关中盆地新生界地层划分对比与第四纪下限

关中盆地巨厚的新生代沉积为研究区域构造、沉积环境演变与古气候变化研究提供了良好的地质记录,但目前对新生界地层划分和第四纪下限问题仍存在争论。基于钻孔和剖面资料,结合古地磁和生物地层,对关中盆地新生界地层进行了梳理和修订,就第四纪下限和新生界地层划分与对比问题进行了探讨。岩性地层、磁性地层、生物地层证据以及气候变化特征等都支持将第四纪下限定在传统三门组的黄三门与绿三门的交界处或风成黄土与红黏土的界线之处,即松山负极性向高斯正极性转换处(M/G),古地磁年龄为2.6 Ma。基于关中盆地钻孔和剖面的古地磁数据及前人资料,划分了新生界地层,重新厘定了各沉积地层的沉积年代,将新近纪和第四纪沉积分为风成相和河湖相两套同期异相沉积地层序列,风成红黏土的年代延伸到中中新世,建议将中新世的风成堆积命名为段家坡组。这对关中盆地沉积环境形成演化与古气候变化研究、盆地资源开发以及地质工程建设具有重要意义。

黄土高原白水县不同种植年限苹果园土壤重金属含量特征与风险评价

为研究不同种植年龄苹果园土壤中的重金属元素分布特点,评价其污染现状和风险。以黄土高原陕西省白水县果园土壤为研究对象,利用电感耦合等离子质谱法方法对5种不同年龄(5年、10年、15年、20年和25年)苹果园土壤和现代农田土壤以及自然土壤的重金属含量状况进行了测量,并结合单因子污染指数和内梅罗多因子综合指数评价法开展重金属污染风险评估。结果表明Cr, Ni, As, Pb, Hg等元素的平均含量在农田土壤中比苹果园土壤中的高,这些重金属元素在农田土壤中更容易富集;而在苹果园土壤中,Ni, Cu, As, Hg等的平均含量在25年苹果园土壤中相对高于其他年龄苹果园土壤;从综合污染指数看,农田土壤中最高,苹果园土壤中则是随着种植年限的增加而增大。由此说明随着种植年限增加,苹果园土壤中重金属的富集会逐渐显现。但是,以无公害果园和绿色食品产地土壤环境质量为标准,白水土壤完全符合无公害和绿色食品产地对土壤环境的要求。

粒度端元模型在新疆黄土粉尘来源与古气候研究中的初步应用

基于新疆伊犁盆地肖尔布拉克黄土剖面粒度数据,以贝叶斯粒度端元模型法为主,粒级标准偏差法为辅探寻对气候变化响应敏感的粒级组分及其对粉尘来源示踪和古气候重建的意义。研究结果表明粒度端元组分EM1(众数粒径:21.22μm)代表大气粉尘中较为稳定的背景值,其含量的变化与高空西风环流强度有关。EM2(75.29μm)主要代表了近源河流沉积物的悬移搬运组分,可视为较敏感的古气候指标。EM3(47.5μm)也代表了近距离的悬移搬运组分,可能主要由较粗颗粒对地表的碰撞磨蚀作用而产生。EM2记录了深海氧同位素2阶段(MIS2)以来的北大西洋气候波动事件,如Heinrich事件、YD事件等。贝叶斯粒度端元模型能够区分不同的沉积动力过程,在新疆黄土古气候研究中具有广泛的应用前景。

天山北麓地区博乐黄土磁化率、粒度特征与古气候意义

受西风控制的天山地区黄土广泛分布,是中亚重要的黄土分布区之一。这些陆相风成沉积物为研究中亚干旱区气候环境变化历史提供了重要的信息载体。本文选取天山北麓博乐地区一个厚为12.7 m的黄土剖面作为研究对象,分析了其磁化率、粒度指标的变化特征,并探讨了其古气候意义。结果表明:(1)博乐黄土粒度组成以粉砂为主,是典型的风成沉积物,成壤作用很弱;(2)博乐黄土磁化率变化主要受控于风力强度;(3)剖面粒度的环境敏感粒级为<31.7μm、31.7—282.5μm,分别可能代表风暴过后的浮尘堆积和风暴过程中风力近距离搬运的沉积物组分;(4)博乐黄土MIS(海洋氧同位素)3阶段记录了多次千年尺度气候事件,能与北大西洋Heinrich事件和D-O事件对应,表明中纬度西风环流在传递北大西洋信号到东亚的过程中扮演着重要角色。

