Loess Palaeosol Research Articles

Geochemical compositions of core sediments in eastern China: Implication for Late Cenozoic palaeoenvironmental changes

Three deep drill holes with depth exceeding 300 m were collected from eastern China for geochemical study in order to reconstruct Late Cenozoic palaeoenvironmental changes. The Late Cenozoic strata in eastern China are predominantly composed of lacustrine, fluvial and littoral sediments. Degrees of chemical weathering during the Late Cenozoic were estimated by using geochemical proxies including CaCO 3 contents, chemical index of alteration and Al 2O 3–CaO–(Na 2O + K 2O) diagrams. The results show that chemical weathering was intense in eastern China in the Late Neogene, and progressively weakened during the Quaternary, albeit with amplified fluctuations. Although the palaeoclimatic conditions reconstructed from the drill holes in eastern China are generally comparable with those records from the loess–palaeosol sequences, red clay, and deep-sea sediments in East Asia, they changed asynchronously in north-central and southeast China during the Neogene. The Late Neogene palaeoclimate was overall warmer in southeast China than on the North China Plain except for some extreme cooling periods in the Late Pleistocene. In contrast, the North China Plain experienced moderate to weak chemical weathering with the intensification of East Asian winter monsoon activities during the Late Quaternary. Regional differentiation of palaeoclimatic variability since the Pliocene in eastern China is comparable with today's climate regimes in the Changjiang and Huanghe drainage basins but with different intensities, suggesting different impacts of the East Asian palaeomonsoon during the Late Cenozoic.

Rock magnetism and geochemistry of two plio–pleistocene Chinese loess–palaeosol sequences—implications for quantitative palaeoprecipitation reconstruction

Stratigraphic and spatial variations in the magnetic properties of Chinese loess are widely accepted as reflecting changes in the intensity of soil forming processes over time and space. Recently, several workers have used statistical correlations between the magnetic susceptibility and related parameters of modern loess plateau soils and modern climate to generate transfer functions to reconstruct past temporal and spatial trends in precipitation. Here we try to assess the viability of this approach by conducting magnetic and geochemical measurements of two long (∼2.5 My) loess–palaeosol sequences from different locations on the modern precipitation gradient across the loess plateau. One site, Duanjiapo, is located on the southern humid margin of the plateau; and the other site, Luochuan, is located in a drier modern environment some 160 km further north. Our results indicate discrepancies between magnetic and geochemical indicators of weathering and soil forming intensity and that any attempt to predict palaeoprecipitation at Duanjiapo using published approaches would be significantly in error. Overall our results indicate a complex response of magnetic mineral transformations to climate, including the production of both ferrimagnetic and antiferromagnetic minerals within the same climatic interval, together with the destruction of magnetic material within some of the palaeosols. Therefore we suggest considerable caution should be exercised in generating quantitative climatic reconstructions from a single magnetic parameter.

Long-term fluvial archives in the Fen Wei Graben, central China, and their bearing on the tectonic history of the India–Asia collision system during the Quaternary

Staircases of large-scale river terraces are striking features of the landscape in the Fen Wei Graben, adjacent to the Qinling orogenic belts, central China. Field investigations indicate that all five river terraces are composed of a basal channel gravel and an overlying, thick loess–palaeosol succession. As Chinese loess stratigraphy has been well studied, it favours age determination of these terraces and their correlation with the marine oxygen isotope stages. Our research indicates that the ages of the five terraces are approximately 2.6, 1.2, 0.9, 0.65, and 0.15 Ma, respectively. The formation of these river terraces within the Fen Wei Graben has been attributed to NW–SE crustal extension, associated with left lateral displacement between the North and South China Blocks, in response to the northward movement of India towards Asia since Cenozoic time. Thus, the stepped terraces in the Fen Wei Graben reflects elements of the India–Asia collision systems, in which terraces define episodes of accelerated northward movement of India towards Asia during the Quaternary.

