RELICTS IN FOSSIL BENTHIC FAUNA AND THEIR LIVING ENVIRONMENT

4- 3 Ma日本海边缘浅海软体动物群可分为两个生态类型。荻洼组、城下组和下三田组的底栖组合以冷水种为主，其中包括许多中新世类型的残遗种，而天德寺组、江组和上三田组的远海组合则包括许多暖水种，但残遗种很少，这一时期的远海组合直接受到了古对马暖流突然涌入日本海的影响。Ranella属并不生活在日本沃茨附近，是由于这种流入而引入的（Amano，1997 a）。许多中新世类型的物种在这一事件中灭绝。但是，许多残遗生物在没有受到暖水流直接影响的冷湾中存活下来，在这个时期，深水类群如Portlandia toyamaensis、Ancistrolepingae和Neptunea没有受到上述事件以及随后的冰川扩张引起的冷事件的影响（Amano，1996 a，B ; Amano et al.，1996 ; Amano，1997 b; 1997 MS）。因此，很明显，冷海湾作为一个生态避难所的浅海残遗。

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.