Red Clay Sequence Research Articles

Goethite in the Red Clay sequences on the western Chinese Loess Plateau and its responses to the middle Miocene Climate Transition

The middle Miocene Climate Transition (MMCT, ca. 14 Ma), with a sharp drop in temperature, is a key transition period in the Earth’s climatic and biotic evolution. However, our knowledge of how arid-monsoon environments were coupled during the middle Miocene Climate transition remains limited, due to the lack of robust proxies from well-dated sedimentary sequences covering the MMCT in monsoon areas. Goethite is an abundant iron oxide in soils, which is sensitive to persistent wet and cold environments. However, aluminium (Al) substitution is ubiquitous in the pedogenic process, and the Al substitution for goethite in the Red Clay sequence is unclear. In this study, we combined the rock magnetic and DRS methods to assess the Al substitution level of goethite and quantify the goethite content in the Zhuanglang (ZL) Red Clay deposits from the western Chinese Loess Plateau. Our results show that Al substitution in the ZL Red Clay sequence is relatively stable, facilitating the quantification of goethite using this approach. Goethite content displays an increasing trend from approximately 0.2% at 18 Ma to 0.5% at 14 Ma, and then gradually decreased towards the late Miocene in the ZL Red Clay deposits. The maximum goethite production at around 14 Ma indicates a cold and wet climate condition during MMCO at this location. Together with other palaeoenvironmental proxies of this sequences and other sedimentary sequences in the Tianshui Basin, we suggest that climate conditions during the MMCT in the monsoonal western CLP were relatively cold and wet, which was different from the cold and dry climate in the central Asian. Global cooling and the uplift of the Tibetan Plateau might be predominantly responsible for the cold and wet climate during the MMCT.

A Humid East Asia During the Early Pliocene Indicated by Calcite Nodules From the Chinese Loess Plateau

AbstractUnderstanding the monsoonal climate over East Asia during the warm Pliocene, the closest analog of the future warm climate, could better inform us of the regional hydrological responses to global climate change. However, the variations and controlling mechanisms of the regional hydrology during this warm period are not determined due to discrepancies among different proxy‐derived records. Here we apply a multiproxy approach based on the geochemistry of calcite nodules from a Red Clay sequence located on the southern edge of the Chinese Loess Plateau. Both the trace metal/Ca ratios and the carbon and oxygen isotopic compositions of calcite nodules show low values during 5.4–4.1 Ma and increased during 4.1–3.3 Ma, together indicating a humid climate during the early Pliocene, the onset of drying starting at ∼4.1 Ma and further intensification at 3.6 Ma. The timings of these hydrological transitions are consistent with global temperature changes, underlining the crucial role of meridional thermal gradient in shaping the regional hydroclimate over East Asia by modulating the strength and position of the East Asian summer monsoon.

Provenance of eolian deposits in the Xorkol Basin: Implications for Eocene dust-transport pattern in western China

Atmospheric circulation in western China significantly affects the inland climate of Asia. Constraining the provenance of eolian sequences can provide robust evidence for dust-transport pathways, and thus the evolution of paleo-atmospheric circulation. Western China has been dominated by the westerly wind regime since the late Oligocene, as demonstrated by provenance studies of eolian deposits. However, the wind regime responsible for the accumulation of eolian deposits during the Eocene is unclear due to a lack of corresponding provenance studies. Here, we present the first provenance analysis for an Eocene (ca. 51−40 Ma) eolian Red Clay sequence in the Xishuigou Formation of the Xorkol Basin in western China, based on multiproxy geochemical and geochronological data. Comparison of zircon U−Pb ages from the Xishuigou sequence with ages from potential source regions reveals that the northern piedmont of the West Kunlun Range was a persistent source, although sediments from the nearby Altun-Xorkol region were an important dust source for the lower part of the Xishuigou sequence which were deposited between ca. 51 Ma and 46.5 Ma. These results reveal that the westerly dust-transport pattern has been dominant in western China since at least ca. 51 Ma. The similarity of provenance between the Eocene Red Clay of the Xishuigou Formation and the Neogene eolian sequence of the overlying Caihonggou Formation in the same area implies that this dust-transport pattern was stable from the Eocene to the Neogene, despite dramatic changes in paleogeography, paleotopography, and global climate.

