珠江口盆地BY7—1—1井晚渐新世浮游有孔虫的发现及其地质意义

THE DISCOVERY OF LATE OLIGOCENE PLANKTONIC FORAMINIFERA IN WELL BY7-1-1 AT ZHUJIANG RIVER MOUTH BASIN AND ITS GEOLOGICAL SIGNIFICANCE

本文系统介绍了珠江口盆地最南的一个探井——BY7—1—1井浮游有孔虫生物地层和海侵层序。通过对该井有孔虫全面系统采样分析,发现了渐新世浮游有孔虫组合。这一重大发现给重新认识该区上、下第三系界线,以及对整个南海北部地层对比提供了新资料。并对有关的一些地质问题进行了讨论。

A systematic planktonic foraminiferal biostratigraphic succession and sequence of marine transgression and regession in well BY7-1-1 located somewhere at the mostsouthern end of Zhujiang River Mouth Basin are introduced in this paper. For comparison with European stratotype, five Late Cenozoic formations in Zhujiang River Mouth Basin were studied chronostratigraphically. The biozone of Late Oligocene planktonic foraminifera P22(N3) is placed just close to the seismic refraction wave(TT) in well BY7-1-1, and therefore three problems around T7, which have been debated for many years, seem to be solved. 1. Upper/Lower Tertiary boundary is on the top of high sea level and fine grain deposit, between N4 and P22(N3) zone of planktonic foraminifera, or in Np25 zone of nannofossil, about 25Ma in age, and nearly in the bottom of Zhuhai Formation. This boundary coincides with European stratotype. 2. Enping Formation between T7 and T8 reflectors belongs to Oligocene strata. 3. 'South Sea movement' marked by T7 occurred in Late Oligocene. A new Late Cenozoic correlation project between the north part of South China Sea and European stratotype is advanced in this paper.