Tertiary Red Clay Research Articles

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.

Fe isotopic composition of the Quaternary Red Clay in subtropical Southeast China: Redoxic Fe mobility and its paleoenvironmental implications

To probe Fe isotopic signatures of the Quaternary Red Clay (QRC) in subtropical southeastern China, two QRC profiles located in southern Anhui Province, Southeast China, were studied. The whole profiles were generally in a narrow range in δ56Fe of −0.040 ± 0.061‰—0.117 ± 0.048‰. The Yellow-brown Earth (YBE) and Uniform Red Clay (URC) of the upper profiles were similar in δ56Fe to the Xiashu Loess along the Yangtze River, Southeast China, and the loess, paleosols and Tertiary red clay in the Chinese Loess Plateaus, Northwest China, as well as the baseline of terrestrial igneous rocks. The slight variation of δ56Fe from the YBE to the URC suggests that the chemical weathering and rubification on the aerobic surface did not fractionate Fe isotopes significantly. The Reticulate Red Clay (RRC) underlying the YBE and URC fluctuated in δ56Fe to some extent. The white veins separated from the lower RRC were depleted of Fe oxides and heavier in Fe isotopes, and the red veins, on the contrary, were isotopically lighter in Fe. δ56Fe of the white veins, 0.345 ± 0.053‰ on average, was significantly higher than the bulk samples, 0.033 ± 0.044‰ on average, and the red veins, −0.021 ± 0.046‰ on average. This suggests that the reticulate textures of the RRC were formed by the reductive removal/re-precipitation of Fe due to the cyclical changes of redoxic conditions. Fe isotopic composition of the QRC was dominantly controlled by the redoxic mobility of Fe, rather than the degree of weathering. δ56Fe of the profiles was not correlated with the paleoclimatic events, and thus cannot be used as a paleoclimatic proxy. The fractionation of Fe isotopes in the lower RRC, however, indicated the occurrence of over-humid paleoclimate with alternations between drought and wetness in Southern China during the Pleistocene.

New evidence for the catastrophic demise of a prehistoric settlement (the Lajia Ruins) in the Guanting Basin, upper Yellow River, NW China

The Lajia Ruins in the Guanting Basin, NW China, are a product of the prehistoric Qijia Culture. Like Pompeii, they are a rare example of an archaeological site preserved by a natural disaster and are therefore important in archaeology, anthropology and geology. However, the nature of the disaster(s) responsible for the destruction of the site remains controversial. Most studies have focused on an earthquake and a red clay layer directly overlying the site and a detailed stratigraphic study of the mid-Holocene sedimentary strata combined with other intervals of red clay deposition (hence possible disasters) is lacking. We identified a mid-Holocene paleosol sequence (the Shanglajia section) at the site which contains two layers of red clay, dated to 3950 a BP and 3500 a BP, intercalated within the mid-Holocene paleosol (S0). Subsequent multi-proxy analysis indicated that the characteristics of the two red clay layers resemble those of typical Tertiary red clay deposits and the modern gully deposit at the foot of the Great Red Hills, but are distinctly different from those of the slackwater deposits of the Yellow River and the mid-Holocene paleosol. Our results suggest that, at 3950 a BP and 3500 a BP, two large-scale rainstorm-induced mudflow events, originating from the gullies to the north, flooded the Lajia area on the second terrace of the Yellow River, devastating and burying the human settlements. We infer that the intensified erosion and mass wasting were caused by human activity; in addition, natural factors such as rainstorms and earthquakes, may also have played an important role in triggering catastrophic mudflow events in the Tertiary Red Clay deposits. Overall, our results provide further insights into prehistoric man-land relationships in this environmentally sensitive region which may have implications for modern land use in this region of China and elsewhere.

