danescombe,

a precision -- the Shakiso crater was investigated by Christian Koeberl from the University of Wien, and he found that there is definitely no impact crater there (the pdf can be downloaded there -- http://www.univie.ac.at/geochemistry/koeberl/publication_list/ ).

His team could never find the shatter cones that were reported to be there in abundance by the Russian who had made a report on this structure (I can't remember his name but I saw the report once).

link fixed