关中盆地城市群发展中几个关键基础地质问题

关中盆地属于断陷盆地,地质构造复杂,活动断裂发育,地震活动频繁,城市建设中面临一系列重大基础地质问题。在搜集分析关中盆地1 000多个各类钻孔数据的基础上,对关中盆地城市群1∶5万综合地质调查中实施的主要钻井和剖面进行研究,探讨了城市群发展中面临盆地形成演化与活动断裂规避、第四系下限与关中盆地三维地质结构重建、水系演化与城市发展、历史时期古洪水事件与海绵城市建设等基础地质问题。研究表明:①关中裂陷形成于中晚白垩纪,始新世开始成湖,经过多次断陷与隆起,形成2个沉积中心,到上新世时湖泊扩展达到最大范围,盆地第四纪以来仍处于持续、缓慢的下降接受沉积过程,受秦岭持续构造隆升的影响,沉积中心由南向北迁移,这将对城市群布局产生重要影响。关中盆地城市群建设要回避断裂交汇处、端点和断层运动的枢纽部位。②建议将绿三门组划为上新统,不宜划分到第四系,三门组的形成时代是穿时的,在关中盆地第四系与地下空间规划的时候需要进行关注和纠正。③城市规划建设要遵循河湖演化的自然规律和区域地质地貌特征,千年、百年一遇的洪水水位分别高于河漫滩7m和2.2m,最大年降水量超过900mm,但季节分布不均,可作为城市防洪水和海绵城市建设的设计依据。

MoO3/TiO2纳米管的制备及其光催化降解多环芳烃的机制

本研究将热分解法制备的MoO3与水热法制备的TiO2纳米管复合,得到具有高太阳光催化活性的MoO3/TiO2纳米管异质结催化剂.研究中以芘为模型多环芳烃(polycyclic aromatic hydrocarbons,PAHs),探究了MoO3/TiO2纳米管模拟在太阳光下催化降解PAHs的效果及效率提升的机制.结果表明,MoO3和TiO2纳米管间形成的p-n异质结结构,降低了材料的能带间隙而获得更高的可见光利用效率,并有效促进了电子和空穴的分离,从而提高了复合材料的光催化活性.1%MoO3/TiO2纳米管催化降解芘速率(k)较MoO3和TiO2(锐钛矿)分别提升了5.3倍和1.5倍.催化体系中产生的·OH和光生空穴在芘的降解中起主要作用.

MIS3以来天山黄土沉积速率时空分布规律及其意义

风尘堆积沉积速率的变化对揭示大气环流与古气候变化具有重要意义。基于中亚东北部天山及其周边黄土剖面已有的释光和放射性14 C年代数据的分析筛选整理,初步获得了该区深海氧同位素MIS3以来黄土沉积速率的时空变化特征,并探讨了可能的原因。结果表明:(1)末次盛冰期(LGM)沉积速率总体上表现出天山西部低、伊犁盆地高的特征。这种空间变化特征可能与地形、大气环流以及伊犁盆地黄土的近源堆积有关。(2)LGM和MIS3b时期是MIS3阶段以来主要的粉尘沉积阶段。MIS3b时期沉积速率最高,LGM次之,而全新世沉积速率较低。MIS3b时期高的沉积速率可能与大规模的冰川发育有关。在全新世期间,中全新世的沉积速率相对较高,可能与中全新世气候湿润、地表捕获粉尘的能力强有关。

Late Cretaceous-Cenozoic Exhumation History of the L(u|¨)liang Mountains,North China Craton:Constraint from Fission-track Thermochronology

The Lüliang Mountains, located in the North China Craton, is a relatively stable block, but it has experienced uplift and denudation since the late Mesozoic. We hence aim to explore its time and rate of the exhumation by the fission-track method. The results show that, no matter what type rocks are, the pooled ages of zircon and apatite fission-track range from 60.0 to 93.7 Ma and 28.6 to 43.3 Ma, respectively; all of the apatite fission-track length distributions are unimodal and yield a mean length of -13 μm; and the thermal history modeling results based on apatite fission-track data indicate that the time-temperature paths exhibit similar patterns and the cooling has been accelerated for each sample since the Pliocene （c.5 Ma）. Therefore, we can conclude that a successive cooling, probably involving two slow （during c.75-35Ma and 35-5Ma） and one rapid （during c.5 Ma-0 Ma） cooling, has occurred through the exhumation of the Liiliang Mountains since the late Cretaceous. The maximum exhumation is more than 5 km under a steady-state geothermal gradient of 35℃/km. Combined with the tectonic setting, this exhumation may be the resultant effect from the surrounding plate interactions, and it has been accelerated since c.5 Ma predominantly due to the India-Eurasia collision.

Red Clay Sediment in the Central Chinese Loess Plateau and Its Implication for the Uplift of the Tibetan Plateau

The widely distributed red clay sediment underlying the Chinese Loess Plateau truly records the Neogene environmental evolution, and its genesis and development are intrinsically related to the uplift processes of the Tibetan Plateau and the evolution of East Asia monsoon system. In this paper, a detailed magnetostratigraphy of a loess-red clay section (107°13′E, 35°02′N) from the central Loess Plateau is reported. The loess-red clay sequence is composed of 175 m Quaternary loess-paleosol sequence and 128 m Neogene red clay sediments. Based on the correlation with the standard geomagnetic polarity time scale, the paleomagnetic results indicate that the age of Chaona red clay sequence extends to 8.1Ma, which is the older red clay deposition in the central Chinese Loess Plateau. The commencement of red clay at ～8.1 Ma may imply that the Ordos planation surface was broken by the movement of the Haiyuan-Liupanshan Faults, which was related to the uplift of the Tibetan Plateau induced by the collision of India Plate and Eurasian Plate. And the western part adjacent to the Tibetan Plateau was uplifted to form the embryo of the Liupan Shan (Mts.) and the eastern part was down-faulted to receive red clay deposition. We link this faulting to an initial uplift of the Tibetan Plateau. The undulating nature of the broken Ordos planation surface may explain the chronological differences and depth discrepancies among various cross-sections of red clay.

North Atlantic Abrupt Climate Signals during the Last Glacial Period in Central Asia：Evidences from Aeolian Loess Sediments

Objective Climate fluctuations over suborbital or millennial timescale display significant instability during the last glacial period,which are often superimposed upon the orbital periodicity.They triggered some abrupt climate events,

Preliminary Studies of Speleothem in Central Asia

The Westerlies is important in linking the Northem high latitude, North Atlantic and East Asian monsoon. The location and intensity of the Westerly jet can not only control the climate of central Asia （including northwest arid China）, but also significantly influence the climate of the East Asian monsoon region. However, it remains unclear of the variability of the Westerlies in Asia on multiple timeseales and their global linkage.

伊犁盆地北部山麓黄土粒度端元指示的粉尘堆积过程

中亚干旱区是全球重要的粉尘源区,是全球变化与区域响应研究的关键区域之一。中亚粉尘形成搬运沉积过程一直是全球变化研究的热点科学问题。本文选取位于伊犁盆地北部、北天山南麓不同地形和气候条件下的两处黄土剖面,对其沉积速率最高的层段进行了粒度测试分析,结合聚类分析和粒度分布曲线拟合两种方法,重建了黄土粉尘的堆积过程。伊犁盆地黄土主要由远源和近源物质组成,分别由高空西风和中尺度的区域风搬运而来。高空西风所携带的远源粘粒级矿物颗粒对盆地东部降雨较高地区有一定的贡献,而在盆地西部不容易沉降下来。中尺度区域风所搬运的近源物质组成了黄土沉积物的主体,而近源区沉积物的可用性在黄土的形成过程中扮演着重要角色。另外,非风暴过程中(沙尘暴过后)出现的浮尘在沙尘暴天气频率减少的时期对黄土的发育有重要贡献,而在沙尘暴天气频发的时期,较差的植被覆盖度能够使得已经沉降下来的浮尘组分重新被扬起至大气中。由此建立了一个粉尘堆积的概念模型。认识黄土粉尘的堆积过程对现代沙尘天气的治理和人类生存环境的改善具有重要作用。

中亚黄土沉积与西风区末次冰期快速气候变化

气候快速变化过程与机制一直是古气候研究的热点科学问题,随着不同地区高分辨率地质记录的增多,年代学方法的改进,此类快速气候变化事件的区域差异性日益突出,对比和认识这些区域之间的变化细节,有助于认识快速气候变化的规律和驱动机制。文章以中亚黄土为主要研究对象,根据黄土沉积特征与现代气候特征,将中亚黄土分为西部、北部和东部3个亚区,在总结中亚西风区黄土古气候研究进展的基础上,回顾了近年来中亚地区末次冰期西风区气候突变事件研究现状与问题,初步探讨了在亚轨道尺度上末次冰期快速气候变化发生过程和机制。结果表明,粒度、矿物学、地球化学等指标均指示中亚这3个黄土亚区末次冰期确实存在千年尺度的快速气候波动信号,但在年代和变率上存在区域差异,这种差异除了缺乏精确的年代学控制外,还与区域水热组合和区域地形结构有关。这些冷暖的快速气候变化与北大西洋高纬地区冰盖收缩扩张、西伯利亚高压强度和范围的变化导致风动力变化和西风带南北迁移有关。今后需进一步加强高分辨率年代序列的建立,进一步遴选中亚黄土中有效的、能够独立反映风力强度、源区信息、古温度、古降水等代用指标,并结合古气候模拟试验研究其驱动机制。

亚洲风尘循环的过程、机制和环境效应研究进展

亚洲风尘是全球风尘循环中的重要组成部分,其对东亚乃至北半球的气候、生态系统和人居环境产生深远的影响。鉴于亚洲风尘循环在气候环境变化研究中的重要性,国家重点研发计划“全球变化及应对”重点专项于2016年7月正式设立“亚洲风尘循环的过程、机制和环境效应”项目开展相关研究。自启动以来,项目针对亚洲风尘的源汇模式、时空特征及其与全球变化的相互作用等关键科学问题、开展了大量的野外调查与实验分析以及数值模拟工作,在现代和地质时期亚洲(中亚-东亚-北太平洋)风尘排放、迁移和沉降的时空变化特征及其影响机制、亚洲风尘源区风沙活动的生态环境效应以及大气环流对亚洲气溶胶分布及亚洲干旱和季风区降水变化的影响等方面,取得了一系列阶段性进展,本文就此进行了概括和总结,在简要描述亚洲风尘研究背景的基础上对已经取得的主要阶段性成果进行了重点介绍。

蚯蚓方解石颗粒——一种新的古气候信息记录载体

近年的研究表明在第四纪土壤和沉积物中广泛存在由蚯蚓特殊腺体产生的方解石颗粒(ECG)。它们一方面可为放射性碳测年提供有效的测年材料,另一方面能够反映其形成时的温度和降水特征。ECG作为潜在的古环境变化信息的新载体,成为古气候研究领域的新方向。在前人研究工作的基础上,分析了ECG的研究现状,介绍了ECG的产生机理及特征,详细阐述了ECG的碳、氧同位素反映古气候、古环境变化的原理与机制,并介绍了其在年代学、古气候环境重建中的应用,探讨了其作为新指标的可靠性及存在的问题,展望了该领域的研究方向和趋势,希望能对未来的黄土古气候研究提供参考。

New eolian red clay sequence on the western Chinese Loess Plateau linked to onset of Asian desertification about 25 Ma ago

The expansion of inland Asia deserts has considerably influenced the environmental, social and economic activities in Asia. Aridification of inland Asia, especially timing of the initiation of Asian desertification, is a contentious topic in paleoclimatology. Late Cenozoic eolian loess-red clay sequences on the Chinese Loess Plateau, which possess abundant paleoclimatic and paleo-environmental information, can be regarded as an indicator of inland Asia desertification. Here we present a detailed magnetostratigraphic investigation of a new red clay sequence about 654 m in Zhuanglang located at the western Chinese Loess Plateau. Sedimentological, geochemical, mineralogical, and quartz morphological lines of evidence show that the red clay is of eolian origin. Magnetostratigraphic correlations indicate that this core sequence spans from 25.6 to 4.8 Ma, and typical eolian red clay appears as early as 25 Ma. This extends the lower limit of the red clay on the Chinese Loess Plateau from the previously thought early Miocene back into the late Oligocene. This new red clay record further implies that the inland Asia desertification was initiated at least by the late Oligocene. This sequence provides a unique high-resolution geological record for understanding the inland Asia desertification process since the late Oligocene.

Magnetostratigraphy of Late Tertiary sediments from the Chinese Loess Plateau and its paleoclimatic significance

The Late Tertiary red clay/bed sediments underlying the Quaternary loess-paleosol in the Chinese Loess Plateau possesses high-resolution paleoclimatic changes related to the uplift of the Tibetan Plateau. Magnetostratigra-phy and susceptibility measurements are discussed in this paper. The paleomagnetic results show that the red clay/bed began to accumulate at about 8.1 Ma, which represents the oldest Late Tertiary deposit continuously in the central Loess Plateau. The magnetic susceptibility curves show stepwise increases since the initiation of red clay, superimposed on several peaks. Moreover, the magnetic susceptibility increased abruptly since 3.8 Ma, which probably indicates the inception of the modern East Asia monsoon system. Between 3.8 and 2.6 Ma, the stepwise increases of susceptibility may imply progressively intensified East Asia summer monsoon activity related with the stepwise uplift process of the Tibetan Plateau.

