Red Clay Sequence Research Articles

New eolian red clay sequence on the western Chinese Loess Plateau linked to onset of Asian desertification about 25 Ma ago

The expansion of inland Asia deserts has considerably influenced the environmental, social and economic activities in Asia. Aridification of inland Asia, especially timing of the initiation of Asian desertification, is a contentious topic in paleoclimatology. Late Cenozoic eolian loess-red clay sequences on the Chinese Loess Plateau, which possess abundant paleoclimatic and paleo-environmental information, can be regarded as an indicator of inland Asia desertification. Here we present a detailed magnetostratigraphic investigation of a new red clay sequence about 654 m in Zhuanglang located at the western Chinese Loess Plateau. Sedimentological, geochemical, mineralogical, and quartz morphological lines of evidence show that the red clay is of eolian origin. Magnetostratigraphic correlations indicate that this core sequence spans from 25.6 to 4.8 Ma, and typical eolian red clay appears as early as 25 Ma. This extends the lower limit of the red clay on the Chinese Loess Plateau from the previously thought early Miocene back into the late Oligocene. This new red clay record further implies that the inland Asia desertification was initiated at least by the late Oligocene. This sequence provides a unique high-resolution geological record for understanding the inland Asia desertification process since the late Oligocene.

Seven million years of wind and precipitation variability on the Chinese Loess Plateau

Recent studies of the eolian deposits in northern China have extended the East Asian monsoon history back to the early Miocene. However, the relative intensities of monsoonal winds and precipitation and the extent of their coupling prior to the Pleistocene epoch remain poorly constrained, mainly due to uncertainties in the interpretation of proxy indices generated from the Mio–Pliocene Red Clay sequences. Here we reconstruct East Asian monsoon oscillations over the past 7 Ma using magnetic susceptibility and carbonate content as summer monsoon (precipitation) proxies, and quartz grain size as a winter monsoon (wind intensity) index. Our results suggest that precipitation and wind intensity exhibited significant orbital-scale variations prior to 4.2 Ma, followed by slightly damped variability between 4.2 and 2.75 Ma. Subsequently, East Asian monsoon circulation experienced two large shifts at about 2.75 and 1.25 Ma, characterized by stepwise strengthening of glacial wind and interglacial precipitation. A remarkable change in East Asian monsoon seasonality occurred around 3.15–2.75 Ma. Prior to 3.15 Ma, strong winds were positively correlated with high effective precipitation, whereas after 2.75 Ma strong winds were negatively correlated with heavy precipitation. This shift was probably induced by a change from an insolation-forced system to one strongly influenced by the combined effects of the phased uplift of the Himalaya–Tibetan Plateau and the simultaneous development of the Northern Hemisphere ice sheets.

Correlation of paleoclimatic records between Chinese eolian sediments and Baikal lacustrine sediments

Paleo-records from continental sources such as lacustrine sediments and loess deposits have shown that terrestrial climatic change is closely synchronized with global climate change. The Baikal Drilling Project (BDP) has retrieved cores containing 1 600 m of sediment from the Baikal Lake (BKL) since 1993 (Williams et al., 2001). The unique archive contains a series of paleoclimate and paleoenvironmental proxies resolvable on different time scales over the last 5–12 million years (Kashiwaya et al., 2001a). These long cores provide essential records not only for compari-son with oceanic records of marine processes, but also for the usage as the benchmarks which can help to in-terpret other continental records. Late Cenozoic eolian deposit including Neogene red clay and Quaternary loess-paleosol sequences is widespread in the Chinese loess plateau (CLP), and is regarded as one of the best continental archives of paleoclimate change. The

A ∼6 Ma chemical weathering history, the grain size dependence of chemical weathering intensity, and its implications for provenance change of the Chinese loess–red clay deposit

