The chemical composition of authigenic illite within two sandstone reservoirs as analysed by ATEM

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Authors:Warren, E. A.; Curtis, C. D.
Author Affiliations:Primary:
Univ. Sheffield, Dep. Geol., Sheffield, United Kingdom
Volume Title:Clay Minerals
Source:Clay Minerals, 24(2), p.137-156. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0009-8558
Publication Date:1989
Note:In English. 31 refs.; illus. incl. 7 tables, sketch map
Summary:Analytical transmission electron microscopy (ATEM) was used to obtain chemical analyses of single illite crystals from Upper Carboniferous reservoir sandstones of the Bothamsall Oilfield, East Midlands, UK, and from Rotliegendes (Permian) sandstones of the North Sea. All samples were found to be highly aluminous, with only minor Mg and Fe, and to have near-ideal dioctahedral sheet totals. No significant variation in chemical composition of illite was found within the Bothamsall reservoir rocks, irrespective of paragenesis or stratigraphic horizon. Similar results were obtained from the Rotliegendes samples. Variation was found, however, between Bothamsall and Rotliegendes analyses populations. The Rotliegendes illites were distinctly more K-rich, which is the result of greater charge deficiency in the octahedral sheet. These results indicate that all the illite in both reservoirs precipitated in equilibrium with the reservoir pore-fluid. Furthermore, they imply that the physico-chemical composition of the pore-fluid did not evolve significantly between the different illite generations in the Bothamsall samples. These data, when compared with published analyses of authigenic illite, indicate that the compositional field for illite in sandstones is restricted in comparison with that of illite in mudrocks.
Subjects:Authigenic minerals; Carboniferous; Chemical composition; Chemical properties; Clastic rocks; Clay mineralogy; Data processing; Experimental studies; Genesis; Illite; Mineral data; Mineralogy; Minerals; Paleozoic; Permian; Rotliegendes; Sandstone; Sedimentary rocks; Sheet silicates; Silicates; TEM data; Upper Carboniferous; Atlantic Ocean; East Midlands; England; Europe; Great Britain; North Atlantic; North Sea; United Kingdom; Western Europe; Bothamsall Oilfield
Coordinates:N510000 N611000 E0110000 W0040000
Abstract Numbers:90M/2645
Record ID:1989080947
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
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