Chinese Loess-paleosol Sequences Research Articles

Eccentricity-paced geomagnetic field and monsoon rainfall variations over the last 870 kyr

Whether there are links between geomagnetic field and Earth's orbital parameters remains unclear. Synchronous reconstructions of parallel long-term quantitative geomagnetic field and climate change records are rare. Here, we present 10Be-derived changes of both geomagnetic field and Asian monsoon (AM) rainfall over the last 870kyr from the Xifeng loess-paleosol sequence on the central Chinese Loess Plateau. The10BeGM flux (a proxy for geomagnetic field-induced 10Be production rate) reveals 13consecutive geomagnetic excursions in the Brunhes chron, which are synchronized with the global records, providing key time markers for Chinese loess-paleosol sequences. The10Be-derived rainfall exhibits distinct ~100 kyr glacial-interglacial cycles, and superimposed precessional (~23 kyr) cycles that match with those in Chinese speleothem δ18O record. We find that changes in the geomagnetic field and AM rainfall share a common ~100 kyr cyclicity, implying a likely eccentricity modulation of both the geomagnetic field and climate.

Variation of summer precipitation δ18O on the Chinese Loess Plateau since the last interglacial

ABSTRACTOrbital‐scale East Asian Summer Monsoon (EASM) variations inferred from loess deposits in northern China and speleothems from southern China display different dominant periods, complicating our understanding of monsoon response to insolation and ice‐volume forcings. Here we integrate a new microcodium δ18O record from a high‐resolution last interglacial loess profile with previously published data and provide a composite microcodium δ18O record on the Chinese Loess Plateau (CLP) since the last interglacial. The composite microcodium δ18O record displays distinct precessional cycles, consistent with speleothem δ18O records, but with different amplitude contrast (particularly during the peak interglacials). We propose that both loess and speleothem δ18O records exhibit covariations at precessional timescale oscillations. The discrepancy between loess and speleothem from southern China can be attributed to the influences of other processes besides summer precipitation on the proxies. A slight difference in amplitude between microcodium and speleothem δ18O records implies that the EASM is also influenced by inland surface boundary conditions, which has important impacts on the occurrence of EASM precipitation. Therefore, microcodium δ18O from the Chinese loess–paleosol sequences can be regarded as a representative proxy of EASM precipitation in northern China and then a reliable proxy reflecting the variation of EASM intensity.

New chronology of the Chinese loess-paleosol sequence by leaf wax δD records during the past 800 k.y.

Abstract The Chinese loess-paleosol sequences provide important archives for studying paleoenvironmental changes. However, the lack of independent and accurate time scales hinders the study between loess and other records. Asian stalagmite δ18O records indicate synchronous patterns of paleoprecipitation δ18O over large geographic regions. The record of hydrogen isotopic composition of plant wax (δDwax) in Chinese loess is also controlled by rainwater δD. Both share a common origin. The linear relationship between rainfall δ18O and δD variance provides the basis to tie together chronologies of the same climate event in different records. Here, we show a new loess chronology by correlating chronologies of marker boundaries of the prominent climate chronozones in stalagmite δ18O and summer insolation to the equivalent climate stratigraphy in the loess δDwax sequence. We first developed and tested this novel methodology with data since the last interglacial on a millennial scale, and then applied this approach to the loess δDwax sequence for the past 800 k.y. to improve the traditional chronology based on magnetic susceptibility and grain size. The new δDwax time series provides not only an improved chronology for studying paleoclimate changes during interglacial intervals, it also represents a unique database with which to better understand the links between the Asian monsoon changes in the Chinese loess and other global climate events, especially for the periods prior to 640 ka, for which stalagmite records are not available.