Controlling factors and palaeoclimatic significance of colour reflectance in the Late Tertiary red clay on the Chinese Loess Plateau

The colour of soil is one of its most striking features, and records the palaeoenvironment conditions when the soil is formed; however, the controlling factors and palaeoclimatic significance of colour reflectance in the Late Tertiary red clay are poorly understood. In this study, the Jiaxian section, on the northern edge of the Chinese Loess Plateau, was selected to explore the aforementioned issue using colour reflectance, diffuse reflectance spectroscopy (DRS), geochemical, and magnetic approaches. In the red clay sequence, (1) the concentration of iron oxides (mainly haematite and goethite) and the intensity of pedogenesis were significantly positively correlated with redness (a*) and yellowness (b*). (2) a*, b*, and a*/b* can be used as proxy indicators of haematite concentration, goethite concentration, and temperature, respectively. (3) The parameters derived from colour reflectance and DRS measurements were proven to be better than magnetic susceptibility (χ) in recording palaeoclimatic evolution, and Ca*b* was better than the chemical weathering index in recording soil development.

The 173‐kyr Obliquity Cycle Pacing the Asian Monsoon in the Eastern Chinese Loess Plateau From Late Miocene to Pliocene

AbstractWe conduct magnetostratigraphy and cyclostratigraphy on an eolian red clay sequence spanning 7–3.1 Ma in the eastern Chinese Loess Plateau. We pay more attention to the unconventional 173‐kyr obliquity modulated cycle which is associated with the secular frequency interference of orbital inclinations between Earth and Saturn. Similar to the 405‐kyr eccentricity cycles, the 173‐kyr obliquity band proved to be an important orbital driving component by the latest astronomical findings, and can serve as a chronometer of terrestrial air circulation reconstruction back to 7 Ma. Comparison with magneto‐cyclo‐bio‐stratigraphic timescales of another noted eolian sequence from the adjacent area, the 173‐kyr cycle is exceptionally presented as a robust recognition of the cyclical sedimentary patterns for the East Asia monsoon deposits.

One and a Half Million Yearlong Aridity During the Middle Eocene in North‐West China Linked to a Global Cooling Episode

AbstractThe Eocene record of substantial aridification near Tibet was reported to mimic the global climate cooling trend, overwriting the previously proposed dominant role of the Tibetan Plateau uplift in the aridification (Li et al., 2018, https://doi.org/10.1038/s41467‐018‐05415‐x). Here we present new paleoclimate data from the red clay sequence deposited between 40 and 50 Ma in Altun Shan at the northeastern edge of the Tibetan Plateau. After building an age model using a compilation of magnetostratigraphy and cyclostratigraphy, we demonstrate that our record of magnetic susceptibility in the Altun Shan red clay exhibits variations linked to eccentricity cycles. Our age model allows us to estimate the age of eight short geomagnetic events, cryprochrons, in Altun Shan. Further we show that the aridification interval in Altun Shan coincides with (i) a cooling event recorded in the global oxygen isotope record, (ii) a sea surface temperature record on the east Tasmanian plateau, and (iii) an aridity record in the surrounding sedimentary basins of Central Asia. The middle Eocene aridity and cooling reached its maximum 45.5‐44 Ma.

Causation and mechanism of magnetic susceptibility trend in Upper Miocene–Pliocene red clay deposits of the eastern Chinese Loess Plateau

