Das holozäne Meteoritenkraterfeld von Kaali auf Saaremaa (Ösel), Estland

The Kaali meteorite crater group (58° 24' N, 22° 40' E) which lies 15 km north of Kuressare /Arens-burg on the island of Saaremaa/ Osel in Estonia, includes a main crater which is filled by water, and eight smaller secondary craters. The first description of the main crater was given by the physician J. W. L. V. LUCE in 1827. Later on various theories as salt tectonics, maare volcanism and gas explosions were made to explain the origin of the craters. In 1927 I. A. REINWALD who was prospecting for salt was joined by a research group including Alfred WEGENER, E. KRAUS and R. MEYER in order to investigate the crater field. They proofed it as meteoritic origin. Later research was made by REINWALD (30th), AALOE (mid 50th till 1980) and TIIRMAA (80th till now). The first found of meteoritic iron was made 1937 by REINWALD. Later excavations brought more than 3500 g of meteoritic fragments: The Kaali iron is a coarse (Og) Octaedrite IA containing 7,25% Ni, 2,2 μg/g Ir, 75 μg/g Ga and 285 μg/g Ge. Mineralography shows a strong terrestrial corrosion on the heavily impactshocked meteorite. Estimations basing on calculation show that the initial mass at an altitude of 25 km was 400-10000 t. The features of the craters show that the meteorite was impacted with a velocity of about 13 km/sec in a 35 to.40 angle from eastern direction. The meteorite who formed the main crater is estimated to 40 to 50 tons, the secondary craters may be formed by masses of about 4 to 6 tons. The zonation of the concentration of Ni spherules in a distinct horizon in the Viruma/Wierland and Laanemaa/ Wiek counties as at the island of Muhu/Moon suggest crash trajectory from the East-Northeast. Recently made pollenanalytical and radiocarbon dates indicated that the craters may be formed before 4000 BP Newer results made by TIIRMAA on microtectites and micros-pherules are changing the date up to 7600 BP. A geological natural park suggested by REINWALD in 1928 was only realised by conservation of the main crater as a nature preserve.