长江三角洲平原BZK03孔更新世以来古环境演变及多重地层划分对比

Palaeoenvironmental Evolution and Multi-stratigraphic Division and Correlation of Yangtze River Delta Plain since Pleistocene:Evidence from BZK03 Borehole

对长江三角洲平原BZK03钻孔进行沉积物同位素测年、孢粉组合、微体古生物、粒度和磁学的测试分析,讨论了更新世以来钻孔揭示的沉积环境演化、沉积相和古气候特征,建立了钻孔的第四纪多重地层划分对比框架。研究结果表明,钻孔自下而上依次为白垩纪衢县组的风化粉砂岩及第四纪沉积的嘉兴组、前港组、东浦组、宁波组、镇海组。孢粉组合可划分出18个孢粉带,按暖期温暖潮湿-冷期寒冷干燥古气候旋回变化的周期律,BZK03钻孔反映该区域共存在6个古气候旋回。根据岩性分层、沉积环境、古气候建立的钻孔多重地层划分对比揭示:144.6~198.5 m为早更新世时期河流相和河湖相交替沉积环境的嘉兴组,存在2个气候旋回过程;88.3~144.6 m为中更新世河湖相-河流相-河湖相-河流相沉积环境的前港组,包含2个气候旋回过程;16.6~88.3 m为晚更新世沉积,沉积环境为河湖相-滨海相河湖相-潮坪相-河湖相的宁波组和河口相-浅海相的东浦组,包括2个气候旋回;0~16.6 m为河湖相-浅湖相-河湖相-潮坪相沉积环境的镇海组,古气候时期对应北方期和大西洋期。

Based on the analysis of sediment isotope dating,sporopollen assemblages,microfossils,grain size and magnetism of the samples from BZK03 borehole in the Yangtze River Delta plain,this paper discusses the sedimentary environment evolution,sedimentary facies and paleoclimate characteristics since Pleistocene,and then the Quaternary multi-stratigraphic division and correlation framework of the borehole has been established.The results show that,from bottom to top,the samples of drilled holes are weathered siltstone of Cretaceous Quxian Formation and Quaternary sedimentary strata of Jiaxing Formation,Qiangang Formation,Dongpu Formation,Ningbo Formation and Zhenhai Formation.Sporopollen assemblages can be divided into 18 sporopollen zones.According to the cycle law of warm,humid,cold,dry paleoclimate cycles,BZK03 borehole shows that there are 6 paleoclimate cycles in this region.In line with lithologic stratification,sedimentary environment and paleoclimate,the division and correlation of borehole multiple strata reveals that 144.6~198.5m is Jiaxing Formation strata with alternating fluvial and fluvial-lacustrine sedimentary environments in early Pleistocene,and there are two climatic cycles.88.3~144.6m is the Qiangang Formation stratum of Middle Pleistocene fluvio lacustrine face-fluvial face-fluvio lacustrine face-fluvial face sedimentary environment,including two climatic cycles.16.6~88.3m is late Pleistocene deposition,and the sedimentary environment is the Ningbo Formation of fluvial-littoral-fluvial-tidal-fluvial facies and the Dongpu Formation of estuarine-neritic facies,including two climatic cycles.0~16.6m is Zhenhai Formation stratum of fluvial-lacustrine-shallow-fluvial-tidal flat sedimentary environment.