Fundamental research on Paleogene dinoflagellate cyst biostratigraphy in Southwest Japan

1)对九州西北部和本州最西部古近系第三系进行了地面地质调查，包括(a)沉积相分析，(b)细粒沉积物取样进行鞭毛藻囊分析，(c)软体动物化石取样。测井剖面包括天草地区的Shimoshima组、高岛地区的Takashima组和Iojima组、崎前-松岛地区的Matsushima组和nishonogi组、佐世保地区的Ainoura组和Sasebo组、卡拉津地区的Ouchi组和Kishima组、Chikuho地区的Ashiya组、Yuyawan地区的Hioki组和三池地区的Manda组。根据前人的研究，总体采样区间为中始新世至晚渐新世。2)在测井剖面的大部分海相层段中，化石鞭毛藻囊连续出现。该组合具有多样性，包括Gla…More phyrocysta、Spiniferites、Homotryblium、Cordosphaeridium、Hystrichokolpoma、Heteraulacacysta、Deflandrea、Dracodinium和Wetzeliella等属。它们表现出明显的地层变化，这对日本西南部可能存在的地层潜力是有利的。提出了初步的生物地层分带。此外，这些组合的组分与东海同代沉积物的组分基本相同，但与北海道-库页岛地区的组分存在较大差异。这支持了太平洋西北海岸的古生物地理分化，这种分化可能在始新世晚期变得明显，这需要高纬度和低纬度的独立生物地层方案。3)对软体动物化石的调查表明，佐世保群的软体动物化石组合应归属于阿希亚动物群，缺乏Kadonosawa动物群的典型元素。这表明，沙世期的年龄范围不应该延伸到中新世。少

1)Surface geologlcal investigation was conducted on the Paleogene Tertiary formations in northwestern Kyushu and westernmost part of Honshu in terms of (a)sedimentary facies analysis, (b)sampling of fine-grained sediments for dinoflagellate cyst analysis, and (c)sampling of molluscan fossils. Logged sections include the Shimoshima Group in the Amakusa area, the Takashima and Iojima Groups in the Takashima area, the Matsushima and Nishisonogi Groups in the Sakito-Matsushima area, the Ainoura and Sasebo Groups in the Sasebo area, the Ouchi and Kishima Groups in the Karatsu area, the Ashiya Group in the Chikuho area, the Hioki Group in the Yuyawan area, and the Manda Group in the Miike area. The overall sampled interval ranges from the Middle Eocene to latest Oligocene in age, based on previous studies.2)Successive occurrences of fossil dinoflagellate cysts were confirmed from most marine intervals of the logged section. The assemblages, being generally diverse, include genera such as Gla … More phyrocysta, Spiniferites, Homotryblium, Cordosphaeridium, Hystrichokolpoma, Heteraulacacysta, Deflandrea, Dracodinium and Wetzeliella. They showed apparent stratigraphic changes, which is positive for feasible blostratigraphic potential in Southwest Japan. A preliminary biostratigraphic zonation was presented. In addition, the constituents of the assemblages are mostly common to those from the coeval sediments in the East China Sea, although at the same time they are very different from those from the Hokkaido-Sakhalin region. This supports the paleobiogeographic differentiation along the northwestern coast of the Pacific that became apparent probably during the Terminal Eocene, which requires independent biostratigraphic schemes for higher latitudes and lower latitudes.3)Our investigation of molluscan fossils indicated that the assemblages from the Sasebo Group should be attributed to the Ashiya Fauna, lacking the elements typical to the Kadonosawa Fauna. This implies that the age range of the Saseboan Stage should not extend up to the Miocene. Less