Carbon and oxygen isotopes of calcified root cells, carbonate nodules and total inorganic carbon in the Chinese loess–paleosol sequence: The application of paleoenvironmental studies

Abstract The continuous loess-paleosol sequence on the Chinese Loess Plateau (CLP) is a major terrestrial archive of paleoclimate changes. The carbon and oxygen isotopes of soil carbonate in the sequence have long been applied to reconstruct Quaternary climate changes, yet which soil carbonates has the integrity to signify the climate variability still remains a controversy. Hence, in this study, we compared carbon and oxygen isotopic compositions of soil inorganic carbon (TIC), carbonate nodules, and calcified root cells (CRCs) found in the Xifeng loess profile on the CLP to test their significance as paleoclimate indicators. The X-ray diffraction and scanning electron microscope analysis performed on CRCs prove that they are pure micro-scale calcite minerals with distinct epidermal cell structures of plant rootlets. The results of 14C dating show that CRCs and nodules have evident translocation of younger carbon while the TIC appears more or less consistent with the model ages. The δ13CCRC values vary from −18.2‰ to −11.6‰, while the δ18OCRC values range from −13.7‰ to −9.2‰ on the V-PDB scale, spanning 6.6‰ and 4.5‰, respectively. The contrast shows that δ13CCRC values are more negative than those of nodules and TIC, and the δ13CCRC values disperse within a large spectrum, which reflects a rapid germination of root cell calcification with little or even no time for diffusion process within individual C3 plant roots. We argue that pure secondary micro carbonates like CRCs are closely associated with the plant-genic carbon. Their isotope values carry seasonal or even single event-based climate signals. Our study also suggests that stable isotope compositions of carbonate nodules and TIC are interfered by primary carbonate minerals. Thus, it should be used with caution when applying those materials for researches of paleoclimate changes.

Records of the Mid-Brunhes Event in Chinese loess-paleosol sequences

The Mid-Brunhes Event (MBE) was a climatic transition characterized by warmer temperatures, smaller ice volume and higher sea levels during interglacials since marine oxygen isotope stage (MIS) 11. Data from numerous long-term sedimentary sequences indicate that the MBE was expressed throughout the whole earth surface; however, conflicting evidence in terrestrial sequences from middle/high latitudes of the Northern Hemisphere mean that the event's existence and global synchronicity are a matter of debate. To address this problem, we investigated the MBE signal in paleoclimate records from the Chinese Loess Plateau (CLP). Higher magnetic susceptibility (χ) since S5 in the Luochuan, Yimaguan, and Lingtai sections, and since S4 in the Jingyuan and Xijin sections indicate that East Asian Summer Monsoon (EASM) precipitation strongly affected the central CLP since MIS 13, but exerts a relatively weak influence on the northwestern CLP until MIS 11 during the past 800 kyr. From MIS 13 to MIS 11, shrinkage of the Northern Hemisphere ice sheet resulted in northward movement of the Intertropical Convergence Zone and elevated sea-level. An ~25 m sea-level rise could have caused the coastline of the Asian continent to shift northwestward by ~50–100 km. These changes induced extension of EASM-domain areas into the northwestern CLP from the central CLP. The response to the MBE in loess-paleosol sequence of the CLP was expressed by variations in the geographic extent of EASM-domain areas, rather than changes in the EASM intensity. The MBE emerged at MIS 11 in the CLP, and was globally synchronous.

Provenance of loess deposits and stepwise expansion of the desert environment in NE China since ~1.2 Ma: Evidence from Nd-Sr isotopic composition and grain-size record

