钙质超微化石在第四纪年代地层学中的应用

APPLICATION OF CALCAREOUS NANNOFOSSILS IN THE QUATERNARY CHRONOSTRATIGRAPHY

钙质超微化石是海洋沉积中最重要的微体化石之一,一直是海相地层划分与对比、进行年代地层学研究的重要手段,在第四纪地层及其年代学研究中发挥着重要作用.第四纪钙质超微化石记录中共存在10个主要生物事件和10个次要生物事件,据此可划分为6个化石带和7个亚带.通过与有孔虫稳定氧同位素地层学与磁性地层学对比,可以获得每个钙质超微化石生物事件的绝对年龄,从而提高生物地层学的年代分辨率.除了生物事件外,钙质超微化石定量分析也可为年代地层学的建立提供依据,如全新世的Emiliania huxleyi高峰带和晚更新世中布容期的Gephyrocapsa caribbeanica高峰带,等等.钙质超微化石的稳定同位素与有孔虫稳定同位素一样,可用来进行地层划分与对比,还可以用于古海洋、古气候研究.

As one kind of most important microfossils in marine sediments,calcareous nannofossils are very useful tool in the stratigraphy and chronology,especially in the Quaternary.The Quaternary calcareous nannofossils are mainly consist of Emiliania,Gephyrocapsa,Pseudoemiliania and Reticulofenestra.Other species include Braarudosphaera,Calcidiscus,Discoaster,Discosphaera,Florisphaera,Helicosphaera,Oolithotus,Pontosphaera,Rhabdosphaera,Syracosphaera,Umbellosphaera and Umbilicosphaera.There are ten major calcareous nannofossil bioevents and ten secondary bioevents in the Quaternary.Six nannofossil zones and seven subzones can be divided according to these bioevents.Compare with the oxygen isotope stratigraphy and magnetostratigrapgy,the age of each calcareous nannofossil event can be obtained.In spite of nannofossil events,the quantitative analysis of nannofossils are also very useful in the stratigraphy and chronology.For example,the Holocene Emiliania huxleyi Acme and the middle Brunhes Gephyrocapsa caribbeanica bloom event.The case study of oxygen and carbon isotope records of calcareous nannofossils for the past 1 Ma from the ODP Site 1143 in the southern South China Sea demonstrated that the δ18O values of calcareous nannofossils for the past 1 Ma vary systematically with those of planktonic and benthic foraminifera from the same site.These indicate that nannofossil oxygen isotope records could be a powerful tool to study the paleoceanography,paleoclimatology and stratigraphy.