Biostratigraphy and correlation of the Turonian - Coniacian succession and the Turonian - Coniacian boundary problem in the Far East Russia based on ammonites and inoceramids

Abstract

The stratigraphy, ammonite and inoceramid content of the Turonian - Coniacian deposits of Far East Russia are presented. The evolution of North Pacific ammonites and inoceramids at the boundary of the two stages was studied and the levels of fundamental changes within the ammonite and inoceramid biota are recognized. The established palaeobiogeographic difference between the Sakhalin and the North-East region palaeobasins is reflected in the existence of two independent local zonal schemes. The main criteria of the Turonian-Coniacian stage boundary in the Far East of Russia were established on the basis of the two schemes. The TuronianlConiacian (TIC) boundary is clearly marked by the change in the taxonomic diversity of the zonal inoceramid assemblages. It is defined at the base of the Inoceramus uwajimensis Zone. The appearance of the endemic ammonite species Jimboiceras mihoense MATSUMOTO is the ammonite criterion for recognising the TIC stage boundary in Sakhalin. This is supported by occurrences of the cosmopolitan Coniacian genera Peroniceras and Forresteria.