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陶陶-大岛带和南秩父带之间。为建立北北北上带的地质剖面，阐明北北北上带侏罗纪增生杂岩的构造地层学和增生时代，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)发现Kuzumaki地区存在晚石炭世海山玄武岩-灰岩杂岩，Akka地区存在晚石炭世燧石岩；2)在Akka地区Otori组发现了深海二叠纪-三叠纪界线层（PTB），并在黑色有机泥岩层基底处确认了13C值的急剧负筛。3)确定了Otori组和takayashki组的增生时代分别为中侏罗世晚bajotian - bathonian和晚侏罗世Oxfordian。4)阿卡地区侏罗系增生杂岩地质构造以座状单元的广泛向斜和背斜为特征，各单元增生年龄由高到低依次变年轻。从这些资料可以得出结论：Kuzumaki-Kamaishi亚带和Akka-Tanohata亚带的边界沿北海道西南部大岛带的中部向北延伸，基于岩石学和大洋板块地层学的相似性，大鸟组及其邻近组与日本西南部秩父带的柏木组和大平山组具有相关性。

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.