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| 渤海湾西岸BZ1钻孔的磁性地层学研究 | |
| 引用本文： | 肖国桥,郭正堂,陈宇坤,姚政权,邵永新,王旭龙,郝青振,卢演俦.渤海湾西岸BZ1钻孔的磁性地层学研究[J].第四纪研究,2008,28(5):909-916. |
| 作者姓名： | 肖国桥 郭正堂 陈宇坤 姚政权 邵永新 王旭龙 郝青振 卢演俦 |
| 作者单位： | 1. 中国科学院地球环境研究所黄土与第四纪地质国家重点实验室,西安,710075;中国科学院研究生院,北京,100049 2. 中国科学院地质与地球物理研究所新生代地质与环境重点实验室,北京,100029 3. 天津市地震局,天津,300201 4. 中国科学院地球环境研究所黄土与第四纪地质国家重点实验室,西安,710075 5. 中国科学院地球环境研究所黄土与第四纪地质国家重点实验室,西安,710075;中国地震局地质研究所,北京,100029 |
| 基金项目： | 中国科学院知识创新工程重要方向项目(批准号:KZCX2-YW-117-2);国家自然科学基金项目(批准号:40730104);天津市“十五”活断层探测与地震危险性评价项目;国家发展和改革委员会发改投资城市活断层探测与评价项目(批准号:20041138)资助 |
| 摘 要： | 文章对位于渤海湾西岸黄骅坳陷内的BZ1钻孔进行了详细的磁性地层学研究。结果表明,204.51m的岩芯记录了布容正向极性时(Brunhes)、贾拉米洛(Jaramillo)和奥尔都维(Olduvai)极性亚时,钻孔底部年龄约为2.21Ma。本项研究结果为该区约2.21Ma以来的古环境和相关研究提供了可靠的地层年代框架。与沧县隆起区的BZ2钻孔地层结果对比表明,两个构造单元的沉积物厚度在布容期以来差异较大,即在此期间黄骅坳陷相对沧县隆起下沉40余米,表明1Ma前后发生的新构造运动导致黄骅坳陷区构造下沉速率显著增加。 |
| 关 键 词： | 渤海湾西岸 磁性地层 第四纪 新构造运动 |
| 收稿时间： | 2008-06-28 |
| 修稿时间： | 2008-07-18 |
MAGNETOSTRATIGRAPHY OF BZ1 BOREHOLE IN WEST COAST OF BOHAI BAY,NORTHERN CHINA |
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| Xiao Guoqiao,Guo Zhengtang,Chen Yukun,Yao Zhengquan,Shao Yongxin,Wang Xulong,Hao Qingzhen,Lu Yanchou.MAGNETOSTRATIGRAPHY OF BZ1 BOREHOLE IN WEST COAST OF BOHAI BAY,NORTHERN CHINA[J].Quaternary Sciences,2008,28(5):909-916. | |
| Authors: | Xiao Guoqiao Guo Zhengtang Chen Yukun Yao Zhengquan Shao Yongxin Wang Xulong Hao Qingzhen Lu Yanchou |
| Abstract: | The Quaternary deposits in the coast of Bohai Bay provide an important archive for addressing Quaternary sea-level changes,interactions between marine and terrestrial environment,and Neotectonic movements.Here we present the magnetostratigraphic results of BZ1 borehole(204.51m)near Tianjin which is located at Huanghua Depression in this region.A total of 417 undisturbed samples were collected from BZ1 borehole at an interval of 0.2～0.8m except for several missing intervals during drilling.290 samples were performed on thermal demagnetization in temperature steps of 20～50℃ until 585℃ or 680℃.Another 127 samples were performed on progressive alternating field demagnetization at peak fields up to 60mT at 5～10mT intervals.Magnetizations were measured by a 2G-760 U-Channel system and performed in the Paleomagnetism and Geochronology Laboratory of the Institute of Geology and Geophysics,Chinese Academy of Sciences where magnetometers and demagnetizers are installed in magnetic shielded house with a field minimized to less than 300nT.Demagnetization results were evaluated on stereographic projections and orthogonal(Zijderveld)diagrams,and standard Fisherian methods were performed to calculate the characteristic remanent magnetization(ChRM)directions.Only about 10.6% of the samples which showed unstable demagnetization trajectories couldn't isolate ChRM directions.The Brunhes/Matuyama boundary is found at the depth of 102.43m.The interval from 102.43m to 204.51m is fairly correlative with the Matuyama reversal in the geomagnetic polarity timescale with two normal polarity zones corresponding to Jaramillo(130.21～133.53m)and Olduvai(159.51～178.05m)subchrons,respectively.The basal age of BZ1 borehole is estimated at about 2.21Ma by extrapolation of the sedimentation rate in the Olduvai subchron.Our results have provided a reliable chronology framework for paleo～environment and related research in this area.The sedimentation rates of the BZ1 core during the past 1Ma is relatively high(ca.132m/Ma)compared with the interval of 1.00～2.21Ma.The thickness of the deposits of this core is 102.4m and around twice of that of the BZ2(56.2m),another borehole located at Cangxian Uplift which we reported previously,during Brunhes epoch,suggesting that the sedimentation rates controlled by Neotectonic movement are quite different between these two tectonic units and that an epoch of Neotectonic movement occurred around 1Ma,which led to accelerated subsidence of the Huanghua Depression compared with that of the Cangxian Uplift.Whilst,the transgression revealed in the upper ca.60m of the BZ1 borehole sequence,contrary to the decreasing global seal level since 800kaB.P.,may be resulted from the accelerated subsidence of the Huanghua Depression since 1Ma. |
| Keywords: | west coast of Bohai Bay magnetostratigraphy Quaternary Neotectonic movement |
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