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Mitta V.V. (2007) The ammonite assemblages of basal part of the Ryazanian (Lower Cretaceous) of Central Russia // Stratigraphy and Geological Correlation, vol. 15, No 2. P. 193-205.
Five successive ammonite assemblages are distinguished in the basal part (Riasanites rjasanensis Zone s. l.) of the Ryazanian Stage of the East European platform. These are (from the base upward) (1) Hectoroceras tolijense; (2) Hectoroceras kochi ; (3) Riasanites swistowianus; (4) Riasanites rjasanensis ; and (5) Transcaspiites ransfigurabilis assemblages. Two lower assemblages consist entirely of boreal taxa, which occur in association with iverse ammonites of the Tethyan origin higher in the section. The data obtained show that three upper assemblages are correlative with the Berriasian Dalmasiceras tauricum, Riasanites rjasanensis–Spiticeras cautleyi, and Euthymiceras euthymic subzones of the northern Caucasus. The succession of five–six ammonite assemblages established in the East European platform above the top of the Craspedites nodiger Zone may correspond to the same number of ammonite assemblages characterizing lower subzones of the standard Berriasian. Berriasella rulevae Mitta, sp. nov. from the upper part of the Riasanites rjasanensis Zone (transfigurabilis biohorizon) is described.