Argillites that strongly luminesce under UV radiation were detected in the Bazhenov Shale Formation (BSF) of the West Siberian Basin during routine core examination and found to be persistent over a wide lateral area. The mineralogy and fabric of these luminescent layers were characterized by optical and fluorescence microscopy, SEM, TEM, XRD and IR methods. Optical and fluorescence microscopy showed that the luminescent layers were to a large extent derived from volcanic ash falls and could be described as meta-tuffites, although normal detrital sedimentation continued at the same time. The layers have a thickness of several mm to a maximum of 3-4cm and can be defined as a clay-rich regional horizons. XRD showed that two principal clay minerals were present, namely a kaolinite, possibly with some dickite stacking, (kaolin-rich) and a mixed-layer illite-smectite (I/S) with R1 to R2 ordering similar to that found in K-bentonite. Total organic matter in the luminescent layers is much lower than that in the enclosing BSF clayey-silty siliceous sediments above and below as shown by pyrolytic analyses. Evidence is presented that the luminescent characteristic of the argillites is related to their clay mineralogy, specifically to their content *Revised Manuscript (clean copy) Click here to view linked References 2 of kaolin minerals, although a contribution from nitrogenous organic matter cannot be entirely discounted. In some ways the luminescent argillites can be compared with bentonites associated with ash transformations or with tonsteins in coal beds, which are also derived from volcanic ash falls and contain highly crystalline kaolinite. However, tonsteins originate at or near land surface whereas the argillites were apparently formed in the deep ocean. But just as tonsteins can be used for detailed stratigraphic studies and are valuable in the context of coal exploration, so may the luminescent argillites prove to be significant both stratigraphically and in the search for economic hydrocarbon deposits, bearing in mind that their clay mineralogy may be sensitive to temperature and depth of burial and related to their placement in the oil and gas window.

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South-east of Western Siberia (Tomsk Region) faces good prospects for developing shale oils from Bazhenov formation. Ample preconditions are available there: high content of organic matter of excellent oil-generating quality in Bazhenov formation rocks and main oil formation stage of primary rocks. However, drilling success appreciably depends on the correct choice of the well spud-in place. Regional geochemical investigations of Bazhenov formation and of Bazhenov genetic type of oils may considerably confine the area of search by choosing the most promising areas for detecting shale oil deposit. Recent investigations permitted to identify a regional pattern of changes in Bazhenov formation rocks catagenesis and to grade the prospective regional oil-bearing capacity associated with hydrocarbon generation by Bazhenov formation rocks. Identification of regularities in expansion of Bazhenov - type oils as well as comparison between the maturity of oils and the maturity of organic matter of Bazhenov formation rocks permitted to mark out areas that are promising for the formation of both oil deposit in traditional oil reservoirs and of shale oil deposit.

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