Red clay landslides are widely distributed worldwide,resulting in severe loss of life and property.Although rainfall-induced red clay slopes have received extensive attention,the role of cracks in the evolutionary pro...Red clay landslides are widely distributed worldwide,resulting in severe loss of life and property.Although rainfall-induced red clay slopes have received extensive attention,the role of cracks in the evolutionary process of red clay slopes and their connection to failure mechanisms is still poorly understood.A comprehensive approach integrating field investigation,laboratory tests,and numerical simulations was conducted to study the 168 red clay landslides in Xinshao County,China.The results show that red clay is prone to forming cracks at high moisture content due to its low swelling and high shrinkage properties.The failure mode of red clay slopes can be summarized in three stages:crack generation,slope excavation,and slope failure.Furthermore,the retrospective analysis and numerical simulations of the typical landslide in Guanchong indicated that intense rainfall primarily impacts the shallow layer of soil within approximately 0.5 m on the intact slope.However,cracks change the pattern of rainfall infiltration in the slope.Rainwater infiltrates rapidly through the preferential channels induced by the cracks rather than uniformly and slowly from the slope surface.This results in a significant increase in both the depth of infiltration and the saturated zone area of the cracked slope,reaching 3.8 m and 36.2 m^(2),respectively.Consequently,the factor of safety of the slope decreases by 13.4%compared to the intact slope,ultimately triggering landslides.This study can provide valuable insights into understanding the failure mechanisms of red clay slopes in China and other regions with similar geological settings.展开更多
This research aimed at testing the viability of using Sorghum Stalk Ash (SSA) as a partial replacement of lime in the stabilization of red clay soils for road subgrade construction. Red clay soils have been identified...This research aimed at testing the viability of using Sorghum Stalk Ash (SSA) as a partial replacement of lime in the stabilization of red clay soils for road subgrade construction. Red clay soils have been identified as highly expansive soils, which are affected by both climatic conditions and loading patterns. The consideration of both traffic loading patterns and climatic effects on these soils has been taken into account. A penetration test of 2.5 mm has been used on both pure red soils and stabilized soils at 10% and 15% partial replacement of lime with SSA and showed an improvement in the CBR of stabilized red clay soils up to 11.6%. Again, the PI of stabilized soils at 15% partial replacement of lime reduced up to 11.2%. The results obtained on both CBR and PI of these red clay soils are within the recommended values for the effective subgrade required for laying both permanent and flexible pavements. As a result, a recommendation of making use of SSA to lower the quantities of lime and its costs used in the stabilization of highly expansive soils have been tested through this research. However, further research on a more percentage partial replacement of lime to improve the PI of these soils to below 10% while keeping the CBR levels within the road construction regulations is welcomed.展开更多
Coagulation of red tide organism cells with clays is discussed in theory and the effects of some fac-tors on it are studied.A quantitative model is presented which describes how the coagulation varies withpH in soluti...Coagulation of red tide organism cells with clays is discussed in theory and the effects of some fac-tors on it are studied.A quantitative model is presented which describes how the coagulation varies withpH in solution.According to the model,within the pH-range between pH<sub>zpc<sub>a</sub></sub>and pH<sub>zpc<sub>b</sub></sub>,V<sub>R</sub> is negativeand the coagulation is strong and strongest at pH=(pH<sub>zpc<sub>a</sub></sub>+pH<sub>zpc<sub>b</sub></sub>)/2.It is also demonstrated that whenthe diameter of clay particles is close to that of cells,the collision probability is low,resulting in weakercoagulation.The model results have been corroborated by experiments and so are scientific and theoreticalbases for application.展开更多
Red clay type gold deposits,located in the south of China,are situated not only in orogenic belts,but also in inner cratons,where climate is tropical-subtropical with clear arid and humid.The lateritic weathering crus...Red clay type gold deposits,located in the south of China,are situated not only in orogenic belts,but also in inner cratons,where climate is tropical-subtropical with clear arid and humid.The lateritic weathering crust often can be divided into five zones,including topsoil,siliceous duricrust zone,multi-color zone(or red clay zone in some deposits),pallid zone and saprolite zone from surface to the base rock,several of which are absent in some deposits.The base rocks are composed mainly of carbonate rocks with minor clastic rocks,intermediate-basic volcanic rocks and intermediate-acid and alkalic intrusions.The orebodies are mainly located in the multi-color zone with part of them in the pallid and saprolite zones.The ore sources include orebodies of Carlin-type gold deposits and porphyry gold deposits,as well as gold-rich base rocks.The red clay type gold deposits experienced early-stage endogenic gold mineralization and laterization during the Tertiary and Quaternary.The areas with endogenic gold deposits,especially Carlin-type gold deposits and porphyry gold deposits in karst depressions on the plateau,structual erosional platforms in the middle-lower mountains,and intermountain basins in southern China are well worth studying to trace red clay type gold deposits.展开更多
