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Prague, Czech Republic

Silurian Spanila Barrande, 1881 (Nepiomorphia Kříž, 2007) of Perunica and the European peri-Gondwana contains two species, Spanila gracilis (Münster in Goldfuss, 1837) and Spanila discipulus Barrande, 1881. It represents an important taxon-range-zone in the middle Ludfordian to the earliest Pr̈ídolí cephalopod limestone facies and may be correlated with the interval from the Neocucullograptus kozlowskii Biozone to the early Monograptus parultimus Biozone. Semi-infaunal Tetinka Barrande, 1881 from the Gorstian of Perunica was most probably the ancestor of Spanila, adapted to the specific semi-infaunal or infaunal mode of life. The assumption of semi-infaunal mode of life is supported by the cyrtiid brachiopod epibionts attached by their triangular ventral interarea to the posterior part of the shell, presumably above the level of the sediment. Spanila occupied narrow spaces between the crowded current-oriented cylindrical cephalopod shells and is commonly preserved with conjoined valves, often in the living position, i.e. with the frontal face down and parallel with bedding plane.

Kriz J.,Czech Geological Survey
Bulletin of Geosciences | Year: 2010

The genus Kenzieana Liljedahl, 1989 (Nepiomorphia Kříž, 2007) from Perunica, the European peri-Gondwana and Baltica is the oldest known, very long ranging Silurian (late Wenlock to late Přídolí) genus of Spanilidae Kříž, 2007, and was most probably the ancestor of the Gorstian Algerina Kříž, 2008, and the Ludfordian Spanila Barrande, 1881. Kenzieana is represented by K. bellula (Barrande, 1881) from the Homerian (late Wenlock), and K. cardiopsis (Barrande, 1881) from the late Wenlock to the late Přídolí. K. angusta Liljedahl, 1989, and K. lata Liljedahl, 1989 from Gotland are the junior synonyms. Distinctly inflated, foreshortened shells of Kenzieana with almost flat and circular frontal face show adaptive convergence with the Silurian Slavinka plicata (Barrande, 1881), Recent Corculum Röding, 1798, Fragum Röding, 1798, and Hippopus Lamarck, 1799. Kenzieana was very shallow and slow burrower resting in the sediment on its anterior, almost subcircular or widely elliptical and flat frontal face with a few byssal threads attached to loose detritus.

Manda S.,Czech Geological Survey | Fryda J.,Czech University of Life Sciences
Bulletin of Geosciences | Year: 2010

Diversity evolution of 197 of the latest Ludlow-Lochkovian cephalopod species from Bohemia (representing more that 70 percent of all species known worldwide) was analysed and compared with changes in the global carbon cycle in the marine ecosystem. Our results show a distinct relationship between cephalopod species diversity and the global carbon cycle.Aprogressive increase in δ13C values in marine carbonates from the Monograptus lochkoviensis Zone to the end of the Monograptus transgrediens Zone reflects an increase of bioproductivity in the marine ecosystem. This increase was probably caused by a shallowing of the upwelling system, thus importing nutrient-rich water. A progressive cooling during the Pr̈ídolí and earliest Lochkovian triggered these changes in the upwelling system. Our data also show an increase in total diversity of cephalopod species, which may be explained by greater availability of new food sources for a period corresponding to the progressive increase in δ13C values. In the latest Silurian, δ13C reached its maximal values while the Lochkovian is characterized by steady conditions with a decreasing tendency in δ13C values. Strong, selective extinction started in the latest Silurian Monograptus transgrediens Zone and continued to the earliest Devonian Monograptus uniformis Zone. This extinction affected benthic and demersal cephalopod species with relatively large eggs and long incubation times. The change in dynamics of the global carbon cycle thus coincides with the beginning of this extinction. An anoxic or hypoxic event in the period between the LAD Monograptus transgrediens Zone (Transgrediens Event) in the latest Pr̈ídolí and the base of the Devonian Monograptus uniformis Zone (documented also from offshore sequences from Poland) is considered to be a cause for the extinction of non-pelagic cephalopods. Our study also revealed a need to revise and define all earlier established bioevents in the Silurian-Devonian boundary interval more clearly.

The construction of the European Geogenic Radon Map in a proposed grid system 10 × 10 km requires the data test to derive the probability of exceeding the indoor action level 200 Bq m -3 from the geologically based data. The Czech Republic disposes both indoor and soil gas data sets to test the real probability to exceed 200 Bq m -3 from indoor radon measurements and to compare it with the probability calculated from soil gas radon concentrations. Comparison of real and calculated probability enables to delineate the areas, where under- or overestimation can be expected. The results of data processing show minor differences between processing the raw data in generalised polygons of geological units and in a grid net, when using the generalised geological characteristics of grid cells. © 2011 Springer-Verlag.

Weinberg R.F.,Monash University | Hasalova P.,Czech Geological Survey | Hasalova P.,Academy of Sciences of the Czech Republic
Lithos | Year: 2015

Water-fluxed melting, also known as fluid- or water-present melting, is a fundamental process in the differentiation of continents but its importance has been underestimated in the past 20. years during which research efforts focused mostly on dehydration melting reactions involving hydrate phases, in the absence of a separate aqueous phase. The presence of a free aqueous phase in anatectic terranes influences all major physical and chemical aspects of the melting process, from melt volumes, viscosity and ability to segregate from rock pores, to melt chemical and isotopic composition. A review of the literature shows that melting due to the fluxing of aqueous fluids is a widespread process that can take place in diverse tectonic environments. Active tectono-magmatic processes create conditions for the release of aqueous fluids and deformation-driven, transient high permeability channels, capable of fluxing high-temperature regions of the crust where they trigger voluminous melting. Water-fluxed melting can be either congruent in regions at the water-saturated solidus, or incongruent at suprasolidus, P-T conditions. Incongruent melting reactions can give rise to peritectic hornblende, or to nominally anhydrous minerals such as garnet, sillimanite or orthopyroxene. In this case, the presence of an aqueous phase is indicated by a mismatch between the large melt fraction generated and the much smaller fractions predicted in its absence. The relatively small volumes of aqueous fluids compared to that of rocks imply that melting reactions are generally rock buffered. Fluids tend to move upwards and down temperature. However, there are cases in which pressure gradients drive fluids up temperature, potentially fluxing suprasolidus terranes. Crustal regions at conditions equivalent to the water-saturated solidus represent a natural impediment to the up-temperature migration of aqueous fluids because they are consumed in melting reactions. In this case, continued migration into supra-solidus terranes take place through the migration of water-rich melts. Thus, melts become the transport agent of water into supra-solidus terranes and responsible for water-fluxed melting. Other processes, such as the relatively rapid fluid migration through fractures, also allow regional aqueous fluids to by-pass the water-saturated solidus fluid trap and trigger melting above solidus conditions. When aqueous fluids or hydrous melts flux rocks at supra-solidus conditions, they equilibrate with the surroundings through further melting, decreasing water activity and giving rise to undersaturated melts. It is in these conditions that hornblende or anhydrous peritectic phases are stabilized. Unlike dehydration melting, the melt fraction generated in this case is not limited by the water contained in hydrous minerals but by the volume of water added to the system. Unlike melting at the water-saturated solidus, these melts are capable of rising without freezing and do give rise to upper crustal granitic bodies. © 2014 Elsevier B.V.

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