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Współczesne obszary występowania mołdawitów : wnioski z eksperymentu transportowania ich przez Nysę Łużycką

Brachaniec Tomasz

Przegląd Geologiczny

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2022

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Vol. 70, nr 1

61--65

EN

Tektites in the sedimentary recordare subject to many geological processes such as fluvial reworking. To observe the glass behaviour during reworking, an experiment was conducted in the Lusatia Neisse river where moldavites are found. It consisted in observing the progressive abrasion of some 500 tektites over reworking distances of 100, 200, 300, and 400 km respectively. The results clearly show that moldavites could survive reworkingover a distance of several hundreds km. The decrease in weight was linear in relation to the distance travelled. Regardless of the initial shape, all tektites became rounded with a smooth surface after travelling 200 km. The experimental results suggest that European tektites were ejected from the Ries crater over distances reaching up to 600 km and were then reworked over short distances from the origin areas of the current substrewn fields.

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Nowe znaleziska polskich tektytów z obszaru niecki żytawskiej

Paszcza Karolina

Przegląd Geologiczny

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2021

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Vol. 69, nr 4

244--247

EN

To date, 36 moldavites have been found in 9 sites from south-western Poland. The newest ones, i.e. 2 tektites, presented herein come from the Turów Mine in the Zittau Basin. Both moldavite specimens were collected from the fluvial sandy gravels of the Gozdnica Formation, of late Miocene age. Taking into account the macroscopic features of the studied glass, it should be assumed that one of them had been reworked over a maximum distance of several kilometres, while the other one had overcome a further reworking, not exceeding50 km though. The moldavites considered herein were most probably ejected from the Ries crater into the Zittau Basin within the Badenian sediments, later transported by the Lusatian Neisse river and finally redeposited within Pannonian sediments.

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Interaction between turbidity currents and a contour current – a rare example from the Ordovician of Shaanxi province, China

Li Hua, van Loon A. J. (Tom), He Youbin

Geologos

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2019

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Vol. 25, No. 1

15--30

EN

The silty top parts of graded turbidites of the Late Ordovician Pingliang Formation, which accumulated along the southern margin of the Ordos Basin (central China), have been reworked by contour currents. The reworking of the turbidites can be proven on the basis of paleocurrent directions in individual layers: the ripple-cross-bedded sandy divisions of some turbidites show transport directions consistently into the downslope direction (consistent with the direction of other gravity flows), but in the upper, silty fine-grained division they show another direction, viz. alongslope (consistent with the direction that a contour current must have taken at the same time). Both directions are roughly perpendicular to each other. Moreover, the sediment of the reworked turbidites is better sorted and has better rounded grains than the non-reworked turbidites. Although such type of reworking is well known from modern deep-sea environments, this has rarely been found before in ancient deep-sea deposits. The reworking could take place because the upper divisions of the turbidites involved are silty and consequently relatively easily erodible, while the contour current had locally a relatively high velocity – and consequently a relatively large erosional capability – because of confinement within a relatively narrow trough.

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Susceptibility of various tektite types to fluvial abrasion

Brachaniec Tomasz

Geological Quarterly

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2019

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Vol. 63, No. 1

150--161

EN

Tektites are glass bodies, rich in silica, resulting from the impact of a large bolide into ground rocks. Similar to other impactites they are prone to erosive processes, including fluvial abrasion. This study reports the results of an experimental tumbling that aimed at estimating the potential distance that tektites from different strewn fields (moldavites, bediasites and indochinites) and Libyan Desert Glass (LDG) can withstand depending on the experimental conditions. The present study consisted of 15 cycles, in which the type of sample deposits (i.e. sand/gravel ratio) and computed transport velocity were changed, the latter being estimated at 2.5-6.5 km/h. The results clearly confirm the susceptibility of tektites to abrasion during tumbling. None of the tektites withstood the estimated distance of 12 km during the experiment, but this may have been the result of the relatively small initial size of the glasses (~1.5 g). These experiments document that LDG, despite its even smaller initial size in the experiments, can resist abrasion and fragmentation better than the tektites, thus, could probably be transported farther in a stream environment. This is most likely caused by a much higher silica content in relation to the tektites from other groups. The estimated maximum transport distances, over which moldavites, bediasites and indochinites survived in the experiments, are all very similar. The greatest weight loss for all the specimens was found after the first estimated 2 km of tumbling. This is undoubtedly caused by the irregular initial shape of the tektites and LDG. Subsequent observations recorded minor weight losses, in association with more and more rounded glass shapes. The results of the study should be treated only as a general scheme for the fluvial abrasion of tektites, due to the inability to accurately reproduce the natural fluvial environment.

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Homotryblium-dominated Eocene dinoflagellate cyst assemblages from Middle Miocene (Badenian) glauconitic sands at Lipowiec (Roztocze, SE Poland)

Gedl P.

