RELICTS IN FOSSIL BENTHIC FAUNA AND THEIR LIVING ENVIRONMENT

4~3 Ma日本海边缘浅海软体动物区系在生态上可分为两种类型。Ogikubo组、Joshita组和下三田组的外海组合以冷水组合为主，包括许多中新世遗迹；而Tentokuji组、科威特组和上三田组的公海组合包括许多暖水物种，但遗迹很少。这一时期，古对岛暖流突然涌入日本海，直接影响了公海组合。这种流入引入了不生活在日本水域的雷尼拉属(Amano，1997a)。该群落中的许多中新世类型物种因这次事件而灭绝。在这一时期，深水类群，如toyamasis Portlandia toyamasis、Ancistroepideae和海藻等，并没有受到上述事件以及随后冰川扩张引起的寒冷事件的影响(Amano，1996a，b；Amano等，1996；Amano，1997b；1997MS)。因此，很明显，冷湾是浅海海洋遗迹的生态避难所。

The shallow molluscan fauna of the Japan Sea borderland during 4-3Ma can be ecologically subdivided into two types. The embaymental associations from the Ogikubo, Joshita, lower Mita Formations are dominated by the cold-water species, including many Miocene-type relicts.On the other hand, the open sea assemblages from the Tentokuji, Kuwae and upper Mita Formations includes many warm-water species, but very few relicts.The open water assemblages were directly affected by the sudden influx of warm Paleo-Tsushima current into the Japan Sea during this period. The genus Ranella, not living around the Japanese waters was introduced by this influx (Amano, 1997a). Many Miocene-type species in the assembages suffered extinction by this event. But many relicts survived in the cold embayment where was not directly affected by the warm-water current.During this age, the deep water taxa such as Portlandia toyamaensis, Ancistrolepidenae and Neptunea were not affected by the above events and the succeeding cold event by the spreading of glaciation (Amano, 1996a, b ; Amano et al., 1996 ; Amano, 1997b ; 1997MS).Consequently, it becomes clear that the cold embayment acts as an ecological refuge of shallow marine relicts.