Duration dependence of magnetic susceptibility enhancement in the Chinese loess–palaeosols of the past 620 ky

Past climate has been interpreted from the loess–palaeosol record found in China. There is no argument that the palaeosols are more strongly weathered than the underlying less well-weathered loess and that these changes have been governed by glacial/interglacial climate fluctuations. However, the duration of pedogenesis may have also contributed to the development of palaeosol properties. Previous studies have not attempted to separate these two factors which both affect the intensity of soil formation, and have assumed that the degree of soil development and pedogenic magnetic susceptibility enhancement depended solely on the climate conditions. We show that the magnetic susceptibility enhancement of palaeosols of the lower Malan and upper Lishi Formations (S 1–S 5 correlated to the interglacials of the past 620 ky) depends partly on the duration of pedogenesis. This suggests that pedogenic magnetic susceptibility enhancement of palaeosols should not be used for such direct palaeoclimate reconstructions as determining the amount of rainfall or the temperature of the soil-forming intervals. However, used in combination with other proxies (other magnetic properties, % Fe d, Fe d/Fe t, color indices, the depth of decalcification, particle size), magnetic properties of palaeosols and loess layers can provide valuable insight into climatic conditions of soil-forming episodes. It follows that multiproxy evidence provides better insight into climate dynamics than the interpretation of a single proxy.

Pedosedimentary development of part of a Late Quaternary loess‐palaeosol sequence in northwest Argentina

AbstractThe field properties, magnetic susceptibility, particle size, calcium carbonate content, soil micromorphology and optical luminescence ages of the upper 6.1 m and lowermost 4.7 m of the 45 m loess–palaeosol sequence at El Lambedero in the Tafí del Valle region of Tucumán Province (Sierras Pampeanas, northwest Argentina) have been used to set up a partial stratigraphy and chronology, as well as a basic pedosedimentary model of loess accumulation, palaeosol development, reworking and erosion for the site. The minimum ages derived from the basal part of the section suggest that loess began to accumulate some time before 165 ka. A thick and well‐developed pedocomplex in the upper profile is correlated with at least the latter part of marine isotope stage (MIS) 5, whereas the overlying palaeosol may be attributable to pedogenic activity during MIS 3. The absence of material younger than 33 ka close to the surface of this rounded spur landform is probably the result of either non‐deposition or erosional stripping in response to climatic change, or episodic uplift in this seismically active region. Copyright © 2004 John Wiley & Sons, Ltd.

The magnetism of a glacial aeolianite sequence from Lanzarote (Canary Islands): coupling between luvic calcisol formation and Saharan dust trapping processes during wet deposition events off northwestern Sahara

SUMMARY In order to better document the climatic origin of pedogenized loess deposits west of Sahara, rock-magnetic measurements were performed on a Last Glacial coastal sand sequence from La Mala (LM) quarry (Lanzarote, Canary Islands) containing six interbedded loess–palaeosol units. Hysteresis and susceptibility data point to a coarse-grained magnetic enhancement in the coastal sand, which contrasts with the superparamagnetic (SP) to pseudo-single domain (PSD) behaviour of the Saharan loess and palaeosol. High- and low-temperature experiments show that oxidized titanomagnetite contributions dominate in the sand, while fine-grained (SP to PSD) iron oxidation products such as maghemite and goethite are evidenced in the Saharan loess/palaeosol units. At room temperature, the detrital PSD–multidomain titanomagnetite contribution of local origin is tentatively estimated from the AC-field dependence of magnetic susceptibility. Surface oxidation of detrital spinel grains and authigenesis of fine-grained iron oxides (including SP goethite) are proposed to explain the magnetic properties of the primarily fine, Saharan-dust-bearing material. The dry, local climate of the present-day and Late Holocene means that loess deposits are not preserved. The six pedogenized loess units, however, point to dust trapping under semi-arid, wetter conditions, probably illustrating periods of reduced latitudinal temperature gradients and climate variability of the North Atlantic climate, respectively. These findings suggest that both the Canary palaeosol and its content of (ultra)fine iron oxide might be constrained by (wet) deposition and trapping of fine Saharan dust.

Holocene dust accumulation and the formation of polycyclic cinnamon soils (luvisols) in the Chinese Loess Plateau

AbstractChinese loess–palaeosol sequences are well known for their records of monsoonal climatic variations. However, the modern processes of dust accumulation and soil formation remain poorly understood. A high‐resolution investigation on modern soils, including the measurement of magnetic susceptibility, particle‐size distribution, total Fe, total organic carbon, CaCO3 content, and optical stimulated luminescence (OSL) dating was carried out on the Zhouyuan loess tableland in the southern Loess Plateau. The results indicate that modern cinnamon soils (luvisols) have developed on contemporarily accumulated aeolian dust during the Holocene. The aeolian loess accumulated during the Younger Dryas was identified in the top part of the Malan Loess that underlay the modern soil by OSL dating and proxy climatic data. It indicates that the Malan Loess accumulated during the last glaciation (marine isotope stages 2–4) does not serve as the parent material for the modern soils. Pedogenesis of the soils started with the increased precipitation and soil moisture that have occurred on the loess tableland since the early Holocene. Precipitation‐driven pedogenesis and organic activities are responsible for the leaching of CaCO3, decomposition of mineral dust and the production of clay and ferromagnetic minerals. Drier intervals have interrupted soil formation several times, and therefore profiles with multiple soils have been developed at many sites on the loess tableland. At places where soil erosion was relatively strong, either a single soil or welded soils are preserved in the Holocene profiles. This does not necessarily mean, however, that modern soils over the plateau have been developed without interruption under a constantly warmer, moister climate. This is significant for understanding the surface processes and climatic variation during the formation of the numerous palaeosols over the Loess Plateau in the Quaternary. Copyright © 2003 John Wiley & Sons, Ltd.

