Paleobotanic evidences for the time of the Sea of Japan origin

Abstract

The comparison of the Tertiary floras of Japan, Korea, and Primorye shows that they are similar in taxonomy and paleoclimate conditions to floras of the Pre-Middle-Miocene time. After the opening of the Sea of Japan accompanied by penetration of the Tsushima warm current (Early-Middle Miocene transitional interval), the climatic conditions on the Honshu western coast became better over a short period of time. In the continental part of the Sea of Japan coast they did not change significantly due to the negative influence of the East-Asian winter monsoon. Paleobotanic data on the time of the Sea of Japan opening corresponds to the data obtained earlier using paleomagnetic methods. However, the data from the deep-sea drilling and data on the age of the sedimentary and volcanogenic rocks in the troughs, surrounding the Sea of Japan, make it possible to consider that the process of this Sea opening began much earlier, about 45 m.y. The authors distinguish two main stages of the formation of the Sea of Japan basin.The first stage (45-17 m.y.) suggests the beginning of the Japan drift southeastward. Japan kept the floristic relations with the continent. The second stage (17-15 m.y.) suggests active drift accompanied by formation of significant water space in the back part of Japan. That was the time when the climatic differences between Japan and continental surroundings of the Sea of Japan appeared.