The Upper Miocene–Pliocene red clay deposits of the Chinese Loess Plateau (CLP), like the overlying Quaternary loess, have recorded abundant paleoclimatic evolution information. In this study, we found that the variation in the magnetic susceptibility of seven sections across a north–south climate gradient in the eastern CLP exhibited an oscillatory upward trend. Prior to this research, much less was known about the causation and mechanism of this trend. Among the seven sections, the Jiaxian and Duanjiapo sections are located in the northernmost and southernmost of the climatic gradient, respectively. These representative sections were therefore selected to investigate the causation and mechanism of the aforementioned trend using magnetic measurements. The results were as follows. (1) The absolute and relative content of fine-grained ferrimagnetic minerals displayed an oscillatory upward increasing trend in both of the red clay sequences, which was the primary reason for the susceptibility increase in fluctuations. (2) The absolute content of antiferrimagnetic minerals was nearly equivalent in each red clay sequence. (3) Based on the combination of the results of present study and previous study findings, we found that the weathering and pedogenesis intensity of the red clay sequence showed an oscillatory upward trend during 7–2.6 Ma, which was closely linked with the strengthened East Asian summer monsoon in oscillations. These findings are probably the main cause for the oscillatory upward increasing fine-grained ferrimagnetic minerals in Upper Miocene–Pliocene red clay sequence. Further, this is likely the mechanism for the oscillatory upward increase of χ in the red clay sequence.

Chlorite weathering linked to magnetic enhancement in Red Clay on the Chinese Loess Plateau

Magnetic parameters are widely used in the loess-palaeosol sequence tracing Quaternary climate change on the Chinese Loess Plateau (CLP). However, the climatic implication and magnetic enhancement mechanism in aeolian Red Clay on the CLP is still debated. Chlorite is a common Fe-bearing silicate in Red Clay and it is easily to be weathered. The transformation of weakly magnetic ferrihydrite, a product in chlorite weathering process, into strongly magnetic iron oxides has been linked to magnetic enhancement in many soils. Here, we present a complete chlorite weathering record within the Red Clay sequence through a detailed mineralogical investigation, from a 125-m thick eolian Red Clay deposit in the Chaona section (~8.1 to 2.6 Ma) of the central CLP to explore the link between changes in chlorite geochemical composition and magnetic susceptibility enhancement and regional climate. The results suggest a concomitant evolution of chlorite Fe content and magnetic susceptibility, indicating that Fe released from chlorite brucite-like interlayers, which induced ferrihydrite formation, is responsible for the enhanced magnetic susceptibility in the CLP Red Clay deposits. Moreover, the results also show that the chlorite Fe content exhibited a stepwise decrease, with two accelerated stages at ~6.2 Ma and ~3.6 Ma. The post-6.2 Ma evolution of chlorite Fe content is related to increased precipitation caused by phased enhancement of the East Asian summer monsoon (EASM). Our study also suggests that changes in chlorite chemical composition and crystallinity linked to soil weathering are useful proxies in tracing past weathering intensity and climate change within arid-less humid regime.

Late Miocene–Pliocene climate evolution recorded by the red clay cover on the Xiaoshuizi planation surface, NE Tibetan Plateau

Abstract. The Pliocene climate and its driving mechanisms have attracted substantial scientific interest because of their potential as an analog for near-future climates. The late Miocene–Pliocene red clay sequence of the main Chinese Loess Plateau (CLP) has been widely used to reconstruct the history of interior Asian aridification and the Asian monsoon. However, red clay sequences deposited on the planation surface of the Tibetan Plateau (TP) are rare. A continuous red clay sequence was recently discovered on the uplifted Xiaoshuizi (XSZ) planation surface in the Maxian Mountains, northeastern (NE) TP. In this study, we analyzed multiple climatic proxies from the XSZ red clay sequence with the aim of reconstructing the late Miocene–early Pliocene climate history of the NE TP and to assess regional climatic differences between the central and western CLP. Our results demonstrate the occurrence of minimal weathering and pedogenesis during the late Miocene, which indicates that the climate was arid. We speculate that precipitation delivered by the paleo East Asian summer monsoon (EASM) was limited during this period and that the intensification of the circulation of the westerlies resulted in arid conditions in the study region. Subsequently, enhanced weathering and pedogenesis occurred intermittently during 4.7–3.9 Ma, which attests to an increase in effective moisture. We ascribe the arid–humid climatic transition near ∼4.7 Ma to the expansion of the paleo-EASM. The warming of the high northern latitudes in response to the closure of the Panama Seaway may have been responsible for the thermodynamical enhancement of the paleo-EASM system, which permitted more moisture to be transported to the NE TP.

