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中国东海自末次冰消期以来,经历了多次海平面快速上升的气候事件,为了解这种频繁的海侵过程对中国东部大陆架海域的影响,本文利用有机地球化学方法分析了位于长江口水下三角洲的柱状岩芯样品,并据此重建了该区域过去1.4万年以来的沉积环境演化.本次记录反映了两种不同的沉积环境,阶段Ⅰ(13.8-8 cal ka BP)以陆相环境为主,具体表现在细菌支链甘油二烷基甘油四醚(缩写为brGDGTs,平均浓度值约143 ng/g沉积物干重,GDGT浓度单位缩写为ng/g dsw)的浓度明显高于古菌类异戊二烯甘油二烷基甘油四醚(缩写为iso-GDGTs,平均浓度值约36 ng/g dsw),陆源输入指标值(BIT)接近陆相端元(>0.78),同时GDGT-0/crenarchaeol(R_(0/5))的比值也在高值区间剧烈波动(0.52-3.81).阶段I还出现了短暂的气候变化事件,分别跟新仙女木事件(YD,12.9-12.2 cal ka BP)和北半球冰融水事件(MWP-1B,11.5-11.1 cal ka BP)相对应.各项环境指标在8-7.9 cal ka BP均发生了显著的变化,以BIT值的快速下降(<0.4)和海洋古菌标志物crenarchaeol的优势丰度为特征,进入海相沉积的阶段Ⅱ.此后,各项参数保持相对平稳,暗示该阶段处于稳定的高海平面的现代海洋沉积环境.BIT指标在本次工作中得到极好的应用,可以准确区分陆相和海相环境.鉴于阶段I陆相环境的BIT高值,由TEX_(86)(TetraEther Index of tetraethers consisting of 86 carbons)衍生的表层海水温度指标TEX_(86)-SST在阶段Ⅰ未能真实地反映表层海水温度信息,该指标在阶段Ⅱ((21.6±0.9)℃,n=49)则反应了年平均表层海水温度.基于MBT’/CBT(Methylation of Branched Tetraethers)/Cyclization of Branched Tetraethers)的平均大气温度(MAT)在整个记录中呈现出缓慢下降的趋势((14.3±0.6)℃,n=68),跟长江流域中下游的年平均大气温度一致,证实了MBT’/CBT-MAT在该海域的适用性.
The East China Sea has undergone several climatic events with rapid sea level rise since the last ice expiration. In order to understand the impact of this frequent transgression process on the continental shelf in eastern China, this paper uses organic geochemical methods to analyze the effects of the sea- Delta columnar core samples and reconstruct the evolution of the sedimentary environment over the past 1.4 million years in this area.This record reflects two different depositional environments, Stage I (13.8-8 cal ka BP) Mainly manifested in the higher concentrations of bacterial branched-chain glycerol dialkylglycerol tetraethers (abbreviated as brGDGTs, with an average concentration of about 143 ng / g sediment dry weight, and GDGT concentration units abbreviated as ng / g dsw) The isoprenoid glycerol dialkylglycerol tetraether (abbreviated as iso-GDGTs with an average concentration of about 36 ng / g dsw) and the terrestrial input index (BIT) approached the continental end-point (> 0.78) while GDGT-0 / crenarchaeol (R_ (0/5)) also fluctuated sharply in the high value range (0.52-3.81) .There were also short-term climate change events in Stage I, which were related to the new fairy wood event (YD, 12.9-12.2 cal ka BP) corresponds to an ice melting event in the Northern Hemisphere (MWP-1B, 11.5-11.1 cal ka BP). Environmental indicators changed significantly from 8 to 7.9 cal ka BP, and were characterized by the rapid decrease of BIT (<0.4) and the dominant abundance of marine archaeon marker crenarchaeol, which entered the phase Ⅱ of marine sedimentation , The parameters remained relatively stable, suggesting that this stage is in a stable high-sea-level modern marine sedimentary environment.BIT indicators in this work has been excellent application, can accurately distinguish between continental and marine environment .In view of stage I land The BIT value of phase environment, TEX_ (86) -SST, which is derived from the TEX_ (86) (TetraEther Index of tetraethers consisting of 86 carbons), did not reflect the surface seawater temperature information accurately in Phase Ⅰ, Phase II (21.6 ± 0.9 ° C, n = 49) reflects the average annual surface seawater temperature. The mean atmospheric temperature (MAT) based on the MBT ’/ CBT (Methylation of Branched Tetraethers) / Cyclization of Branched Tetraethers (14.3 ± 0.6) ℃, n = 68), consistent with the annual mean atmospheric temperature in the middle and lower reaches of the Yangtze River Basin, confirming the applicability of MBT ’/ CBT-MAT in this area.