Biostratigraphic study of Tertiary benthic foraminiferal Family Cassidulinidae.

底栖有孔虫是研究古环境最有用的微体化石之一。近年来，底栖有孔虫在古生物分析中的应用与古生物学研究有了很大的进展。在大多数情况下。然而，这种古环境分析是基于底栖有孔虫的区系变化和广义上确定的物种。本研究以日本列岛底栖有孔虫科Cassidulinidae为研究对象，旨在了解其在日本列岛的地层和地理分布，并阐明第三纪以来的底栖有孔虫科Cassidulinidae的演化克里思和模式。根据9属45种的地层范围，划分出1个古近纪的泥螺组合带和5个新近纪的泥螺共生带，其中古近纪的泥螺带以Globo-dulina globosa为主。在5 Neoge ...更多信息 在中中新世晚期的第三带和第四带之间，发现了最剧烈的变化，在那里，球头类dulinid物种的组成急剧减少，而islandiellid物种的发展则相反。这一变化与南极冰盖扩张导致海水温度下降等古海洋学变化密切相关。另一项研究表明，在日本海山阴近海现代沉积物中，岛壳类的种类数与有机碳含量之间存在正相关关系，这支持了温度下降和初级生产力增强引起的岛壳类的进化。此外，在东印度洋Broken Ridge深海沉积物中，球齿藓G. subglobosa系列）从中中新世开始逐渐增加，该时代的特征是显示温度下降，如氧同位素分析所澄清的。不同的测试以及孔的形状;在中中新世和更晚的年龄发生的Ariddulinid物种中被认为是对以寒冷的底层水为特征的环境的战略适应，增加了有机物积累。少

Benthic foraminifera has been recognized as one of the most useful microfossils in a interpretation of paleoenvironment. The application of benthic foraminifera to paleoenvironmen analyses has recently been much progressed in relation to palcoccanography. In most cases. however, such paleoenvironmental analyses are based on the faunal variation of benthi foraminifera and the species identified sense lato. In this study, I focused on the benthic foraminifcral family Cassidulinidae in order to know the stratigraphic and geographic distributioi of respective species in the Japanese Islands, and also to clarify the tempo and mode of evolutio of cassidulinid foraminiferal species during the Tertiary epoch. The main results are as followsBased on the stratigraphic ranges of 45 species distributed in 9 genus,1 Paleogend cassidulinid assemblage Zonc and 5 Neogene cassidulinid concurrent Zones are recognized Palcogenc cassidulinid zone is predominated by Globocassidulina globosa. In the 5 Neoge … More ne cassidulinid zones, the most dramatic change is found between Zones III and IV in the late Midd Miocene, where globocassidulinid species are drastically reduced in its composition in contrast the development of islandiellid spccics. Such cassidulinid change is intimately related to the paleoceanographic change such as the drop of marine water temperature resulted from the Antarc ice sheet expansion. Another study, suggesting the positive correlation between the number of islandiellid species and the organic carbon contents in the Recent sediments off San'in, Sea o Japan, supports the evolution of cassidulinid species caused by temperature drop and the encrew of primary productivity. Furthermore, in the deep-sea sediments from Broken Ridge, Easten Indian Ocean, the size of cassidulinid species (e.g., Globocassidulina globosa - G. subglobosa series) increases gradually from the Middle Miocene, which epoch is characterized by showing the temperature drop as clarified by oxygen isotopic analysis. Varied test as well as apertural shape; recognized in cassidulinid species occurred from the Middle Miocene and later ages are considered to indicate a strategic adaptation to the environment characterized by cold bottom water are increased organic accumulation. Less