3.45Ma以来滦河冲积扇中部唐山TD1孔记录的区域构造和气候演化

Records of regional tectonic and climatic evolution since 3. 45 Ma BP at Borehole TD1 of Tangshan in the middle part of Luanhe River fluvial fan

对位于渤海湾西北岸晚更新世早期滦河冲积扇中部的TD1孔进行了磁性地层学、14C测年、沉积旋回、测井沉积学、孢粉地层学和介形类研究,结果表明:(1)220m深的钻孔地层记录了古地磁学布容(Brunhes)、松山(Matuyama)和高斯(Gauss)极性时,钻孔底部层位年龄接近3.45 Ma。(2)钻孔揭示了滦河冲积扇中部地层结构,最厚的湖相沉积地层出现在上新世,第四纪以来主要由辫状河流体系分支河道相与相关沉积构成。(3)测井相与岩心沉积相分析结合显示,约3.45Ma以来出现6个大沉积旋回,与冲积扇顶端钻孔所见沉积旋回在深度上基本可以对比,其中3.2、3.0、2.0和0.78Ma的沉积旋回分别覆于全孔4期浅水湖泊—湖沼沉积物之上;末次盛冰期与渤海湾西岸钻孔一样出现浊黄橙色沉积,显示低水位域的沉积特征。(4)尽管古季风可以导致降水增多并出现湖沼沉积,但是该钻孔有机质含量最高的是在6 ka BP层位,中全新世大暖期气候对该地水热状况影响最大。

This paper studied the magnetostratigraphy,14C dating, sedimentary cycle, logging sedi- mentary, pollenstratigraphy and microbiota ostracoda in Borehole TD1, which is located at the middle part of Luanhe River fluvial fan of the early Late Pleistocene on the northwestern coast of Bohai Bay. The results show that： （1） The strata with 220 m thinkness in this borehole recorded the palaeomagnetic Brunhes, Matuyama and Gauss polarity chrons, and the bottom horizon was near 3.45 Ma based on the palaeomag- netic polarity column. （2） The stratigraphy architecture of fluvial fan had been drilled, it was composedof branch channel facies and related sediments in braided fiver system since Quaternary, and the thickest limnetic facies sediment appeared in Pliocene. （3） The analysis of the log facies and sedimentary facies for the borehole suggests that a total of six large sedimentary cycles occurred since circa 3.45 Ma, it can be compared in depth with the borehole that at the head of Luanhe River fluvial fan. The sedimentary cy- cles happened at 3.2, 3.0, 2.0 and 0.78 Ma respectively overlaid the four stages of lake-limnetic facies sediments. The light yellow/orange sediments in the Latest Glacial Maximum Stage is the same with those found in boreholes on the western coast of Bohai Bay, conforming to the sedimentary characteristic of low- stand system trace. （4） The palaeo-monsoon could lead to the increase in precipitation and formation of lacustrine sediments, however, in this borehole, the highest organic matter content occurred at 6 ka BP, which shows that the hydrothermal condition had been influenced by the Middle Holocene megathermal pe- riod climate greatly.