Comparison of Clay and Zeolite Mineral Occurrences in Neogene Age Sediments from Several Deep Wells

B. Velde1 and A. Iijima2
1 Laboratoire de Geologie, Ecole Normale Superieure 46 rue d'Ulm, 75230 Paris Cedex, France
2 Geological Institute, University of Tokyo Hongo, Tokyo 113, Japan

Abstract: Clay and zeolite mineral assemblages were determined for five deep wells in volcano-clastic sediments (Japan) and for one well in mudstones (California). The clay mineral suites in these wells showed a gradual change with depth of illite/smectite (I/S) composition, which increases in smectite content in the upper portion towards a fully expandable mineral (2–3-km depth) and then decreases in smectite content with depth (2–5 km). The temperature of transformation or recrystallization to a fully expandable smectite mineral is about 60°–70°C in non-zeolite bearing rocks and 70°–90°C in zeolite-bearing rocks, with no apparent dependence on time. Comparison is made between the I/S smectite content in the lower part of the wells (i.e., below the occurrence of the fully expandable mineral) and the zeolite mineral zone boundaries. The 60% smectite composition was found at 108°–118°C maximum burial temperatures. The zeolite II/III zone boundary, i.e., the onset of the analcime zone, occurs between 85° and 95°C and may be slightly time-related in the span of 1–15 Ma. The clay and zeolite minerals can be used as temperature indicators in the range of the Neogene age.

Key Words: Analcime • Geothermal temperature • Illite • Diagenesis • Smectite • Zeolite

Clays and Clay Minerals; August 1988 v. 36; no. 4; p. 337-342; DOI: 10.1346/CCMN.1988.0360407
© 1988, The Clay Minerals Society
Clay Minerals Society (www.clays.org)