EARLY VISEAN EUXINIC BASIN IN THE SYSTEM OF PALEO-TETHYS (IN THE LIGHT OF MODERN DATA)
Among ancient euxinic basins of different age and geotectonic position there is one basin deserving of special attention. This is Early-Visean basin in the system of Paleo-Tethys which possess by striking similarity with the Black sea. The fragments of this basin are connected with Dnieper-Donets de...
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| Format: | Article |
| Language: | English |
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Publisher House Akademperiodyka
2020-05-01
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| Series: | Геологія і корисні копалини Світового океану |
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| Online Access: | http://gpimo.nas.gov.ua/sites/default/files/24-48_2-20.pdf |
| Summary: | Among ancient euxinic basins of different age and geotectonic position there is one basin deserving of special attention. This is Early-Visean basin in the system of Paleo-Tethys which possess by striking similarity with the Black sea. The fragments of this basin are connected with Dnieper-Donets depression and Pre-Dobrudga foredeep. This statement about similarity is true for comparative characteristic of Holocene of the Black sea and the time interval which corresponds to rudovski strata. These are typical black shale (hydrocarbopelites) formation which accumulated under conditions of intensive gas-rejection of the sea bottom (СН4—H2S—CO2). Similary to the Black sea this Early-Visean basin had restricted circulation anaerobic regime of sedimentation. Predobrudge-Dnieper-Donets basin also included into euxinic the carbonate phase of euxinic sedimentation. It is characterized by the absence of typical ecologic reefs and are represented by the Waulsortian facies (mud mounds) — dark-coloured micritic limestones (with in creased content of kerogen and microbiogenic FeS2) — carbonate black shales. Nature of this mud mounds is connected with physic-chemical (travertine formation) and microbiogenic processes which connected with gas seeps. They are characterized by intimately related СН4—CO2—H2S degassing. Fragments of pyritizited tubes of cylinder or cane-shaped shapes have been detected as a result of examining under electronic-microscope the rocks of black shale formation (Lower Visean, Dnieper-Donets depression, the cores of oil and gas deep (wells). This tubes are filled by (with) colomorphic, spongic and framboidal forms of microbiogenic pyrite. It constitutes the considerable portions of enclosing black shales. These tubes and associated forms of pyrite are supposedly the segments of microchimney system of deep H2S-degassing. It seems likely that the holes in the walls of these tubes made connected with cavitations of gas bubbles. Their appearance were connected with spraying of two-phased fluid flow. Cavitation microexplosions perforated the tube walls. These brittle ephemeric structures are possible analogues of black smokers. Their discovery allow to reveal the geological conditions of euxinic of black shales. That in turn should promote the development of these formations as a nontraditional source of hydrocarbons and different metals. |
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| ISSN: | 1999-7566 2664-5947 |