Creation of the geologic cross section of the North Kitakami Belt of Northeast Japan

日本东北部的北上带位于道哈-大岛带和南一部带之间，并将其连接起来。为了建立库祖马-赤卡地区北上侏罗纪增生杂岩的地质剖面，阐明其构造地层学和沉积时代，进行了详细的地质调查和古生物调查。主要研究结果如下：1)在久崎地区发现了晚石炭世海山玄武岩-灰岩杂岩，在Akka地区发现了晚石炭世的晚石炭世玄武岩-灰岩杂岩，表明北海板块的形成可以追溯到晚石炭世。2)在Akka地区的Otori组中发现了深海二叠-三叠系界线层(PTB)，证实了黑色有机泥岩层底部存在明显的13C负值。这是日本东北地区首次发现PTB。3)大鸟组和高屋市组的增积年龄分别为巴约-巴松晚期(中侏罗世)和牛津期(晚侏罗世)。4)赤卡地区侏罗纪增生杂岩的地质结构具有广泛的向斜和背斜的坐位单元，这些单元的增积年龄按构造递减的顺序变得年轻。根据这些资料，得出库祖马-龟石亚带和Akka-Tanohata亚带之间的边界可以向北延伸到北海道西南部大石带的中部，根据岩性和大洋板块地层学上的相似性，将大鱼组及其邻区与日本西南部赤部带的柏木单元和俄亥山单元进行对比。

The North Kitakami Belt of Northeast Japan is situated between and links the Taukha-Oshima Belts and South Chichibu Belt. To create a geologic cross section and to elucidate a tectono-stratigraphy and accretion ages of the Jurassic accretionary complexes of the North Kitakami Belt in the Kuzumaki-Akka area, detailed geologic survey and Paleontological investigation were carried out. The key results are as follows:1) We found that there was Late Carboniferous seamount basalt-limestone complex in the Kuzumaki area, and Late Carboniferous chert in the Akka area, suggesting the birth of oceanic plate constitute the North Kitakami Belt is dating back to the Late Carboniferous.2) We discovered a deep-sea Permian-Triassic boundary bed (PTB) in the Otori Formation of the Akka area and confirmed a sharp negative sift of 13C value at the basal part of the black organic mudstone bed. This is the first discovery of PTB in Northeast Japan.3) We elucidated the accretion age of the Otori and Takayashiki Formations as late Bajocian-Bathonian (Middle Jurassic) and Oxfordian (Late Jurassic), respectively.4) The geologic structure of the Jurassic accretionary complexes in the Akka area is characterized by a broad syncline and anticline of seated units, and the accretionary ages of the units are become young in structurally descending order.From these data it is concluded that the boundary between the Kuzumaki-Kamaishi Subbelt and Akka-Tanohata Subbelt is extendable to the north running the, central part of the Oshima Belt of Southwest Hokkaido, and based on the similarities in the lithology and oceanic plate stratigraphy, the Otori Formation and its adjacent formations are correlatable with the Kashiwagi Unit and Ohirayama Unit of the Chichibu Belt of Southwest Japan.