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1.
Song Zhu Zhenhan Wu Xitao Zhao Jianping Li Keyan Xiao 《Boreas: An International Journal of Quaternary Research》2014,43(2):485-504
Field investigation has shown that the middle reaches of the Yarlung Zangbo River, in Tibet (known as the Bhramaputra River in reaches downstream) has 11 terraces. The ages of these terraces were determined as follows: T11>2000 ka, T10 = 1783 ka, T9 = 1238 ka, T8 = 683 ka, T7 = 382 ka, T6 = 150 ka, T5 = 82 ka, T4 = 67 ka, T3 = 43 ka, T2 = 28 ka and T1 = 10 ka. These terraces formed during several stages of the Quaternary when the Tibetan Plateau was uplifting, recording tectonic–climatic cycles or subcycles of 1.2, 0.4, 0.1, 0.04 and 0.02 million years duration. The tectonic–climatic cycles identified by this study are correlated with red soil and palaeosol records. The preservation of the Oligocene to Early Miocene conglomeratic Dazhuka Formation, close to the present altitude of the main planation surface of the Tibetan Plateau and occurring only in the Yarlung Zangbo valley, suggests that this river has existed since at least 7 Ma. Discoveries of old and thick fluvial gravel layers extending to within 630 m of the valley floor show that the Yarlung Zangbo River was already incised by 2000 m or more below the surface of the Tibetan Plateau, that much of the incision from plateau to valley floor had been accomplished and that the plateau was already substantially uplifted prior to the Quaternary. In addition to its importance for understanding the evolution of the Tibetan Plateau, this study documents the impact of varying rates of tectonic uplift on river development. 相似文献
2.
黄河干流奇特的"几"字形格局是其复杂发育历史的表现。由于流域内的地质与气候条件复杂多样,分段开展深入研究是全面认识黄河的基础。晋陕峡谷是研究黄河演化的关键地段之一,河流阶地忠实地记录着河流发育的历史。文章选择山西河曲县城附近黄河阶地发育典型的河段进行研究,在实测河流阶地地貌剖面的基础上,系统采集了20个年代样品进行光释光(OSL)测年。依据地貌类型、沉积特征以及定年结果,建立了该河段黄河阶地的演化序列,得出以下结论:1)河曲地区黄河曲流凸岸形成有4级阶地,T4阶地的形成主要受构造控制,而T3,T2和T1阶地的形成主要与气候变化有关,各阶地的年龄分别是T4为90ka,T3为30ka,T2为20ka,T1为3.4ka。2)河曲地区约140ka以来河流地貌的演化经历了5个阶段,各阶段以下切侵蚀开始,结束于各阶地堆积面的塑造。约90ka以来,该地区河谷谷底下降速度和曲流可能最大侧蚀速度的平均值分别为0.9mm/a和33.4mm/a。在不同阶段,二者的大小变化及组合状况各异,在构造相对稳定条件下,河流以侧蚀作用为主,其侧蚀速度与气候和岩性条件有关。3)河曲地区的黄河曲流是在河流下切过程中逐渐侧蚀、演化而成的,具有内生曲流的特点。4)T4阶地的泥流沉积和加积堆积,可能记录了地方性气候变化,其范围和意义有待进一步研究,另外,T3,T2和T1形成过程中气候变化的作用也有待探讨。 相似文献
3.
