THE STRUCTURAL FEATURES OF CLAY MINERALS FROM THE SUPERDEEP WELL TSG-6 OF THE WEST SIBERIAN PLATE. E.P. Solotchina, T.A. Korneva and P.A. Solotchin, United Institute of Geology, Geophysics and Mineralogy, Siberian Branch RAS, Novosibirsk, Russia

The composition as well as the structural and crystallochemical features of clay minerals of Triassic deposits lying at a depth of 6000-6500 m penetrated by the unique Tyumen superdeep well have been studied. The basic method was X-ray diffraction analysis. Optical and electron microscopy as well as thermal analysis were used in addition.

The widespread development of 7 Å berthierine as mineral with the serpentine-like structure and the composition identical to iron-rich chlorite has been established. Two polytype modifications of berthierine: orthogonal A and monoclinic B (denoted by B. Zvyagin) of different genesis have been revealed. Berthierine is the most abundant mineral of tuffs making up as much as 85 % of rock in association with kaolinite. Two modifications of mixed-layer minerals as illite/smectites with d₀₀₁=10.5-11Å and d₀₀₁=24.5 Å in initial state are dominant in argillites and in a cement of siltstones. Berthierine, chlorite, kaolinite and mica are present in such rocks as an impurity. Illite/smectites with interplanar space 24.5 Å have been revealed in more deep horizons. These minerals contain appreciable amount of adsorbed water ((7.2 %) and interlayer water ((1%) on evidence derived from thermogravimetric curves. When the specimens were saturated with ethylene glycol d₀₀₁ was enhanced to 26.8Å and an integral series of intense basal reflections up to ninth order was observed in the X-ray diffraction pattern. Decoding the structures of mixed-layer minerals has been performed. The content of illite and smectite layers and motive of their interstratifications have been defined.

The established crystallochemical features and the regularities in distribution of clay minerals allowed decompaction zones at significant depths to be found out and the character as well as the degree of epigenetic transformations of Triassic rocks of West Siberian Plate penetrated by TCG-6 well to be refined.

This work was supported by RFFI grant No 96-05-65943.