Geological Quarterly

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2016

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Vol. 60, No. 2

461--472

EN

A section over 20 m thick of the basal Middle Miocene succession exposed at Lipowiec (Roztocze, SE Poland) was studied for palynology. Thirteen samples were collected from quartz and glauconitic-quartz sands and thin clay layers. Sand samples were barren but clay samples yielded dinoflagellate cysts. Their assemblages consist of reworked Paleogene specimens dominated by the Homotryblium floripes complex (H. floripes and morphologically similar H. plectilum and H. vallum). The presence of reworked Paleogene specimens indicates intense erosion of marine Paleogene strata during initial stages of the Middle Miocene transgression at Roztocze. Analysis of stratigraphical ranges of reworked dinoflagellate cysts and comparison with their occurrences in known epicontinental Paleogene sites of SE Poland suggest an Upper Eocene age of the washed-out strata. The taxonomic composition of the assemblages described suggests that the Upper Eocene deposits accumulated in a near-shore, lagoonal embayment characterized presumably by oligotrophic waters of slightly increased salinity. A high proportion of the Homotryblium floripes complex is also characteristic of reworked assemblages found in younger Miocene strata of neighbouring exposures in Roztocze, which indicates widespread Eocene lagoonal environments in this part of Roztocze. Coeval Eocene strata from the eastern part of Roztocze and from the Carpathian Foredeep show different taxonomic compositions suggesting varied sedimentary settings during Eocene transgression in this region. These differences reflect variable amounts of freshwater influence resulting in a range of environments that ranged from oligotrophic to brackish.

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Early Miocene age of Stare Bystre Formation (Magura Nappe, Outer Carpathians, Poland) indicated by the calcareous nannoplankton

Kaczmarek A., Oszczypko-Clowes M., Cieszkowski M.

Geological Quarterly

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2016

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Vol. 60, No. 2

341--354

EN

The area of investigation is situated close to the contact zone between the Pieniny Klippen Belt, Krynica Subunit of the Magura Nappe and the Neogene strata of the Orava–Nowy Targ Intramontane Basin (southern Poland). In the area studied, marine deposits of the Stare Bystre Formation outcrop at the surface where they emerge from beneath freshwater and terrestrial Neogene and Quaternary deposits. Nannofossil assemblages from all samples are strongly dominated by reworked species. The Early Miocene age (NN2) of the Stare Bystre Formation has been determined on the base of the first occurrence of Sphenolithus disbelemnos after Shackleton et al. (2000). During the Late Oligocene (NP25/NN1), the frontal part of Magura Nappe was thrust northwards on to the terminal Krosno flysch basin. The northwards thrusting of the Magura Nappe was accompanied by the formation of the piggy-back basin on the Magura Nappe, filled with the synrorogenic turbidites belonging to the Zawada, Kremná and Stare Bystre formations (NN2).

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Reworked Eocene–Oligocene dinoflagellate cysts in the Miocene of the Carpathian Foredeep Basin : implications for Paleogene palaeogeography in SE Poland

Gedl P.

Geological Quarterly

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2012

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Vol. 56, No. 4

853–-868

EN

Miocene strata of the Carpathian Foredeep Basin in Poland contain reworked Eocene and Oligocene dinoflagellate cysts, which come from two sources: the Flysch Carpathians and the epicontinental basin. The occurrence of the latter is almost the only trace of the epicontinental Eocene–Oligocene sedimentary cover, which extended across southwestern Poland, and is today nearly completely eroded. The distribution of epicontinental Eocene and Oligocene taxa in the Miocene strata of the northeastern part of the Carpathian Foredeep is uneven, clearly pointing to a limited extent of the host deposits and their variable erosion intensity. Erosion of the Eocene and Oligocene platform cover took place prior the Miocene transgression and took place also during the Badenian; its intensity increased during Late Badenian–Sarmatian tectonic movements, resulting in an increased frequency of reworked specimens in strata postdating the mid-Badenian deposits.

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Sedimentary and diagenetic environments of Middle Ordovician iron-rich limestones (Pobroszyn Formation) in the northern Holy Cross Mountains, Poland

Trela W.

Geological Quarterly

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2008

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Vol. 52, No 3

199-199

EN

The Middle Ordovician (Dapingian) of the northern Holy Cross Mountains (central Poland) is represented by condensed limestones that make up the Pobroszyn Formation. They reveal a complex stratification reflecting alternating depositional conditions. The basal limestones were deposited in open-marine conditions during the early Middle Ordovician sea level rise (navis Zone) correlated with the Baltoscandian Gärdlosa drowning. Periods of non-deposition associated with this transgression favoured precipitation of authigenic Fe minerals close to the sediment-water interface. The upper part of this succession appears to representa succeeding depositional phase associated with a second transgressive event, which probably involved reworking of the underlying lithified substrate. High energy events were interrupted by periods of non-deposition favouring development of benthic microbial communities contributing to Fe authigenesis. The Pobroszyn Formation reveals features suggesting an early diagenetic alteration of the parent carbonate sediment in a shallow ma rine setting (e.g., beach shoreface) or even was influenced by meteoric diagenesis, which probably took place during a sea level fall preceding the second transgressive event.