从天津CQJ4孔探讨中国东部海侵层的年代问题

天津CQJ4钻孔磁性地层研究结果表明，该孔第四系底界（258Ma）位于340m处，中更新世底界, 即B/M界线位于74m处。微体生物分析显示该孔岩芯记录了三个海侵层，分别位于42~120m、164~302m和5655~5800m，与渤海湾西岸其他钻孔对比，这三期海侵对应于“第Ⅰ、Ⅱ、Ⅲ海侵层”。古地磁研究表明布容极性期内该孔记录了4次极性漂移，分别对应于Blake（120~110ka）、Jamaica（215~205ka）、Calabrian Ridge 1（325~315ka）和Calabrian Ridge 2（525~515ka）。结合钻孔岩芯磁性参数与深海氧同位素的对比，推测这三个海侵层的年龄分别为120~70ka、240~180ka和500ka左右，可以与中国东部沿海地区的“第Ⅲ、Ⅳ、Ⅴ海侵层”相对应。这一对比方案与目前较普遍接受的沿海平原晚更新世以来三期大海侵的认识，在层位对比上明显冲突，但“晚更新世以来三期大海侵”之说，尚难以解释晚更新世底界与中更新世底界（B/M界线）过近的问题。

Geochronological Study on Transgression Layers of the CQJ4 Borehole at Dagang area in Tianjin, China

Magnetostratigraphic study at the CQJ4 borehole in Dagang area of Tianjin indicates that the Quaternary/Tertiary boundary (2.58 Ma) locates at depth of 340 m, and the base of the Middle Pleistocene series, corresponding to B/M boundary is located at 74 m. Microfossil analysis reveals three transgression layers in the CQJ4 borehole, which are at 4.2~12.0 m, 16.4~30.2 m, and 56.55~58.00 m, respectively. Comparing with data of the drilled boreholes in the Bohai coast, the three transgression layers should belo...