Petrology and clay mineralogy of fine-grain rocks, northern Galilee Basin

Selected core samples of Late Carboniferous, Permian and Triassic rocks from the northern Galilee Basin (Koburra Trough) were examined. The investigation, designed to complement a previous organic geochemical evaluation of source rocks, has provided information on clay mineral suites and the influence of burial diagenesis. Six types of clay identified in the sequence are illite, kaolinite, chlorite, smectite, illite-smectite, and a clay mineral from the serpentine group. Illite and chlorite, present in varying proportions throughout the sequence, are considered to have detrital origins. Kaolinite is confined to the late Permian and Trassic part of the sequence and reflects a change in source area and climate. Illite-smectite mixed layer clay has a more restricted and irregular distribution than other clay types and is mainly associated with lacustrine facies. Burial diagenesis appears to have played a minor role in controlling clay mineral distribution. In the illite-smectite mixed-layer clay, no correlation exists between increase in illite interlayers and increasing depth; furthermore, for a given percentage of illite interlayers, corresponding temperatures are too low compared with published data. However, through lack of adequate sampling, it has not been possible to assess properly the role of smectite-illite diagenesis in the sequence. Nevertheless, available evidence suggests that detrital controls of clay mineral distribution have been more important than clay diagenesis. Therefore, it appears that clay mineral suites in the northern Galilee Basin are unsuitable as indicators of level of organic maturation. Most organic matter is concentrated in late Permian coal-forming facies and is closely associated with illite clay. 21 refs., 4 figs., 3 tabs.