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日本具有4个标志早白垩世的半咸水和淡水软体动物群组合:欧特里沃期—早巴列姆期的立川和菖蒲动物群组合,晚巴列姆期的濑林动物群组合和早阿普特期动物群组合。纯非海相下白垩统大量分布于日本东北部(本州岛北部)的部分地区,以及日本中部、西南部的内带。在日本东北部的部分地区以及日本西南部的外带(四国岛与本州岛中部),从巴列姆阶下部往上有一些海相地层夹在非海相层中,这为研究非海相动物群提供了准确的年代依据。生物组合之间在种一级水平上的区别,主要由环境的差异而引起。1)立川动物群组合(欧特里沃期—早巴列姆期),含有半咸水Hayamina naumanni组合和淡水Megasphaerioides okurodaniensis组合;手取群的Okurodani、Kuwajima和Izuki三个组内的淡水软体动物可与本动物组合相对比;2)菖蒲动物群组合(欧特里沃期—早巴列姆期),含有Eomiodon nipponicus组合;3)濑林动物群组合(晚巴列姆期),含有Costocyrena radiatostriata组合,可与手取群的Kitadani组和日本东北部关门群的Sengoku组以及Monomiyama组的淡水软体动物组合相对比;4)日比原动物群组合(早阿普特期),含有Costocyrena minor组合,关门群Wakamiya组的淡水软体动物可与本动物组合相对比。
The combination of brackish and freshwater molluscs with four signs in the Early Cretaceous in Japan: the combination of Tachikawa and Acorus calamus in the Otterriva-Early Baltimore period, the assemblage of Setaria fauna in the late Balmain Early APT fauna assemblage. Purely non-marine Lower Cretaceous mass distribution in northeastern Japan (Honshu Island northern) in some areas, and Japan’s central and southwestern belt. In parts of northeastern Japan and in the outer belt of Japan’s southwestern region (Shikoku and central Honshu), some marine strata are sandwiched up in the non-marine facies from the lower part of the Balmain stratum, The fauna provides an accurate chronological basis. The differences between the biological combinations at the first level are mainly caused by environmental differences. 1) The Tachikawa fauna assemblage (Autrewoos-Barrum period) consists of a mixture of brackish water Hayamina naumanni and freshwater Megasphaerioides okurodaniensis; the freshwater mollusks of Okurodani, Kuwajima and Izuki (2) Acorus calamus assemblage (Ettolivo-Ebamiella phase) with Eomiodon nipponicus assemblage; 3) Setaria group (Galatians) with Costocyrena radiatostriata Which can be compared with the freshwater mollusc assemblage of the Kitadani group and the Sengoku group of the northeast Japan and the Monomiyama group; 4) the combination of Costocyrena minor, Freshwater molluscs in the Wakamiya group of the closing group can be compared with the animal group.