Ahigh resolution study of sediments,microfaunas(ostracods and foraminifers),and stable isotopes of ostracod shells from core PRD05,sampled from the Da’ao plain of the Pearl River Delta,provides new data about palaeoenvironmental changes during the Late Quaternary.The basal fluvial gravelly sediments of the core,representing the lowest deposits of the Quaternary at the core site,were possibly formed prior to the transgression associated with the last interglacial stage.This fluvial setting changed into a marginal marine setting during the last interglacial stage,any record of calcareous fossils were destroyed by subsequent dissolution during the last glacial phase,when the upper part of the deltaic sediments experienced subaerial oxidation,indicated by a mottled clay layer in the core.The postglacial sealevel rise in the South China Sea began at16,700 cal yr B.P.During the first phase of sea-level rise(from ~16,700 to 10,100 cal yr B.P.),a swamp environment developed at the core site.At ~10,100 cal yr B.P.,marine waters intruded onto the Da’ao plain and reached the core site through the Modaomen channel.This timing was earlier than in other parts of the Pearl River Delta.Since then,a semi-enclosed estuarine environment developed and was maintained until ~5560 cal yr B.P.During this transgressive interval,short-term environmental fluctuations can be recognized based on microfauna and shell geochemical data.From ~10,100 to 8630 cal yr B.P.,the sea-level rose,which was followed by a fall from ~8630 to 8520 cal yr B.P.An expanded transgression occurred between ~8520 and 7900 cal yr B.P.The time intervals from ~8520 to 8200 cal yr B.P.and from ~8080 to 7900 cal yr B.P.were marked by peak transgression.From ~7900 to 5560 cal yr B.P.,the core site generally showed a reduced marine influence and enhanced freshwater input.A fluvial environment developed from ~5560 to 3100 cal yr B.P.,and was succeeded by an alluvial plain setting.
Liu ChunlianFranz T. FürsichWu JieDong YixinYang TingtingYin Jian
The present study deals with the planktonic foraminiferal biostratigraphy of the Miocene-Pliocene sequence of three petroleum exploration wells (BY7-1-1,KP6-1-1 and KP91-1) in the Pearl River Mouth Basin (PRMB).In general,the three wells contain a fairly well-preserved,abundant foraminiferal fauna.The proposed planktonic foraminiferal zonation follows the scheme updated by Wade et al.(2011).Nineteen planktonic foraminiferal zones have been recognized,14 zones (zones M1-M14) for the Miocene and 5 zones (zones PL1-PL5) for the Pliocene.The zonation is correlated with previously published biostratigraphic subdivisions of the Neogene succession in the PRMB and with international foraminiferal zonations.The zonal boundaries are mostly defined by the last appearance datum of zonal taxa of planktonic foraminifera,which is more reliable than the FAD (first appearance datum) events for ditch cutting sampling.Changes in the coiling of Globorotalia menardii (s.l.) are also used to define the zonal boundaries,where no LADs (last appearance datum) are available.The Fohsella fohsi group,comprising useful taxa for delimiting zonal boundaries of the middle Miocene in other areas,has a poor record within the Pearl River Mouth Basin due to unfavorable ecological conditions,and cannot be used for the studied wells.Different from the previously reported zonal scheme for the PRMB,the present zonation is based on correlation with the current standard planktonic foraminiferal zonation,with calibrated absolute ages.
Liu Chunlian 1,2,,Huang Yi 1,Wu Jie 1,Qin Guoquan 3,Yang Tingting 1,2,Xia Lianze 1,Zhang Suqing 1 1.Department of Earth Sciences,Sun Yat-Sen University,Guangzhou 510275,China 2.Guangdong Provincial Key Laboratory of Mineral Resources & Geological Processes,Guangzhou 510275,China 3.Nanhai East Company of China National Offshore Oil Corporation,Guangzhou 510240,China
对珠江三角洲PRD16孔的微体动物群进行了分析,共发现底栖有孔虫12属24种,介形类9属13种,它们可分别划分为3种生态类型。根据有孔虫和介形类微体动物群的分布特征、并结合岩性和沉积粒度特征,推断PRD16孔研究区晚更新世以来沉积环境演化经历了5个阶段:①34 600 cal a BP以前为河流相环境,形成了研究区最早的第四纪河床相砂砾沉积;②34 600～23 900 cal a BP推测为河口湾环境;③23 900～7 960 cal aBP受末次盛冰期影响,研究区暴露地表遭受风化剥蚀,形成花斑黏土;④7 960～2 810 cal a BP为全新世大海侵时期,研究区为河口海湾环境,发育以广盐性有孔虫和中盐-多盐性介形类为主的微体动物群,其间发生了2次小规模海平面波动,受地块区域沉降作用影响,研究区在3 873 cal a BP左右水深达到最大,主要有孔虫和介形类属种的丰度达到全新世最高值;⑤2 810 cal a BP以来海平面持续下降,研究区由潮坪环境变为河口砂坝,随后河流作用增强,又逐渐变为河流冲积-潮上带环境。
The Honggang member of the early Paleogene Buxin Formation is the main source rock in the Sanshui Basin, characterized by organic-rich black shales with the cyclic recurrence of organic- poor sediments. The geochemical characteristics of the Honggang member have been documented to determine the organic matter types and depositional environments in this paper. The organic matter of the black shales mainly consists of a mixture of land plant-derived and phytoplankton-derived organic matter. Total organic carbon content （TOC）-sulfur-iron （Fe） relationships suggest that the organicrich black shales were deposited under dysoxic-to-euxinic water conditions. The time that iron minerals remained in contact with H2S in anoxic waters possibly influenced the formation of syngenetic pyrite, and organic carbon controlled the formation of diagenetic pyrite. Organic-poor intervals usually show pyrite sulfur enrichment and higher degree of pyritization values relative to low organic carbon contents. This resulted from HS- diffusing downward from overlying organic-rich sediments and formed Fe sulfides through reactions with sufficient Fe. Trace elements generally exhibit low concentrations and little TOC dependence, suggesting some degree of depletion in these elements in the early Paleogene sediments of the Sanshui Basin. This probably resulted from cyclic recurrences of oxic benthic conditions, which promoted the remobilization of trace elements and caused the low concentration of trace elements.
LIU ChunlianFranz T. FURSICHCHEN LingCHE XiaoguangWU Jie
