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Massimiliano Ghinassi Wojciech Nemec Mauro Aldinucci Slavomir Nehyba Volkan Özaksoy Francesco Fidolini 《Sedimentology》2014,61(4):952-977
The mode of channel‐bend transformation (i.e. expansion, translation, rotation or a combination thereof) has a direct bearing on the dimensions, shape, bedding architecture and connectivity of point‐bar sandstone bodies within a fluvial meander belt, but is generally difficult to recognize in vertical outcrops. This study demonstrates how the bend transformation mode and relative rate of channel‐floor aggradation can be deciphered from longitudinal outcrop sections aligned parallel to the meander‐belt axis, as a crucial methodological aid to the reconstruction of ancient fluvial systems and the development of outcrop analogue models for fluvial petroleum reservoirs. The study focuses on single‐storey and multi‐storey fluvial meander‐belt sandstone bodies in the Palaeogene piggyback Boyabat Basin of north‐central Turkey. The sandstone bodies are several hundred metres wide, 5 to 40 m thick and encased in muddy floodplain deposits. The individual channel‐belt storeys are 5 to 9 m thick and their transverse sections show lateral‐accretion bed packages representing point bars. Point bars in longitudinal sections are recognizable as broad mounds whose parts with downstream‐inclined, subhorizontal and upstream‐inclined bedding represent, respectively, the bar downstream, central and upstream parts. The inter‐bar channel thalweg is recognizable as the transition zone between adjacent point‐bar bedsets with opposing dip directions into or out of the outcrop section. The diverging or converging adjacent thalweg trajectories, or a trajectory migrating in up‐valley direction, indicate point‐bar broadening and hence channel‐bend expansion. A concurrent down‐valley migration of adjacent trajectories indicates channel‐bend translation. Bend rotation is recognizable from the replacement of a depositional riffle by an erosional pool zone or vice versa along the thalweg trajectory. The steepness of the thalweg trajectory reflects the relative rate of channel‐floor aggradation. This study discusses further how the late‐stage foreland tectonics, with its alternating pulses of uplift and subsidence and a progressive narrowing of the basin, has forced aggradation of fluvial channels and caused vertical stacking of meander belts. 相似文献
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J. Kalvoda O. Babek O. Fatka J. Leichmann R. Melichar S. Nehyba P. Spacek 《International Journal of Earth Sciences》2008,97(3):497-518
The Brunovistulian terrane represents a microcontinent of enigmatic Proterozoic provenance that was located at the southern
margin of Baltica in the early Paleozoic. During the Variscan orogeny, it represented the lower plate at the southern margin
of Laurussia, involved in the collision with the Armorican terrane assemblage. In this respect, it resembles the Avalonian
terrane in the west and the Istanbul Zone in the east. There is a growing evidence about the presence of a Devonian back-arc
at the margin of the Brunovistulian terrane. The early Variscan phase was characterized by the formation of Devonian extensional
basins with the within-plate volcanic activity and formation of narrow segments of oceanic crust. The oldest Viséan flysch
of the Rheic/Rhenohercynian remnant basin (Protivanov, Andelska Hora and Horní Benesov formations) forms the highest allochthonous
units and contains, together with slices of Silurian Bohemian facies, clastic micas from early Paleozoic crystalline rocks
that are presumably derived from terranes of Armorican affinity although provenance from an active Brunovistulian margin cannot
be fully excluded either. The development of the Moravo–Silesian late Paleozoic basin was terminated by coal-bearing paralic
and limnic sediments. The progressive Carboniferous stacking of nappes and their impingement on the Laurussian foreland led
to crustal thickening and shortening and a number of distinct deformational and folding events. The postorogenic extension
led to the formation of the terminal Carboniferous-early Permian Boskovice Graben located in the eastern part of the Brunovistulian
terrane, in front of the crystalline nappes. The highest, allochthonous westernmost flysch units, locally with the basal slices
of the Devonian and Silurian rocks thrusted over the Silesicum in the NW part of the Brunovistulian terrane, may share a similar
tectonic position with the Giessen–Harz nappes. The Silesicum represents the outermost margin of the Brunovistulian terrane
with many features in common with the Northern Phyllite Zone at the Avalonia–Armorica interface in Germany. 相似文献
3.
Dmitry Khangulyan Slavomir Hnatic Felix Aharonian 《Astrophysics and Space Science》2007,309(1-4):261-265
The inverse Compton (IC) scattering of ultrarelativistic electrons accelerated at the pulsar wind termination shock is generally
believed to be responsible for TeV gamma-ray signal recently reported from the binary system PSR B1259-63/SS2883. In such
a system the acceleration takes place in the presence of a dense radiation field provided by a companion Be2-type star. Thus
it is natural to expect an orbital phase dependence of the acceleration efficiency in the system. The HESS collaboration reported
the tendency of reduction of TeV γ-rays around the periastron. In this paper we study a possible explanation of this effect by the “early” (sub-TeV) cutoffs
in the energy spectrum of accelerated electrons due to the enhanced rate of Compton losses close to the periastron. 相似文献
4.
Slavomír Nehyba Daniel Nývlt Uwe Schkade Gerald Kirchner Eva Franců 《Journal of Paleolimnology》2011,45(1):41-55
Facies analysis, magnetic susceptibility, and analysis of grain size, TOC content and isotopes (137Cs, 210Pb, 226Ra, 228Ra, and 238U concentrations) were used to determine the history of the modern deposits of the Brno reservoir. The sedimentary succession
can be subdivided into two main units. The lower unit is formed predominantly by medium- to coarse-grained silty sands and
is interpreted as a fluvial succession deposited before the Svratka River was dammed. The upper unit consists of brownish
planar laminated silts and rarely of clayey or sandy silts and is interpreted as a product of the reservoir deposition. The
concentrations of 238U reflect the history of uranium mining in the upper part of the Svratka River catchment. As a consequence, 210Pb radionuclide concentrations cannot be used for establishing a sediment chronology. Concentrations of 137Cs show two marked peaks, the upper of which is attributed to the Chernobyl reactor accident in 1986, and the lower one is
attributed to the maximum rate of atomic weapons testing in 1963. From these peaks, mean depositional rates of 3.2 cm year−1 for the time period of 1986–2007 and of 3.4 cm year−1 between 1963 and 1986 are calculated. Based on the known age of the reservoir, which was constructed in 1939, we can also
calculate mean depositional rate for the time period of 1939–1963, which is 3.1 cm year−1. 相似文献
5.
Slavomír Nehyba K. Hilscherová J. Jarkovský L. Dušek T. Kuchovský J. Zeman J. Klánová I. Holoubek 《Environmental Earth Sciences》2010,60(3):591-602
Modern fluvial deposits from both small and large rivers were studied at 14 monitoring sites over 2 years (4 successive sampling
seasons) in the area of eastern Moravia (Czech Republic). Grain size, geochemistry, content of persistent organic pollutants
(PAHs, PCBs, HCHs, DDTs, HCBs and PeCB) and TOC were examined with the aim to understand their mutual relations and seasonal
variations in sediment character and pollutant content. Sand and silt fraction predominate and the clay content is relatively
low. Differences in provenance for various river systems were recognised. Both regional and seasonal variations in terms of
content of persistent organic pollutants were documented. The content of TOC and mud was shown to play an important role in
the accumulation of chlorinated persistent organic pollutants PCBs, HCHs, DDTs and HCB. 相似文献
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