Luminescence sensitivities of quartz grains from eolian deposits in northern China and their implications for provenance

The thermoluminescence (TL) and optically stimulated luminescence (OSL) sensitivities of quartz grains from deserts and loess–red clay sequences are used to trace eolian provenances in northern China. Our results indicate that the 110°C TL peak and OSL sensitivities of quartz grains show differences among Chinese deserts, which can be subdivided into four groups according to the spatial variations of luminescence sensitivities. Such differences are related mostly to the regional difference in rock types of mountains surrounding or adjacent to the deserts. We also examine the possible provenance changes between the Quaternary loess and the Tertiary eolian red clay, and the results indicate that the luminescence sensitivity of Tertiary red clay is higher than that of Quaternary loess (L1, L15, and L33), implying source materials of the eolian deposits changed relative to those of the Quaternary.

Temporal variations in Pb isotopes and trace element concentrations within Chinese eolian deposits during the past 8Ma: Implications for provenance change

The Pb isotopes and trace element compositions of the silicate fraction of airborne dust from the Chinese Loess Plateau were analyzed to infer provenance change during the past 8 Ma. The results indicate that the composition of eolian dust changed at 2.6 Ma, coincident with initiation of the Northern Hemisphere ice sheet. The change in trace element composition at 2.6 Ma indicates that a larger component of the eolian dust was derived from felsic rocks after this time. Pb isotopic evidence demonstrates that the source material of Tertiary Red Clay differs to some extent from that of Quaternary eolian deposits. Although chemical weathering may result in compositional changes in eolian deposits, such a scenario is not supported by the present evidence. Given that glacial grinding and frost-weathering processes have been active in the peaks of high mountains during the Quaternary, eolian dust of this age contains a large proportion of material derived from areas of high topographic relief and relatively little material from low-lying cratonic regions. Such alpine processes played an important role in controlling the distinct changes in Pb isotopes and trance element concentrations recorded at around 2.6 Ma.

CPI values of terrestrial higher plant-derived long-chain n-alkanes: a potential paleoclimatic proxy

Carbon Preference Index (CPI values) of higher plant-derived long-chain n-alkanes extracted from 62 surface soil samples in eastern China exhibited a specific pattern of variations, namely gradual increase with the increasing latitudes. Such regular variations existed in both forest soil and grassland soil. Our data implied that CPI values of higher plant-derived long-chain n-alkanes had a certain connection with climatic conditions, and such a connection was not influenced by vegetation types. Together with previous data from marine sediments, loess/paleosol sequences, tertiary red clay and modern plants, our observation made us conclude that CPI values of higher plant-derived long-chain n-alkanes may be used as an excellent proxy for paleoclimatic studies.

Influence of the aging of Fe oxides on the decline of magnetic susceptibility of the Tertiary red clay in the Chinese Loess Plateau

Magnetic properties, free and active Fe oxides, grain size distribution and mineral assemblage of a Quaternary loess–Tertiary red clay (TRC) section in Lingtai County in the Chinese Loess Plateau were studied. The results suggest that the TRC of the Lingtai section shares similar aeolian characteristics with the overlying Quaternary loess-paleosol sequence (QLPS), but the former is generally more intensively weathered than the latter, as indicated by its higher citrate–bicarbonate–dithionite (CBD) extractable Fe (Fe d), finer grain size and lower content of easily weathered primary minerals. However, magnetic susceptibility ( χ lf) and magnetic remanence ( χ arm, SIRM and SOFT etc.) of the main part of the TRC are significantly lower, implying the decline of ferrimagnetic minerals (FM). In contrast, hematite and goethite in the TRC is significantly enhanced, as indicated by its higher HIRM. The acid ammonium oxalate (AAO) extractable Fe (Fe o) of the whole section sharply decreases with increasing age. Fe o and Fe o/Fe d values of the section are significantly correlated with χ lf. Especially in the TRC, the low values of Fe o and Fe o/Fe d correspond to weak χ lf. This suggests a significant influence of the age-related transformation of Fe oxides on the decline of FM in the TRC. Lower FM and higher hematite and/or goethite in the TRC further suggest the transformation of FM into hematite with the aging of Fe oxides during post-depositional processes, though more evidence is needed to understand the processes involved. χ lf of the TRC in the Chinese Loess Plateau mostly cannot be regarded as a promising paleoclimatic proxy because its weak magnetism does not correlate to its strong pedogenesis.

