Stratigraphy of the Oligocene-Miocene boundary sediments in the Nezhinsky brown coal field (Primorye) and the problem of the Paleogene-Neogene boundary in the region

The geological characteristics of the productive coaliferous sequence and the overlying strata (the Nezhino Sequence) at the Nezhinsky brown coal field are provided with detailed geological and paleobotanical data on the Nezhino Sequence (operating quarry), which is proposed as its type section. Based on the analysis of the macro- and microfloral assemblages, the transitional Late Oligocene-early Miocene age is inferred for these sediments. The floras from both the sequences demonstrate no principal differences, being moderately thermophilic in composition, although the Nezhino flora is more thermophilic. The coaliferous and Nezhino sequences are assumed to be separated by a stratigraphic hiatus. It is shown that they are similar to the Oligocene-Miocene boundary sections in the adjacent regions. The Nezhino Sequence (lower Miocene) most likely corresponds to the upper Aquitanian-Burdigalian interval in the Standard stratigraphic scale. The Paleogene-Neogene boundary in the Primorye region is proposed to be placed at the top of the Pavlovka Horizon. In the Nezhino brown coal field, it coincides with the upper boundary of the coaliferous sequence.