Magnetostratigraphy and palaeoclimate of Red Clay sequences from Chinese Loess Plateau

Two Red Clay profiles near Xi' an and Xifeng were investigated in an attempt to determine magne-tostratigraphic and palaeoclimatic records. The results show that aeolian dust accumulation and the related East Asia palaeomonsoon system had begun by 6.5 Ma, and it is deduced that the Tibetan Plateau had reached a significant elevation at that time. The late Tertiary palaeoclimatic history of the Red Clay as reflected by magnetic susceptibility is reconstructed during the period of 6.5-2.5 Ma. Stepwise increase in susceptibility of aeolian dust accumulation appears to have a close correlation to the uplift processes of the Tibetan Plateau. The remarkable increase of aeolian dust accumulation at 3.2 Ma appears to be due to the influence of global ice volume on the East Asia monsoon. Palaeomonsoon variation during the late Tertiary as recorded in the Red Clay sequences from the Chinese Loess Plateau can be regarded as the product of a number of interacting factors, such as uplift of the Tibetan Plateau, solar radiation, global ice volume, etc.

Accumulation sequence of Chinese loess and climatic records of Greenland ice core during the last 130 ka

The present winter climate of continental China is associated with cold air activity.The cold air forming Siberian high pressure comes from the Northern Barents Sea.Northwestern Kara Sea and Northern Atlantic Ocean (fig.1). in other words, mainly fromthe cold northern sea surface. west and east to Novaya Zemlya and the sea surface south

Characteristics of magnetotactic bacteria in Duanjiapo loess section, Shaanxi Province and their environment significance

Magnetotactic bacteria (MB) have been isolated from 61 samples which have been collected from S0, L1, S1 and L2 layers in the Duanjiapo loess section. A few MB (<25 cell counts per sieve mesh) have been found in loess layers (L1, L2), bow-shaped, each cell containing only two magnetosomes. while much more MB (>125 cells counts per sieve mesh) have been found from paleosol layers (S0, S1), rod-shaped, each cell containing 8-26 magnetosomes arranged in irregular chains. Magnetosomes with Fe and Co as the main metallic elements are spheroid-shaped, and mainly round in cross-section. Normal saturated fatty acids in MB ranged from C14 to C28; almost no monounsaturated fatty acids have been identified. Most suitable oxygen content for MB growing is 10%, and low concentration of organic salt (0.02mmol/L qumsic iron) is beneficial to the forming of magnetosomes. Results suggest that the paleosol development stage is suitable for the growing of MB and the climate fluctuation periods for magnetosomes formation.

Loess-paleosol sequence on Loess Plateau and uplift of the Qinghai-Xizang Plateau

Correlation of the loess-paleosol sequence on Loess Plateau and the tectonodimatic cycle it reflects with the moraine-paleosol sequence on Qingbai-Xizang Plateau and the uplift process it reflects, indicates that both sequences are synchronous to each other on phase variation with a quasi-period of 0.4 Ma, i.e. the eccentricity variation period. The response of the variation of the Asian paleomonsoon and the paleoclimatic change to the uplift stages and altitudes and the underlying surfaces is studied.

Evolution of the summer monsoon regime over the Loess Plateau of the last 150 ka

On the magnetic susceptibility data of 30 sections covering the Loess Plateau, contour maps of susceptibility are drawn out for 5 time intervals including the last second glaciation (150 ka B.P.), the last interglaciation (130 - 73 ka B.P.), the interstadial of the last glaciation (24 - 59 ka B.P.), the last glacial maximum (18 ka B.P.) and the Holocene optimum (9ka B.P.). The susceptibility value of the last glaciation maximum loess is regarded as the base value of pedogenic loess or paleosol. The susceptibility increment to the base indicates the summer monsoon activity and its strength. On this assumption and the susceptibility contour maps, the variation sequence of the summer regime are reconstructed for the last 150ka. The extent and the northern boundaries of the summer monsoon front activity are also estimated for every stage. It is suggested that the evolution history of the summer monsoon regimes revealed by the susceptibility contour maps not only provides information of position, strength and their configuration of the climate members influencing the summer monsoon, but also provides some climatic signals from the polar region and southern hemisphere.

