92 research outputs found
An experimental model for the tektite fluvial transport based on the most distal Polish moldavite occurrences
Reworking and redeposition of tektites is a highly complex and multistage
geological process including many factors. A tumbling experiment was therefore undertaken
with the aim of estimating a distance of transport that such moldavites can withstand.
Though the experiment probably did not accurately mimic natural conditions, our results
proved that moldavites can withstand considerable transport only over a distance of a few
kilometers. Observed abrasion of tektites was significant in the early stage of experimental
transport; the rate of abrasion decreased correlatively with increasing distance of transport
as usual. Overall, given the results obtained from this experimental study and their state of
preservation described in the literature, it is very likely that Polish tektites were reworked
and redeposited by rivers from the Sudetes Mountains. Based on the paleoreconstruction of
river flows, it can be assumed that the Polish tektites originated from two independent
sediment supply areas
Shock structures in the Morasko meteorite - preliminary SEM data
This paper is a preliminary review of main shock deformations in the Morasko meteorite. Three main types of metamorphism structures occur in the investigated material: (i) brittle, (ii) plastic and (iii) thermal. Their interpretation may indicate, that Morasko meteorite reveals several stages of shock, eg.: extraterrestrial collisions and fall on the Earth
Variations dans le remaniement fluviatile de moldavites polonaises induites par modification hydrogéologique
Moldavites as ejecta glasses are fragile and transient: they are quickly abraded in fluvial conditions, this was confirmed by tumbling experiments. In the present study, multiple tumbling experiments were conducted to simulate the hydrogeological conditions of deposition of moldavites found in several different gravel pits. These experiments threw new light on the evolution of tektites during reworking. It appears that the original glass shape and mass as well as environmental conditions such as river velocity and the type of sediment with which they are associated are all important variables. However, the experiment did not simulate other significant variables, such as the variability of environmental energy. With given advantageous conditions, moldavite glasses could probably have withstood dozen kilometers of reworking, but this assertion is not sufficient to constrain the distance to their supply areas
The large superpredators' teeth from Middle Triassic of Poland
An unusual large teeth, finding from time to time in marine sediments of Muschelkalk, Silesia, Poland indicate the superpredators occurrence. According to size and morphological features the teeth are similar to archosaurs or giant marine reptiles
New moldavites from SW Poland
Four newly discovered moldavites from the East and West Gozdnica pits, SW Poland, are characterized. All specimens, including other four, reported earlier, are from Upper Miocene fluvial sediments of the Gozdnica Formation. Their weight varies between 0.529 and 1.196 g. The moldavites are bottle green in colour and have bubbles and inclusions of lechatelierite. Low degree of corrosion suggests short river transport, apparently eastward from Lusatia
The first Polish tektites : preliminary SEM investigation
In Lower Silesia, the first Polish moldavites were discovered. To recognize the primary chemical composition and check the morphology of investigated material SE and BSE images were used. The samples show presence of vesicles, which are one of the most typical features of tektite glass. Referring to the preliminary
EDS results and comparing them with literature data, it can be assumed that in all cases the base material for all known moldavites was the same
Susceptibility of various tektite types to fluvial abrasion
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
Les découvertes les plus distales de moldavites en Basse-Silésie, Pologne
The present note reports new findings of moldavites reported from southwestern Poland. The material was found in the Nowa Wieś Kącka sandpit. To date, it represents the most distal locality where moldavites have been found. These moldavites, like other moldavites previously described from Lower Silesia, are recovered from fluvial sands and gravels of the Gozdnica Formation. Like other Polish moldavites, the moldavites in this study display high SiO2 contents (~77 wt.%). Their dimensions range from 9 to 11 mm in maximum diameter. Their relatively large sizes suggest that the distribution of Polish tektites defines a sub-strewnfield larger than previously expected.De nouvelles découvertes de moldavites sont signalées dans le sud-ouest de la Pologne. Le matériel provient de la sablière de Nowa Wieś Kącka. À ce jour, ce site représente la localité la plus distale ayant livré de la moldavite. Ces tectites, comme les autres moldavites répertoriées précédemment en Basse Silésie, ont toutes été extraites des dépôts de la Formation Gozdnica. À l’instar des autres tectites polonaises, le matériel étudié ici se caractérise par une haute teneur en SiO2 (~77 % en masse). Les spécimens étudiés mesurent de 9 à 11 mm dans leur plus grande dimension. Leurs tailles relativement importantes suggèrent que la répartition des tectites polonaises pourrait être bien plus large qu'initialement envisagée
Moldavite finds in Middle Miocene (Langhian Stage) deposits of southwestern Poland
Most of the Ries tektites (moldavites) were deposited in sediments clearly postdating the
Ries crater formation. This suggests secondary deposition for these ejected glasses. Only a few sedimentary
formations known to contain these tektites are of Middle Miocene age and coeval with the Ries
event. One is the Poznańska Formation, which is exposed across southwestern Poland. These mud deposits
formed in the Middle Miocene (Langhian Stage). New moldavites, described in this report were
found in the Poznańska Formation and weigh from 0.851 to 0.907 g. The North Stanisław sandpit,
where the tektite specimens were found, is located 490 km from the Ries structure. These finds agree
with the numerical simulation modelling of the ejection of these moldavites up to 600 km away from
the source crater
Spherules associated with the Cretaceous Paleogene boundary in Poland
The succession of the Lechowka section near Chefm in south-eastern Poland presents the first complete record of the Cretaceous-Paleogene (K-Pg) boundary in Poland. Samples of the boundary clay were examined for mi-crotektites and shocked minerals to confirm the impact origin of the sediment. The spheroidal fraction reveals morphological and mineralogical features, e.g., spherules, similar to material from the K-Pg boundary as described from elsewhere. The impact genesis of the spherules is confirmed by the presence of nickel-rich spinel grains on their surfaces. The spinels are considered to be primary microlites and, thus, the spherules at Lechowka can be classified as microkrystites. No shocked minerals were noted. The deposits with spherules comprise Aland Mg-rich smectite (Cheto smectite). This almost pure Mg-rich smectite, forming up to 100% of the clay fraction, derived from the weathering of the impact glass. It is proposed that the spherules isolated from the Creta-ceous-Paleogene boundary clay at Lechowka come from the Chicxulub crater in Mexico
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