Jiří Pešek

Quality parameters of lignite of the North Bohemian Basin in the Czech Republic in comparison with the world average lignite

Abstract Sulfur is considered to be the most harmful element in atmospheric emissions and fall-out which originate from coal combustion. Total sulfur content (Std) in lignites of the North Bohemian Basin (NBB) has a geometric mean of 1.61 wt.% at n=12 979, and is mostly influenced by the presence of iron disulfides. The distribution of sulfur and many trace elements is log normal. A non-uniform distribution of sulfur in lignite was found within the basin, with the lowest Std contents (i.e., not exceeding 1 wt.% S) confined to the eastern and southeastern margin of the NBB. Contents between 1 and 1.5 wt.% S are most common in lignites of the South-Central NBB. Lower sulfur contents were identified in the area of the Žatec delta and its northern extension. In contrast, high contents of sulfur in lignite (exceeding 1.5 wt.%) are found along the northern margin of the basin at the foot of the Krusne hory Mts and in the westernmost part of the NBB. Three genetically different types of iron disulfides occur in lignite of the NBB—synsedimentary (early diagenetic), diagenetic, and epigenetic. Among those forms, synsedimentary disulfides (mostly pyrite) appear to be most abundant. They form finely dispersed microscopic framboids or veinlets that commonly parallel the coal bedding. The other iron disulfide forms are much less abundant. Dissolved sulfate which was supplied to the NBB during the Miocene is likely to have been derived from sulfides of the Krusne hory Mts crystalline complex. This unit has an isotopic composition of sulfide sulfur varying between −1 and +5‰. Consequently, the sulfate supplying the NBB should exhibit slightly positive δ 34 S values. Syngenetic pyrites forming microframboids or veinlets in coal show δ 34 S values close to 0‰. These values are similar those of sulfur dioxide in gases of power stations burning NBB coal. This implies that no considerable shifts in sulfur isotopic composition occur during thermal oxidation of the dominant pyrite. Arsenic is positively correlated with sulfur (r2=+0.89). Its total content (Astd) is 20.53 ppm at n=9172.

Heat capacity in nonequilibrium steady states

We show how to extend the concept of heat capacity to nonequilibrium systems. The main idea is to consider the excess heat released by an already dissipative system when slowly changing the environment temperature. We take the framework of Markov jump processes to embed the specific physics of small driven systems and we demonstrate that heat capacities can be consistently defined in the quasistatic limit. Away from thermal equilibrium, an additional term appears to the usual energy-temperature response at constant volume, explicitly in terms of the excess work. In linear order around an equilibrium dynamics that extra term is an energy-driving response and it is entirely determined from local detailed balance. Examples illustrate how the steady heat capacity can become negative when far from equilibrium.

Values of δ34S in iron disulphides of the North Bohemian Lignite Basin, Czech Republic

Abstract Three main, genetically different, types of iron disulphides occur in lignite of the North Bohemian Basin — synsedimentary, diagenetic and epigenetic. Among them the synsedimentary disulphide appears to be the most abundant. It forms fine dispersed microscopic framboids or veinlets mostly parallel with the coal bedding. This disulphide is mostly represented by pyrite. The other types are much less abundant. The epigenetic variety consists of large macroscopic clusters of crystals of marcasite twins or crystalline filling of fractures. The shift in sulphur isotopic composition between the original sulphate and the derived sulphides, which originated through bacterial reduction, may vary considerably depending on conditions, particularly on the open or closed nature of the system with respect to sulphate. The largest shifts in the isotopic composition between sulphate and sulphide sulphur are typical for an open system. Dissolved sulphate which supplied the North Bohemian Basin during the Miocene is likely to have been derived from weathered sulphides of the Krušné hory crystalline complex. This unit has isotopic compositions of sulphide sulphur varying between −1 and +5‰ and assuming no significant shifts in sulphur isotope compositions, the sulphate supplying the basin should exhibit a slightly positive δ34S value. Organic sulphur is thought to have played a much less important role. Synsedimentary pyrites, which form microframboids or veinlets in coal, show δ34S values close to 0‰. These values when compared with those of sulphur dioxide in gases exhaled by power stations burning lignite of the North Bohemian Basin indicate that they correspond to mean values for synsedimentary pyrite. This also implies that no considerable shifts in isotopic composition take place during thermal oxidation in power plants.

