Numerous investigations of Morasko meteorites, have so far identified many secondary mineral phases like: goethite, lepidocrocite, akaganeite, siderite, calcite, ankerite, awaruite, nickel native as well as vivianite. Recently studies on a new found meteorites Morasko, allowed the identification of more secondary minerals. They are represented by: aragonite CaCO3, chukanovite Fe2(CO3)(OH)2 and hellyerite (Ni[CO3]·6H2O) (Karwowski et al. 2011). More detailed analysis of the above phases revealed a new secondary phases, which are represented by: reevesite (Ni6Fe3+2CO3(OH)16·4H2O) as well as jarosite (KFe3+3(OH)6(SO4)2).
The main products of terrestrial weathering of metallic phases in Nantan meteorite are represented by: goethite, lepidocrocite and others nonstructural Fe-hydroxides with differ hydratation ratio. Sometimes iron hydroxides are associated with high-nickel phases. Hydrated iron phosphates are observed like, e.g. vivianite, in vicinity schreibersite. Only phosphides, relics of taenite and the hight-nickel phases are preserved in strongly weathered specimens. Generally, both the process of weathering and the types of secondary phases are similar in Nantan and Morasko meteorites. The differences are very small and are caused by slightly different chemical composition of both meteorites.
Weathering processes of minerals which are presented in the Morasko meteorite are characterized by different speed of the secondary changes. The most resistant minerals for the alternations are phosphites (schreibersite, rhabdite, nickielphosphide) and carbides (cohenite) but also the mentioned phases show secondary fluctuation. Phosphites are changing into metallic, phosphorus free phases, which are similar to native nickel or avaurite (awaruitu) with very well visible modification of its crystal morphology. All phosphorus amount is introduced to secondary phosphates like vivianite. The carbides alternation processes occur in a different way than in case of phosphates. Carbon is free to the environment up to time, when the new phase is totally decomposed and replaced by hydroxyoxide of iron. Sometimes, the high-nickel metallic phases are also noted as the products of the weathering. All described mineral phases, that are resistant for secondary alternation might be indicators for high evolved meteoritic material in the Earth’s weathered rocks.
PL
Wietrzenie poszczególnych faz mineralnych, obecnych we fragmentach meteorytu Morasko, przebiega w różnym tempie. Za najbardziej odporne uznaje się fosforki (schreibersyt, rhabdyt, nickielphosphide) oraz węgliki (cohenit). Jednak po pewnym czasie również i te fazy ulegają rozpadowi. Z fosforków wyraźnie ubywa fosforu i przekształcają się one stopniowo w fazy metaliczne, zbliżone do taenitu lub awaruitu. Towarzyszy temu zmiana morfologii kryształów. Uwolniony fosfor wchodzi w skład wtórnych fosforanów typu wiwianit (vivianit). Węgliki zachowują się nieco odmiennie. Węgiel zostaje stopniowo uwalniany do środowiska a w dalszym etapie faza ta ulega całkowitemu rozpadowi przechodząc w wodorotlenki żelaza. Jednymi z ostatnich faz, które można dostrzec wśród wodorotlenków żelaza są wtórne fazy wysokoniklowe. Powyższe odporne na wietrzenie fazy, jako nieobecne na powierzchni Ziemi (z wyjątkiem krzemianów), mogą służyć identyfikacji meteorytowego pochodzenia silnie zwietrzałych skał.
It is considered that The Morasko meteorite shower happened about 5400 years BP with a trajectory from NE to SW (Bronikowska et al. 2015). Recent studies not only prove that this fall could be observed in Februrary 14, 1271, but also that location of most findings in the area to the east side of the craters, should not be taken as the main indicator of impact direction. The proper answer can be given base on knowledge related to oblique impacts, supported by understanding of complicated fragmentation process. The largest crater in Morasko Meteorite Restricted Area has main ejecta plume located in SE, side walls in SW and NE, and free of ejecta Zone of Avoidance (ZoA) in NW. This clearly shows that impact trajectory was approximatelly from NW to SE. There were also discovered other structures, 2 km North from Restricted Area, having common features. Their ejecta plumes as well as few raised ducts (possible traces of underground penetration) are directed to SE, pointing the largest structure – Umultowskie Lake, located approx. 2 km ESE from known main Morasko crater. Shapes of cavities, their walls and ejecta asymmetry allow estimating trajectories and defining new Morasko strewnfield, which matches not only location of impact strucures and discovered meteorite fragments, but also explains smaller (3–4 kg) findings in the neighborhood of Oborniki Wielkopolskie.
It’s over 100 years after discovery of the first iron meteorite in the area of Morasko, but still we are not sure about date of the fall. Recent researches suggest that it happened about 5000 years ago, however there are some other facts proving, that event took place in the last millenium. Verification o 14C radio carbon dating results revealed, that it can give us only the maximum date (meaning: not older than). The main problem was that probes were taken from mixed types of sediments – some created before and some after the impact. Few years earlier there was another 14C examination of sediments lying beyond the floor of 2 small cavities and their age was estimated to be approximatelly 700 years BP. Similar results were received after verification of organic matter under charcoal in the weathering crust of the meteorite, which was found in the Morasko Restricted Area. Another proof was discovery of shrapnel in the root of old tree, which could not be older than 800–1000 years. At least 2 times it was discussed, if finding of Morasko iron meteorites couldn’t be matched with described observation A.D. 1301, mentioned in annales, hovever nobody was able to prove it. Analysis of historical documents lead to information of appearance of 3 suns, after sunrise, what happened in 14 Feb. 1271. Further investigation of other sources gave us even more facts. We can read in annales that in the same year, castles and cities were burned and destructed to the ground. There is also information that Poznan, the largest city in the area (approx 7.5 km South from the Morasko), was burned in (or shortly before) the year of 1274. What is more Annales from Poznan and from its parent town Wielkopolska were finished in A.D. 1271, just in the middle of the sentence. Finally, confirmation is given by archeological researches, which tell us that city walls and castle of Poznan were ruined shortly after they were constructed, but scientists found difficulty to answer, when exactly it could happen. The main problem was unknown weapon, able to leave such a large destruction, even when considered next centuries. As we can find in annales that Poznan in A.D. 1253 had castle and fortifications so only iron meteorite impact in 1271, producing craters in the area of Morasko and Umultowo, can explain the scale of the devastation discovered by archeologists.
I wonder if a description of Morasko meteorite “rainfall” could be found in any medieval chronicles? If Bartoshewitz’s and ‘bolid wielkopolski’ hypothesis’s are only the result of dishonesty of chroniclers and ancient meteorite researchers? A survey of old annals is closing us to the explanation of this catastrophic event from the turn of XIII and XIV century. However, new thesis requires further research.
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