天山北麓黄土记录的30万年以来古气候演变  

Paleoclimatic Changes Since 300 ka Recorded by Loess Deposits Along the North Pediment of Tianshan Mountains

作　　者：陈渠[1] 刘秀铭[2,3] 吕镔[2,3] 叶玮[1] 赵国永 CHEN Qu;LIU XiuMing;LÜ Bin;YE Wei;ZHAO GuoYong(College of Geography and Environmental Sciences,Zhejiang Normal University,Jinhua,Zhejiang 321004,China;School of Geographical Sciences,Fujian Normal University,Fuzhou 350007,China;State Key Laboratory for Subtropical Mountain Ecology of the Ministry of Science and Technology and Fujian Province,Fujian Normal University,Fuzhou 350007,China;School of Geographical Sciences,Xinyang Normal University,Xinyang,Henan 464000,China)

机构地区：[1]浙江师范大学地理与环境科学学院,浙江金华321004 [2]福建师范大学地理科学学院,福州350007 [3]福建师范大学湿润亚热带山地生态国家重点实验室培育基地,福州350007 [4]信阳师范学院地理科学学院,河南信阳464000

出　　处：《沉积学报》2022年第3期679-690,共12页Acta Sedimentologica Sinica

基　　金：国家自然科学基金(41402155,41772180,41877435)。

摘　　要：对天山北麓黄土分布特点与形成年代的研究,以及以此为载体应用各代用指标的古气候重建已经取得了不少进展。在前人工作的基础上,选取黄土—古土壤序列分明,底部S3古土壤发育的鹿角湾剖面为主要研究对象,结合天山北麓的其他多个典型黄土剖面,运用色度、粒度、常量地球化学元素含量和环境磁学参数等指标,探讨大约30万年以来的古气候演变。鹿角湾黄土实验结果显示,各古气候代用指标随剖面深度变化与黄土—古土壤更替大概一致,剖面上部(L2及其以上)与下部区别明显。粒度分布揭示黄土物源输入主要受控于两股不同风系,随黄土古土壤的更替两者的主次地位发生变化。环境磁学实验结果显示,剖面下部磁性弱,频率磁化率低,但古土壤层稳定单畴含量较高,反映湿润成壤环境下超顺磁亚铁磁性矿物溶解或转化为弱磁性矿物;剖面上部比剖面下部的磁性要强,磁性矿物粒度更粗;S0为磁性成壤增强模式,与其他黄土古土壤层不同。再结合其他典型剖面的记录,可以推断研究区30万年以来有干旱化的趋势,但S2发育阶段总体上可能比S3发育阶段略为湿润,这一阶段之后气候明显变干,S1发育阶段明显比S2与S3发育阶段干旱,干旱化趋势一直保持至全新世开始之前。Considerable progress has been made in studies of the distribution,age and paleoclimatic significance of loess deposits in arid central Asia. However,the focus has been on long-term drying trends(since 800 ka)or shortterm moisture evolution(since the last interglacial or during the Holocene). The paleosols are generally undeveloped in the pediment of the Tianshan Mountains,which makes detailed paleoclimate reconstruction difficult. Based on previous work,a number of methods were used in the present study to investigate loess deposit samples from different sections along the north pediment of the Tianshan Mountains. These include a typical loess section at Lujiaowan at relatively high elevation,and sections in low-lying areas along the southern margin of the deserts. The Lujiaowan section consists of four paleosols and intercalated loess dating back to 300 ka. According to the stratigraphic divisions on the Chinese loess plateau,the four down-section paleosols were designated S0,S1,S2(subdivided into S2S1,S2L1 and S2S2),and S3. The sections possess similar variations in color,grain size,geochemistry and rock magnetism with depth,consistent with loess/paleosol alternation. They also indicate a significant change in paleoclimatic proxies at the S2/L2 boundary. The grain size distribution of loess is unimodal,but is bimodal for the paleosols(or broadly unimodal),suggesting that the loess origins are related to two winds,the westerlies and near-surface winds. The variation in the dominance of the winds is consistent with the loess/paleosol alternation. Also,grain sizes are finer in the lower part of the section(S2,L3 and S3)than in the upper part. The chemical index of alteration(CIA)and(CaO+Na;O+MgO)/TiO;ratio indicate more intensive weathering in the paleosols than in adjacent loess units. Integrated rock magnetic analysis indicates that the loess–paleosol sequence experienced three stages in the relation between pedogenetic intensity and magnetic susceptibility in response to different paleoclimates. The lower pa

关 键 词：黄土 古土壤 天山 古气候 气候变化 环境磁学 

分 类 号：P532[天文地球—古生物学与地层学]