Abstract
The Cretaceous clastic sequences in the Naiba area of South Sakhalin, Russian Far East, have been investigated in terms of macrofossil stratigraphy and magnetostratigraphy in conjunction with detailed field mapping since 1990. This paper provides an overview of the lithostratigrahy and magneto-biostratigraphy of the Upper Cretaceous portions that are well-exposed along the River Naiba and its tributaries. The Cretaceous strata in Naiba are subdivided lithologically into the Ai, Naiba, Bykov, and Krasnoyarka Formations, in which the Krasnoyarka Formation and the upper part of the Bykov Formation yield abundant ammonoids and inoceramids that commonly occur in the "Upper Yezo Group" and the "Hakobuchi Group" in central Hokkaido. A stratigraphic sequence of magnetic polarity reversals consisting of 15 magnetozones can be established from the upper Bykov and the entire Krasnoyarka Formations. Although cosmopolitan marker species are few, a continuous biostratigraphic section ranging from Jimboiceras mihoense Zone (Coniacian) to Pachydiscus subcompressus Zone (Maastrichtian) via zones of Canadoceras spp. (Campanian), all of which characterize the North Pacific Realm, is typically observable in the Naiba area. The biostratigraphic age assignments using these ammonoids and other molluscs lead to the correlation of the geomagnetic polarity sequence with polarity chrons from C34n, the Cretaceous long normal interval, through C30n in the upper Maastrichtian.
