河北海兴小山CK3孔磁性地层与第四纪火山活动记录

Magnetostratigraphy of Borehole CK3 and record of the Quaternary volcanic activities in Xiaoshan of Haixing,Hebei Province

基于对渤海湾西岸河北省海兴小山火山丘附近500.25 m深CK3孔进行的磁性地层学研究,确认该钻孔揭示了吉尔伯特(Gilbert)极性时科奇蒂(Cochiti)亚时以来的地层,底部层位年龄约为4.38 Ma;结合14C测年和地层关系,可见本孔中所见4期火山活动分别发生在2.12 Ma、1.34 Ma、35～70 ka和10～15 ka;与渤海湾滨海平原几个质量较高的钻孔古地磁研究成果对比显示,黄骅坳陷第四纪期间整体向NE方向倾斜,沉积物平均粒径变化与测井曲线有较好的对比关系和同步性。依据沉积物特征、沉积构造以及测井相、粒度分析资料综合分析,确定全孔揭露地层大多发育泛滥平原沉积,即使是分支间湾亚相也少见湖泊—湖沼相沉积,沉积物多呈氧化状态。晚更新世以来3期海侵地层皆为潮坪沉积,其底板埋深与整个渤海湾西岸所见相符,可以按海洋氧同位素分期划分。

After the palaeomagenetism study on the 500.25 m deep Borehole CK3, which is located near the Xiaoshan volcanic dome of Haixing County on the western coast of Bohai Bay, it can be determined that this borehole has drilled through the strata since the Cochiti subchron of Gilbert polarity chron, with the basal horizon having an age of 4.38 Ma. Combining with 14C dating data as well as stratigraphic relations, the total four periods of volcanic activities occurred at 2. 12 Ma, 1.34 Ma, 35 -70 ka and 10 - 15 ka, respectively. The comparison with the high-quality palaeomagenetism-studied boreholes on thecoastal plain of the Bohai Bay indicated that the Huanghua Depression was overall tilted northeastwards during the Quaternary. The average grain-size change of sediments and the logging curves showed a good contrastive relationship and synchronicity. The comprehensive analysis of the sediment characteristics, sedimentary structures, log facies and particle sizes suggested that most of the drilled strata were floodplain deposits, and had rare lacustrine-limnetic sediments even in the interdistributary subfacies, while the deposits were mostly in a state of oxidation. All the three periods of transgressive strata since the Late Pleisto- cene were tidal flat deposits with the burial depth of basal horizons conformed to the entire western Bohai Bay, and could be subdivided based on marine oxygen isotope stages.