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

Key words: 
• the Yangtze River Delta /
• Borehole SZ04 /
• Magnetostratigraphy /
• polarity event

Abstract: 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. Combining 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, respectively; Clastic deposit at the bottom of Borehole SZ04 was formed at about 5.23 Ma. Analysis of the dating results indicates 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 about 2.58 Ma, 0.78 Ma and 0.125 Ma.