Remote mineral aerosols in Westerlies and their contributions to the Chinese loess

The concentrations of 28 trace and rare earth elements in the aerosol particle samples were determined for a site at 4800m above the sea level on the Qinghai-Xizang Plateau. The mass of the particulate materials in the mid-troposphere atmosphere over this site is dominated by local dust particles (70%) and remote ones in Westerlies (25%). On the basis of the main dust-derived elements (Al, Fe, Mg and Sc) and corresponding data from the Chinese deserts, an elemental tracer system has been established to proportion the dust input to the loess deposited on the center of the Loess Plateau during the last glacial cyde, which suggests that the contribution of the remote dust in Westerlies is much smaller than that of the Chinese deserts.

A STUDY OF SEDIMENT DELIVERY FROM A SMALL CATCHMENT IN THE LOESS PLATEAU BY THE ^(137)Cs METHOD

A man-made tracer for soil erosion exists in the world-wide fallout of 137Cs from nuclear test. Most of the fallout occurred from 1956 through 1965 with maximum deposition rates in 1963—1964. Reiatively little 137Cs has been deposited since 1970. Cesium-137 is strongly adsorbed within the upper horizons of soil and resists leaching through soil. Since 137Cs has a half-life of 30 a, it is a good tracer for long-term soil particle movement.

Shift of Monsoon Intensity on the Loess Plateau at ca. 0.85 Ma BP

The fluctuations of the Quaternary paleoclimate are characterized by the alternation of cold and warm periods. It is marked on the Loess Plateau in China by alternating loess and buried soils. The Loess Plateau is located in the East Asian monsoon zone and the evolution of its paleoenvironment is thought to be controlled to a large extent by the variations of monsoon intensity. The soil-loess sequence can be therefore considered a good record of paleomonsoon variations and to date, some work has been carried out in reconstructing the history of monsoon evolution. Despite the wealth of

A PRELIMINARY STUDY ON FORMATION OF THE SAND DUNE SYSTEMS IN THE NORTHERN AUSTRALIAN COASTAL ZONE

Ⅰ. INTRODUCTIONDune activity across northern Australia is currently the focus of a joint research project between the Australian National University and the Xi’an Laboratory of Loess and Quaternary Geology, Academia Sinica. Although the project is not yet completed, there is sufficient data available to allow discussion of the general setting of the dune fields studied to date. These include the dune fields near Shelbume Bay and Cape Flattery, eastern Cape York, Cobourg Peninsula, Arnhemland, and Groote Eylandt, Gulf of Carpentaria(Fig. 1).

THE ALTITUDE CALCULATION OF CLIMATIC SNOWLINES AND THEIR CHANGING RULES IN CHINA

Ⅰ. EVIDENCE FOR RESEARCHSnowlines, timber lines, the lower bounds of vertical permafrost zones and the upper bounds of alpine frozen soils are all important physical geographic elements and are controlled by the vertical (altitude)zonality, horizontal (latitude)zonality and regional climatic condition. From the analyses of global spatial distribution, the altitudes and latitudes

RECORDS OF TWO ASTROGEOLOGIC EVENTS IN THE LOESS STRATA,LANTIAN,SHAANXI,CHINA

The thick loess strata in the Loess Plateau of China, which have not been essentially reformed by internal and external agents, are one of the optimum continental deposits preserving the extraterrestrial materials in the last 2.5 Ma. Thus, combining the records with the detailed data of the loess-paleosol sequence, the ages and environmental impacts of the astrogeologic events can be determined.

A PRELIMINARY STUDY ON CHEMICAL COMPOSITION AND TL CHARACTERISTICS OF TEKTITES FROM LEIZHOU PENINSULA AND HAINAN ISLAND

Tektites have been found in many localities over the world, mainly in Asia-Australia, Cote Divoire, Moldavia and North America with isotopic ages of about 0.7, 1.1, 14.5 and 34.5 Ma respectively. Tektites in China are mainly distributed in the Leizhou Peninsula and Hainan Island. Recent discoveries of tektites in Maoming city, Dianbai and Yangjiang counties extend the spread area, which is now within the area of about 18020’—21°50’ N

Preliminary study on the summer monsoon climate of Chinese Loess Plateau during the last interglacial period

Research on long-term climatic variation on the Chinese Loess Plateau has demonstrated that loess is mainly the dust deposits transported by the northern wind of the winter monsoon, and that the paleosol accreted by rather slow dust accumulation was closely related to a strengthened summer monsoon. The climate over the Chinese

