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
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 organic- rich 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
