Tertiary Calcareous Nannofossil Biostratigraphy in the North Part of the South China Sea

Abstract

Abstract The marine Tertiary sequence in the north part of the South China Sea may be divided into 18 Late Oligocene to Pliocene calcareous nannofossil zones and one unnamed Eocene assemblage based on an analysis of calcareous nannofossils from 40 offshore boreholes. The unnamed Eocene assemblage has been found only on the northeast margin of the Zhujiangkou basin. The 18 cakareous nannofossil zones of the Late Oligocene to Pliocene were deposited in succession, but their development degrees are different. Among the 18 calcareous nannofossil zones, those corresponding to Martini's (1971) NN4‐NN5 zones, NN11 zone and NN13‐NN15 zones are well developed, relatively persistent laterally and also widely distributed. They are the important markers for the stratigraphical subdivision and correlation of the Upper Tertiary between the various basins in the north part of the South China Sea. Based on the calcareous nannofossils and the sedimentsry features coup‐led with the foraminifer zonation in certain basins, the present paper discusses the sedimentary characteristics of the marine Tertiary and as well as the distribution and development of the sedimentary hiatus in the region. The calcareous nannofossil markers for the Upper / Lower Tertiary and the Quaternary / Tertiary boundaries, and the characteristics and geological significance of the reworked calcareous nannofossils are also discussed in the paper.