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Vicissitudes of ostracode assemblages and mechanisms involved

介形类组合的变迁及其所涉及的机制

基本信息

批准号：
03640650
负责人：
ISHIZAKI Kunihiro
金额：
$ 1.02万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

项目摘要

Fossil ostracodes from the Cretaceous of Hokkaido were published in two papers proving the position of the Japanese Islands in relative to Tethys at the time and hererochroneity of ostracode faunas between Japan and Europe. Analysis of ostracode fauna from the Pleistocene Omma Formation distributed in and around Kanazawa City disclosed a prominent spike of Kuroshio flowing into the Japan Sea at 1.2 Ma, and distinct fluctuations of water conditions in a cycle of 0.12 to 0.09 My (Alcheringa, in press).Afterward, I concentrated in collecting fossils ostracodes from the Moniwa Formation, one of the Neogene distributed in and around Sendai City, to enable work supplementary to the report in 1966. Ostracode faunas from the Tsunaki Formation distributed near the southern border of Sendai City,were found containing the form which has been reported to date as Cornucoquimba moniwensis from the Pleistocene in Northeast Japan, together with Cornucoquimba moniwensis (s.s.), both being morphologically separated clearly by their carapace ornamentation. The dimorphism invoked at this time is shown subject to an increasing warming toward the end of Miocene time, leading their habitats extended to shallower waters, where a new form was established to linger on, at least, in Pleistocene shallow sea. With respect to the Cretaceous, the genus Krithe was found first appearing from the lowest part of the Hakobuchi Group (Campanian). This occurrence, the oldest record in Japan, may represent some changes in ostracode faunas to allow the introduction of a new element of ostracode faunas, offering us one of the very attractive subjects of our study.

北海道白垩纪的介形虫化石发表在两篇论文中，证明了当时日本群岛相对于特提斯的位置以及日本和欧洲之间介形虫动物群的时代性。通过对金泽市及其周边地区更新世大间组介形类动物群的分析，揭示了1.2Ma时黑潮流入日本海的一个显著高峰，以及0.12 ~ 0.09Ma的一个周期内明显的水环境波动（Alcheringa，出版中）之后，我集中精力收集Moniwa组的介形虫化石，新第三纪之一，分布在仙台市及其周边地区，以使工作补充报告于1966年。分布于仙台市南部边界附近的纲木组介形类动物群中，发现了迄今为止在日本东北部更新世被报道为Cornucoquimba moniwensis的形态，以及Cornucoquimba moniwensis（s.s.），两者在形态上被它们的背甲明显分开。在这个时候调用的二态性显示受到中新世末期的日益变暖，导致他们的栖息地扩展到较浅的沃茨，在那里建立了一个新的形式，至少在更新世浅海逗留。关于白垩纪，Krithe属首次被发现出现在箱渊群（Campanian）的最低部分。这一事件是日本最古老的记录，可能代表介形虫动物群的一些变化，允许引入介形虫动物群的新元素，为我们的研究提供了一个非常有吸引力的主题。