Czech Geological Survey
  • Prague, Bohemia, Czechia
Recent publications
The thicknesses of organic (O) and organomineral (A) horizons are essential parameters for estimating the soil organic carbon stock. They are usually measured at sampling points distributed randomly or regularly over a site, but due to high spatial variability of the soil horizons' thicknesses, the sampling should be dense enough to estimate the carbon stock precisely. Dense soil sampling is cost, time, and labour demanding. Therefore, some studies suggest that geophysical methods such as ground-penetrating radar (GPR) can assist with a more precise estimation of the organic and organomineral horizons thicknesses without digging soil pits. This study evaluates the accuracy of the organic and the organomineral horizons thicknesses repeatedly measured under different soil moisture conditions on two contrasting soil types: Dystric Cambisol and Arenic Podzosol, using GPR with 800 MHz antenna. The results proved this method to be promising; however, we could not distinguish the boundary between organic and organomineral horizons but only the O + A horizon/subsoil boundary. The thickness of O + A horizons was estimated with an error between 25 and 35% in the Dystric Cambisol site and 18 – 24% in the Arenic Podzol site. The results were more accurate under moister conditions for both soil types, but under drier conditions, deeper parts of irregular horizon boundaries were better distinguishable.
This work investigates the pre-collisional (before ca. 650 Ma) history of the Dom Feliciano Belt in southernmost Brazil through geochronological and zircon oxygen isotope study. U-Pb SHRIMP dating of two orthogneiss samples from the Várzea do Capivarita Complex and one metarhyolite sample from the Porongos Complex yielded crystallisation ages of 786 ± 5 Ma, 780 ± 10 Ma and 787 ± 5 Ma, respectively. The mean oxygen isotope values calculated for the ca. 790 Ma zircon cores from the orthogneisses are 8.41 ± 0.13‰ and 8.68 ± 0.14‰, and 8.75 ± 0.72‰ for the metarhyolite. Such values suggest that zircon crystallised in the more evolved magmas, either from the melting of host rocks and sediments or assimilation of crustal material by mantle-derived magmas. The detrital zircon population was analysed in one additional paragneiss sample from the Várzea do Capivarita Complex, and most of the values cluster at 790-750 Ma. The data spread is centred at ca. 790 Ma, which is the crystallisation age of the interleaved orthogneisses. In our interpretation, such dataset suggests a syn-volcanic origin of the paragneiss protolith and, therefore, a volcano-sedimentary origin of the Várzea do Capivarita Complex. The correspondence of geochronological data and zircon oxygen isotope values for the studied meta-igneous samples suggests that the Várzea do Capivarita and Porongos complexes have shared the same igneous history. Therefore, the samples probably represent one magmatic event at different levels of a single basin at ca. 800-770 Ma. Such results bring first-order information about the meaning of tectonic limits in this Gondwana-related belt and implications for reconstructing the pre-collisional history of the orogen.
The mineralogical character of a parent rock strongly affects the uranium (U) and thorium (Th) contents of soils. We have selected five representative soil profiles developed on amphibole–biotite to biotite durbachites in the Třebíč Pluton (eastern part of the Czech Republic) to characterize the radioactivity and variable-intensity weathering. The Endoskeletic Cambisols with a silt loam to loamy sand texture and a well-developed subsurface Bw horizon represented the most common product of the pedogenetic processes on durbachites. All studied soil profiles showed the evidence of pedogenetic alteration with intrasoil weathering. They were moderately deep (70–80 cm) with high rock-fragment concentrations within the B and C horizons. The predominant grain size fractions were silt (12% to 83%) or sand (8% to 87%), and the percentage of clay was up to 15%. A feldspar–quartz–vermiculite (biotite)–amphibole–kaolinite–Fe–Mn (oxy) hydroxide assemblage was typical for the most weathered parts of the profiles. Variation in the U and Th contents within the studied soil profiles resulted predominantly from the changes in the amounts of primary accessory minerals at different depth levels. Uraninite, monazite, thorite, allanite, zircon, thorogummite, REE-(Rare Earth Elements) fluorocarbonates, and minerals of the rhabdophane group were the main carriers of radioactive elements in the parent durbachite and overlying soil profiles. The gamma-ray spectrometry, geochemical and mineralogical analyses show that uraninite was stable only in the parent durbachite and disappeared at the rocks–C horizon interface. This process was followed by the gradual alteration of allanites, thorites, brabantites and secondary U- and Th-rich minerals (e.g., thorogummite, bastnäsite) toward the soil surface.