Xianyan Wang Ronald van Balen Shuangwen Yi Jef Vandenberghe Huayu Lu 《Boreas: An International Journal of Quaternary Research》2014,43(2):469-484
In the Northeastern Tibetan Plateau (NETP), the courses of the Huang Shui and Huang He near their confluence are characterized by alternating gorges and wide depressions, segmenting the fluvial systems. The river valleys have developed terrace staircases, which are used to infer relative tectonic motions between the segments. The terrace staircases are correlated by means of relative height and optically stimulated luminescence (OSL) dating. At least eight terraces are present, two of which have been dated by OSL (the sixth and the third ones; c. 70 and c. 24 ka, respectively). The correlated longitudinal terrace profiles show no distinct relative tectonic movements within the confluence area, demonstrating that this area behaved as one tectonic block. The correlation of the terrace staircase of this block with areas upstream (Xining area) and downstream (eastern Lanzhou area) indicates relative tectonic movements, which therefore represent different tectonic blocks. The fluvial incision rate since c. 70 ka was much higher in the confluence area than in the blocks upstream and downstream, possibly indicating relative uplift. This relatively strong uplift provided more space for differentiation within the terrace staircase as a result of climatic changes, leading to six terraces formed as a response to minor climatic fluctuations (103–104 year timescale) since the last interglacial. This may indicate that the stronger the tectonic movement the better the climatic imprint as expressed in the form of terrace development. Over a shorter timescale, two accumulation terraces with thick stacked deposits (>18 m) may indicate relative subsidence in the confluence, occurring sometime between 20 and 70 ka. This indicates changes in relative vertical crustal motions at timescales of tens of thousands of years. We speculate that the inferred tectonic motions are related to transpression movements in the NETP as a result of the collision of the Indian and Asian plates. 相似文献
4.
Guifang Yang Xujiao Zhang Mingzhong Tian Yamin Ping Anze Chen Zhiliang Ge Zhiyun Ni Zhen Yang 《Environmental Earth Sciences》2011,64(3):671-683
The Zhangjiajie Sandstone Peak Forest Geopark (Zhangjiajie World Geopark) of northwest Hunan, China hosts a well-preserved
sequence of fluvial terraces and karst caves. In this contribution, a comparative study of fluvial terraces with karst caves
along the middle-lower Suoxi River in Zhangjiajie World Geopark is presented to improve the understanding of the development
of striking sandstone landscape in the upper Suoxi River. By integrating geomorphological, sedimentological, and geochronological
techniques, the possible correlation between fluvial terraces and karst caves, as well as their climatic and tectonic implications
is investigated. The available electron spin resonance and thermo-luminescence numerical ages coupled with morphostratigraphic
analysis indicate that aggradation of fluvial terrace levels occurred at ca. 347 ± 34 ka (T4), 104.45 ± 8.88 to 117.62 ± 9.99 ka (T3), 60.95 ± 5.18 ka (T2), and Holocene (T1), followed by the stream incision. Fluvial terrace levels (T4 to T1) correlate morphologically with the karst cave levels (L1 to L4), yet the proposed chronology for the fluvial terrace levels is a bit later than the chronological data obtained from karst
caves. In northwest Hunan, where a unique sandstone peak forest landscape was extensively developed, the fluvial terrace sequences
as well as the cave systems are the important archives for studying the evolution of the sandstone landscape. The beginning
of the sandstone landscape development must be earlier than the aggradation of the fluvial terrace T4, allowing this unique landscape to occur in the Middle Pleistocene. 相似文献
5.
青藏高原西北部晚第四纪以来的隆升作用 ——来自西昆仑阿什库勒多级河流阶地的证据 总被引：6，自引：4，他引：2
青藏高原的隆升是新生代最壮观的地质事件,关于青藏高原隆升研究一直是地学界的研究焦点.河流阶地的发育记录了丰富的构造运动和气候变化的信息,近年来被广泛应用于构造运动和气候演变的研究,但前人研究的河流阶地基本分布在青藏高原的周缘,阶地的形成可能是气候与构造运动共同作用的结果.本文通过高分辨率卫星影像的解译,在青藏高原内部的西昆仑阿什库勒地区发现了多达七级的河流阶地.对该处河流阶地结构、沉积特征、几何特征的研究表明该阶地是典型的构造成因阶地.野外利用全站仪对河流阶地地貌形态进行了精细的测量,获得了各级阶地的拔河高度分别为4～5m(T1)、9～ 10m(T2)、16 ～ 18m(T3)、28～31m(T4)、45～48m(T5).通过宇宙成因核素10Be测年方法对各级阶地面的暴露年龄进行了测定,获得了各级阶地的形成时代分别为7.7±0.7ka(T1)、32.7±3.lka (T2)、53.6±2.5ka(T3)、115.7±23.2ka(T4)、166.8±10.4ka (T5)、19.5±8.5ka (T6).由此确定了晚第四纪166.8ka以来不同时期的河流下切速率总体介于0.2～0.35mm/yr,该速率代表了青藏高原西北部晚第四纪166.8ka以来的平均隆升速率. 相似文献
6.
六盘山东麓泾河上游河流阶地的形成年代及新构造运动意义 总被引：1，自引：0，他引：1
六盘山是研究青藏高原东北缘隆升与构造变形的关键部位,其东麓泾河河流阶地是第四纪以来六盘山构造隆升的地貌载体。通过对泾河上游河流阶地的剖面实测,厘定了河流阶地的级序,泾河上游主要发育5级河流阶地T5-T1,不同地段阶地的形态类型不同,柳树沟T5、T4和T3为堆积阶地,T2和T1为基座阶地,高家山均为侵蚀或基座阶地;利用光释光(OSL)、电子自旋共振(ESR)测年并与黄土-古土壤序列进行对比,建立了河流阶地的年代格架,T5-T1年代分别为541 ka B.P.、477 ka B.P.、279 ka B.P.、60 ka B.P.和8 ka B.P。阶地的形态类型、形成年代与气候阶段的对应关系研究表明,泾河上游河流阶地以构造隆升驱动为主,气候变化影响为辅;541~279 ka B.P.期间柳树沟地区为堆积区,堆积速率为0.31 m/ka,而高家山为构造隆升区,河流下切速率为0.37 m/ka,堆积速率与侵蚀速率基本一致,说明T5、T4和T3阶面上较厚的砾石层是六盘山隆升的相关沉积;279 ka B.P.时期由于六盘山快速隆升驱使山前柳树沟地区由堆积区转为侵蚀区,河流侵蚀作用加强造成T2、T1平均下切速率增大为1.13 m/ka,这次地貌转换事件是在青藏高原扩展隆升的背景下六盘山向东挤出隆升的结果。研究结果为青藏高原东北缘以面积和体积扩张的观点提供了新的依据。 相似文献
7.
祁连山是研究青藏高原隆升与构造变形的关键部位,其中大通河河流阶地是祁连山地区早更新世以来构造隆升和气候变化的载体,厘定大通河河流阶地的形成时代及地质意义对于分析祁连山地区的区域构造和气候环境改变具有重要意义。通过ESR测年技术,并对大通河流域江仓区域的剖面样品实测,获取岩层形成时代数据,分别为(42±4) ka B.P.、(71±5) ka B.P.、(121±12) ka B.P.、(210±20) ka B.P.和(602±60) ka B.P.。根据测年结果,确认剖面为河流相沉积环境,形成时代对应中晚更新世酒泉砾岩和戈壁砾岩时期,表明大通河河流阶地在542~662 ka B.P.之前就已经形成,推测其可能是受到中新世白杨河组之后的盆山运动或早更新世祁连山的褶皱变形影响而形成的。利用测年数据计算抬升速率,从中更新世晚期到晚更新世中期,抬升速率加快,反映了大通河流域的构造运动和气候变化加强,祁连山江仓地区在此期间快速隆升,为青藏高原东北缘以面积和体积扩张的观点提供了新的依据。 相似文献
8.
Baotian Pan Huai Su Zhenbo Hu Xiaofei Hu Hongshan Gao Jijun Li Eric Kirby 《Quaternary Science Reviews》2009,28(27-28):3281-3290
The competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain. Most of recent studies have attributed terrace formation to climatic changes and held that, even in tectonically active settings, climate variations control cycles of terrace planation and abandonment. Based on field investigations of loess-paleosol sequences, magnetostratigraphy and optically stimulated luminescence (OSL) dating, we develop a new chronology for a spectacular flight of terraces along the Yellow River near Lanzhou, China over past 1.24 Ma. All the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads, suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates. However, the ages of terraces cluster in two relatively short time periods (1.24–0.86 Ma and 0.13 Ma – present). During the intervening time between 0.86 Ma and 0.13 Ma, terraces either did not form or were not preserved. We suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation/preservation. Thus, our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision. 相似文献
9.
贵州涟江惠水段级次清晰的四级阶地是流域地貌阶段性演化的直观记录。笔者等利用差分GPS测量法精确厘定了涟江阶地的级序和高程,结合剖面观测发现从上游到下游,涟江惠水段阶地标高和级差逐渐降低,地貌面整体呈“收拢”趋势;阶地沉积物呈现砾石层厚度变小,砾石含量降低、砾径减小,砂质沉积占比增大趋势;阶地类型从基座阶地为主向堆积阶地为主演变。光释光(OSL)测年显示,T1阶地埋藏年龄31.2±2.0 ka BP到14.7±1.3 ka BP,T2阶地122.4±8.5 ka BP到66.9±3.8 ka BP,阶地年龄与贵州高原其他流域十分相近,具有同步演化特征。结合阶地时代和发育特征,认为贵州高原河流阶地是构造运动的产物。涟江四级阶地记录了在更新世以来四次构造抬升背景下,流域经过多期自北向南“削高补低”的地貌改造,逐步由构造洼地演变为山间盆地的地貌过程。 相似文献
10.
贵州涟江惠水段级次清晰的四级阶地是流域地貌阶段性演化的直观记录。笔者等利用差分GPS测量法精确厘定了涟江阶地的级序和高程,结合剖面观测发现从上游到下游,涟江惠水段阶地标高和级差逐渐降低,地貌面整体呈“收拢”趋势;阶地沉积物呈现砾石层厚度变小,砾石含量降低、砾径减小,砂质沉积占比增大趋势;阶地类型从基座阶地为主向堆积阶地为主演变。光释光（OSL）测年显示,T1阶地埋藏年龄31.2±2.0 ka BP到14.7±1.3 ka BP,T2阶地122.4±8.5 ka BP到66.9±3.8 ka BP,阶地年龄与贵州高原其他流域十分相近,具有同步演化特征。结合阶地时代和发育特征,认为贵州高原河流阶地是构造运动的产物。涟江四级阶地记录了在更新世以来四次构造抬升背景下,流域经过多期自北向南“削高补低”的地貌改造,逐步由构造洼地演变为山间盆地的地貌过程。 相似文献
11.
Based on the study of magnetostratigraphy, magnetic susceptibility and grain size of Garzê A section on the southeastern margin of the Qinghai-Tibetan Plateau since the late early-Pleistocene, the basal age of Garzê loess is located at ~1.16?MaBP and a series of abrupt paleoclimatic changes is detected. The times of abrupt changes are of distinct series features, and the interval between each two adjacent abrupt changes is ~50 kyr or ~100?kyr. The most significant abrupt changes occur at around 1.06, 0.85, 0.6, 0.46, 0.39 and 0.14?MaBP. There is a chronological link between the abrupt changes of paleoclimate and the formation of river terraces and it is almost simultaneous with a strengthening trend of neotectonic activities. Therefore, maybe the climatic transition controll the timing of terrace formation, and the tectonic uplift originate potential energy and has a direct effect on channel incision, both the climatic transition and the tectonic uplift are important. Terraces are the products of the interaction of instable climatic variations and tectonic uplift. Like the loess-paleosol sequences, river terrace sequences are also controlled by the climate-tectonic coupling system and are ruled by climate-tectonic gyration with a ~100?kyr paracycle, which may be the short eccentricity period of the earth. 相似文献
12.