Stratigraphy and palaeoclimatic significance of Late Quaternary loess–palaeosol sequences of the Last Interglacial–Glacial cycle in central Alaska

Loess is one of the most widespread subaerial deposits in Alaska and adjacent Yukon Territory and may have a history that goes back 3 Ma. Based on mineralogy and major and trace element chemistry, central Alaskan loess has a composition that is distinctive from other loess bodies of the world, although it is quartz-dominated. Central Alaskan loess was probably derived from a variety of rock types, including granites, metabasalts and schists. Detailed stratigraphic data and pedologic criteria indicate that, contrary to early studies, many palaeosols are present in central Alaskan loess sections. The buried soils indicate that loess sedimentation was episodic, or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input. As in China, loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess/soil formation cycle. Loess deposition in central Alaska took place before, and probably during the last interglacial period, during stadials of the mid-Wisconsin period, during the last glacial period and during the Holocene. An unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period. Our studies lead us to conclude that vegetation plays a key role in loess accumulation in Alaska. Factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods. The most important of these is vegetation; boreal forest serves as an effective loess trap, but sparsely distributed herb tundra does not. Thus, thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central Alaska. Much of the stratigraphic diversity of North American loess, including that found in the Central Lowlands, the Great Plains, and Alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors.

The Siberian loess record and its significance for reconstruction of Pleistocene climate change in north-central Asia

The Siberian loess represents the most significant terrestrial proxy record of Quaternary climatic history in northern Asia. Loess is extensive in southern Siberia, between the Irtysh Basin in the west and the Angara Basin in the east. Palaeoenvironmental multi-proxy data (magnetic susceptibility (MS), grain size, % CaCO 3, % TOC, pollen, etc.) from high-resolution loess–palaeosol sections provide evidence for a strongly fluctuating climatic sequence in north-central Asia during the Late Quaternary, displaying the globally diagnostic sequences found in the deep-sea oxygen isotope records. MS provides the most continuous and detailed record (encompassing the last two interglacial–glacial cycles) in loess sections in the Minusinsk Basin (Yenisei area) and on the northern Altai Plains. Evidence for periodic atmospheric shifts is provided by gradual changes in the main vegetation zones, with parkland-steppe and mixed taiga during warm interglacial/interstadial stages being replaced by boreal tundra-forest and arid periglacial tundra-steppe during stadials. Climatic pulses from warm intervals to cold are recorded by incipient (forest/steppe)-tundra gleysols. The occurrence of the highest sediment accumulation rates in glacial stages (OIS 4 and OIS 2) in the southern plains and depressions indicates that the most intensive aeolian dust deposition followed the glacial maxima, with the most recent interval dated to ca. 19–15 ka BP. Because of its zonal distribution and pronounced climatic continentality, the Siberian loess region represents an important data source for reconstructing past climates in the Northern Hemisphere. It provides a key to the correlation of other loess regions within the West–East Eurasian continental zone.

Bio-climatic imprints on a Holocene loess palaeosol from China

Micromorphology, heavy minerals, pollen and soil properties were examined in a typical Holocene loess profile in the north of the Loess Plateau, consisting of a palaeosol (locally known as the Ansai palaeosol) underlain by the Malan loess and overlain by modern loess. The palaeosol consists of an upper humus-rich (AB) horizon over a clay-rich (Bt) horizon. The humus-rich horizon is intensely weathered, contains precipitated calcitic material derived from the overlying modern loess, and has both high pollen content and diversity. Clay coatings in the clay-rich horizon indicate formation by eluviation–illuviation of clay. Pedogenetic characteristics and pollen analysis imply that the vegetation during the time of most intensive soil development is likely to have been a warm-temperate forest. A complex interpretation of the loess–palaeosol sequence recognizes several development stages. The phase of soil development, maximum and minimum limiting ages for which are ca. 8800 and 4400 14C years BP, involved continuing but reduced loess deposition, and successive Holocene bio-climatic environment overprinted new features on the palaeosol.