Waste materials such as metallurgical slags can be considered as potential resources of valuable elements, including technologically critical metals. Copper slags from Luanshya, the oldest mining and smelting site in the Zambian Copperbelt, produced by smelting local Cu ores in reverberatory furnaces between 1932 and 1999, were deposited on two large dumps in the vicinity of the former ore processing area. The slags exhibit high concentrations of Co (247–5990 ppm, median: 2370 ppm) and Cu (1320–95,300 ppm, median: 8550 ppm). This multi-method mineralogical investigation indicates that the slags are predominantly composed of olivine, clinopyroxene, silicate glass, and spinel-family oxides. Copper-(Fe) sulfides, cobaltpentlandite [(Co,Fe)9S8], Fe sulfides, and metallic Cu prills embedded in the silicate matrix are the major hosts of Cu and Co. The EU regulatory leaching test (EN 12457-2) indicated that the release of contaminants is relatively low and only Cu slightly exceeded the EU limit values for landfilling of inert waste. The secondary phases (Cu hydroxosulfates, Fe (oxyhydr)oxides) observed on the slag surfaces confirm that the slags undergo a weathering process on the dumps. Kinetic abiotic extraction tests were carried out in 0.5 mol/l sulfuric acid at 25 °C and with a pulp density of 1% to determine the release of metals from the milled Luanshya slags under conditions simulating hydrometallurgical recovery via agitation leaching. The Cu and Co extractability correlated with the bulk concentration of these elements, and the highest extraction yields after 24 h of leaching corresponded to 46% of the total Cu and 67% of the total Co. Despite the dramatic increase in Co prices on the global market, the Co recovery from the Luanshya slags appears to be non-economical due to the high costs of the necessary mechanical and chemical processing of the slag materials and the obtained extracts.
Purpose Complexes of organic matter (OM) with iron (Fe) oxyhydroxides (OM-Fe) prevent/reduce microbial degradation and enhance its stabilization in soils and sediments. Missing in most studies regarding the quality of OM-Fe complexes is in this study addressed by optical method characterization using absorbance and fluorescence, which is a unique approach in combination with sequential extraction methods. This study finds the quality of OM which promotes the stability of the OM-Fe aggregates with respect to the rate of redox dissolution of Fe mineral phases. Methods Sediment samples from a mesotrophic freshwater reservoir were sequentially extracted to distinguish Fe oxyhydroxides solubility at different dissolution times. This allowed us to assess the OM-Fe association with easily reducible Fe-bearing minerals vs. more stable yet reducible fractions. The quality of the sequentially extracted DOM associated with different redox reactivity mineral phases was evaluated by UV–Vis and fluorescence spectroscopy using a parallel factor analysis (PARAFAC) model. Results Humic-like substances render soluble and labile OM-Fe associations, while non-humic substances enhance the stability of such associations under reducing conditions. In anoxic sediments, non-humic substances are stabilized in the OM-Fe associations. Conclusion This study described the fate of OM-Fe in anoxic sediments by coupling sequential extractions with UV–Vis and fluorescence spectroscopy characterization. This is a new reliable and simple approach for evaluating the stability of OM-Fe aggregates in sediments, soils, and/or wastewater treatment sludge.
Stephanian fronds from intra-montane basins of the Bohemian Massif in central Europe, previously named Neuropteris nervosa Šetlík, have been transferred to the fossil-genus Laveineopteris. This makes it the youngest known species of that genus. Current evidence suggests that they were more closely related to the Laveineopteris rarinervis fronds from the late Westphalian / earliest Stephanian lowland floras, rather than to Laveineopteris bohemica from the middle Westphalian intra-montane basin floras.
