Modern pollen-vegetation relationship based on discriminant analysis across an altitudinal transect on Gongga Mountain, eastern Tibetan Plateau

Quantitative relationship between modern pollen assemblage and altitudinal vegetation belt is crucial for the reconstruction of paleovegetation in the mountain regions.Modern pollen analysis on 70 topsoil samples was conducted across an altitudinal transect(1100-4500 m) on the eastern slope of Gongga Mountain in the eastern Tibetan Plateau with an elevation interval of 50 m.Distributions of major pollen types along the transect indicated a weak correlation between Pinus pollen and the elevation.Distributions of Picea and Abies pollen(percentage sum of 2%-8%) could fairly indicate the elevation range of 2700-3700 m,as well as the subalpine dark coniferous forest and the timberline in the region.High percentage intervals of alpine types of Ericaceae,Cupressaceae and Cyperaceae were correlated to the high-elevation regions(3700-4500 m) dominated by alpine shrub meadow and alpine meadow.Seven altitudinal vegetation belts on the eastern slope of Gongga Mountain were well defined by discriminant analysis conducted on the modern pollen assemblages,as reflected by high values of probability of modern analog.Most of the modern pollen assemblages(88.5%) were typical for the vegetation types at their sampling locations.Thus,the relationship between the modern pollen assemblages and vegetation across the altitudinal transect based on discriminant analysis can be applied to the quantitative reconstruction of paleovegetation changes in the mountain regions of the eastern Tibetan Plateau.     

Late Cenozoic high-resolution magnetostratigraphy in the Kunlun Pass Basin and its implications for the uplift of the northern Tibetan Plateau

The Kunlun Pass Basin, located in the middle of the eastern Kunlun Mountains, received relatively continuous late Cenozoic sediments from the surrounding mountains, archiving great information to understand the deformation and uplift histories of the northern Tibetan Plateau. The Kunlun-Yellow River Movement, identified from the tectonomorphologic and sedimentary evolution of the Kunlun Pass Basin by Cui Zhijiu et al. （1997, 1998）, is roughly coincident with many important global and Plateau climatic and environmental events, becoming a crucial time interval to understand tectonic-climatic interactions. However, the ages used to constrict the events remain great uncertainty. Here, we present the results of detailed magnetostratigraphy of the late Cenozoic sediments in the Kunlun Pass Basin, which show the basin sediments were formed between about 3.6 Ma and 0.5 Ma and the Kunlun-Yellow River Movement occurred at 1.2 to ～0.78 Ma. The lithology, sedimentary facies and lithofacies associations divide the basin into five stages of tectonosedimentary evolution, indicating the northern Tibetan Plateau having experienced five episodes of tectonic uplifts at ～3.6, 2.69-2.58, 1.77, 1.2, 0.87 and ～0.78 Ma since the Pliocene.     

青藏高原的自然环境特征

 本文基于1950年代至今青藏高原综合考察和研究成果,系统总结了青藏高原自然环境的主要特征。青藏高原是中国三大自然阶梯中最高一级,平均海拔超过4000 m,被称为“世界屋脊”。青藏高原土地辽阔,总面积约为250万km²,占中国陆地总面积的1/4。自新近纪以来强烈的隆升,使青藏高原自然环境明显区别于其他地区,形成了自己鲜明的特征,主要表现为海拔高、温度低、辐射强、河湖众多、冰川冻土广布、生物多样性丰富。青藏高原面积广大,高原内部的自然环境差异显著,并具有明显的区域分异特征,根据拟订的原则、方法和指标,青藏高原可划分为10个各具特色的自然区,包括：果洛那曲高原山地高寒灌丛草甸区、青南高原宽谷高寒草甸草原区、羌塘高原湖盆高寒草原区、昆仑高山高原高寒荒漠区、川西藏东高山峡谷针叶林区、青东祁连高山盆地针叶林草原区、藏南高山谷地灌丛草原区、柴达木盆地荒漠区、昆仑山北翼山地荒漠区、阿里山地荒漠区。     

An ice-core record of vegetation and climate changes in the central Tibetan Plateau during the last 550 years

We present a 550-year ice-core pollen record with a 5-year resolution from the Puruogangri ice field in the central Tibetan Plateau.Analysis of the relationship between pollen record and instrumental observations suggests that the sum of the steppe and meadow pollen taxa is a good indicator of summer (June-August) temperature,whereas the ratios of Cyperaceae/(Gramineae+Artemisia) [Cy/(G+A)] as well as M/S (meadow to steppe percentages) are indicative of humidity changes in this region.Together with δ18O and...     

Formation of the Yazi Spring Stream and its significance on tectonics-climate on the northern slope of Kunlun Mountains

The sequences of fluvial terraces in the Yazi Spring Stream are signs of the stepwise uplift of the Kunlun Mountains in the northern part of the Tibetan Plateau since the Late Pleistocene. Geomorphic and sedimentary features of the terraces reveal that they have resulted from the phased tectonic uplift and the consequent river incision in the northern plateau. Using the method of Single-aliquot Regenerative-dose （SAR） Protocol and Radiocarbon ^14C dating, the deposit ages of three-grade terraces were obtained, which are 57.5, 12.8 and 5.7 kaBP, respectively. The features and ages of terraces reveal that the incision rate of the stream accelerated at the beginning of the Holocene. The incision rate changed suddenly at 12.8 KaBP, from 0.43±0.07 mm/a to 1.59±0.55 mm/a. This implicates that uplift of the Kunlun Mountains is intensive at the first onset of the Holocene, corresponding to the obvious change of slip-rate on the AItyn Tagh Fault. But its uplift rate is much lower than that of the latter, which suggests that growth of the northern margin of the Tibetan Plateau is stronger than its interior.     

δ13C difference between plants and soil organic matter along the eastern slope of Mount Gongga

Carbon isotope ratios (δ¹³C) of plants, litter and soil organic matter (0–5 cm, 5–10 cm and 10–20 cm) on the eastern slope of Mount Gongga were measured. The results show that δ¹³C values of plants, litter and soil organic matter all decrease first and then increase with altitude, i.e δ¹³C values gradually decrease from 1200 to 2100 m a.s.l., and increase from 2100 to 4500 m a.s.l. The δ¹³C altitudinal variations are related to the distribution of C₃ and C₄ plants on the eastern slope of Mount Gongga, because C₄ plants are observed to grow only below 2100 m, while C3 plants occur at all altitudes. There are significantly positive correla-tions among δ¹³C of vegetation, δ¹³C of litter and δ¹³C of soil organic matter, and litter, 0–5 cm, 5–10 cm and 10–20 cm soil or-ganic matter are 0.56‰, 2.87‰, 3.04‰ and 3.49‰ greater in δ¹³C than vegetation, respectively. Considering the influences of rising concentration of atmospheric CO₂ and decreasing δ¹³C of atmospheric CO₂ since the industry revolution on δ¹³C of plants, 1.57‰ is proposed to be the smallest correction value for reconstruction of paleovegetation using δ¹³C of soil organic matter.     

Geomorphologic evolution and environmental changes in the Shaluli Mountain region during the Quaternary

Geologic and geomorphologic evidence from the Shaluli Mountain indicates that the planation surface that formed in the Late Tertiary disintegrated during the Late PUocene-Early Quaternary. At the same time, rift basins appeared on some parts of the planation surface, and began to accumulate fluvial-lacustrine sediment. These are interpreted as being the response of this region to Phase-A of the Qingzang Teetnnic Movement. After this, the Shaluli Mountain eontinued to rise in several pulses. Faulting and incision by some large tributaries of the Jinsha and Yalong Rivers resulted in several rift river valleys and the earliest terraces. Generally. the planation surface in this region had been uplifted to ahout 3500--3700 m a.s.I, no later than 550-600 ka BP. after the Kunlun-Huanghe Tectonic Movement, and coupled with global glacial climate, and resulted in the earliest glaciation recognized so far in the Hengduan Mountains. At the same time, Ioess was deposited in the Ganzi area of the northern Shaluli Mountain. During the last glacial period, the Shaluii Mountain approached its present altitude and developed several large ice caps, such as the Daocheng Ice Cap and Xinlong Ice Cap, as well as several huge valley glaciers. These paleoglaciers produced some of the most Spectacnlar glacial topography on the Tibetan Plateau.     

