Meteoryty, kratery uderzeniowe i inne ślady kosmicznej katastrofy w rejonie Moraska pod Poznaniem

Abstract

Meteorites, impact craters, and other traces of a cosmic disaster at Morasko near Poznań.A b s t r a c t. About 5,000 years ago near Morasko (the district of the present-day city of Poznań, western Poland) the largest known iron meteorite shower in Central Europe took place. The evidence of that impact, documented so far, comprises numerous iron meteorite fragments distributed over an area of approximately 3 km2 and at least six meteorite impact craters with a maximum diameter of about 100 m. The present paper reviews the most recent findings related to the meteorite, craters, processes of their formation, as well as the environmental effects of the impact in the Morasko area. The most important findings, reported in this review cover: 1) the recognition of two new minerals in the meteorite: moraskoite and czochralskiite; 2) the identification and detailed analysis of the ejecta layer around the craters and underlying paleosoil providing evidence for the mid-Holocene age of the impact; 3) the numerical modelling constraining the range of likely physical properties of the impactor, e.g. the diameter of the projectile forming the largest crater and its landing velocity (c. 1.5mand 10 km/s, respectively);4) the studies of the nearby lake and peat deposits revealing restricted environmental effects of the impact. The Morasko craters field is currently one of the best-studied examples of small/moderate-sized meteorite impact in unconsolidated sediments.