OLIGOCENE BIOSTRATIGRAPHY OF WELL W22 IN THE LIWAN SAG OF THE PEARL RIVER MOUTH BASIN
Through the analysis of foraminifers and calcareous nannofossils of 72 samples from the interval of 3 266～3 991 m in Well W22 in the Liwan Sag of the Pearl River Mouth Basin,the biostratigraphic subdivision was setup and the age of the studied interval was determined.The planktonic foraminiferal and calcareous nannofossil distributions showed that the age of studied section was Oligocene.The early Oligocene planktonic foraminiferal zone,P18-P21a was deposited below 3 390 m;the lower part of the late Oligocene P21b-P22 zone to the bottom N4 zone was deposited above 3 380 m,with the age of 33-23 Ma.Calcareous nannofossil analysis revealed that this section contained the fossils from the bottom of the NP25 zone to the NP21 zone,with the Lower/Upper Oligocene boundary at 3 390 m.The LO Coccolithus formosus(32.92 Ma)occurred at 3 841 m,indicating that the age of the formation below 3 841 m was older than 32.92 Ma.However,no Eocene calcareous nannofossils have been found in the deeper strata,indicating that the base age is still of early Oligocene,but close to the Oligocene/Eocene boundary(33.89 Ma).The Oligocene of the Liwan Sag underwent an evolution from a shallow shelf to a semi-abyssal environment on the upper slope.
foraminiferscalcareous nannofossilsbiostratigraphyOligoceneLiwan Sag
万方数据
维普
