长江三角洲SZ04孔磁性地层研究及其意义

Magnetostratigraphy of Borehole SZ04 in the Yangtze River Delta and Its Implications

文章对位于长江三角洲南翼平原区西部的SZ04孔进行了详细的磁性地层学研究。结合绝对测年,并与标准极性柱对比认为269.2 m岩芯清楚的记录了布容(Brunhes)、松山(Matuyama)、高斯(Gauss)极性带,及贾拉米洛(Jaramillo)、奥尔都维(Olduvai)等亚极性带和布莱克(Black)地磁漂移,其中B/M、M/G界限深度分别为100 m和155 m;SZ04孔底部碎屑沉积物形成的年龄大于5.23 Ma。研究发现,钻孔沉积物磁化率、岩石地层特征在特殊的时代界限附近有明显变化可进行区域对比。分析表明,第四纪以来长江三角洲地区一直存在持续的构造沉降,且沉降中心持续往南东方向移动,构造沉降运动的发生和发展存在三个重要的期次分别为2.58 Ma,0.78 Ma和0.125 Ma。

This study aims to establish a high resolution paleomagnetic age scale of Borehole SZ04 （269.2 m in length） which was drilled from the western part of plain region on the south flank of the Yangtze River Delta. Combi ning with the absolute age and compared with the standard polarity column, the results show that the 269.2 m core consists of three polarity events including Brunhes, Matuyama and Gauss and three subpolarity events including Black, Jaramillo and Olduvai. The B/M and the M/G boundary are found at the depth of 100 m and 155 m, respec- tively ; Clastic deposit at the bottom of Borehole SZ04 was formed at about 5.23 Ma. Analysis of the dating results in dicates that obvious changes of the sediments magnetic susceptibility and lithostratigraphy characteristic are existed near each particular boundaries, which can be correlated with in a large region. Therefore, it is concluded that crust subsidence in this region was continuously occurred since Quaternary, accompanied with the subsidence center moving to the south and the crust subsidence activities were concentrated and intensified in three important time phase at a bout 2.58 Ma, 0.78 Ma and O. 125 Ma.