珠江口盆地揭阳凹陷早渐新世-中新世古生物地层及沉积环境

EARLY OLIGOCENE—MIOCENE BIOSTRATIGRAPHY AND SEDIMENTARY ENVIRONMENT OF THE JIEYANG SAG IN PEARL RIVER MOUTH BASIN

位于珠江口盆地揭阳凹陷的S1井是盆地东南部唯一钻井,其地层和沉积环境分析意义重大。本研究通过对S1井孢粉、有孔虫和钙质超微化石地层对比分析,确定了所钻地层时代。井段(3326.5~2950 m)共鉴定孢粉40属62种,孢粉组合无明显变化,以桤木粉-双束松粉为主,组合与盆地内渐新统珠海组相同。整个分析段3326.5~2059.5 m共鉴定浮游有孔虫11属41种,依据标准种首末现事件共划分出P19-N65个带或联合化石带。钙质超微化石共鉴定8属24种,划分NP23-NN4共5个钙质超微化石带。综合判定:地层时代为早渐新世-早中新世(~31-18 Ma),渐新统与中新统的界限在2876.5 m附近。利用浮游有孔虫的丰度和底栖有孔虫的组合来判别该地层的沉积环境,认为揭阳凹陷S1井在早渐新世-早中新世均为陆坡深水环境,水深>1000 m。

Well S1 is the only well in the Jieyang Sag,southeastern part of the Pearl River Mouth Basin.The biostratigraphy and paleo-environment reconstruction for the sediments of this well is significant in studying the regional stratigraphy and petroleum geology.Sporopollen,foraminifers and calcareous nannofossils provide the stratigraphic ages of Well S1 and reveal further geological information of the Jieyang Sag.The sporopollen in the interval of 3326.5 m(hole bottom)~2950 m has a stable assemblage of Alnipollenites-Pinuspollenites.This assemblage is the same as the Oligocene Zhuhai Formation in other parts of the basin.The content of foraminifers is low,dominated with planktonic species;while the calcareous nannofossils are common,though some intervals are abundant or rare.Based on the key species of foraminifers and calcareous nannofossils,5 planktonic foraminiferal zones and 5 calcareous nannofossil zones were identified,indicating the strata of the Early Oligocene to Miocene(~31-18 Ma).By integrating above data,it is concluded that the interval of 3326.5~2876.5 m is of the Oligocene,while that of 2876.5~2059.5 m is of the Miocene.The sedimentary environment is suggested to be the middle slope,with a water depth of more than 1000 m.