The magnetic fabric of some loess/palaeosol deposits

The magnetic fabric of loess–palaeosol deposits in Asia, Europe and Siberia, from different sources and spanning different time intervals is examined in this paper. Magnetic fabric was visualised by measuring the anisotropy of magnetic susceptibility (AMS) of hand-cut samples. The fabric ellipsoids support a bedding-parallel foliation with low lineation in all cases. Maximum susceptibility directions in the upper part of the Wucheng formation on the Loess Plateau of China, confined to the bedding plane, are biased towards a preferential direction (prevailing palaeowind direction?). Soil formation results in decreasing degree of anisotropy and foliation, and in some cases in large deviations of the principal susceptibility directions caused by bioturbation. The orientation of the ferromagnetic fraction was obtained separately, for a limited number of loess–soil couplets, by measuring the anisotropy of anhysteretic remanent magnetization. The two-component model or regression line method of [Tectonophysics 91 (1983) 165], to separate the ferromagnetic AMS from the bulk AMS, was applied to samples with low and high magnetic susceptibilities from loess sections in Belgium and Siberia. The magnetic fabric of loess is composite, mainly reflecting the preferred alignment of crystallographic lattices of phyllosilicates and of shape-oriented multidomain magnetites.

The Matuyama–Brunhes boundary and the nature of magnetic remanence acquisition in the loess–palaeosol sequence from the western part of the East European loess province

Loess–palaeosol sequences from the western part of the East European loess province were palaeomagnetically studied. The position of the Matuyama–Brunhes boundary was found in the sequence at Zahvizdja (East Carpathian Foreland) overlying the surface that corresponds to the VI Dniestre terrace. This boundary is located within the accumulation horizon of an interglacial soil developed during the time equivalent of oxygen isotope stage 19. The lowermost palaeosol of this sequence, located just below the soil containing the Matuyama–Brunhes boundary record, can thus be correlated with oxygen isotope stage 21 and the VI Dniestre terrace was developed during oxygen isotope stage 22. Samples from the palaeosols (especially from their accumulation horizons) revealed the presence of secondary (postdepositional) components of magnetisation, some resistant to alternating field demagnetisation even as high as 100 mT. Fine-grained maghaemite is most probably the carrier of these components. Subsequent thermal demagnetisation can remove them, to establish the primary palaeodirections. Haematite and magnetite are the main carriers of remanent magnetisation of the loess layers. The degree of possible delay of remanence acquisition in loess sequences was assessed on sediments from three sections sampled in the Volhynia and Lublin uplands. Good correlation of directional changes recorded in coeval segments of loess sections shows that the characteristic magnetisation of aeolian deposits from the western part of the East European loess province is approximately syndepositional.

Assessment of the palaeoclimate during 3.0–2.6 Ma registered by transition of Red Clay to loess–palaeosol sequence in central North China

A continuously accumulated section (the Yanyu section) of Red Clay and loess–palaeosol sequence from the southernmost Chinese Loess Plateau was selected for this study of palaeoclimate of the late Pliocene to early Pleistocene period. Termination of the Red Clay accumulation and onset of loess deposition was coincident with the beginning of extensive Northern Hemisphere glaciation at 2.6 Ma. Field observations and compositional analyses suggest an aeolian origin for the Red Clay, much like the processes experienced by the loess–palaeosol sequence. Pedogenic analysis indicates that the late Pliocene Red Clay first experienced complete decalcification and illuviation (mechanical translocation of clays) in all horizons, including the present carbonate precipitation zones, but other chemical alterations have been rather weak and even weaker than experienced by the overlying loess-derived palaeosols. In great contrast to the Pleistocene climate characterised by frequent and large-amplitude fluctuations between cold–dry and warm–wet, a relatively steady warm–dry climate condition is implied for the late Pliocene. Dustfall rate assessment indicates a much lower accumulation rate during the late Pliocene than in the early Pleistocene, in agreement with a notable systematic coarsening from the Red Clay to the overlying loess and palaeosols. Together, these features suggest that the dust transport agent, the northwesterly winds, were weaker over the late Pliocene. The transition from Red Clay to loess possibly marked a significant and rapid shift in the climatic system in east Asia.

