秦岭东段卢氏盆地始新世沉积序列与气候环境变迁  

THE DEPOSITIONAL SEQUENCE AND PALAEOCLIMATIC AND PALEOENVIRONMENTAL VARATIONS AT LUSHI BASIN,CENTRAL CHINA DURING THE MIDDLE EOCENE

作　　者：邵可涵 鹿化煜[1] 梁承弘 李广伟 高鑫 吕帆 赖文 汪颖珊 陈璇璇 吕恒志 SHAO Kehan;LU Huayu;LIANG Chenghong;LI Guangwei;GAO Xin;LU Fan;LAI Wen;WANG Yingshan;CHEN Xuanxuan;LU Hengzhi(School of Geography and Ocean Science,Nanjing University,Nanjing 210023,Jiangsu;School of Earth Science and Engineering,Nanjing University,Nanjing 210023,Jiangsu)

机构地区：[1]南京大学地理与海洋科学学院,江苏南京210023 [2]南京大学地球科学与工程学院,江苏南京210023

出　　处：《第四纪研究》2024年第2期251-264,共14页Quaternary Sciences

基　　金：国家自然科学基金创新研究群体项目(批准号:42021001);国家自然科学基金重点国际(地区)合作研究项目(批准号:41920104005)共同资助。

摘　　要：始新世是新生代重要的暖期,其气候环境的特征与演化备受学界关注。位于秦岭东段的卢氏盆地保存了> 1000 m厚的连续的始新世河湖相沉积物,是揭示古气候和环境变化规律的宝贵沉积记录。在前人工作基础上,本研究利用沉积学、古生物学、碎屑年代学等方法对卢氏盆地始新世地层的沉积特征、年代和环境进行了分析。结果表明:1)碎屑磷灰石裂变径迹与碎屑锆石U-Pb年龄指示沉积序列年代晚于约60 Ma,与前人将张家村组-卢氏组化石组合对比到中始新世的结论基本吻合。2)始新统张家村组沉积相演化表现为冲积扇→河流→洪泛平原或滨湖,反映盆地拉张、初期成湖的过程;卢氏组为滨浅湖→深湖/半深湖→滨浅湖或洪泛平原→浅湖/半深湖,反映湖泊开始稳定出现后的扩张、收缩和复活过程;大峪组为河流→洪泛平原→冲积扇,反映湖泊淤满消亡后河流与冲洪积物相继充填的历史。3)沉积相、化石组合、盐类矿物种类揭示中始新世卢氏盆地古气候为半湿润半干旱,地表景观呈现径流活跃、动物种类多样、树木茂盛、发育淡水至微咸水湖的特征,并可能具有一定的季节性。卢氏盆地沉积序列提供了始新世暖期中国中部气候环境变化的重要证据。Eocene is one of the most important warm periods in Cenozoic era.Reconstruction of paleoclimate and paleoenvironment variations can help us to understand more about the Eocene world.Here we report a comprehensive analysis of age control,sedimentary sequence,and environmental indication of Eocene deposits in Lushi Basin,East Qinling Mountains,Central China.Lushi Basin(33°57'~34°10'N,110°50'~111°14'E)is a rifting basin with an area of approximately 300 km².Over 1000 m thick fluvial-lacustrine sediments of the Eocene continuously deposited in the basin,making it suitable for reconstructing Eocene climate and environment.(1)The youngest age peaks of detrital apatite fission tracks(AFT)and zircon U-Pb dating analyses can constraint the oldest depositional age of sampling sequence.Our youngest AFT age peak(63±12 Ma)and youngest zircon(ca.60 Ma)show that the depositional sequence in Lushi Basin is younger than ca.60 Ma.This result supports the previous biostratigraphy studies suggested that fossil assemblages of mammals in Zhangjiacun Formation to Lushi Formation can be compared to the Middle Eocene.(2)The lowest strata,Zhangjiacun Formation(73.3 m thick)shows transition of sedimentary facies from alluvial fan to river,and then to flooded plain or shallow lake,recorded the process of basin extension and early lake formation.Lushi Formation(265.4 m thick)overlying on Zhangjiacun Formation,mainly consists of carbonates and mudstones,recorded sedimentary faces of shallow lake→deep lake or semi deep lake→shallow lake or flood plain→shallow lake or semi deep lake from the bottom to top,indicating the expansion,shallowing and recovery of Lushi paleolake.The uppermost strata,Dayu Formation(652.3 m thick)shows sedimentary facies transition from river to flood plain,and finally to alluvial fan,indicate that alluvial fans and rivers continued to be active after the vanish of lakes.(3)Paleoclimate and paleoenvironment variations revealed by sedimentary facies,fossils and types of chemical deposits in Lushi Basin shows

关 键 词：中始新世 沉积环境 卢氏盆地 秦岭东段 古气候 

分 类 号：P534.613[天文地球—古生物学与地层学] P512.2[天文地球—地质学]