Smectite-to-illite reactions in Salton Sea shales; a transmission and analytical electron microscopy study

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doi: 10.1306/212F8B20-2B24-11D7-8648000102C1865D
Authors:Yau, Yu-Chyi; Peacor, Donald R.; McDowell, S. Douglas
Author Affiliations:Primary:
Univ. Mich., Dep. Geol. Sci., Ann Arbor, MI, United States
Mich. Technol. Univ., United States
Volume Title:Journal of Sedimentary Petrology
Source:Journal of Sedimentary Petrology, 57(2), p.335-342. Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States. ISSN: 0022-4472
Publication Date:1987
Note:In English. 35 refs.; illus. incl. 2 tables
Summary:TEM/AEM study of a sequence of shales from the Salton Sea Geothermal Field revealed that the mechanism for the reaction of smectite to form illite is markedly different from that for Gulf Coast sediments. Illite in Salton Sea shales occurs principally as individual, euhedral-to-subhedral, pseudohexagonal crystals in open pore space. Smectite was not observed by TEM in proximity to such illite and is shown by XRD data to decrease in amount with depth as the proportion of illite increases. Illite is thus implied to be derived by complete dissolution of smectite (and other phases?), transport of components, and crystallization of illite from solution. However, in shallow sediments detrital smectite is also observed to be in part directly replaced by illite in a manner duplicating Gulf Coast textures. The mechanism by which smectite undergoes complete dissolution to allow precipitation of illite at a distant site is compatible with an open system such as the Salton Sea sediments, characterized by high water/rock ratio and relatively high permeability. In contrast, the mechanism involving a reaction front where the smectite is directly replaced by illite, such as occurred in Gulf Coast shales, is compatible with relatively impermeable shales. [K.A.R.]
Subjects:Chemical composition; Clastic rocks; Clay mineralogy; Clay minerals; Electron microscopy data; Illite; Sedimentary petrology; Sedimentary rocks; Shale; Sheet silicates; Silicates; Smectite; TEM data; California; Salton Sea; United States; AEM data; Areal studies
Abstract Numbers:90M/0089
Record ID:1987045425
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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