Mineral-forming and diagenetic processes related to Tertiary hydrocarbon seepage at the Bohemian Massif/Outer Western Carpathians interface: Evidence from the Hrab暖vka quarry, Moravia, Czech Republic

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• 作者：Zden臎k Dolní ; 膷ek^a ; ^{dolnicek@prfnw.upol.cz" class="auth_mail} ; Tomá ; &scaron ; Lehotský ; ^a ; Marek Slobodní ; k^b ; Eva Hejtmá ; nková ; ^a ; Andrea Grí ; gelová ; ^a ; Jan Zapletal^a
• 关键词：Moravo-Silesian Culm ; Carpathian Foredeep ; Hydrocarbons ; Methane seep ; Methane oxidation ; Authigenic mineralization ; REE
• 刊名：Marine and Petroleum Geology
• 出版年：April, 2014
• 年：2014
• 卷：52
• 期：Complete
• 页码：77-92
• 全文大小：6561 K

文摘

Ancient hydrocarbon seepage occurred in the Hrab暖vka quarry at the boundary between the basement of the Bohemian Massif (represented by folded Lower Carboniferous siliciclastics of the Culm facies) and Tertiary sedimentary cover of the Carpathian Foredeep (formed by Lower Badenian siliciclastics and calcareous clays). The unconsolidated Lower Badenian sediments contain lithified domains composed of limestone and breccias with limestone cement, whereas the basement rocks are cut by subvertical neptunic dykes filled up by limestone and calcite-marcasite-pyrite veinlets representing sealed fluid conduits. The deeply negative 未¹³C values of both vein calcite and limestone (down to 鈭?8.1鈥?V-PDB) indicate that oxidation of hydrocarbons was the major source of carbon for authigenic mineralization. A fluid inclusion study suggests low fluid temperatures (<50聽掳C) and low and variable salinities of aqueous fluids associated with hydrocarbons (0.7-6.7聽wt. % NaCl eq.). The variability of 未¹⁸O values of authigenic carbonates (鈭?.7 to 鈭?.2鈥?V-PDB) could reflect either slight changes in temperature of escaping fluids (mostly within 15聽掳C), and/or some mixing with meteoric waters. The low 未³⁴S values of vein marcasite (鈭尖€?0鈥?V-CDT) are consistent with bacterial reduction of sulfate in the hydrothermal system. Low C₁/(C₂+C₃) ratios in hydrocarbon gas extracted from authigenic carbonates (9.9 and 5.8) as well as the high 未¹³C values of methane (鈭?1.8 and 鈭?2.4鈥?V-PDB) are compatible with a thermogenic source of hydrocarbons. REE data indicate sequestration of REE from finely dispersed detrital material in the apical part of the hydrothermal system. The available data are compatible with two possible scenarios of fluid origin. The hydrocarbons could have been leached from underlying Paleozoic sedimentary sequence by aqueous fluids that infiltrated into the basement after Tertiary tectonic reactivation. Alternatively, an external source of hydrocarbon-bearing fluids can be found in the adjacent Outer Western Carpathians flysch nappes containing petroleum-producing lithologies. Nevertheless, a regional flow of hydrocarbon-bearing fluids is evidenced by the occurrence of very similar hydrocarbon-bearing vein mineralizations in a wider area.