The Quaternary wind-blown Chinese loess-paleosol sequence, which developed as a product of the intensification of Northern Hemisphere glacial-interglacial cycles, is a major source of information on aridification of the Asian interior. In northeastern (NE) China, extensive loess deposits occur that have great potential for reconstructing the long-term paleoclimatic evolution of the region. Despite existing geochemical data indicate that the probable major source areas for these loess deposits were the nearby Horqin and Otindag deserts, it is still unclear that whether there was a long-term change in the detrital source of these loess deposits. In addition, the aridity history and long-term desert evolution of NE China are currently poorly understood. In the present study, we measured the silicate Nd and Sr isotopic composition of the 28–45 μm grain-size fraction from multiple loess sections (NYZG, SBH, and TDJZ). The results show that the loess deposits of the three sites were dominantly sourced from the Otindag sandy desert and that this source remained constant for the past 1.2 Ma. Notably, the 87Sr/86Sr ratios are influenced mainly by variations in the content of clay-sized material present in the form of aggregates or adhering to the surface of coarser particles. Therefore, caution is needed in the use of 87Sr/86Sr ratios of the 28–45 μm fraction as a tracer of eolian dust, when the clay minerals are not completely removed during the pretreatment process. The grain-size variability of the three sections indicates that stepwise enhancement of aridification in the Otindag sandy desert occurred at 1.2 Ma, 0.9 Ma, and 0.7 Ma, which coincided respectively with the beginning of the Mid-Pleistocene transition (MPT), an extremely cold event at ~0.9 Ma within the MPT, and the establishment of a full glacial climate at the termination of the MPT. This finding supports the hypothesis that the growth of high-latitude ice sheets was the major driver of the long-term aridification of Asian dust source areas.

New progress in the geochronology of hominin relics in loess strata of the Chinese Loess Plateau

Many hominin sites have been found since 1920 in the Chinese Loess Plateau and its adjacent areas, such as Nihewan, Shuidonggou, Dingcun, Dali, Kehe, Xihoudu, east Qinling Mts. and Lantian. Recently two very important investigations of hominin occupation in the Chinese Loess Plateau have caused a huge impact in the world. The Homo erectus cranium from Gongwangling, Lantian County, Shaanxi Province of China is the oldest fossil hominin specimen in North China. It was found in 1964 in a layer below the Jaramillo subchron and was initially attributed to loess L15 in the Chinese loess-paleosol sequence, with an estimated age of ca. 1.15 Ma (millions of years ago). Here, we demonstrate that there is a stratigraphical hiatus in the Gongwangling section immediately below loess L15, and the cranium in fact lies in paleosol (S) S22 or S23, the age of which is ca. 1.54~1.65 Ma. High-resolution paleomagnetic investigations at two sections at Gongwangling and one at Jiacun, 10 km to the north, indicate that the fossil layer at Gongwangling and a similar fossil horizon at Jiacun were deposited immediately before a short normal magnetozone above the Olduvai subchron, which is attributed to the Gilsa excursion and dated elsewhere to ca. 1.62 Ma. Our investigations thus demonstrate that the Gongwangling cranium is slightly older than ca. 1.62 Ma, probably ca. 1.63 Ma, and significantly older than previously supposed. This re-dating now makes Gongwangling the second oldest site outside Africa (after Dmanisi in Georgia) with cranial remains, and causes substantial re-adjustment in the early fossil hominin record in Eurasia. At the same time, the earliest hominin evidence outside Africa came from our newly found 2.12-million-year old stone tools, which were found at Shangchen, a paleolithic locality, in Lantian County in the southern margin of the Chinese Loess Plateau. The loess-paleosol sequence and magnetostratigraphy were established by using different methods, including marker layers, sedimentology, mineralogy, geochemistry, paleomagnetism and rock magnetism. The stone artefacts (including cores, flakes, scrapers, points, borers, hammerstones and picks) from the Shangchen locality were found in a successive loess-paleosol section, and 17 stone artefact horizons of early Pleistocene strata (1.26–2.12 Ma) were used to establish the chronological framework of the loess-paleosol-paleolithic culture sequence during the early Pleistocene. The artefact-bearing layers were dated by linking the geomagnetic polarity variations changes in the earth’s magnetic field. The oldest artefacts (2.12 Ma) found within L28 layer between the Olduvai subchron and the Reunion excursion are ca. 270 thousand years older than the 1.85-million-year old skeletal remains and stone tools from Dmanisi, Georgia, which were previously the earliest evidence of hominin outside Africa. Because no skeletal remains were found with the stone tools from Shangchen, we do not know who made them, but it is likely to be an early form of our own genus Homo . Moreover, the length of our artefact sequence with17 stone cultural horizons (probably with a high average occupation of ~ 50 ka) found in the same locality – is very rare world-wide, and indicates a repeated – but not necessarily continuous – hominin occupation of the Chinese Loess Plateau for almost a million years between 1.26 and 2.12 Ma. Most occupations occurred in the paleosol layers (11 layers of total 17 layers) which indicate a kind of warm-wet climate. This breakthrough expands the “Loess lithic industry” and the “Loessic Geoarchaeological Belt” direction of research on the internationally-leading Chinese loess-paleosol sequence, and prompts reconsideration on the pattern of early human’s origin, migration and dispersal.

