西南日本の中部ペルム系層状チャートに記録された堆積サイクルと古流行の解析

Depostional cycles of the Middle Permian bedded chert sequence are examined in view point of lithology, composition and mode of occurrence of microfossils. Cyclic compositional change was veryfied by alternating occurrence of two distinct type of chert beds which are one biogenic called siltite, and the other fine siliceous ones called lutite. Thickness of beds forms cyclic peaks and of which composition of alternatively change between siltites and lutites. This points change of radiolarian blooming and deposition are intimately related to that in low-stand in sea level when activated circulation on botton surface was dominated, while in high-stand in sea level slow flux of coarse siliceous materials with varied biomass fertilized conodonts. These two oceanic conditions were clearly recorded in the lower to middle Middle Permian but it gradually became unclear in upper Middle Permian, prior to Upper Permian regression. Prefered orientation of Follicucullus shell characterized by elongated conical shape indicates bottom currents were regular in direction almost through the Middle Permian and an asymmetry in arrangement of shell vertical to the supposed current alludes possibly inclined paleoslope of the depositional basin and current parallel to this slope.