Surface Indications for Deep Hydrocarbon Deposits in the Central Bohemia, Czech Republic
Department of Petroleum Technology and Petrochemistry, Institute of Chemical Technology, Prague
We describe a number of new small-scale hydrocarbon occurrences ranging from pristine petroleum and gas shows to degraded bitumen that come from various locations in the central part of the Bohemian Massif. We further argue that many if not most of hydrocarbon occurrences in that area, both newly described and already known, are in fact concentrated within five distinct, 25?40 km wide, N-S-trending linear zones that cut across crystalline and sedimentary units. These linear structures seem to provide long-lived and periodically re-activated conduits for various geofluids that include, apart from hydrocarbons, thermal and mineral waters, warm brines, uranium-bearing hydrothermal solutions, CO2, CH4, and He. Geological and geochemical evidence shows that within the linear zones at least several distinct episodes of fluid migration occurred during the geological history. A number of local present-day emissions and small oil seeps are probably indicative of the most recent migration stage that appears to have resumed in the Tertiary period, following the Alpine orogeny. The hydrocarbons found at the surface may point to undiscovered deposits and/or hydrocarbon-producing sequences beneath the surface, though juvenile, deep-mantle (abiogenic) contributions can be also viable. Alternatively, hydrocarbon origin can be also explained in terms of a long-distance lateral migration from unknown sources in the Alpine realm. Regardless the dubious source(s), our analysis indicates that the internal part of the Bohemian Massif shall be seriously considered as an emerging target for future oil and gas exploration; a conclusion that is both fundamental and challenging.
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