Climate controls forest biomass production through direct effects on cambial activity and indirectly through interactions with CO2, air pollution, and nutrient availability. The atmospheric concentration of CO2, sulfur and nitrogen deposition can also exert a significant indirect control on wood formation since these factors influence the stomatal regulation of transpiration and carbon uptake, that is, intrinsic water use efficiency (iWUE). Here we provide 120-year long tree-ring time series of iWUE, stem growth, climatic and combined sulfur and nitrogen (SN) deposition trends for two common tree species, Pinus sylvestris (PISY) and Picea abies (PCAB), at their lower and upper distribution margins in Central Europe. The main goals were to explain iWUE trends using theoretical scenarios including climatic and SN deposition data, and to assess the contribution of climate and iWUE to the observed growth trends. Our results showed that after a notable increase in iWUE between the 1950s and 1980s, this positive trend subsequently slowed down. The substantial rise of iWUE since the 1950s resulted from a combination of an accelerated increase in atmospheric CO2 concentrations (Ca) and a stable level of leaf intercellular CO2 (Ci). The offset of observed iWUE values above the trajectory of a constant Ci/Ca scenario was explained by trends in SN deposition (all sites) together with the variation of drought conditions (low-elevation sites only). Increasing iWUE over the 20th and 21st centuries improved tree growth at low-elevation drought-sensitive sites. In contrast, at high-elevation PCAB sites, growth was mainly stimulated by recent warming. We propose that SN pollution should be considered in order to explain the steep increase in iWUE of conifers in the 20th century throughout Central Europe and other regions with a significant SN deposition history.
Metasandstones from early Cambrian to early Carboniferous stratigraphic successions were sampled in the Rehamna massif of the Western Meseta in Morocco. The early Cambrian sample shows a single Paleoproterozoic population at ca. 2 Ga suggesting a local basement source. The Ordovician sample is largely dominated by a Cryogenian-Ediacaran population and minor Paleoproterozoic peaks. The Devonian sample reveals age populations similar to North-West African Cambrian to Devonian age spectra indicating that the southern-derived West Gondwana source essentially pertained up to the Devonian. The two early Carboniferous samples show more heterogeneous zircon age spectra with a marked Ediacaran peak accompanied by Paleoproterozoic and Mesoproterozoic sub-peaks indicating important re-organization of the drainage systems. One sample also shows presence of Upper Devonian to early Carboniferous zircon grains, which suggests local magmatic sources associated to the formation of intracontinental extensional basins. The comparison of detrital zircon spectra with paleogeographic reconstructions indicate that the early Carboniferous change in detrital zircon sources can be interpreted in the framework of the opening of the Paleotethys ocean with coeval erosion of orogenic topographies linked to the emplacement of a Mid-Variscan Allochthon, and/or collision of an Avalonian indenter to the north.
The distribution of ultrahigh-pressure metamorphism (UHP) at the scale of a mountain belt is of prime importance for deciphering its past subduction history. In the Western Alps, coesite has been recognized in the southern Dora-Maira Massif, in the lens-shaped Brossasco-Isasca Unit, but has not been found up to now in the other parts of the massif. We report the discovery of a new UHP unit in the northern Dora-Maira Massif (Western Alps), named Chasteiran Unit. It is only a few tens of metres thick and consists of graphite-rich, garnet–chloritoid micaschists, whose protoliths may be black shales of Silurian age. Garnet inclusions (chloritoid, rutile) and its growth zoning allow to precisely model the P–T evolution. Coesite crystals, which are pristine or partially transformed to palisade quartz occur as inclusions in the garnet outer cores. According to thermodynamic modelling, garnet displays a continuous record of growth during the prograde increase in P and T (25–27 kbar 470–500 °C) (stage 1), up to the coesite stability field (27–28 kbar 510–530 °C) (stage 2), as well as sub-isothermal decompression of about 10 kbar (down to 15 kbar 500–515 °C) (stage 3). The main regional, composite, foliation, marked by chloritoid and rutile, began to develop during this stage, and was then overprinted by chlorite–ilmenite (stage 4). The Chasteiran Unit is discontinuously exposed in the immediate hangingwall of the Pinerolo Unit, and it is located far away from, and without physical links to the classic UHP Brossasco-Isasca Unit. Moreover, it records a different, much colder, P–T evolution, showing that different slices were detached from the downgoing subduction slab. The Chasteiran Unit is the fourth and the coldest Alpine UHP unit known so far in the entire Alpine belt. Its P–T conditions are comparable to the ones of the Tian Shan coesite–chloritoid-bearing rocks.
