海平面变化和沿海地区的海陆变迁是古环境研究的热点.本研究通过对海南岛东寨港ZK13-22钻孔(19m)AMS 14C测年和粒度分析,结合沉积物岩性和化石组合,重建了东寨港地区约3.9万年以来沉积环境的变化,探讨了沉积环境与海平面变化的关系.结果表明:1)39.4～15.3kaB.P.,ZK13-22钻孔的沉积环境为陆地环境,其中在39.4～32.3kaB.P.、32.3～21.9 ka B.P.和21.9～15.3 ka B.P.期间,沉积环境分别为河床相、河漫滩相和河床相,与古河道的摆动迁移有关;2)15.3～4.4kaB.P.,沉积物中值粒径减小,出现大量海月和螺等化石,且保存完好,表明海洋影响增加,钻孔沉积环境为滨海相沉积,与全球增温导致的海平面快速上升有关;3)4.4 ka B.P.之后,沉积物的中值粒径和细砂含量均有增加,反映了研究区可能受海平面下降或者人类活动的影响.
ENVIRONMENTAL CHANGES OVER THE LAST 39 KA AS RECONSTRUCTED FROM GRAIN SIZE CHARACTERISTICS OF SEDIMENTS IN DONGZHAIGANG HARBOR,HAINAN ISLAND
In 2020,core ZK13-22(19-m long;20°0′38.10″N,110° 38′0.24″E;1.85 m above sea level)was collected from the Dongzhaigang area,Hainan Island.The Dongzhaigang area lies at the border of Haikou,the capital of Hainan Island and Wenchang,situated in a bay area with the Qiongzhou Strait to the north and surrounded by mountains on the other three sides.In this study,an age model was built using 9 AMS 14C dates processed using Bacon software.The base and surface of the core were dated to 39361 a B.P.and 3029 a B.P.,respectively.A total of 518 samples were analysed at 2～10 cm intervals for grain size analysis.The grain sizes are divided into coarse sand(500～2000 μm),medium sand(250～500 μm),fine sand(63～250 μm),silt(4～63 μm)and clay(＜4μm).Based on lithology,fossil and grain size data,the sediments from core ZK13-22 were classified into three depositional units.Unit 1(19.0～13.5 m;39.4～15.3 ka B.P.):This unit displays a pattern of coarse-fine-coarse deposition rhythm,and the grain size distribution is unimodal and bimodal pattern.The coarse sections,situated at the top(15.00～13.50 m;21.9～15.3kaB.P.)and the base(19.00～17.08 m;39.4～32.3 ka B.P.),consist of greyish white and greyish brown coarse to fine sand interbedded with pebbles.The average contents of medium and coarse sand are 14.7％at the top and 32.9％at the base.The central fine section(17.08～15.00 m;32.3～21.9 ka B.P.)comprises black clay and black peat layers containing abundant plant debris(wood and leaves).The average content of medium and coarse sand is 3.6％.It is inferred that the deposits during the intervals of 39.4～32.3kaB.P.,32.3～21.9 ka B.P.and 21.9～15.3 ka B.P.were formed in a fluvial channel,floodplain,and another fluvial channel,respectively.Thus,this unit is interpreted as having been deposited in a terrestrial environment.Unit 2(13.5～2.1 m;15.3～4.4 ka B.P.):This unit is characterized by dark grey clayish silt containing large quantities of well-preserved marine molluscan shells,such as Placuna placenta.The median grain size decreases to 13.4μm at 15.3kaB.P.,then increases to ca.21μm at 10.3kaB.P.,and further increases to ca.35 μm at ca.7 ka B.P.The clay and silt content increases to ca.80％.Samples exhibit three grain size distribution patterns:unimodal,bimodal,and trimodal.These features suggest that this unit was deposited in a littoral environment.Unit 3(2.1～0 m;4.4～3.0 ka B.P.):This unit consists of dark grey silt and grayish yellow,silty to fined-grained sand.The median grain size increases to ca.20～84 μm.The clay and silt content decreases,while the fine sand increases to 40％～60％.The scarcity of molluscan shells suggests a relatively stronger tidal influence or possibly increasing human activity,which needs further investigation.In conclusion,the sedimentary environment of core ZK13-22 was terrestrial at the interval of 39.4～15.3kaB.P.,transitioning to littoral facies from 15.3 ka B.P.to 3.0ka B.P.,and this shift indicates that the increased marine influence was associated with rapid sea level rise due to global warming.Changes in sedimentary facies between 39.4 ka B.P.and 15.3 ka B.P.were driven by channel incision and movement,reflecting the fluvial system's adjustment to sea level fluctuations.The evolution of sedimentary environment in the study area clearly corresponded to sea level changes.
万方数据
维普
