Calcareous nannofossil events of DSDP Hole 31-292

Calcareous nannofossil assemblages from land sections of the Japanese Islands and DSDP Holes in the equatorial to high latitude regions of the Pacific Ocean were analyzed in an effort to reconstruct their late Pliocene paleobiogeography. While the late Pliocene assemblages in the equatorial to middle latitude regions are comprised primarily of discoasters, both the high latitude and Japan Sea samples record an abrupt change from a Reticulofenestra-Dictyococcite assemblage to a Coccolithus pelagicus assemblage at 2.75 Ma. The northernmost boundary of the Discoaster assemblage moved southward in the East China Sea (western Pacific Ocean) at that time. These changes in the calcareous nannofossil paleobiogeography indicate the strong influence of heavy glaciation in high latitude to arctic regions of the Pacific Ocean. This also correlates with the final closure of the Central American seaway at 2.75 Ma.

本研究对日本群岛陆上剖面以及太平洋赤道至高纬度区域内深海钻探计划（Deep Sea Drilling Project, DSDP）钻孔中的钙质超微化石（calcareous nannofossil）组合展开分析，旨在重建其晚上新世的古生物地理格局。尽管赤道至中纬度区域的晚上新世化石组合以盘星石属（Discoaster）为主，但高纬度海域与日本海的样品均记录到在2.75 Ma时发生了一次从网面石属（Reticulofenestra）-网球石属（Dictyococcite）组合向大洋钙石藻（Coccolithus pelagicus）组合的突变。彼时，盘星石属组合的最北界在东海（西太平洋）发生了南移。钙质超微化石古生物地理格局的上述变化表明，太平洋高纬度至北极区域的大规模冰川作用对其产生了强烈影响。这一演化事件同样与2.75 Ma时中美洲海道的最终闭合存在关联。