Determining the age and possibility for an extraterrestrial impact formation mechanism of the Ilumetsa structures (Estonia)

1,2A. Losiak,3A. Jõeleht,3J. Plado,4M. Szyszka,3K. Kirsimäe,5E. M. Wild,5P. Steier,2C. M. Belcher,1A. M. Jazwa,3R. Helde
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13431]
1Planetary Geology Lab, Institute of Geological Sciences, Polish Academy of Sciences, Warsaw, Poland
2wildFIRE Lab, Hatherly Laboratories, University of Exeter, Exeter, UK
3Department of Geology, University of Tartu, Tartu, Estonia
4Institute of Geology, Adam Mickiewicz University in Poznań, Poznań, Poland
5VERA Laboratory, Faculty of Physics—Isotope Physics, University of Vienna, Vienna, Austria
Published by arrangement with John Wiley & Sons

The Ilumetsa site, in Estonia, consists of two round, rimmed structures that are 725 m apart. The structures are listed as proven impact craters in the Impact Earth database, despite lack of commonly accepted, unequivocal proof of extraterrestrial collision identified at this location. We excavated trenches though the Ilumetsa Large and Ilumetsa Small structures and found small pieces of charcoal within the putative proximal ejecta in both structures, in a similar geological setting as previously identified charcoal in Kaali (Losiak et al. 2016) and Morasko craters (see Szokaluk et al. 2019). Our 14C dating of charcoal allowed us to conclude that these crater‐like features formed simultaneously between 7170 and 7000 cal. years bp, about 7 ka after deglaciation of this area. A ground penetrating radar survey of the nearby bog shows that no additional Ilumetsa structures bigger than 40 m exist. Geochemical studies of the ejecta and a search using a metal detector did not reveal any clear indication of extraterrestrial material. This suggests Ilumetsa may have been formed by an impact of stony‐iron or stony body, which got significantly weathered in a wet‐temperate climate. The mystery of the formation of the structures at Ilumetsa remains; however, due to significant circumstantial evidence discussed herein, we are confident to call it a “probable” impact site.

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