The nature, origin and significance of luminescent layers in the Bazhenov Shale Formation of West Siberia, Russia

Abstract

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.

Alginite-Rich Layers in the Bazhenov Deposits of Western Siberia

“…The layers show bright yellow t ange luminescence under ultraviolet (UV) light, most probably due to their OM algal esis. Their properties differ from other luminescent layers in the Bazhenov cross-sect including oil saturated intervals and luminescent tuffs described in [9][10][11], which d contain a high amount of organic carbon. Through a comprehensive analysis, we proven the presence of type I kerogen in these layers, which is unique for the Bazh Formation.…”

Вулканогенные Прослои В Баженовской Свите Западно-Сибирского Осадочного Бассейна

“…а, б, г -с анализатором, вбез анализатора. На пепловую природу образования прослоев глинистого типа также указывают ранее выявленные геохимические особенности пород [2,4]. Об этом свидетельствует, например, аномально высокое содержание тория в породах (диапазон концентраций 44,7-77,3 г/т).…”

“…Photos under UV light: c) luminescent clay-type layers in the rocks of the Bazhenov formation; d) ash layers in the rocks of the Eagle Ford province [18,19] Дискуссионным вопросом остается причина люминесценции выделенных горизонтов. По результатам ранее проведенных исследований причина свечения связывается с ОВ, а именно с особенностями его преобразования в условиях «ураганного» поступления пирокластического материала и резкой смены условий в иловых водах [1,2,4]. По мнению И.В.…”

“…Изучаемые прослои были отмечены в 63 скважинах на 12 площадях (месторождениях) в центральной части Западно-Сибирского бассейна -Широтное Приобье (Ханты-Мансийский автономный округ, далее ХМАО) и в 41 скважине на 30 площадях (месторождениях) в юго-восточной части бассейна (Томская область). Ранее проведённые исследования петрографии и минералогии выделенных прослоев подтвердили их вулканическое происхождение [1][2][3][4].…”

Oil as the result of lithogenesis complicated by intensification of tectonic-hydrothermal activity (on the example of Western Siberia)

“…Вместе с тем в верхнеюрско -нижнемеловых отложениях Западной Сибири при-Запасы, % сутствует пирокластический материал основного состава [32]. В частности, обнаружены люминесцирующие вулканические стёкла в нефтематеринской баженовской свите [35]. Однако это также не может служить доказательством проявления мезозойского вулканизма на территории Западно-Сибирской плиты.…”