摘要
西沙群岛西琛一井和西永二井丰富的有孔虫动物群,揭示了第四系下限在两井中分别为210m和235m井深;上上新统和中上新统的分界分别位于236.5m和284.5m井深;中上新统与下上新统的分界分别位于289m和337m井深;上新统与中新统的分界在西永二井位于350m井深。 动物群的特征显示,两孔的古环境在晚中新世为泻沏湖滨环境;上新世至更新世早期,以水深较大的开放泻湖环境占优势,其中有几次大的海平面相对变化;第四纪时期,大部分为礁坪环境,后期出现一次水深不大的开放泻湖环境,尔后转为灰砂岛。
The foraminiferal fauna from two drill holes in the atolls of the Xisha Islands, South China Sea, provides a lot of important information on the biostratigraphical boundaries and environmental changes from Late Miocene to Holocene. The vertical distributions of the Quaternary index fossil Globorotalia truncatulinoides (d'Orbigny) and the change in the coiling direction of Globorotalia menardii (Parker, Jones et Brady) from dextral to sinistral in Cores Chenhang-1 and Yongxing-2 show the Pleistocene/Pliocene boundaries at the drilling depths of 210m and 235m respectively. According to the last occurrences of Globigerinoides obliquus Bolli, Globoquadrina altispira Cushman et Jarvis and Pulleniatina which are coiling dextrally, the boundaries between Late and Middle Pliocene are placed at 236.5m in Core Chenhang-1 and at 284.5m in Core Yongxing-2. The last occurrences of the index fossil Globorotalia margaritae Bolli et Bermudez and the larger foraminifera Lepidocyclina (Nephrolepidina) rutteni van der Vlerk, the first occurrence of Globorotalia inflata d'Orbigny together with the change in the coiling trend of Pulleniatina from sinistral to dextral indicate the Middle/Early Pliocene boundaries at 289m and 337m in Cores Chenhang-1 and Yongxing-2 respectively. The Pliocene/Miocene boundary in Core Chenhang-1 is determined at 350m according to the abrupt change in the foraminiferal fauna and the geological time of overlying and underlying sediments (Figs. 2 and 3).The paleoenvironments are identified based on the characteristics of the foraminiferal fauna, especially the abundances of planktic foraminifera in each sample and Amphistegina radiata (Fichtel et Moll) in the genus Amphistegina. In Late Miocene, the sediments were yielded under a littoral environment. An open lagoon covered the places of the two drill locations from the beginning of the Early Pliocene to the first period of the Pleistocene. Several fluctuations of the sea level took place in this duration and sometimes the lagoon reached a depth down to over 100m. The reef flats dominated most parts of the environment during the remaining period of the Quaternary followed by a short-term open lagoon and then by the beach environment in the last period of the Quaternary (Figs. 6 and 7).
出处
《微体古生物学报》
CSCD
北大核心
1989年第4期345-356,438,共12页
Acta Micropalaeontologica Sinica