Major element chemical analyses of the Baishui loess–red clay sequence (35° 24′ 10″N, 106° 54′ 43″E, Gansu Province, China) reveal that, the chemical weathering intensities inferred from CIA (chemical index of alteration) values have progressively weakened and increased in amplitude with decreasing age. The general trend of the CIA can be correlated well with the oxygen isotope variations of the deep sea sediments. Analyses of multiple size fractions (<5 μm, 5–20 μm and 20–63 μm) indicate that the CIA and the major element abundances are strongly grain size dependent. The chemical alternation of all three size fractions is relatively weak, and the long-term variation in chemical composition of the loess–red clay is mainly controlled by the mixing of fresh detritus from different source areas. The CIA variability of the coarse fractions (5–20 μm and 20–63 μm) within the section is apparently different from that of the fine fraction (<5 μm), implying a different erosion–transportation–deposition–weathering history. From 1 Ma onward, CIA values for all size fractions decrease, indicating an increasing input of fresh or poorly weathered detritus in the desert source regions of loess deposits. Sequential variations in the K 2O/Al 2O 3, Na 2O/Al 2O 3, CaO/Al 2O 3 and MgO/Al 2O 3 ratios from 4.5 Ma to about 0.6 Ma in bulk and size fractioned samples may reflect provenance change as well as changing chemical weathering processes.

Non-stationary response of Plio-Pleistocene East Asian winter monsoon variation to ice volume forcing

Abstract Recent progress both in studies of Chinese loess and deep-sea sediments have provided robust and longer records of winter monsoon variation and ice volume change back to the Late Miocene. However, when and how the winter monsoon became coupled with global ice volume change remains uncertain. Here we compare quartz grain size (a reliable winter monsoon proxy) generated from two loess-palaeosol and red clay sequences with a stacked benthic δ 18 O record (a global ice volume proxy). Our results indicate that at longer (&gt;500 ka) timescales, the winter monsoon became strongly coupled with global ice volume change at 2.1 Ma, while at orbital timescales the winter monsoon variations started to be influenced by global ice volume change at c . 3.3 Ma. Correlation coefficients between these two records further indicate that winter monsoon intensity was strongly coupled with global ice volume change during intervals of 0–1.1 Ma, 1.4–1.8 Ma, and 2–2.85 Ma. In spite of these close connections amplitude mismatches between these two records are evident in terms of both long-term trend and glacial–interglacial fluctuations, suggesting that additional processes might have played a role in modulating the response of the winter monsoon variation to ice volume forcing.

HIRM variations in the Chinese red-clay sequence: Insights into pedogenesis in the dust source area

Although extensive rock magnetic studies have been performed on the Chinese loess–paleosol sediments, few comparable studies have been applied to the underlying red-clay sediments. Because of this paucity of data, our understanding of the mineral magnetic properties of the red-clay sequence, and the paleoenvironmental information encoded in them, is limited. Here we report “hard” isothermal remanent magnetization (HIRM) variations from ∼8.1 to ∼1.2 Ma in the lower part of the loess–paleosol and the underlying red-clay sequences of the Chaona section on the Chinese Loess Plateau. The results indicate that there is a negative correlation between HIRM and frequency dependence of magnetic susceptibility χ fd ( χ fd = χ lf − χ hf, where χ lf and χ hf are magnetic susceptibility measured at 470 Hz and 4700 Hz, respectively) from ∼3.4 to ∼2.6 Ma and a positive correlation between these two proxies from ∼8.1 to ∼3.4 Ma and ∼2.6 to ∼1.2 Ma. We argue that the HIRM variations from ∼8.1 to ∼3.4 Ma and from ∼2.6 to ∼1.2 Ma reflect hematite availability in the dust source region, determined by the size of the area and climatic conditions of the dust source region. The negative correlation between HIRM and χ fd between ∼3.4 and ∼2.6 Ma suggests that magnetic enhancement during this time interval may be related to the alteration of hematite/goethite to magnetite/maghemite. We also find that HIRM data between 8.1 and 3.4 Ma show high coherence with the 100-kyr eccentricity signals, suggesting eccentricity forcing of concentration variations of hematite in the dust source area. Higher resolution samples are needed to determine if concentration variations of hematite in the dust source area are coherent with the orbital obliquity and precession forcing signals.

An 11-Ma-old red clay sequence on the Eastern Chinese Loess Plateau

Older red clay deposits on the Chinese Loess Plateau contain information of early paleomonsoon evolution and tectonic history of the Ordos platform and the Tibetan Plateau. A well-conserved eolian red clay sequence was recently discovered at Shilou, on the Eastern Chinese Loess Plateau. Paleomagnetic measurements demonstrate that polarity zones recorded in the Shilou red clay profile correspond well with polarity zones between C2An.1n and C5n.2n of the GPTS, and the basal age of the study profile is approximately 11.0 Ma. Field observation, grain-size frequency distribution and quartz grain morphology suggest a wind-blown origin for this sequence. This indicates that the Eastern Loess Plateau began to accumulate dust deposits at 11 Ma ago, implying earlier establishment of the East Asian paleomonsoon probably owing to uplifting of the Tibetan Plateau and ongoing global cooling. It also demonstrates that the Eastern Loess Plateau belonging to the Ordos platform was slowly uplifted and suffered from erosion in the early Neogene, and has no conserved eolian deposits older than 11 Ma as in the Western Chinese Loess Plateau.

Optically stimulated luminescence dating as a tool for calculating sedimentation rates in Chinese loess: comparisons with grain‐size records

AbstractUnderstanding loess sedimentation rates is crucial for constraining past atmospheric dust dynamics, regional climatic change and local depositional environments. However, the derivation of loess sedimentation rates is complicated by the lack of available methods for independent calculation; this limits interpretation of the environmental changes revealed by the loess record. In particular, while the Quaternary/Neogene Chinese loess and Red Clay sequences have the potential to provide detailed records of past sedimentation and climate change, there is great uncertainty concerning: (i) the influences on sediment grain‐size and accumulation; and (ii) their relationship through time and across the depositional region. This uncertainty has led to the widespread use of assumptions concerning the relationship between sedimentation rate and grain‐size in order to derive age models and climate reconstructions. To address this uncertainty, detailed independent age models, based on optically stimulated luminescence dating, undertaken at 10 to 40 cm intervals at five sections across the Loess Plateau in China, have been used to calculate sedimentation rates and make comparisons with grain‐size changes over the late Pleistocene and Holocene. The results demonstrate that sedimentation rates are site specific, extremely variable over millennial timescales and that this variation is often not reflected in grain‐size changes. In the central part of the Loess Plateau, the relationship between grain‐size and sedimentation rate appears most complex, suggesting an interplay between local conditions at source and sink and a changing emplacement mechanism. This observation further undermines the common use of loess sedimentation age models that rely on a derived relationship between grain‐size and sedimentation rate from a type section. The results also highlight the difficulty in assigning specific environmental causes to sedimentation rate changes and, to a lesser extent, grain‐size shifts.

AC magnetic susceptibility studies of Chinese red clay sediments between 4.8 and 4.1 Ma: Paleoceanographic and paleoclimatic implications

Recent studies show that measuring AC magnetic susceptibility (with in‐phase χ′ and quadrature χ″ components) versus temperature provides an effective way to map the grain‐size distribution of pedogenic maghemite. Applying this method, we mapped the pedogenic maghemite grain‐size distribution of samples of the red clay sediments deposited on the Chinese Loess Plateau (CLP) during the interval 4.8–4.1 Ma, during which the validity of magnetic susceptibility as an East Asian summer monsoon precipitation intensity proxy has been questioned. The results show that the pedogenic maghemite grain‐size distribution is the same as in the overlying loess‐paleosol sequence and in the other intervals of the red clay sequence, suggesting similar pedogenesis mechanisms and marked precipitation seasonality on the CLP between 4.8 and 4.1 Ma compared with the other intervals. We argue that the seasonal position shift of the polar westerlies produces the required precipitation seasonality and thus produces a uniform pedogenic grain‐size distribution during this time interval. Reconstructing paleo‐rainfall on the central CLP on the basis of surface calibration results suggests that the intensification of the East Asian summer monsoon might be a key trigger for the subsequent significant ocean and cryosphere adjustments during the Pliocene.