Regional lithofacies and pedofacies variations along a north to south climatic gradient during the Last Glacial period in the central Loess Plateau, China

Five lateral sand–loess–palaeosol continua occur within the last glacial sediments of the central Loess Plateau of China along a 500 km north to south climatic gradient. The continua shift southward or northward in concert with desert expansion or contraction, respectively. Lateral lithofacies (desert sand to loess) variations are evident at the north end of the gradient and follow Walther's Law of the correlation of facies. Lateral pedofacies (loess to palaeosol) variations are present near the south end of the gradient, where the climate was warmer and wetter. The lateral stratigraphic changes from sand to loess or loess to soil are driven by variations in the rate of sedimentation along a climatic gradient. Vertical stratigraphic profiles at the north end of the gradient reveal alternating sand and loess beds. In contrast, alternating loess and palaeosols occur within the same stratigraphic interval in the southern Loess Plateau, where dust accretion rates were lower. However, in high resolution studies of climate change vertical profiles of alternating loess and palaeosols (especially weak palaeosols) may not reflect regional or global climate change. Alternating loess and weak palaeosols may reflect local variations in the balance between the rates of dust accretion and pedogenesis. Local fluctuations in either of these rates could result in the presence of time equivalent loess and palaeosols at high resolutions. Thus, some of the high resolution loess-palaeosol alternations may reflect local climatic variation rather than global or hemispherical climate change.

Abrupt shifts in the late Cenozoic environment of north‐western China recorded in loess–palaeosol–red clay sequences

Aeolian deposits can provide a sensitive record of climatic change. Two abrupt changes in grain size and accumulation rate have been identified at c. 2.4–2.6 Ma and 1.1–1.2 Ma in the loess–palaeosol–red clay sequences from the Loess Plateau of China. These changes are apparent in two major stepwise increases in grain size and accumulation rate following two abrupt prominent change events of grain size, implying a two‐step reorganization that was probably connected with two abrupt environmental change events. The correlation among different sections suggests that regional rather than local environmental processes are responsible for these changes. These changes likely record abrupt fluctuations in winter monsoon and the provenance of sediments associated with renewed Plio‐Pleistocene uplift of the Tibetan plateau, and its role on climate and detrital sediment yield.

Climatic implications of loess deposits from the Beijing region

AbstractVariations in magnetostratigraphy, pedostratigraphy, grain size and magnetic susceptibility of the loess deposits near Beijing have been studied at two sections. The sections are about 400 km east of the main loess deposits in China, have a maximum thickness of 100 m and extend back to 1.1 Ma. The sequence consists of 14 loess–palaeosol couplets (S0‐S14), which correlate well with sequences in the Loess Plateau. Susceptibility records from the sites near Beijing are comparable to the Xifeng, Luochuan and Baoji sections located in the middle part of the Loess Plateau; however, the down‐core variations in the grain size in the Upper Lishi Formation exhibit some differences. The median grain size increases by about 25–30 µm from L4 to L2, with the sandy grains (>63 µm) increasing from 10–20 wt% to 40–50 wt% . This implies that the depositional environment of the dust sources in the Beijing loess section is different in some aspects from the Loess Plateau. The Beijing loess may have had a different dust source than the Loess Plateau. Copyright © 2001 John Wiley & Sons, Ltd.

Pleistocene climate change, natural environments and palaeolithic occupation of the upper Yenisei area, south-central Siberia

The upper Yenisei River area, near the geographical centre of Asia, is of major importance for mapping the Pleistocene climate evolution over Siberia. An extensive loess cover with a suite of buried palaeosols from the Northern Minusinsk Basin has provided one of the most complete, high resolution Late Quaternary palaeoclimatic archives currently described in north-central Asia. Coupled with the pollen evidence, the loess–palaeosol records indicate establishment of periglacial steppe–tundra during cold stadial intervals, replaced by parkland steppe and boreal forest during warm interstadial intervals. Zonal transformations of the Pleistocene environments due to marked climatic variations are reflected by the diversity of fossil faunal species, including non-analogue communities. Geoarchaeological records incorporated in the loess–palaeosol formations represent important palaeoenvironmental multi-proxy data complementing the fossil biotic and palaeopedological evidence. Abundant “pebble tool” assemblages provide explicit evidence of human occupation of the upper Yenisei area prior to the last interglacial (>130 ka BP). The morphological and technological variability of the palaeolithic industries displaying a differential degree of patination and aeolian abrasion attest to several stages of the initial peopling of the southern Siberian territory. The cultural finds associated with the Middle Pleistocene cold-adapted fossil fauna indicate that early humans were able to survive in local periglacial environments. Favourable climatic conditions during the last interglacial promoted expansion of the more advanced Mousterian (Levallois) tradition that persisted until the early last glacial stage (OIS 4). Warming during the mid-last glacial stage (OIS 3) accelerated formation of the Late Palaeolithic cultures dominated by developed blade reduction techniques. Intervals of significant climatic deterioration and onset of full glacial conditions are manifested by the absence of any archaeological record. The main focus of the current Quaternary investigations is to refine the established chronological framework and detail contextual settings of the cultural records within the larger study area.

