摘要
泥河湾盆地是中国北方很重要的沉积盆地,但由于盆地范围较广,局部地区环境变化差异较大,目前对泥河湾盆地的环境变化的认识还较为局限。文章通过对下沙沟剖面(厚度260 m)的河湖相沉积物进行详细的岩石磁学和磁组构研究,以尝试恢复下沙沟地区以及盆地东部古湖环境的演化过程,希望能够对泥河湾盆地环境变化提供一些新的指示。研究结果显示,样品中磁性矿物以PSD的磁铁矿颗粒为主,部分样品中含有少量赤铁矿。下沙沟剖面的沉积物受后期扰动很小,属于正常的重力沉积。沉积物磁面理(F)比磁线理(L)更发育,磁组构参数中磁面理F、各向异性度P;和水流速度函数Fs对环境变化的响应更加明显,古水流分析结果显示下沙沟地区没有长期稳定的流向,环境变化情况复杂。根据下沙沟剖面河湖相沉积物的磁性地层学年龄框架,以郝家台剖面顶部河湖相沉积物的年龄作为该剖面的顶界,得到了下沙沟剖面2.7~0.3 Ma的磁组构参数变化特征。结合岩性和磁组构参数变化的阶段性特征,将下沙沟地区以及盆地东部古湖环境演化历史分为5个阶段:2.7~2.4 Ma,古湖早期逐渐扩张,于早更新世达到了古湖发育的最盛时期,水体动荡,略不稳定;2.4~1.9 Ma,环境变化主要受气候因素影响,下沙沟地区水动力频繁变化,古湖经历了一次扩张和收缩;1.9~1.3 Ma,下沙沟地区的沉积主要受控于河流作用,盆地东部主要受到构造因素的影响,古湖处于持续收缩的阶段;1.3~0.9 Ma,下沙沟地区环境变化剧烈,受中更新世气候转型的影响较大,古湖东部也较大范围的受到中更新世气候转型的影响;0.9~0.3 Ma,全球气候变化剧烈,对古湖东部环境也有一定的影响,但整体还处于水体较为稳定的湖泊环境,古湖并未开始消亡。
The Nihewan Basin where there are thick fluvio-lacustrine sequences,are rich sources of mammalian faunas and Paleolithic sites,which is a very important sedimentary basin in North China.However,the information about the local regional environments in the Nihewan Basin is limited.In this study,456 oriented samples were collected from the fluvio-lacustrine sequences of Xiashagou section(thickness 260 m)for detailed rock magnetic and magnetic fabric studies.We try to rebuild the environmental evolution process of Xiashagou area and then discuss the evolution of the ancient lake,and provide some new instructions for the environmental changes in Nihewan Basin.We selected 12 typical samples to measure hysteresis loops,isothermal remanence magnetization acquisition and its back-field demagnetization characteristics.The results show that the magnetic minerals in the fluvio-lacustrine sequences are mainly Pseudo-Single Domain(PSD)magnetite particles and a small amount of hematite.The results of magnetic fabric are typical for a primary sedimentary magnetic fabric,which show that the original sedimentary fabric has been preserved in the Xiashagou deposits.The magnetic foliation(F)of sediments was found to be larger than the magnetic lineation(L).F and anisotropy degree(Pj)and the flow velocity function(Fs)in the magnetic fabric parameters are more obviously sensitive to environmental changes.There is no long-term stable flow direction in Xiashagou area.According to magnetostratigraphic age framework of fluvio-lacustrine sequences in Xiashagou section and the top age of fluviolacustrine sediments in the Haojiatai section,the age of the magnetic fabric parameters and magnetic susceptibility change curves in the Xiashagou section is from 2.7 Ma to 0.3 Ma.The analysis of the lithology and the periodic changes of the parameters of the Xiashagou section showed that the environment of the lake has undergone several significant changes during the period of 2.7~0.3 Ma,which occurred at 2.4 Ma,1.9 Ma,1.3 Ma and 0.9 Ma.So the environ
作者
高显丽
李嘉皓
刘平
GAO Xianli;LI Jiahao;LIU Ping(Key Laboratory of Computational Geodynamics,College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049)
出处
《第四纪研究》
CAS
CSCD
北大核心
2022年第2期562-576,共15页
Quaternary Sciences
基金
国家自然科学基金项目(批准号:41974075)
中央高校基本科研业务费专项项目(批准号:Y954025XX2)共同资助。
关键词
泥河湾盆地
下沙沟剖面
磁组构
古湖环境
Nihewan Basin
Xiashagou section
magnetic fabrics
ancient lake environment
