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Diagenesis to very low-grade metamorphism in lower Palaeozoic sediments: A case study from deep borehole Tobolka 1, the Barrandian Basin, Czech Republic
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SYSNO ASEP 0444043 Document Type J - Journal Article R&D Document Type Journal Article Subsidiary J Článek ve WOS Title Diagenesis to very low-grade metamorphism in lower Palaeozoic sediments: A case study from deep borehole Tobolka 1, the Barrandian Basin, Czech Republic Author(s) Suchý, V. (CZ)
Sandler, A. (IL)
Slobodník, M. (CZ)
Sýkorová, Ivana (USMH-B) RID, ORCID
Filip, Jiří (GLU-S) RID, SAI
Melka, Karel (GLU-S) SAI
Zeman, Antonín (UTAM-F) RID, SAISource Title International Journal of Coal Geology. - : Elsevier - ISSN 0166-5162
Roč. 140, FEB 15 (2015), s. 41-62Number of pages 22 s. Publication form Print - P Language eng - English Country NL - Netherlands Keywords graptolite ; chitinozoan ; illite-smectite ; fluid inclusion ; apatite ; petroleum Subject RIV DB - Geology ; Mineralogy R&D Projects IAA3012703 GA AV ČR - Academy of Sciences of the Czech Republic (AV ČR) GA13-18482S GA ČR - Czech Science Foundation (CSF) Institutional support USMH-B - RVO:67985891 ; GLU-S - RVO:67985831 ; UTAM-F - RVO:68378297 UT WOS 000354341000005 EID SCOPUS 84922440360 DOI 10.1016/j.coal.2014.12.015 Annotation The diagenetic grade of a 2.7 km thick sequence of lower Palaeozoic marine sediments in the Tobolka 1 deep exploration borehole was investigated by analysing organic and mineral components and fluid inclusions embedded in vein minerals. The reflectance of organic matter (R-r %) increases down-section from values of about 0.77% at the top of the Devonian Srbsko Formation to values around 3% at the base of the Ordovician Letna Formation. In the Devonian and Silurian sediments the reflectance values of vitrinite-like and graptolite fragments (0.77-1.13% R-r and 1.09-1.46% R-r respectively) and the composition of fluid inclusions entrapped in vein minerals (CH4 + CO2 + complex saline solutions +/- light gaseous hydrocarbons +/- liquid petroleum; T-h = 170-230 degrees C) collectively indicate organic maturation within the high-temperature part of the oil window to the wet gas stage. In the Ordovician sediments below 1000 m, chitinozoan reflectance values (1.38-3.03% R-r) and the CH4-dominated composition of the fluid inclusions (T-h = 250-310 degrees C) indicate a wet gas/condensate stage to an advanced dry gas stage. The clay mineral assemblage remains uniform throughout the whole succession and consists of illite, mixed-layered illite-smectite (IS); chlorite and kaolinite. Below 1400 m the illite content gradually increases down-hole, forming up to 45-55% of the clay fraction in the deeply-buried Ordovician sediments. Throughout the borehole, the IS displays uniformly low expandability (7-12 +/- 3% of smectite layers) and an ISII ordering. The illite crystallinity broadly correlates with organic matter reflectance values and improves with depth (from 1.1 to 0.54 degrees Delta 2 theta according to the Crystallinity Index Standard (CIS) scale) indicating high-grade diagenesis to incipient anchimetamorphism. The chlorite crystallinity (ChC index), however, shows no systematic correlations with depth. Workplace Institute of Rock Structure and Mechanics Contact Iva Švihálková, svihalkova@irsm.cas.cz, Tel.: 266 009 216 Year of Publishing 2016
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