Strontium isotopic and elemental characteristics of calcites in the eolian dust profile of the Chinese Loess Plateau during the past 7 Ma

Strontium isotopic ratios, calcium and strontium contents of calcites in the eolian dust profile during the last 7 Ma at Lingtai were systematically studied. 87Sr/86Sr ratios of calcites change with three secondary fluctuations in the Quaternary loess-paleosol sequence: slight fluctuations from L33 to S15, a slight increase from L15 to L6, and a dramatic decrease from S5 to L1. They are usually lower in the Quaternary loess than in the interstratified paleosols. 87Sr/86Sr ratios of calcites in the Tertiary red clay are relatively stable, mostly higher than in the Quaternary loess and paleosols. Ca2+ and Sr2+ contents of calcites are relatively high in the Quaternary loess and the Tertiary red clay but low in the Quaternary paleosols. Sr2+ is well correlated with Ca2+, and can thus be an effective tracer for Ca2+. High contents of Ca (Sr) in the Tertiary red clay show that carbonates were poorly leached out of the Tertiary red clay. Like Ca contents, Ca/Sr ratios in the Tertiary red clay are close to those in the Quaternary loess. Elemental ratios and contents have different variations from the Sr isotopic ratios of calcites in the Lingtai profile, implying that isotopic ratios were better proxies for climate change than elemental ratios and contents. Primary carbonate and silicate comprised two endmembers determining the range of the Sr isotopic ratios of calcites, and chemical weathering was an inner driver to induce strontium isotopic variations of calcites in the eolian dust profile. Our isotope data indicate that chemical weathering was strongest in the Tertiary red clay, the second in the Quaternary paleosols, and weakest in the Quaternary loess. Strontium isotopic variations of calcites are in a good agreement with pedogenic characteristics in the Lingtai profile, broadly consistent with a proxy of the summer monsoon—Fe2O3(f)/Fe2O3(t) ratios, and correlate with variations of Fe2+/Fe3+ ratios in the Lingtai profile and the dust flux in ODP885/886 during the late Cenozoic. Strontium isotopic variations of calcites are different from the magnetic susceptibility records in the Lingtai profile, further demonstrating that magnetic susceptibility of the Tertiary red clay could not reliably indicate the Tertiary summer monsoon. As a result, strontium isotopic characteristics of calcites in the Lingtai profile indicate that the Quaternary summer monsoon had a glacial-interglacial alternation and weakened with large-amplitude oscillations since 0.5 Ma B.P., and also reveal that the Tertiary summer monsoon was more stable and overall stronger than the Quaternary, nevertheless, similar climates to those in the Tertiary probably occurred during a few paleosol developments of the Quaternary.

Mineralogical evidences of a warm and dry summer monsoon for the late Tertiary red clay formation, China

In the past decade, field observations and geochemical and sedimentological studies have demonstrated that the late Tertiary red clay formation underlying the Pleistocene loess–paleosol sequence on the Chinese Loess Plateau are also wind-blown in origin, thus providing a good opportunity to reconstruct monsoon changes over the late Tertiary. In this study, we examined the classic Lingtai loess–plaeosol sequence and red clay formation on the Chinese Loess Plateau with a diffuse reflectance spectrophotometer. From the reflectance data we calculated sample redness, a reasonable proxy for iron oxide minerals which are responsible for the color changes in the eolian sequence. Sample redness of the red clay varies from about 31.1% to 36.6%, higher than the overlain loess and paleosol samples (29.1%–35.1%) as expected (Fig. 1). Changes of iron oxide minerals were identified by analyzing the reflectance spectra. Both hematite and goethite are present in the red clay formation, but hematite content and the ratio of hematite to goethite are much higher than the overlain loess and paleosol. Based on this comparison, the early Pliocene red clay formation is characterized by conditions that are warmer and drier than the Pleistocene paleosols.