An Wang Jacqueline A. Smith Guocan Wang Kexin Zhang Shuyuan Xiang Demin Liu 《Journal of Asian Earth Sciences》2009,34(4):532-543
The Kunlun Range, a reactivated orogenic belt, constitutes the northern margin of the Tibetan Plateau. The extreme relief and major landforms of the Kunlun Range are a product of late Cenozoic tectonics and erosion. However, well-developed late Quaternary terraces that occur along the northern slope of the Kunlun Range probably resulted from climatic change rather than surface uplift. The terrace sequences formed in thick Quaternary valley fills and have total incision depths of 50–60 m. Optically stimulated luminescence dating was employed to place time controls on the valley fills and associated terraces. Dating results suggest that periods of significant aggradation were synchronous between different rivers and correspond to the last glacial stage. The abrupt change from aggradation to incision occurred between 21.9 ± 2.7 and 16 ± 2.2 ka, coincident with the last glacial–interglacial transition. Additional terraces developed during the late glacial period and early to middle Holocene. Based on a broader set of chronological data in northern Tibet, at least four regional incision periods can be recognized. Chronological data, terrace elevation profiles, and climate proxy records suggest that these terracing periods were triggered by cool and/or wet climatic conditions. A geometric survey of the riverbed longitudinal profile suggests that surface uplift serves as a potential dynamic forcing for long-term incision. A model is proposed for terrace formation as a response to climatic perturbation in an uplifted mountain range. 相似文献
13.
揭示河流系统响应气候变化和地表抬升的机制是理解流域地貌演化以及水系发育过程的基础,其核心难题是如何充分认识它们在阶地发育中扮演的角色。以往的研究倾向于分开讨论气候变化和地表抬升在河流阶地发育中的作用,认为河流堆积/侧蚀和下切行为分别与冰期和间冰期气候对应,或者将阶地作为地表抬升的直接证据。首先,从上下游河段对比的视角初步解释了黄河中游响应气候变化和地表相对汾渭盆地抬升发育阶地的过程。1.2 Ma以来黄河下蚀鄂尔多斯地块和峨眉台地分别形成了7级阶梯状阶地和6级堆积阶地序列。黄土地层分析结合年代学研究揭示这些阶地面都直接上覆一层古土壤,指示它们形成于气候由冰期向间冰期的过渡阶段,即使在沉降的盆地依然如此。然而,黄河中游并没有在1.2 Ma以来的每一次冰期向间冰期转换都发育阶地,说明气候虽能通过控制河流堆积-侧蚀与下切行为的转换决定阶地的形成时代,但其本身并不是阶地形成的唯一控制因素。在峨眉台地沉降的背景下,黄河无法形成正常的阶梯状阶地序列,取而代之的是堆叠的阶地序列（阶地越年轻拔河高度越大）;而当鄂尔多斯地块相对汾渭盆地抬升缓慢时,黄河仅能在极为干旱的冰期向间冰期过渡阶段形成阶地;相比之下,它们相对汾渭盆地抬升速率都足够快速时,驱动黄河近乎对每一次的冰期向间冰期转换都能做出响应而发育阶地。以上黄河中游阶地与气候和地表抬升的对比模式揭示出,快速地表抬升也是阶梯状阶地序列发育不可或缺的因素,能驱使河流在冰期向间冰期过渡阶段显著下切,拉大相邻阶地面垂直距离从而利于后期保存。因此,研究认为黄河中游发育的系列阶地是响应气候变化和地表相对汾渭盆地抬升的结果。 相似文献
14.
