Palaeosol Sequences Research Articles

Recuperated OSL dating of fine-grained quartz in Chinese loess

The thermally transferred optically stimulated luminescence (OSL) signal from fine-grained quartz extracted from Chinese loess can be separated into two components, the recuperated and the basic transferred OSL signal. The recuperated OSL signal continues to grow with dose, beyond the dose region where the conventionally measured fast component of the OSL signal is close to saturation. A multiple-aliquot, two-part, regenerative-dose protocol, has been developed as a recuperated OSL dating method to extend the application of luminescence dating further back in time. Using the protocol the recuperated OSL signal is separated and used to estimate the equivalent dose for fine-grained quartz in Chinese loess. Ages obtained using equivalent doses determined by the recuperated OSL dating method for 12 samples from the last interglacial–glacial loess–palaeosol sequence are in agreement with multiple aliquot OSL ages and previous stratigraphic information. Ages obtained for four Chinese loess samples from close to the Brunhes/Matuyama (B/M) boundary were also consistent with the expected age of 776 ka. The recuperated OSL dating method, therefore, can go beyond the last interglacial and cover the total Brunhes epoch in Chinese loess.

East European loess–palaeosol sequences: Palynology, stratigraphy and correlation

In this paper the results of pollen analyses of the loess–palaeosol sequences (LPS) of the East European Plain are presented. Environment and vegetation evolution during the time of loess and soil formation has been characterized by pollen data of the reference sections of the Upper Oka (Likhvin–Chekalin section), the Upper Don (Strelitsa section), the Middle Kuma (Otkaznoe section), the Middle Dniester (Molodova and Ketrosy sections), and the Middle Desna (Arapovichi section) regions. Palaeomagnetic studies indicate that the sediment sequence studied spans at least the last 800 ka. The palynological climate proxies show a pattern of periodic variations comprising nine interglacial and eight glacial stages. On the basis of palynological results coupled with the electron spin resonance (ESR)-chronostratigraphic data on mollusc shell-bearing marine and terrestrial deposits, the reconstruction, periodization and distant correlation of palaeoclimatic events and deposits of glacial, periglacial and extraglacial zones of Northern Eurasia over the last 600,000 years have been carried out. Based on palaeoenvironmental evidence, it has been established that the full-interglacial conditions revealed are centred at about 580, 400, 310, 220 and between 145 and 70 ka. A broad correspondence between the long palynological sequence, directly ESR-dated warm-climate-related events and other palaeoenvironmental records described in the literature is noted at least for the 11 upper marine isotope stages (MIS 11–1).

The loess sequence from Remisowka (northern boundary of the Tien Shan Mountains, Kazakhstan)—Part I: Luminescence dating

Similar to the Chinese loess, the loess deposits surrounding the high mountain regions of Central Asia play an important role in understanding the climate and environmental change during the Pleistocene in Eurasia. Despite their thickness and widespread distribution, the loess deposits in southeast Kazakhstan have so far not been investigated in detail. The Remisowka loess–palaeosol sequence is located in the vicinity of the North Tien Shan Mountains at an altitude of 1070 m above sea level. In the profile under study nine loess layers were distinguished, intercalated by eight pedocomplexes and so indicating a similar cyclicity like the loess–palaeosol sequences in Central Asia and China. At the Remisowka section, 12 loess samples were taken to set up a more reliable chronological model for the section, using a luminescence dating approach. Polymineral fine grains were investigated by infrared optically stimulated luminescence applying the multiple aliquot additive dose protocol. Preliminary fading experiments were carried out for one sample taken from the uppermost loess layer. While the results of the uppermost layer are in agreement with geological age estimates and indicate a correlation to the Late Glacial, age underestimation is very likely for the samples below the first weak palaeosol. No significant age increase with depth was recognised. The reason for this age underestimation is not yet fully understood but could be related to anomalous fading. Further methodological approaches are necessary as well as a combination of different chronometric techniques for improvement of the results.

A Rb/Sr record of catchment weathering response to Holocene climate change in Inner Mongolia

AbstractVariation in the rubidium to strontium (Rb/Sr) ratio of the loess–palaeosol sequences has been proposed to reflect the degree of pedogenesis and weathering in the northwestern region of China. To characterize the Rb/Sr ratio of the dissolved loads of a single catchment, we analysed a 12·08 m sediment core from Daihai Lake in Inner Mongolia, north China. Dating control was provided by 210Pb, 137Cs and AMS‐14C. Sequential extraction experiments were conducted to investigate the concentrations of Rb and Sr on various chemical fractions in the lake sediments. Down‐core variation in the Rb/Sr ratios provides a record of Holocene weathering history. From 9 to 3·5 ka bp, accelerated chemical weathering was experienced throughout the Daihai catchment under mainly warm and humid conditions, and this reached a maximum at c. 5 ka bp. However, weathering was reduced between c. 8·25 and 7·90 ka bp, which may reflect the global 8·2 ka cooling event. After c. 2·5 ka bp, increased Rb/Sr ratios with higher frequency of fluctuations indicate reduced weathering within the Daihai catchment. The highest Rb/Sr ratios in the Little Ice Age lake sediments indicate the weakest phase of Holocene chemical weathering, resulting from a marked reduction in Sr flux into the basin. The Rb/Sr record also shows an enhancement of chemical weathering under today's climate, but its intensity is less than that of the Medieval Warm Period. Increased Rb/Sr in lake sediment corresponding to reduced catchment weathering is in striking contrast to Rb/Sr decrease in the glacial loess layers in the loess–palaeosol sequence. Copyright © 2005 John Wiley & Sons, Ltd.

Astronomical timescale and palaeoclimatic implication of stacked 3.6-Myr monsoon records from the Chinese Loess Plateau

Magnetic susceptibility and grain size records from two continuous red-clay and loess–palaeosol sequences on the Chinese Loess Plateau have been generated to investigate the evolution and variability of the East Asian monsoon (EAM) during the late Pliocene and Pleistocene. Tuning the grain size records to orbital obliquity and precession yields an improved astronomical timescale for the loess–palaeosol sequence (0–2.6 Ma), and an extended age model for the upper red-clay formation (2.6–3.6 Ma). This timescale indicates older ages for a number of the magnetic polarity boundaries, consistent with lock-in depth offsets in loess sequences. Good site-to-site correlation enables generation of stacked grain size and susceptibility records spanning the last 3.6 Myr. These records indicate that monsoon evolution since the late Pliocene can be subdivided into three phases: 0–1.25, 1.25–2.72 and 2.72–3.4 Ma; each phase is characterized by unique amplitude and frequency characteristics for both summer monsoon (magnetic susceptibility) and winter monsoon (grain size). Spectral analyses of the stacked monsoon proxies indicate that characteristics of both the summer and winter monsoons are dominated mainly by variance in the eccentricity (410- and 100-kyr), obliquity (41-kyr) and precession (23- and 19-kyr) bands over the past 3.4 Myr, implying a non-linear response of the long-term EAM evolution to orbital and glacial forcing.

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.

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.

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.

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.

Polycyclic luvisols in Northern Italy: palaeopedological and clay mineralogical characteristics

Two long Pleistocene palaeosol sequences in the southwestern fringe of the Lago Maggiore region (Northern Italy) were studied by a wide range of pedological methods. Particular emphasis was placed on clay mineralogy in order to distinguish the weathering intensity of different palaeosols. The clay mineralogical analyses showed a gradual transformation from the top to the central part of the studied sequences. Whereas the uppermost horizons include chlorite as a sign of weak alteration processes, the underlying palaeosols are dominated by vermiculites and mixed layers. The lowermost parts of the palaeosol sequences show different conditions as they contain neoformed kaolinite. Paleosols and pedocomplexes were correlated by mean of their pedologicial characteristics. Six main pedogenetic units have been identified in both sequences, representing different stages of soil formation. Paleopedological and clay mineralogical results indicate at least four interglacial phases, two of them showing warmer and more humid conditions than today and two of them showing climatic conditions comparable with the present day climate.

Holocene loess accumulation and soil development at the western edge of the Chinese Loess Plateau: implications for magnetic proxies of palaeorainfall

A high-resolution Holocene sequence of loess, palaeosols and incipient soils at the western edge of the Chinese Loess Plateau, dated using optically stimulated luminescence techniques, is used to identify the respective influence of dust accumulation rate, time and climate on soil magnetic properties. Dust deposition and soil formation have both been quasi-continuous through the Holocene at this site; the soils are thus accretionary in nature. The degree of soil development (as indicated both by geochemical and magnetic properties, which correlate strongly) varied through the Holocene. Compared with the less-weathered loess units, each palaeosol is enriched in nitrogen and organic carbon, depleted of carbonate due to leaching, and displays higher values of pedogenic magnetic susceptibility, frequency-dependent susceptibility (%), remanences and magnetisation. Magnetic grain size indicators show that the pedogenic ferrimagnets are ultrafine, of single domain and superparamagnetic dimensions. Sediment accumulation rates were lowest from ∼12 to 2.5 ka, providing ample time (100 s of years) for weathering and soil formation to proceed, yet pedogenesis through this interval was relatively weak. Conversely, soil development was stronger during later intervals—when loess accumulation rates were higher, and soil-forming intervals were correspondingly shorter. In terms of Jenny's (1941) soil-forming equation, accumulation rate (and thus time), sediment source (parent material) and topography show no systematic variation between the loess and the palaeosols. Therefore, climate seems to be the key soil-forming factor which has controlled the geochemical and magnetic properties of these Holocene palaeosols.

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.

An early Holocene erosion phase on the loess tablelands in the southern Loess Plateau of China

A Holocene loess profile to the west of Xi'an China was studied multi-disciplinarily to investigate the relationships between soil erosion and monsoonal climatic change. The proxy data obtained from this aeolian loess and palaeosol sequence indicate large-scale variations of climate in the southern Loess Plateau since the last glaciation. A rainwash bed, indicative of a wetter climate, excessive runoff and erosion on the loess tablelands, was identified relating to the early Holocene before the onset of the “climatic optimum”. This is synchronous with the early Holocene physiographic erosional stage identified in the valleys in North China. It means that severe erosion took place when the region was undergoing climatic amelioration during the early Holocene. The evidence presented in this paper shows that the erosion occurred as a regional response to a monsoonal climatic shift in the southern Loess Plateau. During the last glaciation, prior to the erosion phase, the land surface on the tablelands had been largely stable except for the rapid accumulation of aeolian dust and the resultant increase in its elevation. Relatively slow dust accumulation and intensive bio-pedogenesis responding to the Holocene “climatic optimum” followed the erosion phase. The loess tablelands were most vulnerable to erosion during the large-scale monsoonal climatic shift from dry-cold glacial to humid-warm post-glacial conditions in the southern Loess Plateau.

Environmental variability within the Chinese desert-loess transition zone over the last 20000 years

The desert/loess transition zone in northern China is sensitive to climate variability, which is controlled mainly by the relative strengths of the East Asian summer and winter monsoons. Sandy loess layers found in the Loess Plateau and palaeosol sequences found in the sandy desert demonstrate latitudinal shifts of the southern desert margin over the last 20000 years. Stratigraphic investigations together with radiocarbon and some thermoluminescence dating, show that during the last glacial maximum the desert margin was at its most southerly position (38°N). During the early Holocene, it moved northward about three degrees in latitude (41°N). At present, the desert margin is again close to its most southerly position (38°21 N), yet the northern boundary position of modern summer monsoon activity is placed at 41°45 N, which is close to the estimated Holocene Optimum desert margin (41°N). This situation cannot be explained from natural climate models. Hence, an external driving mechanism needs to be considered, and the most obvious one is that caused by human activity on the natural environment over the last 3000 years. Historical evidence tends to reinforce this consideration.

Climate of the last 53,000 Years in the eastern Mediterranean, based on soil-sequence Stratigraphy in the coastal plain of Israel

In this paper we present a detailed record of proxy-climatic events in the coastal belt of the eastern Mediterranean during the past 53,000 years. A sequence of alternating palaeosols, aeolianites, and dune sands, which have been dated by luminescence and by 14C, was studied by the magnetic susceptibility, particle-size distribution, clay mineralogy and soil micromorphology. Thirteen proxy-climatic events, demonstrating fluctuations of relatively dry and wet episodes, were recognized. The soil parent materials, as well as the different soil types, were rated in a semi-quantitative “dry” to “wet” scale. The palaeosol sequence is compared to a proxy-climatic record of oxygen and carbon isotopes in speleothems from a karstic cave in central Israel and to a record of lake levels of Lake Lisan and its successor, which is known as the Dead Sea. A genuine red Mediterranean Soil (Rhodoxeralfs), localy designated as “Hamra Soil” developed during the Last Glacial Stage, from 40 to 12.5 thousand calendar years BP. Climatic fluctuations that were recorded in speleothems and in changing lake levels were not preserved in this soil. During the cold and dry Younger Dryas, ca 12.5 to 11.5 calendar ka BP, a thick bed of loess material, deriving from atmospheric dust of the Sahara and Arabian deserts, covered the entire coastal belt. During this phase Lake Lisan was desiccated and turned into the modern, smaller Dead Sea. During the early Holocene, some 10–7.5 calendar ka BP, a second Red Hamra soil developed in warm and wet environments, associated with a relatively high stand of the Dead Sea level. A depletion of δ 18O and a significant enrichment of δ 13C in the speleothems were recorded during this episode. This event was in phase with the widespread distribution of freshwater lakes in the Sahara Desert and the accumulation of the S1 Sapropel in the eastern Mediterranean. Several small-scale dry and somewhat wet fluctuations of the Late Holocene, from 7.5 calendar ka BP to the present, were recorded in the coastal belt. Changes in human history, as reflected in archaeological records, are associated with proxy-climatic fluctuations. Periods of desertification and deterioration are coupled with dry episodes; periods of relative human prosperity are coupled with wetter episodes.

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.