Does δ13C carb of the Chinese loess indicate past C 3/C 4 abundance? A review of research on stable carbon isotopes of the Chinese loess

Current research on stable carbon isotopes of the Chinese loess is reviewed. The stable carbon isotopic composition of soil organic matter (SOM) ( δ 13C org) of paleosols formed during interglacials is more positive than that within loess accumulated during glacials. Spatially, it becomes progressively more negative from the eastern Chinese Loess Plateau (CLP) to the western. However, stable carbon isotopic composition of pedogenic carbonates ( δ 13C carb) from the same sequence produces an opposing trend, both temporally and spatially, and variation differs from expectations under conditions of equilibrium. This indicates that δ 13C carb in the Chinese loess cannot be used to reconstruct the relative proportion of C 3/C 4 plants in past ecological communities. Furthermore, use of δ 13C carb to reconstruct the expansion of C 4 plants in older Tertiary red clay deposits is considered unreliable. We believe δ 13C carb may act as an indirect indicator of vegetation density, following on changes in moisture supply controlled by the intensity of the Asian Summer Monsoon, but conclude that full understanding of the paleoclimatic significance of δ 13C carb in the Chinese loess and underlying Tertiary red clay requires better understanding of modern isotopic processes.

Nd and Sr isotopic variations in Chinese eolian deposits during the past 8 Ma: Implications for provenance change

A record of changes in Nd and Sr isotopic composition of the eolian deposits from the central Loess Plateau has been determined for the past 8 Ma. The isotopic records of the silicate fraction of the Quaternary and Tertiary eolian deposits allow interpreting the interplay between the Sr isotopic variations in the eolian deposits and the late Cenozoic tectonic and climatic changes. The results indicate that the temporal variations of Nd and Sr isotopes show remarkable changes around the beginning of the Quaternary. The lower values of the 143 Nd/ 144 Nd and the decreasing trend of the 87 Sr/ 86 Sr ratios after 2.58 Ma ago are attributed to the additions of relatively younger crust materials in response to the climatic cooling and the late Cenozoic uplift induced glacial grinding in the high orogenic belts in central Asia. In this context, the substantial changes in climate and tectonics have modified dust sources significantly, and the Quaternary loess forming processes are preferentially sampling relatively younger and high relief crust materials than that of the Tertiary Red Clay. D 2005 Elsevier B.V. All rights reserved.

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.

Terrestrial mollusk evidence for the origin and sedimentary environment of the Late Tertiary Red Clay Formation in the Loess Plateau, China

The origin and sedimentary environment of the Late Tertiary (Neogene) Red Clay Formation in northern China had long been controversial. A new mollusk record from the Xifeng red clay (red-earth) sequence in the central Loess Plateau provides the biological evidence for addressing questions of its origin and environmental implication. The study of composition and preservation condition of seventy mollusk fossil assemblages reveals the initial ecological condition of the red clay formation, avoiding the effect of post-deposited alteration. The result shows that all of identifiable mollusk species are composed of terrestrial taxa, most of them are the common species found in the overlying Quaternary loess-paleosol sequence. Most of fossil individuals preserved in the red clay strata are in living conditions based on the investigation of fieldwork, indicating the original population. Thus, the mollusk fossil assemblages can be used as an indicator of primary environment of the red clay formation. The mollusk record from the Xifeng red clay sequence supports the view that the red clay is an aeolian origin, similar to the overlying Quaternary loess deposits. Our data also reveal the history of environmental changes at Xifeng from 6.2–2.4 Ma, which is coupled in phase with the formation and development of the Arctic ice sheets and the process of the Tibetan Plateau uplift. Both may be the major cause and forcing mechanisms of the late Tertiary environmental changes in the Loess Plateau.

