The Structure and Age of the Kaali Main Crater, Island of Saaremaa, Estonia

Abstract

We have studied in detail the main crater at Kaali with 98 borings and several diggings, carefully levelled. As a result, the first detailed morphologic map of the crater is presented. The diameter of the meteorite, which formed the main crater, was probably not more than 3 m and the weight about 40–50 t. Bronšten and Stanyukovich (1963) maintained that at the time of impact, its weight was probably 20–80 t. According to Pokrovski (1963), the diameter of the Kaali meteorite was evidently 4.8 m and its mass 450 t. Thus, the explosive energy released by the event was not powerful enough to induce remarkable environmental consequences. Pollen stratigraphy and radiocarbon dates up to 3390±35 BP from the bottom sediments in the main crater suggest that the Kaali crater group is more than 4000 years old. Based on an iridium-rich layer in the Piila Bog, 8 km NW of Kaali, Rasmussen et al. (2000) and Veski et al (2001 2001a) concluded that this event took place about 800 to −400 BC. Our budget calculations of the spatial-temporal distribution of mineral impurities in the peat layers do not support the hypothesis about direct extraterrestrial origin of Ir in the Piila Bog. The changes in the iridium content in the vertical profile of the peat section are due to natural geochemical processes and have no connection with the Kaali impact.