Uplift of the Lüliang Mountains at ca. 5.7 Ma: Insights from provenance of the Neogene eolian red clay of the eastern Chinese Loess Plateau

The Lüliang Mountains, located at the western margin of the Trans-North China Orogen, are thought to have undergone several uplift events during the late Mesozoic and Cenozoic due to far field effects of the India–Eurasia collision and/or Pacific Plate subduction. However, the timing and mechanisms of late Cenozoic uplift of the Lüliang Mountains are not clear. Our investigation of the source characteristics of the Shilou red clay sequence, an eolian deposit on the eastern Chinese Loess Plateau adjacent to the Lüliang Mountains, provides a new understanding of the relationship between the material composition of the eolian sediment and regional tectonic activity. Grain size data for the Shilou red clay sequence reveal an abrupt increase at ca. 5.7 Ma, and UPb detrital zircon geochronology indicates that the major source areas of Shilou red clay shifted after ca. 5.7 Ma, from the Junggar Basin, western Mu Us desert, and Gobi-Alxa arid lands, to the eastern Mu Us desert and the Lüliang Mountains. Detrital zircons younger than 5.7 Ma in the Shilou red clay have similar U and Th contents to zircons from the Lüliang Mountains, indicating that the mountains acted as a proto-source for the red clay after ca. 5.7 Ma. We suggest that the influx of coarser grained sediment is due to rapid uplift of the Lüliang Mountains at ca. 5.7 Ma, and that this timing is consistent with northeastward propagation of mountain uplift in response to the India–Eurasia collision.

A new record of late Pliocene-early Pleistocene aeolian loess–red clay deposits from the western Chinese Loess Plateau and its palaeoenvironmental implications

The loess–red clay sequences in northern China provide high-resolution terrestrial records of Asian monsoon evolution and aridification of the Asian interior. To date, however, aeolian deposits of late Pliocene-early Pleistocene age (3.5–2.4 Ma) have only rarely been reported from the western Chinese Loess Plateau (CLP), which significantly hinders our understanding of the distribution of aeolian deposits and the palaeoenvironmental evolution of the region. Here, we present magnetostratigraphic, lithologic and magnetic susceptibility results for two recently-drilled boreholes from the north bank of Baxie River, central Linxia Basin, which are highly correlative with those of the loess–red clay deposits spanning the interval from 3.6 to 2.4 Ma in the eastern CLP. Our results provide the first direct evidence for the occurrence of late Pliocene-early Pleistocene aeolian deposits in the western CLP and provide new insights into the distribution of aeolian deposits in northern China. The spatial coherence of the magnetic susceptibility fluctuations further indicates that magnetic susceptibility is a powerful tool for stratigraphic correlation of late Pliocene aeolian deposits in the western CLP. In addition, our results demonstrate that erosional events may have occurred in the early or middle Pleistocene, and they may provide new insights into the reasons for the absence of loess–red clay deposits from 3.5 to 2.4 Ma in most parts of the western CLP.

Aeolian silt transport processes as fingerprinted by dynamic image analysis of the grain size and shape characteristics of Chinese loess and Red Clay deposits

