第三紀頁岩・砂岩中におけるスメクタイト-イライト変換反応
1991 年 31 巻 1 号 p. 32-37
詳細
1991 年 31 巻 1 号 p. 32-37
Diagenetic illite/smectite interstrafitied minerals (I/S) from Neogene shales and sandstones in the regions of the Yachi River and Nakanomata River, Niigata Pref.(Japan) are examined by X-ray diffraction (XRD).The decrease of smectite percentage in I/S takes place continuously from 100% to 30%. The I/S from sandstone laminae tend to be of higher expandability than from adjacent shale laminae belonging to the same horizon. Some of XRD patterns indicate that intermediate stage exists at the conversion process from g=0 to g=1. It is due to the mixture or the segregated structure with random and ordered I/S. The properties of expandable layer in I/S are investigated by Greene-Kelly test, and the following points are suggested:
(1) the expandable layer in I/S at early stage of illitization is composed of beidellite-like and montmorillonite-like layers,
(2) the expandable layer in I/S appears to be segregated structure or mixture of the two component layer,
(3) the amount of beidellite-like layer decreases with increasing the amount of illite layer,
(4) the intermediate stage between g=0 and g=1 appears after disappearance of the reflection pattern of beidellite-like layer.
Therefore, the segregation of the mixture in the intermediate stage is due to the properties of precursive smectite before illitization, and the beidellite-like layer in I/S contributes more effectively to formation of ordered I/S than does the montmorillonite-like layer.
