Depositional and Diagenetic Environments of Carbonate-Siliciclastic Rocks of the Glen Dean Formation (Upper Mississippian), Illinois Basin, u.s.a

Abstract

219 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.About 1200 vertically oriented carbonate, sandstone and shale samples were collected from twenty three stratigraphic sections of the Glen Dean Formation in the Illinois Basin.Detailed petrographic investigation using the microfacies approach has led to the recognition of sixteen distinct carbonate microfacies. Their vertical succession and reciprocal relationships in the different sections and their correlation coefficients led to the recognition of an ideal shallowing upward sequence in turn converted into a horizontal depositional model. The model consists of a shallow open marine subtidal carbonate platform with the following environments from offshore to onshore: lower slope; upper slope; outer bank with three sub-bank environments (foraminiferal, crinoidal, and oncolitic); inter bank; inner bank with three sub-bank environments (bryozoan, oncolitic, and oolitic); lagoon.The petrographic analysis of the siliciclastic rocks led to the recognition of five microfacies: siltstone, quartz arenite, quartz arenite with argillaceous matrix, quartz wacke and shale. A depositional model was developed which consisted of a deltaic complex periodically prograding over the eastern shelf of the Illinois Basin. Consequently, three distinct environments were juxtaposed: delta system, carbonate platform and basin. At times sands and muds cut across the carbonate platform by means of channel systems and were deposited in the basin by gravity flows or major storm surges.The clay mineral assemblage of the shales from the deltaic fringe consists of discrete illite, kaolinite or chlorite, and mixed layer illite/smectite. Kaolinite and chlorite display a north-south zonation due to their physical segregation in the depositional environment with kaolinite in more shoreward and chlorite in more marine environment. The illite/smectite composition ranges from 50 to 85% illite and from 15 to 50% smectite. Its mixed layered structure is short range ordered and/or random. These samples mainly reflect the effects of provenance.The clay mineral assemblage of the shales from the central part of the basin contains long range ordered illite/smectite with the composition of 90 to 95% illite and 5 to 10% smectite. These samples mainly reflect the effects of thermal diagenesis probably due to burial.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD