张瀚之,
王逸超,
赵琳,
王翰林,
孙文峰,
张红艳
南京大学地理与海洋科学学院, 江苏省气候变化协同创新中心, 江苏 南京 210023
基金项目: 国家自然科学基金项目（批准号：41690111）和国家重点研究发展计划——全球变化及应对项目（批准号：2016YFA0600503和2016YFE0109500）共同资助
详细信息
作者简介: 鹿化煜, 男, 50岁, 教授, 环境演变、地貌过程、古气候和全球变化研究, E-mail:huayulu@nju.edu.cn
中图分类号: P534.6;P56;P532 收稿日期:2018-06-26
修回日期:2018-07-28
刊出日期:2018-09-30
Cenozoic depositional sequence in the Weihe Basin (Central China): A long-term record of Asian monsoon precipitation from the greenhouse to icehouse Earth
Lu Huayu,Zhang Hanzhi,
Wang Yichao,
Zhao Lin,
Wang Hanlin,
Sun Wenfeng,
Zhang Hongyan
School of Geography and Ocean Science, Jiangsu Provincial Collaborative Innovation Center of Climate Change, Nanjing University, Nanjing 210023, Jiangsu
MSC: P534.6;P56;P532
--> Received Date: 26 June 2018
Revised Date: 28 July 2018
Publish Date: 30 September 2018
摘要
摘要:亚洲季风气候起源与演化受海陆地貌格局和全球温度变化等影响。关于亚洲季风气候起源的时间，有第四纪早期、晚中新世、早中新世至渐新世晚期、始新世等多种说法。获得连续的长时间的季风气候变化记录，是认识亚洲季风起源和演化过程的关键。渭河盆地位于我国中部，是一个处于现代亚洲季风降水影响边缘区域的断陷盆地。从始新世开始，渭河盆地接受了厚度超过7000 m的较为连续的河湖相沉积物，在晚中新世约7 Ma开始堆积同期异相的风尘沉积。盆地汇集了1.35×105 km2受季风降水控制的渭河流域地表径流，因此，渭河盆地可以看作是新生代亚洲季风降水的雨量筒。过去10年，我们对渭河盆地新生代红河组、白鹿塬组、冷水沟组、寇家村组、灞河组、蓝田组和三门组、洩湖组等沉积序列进行了调查研究，通过生物地层、磁性地层和古气候代用指标的综合分析，认为渭河盆地的沉积序列记录了从中始新世温室地球（greenhouse）到渐新世、中新世、上新世和更新世与全新世冰室地球（icehouse）亚洲季风降水阶段演化的过程。研究认为，在从中始新世约45 Ma到晚上新世约3.4 Ma漫长的气候演化过程中，渭河流域处于相对温暖湿润的气候环境，降水量较多；早更新世约2.6 Ma以来，降水总体减少，在冰期-间冰期时间尺度变幅和变频增大。季风降水的这种两阶段演化可能受到全球温度（尤其是北半球冰量）演化的驱动，也与海陆地形格局、喜马拉雅-青藏高原生长和副特提斯海退缩有一定的联系。亚洲季风降水演化是在新生代全球气候变化背景下的区域响应，与在不同温度条件下赤道辐合带（ITCZ）移动驱动的季风降水带位置和宽度有关。
关键词: 渭河盆地/
新生代/
河湖相沉积/
温室地球/
季风降水/
亚洲季风起源和演化
Abstract:The onset and evolution of the Asian monsoon system has long been a topic of hot debate. Suggested onset time in past studies include Eocene(ca. 50 Ma), Early Miocene(ca. 22 Ma), Late Miocene(ca. 8 Ma), Late Pliocene and Early Pleistocene(ca. 2.6 Ma) based on different geological records, proxy indicators, as well as numerical simulations. Several factors contribute to such great uncertainties in these results, such as misinterpretation of proxy indices of paleoclimate, incomplete geological records, and poor age constraints for the depositional sequences. Therefore, there is a great need for a reliable long-term and continuous record of Asian monsoon variations. The Weihe Basin is a mid-sized basin formed during Cenozoic in Central China. It is located at the margin of the Asian monsoon region, therefore sensitive to changes in monsoon precipitation. The basin contains more than 7000 meters of unconsolidated fluvial-lacustrine deposit, forming a nearly continuous sequence from mid-Eocene to Holocene. Monsoon precipitation determines the amount of runoff in the Weihe River catchment, which in turn controls the deposition. Therefore the sedimentary sequence is an excellent archive of the long-term variations of the Asian monsoon system. We conducted comprehensive analyses of the depositional facies and stratigraphy, mammal fossil assemblage, pollen, and stable oxygen and carbon isotope composition of the sedimentary records. Our results show that monsoon precipitation probably started during the mid-Eocene, at least ca. 45 Ma, with an annual precipitation of ca. 1200 mm, but the modern monsoon circulation pattern was not established until the Early Pleistocene, ca. 2.6 Ma, with the annual precipitation of 600~700 mm. The collision of the Indian and Eurasia Plates at Paleogene e.g. 60 Ma built the Asian topography, and the thermal contrast between the great continent and the oceans at that time could have initiated the Asian monsoon circulation. This monsoon circulation was then further strengthened by each of the following events:close of the para-Tethys Sea during Late Eocene and Early Oligocene(ca.34 Ma), the orographic growth of Himalayan-Tibetan Plateau during the Early Miocene(ca. 24 Ma), and the high-latitude cooling in the Northern Hemisphere during the Late Miocene(ca. 8 Ma). However, before the Late Pliocene, ca. 3.4 Ma, the changes in monsoon intensity was small and incremental. The modern monsoon circulation is likely to be finally established at ca. 2.6 Ma, when the great Northern Hemisphere Glaciation pushed the intertropical convergence zone(ITCZ) toward the equator and compressed the monsoon rain belt. The monsoon system evolved through the shift between the greenhouse and icehouse Earth at Early Oligocene with the onset of the Antarctic ice sheet, but the global climatic cooling and the topographic change at that time did not completely set up the modern Asian monsoon circulation. The monsoon circulation was finally established by the northern hemisphere cooling during the Late Pliocene and Early Pleistocene. Moreover, the Asian deformation and surface uplift has contributed to the Asian monsoon evolution during Cenozoic.
Key words:Weihe Basin/
Cenozoic/
fluvial-lacustrine depositional sequence/
greenhouse Earth/
monsoon rainfall/
onset and evolution of Asian monsoon
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