Synchysite was identified in the Rožná uranium deposit in a quartz–carbonate–sulfide vein, which is a part of the late (post-uranium and, post-Variscan) stage of the development of the hydrothermal system. The synchysite forms needles or lamellae, which are almost exclusively bound to the quartz filling of the veins. The structure of the quartz vein-filling, i.e., the preserved tubular syneresis crack pattern, Liesegang bands formed by hematite, chaotic grain size distribution of quartz grains, and ribbons of fibrous SiO2 grains, indicate that the synchysite crystallized in a silica gel. Its formation may be explained by the reaction of hydrothermal acid fluids rich in Fe2+ and rare earth elements (REEs) with alkaline Ca2+ HCO3− and F-rich fluids expelled from the gel during syneresis, or by its ageing. The subsequent recrystallization of the gel to form euhedral quartz grains was accompanied by the deformation of previously formed Liesegang rings, and the development of quartz rosettes. The study of fluid inclusions indicated that the silica gel originated at a very low temperature. The temperatures of the homogenization of two-phase inclusions in carbonate and quartz vein-filling varied between 38 and 74 °C, and the salinity ranged between 4 and 10 wt.% NaCl equiv. The δ13C carbonate values (from −4.65 to −5.21‰, PDB) indicate the deep-seated source of CO2, and δ18O values (from 14.76 to 18.22‰, SMOW) show that the source of the hydrothermal fluids was mainly surface water, with a possible admixture of fossil saline brines. The main sources of REEs are thought to have predominantly been uranium minerals (coffinitized uraninite and coffinite) that form a part of the breccia fragments embedded in the vein filling. The results illustrate the significant mobility of REEs in the late, low-temperature hydrothermal system, and they indicate the multiple remobilizations of REEs in the uranium deposits in general.
The Barrandian area of the Teplá-Barrandian Unit is one of the richest trilobite-yielding areas in the world. In the middle of the nineteenth century, four main workers studied trilobites in this region, Joachim Barrande, Heinrich Ernst Beyrich, Ignatz Hawle, and August Carl Joseph Corda. Heinrich Ernst Beyrich, an excellent German palaeontologist studied and figured five species of Ordovician trilobites from the Barrandian area in two important contributions. One trilobite species, Cheirurus claviger (= Eccoptochile clavigera) was described in the year 1845; the other four trilobites, Odontopleura inermis (= Selenopeltis inermis), Calymene parvula (= Calymenella parvula), Calymene pulchra (= Prionocheilus mendax), and Trinucleus ornatus (= Deanaspis goldfussii goldfussii) were described in the year 1846. Well-preserved materials used in both Beyrich’s contributions were collected from Sandbian quartzose sandstone of the Letná Formation and from Sandbian to Katian greywacke of the Zahořany Formation. Original specimens of these Late Ordovician taxa are newly revised and actual systematic position of all species is discussed in detail. The history of Beyrich’s original specimens in the twentieth century is briefly summarized.
