Стратиграфия Маастрихтских отложений бассейна р. Каканаут (восточная часть Корякского нагорья)

Abstract

Recent discovery of rich dinosaur fauna at high latitudes in northeastern Russia required the additional investigation of the Kakanaut locality for more precise definition of its age and stratigraphic position. This locality is situated in the southern part of the Koryak Upland, in the Kakanaut River basin near Pekulneyskoe Lake (Chukotka Autonomous Region). In the result of field work 2007-2009, five particular sections were described and joint geological column of the Maastrichtian deposits was composed. In this column three parts were distinguished: the marine siltstone strata, the Kakanaut Formation and the Kokuy strata. The Maastrichtian deposits are covered by effusive-pyroclastic deposits (possibly, early Paleogene in age). The marine siltstone strata contains inocerams and ammonites of the lower and lower part of upper Maastrichtian (Inoceramus (Cataceramus) pilvoensis Sok., Schachmaticeramus shikotanensis (Nagao et Mat.) Schachmaticeramus kusiroensis (Nagao et Mat.). Hypophylloceras marshalli (Shimizu), Diplomoceras sp., Pachydiscus subcompressus Mat.). The Kokuy strata contains remains of the late Maastrichtian-early Palaeocene foraminifers (Rzehakina epigone zone) and of undetermined fragments of ammonites. The Kakanaut Formation are represented by nonmarine volcanogenous-terrigenous sediments. It consists of tuffaceous sandstone and siltstones, tuffs, tuffites and andesite-basaltic rocks and represents lacustrine and fluviodeltaic deposition on near-sea lowland. These deposits contain joint association of fossil plants and dinosaur bones, teeth and eggshell fragments. The dinosaur assemblage represented by basal ornithopods, hadrosaurids, ankylosaurians, neoceratopsians, troodontids, dromaeosaurids and tyrannosaurids. Dinosaur eggshell fragments, belonging to hadrosaurids and non-avian theropods, indicate that at least several dinosaur taxa could reproduce in polar region. The Kakanaut flora includes about 50 taxa. The cycadophytes (Nilssonia, Encephalartopsis) and Ginkgo are very abundant in certain layers. The conifers are represented by mixture of the typical Late Cretaceous elements with an admixture of younger Paleocene elements belonging to families Taxodiaceae, Cupressaceae and Pinaceae. Angiosperms include about 30 species. Families that can be confidently recognized are Platanaceae (Platanus), Cercidiphyllaceae (Trochodendroides), Betulaceae (Corylus), Fagaceae (Fagopsiphyllum), Rosaceae (Peculnea, Arctoterum). Other species appear to belong to ancient groups, without clear phylogenetic links to modern taxa. The age of the fossiliferous beds can be estimated as the beginning of late Maastrichtian. The correlation of the Maastrichtian deposits of different areas at eastern part of Koryak Upland was carried out.