南海西沙群岛西科1井早中新世-第四纪生物礁地层中钙质超微化石的发现及其意义

EARLY MIOCENE TO QUATERNARY CALCAREOUS NANNOFOSSILS FROM THE BIOGENETIC REEF COMPLEXES AND THEIR SIGNIFICANCE OF WELL XK1,XISHA ISLANDS,SOUTH CHINA SEA

西科1井0.10—1267.80m岩芯中钙质超微化石丰度低,属种比较单调。分析831个样品,仅在48个样品中发现钙质超微化石,共鉴定10属17种及1个未定种,主要化石种为Calcidiscus leptoporus,C.macintyrei,Coccolithus pelagicus,Cyclicargolithus floridanus,Gephyrocapsa caribbeanica,G.oceanica,Helicosphaera carteri,H.euphratis,Pontosphaera multipora,Pseudoemiliania lacunosa,Reticulofenestra minuta,R.minutula,Sphenolithus abies,S.moriformis和S.neoabies等。根据钙质超微化石生物事件及组合特征,结合有孔虫和大型底栖钙藻等研究结果,对西科1井0.10—1267.80m地层进行了划分,大致可划分为5段:1)0.10—212.20m地层属于第四系NN21—NN19带;2)214.29—328.69m归属于更新统NN18带至上新统;3)330.97—598.12m属于上新统NN15带至上中新统;4)599.53—1231.62m归属于中中新统至下中新统;5)1233.62—1267.80m为下中新统。由于化石丰度和分异度均较低,未建立完整的钙质超微化石带序列。根据钙质超微化石标志种及组合特征,确定研究井段的地层时代为早中新世至第四纪。西科1井生物礁地层中钙质超微化石的发现,对该井生物地层的划分起到了十分关键的作用。

This paper deals with the calcareous nannofossils from biogenetic reef complexes in the early Miocene to Quaternary of well XK1, Xisha Island, South China Sea. A total of 831 core samples at 1.5 m sampling intervals have been analyzed from the 0.10-1267. 80 m of the XK1 well. Calcareous nannofossils has a lower abundance and diversity, and they are found in only 48 samples. 17 species and 1 indet, species referred to 10 genera have been identified. The main species are Calcidiscus leptoporus , C. macintyrei , Coccolithus pelagicus , Cyclicargolithus floridanus, Gephyrocapsa carib- beanica , G. oceanica, Helicosphaera carteri , H. euphratis, Pontosphaera multipora , Reticu [o f enestra minuta , R. minutula , Sphenolithus abies, S. moriformis, S. neoabies. Based on the calcareous nannofossil events, assemblages and distribution, combined with zones of foraminifera and calcareous algae, five stratal sections can be divided. They are discussed from the top to the bottom as follows. 1） 0.10-212. 20 m is assigned to Quaternary; 2） 214.29-328.69 m belongs to Pleistocene--upper Pliocene; 3） 330. 97--598.12 m is divided into lower Pliocene - upper Miocene;4） 599. 53--1231. 62 m is assigned to middle Mio- cene-lower Miocene; 5） 1233. 62-1267. 8 m belongs to lower Miocene. According to the calcare- ous nannofossils, the age of the interval 0. 10- 1267.80 m is early Miocene to Quaternary. The discovery of calcareous nannofossils is very important to the biostratigraphic division of well XK1.