A mid－Holocene drought interval as evidenced by lake desiccation in the Alashan Plateau,Inner Mongolia,China

The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong sum-mer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lakegeomorphologic and lithologicai evidence from the Alashan Plateau, part of the Mongolian Plateau, that indicates stronglake desiccation during the mid-Holocene. High resolution pollen data from Zhuyeze Lake, at the present summermonsoon margin, is also presented. These data show that present lakes and wetlands in the Juyanze Lake basin west of the Badain Jaran desert, in the Zhuyeze Lake basin between the Badain Jaran and Tengger deserts, and in lakes in the eastern Tengger desert, dried or experienced low lake levelsin the mid-Holocene around 5000-7000 cal yr BP. Pollen data further indicate that the vegetation cover declined in both the local areas and in the Qilian Mountains, suggesting the climate was drier than that associated with the presentAsian summer monsoon. This mid-Holocene drought interval was present throughout a quite large region of the south In-ner Mongolian Plateau. The period was also probably colder,at least in the high Asian plateaus and mountains.     

Evidence of crustal ＇channel flow＇ in the eastern margin of Tibetan Plateau from MT measurements

Magnetotelluric （MT） survey has been carried out in the eastern margin of the Tibetan Plateau and its neighboring Shimian-Leshan area, Sichuan Province. Analysis of this MT data reveals that the electric structure of the Tibetan Plateau differ much from that of the Sichuan block. In general, the electric resistivity of crust beneath the Sichuan block in the east is larger than that of the eastern margin of the Tibetan Plateau in the west. The crust of the plateau is divided into upper, middle, and lower layers. The middle crust is a low resistivity layer with minimum down to 3-10Ωm about 10-15 km thick. It presumably contains partial melt and/or salt-bearing fluids with low viscosity, prone to deform and flow, producing a ＂channel flow＂ under the southeastward squeeze of the eastern Tibetan Plateau. This low-resistivity layer makes the upper crust decoupled mechanically from the lower crust. In the brittle upper crust, faults are dominated by left-lateral strike-slip and thrust motions, leading to surface rising and shallow earthquakes. The low-resistivity layer also cut the Xianshuihe-Anninghe fault zone into two sections vertically. In this region, the thicknesses of upper, middle, and lower crust vary laterally, producing a transitional zone in the eastern margin of the Tibetan Plateau characterized by thicker crust and higher elevation in the west and thinner crust and lower elevation in the east.     

Uplift processes for the Qinghai-Tibet Plateau: A comparative study of Yecheng section and Siwalik group

Comparative studies of the Yecheng section at the northern piedmont of the Kunlun Mountain, and the Surai Khola section at the southern piedmont of the Himalayan Mountain, indicates that the Qinghai-Tibet Plateau is dominated by continuous uplift over the past 10 Ma. And the effective time scale for dividing the uplift stages would be 1 Ma. The uplift processes of the entire plateau can be divided mainly into three stages, i.e., a slow uplift stage (10.0-6.0 MaBP), a transitional uplift stage (6.0-2.5 MaBP) and a rapid uplift stage (since 2.5 MaBP). The plateau might have risen to 2000 m above sea level by 4.6 MaBP in response to uplift and to more than 3000 m by 2.5 MaBP.     

贡嘎山木本植物碳同位素沿海拔梯度的变化

对贡嘎山东坡不同海拔的主要木本植物稳定碳同位素的组成进行了测定。结果表明:22种木本植物叶片δ_¹³C值变化范围为-3.236%～-2.521%,平均值(-2.957±0.163)%; 不同海拔间植物叶片δ_¹³C值差异显著,随海拔上升叶片δ_¹³C值呈增加趋势; 同种植物(大叶金顶杜鹃、峨眉冷杉、水青树、箭竹)的δ_¹³C值随海拔的增加也呈相同的变化趋势。不同生活型植物叶片δ_¹³C值之间差异显著,落叶树种显著高于常绿树种。叶片δ_¹³C值与6—9月平均温度呈显著的负相关关系,与6—8月降水量呈显著的正相关关系,温度、降水是影响木本植物叶片δ_¹³C值海拔差异的主要因子。     

