The middle Devonian Kaluga impact crater (Russia): new interpretation of marine setting

In the Middle Devonian, a hypervelocity impact occurred in the central part of the East European craton that was occupied by the epicontinental sea. This event produced a circular crater depression filled with impact breccias and melt rocks, which were overlain by a resurgent sedimentary breccia and later buried under a thick sequence of Upper Devonian and Carboniferous beds. In the 60s, this underground depression, known as the Kaluga impact crater (54°30′N, 36°12′E, diameter 15 km, age 380 Ma), was investigated in detail by intensive drilling, as well as geophysical and geological techniques. The current paper provides a reinterpretation of previously published data based on a petrographic study. The new observations allow reconstruction of the displacements of target rocks in the crater rim, and help to understand the following period of prolonged sedimentation in the marine setting. In addition, it is proposed that a specific type of breccia, the Narva Breccia that occurs in a widespread area approximately 500 km north-west off the impact site in the appropriate stratigraphic level, is the result of seismic shock and the accompanying tsunami wave.