The Muro Group in the study area, which occupies the northern and central part in the northern subbelt of the Muro Belt, is divided into the Yasukawa, Uchikoshi and Kogawa Formations in ascending order. The Yasukawa Formation consists of bedded mudstone (the Yl Member) and mudstone-rich alternating beds of sandstone and mudstone (the Yu Member). The Uchikoshi Formation is mainly composed of massive and thick-bedded sandstone with pebbly mudstone at top. The Kogawa Formation shows a marked lateral change in lithofacies. It is made up of mud-rich alternation of sandstone/shale (the K_<O1> Member) and sand-rich alternation of sandstone/shale and mudstone (the K_<O2> Member) in the northern area, and mudstone (the K_<W1> Member), thick-bedded sandstone with conglomerate and shale (the K_<W2> Member), and mudstone with rippled siltstone parting (the K_<W3> Member) in the central area. Based on the radiolarian fossils, the geologic age of the Muro Group in this reported area is assigned to middle Middle Eocene to early Late Eocene. The Yasukawa Formation, and Uchikoshi Formations and the K_<O1> and K_<W1> Members of the Kogawa Formation show characteristic features of the turbidite facies suggesting the basin plain and the deep-sea fan, respectively. On the contrary, the K_<W2> Member of the Kogawa Formation is characterized by the trough-fill deposits consisting of a high-density gravity flow deposits with southwest-ward unidirectional paleoflow, which is overlain by the slope sediments (the K_<W3> Member). Some contractive deformations in the Muro Group might be active during the sedimentation of the group. The change from the uniform and widespread submarine fan environments to the forearc basin with several trough-shaped narrow basins may be related with the change of convergent direction of oceanic plate consumed. The sediments at the latest stage of the group demonstrate the shallowing and the differentiation of the sedimentary basin caused by the change of tectonics in forearc region.

View full abstract

Various metazoan fossils have been found from the Jiuliqiao Formation of Sinian System, and from the Liulaobei Formation of Qingbaikou System in the district of Mt. Bagong near Shouxian County, Anhui Province, China. The radiometric age of the former is 738.5 Ma (K-Ar), and that of the latter is 840 Ma (Rb-Sr). These fossils are associated by algal fossils, called as Huainan Biota. In this paper the second author divided the Huainan Biota into two horizons, and summarized fossil components of them. And the first author of this paper have ever described two new genera and three new species among the specimens of cyphomegacritarchs found from the Liulaobei Formation, with the mathematical simulation of their form in 1986. He redescribed them with addition of some discussions.

View full abstract