Pradeep Srivastava Surendra S. Bhakuni Khayingshing Luirei Dileep K. Misra 《第四纪科学杂志》2009,24(2):175-188
Morphological and sedimentary records at the exit of Brahmaputra River at Pasighat in the NE Himalaya inform about the climate–tectonic interplay during the past ca. 15 ka. The geomorphology of the area comprises (1) fan terrace T3, (2) a high‐angle fan (3) terrace T2, (4) terrace T1 and (5) a low‐angle fan. Geomorphic consideration suggests that the fan terrace T3 and high‐angle fans are the oldest units and were coeval. The low‐angle fan is the youngest geomorphic unit. Sedimentological studies and optically stimulated luminescence chronology suggest that (i) fan terrace T3 formed between 13 and 10.5 ka and comprised multiple events of debris flows separated by the aggradation as channel bars in a braided river environment; (ii) the high‐angle fan formed during 15–10 ka and comprises channel bar aggradation in braided river conditions; (iii) terrace T2 formed during 10–8 ka due to aggradation in a braided channel environment with lesser events of debris flows; (iv) terrace T1 formed during <7 and 3 ka took place as bars of the braided river. Sudden coarsening of the sediment indicated a tectonic rejuvenation in the provenance region between 7 and 3 ka; and (v) the low‐angle fans dated to <3 ka formed due to aggradation in a small tributary joining the Brahmaputra River. This implies a phase when the main channel of the Brahmaputra did not flood regularly and the tributaries were actively aggrading. The sedimentation style and incision of these geomorphic units responded to contemporary climatic changes and uplift in the Siwalik range along the Himalayan Frontal Fault. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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西藏纳木错湖相沉积的U系和^11C测年结果表明，湖泊沿岸的6级湖岸阶地及拔湖约48～139．2m的高位湖相沉积形成于约120ka BP以来的晚第四纪。本文根据该套湖相层的发育和其中的孢粉组合特征对纳木错地区约120ka BP以来的湖面变化与古植被、古气候变迁进行了探讨。结果表明，纳木错地区晚更新世以来经历了频繁的湖面波动、气候的冷暖与干湿变化以及森林—草原与草原植被的交替演化。其总体特征是：约115．9ka BP时，纳木错湖面最高。在116～78ka BP期间，该区气候温和凉爽或温和偏湿，植被以疏林草原与森林草原或森林的交替出现为特征，湖面经历了较大幅度的波动，但基本保持在拔湖140～88m之间。在78～53ka BP期间，该区气候干冷，植被以疏林草原为主，湖面大幅度下降，并在拔湖约36～48m之间波动。约53～32ka BP期间，气候转为温暖偏湿或温暖湿润，湖面波动于拔湖约15～28m之间，波动较为频繁。与阶地的发育相对应，该时期内包含了3次明显的暖期和湖面波动过程，区域植被主要以松、蒿、桦为主，为含一定量的冷杉的森林。其中36ka BP左右气候最温暖湿润，区域内可能出现针叶林或针阔混交林。约32～12ka BP期间，该区气候最为干冷，古植被以草原和疏林草原为主，湖面再次发生较大幅度的下降，最低可至拔湖约8m处，但通常维持在拔湖约12～17m之间。约11．8～4．2ka BP期间，气候整体较为暖湿，其中在约8．4～4．2ka BP期间气候最温暖湿润，该区可能发育针叶林或针阔混交林，湖面波动于拔湖2～9m之间，整体波动幅度较小，但波动最为频繁。区域气候对比发现，纳木错地区的冷、暖气候变化过程与整个青藏高原乃至北半球的气候变化基本是一致的，特别是阶地下切所反映的湖面退缩过程与北大西洋的Henrich冷事件之间具有很好的对应关系。 相似文献
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内蒙古狼山山前台地成因及其新构造运动意义 总被引：3，自引：0，他引：3
内蒙古狼山地处阴山造山带西段、河套断陷带的西北缘,晚新生代以来狼山山前断裂广泛发育、构造抬升强烈。研究晚更新世以来狼山的构造隆升对深入了解河套断陷带的形成演化机制及其隆升过程对河套盆地古地理格局的影响具有重要的意义。狼山山前翁格勒其格和乌兰敖包台地的沉积学、地貌学和年代学研究表明,T1台地形成于47.4 kaB.P.,其沉积物为晚更新世河套古大湖沉积;T2台地形成于69 kaB.P.,其沉积物可能为黄河流经狼山山前的冲积物。台地特征的分析显示,狼山山前台地主要由构造抬升形成,两级台地记录了狼山晚更新世晚期(Qp3-2)以来的构造隆升过程。69 kaB.P.到47.4 kaB.P.翁格勒其格和乌兰敖包地区的隆升速率分别为1.34 m/ka和1.25 m/ka,47.4 kaB.P.以来分别为0.81 m/ka和1.18 m/ka,狼山南段(翁格勒其格地区)构造抬升有减小的趋势。晚更新世晚期(Qp3-2)以来由于狼山的快速隆升,导致黄河河道不断东迁,河套平原的古河道是其迁移的证据。狼山山前湖岸阶地的研究进一步证实晚更新世晚期河套地区发育统一古大湖。 相似文献
