南海西南次海盆晚中新世钙质超微化石与古海洋演化

LATE MIOCENE CALCAREOUS NANNOFOSSILS AND PALEOCEANOGRAPHY OF THE SOUTHWEST SUBBASIN,SOUTH CHINA SEA,CHINA

本文对南海西南次海盆IODP U1433站上中新统远洋粘土中的钙质超微化石生物地层学与属种组合作了较为详细研究。结果显示研究层位底部年龄在10.40-9.75 Ma之间,属于NN9带,向上共识别出8个钙质超微化石生物地层事件。依据生物地层框架、钙质超微化石总丰度与属种百分含量,发现西南次海盆在8.3-8 Ma以前处于上层海水分层性好,表层海水生产力较低的阶段;大约在8 Ma以后,生产力大幅增加。结合前人U1433站位物源研究结果,以及南海东亚季风强度变化史,作者认为钙质超微化石显示的生产力变化,与越南中部高地的抬升,以及东亚夏季风增强有关。

We studied the Upper Miocene biostratigraphy and assemblages of calcareous nannofossils from the IODP Site U1433 located on the Southwest Subbasin,South China Sea,China. The bottom age of the sediment cores of this study is about 10.40--9.75Ma,and 8 bioevents were identified upward. The abundances and assemblages of nanno- fossils imply that before 8.3--8Ma the upper-column seawater of Southwest Subbasin was well stratified and the pri- mary productivity was low. After 8Ma, the productivity increased sharply. Comparing with former study of Site U1433 clay provenance, and the monsoon history in the South China Sea, the change of primary productivity might due to uplift of the Central Highland and strengthening of the summer monsoon.