Paleolimnologic and paleoceanographic history of the Sea of Japan - a reconstruction based on diatoms -

近年来的古地磁资料表明，日本大陆原本是亚洲大陆的一部分，随后随着日本西南部的顺时针旋转和日本东北部的逆时针旋转而断裂并向东南方向扩展。因此，“日本海”起源于一个湖泊。本研究的目的是描述海为淡水湖或浅海时形成的20种沉积物中的硅藻区系，为重建海的古湖泊和古海洋学历史提供信息。特别地，我用扫描电子显微镜对Aulacosira和放线素环菌（Actinocyclus）两种进行了“形式”分类，并显示了它们的地理和地层分布。1. 在20份沉积物样品中鉴定出25种不同的“形态”（A- u和X）和3种放线素属（A、B和C）。2. RC12-394：通过丰度区分了三种不同的白弧菌“形式”。3. 2 .更多的岛，Abura，所谓的Futoro组：Aulacosira“形式”协会的特点是“形式”b占主导地位。佐渡群岛、关岛、Masaragawa组：Aulacosira“form”I最丰富。4. 山田北中岛北藤半岛泥岩段：在该泥岩段中发现显性的B型和罕见的C型放线菌A。5. Fukui， Demura和Hikime， Itoo组：在地层中只发现了再结晶的Aulacosira Sp.（“形式”X）。6. Oki Islands、Nogoe、Yui组：组内少见几种Aulacosira“form”（B、H等）和单一放线菌“forni”(C)。根据这些结果，可以推导出：1. Seki植物群完全由淡水硅藻组成，当海洋是一个湖泊时沉积。与“Futoro组”和“Yamatoda泥岩段”的植物区系差异很大，这可能是由于湖水较冷造成的。2. Futoro组硅藻区系与ludstone组Yamatoda 11/2有相似之处。后者最上层的海洋物种混合表明，这些地层可能与暖流第一次入侵海洋的时间相同。3. RC12-394中的三种黄弧菌“形式”组合在上述陆地暴露的淡水源硅藻岩中没有发现。少

Recent paleomagnetic data suggest that Japanese mainland was originally a part of the Asian continent, and subsequently broke off and spread southeastward with the clockwise rotation of southwest Japan and the counterclockwise rotation of northeast Japan. The "Sea of Japan" thus originated as a lake. The purposes of this study are to described the diatom floras in 20 sediments formed when the sea was a fresh-water lake or shallow sea, and to provide information to reconstruct the paleoliminologic and paleoceanographic history of the sea. In particular, I classified Aulacosira and Actinocyclus species into "forms" by scanning electron microscopy, and showed their geographical and stratigraphical distributions. 1. Twenty-five different "forms" (A-U and X) of the genus Aulacosira and three (A, B and C) of the genus Actinocyclus were identified in the twenty sediment samples. 2. RC12-394: Three different associations of Aulacosira "forms" were distinguished by their abundances. 3. Oshima P … More eninsula, Abura, so-called Futoro Formation: Aulacosira "forms" association was characterized by the predominance of "form" B. 3. Sado Islands, Seki, Masaragawa Formation: Aulacosira "form" I was most abundant. 4. Noto Peninsula, Notonakajima, Yamatoda Mudstone Member: Dominant "form" B and rare Actinocyclus sp. A ("form" C) were observed in the member. 5. Fukui, Demura and Hikime, Itoo Formation: Only recrystallized Aulacosira Sp. ("form" X) was found in the formation. 6. Oki Islands, Nogoe, Yui Formation: scarce occurrence of several Aulacosira "form" (B, H and others) and single Actinocyclus "forni" (C) were observed in the formation. From these results, the following are deduced; 1. The Seki flora consists of exclusively fresh-water diatoms deposited when the sea was a lake. The flora is very different from that observed in "Futoro Formation" and Yamatoda Mudstone Member, and the difference could be caused by colder water of the lake. 2. The diatom flora in "Futoro Formation" has some resemblance to that of Yamatoda 11/2,ludstone Member. Admixture of marine species in the uppermost layer of the latter suggests that these strata may hence occupy the same time frame as the first invasion of warm current to the sea. 3. Three associations of Aulacosira "forms" in RC12-394 are not found in the aforementioned land-exposed fresh-water origin diatomaceous rocks. Less