长江三角洲北翼J9孔揭示地层和古地磁特征

长江三角洲北翼地区缺少较长尺度的第四纪海陆变迁及环境演变的深入探讨,深达423m的海安县基岩标J9孔为此提供了较好的研究对象。通过观察该孔松散层岩心,总结其沉积特征,认为岩心可明显地划分为6个特征岩性段。同时,地层古地磁测试结果显示:0～200m为布容正极性世,200～334m为松山负极性世,334m以下为高斯正极性世。综合分析岩心沉积特征并参考古地磁测试结果对地层进行了初步划分,认为:0～39m为全新世地层,39～153m为晚更新世地层,153～200m为中更新世地层,200-334m为早更新世地层,之下为新近纪地层。地层中存在晚更新世晚期特征的硬粘土标志层,指示本地不是冰后期古河谷的发育地。

Stratigraphic and paleomagnetic characteristics revealed by the J9 hole in the north flank of the Yangtze River delta

Quaternary land and sea shift and environmental evolution with a relatively long duration on the north flank of the Yangtze River delta are lacking in a deep-going study. A 423 m deep hole, named J9, was drilled in bed rocks at Hai'an County of the Yangtze River delta, which provides a good research target. Based on observations of its core in the loose bed and summarizing the sedimentary characteristics, it is evident that this core may be divided into six characteristic lithological intervals. In addition, the paleomagnetism data of the strata suggest the following: the interval 0-200 m belongs to the Brunhes normal polarity epoch, the interval 200-334 m to the Matuyama reverse polarity epoch, and the interval below 334 m depth to the Gauss normal polarity epoch. Through an integrated analysis of the sedimentary characteristics of the core and by referring to the results of the paleomagnetic measurements, the authors made a preliminary stratigraphic division and think that: the interval 0-39 m is Holocene strata, the interval 39-153 m Late Pleistocene strata, the interval 153-200 m middle Pleistocene strata, the interval 200-334 m early Pleistocene strata and the interval below 334 m depth Neogene strata. There is a late Pleistocene hard clay marker bed, which indicates that the postglacial river valley was not developed in this area.