河南平原濮阳市BK1钻孔第四纪地层划分和环境演化

STRATIGRAPHIC SUBDIVISION OF QUATERNARY SEDIMENTS AND ENVIRONMENT EVOLUTION OF BK1 BOREHOLE IN PUYANG CITY,HENAN PLAIN

第四纪标准钻孔地层剖面可以为浅层地震勘探剖面的反射层位标定和地质解释提供有效的标尺,是城市活断层及地震危险性评价的基础工作。本文在地层岩性特征分析的基础上,利用孢粉和古地磁、电子自旋共振(ESR)、光释光(OSL)等测试分析技术,将濮阳市BK1钻孔自下而上划分为早更新世晚期、中更新世、晚更新世早期及全新世地层沉积序列,缺失晚更新世晚期沉积地层。钻孔揭露下更新统厚31.35 m(180.5—149.15 m,未揭穿),为冲积-湖积相;孢粉带Ⅰ(173.5—149.5 m)记录了早更新世晚期冷干气候。中更新统厚79.7 m(149.1—69.4 m),以冲积相为主,夹洪积相;孢粉带Ⅱ(139.5—137.6 m)、孢粉带Ⅲ(117.5—96.5 m)、孢粉带Ⅳ(96.5—92.0 m)记录了中更新世冷干-温干-冷干气候特征。上更新统厚27.4 m(69.4—42.0 m),底界面埋深69.43 m,为冲积相;孢粉组合带Ⅴ(69.5—42.5m)记录了晚更新世早期温干气候。孢粉组合带缺失晚更新世晚期凉干气候记录,结合地层年龄数据,笔者认为BK1钻孔缺失晚更新世晚期沉积地层。全新统厚42m(42.0—0m),底界面埋深42m,为冲积相夹沼泽相;孢粉带Ⅵ(15.3—1.4 m)记录了全新世晚期凉干气候。BK1钻孔揭示的第四纪不同时段较大的沉积速率差异是长期构造沉降、气候变化等因素共同作用的结果。

Standard borehole exploration is the main technical means of Quaternary research.Reasonable division of the Quaternary is of great significance for the calibration of the reflection horizon in the shallow seismic exploration.Quaternary strata of the BK1 borehole from Puyang City have been carried out,based on the systematic analysis of Optical Stimulated Luminescence Dating(OSL),Electron Spin Resonance Dating(ESR)and pollen data.Results show that the sediments with the depth of 180.5-149.1 m,149.1-69.4 m,69.4-42.0 m and 42.0-0 m have been formed during the late stage of Early Pleistocene,Middle Pleistocene,early stage of Late Pleistocene and Holocene,respectively.Late stage of Early Pleistocene were alluvial and lacustrine fancies.The pollen groupⅠrecords the cold and dry climate during the late stage of the period.Middle Pleistocene were alluvial and flood facies.The pollen groupsⅣ-Ⅲ-Ⅱrecord the climate change of cold and dry-warm and dry-cold and dry in this period.Early stage of Late Pleistocene were alluvial facies.The pollen groupⅤrecords the warm and dry climate during the early stage of the period,but lack in the information of cold and warm climate of the late stage of the Late Pleistocene.Holocene were alluvial and swamp facies.The pollen groupⅥwith the depth of 15.3-1.4 m records the cold and dry climate during the late stage of the period.And the large differences of sedimentary rate of the Quaternary BK1 hole were obviously influenced by regional tectonic activities and climatic change.