MIS 3以来浙江温瑞平原YQ0902孔古环境与古气候变化记录*

YQ0902孔位于浙江南部瓯江三角洲南侧温瑞平原上。沉积相、粒度分析以及AMS ¹4C测年数据表明，硬土层之下为海洋氧同位素3阶段(MIS 3）形成的潟湖相沉积，据此推测MIS 3高海平面至少达到现今海平面之下30m左右(未经构造升降和沉积物压实作用等影响的校正，下同）。硬土层的成土过程发生于MIS 2，其母质部分为MIS 3的潟湖沉积，部分为河漫滩沉积。硬土层之上是一套形成于全新世的海侵—海退旋回，与长江三角洲南翼前缘的沉积相组合类似。研究钻孔初始海泛面约形成于9 cal ka BP，推算当时的海平面约低于现今海平面25 m。中全新世最大海侵前后，东亚季风较强，通过径流或沿岸流输入本区的沉积物较充足，沉积速率较大。随着海平面相对稳定或略有下降，东亚季风减弱，可容空间减小，中晚全新世(5～2 cal ka BP）沉积速率较低。高分辨率的XRF岩心扫描获得的元素相对含量是古环境与古气候研究的重要指标，其中Cl/Ti、Fe/Ti值可分别作为海相性(与海洋联通程度）与东亚季风强弱的替代指标。

Records of palaeoenvironment and palaeoclimate changes since the MIS 3 in Borehole YQ0902 at Wenrui Plain，Zhejiang Province

Borehole YQ0902 is located at the Wenrui Plain along the south flank of Oujiang delta in southern Zhejiang Province.Sedimentary facies，grain-size analysis and AMS ¹4C dating results show that the palaeosol is underlain by the lagoon facies formed during MIS(Marine Isotope Stage)3.It was therefore indicated that the sea level in the early and middle MIS 3 should reach a point at least 30m below the present sea-level(not calibrated by tectonic movement and sediment compaction).The pedogenesis of the palaeosol should have taken place in the MIS 2 and its original strata are lagoon deposits at the lower and floodplain deposits at the top.A transgression-regression sequence overlying the palaeosol was formed in the Holocene and it has similar sedimentary facies assemblages with those at the frontal part of the southern flank of Changjiang delta.The initial flooding surface was formed at about 9 cal ka BP in Borehole YQ0902，suggesting that the sea level at the time was approximately 25m below the present sea-level.In the middle Holocene，the strengthening East Asia Monsoon (EAM)increased sediment input to the study area by the river or through the longshore currents，consequently resulting in high accumulation rate.The sedimentation rate was low in the Mid-Late Holocene(5～2 cal ka BP)with stable or a little fall in sea level and the weakened EAM.High resolution X-ray fluoroscopy(XRF) core scanning data of relative element ratios were considered as important proxy of palaeoenvironment and palaeoclimate research.For example，Cl/Ti and Fe/Ti are good indices of mariness (the degree connected to sea) and EAM strength，respectively.