渤海湾北岸Bg10孔磁性地层研究及其构造意义

摘要

Based on detailedsedimentological and magnetostratigraphic study of Bg10 borehole (600m)in the northern coast of Bohai bay,there are 39 sedimentary units and 8 normal magnetozones and 7 reverse magnetozones according on 516 specimens (456 specimens subjected to progressive thermal demagnetization and 60 specimens subjected to alternating field demagnetization ) calculated the characteristic remanent magnetization (ChRM)directions.Thinking about sedimentation rates of different magnetozones,Comparing to the geomagnetic polarity timescale (Cande et al.,1995;Gradstein et al., 2004),the normal magnetozones N1,N2,N3,N4,N5,N6 and N7 can be correlated with C1n,C1r.1n, C2n,C2r.1n,C2An.1n,C2An.2n and C2An.3n,the reverse magnetozones R1,R2,R3,R4,R5 and R6 can be collated with C1r.1r,C1r.2r+C1r.3r,C2r.1r,C2r.2r,C2An.1r and C2An.2r.The B-M and M-G boundary of borehole are located in 162.3m and 475.8m respectively,and the age of the bottom is less than 3.596Ma.There have been three sedimentation phases.The Ⅰphase which age was 3.3~3.5Ma and sedimentation rate was more than 130m/Ma was tectonic active period and could be correlated with the phase A of Qingzang movement.The Ⅱ phase which age was 1 .9~3 .3 Ma and sedimentation rate was 112m/Ma was tectonic silent period,and the sedimentary process could be controlled by climate change, but there had the different subsidence rate between Huanghua depression and Cangxian uplift.There was a tectonic active period aged 1 .0~1 .2 Ma in the Ⅲ phase which age was 0~1 .9 Ma and sedimentation rate was 202m/Ma,which could be correlated with Kunhuang movement.The sedimentary process should be controlled by tectonics and climate and the subsidence rates of Huanghua depression and Cangxian uplift have been different since 1.0Ma.Tangshan-Xingtai fault could be formed at 1.9Ma,and has developed one sag at the intersection with Zhangjiakou-Penglai fault.%对渤海湾北岸孔深600m的Bg10孔进行了详细的沉积学和古地磁研究，划分了39个沉积单元；基于516个样品（60个交变样品，456个热退样品）分离出的特征剩磁，建立了钻孔的磁性地层，并与标准极性年表相对比，确定正极性 N1、N2、N3、N4、N5、N6和 N7分别对应 C1n、C1r．1n、C2n、C2r．1n、C2An．1n、C2An．2n 和C2An．3n，R1、R2、R3、R4、R5和R6分别对应C1r．1r、C1r．2r＋C1r．3r、C2r．1r、C2r．2r、C2An．1r和C2An．2r。钻孔B/M界限埋深162．3m，M/G界限埋深为475．8m，钻孔底部位于C2An．3n内，其年龄应小于3．596Ma。Bg10孔包括3个沉积阶段：Ⅰ阶段为3．3～3．6Ma，沉积速率略大于130m/Ma，为构造活动期，唐县期夷平面结束后，盆地沉降和山体隆升的差异增大，并与西部地区的青藏运动A 幕相对应；Ⅱ阶段为1．9～3．3Ma，沉积速率为112m/Ma，为盆地的填充过程，气候变化控制沉积过程，但沧县隆起和黄骅坳陷之间沉降仍有差异。Ⅲ阶段为0～1．9 Ma ，沉积速率为202m/Ma，约在1．0～1．2Ma发生一期构造活动，与西部地区的昆黄运动时代大体相当。1．0Ma以来，沉积过程受构造和气候变化双重影响，沧县隆起和黄骅坳陷之间仍有差异沉降。唐山-邢台断裂带可能在1．9 Ma之后活动性增强，并和张家口-蓬莱断裂带在沧县隆起上的交汇区域形成一个次级凹陷。