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Late Quaternary landform evolution in monsoon-dominated middle Satluj valley is reconstructed using the fragmentary records of fluvial terraces, alluvial fans, debris flows, paleo-flood deposits, and epigenetic gorges. Based on detailed field mapping, alluvial stratigraphy, sedimentology and optical chronology, two phases of fluvial aggradations are identified. The older aggradation event dated between ～13 and 11 ka (early-Holocene), occurred in the pre-existing topography carved by multiple events of erosion and incision. Climatically, the event corresponds to the post-glacial strengthened Indian summer monsoon (ISM). The younger aggradation event dated between ～5 and 0.4 ka (mid- to late-Holocene), was during the declining phase of ISM. The terrain witnessed high magnitude floods during transitional climate (～6.5–7 ka). The fluvial sedimentation was punctuated by short-lived debris flows and alluvial fans during the LGM (weak ISM), early to mid-Holocene transition climate and mid- to late-Holocene declining ISM. Based on the terrace morphology, an event of relatively enhanced surface uplift is inferred after late Holocene. The present study suggests that post-glacial landforms in the middle Satluj valley owe their genesis to the interplay between the climate variability and local/regional tectonic interactions. 相似文献
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Hanchao Jiang Xue Mao Hongyan Xu Jessica Thompson Ping Wang Xiaolin Ma 《Quaternary Science Reviews》2011,30(5-6):769-781
The vegetation on the northeastern margin of the Tibetan Plateau is highly sensitive to climatic changes and thus represents a potentially interesting environmental archive. Pollen samples from the Fanjiaping Loess section in Lanzhou on the western Chinese Loess Plateau (CLP) were analyzed in conjunction with OSL dating. The results indicate that pollen zone B (60.6–46.0 ka, correlative to the early MIS 3) had the greatest abundances of Cupressaceae, Tsuga, Gramineae and Cyperaceae of the entire section, suggesting a warm phase during the last glacial period. These pollen taxa decreased significantly in abundance in the zones C (46.0–39.0 ka) and D (39.0–27.0 ka), reflecting a substantial climate cooling from the middle MIS 3 to MIS 2. These results correlate with climate records from the South China Sea, the CLP, Baikal Lake, North America, North Atlantic Ocean and other regions, and probably correspond with the decline of northern high-latitude insolation and the increase of global ice volume from 50 to 20 ka. In particular, arboreal pollen, fern spore and algae abundances declined sharply since ～40 ka, while shrub and herb pollen reached the highest abundances. Conifer pollen Picea and Abies abundance also rose markedly and increased up the section. This implies significant climate deterioration and likely corresponded with substantial growth of the polar ice sheets since ～40 ka. The decreasing temperature caused by an insolation decline during the last glacial period probably reinforced the cooling effect in a ‘snow/ice/albedo’ feedback, which would result in less climate sensitivity to radiative forcing. Meanwhile, vegetation decline in the Northern Hemisphere during the last glacial period and tundra development at high latitudes possibly caused additional cooling, enhancing the growth of polar ice sheets since 40 ka. The development of polar ice sheets increased the polar-to-equator temperature and pressure gradients, strengthening the westerlies and supplying plenty of moisture to Northwest China during 40–30 ka. Lake sediments developed widely on the Tibetan Plateau during 40–30 ka, probably related to an increase in the seasonality of middle-to-low latitude insolation which caused an enhancement of glacier melting on the Plateau. 相似文献