About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Petrology
Vol. 57 (1987)No. 2. (March), Pages 335-342

Smectite-to-Illite Reactions in Salton Sea Shales: A Transmission and Analytical Electron Microscopy Study

Yu-Chyi Yau, Donald R. Peacor, S. Douglas McDowell

ABSTRACT

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 Co st 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.


Pay-Per-View Purchase Options

The article is available through a document delivery service. Explain these Purchase Options.

Watermarked PDF Document: $14
Open PDF Document: $24