Identification of aeolian loess deposits on the Indo-Gangetic Plain (India) and their significance

Aeolian loess deposits contain abundant information about the evolution of the paleoenvironment. For example, paleoclimate changes recorded in Chinese loess area obtained significant achievement in the past few decades. Compared to Chinese loess, research on Indian loess is lacking. Currently, most studies focus on the Kashmir area located in the southern Himalayas, and studies on other areas are rare. However, field observations demonstrate that the sediments around the New Delhi-Agra-Jaipur Plain are similar to Chinese loess-paleosol sequences. For example, the boundary between two strata is transitional and without horizontal bedding. Moreover, obvious pedogenic horizons developed among sediment sequences, probably indicating unrecognised aeolian deposits in the Indo-Gangetic Plain (IGP). To confirm this, pilot samples were obtained from the IGP and detailed indoor measurements conducted. The results indicate that the distribution patterns of particle size and rare earth elements (REE) of the pilot samples are similar to Chinese loess. Furthermore, the scanning electronic microscopy (SEM) images of pilot samples show obvious conchoidal fractures, dash-shaped concavities, and abundant small pits that usually form through mechanical impact. These are typical characteristics of aeolian particles. In addition, environmental and rock magnetic measurements indicate that the dominant magnetic minerals in the pilot samples are magnetite and maghemite, and that they likely contain small amounts of hematite. Furthermore, conventional magnetic parameters are comparable with Chinese loess. Based on this, aeolian loess deposits are widely distributed in the IGP, which may have promoted the development of Indian farming and contributed towards the prosperity of ancient Indian civilisation. This study also provides a new and valuable record for the research on paleoclimate changes in the study area in the future.

Early Pleistocene occurrence of Acheulian technology in North China

Acheulian tools with their associated level of cognizance heralded a major threshold in the evolution of hominin technology, culture and behavior. Thus, unraveling occurrence ages of Acheulian technology across different regions worldwide constitutes a key aspect of understanding the archeology of early human evolution. Here we present a magneto-cyclochronology for the Acheulian assemblage from Sanmenxia Basin, Loess Plateau, North China. Our results place a sequence of stable normal and reversed paleomagnetic polarities within a regional lithostratigraphic context. The Acheulian assemblage is dated to be older than the Matuyama–Brunhes boundary at 0.78 Ma, and is found in strata that are probably equivalent to a weak paleosol subunit within loess layer L9 in the Chinese loess-paleosol sequence, which corresponds to marine isotope stage (MIS) 23, a relatively subdued interglacial period with age range of ∼0.89–0.92 Ma. This age of ∼0.9 Ma implies that Acheulian stone tools were unambiguously present in North China during the Early Pleistocene. It distinctly enlarges the geographic distribution of Acheulian technology and brings its occurrence in North China back into the Early Pleistocene, which is contemporaneous with its first emergence in Europe. Combined with other archeological records, the larger area over which Acheulian technology existed in East Asia during the terminal Early Pleistocene has important implications for understanding early human occupation of North China.