Distribution of Palygorskite in the Lingtai Profile of Chinese Loess Plateau: Its Paleoclimatic Implications

AbstractPalygorskite is a typical indicator mineral of the arid and strong evaporation environment. Distribution of palygorskite in loess‐red clay sequences may act as an important indicator for reconstruction of the paleoenvironment and paleoclimate. In this paper, field emission scanning electron microscope and high‐resolution transmission electron microscope observations on the red clay‐loess‐paleosol of the Renjiapo profile at Lingtai, Gansu Province indicate that palygorskite occurs widely in red clay sequences formed before 3.6 Ma, but no occurrence has been found in eolian sediments since 3.2 Ma. Micromorphological features and microstructure of palygorskite show that it is an autogenic mineral formed during pedogenesis, and transformed from illite‐montmorillonite under the pore water action. In the Lingtai profile, the disappearance horizon of palygorskite is consistent with those of increasing magnetic susceptibility, dust flux and depositional rate. The distribution of palygorskite in the profile indicates that the interval of around 3.6 Ma was an important transformation period of the East Asian paleomonsoon, when changes took place in the East Asia paleoclimate pattern, i.e. a high‐frequency strong fluctuation alternative evolution of the environment. Therefore, palygorskite is a key indicator mineral of the East Asian paleomonsoon evolution of that time.

Chemical weathering intensity of the Late Cenozoic “Red Clay” deposits in the Carpathian Basin

INTRODUCTIONVery little work had been previously done on thistopic in Hungary. In the past decade, little attention hasbeen paid to the red clay in the Carpathian Basin. Dif-ferent views on the formation, properties, and distribu-tion of red clays have been published by severalauthors. Many geologists draw parallels between redclays and bauxites [1–3]. Complex investigationsincluding geology, geomorphology, mineralogy, andgeochemistry were carried out by only a few authorslike Schweitzer and Szo r [4] and Kovacs [5].The most significant progress made on the red clayresearch worldwide is that sedimentology, geochemis-try, geomorphology, and the field survey all demon-strate a wind-blown origin for the red clay [6–9], likethe overlying Pleistocene and Holocene loess. Further-more chemical weathering was studied using geochem-istry [10–13].Important key formations in the Late Cenozoicstratigraphy are the red (silty) clays in the CarpathianBasin. Litho-, bio-, chemo-, and magnetostratigraphicdata show that they were formed in different periods [4,5]. The youngest red paleosol (or reddish clay) is ofEarly Pleistocene age. The older one (red clay) wasformed in the Early and Middle Pliocene [4, 5, 14, 15].This paper deals with the geochemical analysis ofthe red clay formation in the Carpathian Basin and eval-uates chemical weathering intensities.MATERIALS AND METHODSThe investigated sections selected for this study arelocated mainly on the foothills of Hungarian mountains(Fig. 1). These sections are of Pliocene and Early Pleis-tocene age [4, 5, 14, 15]. It consists mainly of threetypes of sediments from upper to the lower: Quaternaryloess–paleosol sequence, Pliocene red clay sequence,and sand or sandy sediments (Fig. 2). Geochemicalanalyses were carried out on 50 samples from 15 redclay sequences from the northern, the southern, and thewestern part of Hungary (Fig. 1). All samples were

Grain size of loess, palaeosol and Red Clay deposits on the Chinese Loess Plateau: Significance for understanding pedogenic alteration and palaeomonsoon evolution

To assess pedogenic modification to grain size distributions of loess, palaeosol and Red Clay deposits on the Chinese Loess Plateau and to understand long-term evolution of the East Asian palaeomonsoon since the late Miocene, we investigate a continuous loess–palaeosol–Red Clay sequence at Lingtai (south Chinese Loess Plateau) and another parallel Red Clay sequence at Zhaojiachuan (central Chinese Loess Plateau). By analyzing the grain size distributions of bulk samples and chemically isolated quartz samples, the relative intensity of pedogenic alteration of the loess, palaeosol and Red Clay deposits can be quantified. Comparisons of the grain size distributions and contents of different grain size fractions between the bulk and the quartz samples suggest that pedogenic alteration is apparently stronger in the Red Clay sequence than in the overlying loess–palaeosol deposits. Furthermore, grain size parameters derived from the bulk and the quartz samples, such as mean grain size, coarse fraction content and U-ratio, exhibit similar variations in the loess–palaeosol sequence (Quaternary, 0–2.6 Ma), whereas these grain size parameters of quartz samples show different variability from those of bulk samples in the Red Clay sequence (late Miocene to Pliocene, 2.6–7 Ma). Grain size of quartz from the loess–palaeosol and Red Clay deposits exhibits distinct and persistent oscillations from the late Miocene to the Pleistocene, implying that significant fluctuations of the palaeomonsoon climate in East Asia might have occurred at least since late Miocene time.

