The age of the Ilumetsa meteorite craters in southeast Estonia

The Ilumetsa impact craters were discovered in 1938 in the course of geological mapping. In the crater field area, the Middle Devonian bedrock consists of light-yellow weakly cemented siltstones and sandstones of the Givetian Burtnieki Regional Stage, which are overlain by a 1-2-m-thick layer of reddish-brown loamy till. Porguhaud, the biggest crater, has a diameter of 75-80 m at the top of the uplifted rim and is 12.5 m deep. The zone of authochtonous breccias below the apparent crater extends to 30 m deep. The crater is partly filled with a thin layer of gyttja and peat up to 2 m thick. Radiocarbon ages of 6030 +/- 100 (TA-310) and 5910 +/- 100 (TA-725) years B.P. from the lowermost organic layer and palynological evidence suggest that the age of the impact was approximately 6000 14C-years B.P. The Sügavhaud crater has a diameter of 50 m at the top of the rim and is 4.5 m deep. Organic matter on the bottom of the crater is absent. As precise age determination of the Ilumetsa craters by direct dating methods has proved inconclusive, we proposed a method of geological correlation which is based on the occurrence of impact spherules in lake and bog sediments around the crater field. Radiocarbon dating of samples from a peat layer with glassy spherules of impact origin in the Meenikunno Bog, 6 km southwest of the Ilumetsa crater field yielded the ages of 6542 +/- 50 (Tln-2214) for the depth interval 5.6 - 5.7 m and 6697 +/- 50 (Tln-2316) years B.P. for the depth interval 5.7 - 5.8 m. These dates suggest that the Ilumetsa craters were formed about 6600 years ago.