A variable assemblage of ultrabasic rocks along with minor eclogites investigated on a small area of a few km2 (Gföhl unit, Moldanubian Zone of the Bohemian Massif) reflects incorporation of contrasting mantle domains within a subduction-related tectonic mélange during the Variscan orogeny. Based on mineral composition, whole-rock chemistry, isotopic signatures, and pressure-temperature (P–T) estimates, four principal lithological types have been distinguished (1) spinel harzburgite (2) garnet lherzolite (3) spinel websterite and (4) eclogite. Spinel harzburgite, exclusively associated with HT migmatized gneisses, corresponds to the refractory oceanic lithosphere, as demonstrated by whole-rock composition (low Al2O3, CaO), chemistry of spinel (Cr# <0.4) and Al-rich pyroxene (Al2O3 up to 9 wt%). By contrast, garnet lherzolite, predominantly enclosed in HP felsic granulite, represents a fragment of the subcontinental mantle wedge, considering the strong fertile character (high Al2O3, TiO2, Yb) and spinel chemistry (Cr# >0.5). Websterites likely represent products of decompression partial melting of the asthenospheric mantle with a variable input of crustal component, whereas eclogites correspond to HP crystal cumulates from partial melts migrating through the Variscan mantle wedge. Both peridotite protoliths experienced various degrees of secondary refertilization, recorded as a cryptic metasomatic overprint, due to interaction with subduction-related silicate melts, from which numerous websterite and rare eclogite layers crystallized. The secondary mantle refertilization via melt-peridotite reaction is well-documented by decreasing bulk Mg# along with MgO/SiO2, elevated Al2O3/SiO2, TiO2 and FeOtot contents, and isotopic composition (87Sr/86Sr338 ~ 0.7051). Moreover, the positive correlation between highly fluid-immobile incompatible trace elements (e.g. Ti, Sc, V, Zr, Yb) and distribution of REE and Li is consistent with the melt refertilization trend. During the Variscan subduction, lherzolite experienced UHP conditions (42 kbar, 1100 °C). The presence of Cr-spinel relics preserved in garnet suggests that lherzolite was dragged from the shallow mantle wedge to deeper levels of the subduction zone, probably along with the underlying subducting oceanic plate involving refractory harzburgite. This deep burial during the Variscan subduction was closely followed by rapid exhumation dated by the Lu-Hf age of 338.4 ± 6.3 Ma, corresponding to re-equilibration at lower crustal levels or possibly at greater depths, closer to peak P conditions. Decompression-induced partial melting of upwelling asthenosphere with a contribution of crustal material resulted in derivation of primitive to mildly evolved transient melts (87Sr/86Sr338 ~ 0.7049–0.7062) represented by websterites, percolating through and metasomatizing wall-rock peridotites. The rapid exhumation and following juxtaposition of genetically diverse yet closely associated ultrabasic rocks provide a unique insight into the history of Earth mantle, evolving during the formation of the Variscan orogenic belt in Central Europe within contrasting geological settings, from ocean ridge environment to great depths of subduction zone.
Evolution of groundwater geochemistry in the Sulaimani-Warmawa Sub-basin in the Kurdistan Region of Iraq has been investigated using hydrogeochemical and isotopic methods. This is a semiarid region with seasonal precipitation in winter. Water chemistry generally evolves from Ca-HCO3 groundwater type close to the basin boundaries towards Ca-Mg-HCO3 groundwater type close to the Tanjero River along the axis of the basin. Some samples have increased concentrations of Na, Cl, and SO4 as a consequence of dissolution of halite and gypsum embedded in carbonates. Values of pH are slightly alkaline or alkaline, and redox parameters indicate a moderately reducing environment. Isotopes δ2H and δ18O indicate recharge from winter precipitation with no evaporation. Values of dissolved 13C(DIC) correspond to equilibrium with carbonates and C4 plants as the source of CO2. Values of 87Sr/86Sr in groundwater are in a good agreement with carbonate dissolution as a principal process. The principal geogenic contaminant is Ba with concentrations up to 0.383 mg/L. Dissolved concentrations of other geogenic contaminants such as As, F, Mn, and Cr are low or below the detection limit as expected based on their low contents in carbonate rocks. Inverse geochemical modeling on selected profiles calibrated using δ13C values provided mass transfer coefficients for possible geochemical reactions. Future work should focus on interactions in the hyporheic zone of the Tanjero River.
