Diagenesis of Dioctahedral and Trioctahedral Smectites from Alternating Beds in Miocene to Pleistocene Rocks of the Niigata Basin, Japan

Byeong-Kook Son1, Takahisa Yoshimura2, * and Hikaru Fukasawa3
1 Korea Institute of Geoscience and Mineral Resources (KIGAM), 30, Kajungdong, Yusungku, Taejon, Korea
2 Department of Environmental Sciences, Faculty of Sciences, Niigata University, Ikarashi-2, Niigata, Japan
3 Exploration Department, Japan Petroleum Exploration Co. Ltd, Higashi-Shinagawa, Tokyo, Japan
*Present address: 7910-22, 2-No-Cho, Ikarashi, Niigata, Japan. E-mail of corresponding author: sbk@rock25t.kigam.re.kr

Abstract: Clay mineral diagenesis in the Niigata basin is documented by mineralogical and chemical analysis of clay minerals from cuttings from the Shinkumoide SK-1D (SSK-1D) well which is characterized by alternating beds containing dioctahedral and trioctahedral smectite minerals with increasing depth. Dioctahedral smectite shows a progressive increase in illite interstratification with increasing depth. The transition of dioctahedral smectite to interstratified illite-smectite (I-S) is supported chemically by an increase in K and Al and a decrease in Si with increasing depth. In contrast, trioctahedral smectite (saponite) reacts to form a 1:1 interstratified chlorite-smectite (C-S) with increasing burial depth and temperature. Considering the geology and the occurrence of smectite, the SSK-1D smectites probably altered diagenetically from two different parent materials: dioctahedral smectite is derived from clastic sediments and transforms to interstratified illite-smectite, whereas trioctahedral smectite is derived from andesitic pyroclastic rocks and transforms to interstratified chlorite-smectite.

The C-S occurs at the same depth of ∼3200 m as the conversion of randomly interstratified (R = 0) I-S to (R = 1) I-S. Furthermore, the depth is compatible with a Tmax temperature of 430–435°C, which indicates the starting temperature for oil generation from organic matter. The temperature of the conversion of (R = 0) I-S to (R = 1) I-S and the start of corrensite formation is estimated at 110–120°C based on the time-temperature model suggested by others. The clay-mineral diagenesis in the SSK-1D further suggests that I-S and C-S can act as geothermometers in clastic and pyroclastic sediments provided that the effect of time is considered.

Key Words: Chlorite-Smectite • Clay Mineral Diagenesis • C-S • Geothermometer • Illite-Smectite • I-S • Niigata Basin • Saponite

Clays and Clay Minerals; August 2001 v. 49; no. 4; p. 333-346; DOI: 10.1346/CCMN.2001.0490407
© 2001, The Clay Minerals Society
Clay Minerals Society (www.clays.org)