Temperature variability since A.D. 1837 inferred from tree-ring maximum density of <Emphasis Type="Italic">Abies fabri</Emphasis> on Gongga Mountain,China

Two tree-ring MXD (maximum latewood density) chronologies of Abies fabri were developed from the eastern slopes of Gongga Mountain, and a regional chronology (RC) was established based on the two MXD chronologies. There were significant positive correlations between the three MXD chronologies and August–September temperature, and the RC had the highest correlation (r=0.733, n=48, P<0.001) with mean August–September temperature. Based on growth-climate analyses, we reconstructed mean August–September temperature during the past 171 years for the study area. The reconstruction explained 53.5% of the instrumental temperature variance during the period 1960–2007 (F=52.8, R²_adj =52.4%). In the past 171 years, there were 22 very warm years and 23 very cold years, four cold periods (1837–1842, 1884–1891, 1899–1905 and 1984–1989) and three warm periods (1966–1973, 1916–1924 and 1876–1881). Our reconstruction was validated by other tree ring-based temperature reconstructions from the surrounding area and documented climate disaster events.     

苍山东坡植被垂直分布格局研究

 苍山是中国高山植物模式标本的产地之一,具有较完整的植被垂直带谱.在对苍山东坡1966~4092 m沿海拔梯度进行植被调查的基础上,利用地形图和ETM+遥感影像进行苍山东坡植被制图,与数字高程模型(DEM)数据叠加,对苍山东坡植被景观的垂直分布格局进行了分析,并与顶级群落进行了对比.结果表明:苍山东坡绝大部分山体位于2500~3500 m范围.苍山东坡现状植被垂直分布格局明显,具有6个垂直分布带.该垂直植被带谱与顶级群落垂直带谱相比有一定变化.研究结果进一步量化了前人对苍山植被的垂直分布格局所做的定性和半定量的研究结果,找出了两者的差异,并进行了原因分析.     

Age and genesis of the Shagou River terraces in eastern Qilian Mountains

The fluvial terrace sequence in eastern Qilian Mountains is a record of periodic uplift events of the Tibetan Plateau. Based on paleomagnetic dating, thermolumines-cence dating, radio carbon dating and loess-paleosol sequence on terraces, we preliminarily determine the ages of five major terraces of the Shagou River, northern side of the Qilian Mountains. The ages of five terraces were about 830, 418, 250,140 and 10 ka, respectively. Analysis on characteristics of terraces show that five major terraces were mainly tectonic genesis. Therefore, five major terraces recorded five strong rising events in the Qilian Mountains during the past 830 ka. The ages of those rising events are about the same as those terraces formation. Sub-terraces, constituting a main terrace, were perhaps mainly formed by climatic changes.     

天水盆地古近纪地层年代及其意义

天水盆地位于青藏高原东北缘六盘山与西秦岭二重要构造带交汇处,该盆地充填的新生代沉积序列记录着该区构造变形历史,因此研究该盆地沉积记录对探讨青藏高原东北缘新生代构造活动事件具有重要意义.通过对天水盆地古近纪砾石层砂质透镜体中碎屑颗粒磷灰石裂变径迹热年代学研究,获得样品地层的最大沉积年龄为24.8士1.5 Ma.结合前人的工作,厘定该套古近纪地层最顶部地层年龄为22～24.8 Ma,并确定天水盆地古近纪沉积物源区在24.8 Ma左右发生了构造冷却事件,推断印度板块与欧亚大陆碰撞的远程效应在古近纪末-新近纪初已传递到青藏高原的最东北缘.     

New evidence for human occupation of the northern Tibetan Plateau, China during the Late Pleistocene

The described stone artifacts are recovered from the 70 m-high terrace (4600 m a.s.l.) at the southeastern shore of the Siling Co on the northern Tibetan Plateau. The terrace was formed during the Interstadial period before the LGM, ca. 40-30 ka B.P. based on paleoenvironmental research. The Paleoliths from the Siling Co provide evidence for early human occupation of the northern Tibetan Plateau. They show technological and typological affinities with the European Middle Paleolithic suggesting that the early human occupation here might relate to migratory waves during the Late Pleistocene that dispersed humans across the Old World.     

