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1 有关日本海形成时期的各种推断如图1所示,日本海洋底由大和海盆、大和浅滩,日本海盆和朝鲜海台组成。据地震波速度解释,认为仅日本海盆及大和海盆具有洋壳,其它地壳为陆壳。迄今为止,已有不少例子采用洋底岩石测定放射性年代以外的方法来推断日本海的形成时期。如用硅藻微化石推断了日本海区域最老的海相沉积物年代为中新世。在日本海周边区域所见到的早期底栖动物化石的年代为西黑泽阶(中中新世早期),并把它作为日本海的形成时期等。此外,还试图据洋底磁异常条带来推断日本海的形成时期,但由于日本海的磁异常
1 Various inferences regarding the age of formation of the Sea of Japan As shown in Figure 1, the bottom of Japan’s oceans consists of the Yamato basin, the Yamato shoal, the Japanese basin and the North Korean seaside. According to seismic velocity interpretation, only the Japanese basin and the Yamato basin have the oceanic crust, and the other crust is the continental crust. To date, many examples have been used to extrapolate the formation of the Japan Sea using oceanographic methods other than radioactive dating. For example, diatom micro-fossils deduced that the oldest marine sediment in the Sea of Japan region was Miocene. The age of the early zoobenthos fossils seen in the area around the Sea of Japan is the Western Heise Strait (early Middle Miocene) and is considered as the age of formation of the Sea of Japan. In addition, an attempt was made to infer the formation of the Sea of Japan from the magnetic anomaly stripes on the ocean floor. However, due to the magnetic anomaly in the Sea of Japan