摘要
本文依据西琛1井和西永2井400m以上井段岩心样品中的有孔虫鉴定结果,将西沙礁相地层中的有孔虫分为6个组合段,并依据有孔虫带化石的分布对晚第三纪以来的地层时代进行了划分。并对研究西沙珊瑚礁发育与演化起到一定的作用。
Based on the analysis of foraminifera in two 400-m-up core sections from hole Xichen-1 and Xiyong-2, this paper discusses foraminifera distribution in reef-facies beds since late Miocene in Xisha Islands and makes a dating of late Tertiary beds.
Reef sediments from late Miocene can be, from up to down, divided into 6 facies sections, each of which has a some what distinct foraminifera assemblage.1. Lime-sand-island facies, 10-14m thick, with rich foraminifera species and numbers. The tests are mostly seriously abraded. Dominant species are Calcarina spp. and A. madagascariensis d'Orbigny. Planktonic foraminifer is rarely seen.
2. Reef-flat depression facies, 4-6.5m thick, with the richest foraminifera species and numbers and highest diversity. Tests are well preserved. Dominant species appear to be the same as the above. A little number of planktonic foraminifers can be found.
3. Reef frame facies, 17-18m thick, with a little number of species and tests and relalively low diversity. Tests are mostly abraded. A. madagascariensis and Calcarina spp. dominate. Planktonic foraminifers are rarely seen.
4. Reef flat facices, 160-163m thick, foraminifera species are similar to those of the lime-sand-island facies, but with a smaller number. Diversity is low and tests mainly abraded. Dominant species are found the same as those of the lime-sand-island facies Planktonic foraminifers are rarely seen.
5. Back-reef lagoon facies, 191-196m thick, with a large number of species and a high diversity. Tests are well preserved. A. radiata dominates, and planktonic forminifers greatly appear.
6. Lagoon shore facies, located in the section under 350m in hole Xic en-1. Only two species are found and no planktonic foraminifers.
Division of stratigraphic ages can be asfollows: Quaternary reef sediments in Xisha lays the bottom at the hole depth of 213-235m, according to the lower bonud of distribution of Globorotalia truncatuHnoides (d'Orbigny) and changes of coiling direction of Gr. menardii (d'Orbigny); the bottom of Pliocene sediments is determined to be at the depth of 350-387m, based on the lower bound of distribution of Globigerinoides conglobatus (Brady), Pulleniatina and Neogloboquadrina dutertrei (d'Orbigny); bottom part of late Pliocene sediments lies at the depth of 232-259m, according to the upper bound of distribution of Globigerinoides obliguus Bolli, Globoquadrina altispira Cushman and Jarvis; and bottom part of middle Pliocene sedimehts is at the depth of 289-337m, according to the upper bound of distribution of Globorotalia margaritae Bolli and Bermudez and Lepidocyclina (Nephrolepidina) sp.
出处
《海洋地质与第四纪地质》
CAS
CSCD
北大核心
1990年第2期65-81,共17页
Marine Geology & Quaternary Geology
