长江三角洲上新世以来磁性地层及天文调谐年代标尺

Magnetostratigraphy and Astronomically Tuned Time Scale of Yangtze Delta since Pliocene

长江三角洲地区的磁性地层认识存在很大不确定性.为建立一个可靠的年代标尺,为区内沉积环境和气候演化研究提供约束,在年代地层和磁性地层基础上,以频率磁化率为信号源、ETP为靶曲线,通过轨道调谐方法对区内LZK1孔开展了天文年代标尺研究,建立了年代序列框架.结果显示,M/B界线埋深约为143.0m、Ga/M界线埋深约为219.0m、Gi/Ga界线埋深约为296.6m.受气候和沉积环境控制,沉积旋回特征清楚,沉积速率具有明显的阶段性.调谐后的频率磁化率显示了显著的125ka、96ka、41ka、23ka、22ka、18ka等轨道周期,并在轨道周期上与ETP曲线高度相关,相关性超过了95%检验标准.100ka、41ka和23ka周期的带通滤波曲线与偏心率、斜率和岁差在振幅和相位上吻合较好,但局部时间段有差异,可能与低沉积速率、沉积速率突变或短时间尺度的地层缺失等因素有关.研究表明,在具有短暂沉积缺失的持续沉降区域,只要保证样品分辨率,可以通过轨道调谐方法建立可靠的年代框架.

There is also uncertainty about the magnetostratigraphy in the Yangtze delta.In order to establish a reliable time scale,and provide constraints for sedimentary environment and climate evolution,based on chronostratigraphy and magnetostratigraphy,in this paper astronomical time scale of the LZK1 borehole in the Yangtze delta is researched,and established the chronological framework is established.The results show that M/B,Ga/M and Gi/Ga boundaries locate at 143.0 m,219.0 mand 296.6 mseparately.The deposit cycles are clear and the sedimentary rate has obvious phases,which was influenced by the climate and sedimentary environment.The tuned frequency dependent susceptibility record reveals orbital periods including 125 ka,96 ka,41 ka,23 ka,22 ka,18 ka,and is correlated with ETP curves enormously in orbital periods,the confidence interval exceeds 95%.The band-pass filtering curves of 100 ka,41 ka,23 ka circles coincide with the corresponding orbital parameter curve in phase and amplitude in total,while existing some inconformities at certain times.The inconformities may be caused by low sedimentary rate or abrupt change of sedimentary rate.In this paper,a conclusion is drawn that in the ongoing subsidence areas with temporary depositional hiatus,as long as the sampling resolution can be assured,we can establish relia-ble chronological framework by orbital tuning.