Introduction

Within western Russia and the adjoining states, the Upper Pliocene and Quaternary (Anthropogene) sequences are abundantly documented in terms of fossil mammals, marine and fresh-water mollusks, foraminifera, ostracodes, macro- and microflora, and remains of human occupation, as well as extensive data on neotectonics, lithology, and paleomagnetism. For many years, however, the stratigraphers in that vast region did not share a unified point of view on the location of the lower boundary of the Quaternary. Although the majority considered that the lower boundary of the Quaternary should be correlated to the base of the Bakuan Stage, some favored the base of the Akchagylian Stage, whereas others preferred the base of the Apsheronian.

At a joint meeting of the IGCP-41 working group and INQUA Subcommission 1-d at the XI INQUA Congress in Moscow in 1984, the proposal was adopted to place the Pliocene–Pleistocene boundary, and thus the Neogene-Quaternary (N/Q) boundary, in a physical reference point, or boundary-stratotype, at Vrica, Calabria, located at the base of the claystone layer conformably overlying sapropelic marker e in component-section B of Selli et al. (1977) (Aguirre and Pasini, 1985). According to Tauxe et al. (1983), with slight modification by Zijderveld et al. (1991), that level is close to the top of the Olduvai normal-polarity subchron. Following that concept, the N/Q boundary should be located somewhere in the lower part of the Apsheronian beds of the Caspian Basin and their stratigraphic equivalents. That boundary level has now been officially accepted by stratigraphic workers in the former USSR.