Glacial advances and ESR chronology of the Pochengzi Glaciation,Tianshan Mountains,China

The Pochengzi Glaciation is a typical glaciation in Quaternary in the Tianshan Mountains. The glacial landforms comprise several integrated end moraines, like a fan spreading from the north to the south at the mouth of the Muzhaerte River valley and on the piedmont on the southeastern slope of the Tumur Peak, the largest center of modern glaciation in the Tianshan Mountains. The landforms recorded a complex history of the ancient glacier change and contained considerable information of the glacial landscape evolution, and dating these landforms helps us understand the temporal and spatial shifts of the past cryosphere in this valley and reconstruct the paleoenvironment in this region. Electron spin resonance (ESR) dating of the glacial tills in the upper stratum from a well-exposed section, end moraines, and associated outwashes was carried out using Ge centers in quartz grains, which are sensitive to the sunlight and grinding. The results could be divided into three clusters, 13.6–25.3, 39.5–40.4 and 64.2–71.7 ka. Based on the principle of geomorphology and stratigraphy and the available paleoen- vironmental data from northwestern China, the end moraines were determined to deposit in the Last Glaciation. The landforms and the three clusters of ages demonstrate that at least three large glacial advances occurred during the Pochengzi Glaciation, which are corresponding to marine oxygen isotope stage 4 (MIS4), MIS3b and MIS2. The landforms also indicate that the gla- ciers were compound valley glacier in MIS2 and MIS3b and piedmont glacier in MIS4, and the ancient Muzhaerte glacier were 94, 95 and 99 km at their maximum extensions in these three glacial advances.

Development of a pediment on western slopes of Liupan Mountain related to the Neotectonic Uplift

The late Cenozoic uplift of Qinghai-Xizang Plateau plays an important role in adjacent geomorphic evolution and depositional environments. Liupan Mountain, located at the northeast margin of Qinghai-Xizang Plateau, has different landforms on the east and west sides. Recently, a pediment, which lies above the highest terrace of the Yellow River at the northeast edge of Longzhong Basin, has been described. The paleomagnetic measurements indicate that the pediment had developed at least 1.8 MaBP and its age is in accordance with that of the peneplains near Lanzhou and Linxia, in the southwest of Longzhong Basin. The results suggest that the Longzhong Basin lying to the west of Liupan Mountain had been subject to erosion and developed an extensive pediment; this pediment is named the Gansu Period Peneplain. It also indicates that Qinghai-Xizang Plateau and Liupan Mountain were uplifted strongly at that time, which caused not only the end of pediplanation but also Yellow River appearance and loess

Clay mineral records of the Erlangjian drill core sediments from the Lake Qinghai Basin, China

Located at the northeastern margin of the Qinghai-Tibet Plateau(QTP) in the Asian interior, the Lake Qinghai is sensitive to environmental change and thus an outstanding site for studying paleoenvironmental changes. Thick deposits in the Lake Qinghai provide important geological archives for obtaining high-resolution records of continental environmental history. The longest drilling core obtained from the Lake Qinghai, named Erlangjian(ELJ), reached about 1109 m and was investigated to determine its clay mineral assemblage and grain size distributions. Clay mineralogical proxies, including type, composition, and their ratios, as well as the illite crystallinity(KI) and chemical index(CI), in combination with grain size data, were used for reconstructing the history of paleoenvironmental evolution since the late Miocene in the Lake Qinghai Basin. The clay mineral records indicate that the clay mainly comprise detritus originating from peripheral material and has experienced little or no diagenesis. The proportion of authigenic origin was minor. Illite was the most abundant clay mineral, followed by chlorite, kaolinite, and smectite. Variations of clay mineral indexes reflect the cooling and drying trends in the Lake Qinghai region, and the grain size distribution is coincided with the clay minerals indexes. The paleoclimatic evolution of the Lake Qinghai Basin since the late Miocene can be divided into five intervals. The climate was relatively warm and wet in the early of late Miocene, then long-term trends in climate change character display cooling and drying; later in the late Miocene until early Pliocene the climate was in a short relatively warm and humid period; since then the climate was relatively colder and drier. These results also suggest multiple tectonic uplift events in the northeastern QTP.