There is fine and uniform clay with aluminous and ferrous cementation in the red clay found in Guigang, Guangxi. It has the characteristics of shrinkage outwardly, rigid upper but soft lower and well grown fissure. I...There is fine and uniform clay with aluminous and ferrous cementation in the red clay found in Guigang, Guangxi. It has the characteristics of shrinkage outwardly, rigid upper but soft lower and well grown fissure. In addition there are engineering characteristics such as high water content, low compactness and low compressibility, high strength and high contractility but slight expansibility. This paper discusses the red clay's engineering characteristics and its change regulation with depth by analyzing changes in the red clay's grain size composition, mineralogical constitution, and chemical composition.展开更多
Completely weathered phyllite(CWP)soil is a kind of special soil with high swell potential,while red clay is a special soil with high shrinkage.This means that these two kinds of special soils are usually not suitable...Completely weathered phyllite(CWP)soil is a kind of special soil with high swell potential,while red clay is a special soil with high shrinkage.This means that these two kinds of special soils are usually not suitable for direct use as subgrade fill.To reduce the swell index of the CWP soil and the shrinkage of red clay at the same time,it was proposed to blend the CWP soil with red clay to improve their basic characteristics.A series of swell index tests and dry-wet cycle tests of the blended soils have been carried out at varying blending ratios,compaction coefficients and moisture contents.The test results show that the free swell index of the blended soil decreases with the increase of red clay,moisture content and compaction coefficient,respectively.The fissure density of the blended soil first decreases and then increases with the blending ratio,with the lowest being zero when the blending ratio is ranging from 20%to 40%.Through particle microscopic analysis and elemental composition analysis,it is found that the neutralization effect,the dilution effect of swell minerals,and the partition effect of coarse particles play an important role in restraining expansion and shrinkage deformation of the blended soil.Based on the liquid limit requirement of Chinese Railway Design Code(TB 10001-2016),the optimal blending ratio of red clay has been proposed to be 50%.Compared with the CWP soil,the free load swell index of the blended soil is reduced by 45.0%and the fissure density is reduced by 99.3%compared with that of red clay.Therefore,it is feasible to improve the CWP soil by blending it with red clay at an optimal ratio of 50%by using the neutralization effect of the expansion of CWP and shrinkage of red clay.展开更多
To explore an environmentally friendly improvement measure for red clay,the function and mechanism of xanthan gum biopolymer and polypropylene fibers on the strength properties of red clay were investigated by unconfi...To explore an environmentally friendly improvement measure for red clay,the function and mechanism of xanthan gum biopolymer and polypropylene fibers on the strength properties of red clay were investigated by unconfined compressive strength and scanning electron microscopy tests.The test results demonstrated that the contents and curing ages of xanthan gum had significant influences on the unconfined compressive strength of red clay.Compared with untreated soil,1.5%xanthan gum content was the optimal ratio in which the strength increment was between 41.52 kPa and 64.73 kPa.On the other hand,the strength of xanthan gum-treated red clay increased,whereas the ductility decreased with the increase in curing ages,indicating that the xanthan gum-treated red clay started to gradually consolidate after 3 days of curing and stiffness significantly improved between 7 and 28 days of curing.The results also showed that the synergistic consolidation effects of the xanthan gum–polypropylene fibers could not only effectively enhance the strength of red clay but also reduce the brittle failure phenomenon.The strengths of soil treated with 2.0%xanthan gum-polypropylene fibers were 1.9–2.41 and 1.12–1.47 times than that of red clay and 1.5%xanthan gum-treated clay,respectively.The results of study provide the related methods and experiences for the field of ecological soil treatment.展开更多