Observations Concerning the Thickness of Rocks Eroded Between the Cambrian and Bolsovian (= Westphalian C) in Central and Western Bohemia

Abstract Carboniferous outliers are found west of the late Carboniferous West Bohemian basins and also south of the West and Central Bohemian basins. The West Bohemian group is Asturian (= Westphalian D) or younger and is notably coal-bearing, the other group of outliers consists mostly of coal-bearing upper Carboniferous volcaniclastic rocks of Bolsovian (= Westphalian C) and/or Asturian age. They form a discontinuous belt extending through the area between and around the towns of Merklín and Beroun. These rocks are underlain chiefly by rocks of ages varying from the Neoproterozoic or Cambrian up to the Ordovician. If the nappe structure of the Barrandian Lower Paleozoic proposed by Melichar and Hladil (e.g. 1999) is not widely present, then it can be assumed that as much as 1850 m of Lower Paleozoic sediments and volcanics could have been eroded prior to the onset of sedimentation of the Bolsovian rocks. In the upper Carboniferous outliers near Mirošov, Skořice and Kamenný Újezd, where sedimentation began as late as in the Asturian, the thickness of eroded deposits might have been even greater, reaching as much as 3150 m.

Significant hiatuses in the terrestrial Late Variscan Central and Western Bohemian basins (Late Pennsylvanian–Early Cisuralian) and their possible tectonic and climatic links

Abstract Significant changes in the stratigraphy of the Central and Western Bohemian Upper Palaeozoic basins occur during or shortly after hiatuses. The different extent and changes in the depocentres of the Radnice and Nýřany members (Moscovian) in the Plzeň Basin clearly indicate changes in the structure of this basin taking place during a break in sedimentation between these two units (311.9–308.3 Ma). Thick weathered rocks that occur in boreholes in the Mšeno–Roudnice Basin indicate another sedimentation break (305.9–304.1 Ma) between the Nýřany Member and the Týnec Formation (Kasimovian). Another possible hitherto undiscovered hiatus occurred between the Týnec and Slaný formations (Kasimovian–Gzhelian, about 304–303 Ma). The most significant changes in the configuration of the basins occurred between the Slaný and Líně formations (Gzhelian–Asselian, 301.6–300.6 Ma). This is indicated by deeply cut river valleys at the top of the Slaný Formation, by high thickness of weathered deposits occurring immediately beneath the Líně Formation, and mainly by the shift of depocentres from the southern to the northern part of the Central Bohemian basins. The hiatuses between the Radnice and Nýřany members and between the Slaný and Líně formations are accompanied by significant changes in the depocentres, and they are therefore interpreted primarily as tectonic events related to the extensional collapse of the Variscan orogenic belt. By contrast, the hiatuses beneath and above the Týnec Formation are interpreted as being the products of lower sedimentation rates during drier climates, which is consistent with the characteristics of the sediments, correlation with other Central European basins, and with climate models for this period. Due to the characteristics of the Líně Formation, in which the effects of climate aridization are clearly seen, the authors presume that tectonic as well as climatic changes occurred at the hiatus between the Slaný and Líně formations.

Comparison of structures derived from mine workings and those interpreted in seismic profiles: an example from the Kačice deposit, Kladno Mine, Bohemia

Abstract Five seismic profiles across the Kačice coal deposit were reinterpreted and compared with observations in mine galleries. The comparison shows that approximately 80% of normal faults with displacement exceeding 5 m detected on the seismic profiles really exist. In contrast, in only two cases have mine workings shown faults (vertical displacement 10–15 m) that have not been identified by seismic measurements. Discrepancies may be mostly explained by: (i) misinterpretation of the fault with slope of the presedimentary palaeorelief accompanied by differential compaction; (ii) virgation of faults and misinterpretation of a fault zone composed of several small faults individually below the detection limit but whose aggregate displacement is detected, giving the appearance of a single fault; (iii) faults which die away toward the overburden indicating synsedimentary movements in the deposit.