摘要
始新世暖期可为理解现代增温过程和机制提供历史相似型。广泛分布于渭河盆地的红河组为中始新世到晚始新世的滨浅湖相-冲积扇堆积,剖面出露厚度超过330 m,盆地沉积中心钻探厚度大于1000 m,为一套红色的碎屑沉积间化学沉积序列。盆地边缘的红河组沉积物含碳酸盐岩、泥岩、砂岩和少量砾岩,沉积中心以泥质灰岩、泥岩和粉砂岩为主。对蓝田支家沟红河组(时代为46~33 Ma)2910个样品的磁化率测试表明,红河组沉积物磁化率值在0~20×10^(-8)m^(3)/kg之间,整体偏低,频率磁化率值也相对较低(0~11%),与中国西北部新生代红层磁化率总体较低相似。高分辨率磁化率测试证实了红河组堆积时期干湿变化的多旋回和阶段性,受到太阳辐射变化影响,并受到下垫面的反馈驱动。红河组泥岩和粉砂岩的磁化率值偏高,而砂岩的磁化率值较低,载磁矿物以赤铁矿为主。盆地周围岩体弱磁性物质的快速输入,降低了红河组粗颗粒沉积物的磁化率值。在中、晚始新世的轨道-构造时间尺度,红河组沉积序列粒度变化受到湖面波动控制。湖面上升时湖滨地区沉积物颗粒偏细,磁化率值高;反之,磁化率值低。因此,磁化率高低变化指示了湖面高低波动,进而指示了气候的干湿变化。分析还表明,中、晚始新世渭河盆地湖面多旋回变化和阶段性变干,与全球温度变化和降温过程可良好对比,指示全球温度降低可能抑制水汽循环,进而驱动始新世东亚内陆干旱的发展。
The Eocene warm period can provide an analog for understanding current climate warming and its forcing mechanism.The Honghe Formation,an alluvial to lacustrine deposits,is widely distributed in deep part of the Cenozoic deposit of the Weihe Basin,Central China.There are more than 330 m thick in the outcrop and more than 1000 m deep in the depocenter,the Honghe Formation is red sedimentary sequence with detritus and chemical deposits.There are carbonate,mudstone,sandstone and few conglomerate at the margin of basin and mainly argillaceous limestone,mudstone and siltstone in depocenter in the Weihe Basin during the Eocene.We took samples from the 330 m sedimentary stratum of the Honghe Formation at 10 cm intervals from Wangpingcun(WPC)site(34°18′N,109°12′E).The sequence of Honghe Formation is dated between 46~33 Ma by a magnetostratigraphy analysis.Our low-and high-frequency magnetic susceptibility(MS)analyses of 2910 bulk samples show that the MS varied in 0~20×10^(-8) m^(3)/kg,these are lower MS value compared with the Chinese loess-paleosol deposit sequence at same site,but corresponding the low MS value of Paleogene sediments in North China;meanwhile,the frequency MS is relatively lower with value of 0~11%,showing a strongly weathering thus magnetite and maghematite were oxidized to hematite,along with low MS and/or anti-magnetic sediments input,caused the lower MS value of sediments of the Honghe Formation.Our MS time series show multi-cycle and long-term hydroclimate variations,which are influenced by variations of insolation and earth surface feedback.Our analysis also show that mudstone and siltstone samples have higher MS,but sandstone samples have lower MS.The thermal demagnetization curve reveal that hematite is the main magnetic mineral in the bulk samples.Moreover,grain size variations of Honghe Formation sedimentary sequence were controlled by variations in lake levels.During high lake level,sediment in lakeshore was finer and MS values were higher,and vice versa.Therefore,variations of MS values can indicate fluctuations of lake level and variations of hydroclimate.The multi-cycle variations of lake level and stepwise drying in the Weihe Basin during the Middle to Late Eocene can be well compared with decrease in global temperature,which may modulate water cycle and aridification of interior East Asia during the Cenozoic era.
作者
郁晓春
鹿化煜
吕恒志
王可欣
杨帆
赖文
YU Xiaochun;LU Huayu;LU Hengzhi;WANG Kexin;YANG Fan;LAI Wen(School of Geography and Ocean Science,Nanjing University,Nanjing 210023,Jiangsu;Institute of Global Environmental Change,Xi'an Jiaotong University,Xi'an 710054,Shaanxi)
出处
《第四纪研究》
CAS
CSCD
北大核心
2024年第2期325-337,共13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。
关键词
中-晚始新世
渭河盆地
磁化率
河湖相沉积物
古气候变化
Middle to Late Eocene
Weihe Basin
magnetic susceptibility
fluvial and lacustrine deposit
paleoclimate variations
