Bol’shoi Ilek as the ilek formation stratotype of the Lower Cretaceous, and the new dinosaur and mammoth faunae site in the south-east of Western Siberia

Abstract

The geological section of Bolshoi Ilek (up to 83 m high), southeast of Western Siberia, represented by Cretaceous and Quaternary systems has been reassessed. Its major part is composed with the Lower Cretaceous deposits of deltic genesis that reached 80 m thickness and characterized the Ilek Formation stratotype. During the screen washing of sand fraction the remains of fishes, lizards, turtles, crocodiloformes, dinosaurs, and mammals, typical for the Barremian - Lower Albian, have been revealed. Mesozoic strata are covered by eolian-deluvial and eluvial Quaternary deposits from 3 to 13,5 m. Three layers with mammoth fauna remains were distinguished there. The middle one is dated by 14С as ~ 22500 years ago. The observation have revealed that Bolshoi Ilek is a large landslide more than 1 square kilometre area. All of it allowed to compare it with the coeval section of Shestakovo outcrop that also exposes the part of giant landslide, caused by earthquakes more than 9 points by Richter scale, which indicates a powerful seismic event, occurred in the southeast of region at the very end of Pleistocene.