This study applied dynamic image analysis (DIA; Sympatec Qicpic) to characterize the grain size and shape of Chinese aeolian sediments in order to fingerprint their transportation processes. This is the first time this technique has been applied to late Neogene and Quaternary silt particles (2–63μm) from the Chinese Loess Plateau (CLP). We selected four well-studied Quaternary loess-palaeosol sequences along a north-south transect across the CLP and compared their grain size distribution obtained by DIA with that yielded by laser diffraction particle size analysis (LD; Fritsch Analysette 22 and Sympatec HELOS KR). This comparison demonstrated that DIA is successfully able to differentiate loess units from palaeosols, and to characterize clearly spatiotemporal variations in the grain size records of loess-palaeosol sequences formed during the last two glacial and interglacial periods. This is consistent with grain size results obtained using LD. DIA is also able to characterize spatial variations in the more fine-grained aeolian Red Clay deposits underlying the Quaternary loess, and allows the quantification of the fluvial contribution to Red Clay sequences. DIA of the characteristics of grain shapes in loess-palaeosol sequences and Red Clay deposits revealed a systematic pattern, whereby the aspect ratio decreased with increasing grain size, indicating that systematic shape sorting occurred during the aeolian transportation of these dust particles. It could be inferred from our study that particles in a certain grain size range correspond to a specific aspect ratio range, and may in turn be aerodynamically distinguishable from each other and further correlated with the wind velocity/strength. Also evident from analysis of our DIA data was a subtle but systematic downwind decrease in the aspect ratio of the particles in the loess units. This observation suggests that elongated and/or flat particles (with a low aspect ratio) were transported further downwind than more symmetrically shaped particles (with a high aspect ratio). This study indicates that DIA of grain size and shape characteristics can be an additional powerful tool for identifying grain size and shape sorting trends, determining the dominant mode of transport, and reconstructing transport pathways of silt-sized aeolian sediments.

Goethite Concentration Variations in the Red Clay Sequence on the Chinese Loess Plateau

AbstractThe Goethite is a common magnetic mineral in soils and is important for understanding past climatic and environmental change. Although goethite concentration records are available for the Quaternary loess‐paleosol sequences from the Chinese Loess Plateau (CLP), no goethite concentration record is available for the underlying Red Clay sequence. Here, we generate a record of goethite concentration from the Chaona section on the CLP and investigate the relationship between goethite and ferrimagnetic mineral concentration and climate parameters on the Red Clay sequence deposited from 6 to 2.7 Ma. We found that increasing goethite concentration generally corresponds to decreasing magnetic susceptibility for the Red Clay sequence, with the exception of an anomalous section from 4.3 to 3.7 Ma where both records show increasing trends. Precipitation seasonality could explain this opposite variation pattern between magnetic susceptibility and goethite concentration in the Red Clay sequence. From 3.6 to 2.7 Ma, goethite concentration has a decreasing trend while magnetic susceptibility increased, which we interpret as more seasonally distributed precipitation associated with intensification of the East Asian summer monsoon (EASM). Similar pattern was observed from 0.65 to 0 Ma from the Lingtai section. Taken together, the goethite record reveals that the EASM experienced two stages of rapid intensification with apparent seasonally distributed precipitation since 6 Ma.

Mineral magnetic record of the Miocene-Pliocene climate transition on the Chinese Loess Plateau, North China

AbstractPre-Quaternary terrestrial climate variability is less well understood than that during the Quaternary. The continuous eolian Red Clay sequence underlying the well-known Quaternary loess-paleosol sequence on the Chinese Loess Plateau (CLP) provides an opportunity to study pre-Quaternary terrestrial climate variability in East Asia. Here, we present new mineral magnetic records for a recently found Red Clay succession from Shilou area on the eastern CLP, and demonstrate a marked East Asian climate shift across the Miocene-Pliocene boundary (MPB). Pedogenic fine-grained magnetite populations, ranging from superparamagnetic (SP)/single domain (SD) up to small pseudo-single domain (PSD) sizes (i.e., from <30 nm up to ~1000 nm), dominate the magnetic properties. Importantly, our mineral magnetic results indicate that both pedogenic formation of SP grains and transformation of SP grains to SD and small PSD grains accelerated across the MPB in the Shilou Red Clay, which are indicative of enhanced pedogenesis. We relate this enhanced pedogenesis to increased soil moisture availability on the CLP, associated with stronger Asian Summer Monsoon precipitation during an overall period of global cooling. Our study thus provides new insights into the Miocene-Pliocene climate transition in East Asia.

