CO-OPERATIVE STUDY OF TERTIARY SILICEOUS SHALE FORMATIONS

日本北部新近系硅质页岩是北太平洋地区第三系硅质沉积的一部分。建立了本州东北部青森地区硅质页岩地层的岩石地层学和微生物地层学（硅藻、放射虫、钙质纳米化石、有孔虫和花粉）。硅质页岩地层覆盖中中新世至上新世，其中中中新世最为广泛。青森西部Ajigasawa地区中中新世Ohdoji组底部存在滩状海绿石层；黑崎川路线上7.3 m厚的海绿石层代表330 m.y.，平均堆积速率约为45 m.y./m或2.2 cm/m.y.。在Ajigasawa地区，从中中新世到上新世，生物源二氧化硅的平均沉积速率几乎不变，为7.3 ~ 9.3 g/cm^2kry，尽管中中新世到上新世，硅质页岩组的平均沉积速率有所增加。更重要的是，硅质页岩地层的不同沉积速率不是由于硅质生物，特别是硅藻生产力的差异，而是由于陆源物质的流入。稀土元素。硅质页岩构造模式显示正常或正Ce异常，表明强烈的陆地影响。铀含量为1 ~ 18ppm，青森里西部大部分为10ppm，东部小于5ppm；这些数值远低于加州蒙特利组硅质页岩的数值。在青森的硅质页岩地层中，既没有发现磷矿层，也没有发现磷矿岩。迄今为止，在青森以南秋田地区船川组上中新世黑色泥岩中发现了一些晚成岩成因的磷矿结核，在诺藤半岛发现了鸟粪型磷矿。本州岛弧东北部和诺托半岛的中中新世硅藻质和岩化硅质矿床聚集在沿日本西海岸裂谷带形成的狭长型上-中深盆内。盆地的东侧与北上高原和武间高原的小陆地接壤，而其西侧则受到海底隆起或陆地块的限制，将盆地与新生的日本海的古大和盆地分开。充填中中新世硅质页岩的盆地宽度约为200 ~ 250 km。少

Neogene siliceous shale formations in northern Japan are a part of the Tertiary siliceous deposits of the North Pacific region. Lithostratigraphy and microbiostratigraphy (diatom, Radiolaria, calcareous nannofossils, foraminifera, and pollen) of the siliceous shale formations of Aomori, Northeast Honshu have been established. The siliceous shale formations cover from Middle Miocene to Pliocene, of which the Middle Miocene is most widespread. Glauconite bed deposited on a bank exists at the base of the Middle Miocene Ohdoji Formation in the Ajigasawa area of western Aomori; the 7.3 m-thick glauconite bed on the Kurosakigawa route represents 330 m.y. with an average accumulation rate of about 45 m.y./m or 2.2 cm/m.y. In the Ajigasawa area, the average sedimentation rate of biogenic silica had been nearly constant, 7.3 - 9.3 g/cm^2kry, from Middle Miocene to Pliocene, although the average sedimentation rates of the siliceous shale formations increase from Middle Miocene to Pliocene. There … More fore, the variable sedimentation rates of the siliceous shale formations are not due to the difference in the productivity of siliceous organisms, in particular diatom, but due to the inflow of terrigenous material. REE. patterns of the siliceous shale formations show normal or positive Ce anomalies, suggesting strong terrestrial influence. The uranium content is 1 - 18 ppm, largely 10 ppm in the west of Aomosri and less than 5 ppm in the east; these values are far less than those in siliceous shale of the Monterey Formation of California. Neither phosphorite beds nor phosphatic rocks have not been recognized in the siliceous shale formations of Aomori. So far as known, some phosophatic nodule of a late diagenesis origin were reported from Upper Miocene black mudstone of the Funakawa Formation of Akita on the south of Aomori and guano-type phophorite was mined in the Noto Peninsula. The Middle Miocene diatomaceous and lithified siliceous deposits of the Northeast Honshu Arc and Noto Peninsula were accumulated in an elongated, upper to middle bathyal basin which was formed along a rift zone on the west coast of Japan. The east side of the basin was bordered by the small landmasses of the Kitakami and Abukuma Plateaus, whereas its west side was limited by a submarine rise or landmass separating the basin from the Paleo-Yamato Basin of the newly-born Sea of Japan. The width of the basin filling the Middle Miocene siliceous shale formations would be 200 - 250 km. Less