The tectonic evolution of the Himalayan orogenic belt before Cenozoic convergence is important to understand its modern structural framework. There is still controversy regarding the tectonic history of the lower Lesser Himalaya Sequence (LHS) in the frame of the Paleoproterozoic geological record. In this study, integrated analysis of field geology, zircon U-Pb age, Hf isotope, and whole-rock geochemistry was conducted across the LHS and the Main Central Thrust zone in the Arun Valley, eastern Nepal, to address their Precambrian tectonic evolution and the later convergence. Two groups of metasedimentary rocks with different age spectrums of detrital zircons and Hf isotope in the Paleoproterozoic can be distinguished in an imbricated duplexing system in the study area. One group with a maximum depositional age around ca. 1800 Ma has a unimodal detrital zircon pattern and negative zircon ƐHf (t) values ranging from −8.9 to 0.9. These data can be interpreted to reflect the deposition of zircons close to a Japanese-type arc that was isolated from the northern Indian Craton. The other group of calc-silicate rocks and quartzite with multiple peaks of detrital zircons in the Paleoproterozoic show a younger maximum depositional age around ca. 1,600 Ma and variable zircon ƐHf (t) values ranging from −6.7 to 8.8, indicating their deposition in a back-arc basin of an Andean-type arc established on the northern Indian Craton. The geochemistry of an orthogneiss sample dated at 1783 ± 11 Ma indicates high potassium, peraluminous granodiorite protolith emplaced in a volcanic arc or syn-collisional tectonic setting, supporting the existence of the Paleoproterozoic Andean-type arc. We hypothesize that possibly two arc systems developed, respectively, onto and in the proximity of northern Indian Craton in the Paleoproterozoic at the final stages of the Columbia supercontinent formation. These two arcs were juxtaposed either in the Paleoproterozoic or Cenozoic time, and were finally imbricated during the Cenozoic duplexing.
The Danube Basin represents a northwestern depocenter of the Middle Miocene Central Paratethys Sea, which was succeed by the Late Miocene Lake Pannon. Although this is an extensively examined area, the application of multidisciplinary studies has proven capable of drawing attention to novel information concerning the depositional environment. Thus, this study aims to reveal climatic and paleoenvironmental changes by using both archive and fresh data drawn from biomarkers, palynology, sedimentology, and geochemistry. The article also addresses the quality, quantity, and thermal maturity of organic matter in relation to hydrocarbon potential. In general, the beginning of Serravallian stage relates to a regression forced by the development of the Antarctic icesheet followed by a pronounced transgression. The results presented here show that the Central Paratethys Sea reacted to the late Badenian (Serravallian) flooding, an event which triggered a dysoxic, but not euxinic, bottom waters. The climate remained warm and humid, with paratropical to subtropical forests on the continent. While several new depocenters developed during the Sarmatian and divided the depositional environments into a shelf-brake slope in the central part of the Danube Basin, and into deltaic and swamp environments on the basin margins. The climate changed to temperate, leading to the disappearance of subtropical taxa. A shallow lake and swamp environment developed at the beginning of the Pannonian (Tortonian), forcing a salinity decrease connected to the increase in humidity. The degree of hydrocarbon richness of the mudstones is generally fair to good, and the kerogen is of mixed marine-terrestrial origin (II and III). Nonetheless, the sediments are clearly immature due to insufficient burial.
Most chromium (Cr) entering the ocean originates from continental weathering of ultramafic rocks. Recent data indicate that (i) mantle-derived rocks are characterized by homogeneous δ⁵³Cr values of approximately −0.12‰; (ii) some serpentinized peridotites, serpentinites and weathered serpentinites contain isotopically heavier Cr than mantle protoliths; and (iii) Cr transported by rivers is isotopically variable, but positive δ⁵³Cr values predominate. There is a need to identify solid materials that, in sufficient volumes, store the complementary isotopically light Cr. We studied δ⁵³Cr systematics in three mantle domains belonging to the Paleozoic Central European orogenic belt. These domains are characterized by contrasting P–T histories. At two of six study sites, a 30-m deep drilling was carried out to assess spatial gradients in Cr concentrations ([Cr]) and δ⁵³Cr values toward the weathering front. The studied rocks, comprising serpentinized peridotites with preserved mantle signature, serpentinites, carbonatized serpentinites, and hornblendites, were characterized by a variable degree of weathering. Spinel in these rock types contained up to 33 wt% Cr but represented less than 1% of the rock volume; chromite was not detected in any of the samples. Silicates, such as pyroxene, serpentine, hornblende and chlorite, with an average [Cr] of 0.24% were likely the predominating potential Cr source for the environment. Despite the known higher weathering rates of Cr-silicates compared to Cr-spinelides, no systematic trends toward lower [Cr] and higher δ⁵³Cr values were detected upcore. The overall range of whole-rock δ⁵³Cr values was from −0.25 to 0.14‰ (mean of −0.09 ± 0.01‰). There was no relationship between whole-rock δ⁵³Cr values and indices of alteration/weathering, such as water content, loss on ignition, and leaching of alkalies. We did not observe progressive removal of isotopically light Cr during continental weathering of serpentinized mantle-derived rocks that had been previously reported from altered and hydrated ultramafic rocks at some other sites. Our data suggest that such Cr isotope fractionation, if present, may be associated with earlier hydrothermal alteration rather than with weathering. Mean δ⁵³Cr values of soils were indistinguishable from the underlying ultramafic rocks, indicating only small sensitivity of Cr isotope composition to pedogenesis.