Monsoon and westerly circulation changes recorded in the late Cenozoic aeolian sequences of Northern China

Systematic grain-size measurements indicate that aeolian sediment in Northern China is generally composed of a coarse component (ca: 10–70 μm) and a fine overlapping component (ca: <10 μm), which can be numerically partitioned through grain-size distribution function fitting. Sedimentological consideration, modern dust investigation and the temporal–spatial variations of the two components suggest that the coarse component is produced mainly by low-altitude winds of East Asian winter monsoon circulation, and most part of the fine component probably is transported mainly by high-altitude westerly stream. Grain-size records of the last glacial cycle sections over Chinese Loess Plateau suggest that the strength of winter monsoon and westerly circulation intensified synchronously in glacial stages and weakened in interglacial stages, while the zone axis of the northern westerly probably shifted between about 35 and 37°N in glacial–interglacial cycles. Grain-size records of Quaternary loess and late Tertiary Red Clay indicate that the relative contribution of monsoon/westerly to aeolian accumulation increased progressively in the late Cenozoic, meanwhile, the winter monsoon intensity increased along with simultaneous decreasing of westerly intensity, which are marked by abrupt changes at 3.2 and 1.2–0.9 Ma. These atmospheric changes coincide with the intensification of summer monsoon and drying processes of internal Asia at the two crucial times, revealing a unique high-level forcing of Asian climate evolutions in Late Cenozoic, probably the uplifts of northern Tibet Plateau. Amplified fluctuations of grain-size in the last 2.6 Ma in the orbital time scale likely reflect the dominant role of the global ice volume on the circulation regimes of Northern China in glacial–interglacial cycles.

Terrestrial mollusk evidence for the origin and sedimentary environment of the Late Tertiary Red Clay Formation in the Loess Plateau, China

Terrestrial mollusk evidence for the origin and sedimentary environment of the Late Tertiary Red Clay Formation in the Loess Plateau, China

The ecological sequence of Hipparion fauna in the middle reaches of the Yellow River during Neogene

The faunal ecological type and sequence in the Tertiary red clay indicate that Hipparion fauna during the period 7.4–6.1 Ma in the middle reaches of the Yellow River is composed mainly of dorcadoides and mixed types. This represents semiarid veld environment with small fluctuation. The fossil assemblages characterized by the abundance of gaudryi types and even the occurrence of some Hominoid and Chalicotherium indicate an obviously warm and humi period since 5.3 Ma. The fossil assemblages during 3.4 Ma show the typical steppe fauna representing dry climate. It is indicated by the changes of ecological sequence that the climatic conditions in Pliocene are drier than that in late Miocene. The clay-skin content of red clay, which has a synchronous change with faunal features, is a rather good replacing palaeoclimatic index.

Magnetic properties of the Tertiary red clay from Gansu

The study on magnetic properties of the red clay indicates that the red clay and loess-paleosol sequence have a common magnetic mineralogy, with magnetite, maghemite, hematite (and possibly goethite) contributing to the magnetic behavior. The red clay magnetic susceptibility is also found to have a positive relation with extrafine superparamagnetic grains. This suggests that, like the Quaternary loess-paleosols, an ultrafine ferrimagnetic component produced during pedogenesis in the red clay under humid conditions also plays an important role in susceptibility enhancement in the soil units. This is supported by the correlation between Rb/Sr ratio and magnetic susceptibility. This signifies that, like the above loess-paleosol sequence, the magnetic susceptibility of the red clay can be used as a general proxy paleoclimatic indicator, although whether its susceptibility in the red clay is comparable to pedogenesis intensity and requires further investigation. Magnetic susceptibility variation in the red clay thus also provides an eolian/pedogenic record of paleoclimatic evolution. Study of the background susceptibility indicates that, on average, the absolute scale of the paleoclimatic shift from red clay development to Quaternary loess deposition is similar to the climatic shift from stage 5 (S1) to stage 2-4 (L1). This may suggest that during the Quaternary there is an evident strengthening of the absolute wind intensity to bring more (about double) coarser and less weathered (non-SP fraction) eolian magnetic input from the source regions to the Loess Plateau than during the Pliocene. The presence of eolian red clay since 7.5 Ma BP in central-northern China implies an important environmental change from the underlying Cretaceous red sandstone. The red clay development was closely related to global drying and climate cooling since the Cretaceous and closely associated with the abrupt uplift of the Qinghai-Xizang Plateau at about that time. This uplift of the plateau intensified the East Asia monsoon system and started red clay deposition.