Increasing interest in recent years has focused on vermicular red clay(VRC) in southern China due to its controversial sedimentary environment and provenance. Grain size is a useful way to determine sedimentary enviro...Increasing interest in recent years has focused on vermicular red clay(VRC) in southern China due to its controversial sedimentary environment and provenance. Grain size is a useful way to determine sedimentary environment and provenance. Fisher Linear Discriminant Analysis(LDA) is a common and widely used method for multivariate statistical analysis. Based on a proper training sample set, the LDA can be used to discuss the sediment provenance. In this study, grain size data for 77 Malan loess samples and 41 floodplain deposit samples were used as a training sample set to deduce a Fisher linear discriminant function. Then, 299 VRC samples from 6 Quaternary red clay profiles were analyzed using the discriminant function. Grain size parameters and microscopic images of quartz grains separated from the VRC were evaluated in detail to determine the VRC sedimentary environment in south China. The results show that VRC profiles can be classified into two regions: the Chiang-nan Hilly Region and Wuyi Mountains Region. The VRC samples in the Chiang-nan Hilly Region originated from eolian dust deposits. This VRC is characterized by a higher content of fine particles(<20 μm) and lower average transport kinetic energy than loess in a C-M plot. The quartz grain sizes and microscope images of this VRC suggest that it could be a polyphyletic mixture of far-sourced and nearsourced eolian deposits. The far-sourced eolian deposits share similar provenance with Xiashu loess and were transported by the East Asian winter monsoon. The near-sourced eolian deposits were dust emitted from the adjacent floodplain. In the Wuyi Mountains Region, the rugged topography weakened the dustfall and strengthened the reconstructive effect of hydrodynamic forces during the Quaternary glacial periods. The VRC in this region was reworked strongly by water and retained typical hydraulic characteristics no matter the source.展开更多
Completely weathered phyllite(CWP)has the characteristics of difficult compaction,low shear strength after compaction and large settlement after construction.The traditional improvement method using a single agent of ...Completely weathered phyllite(CWP)has the characteristics of difficult compaction,low shear strength after compaction and large settlement after construction.The traditional improvement method using a single agent of red clay or cement for CWP satisfies the subgrade requirements for ordinary railway,but cannot meet the requirements of immediate strength and long-term post-construction settlement of high-speed railway at the same time.A series of experimental investigations were undertaken for the blended CWP soils,with three additives used.The first additive was red clay,the second was cement and the third was a combination of both red clay and cement at various portions.Results of consolidation test and shear strength test carried out for the treated CWP soils show that:1)The effect of cement on improving the compression modulus of CWP is much better than that of red clay;2)The settlement of an embankment of 10 m high formed by blended soil of CWP with 3%cement can be controlled within 15 mm,while the settlement will be 25.15 mm for the same embankment of blended soil of CWP with 40%red clay;3)The shear strength and ultimate bearing capacity of CWP improved by red clay are much better than those of 5%cement;4)The ultimate bearing capacity of CWP improved by 40%red clay is 3.42 times of that by 3%cement and 2.95 times by 5%cement.Furthermore,the bearing capacity of CWP when improved by red clay can meet railway subgrade requirements immediately after compaction,while cement improved CWP needs a curing time of 1 day or longer.This is an impediment to rapid construction process.The improvement mechanism of red clay is mainly filling effect and grading improvement effect,while the improvement mechanism of cement is mainly hardening reaction,which produces high strength material to cement.It is found that 40%red clay and 3%cement treated CWP,which is considered to be optimum,can meet the subgrade requirements of both immediate bearing capacity and long-term post-construction settlement for the high-speed railway.展开更多
Objective Aeolian sediments on the Chinese Loess Plateau contain some of the best continental archives of palaeoclimate change in the Late Cenozoic. The consensus that alternating MS in loess-paleosols in China was du...Objective Aeolian sediments on the Chinese Loess Plateau contain some of the best continental archives of palaeoclimate change in the Late Cenozoic. The consensus that alternating MS in loess-paleosols in China was due to the strengthening and weakening of the East Asian palaeomonsoon provides an excellent climate record when correlated with global ice volume. Significantly, new basal dates from the red clay underlying the loess-paleosol sequence indicate that wind-blown dust began to accumulate on the Chinese Loess Plateau at least 22 million years ago. There are differences of opinion,展开更多
In this study, a new composite ceramic material using a red clay matrix with different amount of clinker from the cement industry has been developed. The aim is to valorize some natural resources such as red clay and ...In this study, a new composite ceramic material using a red clay matrix with different amount of clinker from the cement industry has been developed. The aim is to valorize some natural resources such as red clay and sub-products from the cement industry as clinker in order to develop new materials for industrial and/or catalytic uses. Raw materials were grounded in order to reduce the particle size and obtain a homogeneous slip. The samples were mixed and compressed into pellets and undergo a heat treatment up to 1100℃. Geotechnical characterization has been carried out. Firing proprieties (shrinkage, water absorption, and mechanical resistance to the inflection) were measured. The composition of the ceramic material was investigated by X-ray diffraction, XRF, SEM and EDS methods. The incorporation of clinker in the ceramic composite material up to 50 wt% exhibits good behaviors (physical and mechanical proprieties) and can be used as a ceramic product.展开更多