Monsoon Variations of the Qinghai-Xizang Plateau During the Last 12,000 Years——Geochemical Evidence From the Sediments in the Siling Lake

Although the monsoon circulation of the Qinghai-Xizang (Tibetan) Plateau, in response to the seasonal variation of the atmospheric heat contrast between the plateau and the surrounding free atmosphere, is important in influencing the atmospheric circulation of the Northern Hemisphere, there are only a few continuous paleoclimatic records available, and these are limited to the plateau’s margin. Here we present a 12,000-a climatic record from Siling Lake in the central Qinghai-Xizang Plateau, constructed from the geochemical and stable isotopic studies on the sediment core CH8803, which shows that

^(14)C CHRONOLOGY OF BEIZHUANGCUN SEDIMENTATION SEQUENCE SINCE 30,000 YEARS B. P.

The Beizhuangcun profile located at Weinan County, Shaanxi Province at an altitude of 570 m a. s. l. (34°30′N, 109°30′ E) is 16.5 m thick and is located at the eastern bank of Zhuoshui River (muddy river), a west tributary of You River upstream. The profile records the relative continuous sedimentation sequences of about 30,000 a B. P. and is des-

PALEOMONSOONS OF CHINA OVER THE LAST 130,000 YEARS——PALEOMONSOON VARIATION

Based upon the effect of land-sea interaction on the paleomonsoon variation and the time series of climatic proxy-indicators, the historical Asian monsoon variation over the last 130,000 and 18,000 years has been reconstructed with an emphasis on the basic characteristics of summer monsoon circulation. The monsoon-climatic cycles and associated model of environmental development over the central and eastern China are proposed and the mechanism of paleomonsoon variation of China preliminarily discussed. The variation of East Asian monsoon circulation should be regarded as a regional result of both solar-radiation changes and the global glacial-interglacial cycles. The episodic uplifting of the Qinghai-Xizang Plateau since the late Miocene has to a large extent controlled the forming and evolution of the paleomonsoon circulation of China.

STUDY ON THE EOLIAN DUST FLUX OVER THE LOESS PLATEAU:AN EXAMPLE

The wind is a basic factor in the atmosphere subsystem in the Earth system, and an agent in transferring the mass and energy within the system. The grain size and mass flux of the eolian dust in the Neocene deep-sea sediments recorded the intensity of the atmospheric circulation and the aridity in the dust source area. The loess on the Loess Plateau, the dust accumulation after its origin, transportation, deposition, and reworked process, is

Organic Carbon Stable Isotopic Composition From Peat in Ruoergai Plateau, Eastern Part of Qinghai-Xizang Plateau

Ruoergai Plateau (32°20′—34°10′, 102°15′—103°50′), 3600m above sea level, is located in the eastern part of the Qinghai-Xizang Plateau. It is the major region in China for high-altitude peat deposition with thickness that varies from 2—3m to over 10m. Such thick peat deposition is one of the best ideal materials for the research on the environmental changes since the Late Glacial in the eastern part of Qinghai-Xizang Plateau, because in peat is reserved abundant information about environmental changes. The

PALEOMONSOONS OF CHINA OVER THE LAST 130,000 YEARS——PALEOMONSOON RECORDS

The characteristics of the modern monsoon climate o?China may be used as clues for recognizing the records of paleomonsoon climate. The present paper deals primarily with the various paleomonsoon records of the last 130,000 years in the southeast monsoon area. These records mainly come from the following three fields: (i) the historical, (ii) the geological, including loess-paleosol sequence, deserts, lakes, snowlines, timberlines, the phenomena of continental desertization and so on, and (iii) the biological, presented by vegetation and mammals. Among these records, the loess-paleosol sequence in the Loess Plateau reflects a climatic history characterized by alternation of two different climatic periods when the Asian winter monsoon and summer monsoon showed pronounced effects on environment, respectively.

SOME PROBLEMS ON WIND-DRIFT SAND GEOMORPHY IN EAST TAKLIMAKAN DESERT

The authors put forward some ideas on the strata and age of the wind-drift sand geomorphy in the east Taklimakan Desert as well as the cause on the basis of the extensive investigations on the strata of the wind-drift sand geomorphy in the Taklimakan Desert mainly according to the record, the result of particle analysis and chronological data in T8710 section located in the dense drifting sand area in the east Taklimakan Desert.