Re-investigation of the type material of beraunite from the Hrbek Mine, Svatá Dobrotivá, Czech Republic, proved the identity of beraunite and eleonorite. Based on this study, the mineral eleonorite was discredited, and the ideal formula of beraunite was redefined from Fe2+Fe53+(PO4)4(OH)5 ⋅ 6H2O to Fe63+(PO4)4O(OH)4 ⋅ 6H2O. Beraunite from Hrbek Mine usually forms prismatic crystals flattened on {100}; elongated along b axis, striated on {100} || b, up to 0.2 × 0.5 × 3 mm, often in radial clusters up to 6 mm in size in association with black goethite, olive-green to dark green dufrénite and yellow to orange cacoxenite. Beraunite is hyacinth red, dark red, or red-brown and has a light orange-red streak; crystals are translucent, with a vitreous luster. The symmetry of the structure was found to be lower (Cc) than reported in the past (C2/c); this has been proven by the crystal structure refinement, Robs= 2.7 % for Cc and ∼ 8 % for C2/m. Refined unit-cell parameters obtained from powder X-ray diffraction data of the original material of Friedrich August Breithaupt are a= 20.653(2), b= 5.1433(6), c= 19.241(2) Å, β=93.560(9)∘, and V= 2039.9(2) Å3. Calculated density is 2.961 g cm−3. Beraunite is optically biaxial (+), α= 1.768(2), β= 1.781(3), γ>1.805, 2Vmeas= 69(4)∘, and 2Vcalc is not possible to calculate. Dispersion of optical axes is strong, r>v. The orientation is Y=b, X≈a, and Z≈c. Pleochroism is strong; Z (brown-red) ≫Y>X (both brownish yellow). The empirical formula of the original beraunite sample calculated on the basis of P = 4 apfu is (Fe5.763+Al0.15Zn0.01)5.92(PO4)4.00O0.99(OH)3.77 ⋅ 6H2O. The 57Fe Mössbauer spectrum of beraunite neotype (National Museum, Prague) from type locality implies that all iron atoms in beraunite structure are exclusively trivalent, located at the M site with different next-nearest-neighbor configurations. There is no spectral evidence for Fe2+ or iron in some impurities (e.g., limonite).
The mid-Ludfordian Lau carbon isotope excursion (Lau CIE) represents the largest positive carbon isotope excursion in the Phanerozoic (∼9‰), coincident with the biodiversity loss of many marine animal clades. Two main explanations for the Lau CIE are enhanced organic carbon burial via increased marine productivity and preservation-driven expansion of anoxia. While these two explanations are not mutually exclusive, the main driver of Lau CIE is yet to be constrained. Here, we resolve this longstanding debate using barium isotopes (δ138Ba) of marine carbonates deposited across the Lau CIE. Our δ138Ba data from the Kosov section (Czech Republic) record a large negative excursion in correlation to the positive shift in δ13Ccarb. We suggest that the observed negative shift in δ138Ba to values as low as −0.33‰ can be best interpreted as upwelling of isotopically light Ba from deeper waters due to pelagic barite dissolution under euxinic conditions. This hypothesis is consistent with results from barium concentration data as well as the results from the sulfate mass balance modeling that indicates a contraction in the seawater sulfate reservoir, with seawater sulfate concentrations decreasing from several mM ranges before the Lau CIE to less than 100 μM during Lau CIE. Taken together, evidence for a strong negative correlation between δ138Ba and δ13Ccarb suggests that shallow water anoxia, rather than enhanced marine productivity, was a primary driver of the Lau CIE that resulted in a notable decrease in the size of seawater sulfate reservoir.
