Diagenesis to very low-grade metamorphism in lower Palaeozoic sediments: A case study from deep borehole Tobolka 1, the Barrandian Basin, Czech Republic

0444043 - ÚSMH 2016 RIV NL eng J - Článek v odborném periodiku
Suchý, V. - Sandler, A. - Slobodník, M. - Sýkorová, Ivana - Filip, Jiří - Melka, Karel - Zeman, Antonín
Diagenesis to very low-grade metamorphism in lower Palaeozoic sediments: A case study from deep borehole Tobolka 1, the Barrandian Basin, Czech Republic.
International Journal of Coal Geology. Roč. 140, FEB 15 (2015), s. 41-62. ISSN 0166-5162. E-ISSN 1872-7840
Grant CEP: GA AV ČR IAA3012703; GA ČR(CZ) GA13-18482S
Institucionální podpora: RVO:67985891 ; RVO:67985831 ; RVO:68378297
Klíčová slova: graptolite * chitinozoan * illite-smectite * fluid inclusion * apatite * petroleum
Kód oboru RIV: DB - Geologie a mineralogie
Impakt faktor: 3.294, rok: 2015

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.
Trvalý link: http://hdl.handle.net/11104/0246641