A tropical paleosol at high elevation in the Yulong Mountains and its implication on the uplift of the Tibetan Plateau

A paleosol dated for about 500–700 kaBP and developed on a glacial deposit at ～3 000 m a.s.l. in the Yulong Mountains is studied using soil chemical, morphological and mineralogical methods. The analytical results indicate that this soil was formed under tropical and humid conditions and can be classified as red soil, which cannot be formed in the present alpine environment at the studied site. This implies that the southeast margin of the Tibetan Plateau has experienced intense uplift since the formation of the paleosol. According to the necessary conditions for the formation of the modern red soil in China, we estimate that the uplift height of the Plateau since 500–700 kaBP would have exceeded 800 m.     

“引雅入塔”工程的可行性分析

“引雅入塔”工程,即引雅鲁藏布江之水入塔里木盆地之引水工程,这是一个大胆的设想.其基本内涵是将发源于喜马拉雅山北麓素称“悬河”的雅鲁藏布江的水量,通过西藏高原开挖一条运河,将高原之水引入盆地,以便改变大西北干旱荒漠区的水文气象面貌.本文着重分析了雅鲁藏布江之水源现状和昆仑山北麓山前平原绿洲的情况.同时,对引水工程和应采取的技术措施进行了初步分析.     

Northern Tibetan Plateau cooling and aridification linked to Cenozoic global cooling: Evidence from <Emphasis Type="Italic">n</Emphasis>-alkane distributions of Paleogene sedimentary sequences in the Xining Basin

The Xining Basin on the northeastern Tibetan Plateau holds the longest continuous Cenozoic stratigraphic record in China. The sequence record contains considerable information on the history of Tibetan uplift and associated climatic change. In particular, high resolution n-alkane biomarker proxy and pollen records have been obtained from the Paleogene sediments of the Xiejia section of the basin. A combination of the n-alkane and palynological records reveals that the paleoclimate in the Xining Basin experienced a long-term cooling trend from 50.2 to 28.2 Ma with a distinctive ecological event spanning 37.5 to 32.7 Ma. Since this ecological event, a vertical zonation of vegetation from lowland arid grasses, to middle-elevation subtropical broad-leaf plants, to high-elevation coniferous trees was established. We interpret that these changes in climate and vegetation were probably responses to a combination of long term global cooling since the Eocene climatic optimum and uplift of the surrounding mountains on the northern Tibetan Plateau in the early Cenozoic.     

黑河中游山前荒漠和绿洲荒漠过渡带土壤植被空间分布特征研究

干旱区呈现荒漠和绿洲邻接共存的独特景观,区域内土壤植被起到维持生态系统结构功能稳定的基础性作用.本文以黑河中游山前荒漠及绿洲荒漠过渡带作为典型区域,设置土壤植被调查样带,在采样分析土壤机械组成、水分、盐分离子、有机质质量分数及植被覆盖度、冠幅、高度等数据的基础上,探究土壤植被在垂直和水平方向的空间分布特征.得到以下结论:1)黑河中游样带土壤平均质量含水量在1.49%~5.57%范围内,祁连山前样带北山前样带,体现祁连山区对于荒漠的水分补给;2)祁连山前样带土壤质地主要为粉壤土和砾质壤土,盐分和有机质含量较高,相反,北山前样带土壤质地主要为砾石土和砂土,盐分和有机质含量较低,土壤含水量与土壤颗粒组成、盐分、有机质含量等其他土壤属性存在显著的相关关系;3)植被覆盖度在祁连山前荒漠较高,北山前荒漠较低,远离绿洲方向的样带土壤含水量及植被覆盖度总体呈上升趋势,表现生态裂谷特征,威胁黑河中游绿洲生态系统安全;4)植被与土壤属性之间高度相关,主要表现在植被覆盖度与土壤水分、土壤细粒径颗粒和有机质含量的正相关关系,以及植被覆盖度、高度和冠幅随盐分先增加后降低的二次抛物线关系,表明盐分对植物的生长具有一定的抑制作用.