Using charcoals as a proxy to estimate energy released from small impact cratering processes
Over the last half a century there has been much debate over the quantities and mechanisms of thermal energy release during impacts of small asteroids such as Tunguska event (Russia) or Kaali craters. This has been caused in a large part by the fact that the existing observational and modelling approaches have focused on large impact craters that generate high temperature/pressure transitions which leave noticeable signatures in the rocks they affect. However, small impacts craters developed in unconsolidated materials have not been thought to leave long lasting traces of the thermal energy released during their formation. Recently however, Losiak et al. (2016) found charcoal buried within ejecta blanket of Kaali Main crater where sedimentological analyses and 14C dating suggest that the charcoal was formed at the same time as the craters within which they were found. Subsequently Losiak identified charcoal in Kaali 2/8, Ilumetsa Small, Ilumetsa Large and the Morasko Main craters, indicating that charcoal is not restricted to a single crater, single impact or single location. Project ImpCHAR will use a novel analysis method that measures the reflectance properties of charcoal, which has been recently shown to relate to the energy that created it. ImpCHAR will use this method to determine the heating regime from which the chars were created. In order to achieve this Project ImpCHAR will experimentally recreate the heating conditions in a laboratory setting in order to determine the most likely mechanism of charcoal formation. This will allow developing a method of unequivocally identifying small impact craters developed in vegetated unconsolidated sediments: up to this point most of those kinds of structures could be identified only based on circumstantial evidence of co-existing crater-like shape and occurrence of meteorites. Additionally, ImpCHAR will critically disentangle debate surrounding the energy release during formation of small impact craters.