珠江口盆地渐新统—上新统高分辨率生物地层学研究方法

The Method of High Resolution Biostratigraphic Analysis of the Oligocene-Pliocene Strata in Zhujiang River Mouth Basin

珠江口盆地第三系的沉积环境按常规可粗略地划分为陆相、过渡相(潮间带)、浅海相和深海相。研究的材料主要是钻井岩屑样品。按每10m 的深度间距,采集每一样品中指示不同相的有孔虫、钙质超微化石、沟鞭藻、微形有孔虫和孢粉(双气囊花粉和红树花粉)化石,获得其可比的、定量的丰度与分异度资料。据这些定量的生物地层资料推断各样品的沉积环境,并据被研究剖面中所有样品的环境的连续变化来判断沉积环境的演变周期,由此再识别出海平面升降旋回。每个旋回内浮游生物的丰度和分异度的最高值示最大海泛面,而双气囊花粉和红树花粉的高值及浮游生物的少见或缺乏则示层序边界。按此方法识别了本区渐新一上新统的三级层序以及层序边界年龄和最大海泛面年龄。

The Tertiary detpoitional environments of the basin may be roughly divided into continental,trasitional(tidal zone),neritic and deep sea facies by the routine method.Drill cuttings are the major material for the studied samples.Facies fossils including foramilifera,nanofossils,dinocysts,microforaminifera and palynomorhs(bisaccate and mangrove pollen)are collected from one sample for each 10m interval and analysized to get the comparable quantitative records of the diversisties and the abundances of the fossils.The environment for each sample is interpreted on the basis of these quantitative biostratigraphic records and then,the cycles of the environment are determined according to the sequential changes of all samples in the studied transverse section before the eustatic cycles are recognized.The greatest values of the planktonic diversity and abundance indicate the highest flooding surface of the sea while the greater abundances of the bisaccate and mangrove pollen,as well as rare or absent marine plankton,in each cycle imply the sequence boundary.By this means,the ages of Oligocene-Pliocene sequence boundaries and flooding surfaces are determined.