Rock magnetic record of late Neogene red clay sediments from the Chinese Loess Plateau and its implications for East Asian monsoon evolution

The Quaternary loess–paleosol and underlying Neogene red clay sequences on the Chinese Loess Plateau (CLP) contain a remarkable continental record of past East Asian monsoon changes and aridification of the Asian interior. While monsoon variability during the Quaternary is reasonably well understood, the evolution and dynamics of the monsoon during the Neogene are still debated. The rock magnetism of aeolian sediments is a well-established tool for reconstructing the palaeoclimatic history of Asia. Here, we present a rock magnetic record from Late Neogene red clay sediments of the Chaona section in the central CLP. The results indicate that the main magnetic minerals in the red clay are magnetite, maghemite, hematite and goethite, similar to the overlying Quaternary loess-palaeosol sequences. The high-resolution rock magnetic record, combined with the results of other proxies, demonstrate a stepwise intensification of the summer monsoon and a progressive enhancement of the winter monsoon in East Asia during the Late Neogene. Based on the results, the climatic evolution of East Asia can be divided into three intervals: Interval III, from 8.1 to 6.8Ma, is characterized by a cool, dry climate with a relatively weak East Asian Summer Monsoon (EASM) and East Asian Winter Monsoon (EAWM); Interval II, from 6.8 to 4.3Ma, is characterized by cool/warm cycles; and Interval I, from 4.3 to 2.8/2.6Ma, was warm and humid, and within which the EASM strengthened rapidly and the EAWM fluctuated considerably, with an increasing trend. We infer that before 4.3Ma the variations of both the EASM and EAWM were closely related to global cooling and that the intensified EASM during the late Pliocene was primarily caused by tectonic events, including the gradual closure of the Panama Seaway and the uplift of the Tibetan Plateau, rather than by global cooling.

Late Miocene-Pliocene geomorphological evolution of the Xiaoshuizi peneplain in the Maxian Mountains and its tectonic significance for the northeastern Tibetan Plateau

As a remnant elevated peneplain, the Tangxian planation surface is widely distributed in North China and the Ordos Plateau. Further into the Tibetan Plateau (TP), the Main planation surface can also be traced across this, the highest plateau on the Earth's surface. What the relation is between these two planation surfaces and whether they represent the remnants of a unique planation surface remains open to question. As the intermediate region between the low-altitude North China and the high-altitude TP, the Maxian Mountains and such bilateral basins located in the northeastern TP margin retain a series of well-preserved geomorphic features such as planation surfaces, pediment surface, and the fluvial terraces of the Yellow River. When and how the Xiaoshuizi peneplain was formed are crucial questions to elucidate the geomorphic evolution of the northeastern TP and infer the tectonic history of the TP. Here we present two parallel red clay-loess drill cores from the uplifted Xiaoshuizi bedrock peneplain in the Maxian Mountains, which document both the upper formation age of the planation surface and the evolution of Asian aridification. Based on the integration of high-resolution magnetostratigraphy analysis and Pliocene mammal fossils, we demonstrate that the red clay-loess succession deposited on the Xiaoshuizi peneplain probably began to accumulate at ~6.9Ma, implying that the Xiaoshuizi peneplain had begun to form before this. These results support the hypothesis that the Xiaoshuizi planation surface is equivalent to Tangxian planation surface of North China and Main planation surface of the TP. Furthermore, the onset of red clay sequence may indicate that the Xiaoshuizi peneplain was ultimately destroyed by the intensive tectonic uplift of the northeastern TP before 6.9Ma. Taking into account the synchronous Late Miocene red clay deposition between the Xiaoshuizi peneplain and central Chinese Loess Plateau (CLP), we propose that the onset of interior Asian aridification occurred in the Late Miocene and was principally triggered by the rapid uplift of TP.

