东太平洋海盆早中新世钙质超微化石及其地质意义

EARLY MIOCENE CALCAREOUS NANNOFOSSILS FROM THE EAST PACIFIC OCEAN BASIN AND THEIR GIOLOGICAL SIGNIFICANCES

本文对“海洋四号”船于ＤＹ８５－３航次在东太平洋海盆ＣＣ区南部取得的ＰＣ５７９４和ＰＣ５６５３二个柱状沉积样的钙质超微化石作了详细的分析研究，进行了生物化石带的划分与对比。其中，ＰＣ５７９４自下而上划分出ＮＮ１（未见底）、ＮＮ２和Ｎ３（仅见底部）二个化石带；ＰＣ５６５３仅识别出ＮＮ２化石带。据超微化石资料，认为柱状样所揭露的最老地层为早中新世早期沉积，时代至少为２２．０Ｍａ。在进行化石带讨论的同时，对沉积环境进行了初步的讨论。

Calcareous nannofossils in piston cores PC5794 and PC5653,which were drilled bythe R/V HY-4 during DY85-3 cruise in the southern CC Zone of the East Pacific OceanBasin,are analysed and studied in this paper, Biofossil zones are divided and correlated. Three Miocene nannofossil zones can be distinguished in core PC5794,which are Tri-quetrorhabdulus carinatus zone(NN1,only the upper part),Discoaster druggii zone(NN2)and Sphenolithus belemnos zone(NN3,only the lower part).And only NN2 nan-nofossil zone can be recognized in core PC5653.Based on the calcareous nannofossil da-ta,the oldest strata revealed in the two cores are early Early Miocene sediment with anage of at least 22.0Ma,Meanwhile,sedimentary environment in the study area is dis-cussed preliminarily.