Palynological evidence for Late Miocene–Pliocene vegetation evolution recorded in the red clay sequence of the central Chinese Loess Plateau and implication for palaeoenvironmental change

In northern China, the Late Miocene–Pliocene red clay in the eastern Loess Plateau fills a gap of climate records between the well-known loess-soil sequences of the last 2.6 Ma and the Miocene loess-soil sequences from the western Loess Plateau. Previous studies indicate that the red clay is also of wind-blown origin, covering the period from ∼ 7–8 to ∼ 2.6 Ma. The red clay therefore provides a good archive to reconstruct paleoecological succession and paleoclimate change. In this study, a palynological investigation was conducted on the late Miocene–Pliocene red clay sequence at Xifeng, central Loess Plateau, which provides new insights into the nature of the evolution of vegetation and climate change from ∼ 6.2 to ∼ 2.4 Ma. Our results show that during this period the central Loess Plateau region was covered mainly by a steppe vegetation, indicating long lasting dry climatic condition. Three vegetational zones were recognized during this period. Zone A (∼ 6.2 to ∼ 5.8 Ma) is characterized by a steppe ecosystem; Zone B (∼ 5.8 to ∼ 4.2 Ma) is characterized by a significant increase of temperate forest plants, indicating a relatively humid regional climate; Zone C (∼ 4.2 to ∼ 2.4 Ma) indicates a typical steppe ecosystem. The vegetation shift at about 4.5–3.7 Ma, when the temperate forest plants decrease, the vegetation gradually changed to typical grassland and even to desert steppe. This is interpreted to represent a drying event. The uplift of the Tibetan Plateau at about 4.5 Ma that resulted in the intensification of the monsoon reversal is thought to have played an important role in this significant ecological change. High-latitude cooling may have partially contributed to the climate shift during ∼ 4.5 to ∼ 3.7 Ma in the Loess Plateau region, and most likely was the driving force for the ecological shift at about 3.7 Ma.

Evaluation of osmium isotopes and iridium as paleoflux tracers in pelagic carbonates

New osmium (Os) isotope and platinum group element (PGE) concentration data are used in conjunction with published 3He and Th isotope data to determine the relative proportions of lithogenic, extraterrestrial and hydrogenous iridium (Ir) in a Pacific pelagic carbonate sequence from the Ocean Drilling Program (ODP) Site 806 on the Ontong Java Plateau (OJP). These calculations demonstrate that lithogenic and extraterrestrial contributions to sedimentary Ir budget are minor, while hydrogenous Ir accounts for roughly 85% of the total Ir. Application of analogous partitioning calculations to previously reported data from a North Pacific red clay sequence (LL44-GPC3) yields very similar results. Total Ir burial fluxes at Site 806 and LL44-GPC3 are also similar, 45 and 30 pg cm −2 kyr −1, respectively. Average Ir/ 3He and Ir/xs 230Th initial ratios calculated from the entire Site 806 data set are similar to those reported earlier for Pacific sites. In general, down-core profiles of Ir, 3He and xs 230Th initial, are not well correlated with one another. However, all three data sets show similar variance and yield sediment mass accumulation rate estimates that agree within a factor of two. While these results indicate that Ir concentration has potential as a point-paleoflux tracer in pelagic carbonates, Ir-based paleoflux estimates are likely subject to uncertainties that are similar to those associated with Co-based paleoflux estimates. Consequently, local calibration of Ir flux in space and time will be required to fully assess the potential of Ir as a point paleoflux tracer. Measured 187Os/ 188Os of the OJP sediments are systematically lower than the inferred 187Os/ 188Os of contemporaneous seawater and a clear glacial–interglacial 187Os/ 188Os variation is lacking. Mixing calculations suggest Os contributions from lithogenic sources are insufficient to explain the observed 187Os/ 188Os variations. The difference between the 187Os/ 188Os of bulk sediment and that of seawater is interpreted in terms of subtle contributions of unradiogenic Os carried by particulate extraterrestrial material. Down-core variations of 187Os/ 188Os with Pt/Ir and Os/Ir also point to contributions from extraterrestrial particles. Mixing calculations for each set of several triplicate analyses suggest that the unradiogenic Os end member cannot be characterized by primary extraterrestrial particles of chondritic composition. It is noteworthy that in efforts aimed at determining the effect of extraterrestrial contributions, 187Os/ 188Os of pelagic carbonates has greater potential compared to abundances of PGE. An attempt has been made for the first time to estimate sediment mass accumulation rates based on amount of extraterrestrial Os in the OJP samples and previously reported extraterrestrial Os flux. Throughout most of the OJP record, Os isotope-based paleoflux estimates are within a factor of two of those derived using other constant flux tracers. Meaningful flux estimates cannot be made during glacial maxima because the OJP sediments do not record the low 187Os/ 188Os reported previously. We speculate that this discrepancy may be related to focusing of extraterrestrial particles at the OJP, as has been suggested to explain down-core 3He variations.

Marked ecological shifts during 6.2–2.4 Ma revealed by a terrestrial molluscan record from the Chinese Red Clay Formation and implication for palaeoclimatic evolution

A new molluscan fossil record from the late Miocene–Pliocene Xifeng Red Clay sequence in the central Loess Plateau, northern China, reveals the process of ecological environmental changes during ∼ 6.2–2.4 Ma. Three marked ecological shifts in mollusk assemblages occurred at about 5.4, 4.5, and 3.4 Ma, which reflect changes in the East Asian monsoon circulation. A predominantly cold-aridiphilous group reveals an extremely cold dry climate due to strengthened East Asian winter monsoon during ∼ 6.2–5.4 Ma. A predominantly thermo-humidiphilous group from ∼ 5.4–4.5 Ma indicates a strengthening of the East Asia summer monsoon circulation. The marked occurrence of meso-xerophilous taxa during ∼ 4.5–3.4 Ma implies mild climatic conditions. From 3.4 Ma, the cold-aridiphilious species again became dominant in the fossil assemblages, indicating that the winter monsoon was gradually intensifying towards the Quaternary glaciations. Climate changes in this region were characterized by stepwise cooling from 5.4 to 2.4 Ma with a 1 Ma rhythmicity. The cooling trend is in good agreement with the general global cooling trend during this period, as documented by marine δ 18O records. The formation and development of the Northern Hemisphere ice sheets during the late Pliocene accelerated the climate deterioration towards the Quaternary glaciations. The history of environmental changes revealed by the Red Clay molluscan fossils is coupled in phase with the process of Tibetan Plateau uplift, which may be the major cause and forcing mechanism of late Miocene–Pliocene environmental changes in the Loess Plateau.

Pollen record from red clay sequence in the central Loess Plateau between 8.10 and 2.60 Ma

The Late Miocene and Pliocene are the key periods for understanding the origin and development of the present Asian monsoon circulations and ecologic environments. Here we present a pollen record from Chaona Red Clay section located in the central Loess Plateau in attempt to establish the histories of vegetation and associated climate changes between 8.10 and 2.60 Ma. Our results show that Gramineae-dominated woodland-grasslands developed in this region withCedrus- and Pinus-characterized montane coniferous forests distributing in higher elevations from 8.10 to 6.73 Ma, probably suggesting a semi-humid climate in a warm-temperate zone. A subsequent expansion ofUlmus-dominated deciduous forests and a synchronous increase of Gramineae-dominated grassland reflect a warmer and more humid climate between 6.73 and 5.67 Ma. The vegetation changed to anArtemisia- and Gramineae-characterized steppe in lower elevations and to a coniferous forest in higher elevations from 5.67 to 3.71 Ma, implying probably a warm and semiarid climate in lowland and hill, and a colder and moister climate in mountain. During this period, a considerable warmer and more humid climate occurred between 4.61 and 4.07 Ma as indicated by pollen assemblages. The period between 3.71 and 2.58 Ma was characterized by the disappearance ofCedrus andTsuga and also by an abrupt expansion of Cupressaceae, reflecting a drastic enhancement of monsoon-related climatic seasonality.