Current knowledge about the formation of calcite rafts was summarized and expanded with new data from the environment of a technical adit excavated in the 1950s in the central part of the Moravian Karst (Czech Republic). The location is within the temperate zone with an average annual temperature of 7–8 °C and an annual precipitation of 550–650 mm. Two different types of calcite rafts were identified: fine floating rafts (FF rafts) and massive calcite crusts (MC rafts). The transition from the FF raft to the MC raft requires the raft to be anchored to the side bank of the water pool. Once the FF rafts are anchored, they can grow on both sides (top and bottom) of the original air-water interface to form MC rafts. A comparison of water evaporation with CO2 degassing under given conditions showed that just degassing has been the key factor in achieving adequate supersaturation of drip water for nucleation of calcite at the air-water interface and for subsequent crystal growth. The conceptual two-layer model was designed and discussed in terms of the partial pressures of CO2 in the air and water in the adit. The discussion of the role of rafts in speleogenesis and paleohydrological reconstruction is supported by examples from the Sloup-Šošůvka caves (Moravian Karst).
Lithium and hydrogen are volatile elements which diffuse rapidly in crystals and melt, making them powerful geochemical tools to reconstruct geological processes that take place on short time scales, such as syn- and post-eruptive degassing. Although the dynamics of hydrogen are fairly well understood to better constrain such processes, the assessment of Li behaviour within the magma reservoir relevant for ascent-related degassing still lacks detailed evaluation. Here, the first in situ Li concentrations and isotopic compositions (using SIMS analysis) of rhyolitic quartz-hosted, naturally glassy or crystallised melt inclusions (MIs) and groundmass glass (Mesa Falls Tuff, Yellowstone) are used to reconstruct Li elemental and isotopic evolution in the magma reservoir. Lithium concentrations in quartz-hosted glassy MIs (10–61 ppm) from a fallout deposit overlap with their groundmass glass (32–46 ppm) and their host quartz (8–15 ppm). Crystallised MIs from a later erupted flow pumice clast sample have higher Li concentrations (8–190 ppm) compared to the groundmass glass (32–51 ppm) and their host-quartz (15–24 ppm). Li content in quartz from the early erupted sample is relatively homogenous, whereas it is up to a factor of two higher in the later erupted sample and heterogeneous, with a simultaneous increase in Li versus a decrease in H towards crystal rims. The δ⁷Li difference (expressed as Δ⁷LiMI–glass) between MIs (−8.0‰ to +12.3‰) and groundmass glass (+9.0‰ to +20.5‰) of two pyroclastic deposits reaches up to 29‰. Glassy MIs are internally heterogeneous in δ⁷Li and Li abundance. The cores of the glassy MIs record the δ⁷Li of the least modified melt during entrapment and the data distribution can be modelled by equilibrium fractionation between the melt and vapour phase during early open-system degassing in the magma reservoir. Late degassing during eruption triggers Li–H diffusional exchange between quartz and melt, as the degassing of H2O and the accompanying pressure change trigger H diffusion out of the host quartz and the MIs, which is charge balanced by Li inward diffusion. This results in the modification of Li contents in quartz and δ⁷Li values in the rims of the glassy MIs. Crystallised MIs reflect the loss of H2O from the MIs and the resulting enrichment of Li during the crystallisation. Additionally, the variations of δ⁷Li in the groundmass glass can be explained through modelling by kinetic fractionation between the melt and vapour during late stage open-system degassing linked with magma ascent.
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95 members
Filip Oulehle
  • Biogeochemistry
Petr Budil
  • Collections
Pavlína Hasalová
  • Centre for Lithospheric Research
Jiří Otava
  • Regional geology of Moravia
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Mgr. Zdeněk Venera, Ph.D.
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