Magnetostratigraphy and sedimentology of the Jingchuan red clay section and correlation of the Tertiary eolian red clay sediments of the Chinese Loess Plateau

A 325‐m‐thick loess and red clay sequence was recently discovered at Jingchuan, which is situated about 45 km north of the previously studied Lingtai section in the middle part of the Chinese Loess Plateau. The Jingchuan section is composed of 199 m of Pleistocene loess and 126 m of Tertiary red clay deposits. Paleomagnetic studies show that the Jingchuan red clay has a basal age of at least 7.7 Ma, which represents the oldest red clay deposits presently known in the Loess Plateau. Field observations and grain size analyses both suggest an eolian origin of the red clay, thus extending available records of the eolian deposits in the Loess Plateau from about 7.0 Ma to 7.7 Ma. Correlation of both pedostratigraphy and magnetic susceptibility records suggests that the late Cenozoic red clay records in the Loess Plateau have a general continuous nature, thereby providing potential for deriving long‐term climatic evolution signals from this eolian loess and red clay sequence.

Geochemistry of the Pliocene red clay formation in the Chinese Loess Plateau and implications for its origin, source provenance and paleoclimate change

Recent field observations and sedimentological studies suggest the eolian origin of the late Tertiary red clay formation underlying the Pleistocene loess-soil sequence in the Loess Plateau, thereby extending the wind-blown record from ∼2.6 Ma down to ∼7.0 Ma in north-central China. To address the source provenance of the red clay, major and trace element concentrations were analyzed on the samples from a north-south loess transect of the Loess Plateau and a red clay section at Jiaxian. Results show that there is a good agreement of both major and trace element compositions between the last glacial-interglacial loess-soil units and the Jiaxian red clay record. The REE distribution patterns of the loess-soil and red clay samples are remarkably similar in shape, with enriched LREE and fairly flat HREE profiles and clear negative Eu anomaly. The geochemical features of the red clay are also identical to those of upper continental crust. These chemical characteristics provide further evidence for eolian sedimentation of the red clay. From the relations both between Na 2O/Al 2O 3 and K 2O/Al 2O 3 ratios and between U/Pb and Th/Pb ratios, the eolian loess and red clay materials must have been subject to thorough sedimentary differentiation and moderate chemical weathering in the source area. The chemical similarity between soil unit S1 and the red clay implies that such an environment as occurred in the last interglacial period may have already formed in northwestern China during the late Tertiary. Comparison of down-section variations in elemental ratios with field observations of pedogenic development of the red clay suggests that CaO/Al 2O 3, Sr/Rb and Sr/Ba are more sensitive to climate changes than magnetic susceptibility, and can be used to reconstruct the climate history of the late Cenozoic.

Seven million-year iron geochemistry record from a thick eolian red clay-loess sequence in Chinese Loess Plateau and the implications for paleomonsoon evolution

Recently, the Tertiary red clay sequence underlying Pleistocene loess has attracted much attention. The remarkable progress is the recognition that the Tertiary red clay sequence is also wind-blown in origin, thus providing a good opportunity to reconstruct long-term monsoon changes. In contrast to the loess deposits, the magnetic susceptibility and the pedogenic characteristics are almost independent of each other in the red clay, thus challenging the validity of the readily measurable magnetic susceptibility in describing the monsoon history recorded by the red clay. With the objective to address the long-term East Asia summer monsoon evolution, the free to total Fe2O3 ratios were calculated in a continuous eolian red clay-loess sequence at Lingtai, the Chinese Loess Plateau, which has a thickness of 305 m and a basal age of 7.0 Ma. The seven million-year Fe2O3 ratio record from the red clay-loess sequence indicates that (i) variations of the free to total Fe2O3 ratios of the loess can correlate generally with the alternations of the loess and paleosol horizons; (ii) the East Asia summer monsoon was stronger as a whole in Neogene than that in Quaternary; (iii) the strongest East Asia summer monsoon may occur between 4.0 and 4.8 Ma. The relatively small ice volume and high global temperature may be responsible for the strong summer monsoon during the early Pliocene.