摘要
磁性地层学研究是建立渤海地区第四纪沉积序列地层年代框架的主要技术手段之一。通过对渤海海峡地区BHS01孔(孔深121.3 m)进行详细的磁性地层学研究,结果表明:BHS01孔岩心记录了布容(Brunhes)正极性时至松山(Matuyama)负极性时底部,包括贾拉米洛(Jaramillo)和奥尔都维(Olduvai)正极性亚时。早、中更新世界线即布容(Brunhes)正极性时/松山(Matuyama)负极性时界限(B/M)深度位于该钻孔的46.4 m处。根据沉积速率,推测钻孔底部121.3 m处的年龄约2.25 Ma。综合沉积物的岩性、磁性及沉积速率变化特征,将BHS01孔沉积物记录的区域沉积过程自下而上划分为3个阶段:阶段Ⅰ(2.25～1.46 Ma)以河流相沉积为主;阶段Ⅱ(1.46～0.78 Ma)为稳定的湖泊相沉积;阶段Ⅲ(0.78～0 Ma)发育海陆交互相沉积。这一研究为该钻孔提供了可靠的年代标尺,为渤海海峡及邻区第四纪地层的划分对比和沉积演化过程提供了新的依据。
Magenetostratigraphy is an effective method to establish reliable geochronological framework,which is critical for reconstructing long-term history of climatic and environmental changes in the past. A detailed palaeomagenetism study on sediments from borehole BHS01(121.3 m) which is located in the Bohai Strait has been carried out. The results show that the core from the borehole consists of three normal magnetozones which can be correlated to Brunhes,Jaramillo,Olduvai. The basal age of the core is estimated at about 2.25 Ma by the extrapolation of the sedimentation rate in the Matuyama Chron. The Brunhes/Matuyama boundary was found at the core depth of 46.4 m. Thus,through the comprehensive analysis of lithologic,magnetic and sedimentary rate characteristics,we divide the evolutional process of BHS01 into three sedimentary phases: phaseⅠ(2.25 to 1.46 Ma) mainly develops in a fluvial sedimentation; phaseⅡ(1.46 to 0.78 Ma) is accompanied with a stable lacustrine sedimentation; and phaseⅢ(0.78 to 0 Ma) develops in a marine and terrestrial sedimentation.Our results provide a reliable chronological framework for the borehole,facilitating the stratigraphic division and evolutional process of the Quaternary in the Bohai Strait and its neighboring regions.