Liu Tungsheng

Baoji-type pedostratigraphic section, Loess Plateau, north-central China

Abstract The Baoji section is judged to be the most complete pedostratigraphic section on the Loess Plateau of north-central China. It is located about 5 km north of the city of Baoji and consists of 37 paleosols formed during more than the last 2.5 Ma. It is designated here as the type pedostratigraphic section with formally named geosols following the rules of the North American Commission on Stratigraphic Nomenclature. Geochronological control is based largely on magnetostratigraphy with the Brunhes, Matuyama and Gauss epochs, and Jaramillo and Olduvai events clearly recognized. The Baoji geosols can be correlated with equivalent pedostratigraphic units throughout the Loess Plateau by a combination of magnetostratigraphy and character, position and the association of the pedostratigraphic units within the Quaternary succession. The variation of the geosols suggests climatic cycles of varying intensity and duration; but generally warmer and moister conditions when compared with the loess units that suggest colder and drier periods.

Pedostratigraphy of Chinese loess deposits and climatic cycles in the last 2.5 Myr

Summary The pedostratigraphy and magnetostratigraphy of several sections in the Loess Plateau of north-central China have been investigated and correlated. The most complete and distinct loess-paleosol sequence occurs in the Baoji section of the southern part of the Plateau. Thirty seven pedostratigraphic units are identifiable in the Baoji section and correlated with those in other parts of the Plateau. The sequence represents thirty seven major cold to warm climatic cycles in the last 2.5 Myr. At about the time of the Matuyama-Gauss magnetic reversal an abrupt climatic event occurred in north China, represented by the shift of the well weathered Red Clay formation below the M/G boundary to the alternating loess and paleosol units above, marking the beginning of a new epoch in the course of climatic evolution. In addition there are two other major shifts of dominant periods of climatic cycles recorded in the loess-paleosol sequences, one occurring at about 1.5 Myr and another at about 0.8 Myr. The pedostratigraphy of loess deposits in north-central China provides an independent measure of the world-wide climatic fluctuations and is now the most complete and reliable record of the major climatic cycles in the last 2.5 Myr.

10Be in Chinese loess

We report a first series of10Be measurements on Chinese loess covering the last 750,000 years. The10Be concentration shows a tendency to decrease with increasing grain size. Leaching experiments with acid solutions show that10Be is strongly bound to particles and therefore mobility due to dissolution can be excluded. The10Be record in loess shows features similar to those observed inδ180 records from deep-sea sediments which strongly reflect climatic variations. This allows one to correlate the10Be loess records withδ180 deep-sea records and to establish a time scale. Based on this time scale, accumulation rates of loess and10Be fluxes can be calculated. These reveal generally higher values for cold, arid and windy periods than for warm, humid and calmer intervals.

Gravel deposits on the margins of the Qinghai-Xizang Plateau, and their environmental significance

Abstract The thick deposits of Quaternary gravels found along the margins of the Qinghai-Xizang (Tibet) Plateau have been studied for decades. Here, we concentrate on two sediment series widely developed along the Kunlun, Tian Shan and Qilian mountains: the Xiyu Formation, a molassic series of Lower Pleistocene age, and the Middle and Upper Pleistocene Gobi Gravels. These two series, with their contained fossil assemblages, throw light on the question of the mean altitudes and uplift rates of the Tibetan Plateau during the Quaternary and on the related problem of the vigour and penetration of advected summer monsoonal moisture into central Asia. The sedimentary series on the northern piedmonts of the Tibetan Plateau considered here challege the view that Plateau uplift accelerated in the Upper Pleistocene. They indicate that the Plateau had reached mean altitudes in the range 4000–5000 m perhaps by the end of the Lower Pleistocene, and certainly by the Middle Pleistocene. This diminished the incursion of southerly monsoonal moisture, and so imposed arid and semi-arid conditions across much of a vast region north of the Plateau which, among other effects, precluded widespread mountain glaciation in the Lower Pleistocene and general (ice sheet) glaciation of the Tibetan Plateau as a whole.

The global surface energy system and the geological role of wind stress

Abstract Deserts and the Loess Plateau in North China constitute an environmental coupling system which has undergone periodic changes in the Quaternary period, attributable mainly to the variations of the global surface energy system. Thirty-seven loess-paleosol formations of the last 2.5 Ma have been identified in the Loess Plateau, representing thirty-seven cycles of climate from cold to warm and of wind intensity from strong to weak. In historical literature, more ‘loess falling’ events in relatively cold-dry periods have been recorded, than in comparatively warm-humid periods. Loess is being currently deposited. Analyses on three contemporary ‘dust storm’ events show that the scope, mass fluxes, and manners of loess deposition are controlled by different atmospheric circulation systems.

Magnetic susceptibility of the Chinese loess-palaeosol sequence: environmental change and pedogenesis

Pronounced differences in concentration, alignment and grain-size distribution of the magnetic minerals have been identified between loess and palaeosol samples from the section at Xifeng (Central Chinese loess plateau). Superparamagnetic magnetite formed in situ plays an important role in controlling magnetic low field susceptibility. The variable brown-red colouration of the loess-palaeosol sequence is due to a significant hematite component produced by pedogenesis. The magnetic fabric of the palaeosols is weaker than that of the loesses. This is taken as evidence that the formation of ultrafine ferromagnetic minerals by pedogenesis is the most likely explanation for the observed susceptibility enhancement in palaeosols (4 to 10 times higher than in loesses). It is argued that variations of frequency dependent susceptibility are sensitive recorders of second order palaeoclimatic variations during glacial periods, whereas bulk susceptibility seems to be an appropriate measure of palaeoclimate change during interglacial periods.

The paleosol complex S5 in the China Loess Plateau — A record of climatic optimum during the last 1.2 Ma

Having investigated the loess-paleosol sequence in various loess deposition basins in the China Loess Plateau, authors have found that the paleosol complex S5 is of special significance in terms of Pleistocene paleoclimate. Paleopedological, micromorphological, palynological and paleomagnetic evidences indicate that this paleosol complex formed in the interval of 460,000 to at least 560,000 years BP, which was a climatic optimum.