Burial diagenesis of illite/smectite in shales and the origins of authigenic quartz and secondary porosity in sandstones

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doi: 10.1016/S0016-7037(97)00066-5
Authors:Lynch, F. Leo; Mack, Lawrence E.; Land, Lynton S.
Author Affiliations:Primary:
University of Texas at Austin, Department of Geological Sciences, Austin, TX, United States
Volume Title:Geochimica et Cosmochimica Acta
Source:Geochimica et Cosmochimica Acta, 61(10), p.1995-2006. Publisher: Pergamon, Oxford, International. ISSN: 0016-7037
Publication Date:1997
Note:In English. 68 refs.; illus., incl. 4 tables, sketch map
Summary:Chemical analyses are presented of interlayered illite/smectite, the most abundant mineral in Frio formation shales from the Gulf of Mexico basin. Samples of nearly monomineralic purity were separated from 19 cores of shales between 6898 and 15 640 ft depth; the modes and chemistry are given for the <<<[dollar]I> 0.1 µm fraction. Progressive burial of the rocks was responsible for chemical and mineralogical changes in the I/S and these are listed; the Δ^>18O composition of the mixed-layer I/S decreases from ∼ 25 to ∼ 170/00 (SMOW). The crystallography changes also with depth from random-interstratification with low % I to ordered-interstratification with high % I. burial diagenesis of the formation was an open-system process requiring addition of K2O and Al2O3 with loss of SiO2 - the latter forming quartz overgrowths in the associated Frio sandstones. Reduction of Fe3+ in I/S and concurrent oxidation of C in organic matter is a source of acid dissolving feldspar and rock fragment framework grains producing secondary porosity. [R.K.H.]
Subjects:Authigenic minerals; Burial diagenesis; Cenozoic; Chemical reactions; Clastic rocks; Clay mineralogy; Clay minerals; Diagenesis; Experimental studies; Framework silicates; Frio Formation; Geochemistry; Illite; Oligocene; Open systems; Overgrowths; Paleogene; Petroleum; Porosity; Precipitation; Quartz; Reservoir rocks; Sandstone; Secondary porosity; Sedimentary rocks; Shale; Sheet silicates; Silica minerals; Silicates; Smectite; Solution; Tertiary; X-ray diffraction data; Aransas County Texas; Brazoria County Texas; Fort Bend County Texas; Gulf Coastal Plain; Kenedy County Texas; Nueces County Texas; San Patricio County Texas; Texas; United States
Abstract Numbers:97M/3591
Record ID:1997042395
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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