南海北部琼东南盆地崖北凹陷Y-8-X井晚渐新世—更新世钙质超微化石

OLIGOCENE TO PLEISTOCENE CALCAREOUS NANNOFOSSIL OF WELL Y-8-X IN THE YABEI SAG,QIONGDONGNAN BASIN,NORTHERN SOUTH CHINA SEA

对南海北部琼东南盆地崖北凹陷Y-8-X井1 338.1~3 086.1 m井段内的110块样品进行了钙质超微化石分析,发现上部1 338.1~2 075.7 m地层含较丰富的钙质超微化石,而下部2 091.0~3 086.1 m井段化石丰度低或未见。根据钙质超微化石标志种的存在,识别出NN17带、NN15带、NN11带、NN6带、NN4带和NP25带等6个钙质超微化石末现面事件,由此对该井的生物地层进行了划分,认为研究井段的地层时代为晚渐新世—更新世,推测本井缺失了部分中新统沉积。依据钙质超微化石总丰度、分异度及特征性环境指示属或种的丰度变化,探讨了1 338.1~3086.1 m井段的沉积环境演化过程,可分为6个演化阶段。从晚渐新世至更新世,经历了海水由浅变深再变浅的过程,其中早中新世早期水深最浅,中中新世—早上新世水体温暖且水深最大。

A total of 110 samples have been analyzed for calcareous nannofossils from the interval of 1 338.1~3 086.1 m in Well Y-8-X, Yabei Sag, Qiongdongnan Basin, northern South China Sea. Calcareous nannofossils were abundant in the upper 1 338.1~2 075.7 m, while the lower part(2 091.0~3 086.1 m) were rare or absent. Six top biohorizon of calcareous nannofossils including NN17, NN15, NN11, NN6, NN4 and NP25 are recognized depending on the marker species. It is considered that the interval of 1 338.1~3 086.1 m belonging to the Late Oligocene to the Pleistocene, while missing a part of Late to Middle Miocene. According to the statistics of calcareous nannofossils abundance, diversity and assemblage characteristics, depesitional and paleoenvironmental history are discussed in detail. Six evolution stages of the sedimentary environments can be divided. From the Late Oligocene to the Pleistocene, the water depth changed from shallow to deep and then to shallow again, among which the water is the shallowest during the early Early Miocene and the deepest during the Middle Miocene to the Early Pliocene.