Sediments from Lake Cheko (Siberia), a possible impact crater for the 1908 Tunguska Event

Cheko, a small lake located in Siberia close to the epicentre of the 1908 Tunguska explosion, might fill a crater left by the impact of a fragment of a Cosmic Body. Sediment cores from the lakes bottom were studied to support or reject this hypothesis. A 175-cm long core, collected near the center of the lake, consists of an upper 1 m thick sequence of lacustrine deposits overlaying coarser chaotic material. 210 Pb and 137 Cs indicate that the transition from lower to upper sequence occurred close to the time of the Tunguska Event. Pollen analysis reveals that remains of aquatic plants are abundant in the top post-1908 sequence, but are absent in the lower pre1908 portion of the core. These results, including organic C, N and d 13 C data, suggest that Lake Cheko formed at the time of the Tunguska Event.