秩父累帯の中・古生界研究の最近の進歩(<特集>日本の中・古生界研究の発展と現状)

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Through intensive and extensive studies of radiolarian fossils, it has been recently revealed that the so-called Honshu geosynclinal deposits are mainly composed of the middle Mesozoic complexes associated with the upper Paleozoic and Triassic rocks. The Chichibu belt was formerly divided into the northern, middle and southern subbelts by the Kamanokawa-Sakashu thrust and the Uonashi-Kanbaradani-Junisha thrust respectively in Shikoku. However, the boundaries among them are modified on the basis of the recent stratigraphical results and of pre-Cretaceous terrane analysis. In the northern subbelt, lower to middle Jurassic olistostromes are widely distributed, which include olistoliths of late Paleozoic limestone-greenstone-chert and Triassic chert. The Paleozoic-Mesozoic complexes of the middle subbelt are composed of the lenticular bodies of the Kurosegawa tectonic zone, "the upper Paleozoic formations", the middle and upper Triassic formations, the middle to upper Jurassic formations and the Cretaceous formations. The Mesozoic complexes of the southern subbelt generally consist of sequences of three different types, i. e., middle Triassic to upper Jurassic chert-clastic sequences, Jurassic to lower Cretaceous olistostromes and the Torinosu Group (upper Jurassic-lowest Cretaceous). The olistostromes contain various kind of olistoliths such as late Paleozoic limestonegreenstone-chert, late Triassic limestone and middle Triassic to earliest Jurassic chert. The geologic structure in the northern subbelt is characterized by nappes and open upright folds. They were formed by the tectonic movements which may be correlated with the Ozu-Nagahama phase and the Hijikawa phase of the Sambagawa belt. In the middle sub-belt, main tectonic movements took place at Permian - earliest Mesozoic time and at late Jurassic-earliest Cretaceous time. Through the latter event, the Kurosegawa tectonic zone revealed the character of serpentinite melange zone. The southern subbelt is characterized by imbricate structure dipping northward which was originally constructed through the accretional process during Jurassic to early Cretaceous time. Then, it was reconstructed by the Paleogene tectonic movements. The pre-Cretaceous tectonic movements in the Chichibu belt are regarded as the events which took place in allochthonous state prior to its final fusion to the Paleo-Asian Continent.
地学団体研究会の論文
1985-01-25

秩父累帯の中・古生界研究の最近の進歩(<特集>日本の中・古生界研究の発展と現状)

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