Pedogenic modification of loess: significance for palaeoclimatic reconstructions

This review considers the role of pedogenic processes in modifying wind-blown dust (loess), concentrating particularly on the ways that resulting properties may be interpreted as indicators of past climatic conditions and changes. Emphasis is placed on the sequences of palaeosols developed within loess deposits that are frequently regarded as some of the best terrestrial equivalents of marine-sediment records of long-term global climatic change. A palaeosol is generally interpreted in terms of the broad pedogenic processes and environments assumed to be currently responsible for that type of soil forming at the present surface. Even the very presence of a palaeosol may have palaeoclimatic significance, however, in that it is often taken to indicate a period of relative land surface stability and warmer and/or moister conditions between cold and/or arid phases of loess accumulation. In reality, it may be more useful to consider many loess–palaeosol sequences in terms of changing balances between pedogenesis and loess accumulation over geological time. In most regions, it seems that the balance swings towards pedogenesis during interglacials or interstadials when sediment supply and transport are limited and the climate is warmer and/or wetter. Where accumulation rates are still appreciable during these ‘soil-forming intervals’, however, the soils and palaeosols may be accretionary with surface build-up keeping pace with pedogenesis. Welding may also occur where covering sediments are insufficiently thick to isolate an underlying palaeosol from the effects of pedogenesis active at a new land surface. Further complications occur due to reworking of palaeosols and syndepositional pedogenic alteration of loess units. Generally, such pedocomplexes can only be deciphered if the different pedogenic, geomorphic and sedimentary processes are identified and ordered within a pedosedimentary reconstruction. A recent trend has been to treat some loess–palaeosol sequences as quasi-continuous time series, particularly when comparing depth functions of climatic-proxy properties such as magnetic susceptibility and grain size with marine and ice-core isotope curves.

Luminescence dating of loess–palaeosol sequences and coversands: methodological aspects and palaeoclimatic implications

Of the terrestrial archives, loess–palaeosol sequences provide a most complete record of climatic change. This may be compared with the Marine oxygen isotope stratigraphy, and may help in the reconstruction of past atmospheric circulation patterns. Numerical chronometry of loess–palaeosol sequences has generally been based on correlation of variations in climatic proxies (such as magnetic susceptibility and particle sizes) with Marine isotopic data. Such chronometric assignments involve implicit assumptions about the constancy of sedimentation rates and particle fluxes through time. This review presents a brief survey of the present status, methodology, outstanding problems and interpretational aspects of luminescence techniques, and discusses the import of luminescence ages on global land–sea correlations. Statistical analysis of the ages suggests episodicity of loess accumulation with extended periods of quiescence. Recent luminescence dating studies on closely spaced samples also lead to a similar inference. Luminescence ages imply high variability in loess sedimentation rates. This conflicts with the assumption, made in some current attempts to correlate loess records with marine records, of almost constant particle fluxes. A review of source-proximal coversand deposits of northwest Europe is also presented. Evidence of the onset of coversand deposition at 15 ka, with a peak in accretion during the Younger Dryas and subsequent minor reactivation episodes, is discussed.

Magnetic grain-size distribution of the enhanced component in the loess-palaeosol sequences in the western Loess Plateau of China

SUMMARY Rock magnetic measurements of Chinese loess–palaeosol samples from the Beiyuan section in Linxia City suggest the presence of two magnetic components: a background component and an enhanced component. The magnetic properties of the enhanced component suggest strong grain-size control, which is in contrast with variable grain-size distribution in loess–palaeosol from the central Loess Plateau. Chemically formed magnetic grains do not fulfil the requirements in the case of the western Loess Plateau because they may show shifts in the grain-size distribution. The difference in climate between the western and central Loess Plateau may lead to different origins and different preservation conditions of the pedogenic magnetite.