南海北部陆缘中、晚第三纪古地理、古环境研究

MIDDLE AND LATE TERTIARY PALAEOGEOGRAPHY AND PALAEOENVIRONMENTS ON THE NORTHERN CONTINENTAL MARGIN OF THE SOUTH CHINA SEA

本文主要依据钙质超微化石成果,并结合其它微体化石和若干次一级的沉积间断,讨论包括台南盆地、珠江口盆地、琼东南盆地和北部湾盆地在内的南海北部陆缘中、晚第三纪海相沉积划分标志和对比意见,古地理和古环境演化史及古气候概况。研究结果表明,除北部湾盆地外,全区上渐新统至上新统基本由海相沉积构成。包括滨海和浅海、三角洲租碳酸盐岩-生物礁灰岩沉积。海侵自东南向北西推进,出现相当超微化石NN4—NNS,NN11和NN13—NN15带沉积期的3个海侵高峰。

On the basis of the results of an analysis of calcareous nannofossils combined with other microfossil data and secondary depositional breaks, the authors put forward their opinoins about the criteria of division and comparison of the middle and late Tertiary marine sediments on the northern continental margin of the South China Sea, including the Tainan basin, Pearl River Mouth basin, Southeastern Hainan basin and Beibu Gulf basin. Appreciable changes have taken place in the palaeogeographical framework and depositional environments in northern South China Sea since the late Oligocene as compared with the early Tertiary. Exploration has revealed that the upper Oligocene to Pliocene strata in the whole area consist essentially of marine sediments except in the Beibu Gulf basin. They comprise littoral, neritic and deltaic sediments and carbonate reefy limestone. The seawater advanced from southeast to northwest. The culmination of the marine transgression occurred at times respectively coinciding with the stages of deposition of nannofossil zones NN4—NNS, NN11 and NN13—NN15. The three stages were separated by two depositional breaks. The late Late Pliocene regression continued till the early Pleistocene, when, in addition to marine deposits there might also be paralic deposit near the coasts and on some uplifts. Finally this paper presents a brief account of the middle and late Tertiary climate in the area.