A warmer but drier Marine Isotope Stage 11 during the past 650 ka as revealed by the thickest loess on the western Chinese Loess Plateau

Marine Isotope Stage 11 (MIS 11; ca. 423–362 ka) is generally considered to be the best analogue for the present interglacial (Holocene), and investigation of it will improve our understanding of current climate variability and assist in predictions of future climate change. However, many recent studies primarily focus on the structure and duration of MIS 11. Little research has focused on climate warmth and stability recorded in the Chinese loess-paleosol sequences (LPS) during the S4 paleosol formation (equivalent to MIS 11). On the basis of previous work, this study presents a high-resolution record (ca. 75 a/cm) that spans from MIS 1 to MIS 15, as preserved in the thickest known Jingyuan loess section on the western Chinese Loess Plateau (CLP). This LPS is almost 165 m thick and was sampled from the upper part of L6 to the modern soil at 2-cm depth intervals. Measurements of magnetic susceptibility, mean grain size and >63 µm particle content, carbonate content, total organic carbon, and soil color of samples were made to reconstruct the paleoclimate variation, and a grain-size age model was used to constrain the chronological framework. The primary results show that a generally warm-humid climate dominated the S4 paleosol development, but the climate condition was extremely unstable during the whole of MIS 11. Two obviously different climate regimes controlled the MIS 11 climate variation: the early part of MIS 11 was extremely warm and stable, but the latter part was relatively cool (non-glacial) and unstable. This climate pattern was consistent with records on the central CLP and wavelet analysis suggested that it was forced by the 65°N insolation variability modulated by a quasi-100-ka cycle. In addition, a multi-proxy comparative study on the climate conditions during S0 to S5 paleosol development indicates that the period of S4 development might be the warmest interglacial of the past 650 ka. However, the climate condition during S4 development was not the most humid episode as recorded in Xifeng and Luochuan loess sections on the central CLP. On the contrary, it was drier than both the MIS 15 and the present interglacial on the western CLP, which is somewhat similar to the present climate pattern on the central CLP.

Study on the Grain Size Characteristics and Magnetic Susceptibility of Aeolian Sediments at Zhuli in Shandong Province: Implications for Paleoclimatic Change

Chinese loess-paleosol sequence has archived the most detailed terrestrial records of past climatic and environmental changes. In this study, we concentrate on Zhuli loess section in northern Shandong, by sedimentary and magnetic and optically stimulated luminescence (OSL) methods. Based on the OSL ages, the basal age of the Zhuli section is 60ka extrapolated by sedimentation rates. Grain-size curves indicate that environment-sensitive size fractions of Zhuli section are 39.81-44.67μm and 79.43-89.12μm respectively, by analyzing grain-size class vs. standard deviation values method. The low-frequency magnetic susceptibility has a good correlation with the high-frequency magnetic susceptibility, and the grain size has a good correlation with the magnetic susceptibility.

Introducing an improved multi-proxy approach for paleoenvironmental reconstruction of loess–paleosol archives applied on the Late Pleistocene Nussloch sequence (SW Germany)