Magnetic properties of Jiaxian red clay sequences from northern Chinese Loess Plateau and its paleoclimatic significance

Detailed rock magnetism investigation of the Jiaxian red clay sequences indicated that there are common magnetic mineralogy properties in red clay and loess-paleosol sequences from the Chinese Loess Plateau as well as the marked properties of themselves, magnetic minerals mainly with magnetite, maghemite, hematite, and possibly limonite/goethite contributing to the magnetic behavior. Meanwhile, it is found that the strong paleosol in red clay sequences has a lower coercivity and higher content of ultra-fine ferrimagnetic grains than that of the weak paleosol, which is similar to loess and paleosol in upper Wucheng Loess sequences, and indicates that humid conditions and relatively strong pedogenesis play a significant role in the increase of ultra-fine magnetic minerals and transformation of the magnetic minerals. This suggests that, like Quaternary loess-paleosols, the change of characteristics of paleoclimatic conditions of the late Tertiary red clay deposits is fluctuant. In addition, the results of magnetic hysteresis properties show that the applied saturated field for samples from the Jiaxian red clay sequences is higher than that of the samples from eastern and southern Chinese Loess Plateau. It is obviously shown that there exist more hard magnetic minerals and relatively weak biochemical processes in the Jiaxian red clay sequences on northern Chinese Loess Plateau. We conclude that the paleoclimatic environment is different between northern and eastern/southern Chinese Loess Plateau, and it should be more arid in northern Chinese Loess Plateau.

Salinity episodes and their reversal in the late Pliocene of south-western Australia

Fossil pollen and grain size analysis of sediments from Yallalie in south-western Australia is used to reconstruct the history of salinization and aridity of the region between 2.63 and 2.56 Ma. Three well-defined episodes of aridity are defined by a reduction in humid woodland and expansion of chenopod shrubland around 2.59, 2.56 and 2.558 Ma. Each episode lasted an estimated 2–3000 years. The grain size data supports the general aridity conclusion but also demonstrates there was a large amount of environmental variability, especially between about 2.59 and 2.56 Ma, which included short term wetting and drying cycles. These cycles are at sub-Milankovitch time scales and suggest that the vegetation patterns show much more inertia to change than do the sediment dynamics. The general pattern of change at Yallalie is similar to that revealed in the Chinese Loess and Red Clay sequence but the detail of change is much greater in the lake sediment than revealed for the aeolian sediment of central Asia.

Red clay sediment in the central Chinese Loess Plateau and its implication for the uplift of the Tibetan Plateau

The widely distributed red clay sediment underlying the Chinese Loess Plateau truly records the Neogene environmental evolution, and its genesis and development are intrinsically related to the uplift processes of the Tibetan Plateau and the evolution of East Asia monsoon system. In this paper, a detailed magnetostratigraphy of a loess-red clay section (107°13′E, 35°02′N) from the central Loess Plateau is reported. The loess-red clay sequence is composed of 175 m Quaternary loess-paleosol sequence and 128 m Neogene red clay sediments. Based on the correlation with the standard geomagnetic polarity time scale, the paleomagnetic results indicate that the age of Chaona red clay sequence extends to 8.1 Ma, which is the older red clay deposition in the central Chinese Loess Plateau. The commencement of red clay at ∼8.1 Ma may imply that the Ordos planation surface was broken by the movement of the Haiyuan-Liupanshan Faults, which was related to the uplift of the Tibetan Plateau induced by the collision of India Plate and Eurasian Plate. And the western part adjacent to the Tibetan Plateau was uplifted to form the embryo of the Liupan Shan (Mts.) and the eastern part was down-faulted to receive red clay deposition. We link this faulting to an initial uplift of the Tibetan Plateau. The undulating nature of the broken Ordos planation surface may explain the chronological differences and depth discrepancies among various cross-sections of red clay.

Pollen record from red clay sequence in the central Loess Plateau between 8.10 and 2.60 Ma

Pollen record from red clay sequence in the central Loess Plateau between 8.10 and 2.60 Ma