Magnetism of a red soil core derived from basalt, northern Hainan Island, China: Volcanic ash versus pedogenesis

AbstractSimilar to loess‐paleosol sequences in northwestern China, terrestrial sedimentary sequences (red soils) in southern China also provide sensitive Quaternary records of subtropical/tropical paleoclimate and paleoenvironment. Compared with red clay sequences originated from eolian dust, red soils derived from bedrock have received little attention. In this study, a long core of red soil derived from weathered basalt in northern Hainan Island, China, was systematically investigated by using detailed magnetic measurements and rare earth element analyses. The results show that an extremely strong magnetic zone with a maximum magnetic susceptibility (>10 × 10−5 m3 kg−1) is interbedded in the middle of the core profile. This layer contains a significant amount of superparamagnetic magnetite/maghemite particles that primarily originated from volcanic ash, with secondary contributions from pedogenesis. The former has an average grain size of ~19 nm with a normal distribution of volume, and the latter has a much wider grain size distribution. The presence of volcanic ash within the red soil indicates that these Quaternary basalts were not formed by continuous volcanic eruptions. Moreover, the magnetic enhancement patterns differ between the upper and lower zones. The upper zone is more magnetically enhanced and experienced higher precipitation and temperature than the lower zone. Discrimination of superparamagnetic particles originating from pedogenic processes and volcanic ash thus provides a sound theoretical base for accurate interpretation of magnetism in red soils in this region.

U-Pb ages of detrital zircon and provenances of Red Clay in the Chinese Loess Plateau

The Chinese Loess Plateau (CLP), which is located in the central part of China, mainly contains two sequences: the Quaternary loess-paleosol sequence and the late Miocene-Pliocene Red Clay sequence. U-Pb ages of detrital zircon from the Quaternary loess-paleosol sequences indicate that the current spatial pattern of central Asian aridification was largely established during the early Quaternary. U-Pb ages of detrital zircon from the underlying Red Clay sequences demonstrate that the northern source regions were important contributors for the dust since the late Miocene, except for the periods of ∼8Ma and ∼5.5 to ∼4Ma. These two periods correspond to increased and decreased dust deposition in the North Pacific, respectively, ascribed to the late Miocene aridification of the Qaidam Basin (in the west of the CLP) and the early Pliocene aridification of the Tarim Basin (in the west of the CLP). We attribute the increase of the Qaidam Basin-derived North Pacific dust fluxes to the uplift of the NE Tibetan Plateau. Such uplift also controlled the climatic and environmental changes in central Asian during the late Miocene. This study highlights the dynamical process of the central Asian aridification during the late Miocene-Pliocene.

Origin and weathering of landslide material in a loess area: a geochemical study of the Kulcs landslide, Hungary

Geochemical characteristics of sediments are responses to physical and chemical alteration in landslides. However, consequences of in situ interactions associated with landslides are difficult to distinguish from those related to long-term weathering in young soft sediments such as loess. In this study, geochemical characteristics of the Kulcs landslide in Hungary are studied to identify the provenance of the loess–paleosol–red clay sequence and geochemical signatures that can potentially be attributed to the effects of landsliding. Results indicate that sliding is largely initiated by the lithological changes within the landslide body. Sediments above the sliding zone closely resemble the non-slipped Pleistocene old loess deposits from Hungary. It is also confirmed that the sliding zone develops in old paleosols in the loess sequence and red clays at its base which are all characterized by the enrichment of Al, K, Na, H2O and considerable depletion in Ca and Mg associated with carbonates. Altogether, these geochemical characteristics indicate that chemical weathering trend of unconsolidated landslide sediments is slightly modified by the redistribution of carbonates and decomposition of plagioclase. It is assumed that the distribution of Mn and Ba is modified by the water–sediment interaction in the landslide.

A comparison of zircon U-Pb age results of the Red Clay sequence on the central Chinese Loess Plateau.

Single grain zircon U-Pb geochronology has demonstrated great potentials in extracting tectonic and atmospheric circulation signal carried by aeolian, fluvial, and fluviolacustrine sediments. A routine in this sort of studies is analyzing 100–150 grains and then compares zircon U-Pb age spectra between the measured sample and the potential sources. Here we compared the zircon U-Pb age results of the late Miocene-Pliocene Red Clay sequence of two neighboring sites from the Chinese Loess Plateau where similar provenance signal is expected. Although the results from the 5.5 Ma sediment support this prediction, the results from the 3 Ma sediment at these two sites differ from each other significantly. These results emphasize the importance of increasing analysis number per sample and combining the zircon U-Pb geochronology with other provenance tools in order to get reliable provenance information.