To study paleoenvironmental and paleoclimatic changes in loess–paleosol sequences (LPS), most proxies except for screening parameters have often been applied at low sampling density, typically 1–2 per stratigraphic unit. This might lead to results that overlook paleovegetation effects that were not only restricted to paleosols but also affected underlying loess material. Here, a new profile was investigated in the loess–paleosol sequence (LPS) at Nussloch, SW Germany using a high resolution multi-proxy approach to improve our understanding of the Late Pleistocene record which serves as a standard sequence in Central Europe. This approach included several geophysical and geochemical parameters, as well as frequencies of root-related features.Grain size distribution and OSL dating enabled correlation of the new section with the nearby standard profile P4, revealing considerable variations of the thickness of stratigraphic units due to local small-scale variations in depositional conditions and paleogeomorphology of longitudinal greda structures. Magnetic susceptibility revealed weathering of the entire LPS under more humid conditions than those described for SE European and Chinese LPS. It further enabled a rough differentiation between an interval that was influenced by pedogenic processes (Lower Pleniglacial to lower part of the Upper Pleniglacial), and loess that was not markedly affected by soil formation. Color measurements confirmed these results and enabled the identification of several paleosols in the Upper Pleniglacial. For the uppermost part of the LPS, low magnetic susceptibility and inorganic geochemical parameters such as low Fe/Ti ratios indicated only weak or no pedogenic influence. In contrast, considerable variations e.g. in carbonatic carbon contents and organic carbon/nitrogen (C/N) ratio might be related to the high frequency of calcified root remains (up to 200rhizolithsm−2 and up to 12,500microrhizolithsm−2) in certain depth intervals of the LPS, entailing incorporation and degradation of organic matter. Frequencies of biopores, which are suggested to derive largely from former root growth and, to a lesser extent, from insect and earthworm bioturbation, were related to paleosols, and thus confirmed the pedostratigraphy.An improved assessment of terrestrial sedimentary archives can be achieved by high-resolution multi-proxy analysis and three-dimensional investigation of terrestrial sediments that are prone to bioturbation.

Asynchronous records of Brunhes/Matuyama reversal in marine sediments and Chinese loess: Review and discussion

Geomagnetic polarity reversals are generally considered to occur synchronously around the world, and are commonly used as time markers to correlate events between different sediment archives. They also play an indispensable role for understanding the mechanisms which generate the Earth's geomagnetic field. Nevertheless, in the case of the most recent reversal, the Brunhes–Matuyama (B/M) reversal (∼780 ka), comparison of paleomagnetic studies in Chinese loess–paleosol sequences versus marine cores reveal a marked discrepancy in timing of this event. This timing offset has led to uncertainties in correlating the Chinese loess-paleosol sequences with other global climate records. This paper briefly reviews the history of study on the B/M reversal both in marine and Chinese loess sediments, and reviews several contentious explanations of the aforementioned B/M boundary offset. Finally, the most recent progress of paleogeomagnetic field variation studies using cosmogenic 10Be in Chinese loess is introduced, with the purpose of suggesting a potential way to address this B/M boundary timing offset issue.

Is the Dingcun lithic assembly a “chopper-chopping tool industry”, or “Late Acheulian”?

The famous Palaeolithic site of Dingcun (Ting-ts'un) in North China is located on the third terrace of the Fenhe River, which is one of the main tributaries of the Yellow River. After it was discovered, a series of localities with similar stratigraphic profiles was excavated in 1954. Since then, the artifacts from Dingcun have been classified as a chopper-chopping tool industry assigned to the Late Pleistocene. The authors re-examined the lithic assemblage and carried out an additional field survey at these localities. The local geomorphologic background and especially the Chinese loess-paleosol sequence re-define the chronology of the site. Uranium-series dates on mammal teeth are 160 ka–210 ka. Hence, the site is re-assigned to the late Middle Pleistocene. The Dingcun lithic assemblage is also re-classified as Late Acheulian, characterized by classic Acheulian tools such as handaxes, cleavers, and picks, with the addition of some light-duty tools, including scrapers, notches, borers and denticulates. This paper aims to present a new interpretation of the chronology and the cultural characteristics of the Dingcun site.

Validation and application of a thermal–optical reflectance (TOR) method for measuring black carbon in loess sediments

Three techniques were used to measure black carbon (BC) in samples from Chinese loess-paleosol sequences. The results obtained by (1) chemo-thermal oxidation (CTO, performed two ways), (2) acid dichromate oxidation (Cr2O7), and (3) thermal–optical reflectance (TOR) were intercompared because prior studies have shown that the methods can yield disparate results. BC concentrations did vary among the methods, most likely because they measured different components of the BC continuum, but the high-temperature BC (soot) determined by CTO was correlated with the BC and soot obtained by TOR. The CTO and TOR methods both yielded statistically significant linear relationships for loess and lake sediments that had incremental additions of a standard (SRM-1649a). The results also showed that charred material was more abundant in these test sediments than soot carbon. Data for BC in Luochuan loess generated using TOR showed a trend similar to that of magnetic susceptibility, that is, high BC and large susceptibilities during the last interglacial and low values for both variables in the last glacial. The results thus indicate that the TOR method is well suited for studies of sedimentary materials and that more biomass burned during the last interglacial than in the last glacial.

New insights into magnetic enhancement mechanism in Chinese paleosols

Magnetic susceptibility of Chinese loess–paleosol sequences has been extensively used as a reliable paleoclimatic proxy for reconstruction of the Asian summer monsoon system, and its enhancement is usually attributed to neoformation of fine-grained ferrimagnetic particles via pedogenesis, but there is little understanding of either the formation process of such magnetic particles or their actual form and grain sizes. To investigate these problems, scanning electron microscope observations were conducted on magnetic extracts from pristine loess and strongly-pedogenic paleosol samples from Xifeng on the Chinese Loess Plateau. Both magnetic extracts commonly contained coarse-grained detrital magnetite with grain size ranging from a few μm to several tens of μm. However, the magnetic extract from the mature paleosol sample additionally included coarse silicate particles with ultrafine ferrimagnetic inclusions, while that from the pristine loess sample did not. The size of the ferrimagnetic inclusions mainly ranged from tens to hundreds of nanometers. The temperature-dependent susceptibility and hysteresis loops of the paleosol sample, combined with the stratigraphic variations of rock-magnetic parameters, showed that the pedogenic maghemite inclusions should be a potential contributor to magnetic enhancements in Chinese paleosols. The fine-grained ferrimagnetic inclusions have been pedogenically formed by weathering of coarse-grained Fe-bearing silicate minerals. Our proposed magnetic enhancement mechanism is consistent with the accepted rock magnetic result that magnetic enhancement in Chinese paleosols is caused by pedogenic maghemite grains in superparamagnetic and single-domain size regions. The presence of ultrafine ferrimagnetic grains as inclusions within coarse silicate particles is also consistent with Han and Jiang's (1999) significant experimental result that magnetic enhancement in Chinese paleosols is mainly contributed by the >0.5μm sediment fractions.

Magnetic properties of aeolian deposits in Paleolithic sites in Korea and correlation with the Chinese loess-paleosol sequence

We report here data on the pH, electrical conductivity (EC) and environmental magnetic properties (χlf, χfd, χARM, IRMs at different field strengths) of modern tropical lateritic soils from Aribail, Miyapadavu and Uliyathadka, all in the Kasaragod District of Kerala, southern India. This study aims to characterize the rock magnetic properties of lateritic soils that formed under tropical high-rainfall conditions and determine the effects of pedogenesis on soil magnetic properties in comparison with temperate soils. The profiles may be divided into two or three zones based on differences in magnetic mineral concentration, grain size and mineralogy. There is no magnetic enhancement of topsoil in any of the profiles studied. As the lateritic rocks in the region are ferruginous, the lateritic soils developed over them contain significant amounts of coarse grained lithogenic magnetite as well as hematite. Because of the presence of this ‘laterite-derived’ magnetite and hematite, the lateritic soils have much higher susceptibility values when compared to temperate soils. The upper zone is characterized by a higher proportion of lithogenic grains and the lower zone by superparamagnetic (SP) grains. This is probably because of iron reduction and dissolution of fine magnetic grains at the profile-top because of the excessively high rainfall (average = ~ 3500 mm/year) in the region. The slight increase in χlf and SIRM values toward the top of the Aribail and Miyapadavu profiles is due to the presence of coarse magnetic grains. This characteristic is common to all the three profiles irrespective of the topography. Compared to pre-monsoon samples, post-monsoon samples exhibit an increase in the proportion of SP grains. However, the magnetic grain size of lateritic soils from the three locations is similar to that of temperate soils.

Ages of Liangshan Paleolithic sites in Hanzhong Basin, central China

Thermally transferred optically stimulated luminescence (TT-OSL) dating extends the age range beyond current limits of OSL dating in Chinese loess. In this study, we use a single-aliquot regenerative-dose procedure for TT-OSL protocol to date Yaochangwan and Hejialiang localities of loess-covered Liangshan Paleolithic sites in Hanzhong Basin, which is an important area for the study of Paleolithic industries during the middle Pleistocene in central China. The results suggest that buried culture layer at the Hejialiang locality is correlated with the last interglacial paleosol S1 in Chinese Loess Plateau, it is dated at 86.3 ± 6.4 ka. The Yaochangwan locality spans from approximate 600–100 ka and correlates with S5–S1 in the typical Chinese loess–paleosol sequences, respectively. These ages suggest that hominins already occupied the Hanzhong Basin since approximately 600 ka ago.

An astronomically tuned 8.1 Ma eolian record from the Chinese Loess Plateau and its implication on the evolution of Asian monsoon

The Chinese loess-paleosol sequences have led to a great understanding of the evolution of the East Asian monsoon (EAM) in the Quaternary. However, evolution of the EAM in the late Miocene and Pliocene is quite blurry, hindering our understanding of the mechanisms driving the EAM. Thus, we obtained high-resolution grain size records of 8.1 Ma from the thickest eolian Red Clay sequence at Chaona on the Chinese central Loess Plateau, and astronomically tuned the grain size records to the orbital variation with a time resolution of 1.5 ka to 5.8 ka. The variability of coarse size fraction, a recognized proxy for the East Asian winter monsoon (EAWM), indicates a persistent but stepwise intensification of the EAWM at ca. 5.5 Ma, 3.6 Ma, 2.6 Ma and 1 Ma. Filtering of this proxy record at 100, 41, and 21 ka bands was conducted to trace the evolution of the EAWM in a frequency domain over 8.1 Ma. Temporal variations of these three cycles show a remarkable simultaneous enhancement at ca. 5.5 Ma, indicating a synchronous intensification of high and low latitude signals in the EAWM record. We suggest that the closure of Panama Seaway to form the North Atlantic thermohaline circulation and the high latitude cooling during this time might collectively trigger such a response. Copyright 2011 by the American Geophysical Union.

Differences between East Asian and Indian monsoon climate records during MIS3 attributed to differences in their driving mechanisms: Evidence from the loess record in the Sichuan basin, southwestern China and other continental and marine climate records

Asian monsoons vary with global climatic change, as is well recorded by Chinese loess–paleosol sequences. A radiocarbon and OSL dated, grain size and magnetic susceptibility record of the loess–paleosol sequence from the Chengdu Basin, southwestern China, contains a greatly amplified MIS 3 Indian monsoon climate record. Comparison of this record with other continental and marine climate records in the temporal and frequency domains indicates that the “high-amplitude MIS3” feature dominates the Indian monsoon region and weakens northward but is not observed in East Asian monsoon climate records. These observed differences in the amplitude of MIS 3 climate variations between the two monsoonal regions may be caused by the different effects of the precession insolation forcing on the very different monsoonal driving mechanisms. The Indian monsoon, which originates from the subtropical Mascarene High in the Southern Hemisphere, carries large precession signals from the equatorial and tropic zones, leading to the overall intensification of MIS 3 climate signals. The northward decrease of the Indian monsoon strength reduces precessional climate signals carried by the monsoon. On the other hand, the East Asian monsoon is largely generated from the Western Pacific Subtropical High in the northern subtropical zone where the impact of precessional insolation forcing and heat-vapor transport are much weaker, thus exerting a more limited spatial and temporal influence on climate records.