelletoidal calcarenite to calcirudite with calcisiltite matrix (back-bar flat); dolomitized pelletoidal calcilutite to calcisiltite (lagoon); dolomitized stromatolite-constructed limestone (stromatolitic ridge); dolomitized mud-support to grain supported oolitic-intraclastic calcarenite with calcisiltite matrix (oolitic flat); dolomitized stromatolite-bearing calcisiltite (carbonate flat); dolomitized pelletoidal calcisiltite with fenestral fabric (inner stromatolitic ridge); dolomitized calcilutite with anhydrite and gypsum (evaporitic flat); pure quartz arenite (dunes). Unimodal and bimodal quartz arenites of the Joachim Dolomite deposited respectively in dune and interdune positions by winds were taken as an independent evidence to demonstrate the desert environment and its temporary extension over the carbonate platform.
The offshore through lagoonal microfacies of the Joachim Dolomite were secondarily dolomitzed by a freshwater-seawater mixing process (Dorag model), while the rest of the microfacies were dolomitized penecontemporaneously by an evaporative pumping mechanism of sabkha type.
The general environmental evolution of the microfacies shows that a complete section of the Joachim Dolomite consists of the superposition of eleven asymmetric cycles which display a slow shallowing-upward phase followed by a rapid deepening phase.
Paleoclimatic data confirm that the investigated area was located during the Middle Ordovician at the appropriate latitude for development of an arid climate and that the Joachim Dolomite can be interpreted as a large-scale sabkha covering the middle part of Illinois with a transition to open sea conditions in a southward direction.
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