Artur Kędzior

2019. Origin and significance of early-diagenetic calcite concretions and barite from Silurian black shales in the East European Craton, Poland. Acta Geologica Polonica, 69 (3), 403-430. Warszawa. The Silurian Pelplin Formation is a part of a thick, mud-prone distal fill of the Caledonian foredeep, which stretches along the western margin of the East European Craton. The Pelplin Formation consists of organic carbon rich mudstones that have recently been the target of intensive investigations, as they represent a potential source of shale gas. The Pelplin mudstones host numerous calcite concretions containing authigenic pyrite and barite. Mineralogical and petrographic examination (XRD, optical microscopy, cathodoluminoscopy, SEM-EDS) and stable isotope analyses (δ 13 C org , δ 13 C and δ 18 O of carbonates, δ 34 S and δ 18 O of barite) were carried out in order to understand the diagenetic conditions that led to precipitation of this carbonate-sulfide-sulfate paragenesis and to see if the concretions can enhance the understanding of sedimentary settings in the Baltic and Lublin basins during the Silurian. Barite formed during early diagenesis before and during the concretionary growth due to a deceleration of sedimentation during increased primary productivity. The main stages of concretionary growth took place in yet uncompacted sediments shortly after their deposition in the sulfate reduction zone. This precom-pactional cementation led to preferential preservation of original sedimentary structures, faunal assemblages and early-diagenetic barite, which have been mostly lost in the surrounding mudstones during burial. These components allowed for the reconstruction of important paleoenvironmental conditions in the Baltic and Lublin basins, such as depth, proximity to the detrital orogenic source and marine primary productivity. Investigation of the concretions also enabled estimation of the magnitude of mechanical compaction of the mudstones and calculation of original sedimentation rates. Moreover, it showed that biogenic methane was produced at an early-diagenetic stage, whereas thermogenic hydrocarbons migrated through the Pelplin Formation during deep burial.

Although chemical (non-isotopic) U–Th–Pb dating of monazite by electron microprobe is well-established, dating of zircon by this method is still controversial. Relatively U-rich zircon (up to 2500 ppm of U) from the Třebíč Pluton provides a test case for the technique. Zircon grains are commonly partially or completely metamict, and therefore susceptible to Pb loss and common Pb contamination. Using Ca and K contents as indicators of damaged or contaminated zircon, a CHIME (Chemical U–Th–total Pb method) age of 347.8 ± 18 Ma was obtained from data with < 0.03 wt.% of CaO and K2O, and > 0.0062 wt.% of PbO. This age was confirmed by isotopic U–Pb SHRIMP dating (341.6 ± 2.8 Ma). These results are in agreement with previous estimates for the timing of durbachitic intrusions into the root of the Variscan orogen and from the Variscan basement incorporated into Western Alps, between 343 and 332 Ma.

Summary. Thecoal-bearing succession in the Upper Silesia Coal Basin consists of molasse deposits filling a flexural foredeep basin. Analysis of lithofacies in cores from deep boreholes revealed the presence of depositional environments typical of alluvial plains and coastal (in a broad sense) environments. Accumulation compensated regional subsidence, so that general depositional surface remained nearly flat. The higher part of the

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Summary. Thecoal-bearing succession in the Upper Silesia Coal Basin consists of molasse deposits filling a flexural foredeep basin. Analysis of lithofacies in cores from deep boreholes revealed the presence of depositional environments typical of alluvial plains and coastal (in a broad sense) environments. Accumulation compensated regional subsidence, so that general depositional surface remained nearly flat. The higher part of the

ABSTRACT The coal-bearing succession of the Upper Silesia Coal Basin consists of deposits filling a flexural foredeep basin. Accumulation initially compensated for regional and differentiated subsidence, after which the general depositional surface remained nearly flat. The deposition of the coal-bearing succession started at the end of Mississippian times (Pendleian Subage) and continued with hiatuses through almost the whole of Pennsylvanian times, and stopped in the Westphalian D Subage. The up to 8500 m thick coal-bearing succession traditionally has been divided into four main units called , and all of them are subdivided into subsidiary units known as . The occurrence of the intervals containing marine faunas within the lower part of the coal-bearing succession resulted from eustatic ingressions. The higher part of the succession was laid down in fluvial systems, while the lower part was formed mostly in a fluvial and, to a lesser extent, complex coastal system. Sedimentation of the coal-bearing succession was controlled by both autogenic and allogenic factors.

This paper reports the results of CHIME (chemical Th–U–Pb isochron method) dating of detrital monazites from Carboniferous sandstones in the Upper Silesia Coal Basin (USCB). A total of 4739 spots on 863 monazite grains were analyzed from samples of sandstone derived from six stratigraphic units in the sedimentary sequence. Age distributions were identified in detrital monazites from the USCB sequence and correlated with specific dated domains in potential source areas. Most monazites in all samples yielded ca. 300–320 Ma (Variscan) ages; however, eo-Variscan, Caledonian and Cadomian ages were also obtained. The predominant ages are comparable to reported ages of certain tectonostratigraphic domains in the polyorogenic Bohemian Massif (BM), which suggests that various crystalline lithologies in the BM were the dominant sources of USCB sediments.