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Późno dewońskie impakty

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Brachaniec T., Brom K.
Acta Societatis Metheoriticae Polonorum
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2015
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vol. 6
34-37
EN
In 1970 the first hypothesis, which claimed that large meteorite landed in ocean at Frasnian/Famennian boundary and caused mass extinction was proposed. In Late Devonian deposits there are many potential impact evidences. Nonetheless, many years of searching for iridium anomaly, shocked minerals, microtektites and craters in the F/F boundary passage deposits have failed. The most probably crater, which could be connected with F/F boundary is Siljan Ring in Sweden.
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‘Aegean’ – kolisty obszar w południowej Europie – jego geologia a największe kratery na Ziemi

63%
Walesiak T.
|
EN
Analysis of online available references suggests that circular characteristics observed around Aegean Sea in southern Europe may represent protobasin class of impact craters, which small central peak and surrounded peak ring appear to be formed by the Cyclades. Thinner crust, upper mantle deformation (uplift), recognition of basin in upper mantle re-filled with rocks having lower density than surrounding mantle, central Aegean Sea area free of sediments and almost perfect circular anomaly of density with diameter over 500 km are only few arguments which may indicate its real origin. The strongest fact standing for hypothesis of impact is presence of deep, lithospheric fracture zones with both circular and radial character, detected up to the distance of ~516 km from common geometric point of all rings (providing estimated diameter of the largest circle over 1000 km). Existence of pseudotachylite veins and breccias in central Cyclades are contributory evidence. Mélange covered by Fe-Ni rich ores in Jurassic/Cretaceous boundary, if related to impact, may give clue to explanation of localized in Europe Tithonian mass extinction event 145 Ma. However, pseudotachylites and breccias can be produced by endogenic processes (e.g., plate tectonics). A further research is required to find evidence of passage of shock wave through target rocks.
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