Cretaceous Sakhalin and Cretaceous events in North Pacific-II

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The Upper Cretaceous System in the southwestern part of the Kril'on Peninsula was studied biostratigraphically, succeeded from our first expedition to Southern Sakhalin in 1993-1994. Supplementary, the Upper Cretaceous in the Naiba area, including the type sections along the Naiba and Krasnoyarka rivers, was also studied in both the biostratigraphy and paleomagnetic stratigraphy.The correlatives to the Bykov and Krasnoyarka formations, ranging from the Santoinian to earlier Maastrichtian, are exposed in the western and eastern parts of Kril'on, from which successive occurrences of many well-preserved ammonoids, inoceramids and other invertebrate and plant megafossils were confirmed. Almost complete Campanian sequence was found along the Kura River in the eastern part. In this Kura River section, seven biostratigraphically important megafossil assemblages were recognized, including the occurrence of such index ammonoid taxa as Pachydiscus awajiensis and "P." soyaensis. In the Naiba area of the central Southern Sakhalin, we collected the samples for paleomagnetic stratigraphy at 36 sites (ca.250 specimens). The result of the paleomagnetic measurements are quite consistent with our results of biostratigraphy and carbon isotope stratigraphy. Combining with these results, precise bio- and chronostratigraphy can be established in Sakhalin, which provide a sound basis for the correlation of the Upper Cretaceous between Sakhalin and Hokkaido, and for the interpretation in biotic and physical evolution during the Late Cretaceous in the North Pacific.