The red clay in Chenzhou, Hunan province is mostly in unsaturated state. Simply applying the mechanical properties that derived from classic saturated soil mechanics often leads to slope failures in this region. In or...The red clay in Chenzhou, Hunan province is mostly in unsaturated state. Simply applying the mechanical properties that derived from classic saturated soil mechanics often leads to slope failures in this region. In order to study the shear strength characteristic of unsaturated red clay in Chenzhou and to explore a shear strength equation that can be easily applied in engineering practice, a series of triaxial tests of saturated and unsaturated red clay samples were performed using the regular triaxial testing apparatus. The testing results show that the peak strength of red clay drops slightly before the moisture content of 30% but decreases sharply after that. The friction angle of red clay under unsaturated state is basically equal to the effective friction angle under saturated state, while the cohesion of unsaturated red clay is far much bigger than that of saturated one, which indicates that the matric suction makes a great contribution to the cohesion. By fitting the testing results with appropriate curves, the relationships between total strength parameters and with moisture content were obtained. The total increases logarithmically before the moisture content of 35% then decreases linearly, while decreases cubically with increasing moisture content.展开更多
Reflectance spectroscopy is rapid,inexpensive,and non-destructive and can provide important information about the mineralogy of rocks and sediments.We measured the reflectance spectroscopy of Miocene red clay deposits...Reflectance spectroscopy is rapid,inexpensive,and non-destructive and can provide important information about the mineralogy of rocks and sediments.We measured the reflectance spectroscopy of Miocene red clay deposits on the northeastern margin of the Tibetan Plateau,with the aim of developing a rapid methodology for detecting paleoclimatic changes.We obtained visible/near-infrared(VNIR)and short-wave infrared(SWIR)spectroscopy data from the red clay in the Jianzha Basin,and analyzed their relationship with independent paleoclimatic records,including mineral contents and environmental magnetic parameters.The results show that the VNIR parameters,including D500,D900,R500,and R900(where D and R represent the depth and reflectance of the absorption peaks around 500 and 900 nm,respectively)are temperature-sensitive and correlated with the magnetic susceptibility,frequency-dependent magnetic susceptibility,and the marine δ^(18)O record.The results of frequency-domain analysis of the VNIR parameters show that they reflect climate change on orbital timescales.SWIR parameters,such as AS1400,D1400/D1900 and D1900(where AS represents the asymmetry of the absorption peaks around1400 nm),are correlated with the illite and montmorillonite content,and they are sensitive to the weathering intensity.The spectral parameters of the eolian red clay in the Jianzha Basin reflect regional climatic changes caused by the uplift of the Tibetan Plateau at~8.5 Ma and global climatic cooling at~7.2 Ma,and thus they are applicable as both regional and global paleoenvironmental indicators.展开更多
This study collected the early Oligocene to middle Miocene sediments from the Gerze Basin of Tibet, and used X-Ray diffraction (XRD) and Scanning Electron Microscope (SEM) to discuss their clay mineralolgy, clay i...This study collected the early Oligocene to middle Miocene sediments from the Gerze Basin of Tibet, and used X-Ray diffraction (XRD) and Scanning Electron Microscope (SEM) to discuss their clay mineralolgy, clay indices, better understand the clay mineralogy and its paleoclimatic significance. The results show that clay minerals of the Gerze Basin sediments are mainly composed of iilite and chlorite, with minor amounts of smectite and kaolinite, and their relative content varies along the section. Variations of relative contents and clay indices suggest that the Gerze Basin has experienced three-stage evolution of paleoclimate: I ) high ilUte and chlorite contents, with fluctuant smectite and low (I+Ch)/(K+S) ratio, indicative of a dominant seasonal arid climate from the early Oligoeene to late Oligocene; Ⅱ) higher illite and chlorite contents and larger (I+Ch)/(K+S) ratio but absence of kaolinite, indicating a colder and drier climate from the late Oligocene to early Miocene; Ⅲ) high iilite and chlorite contents with fluctuant (I+Ch)/(K+S) ratios and occasional occurrence of kaolinite, suggesting that the climate became warmer and more humid compared with that of stage Ⅱ in the mid-Miocene. These conclusions were also reinforced by the clay morphology, which suggests that physical weathering dominated in stage Ⅱ, while relatively strong chemical weathering was dominant in stages Ⅰ and Ⅲ Clay minerals of the sediments mainly consist of illite and chlorite, indicating that the source rock played a significant role in clay origin. It is inferred that global cooling and the enhancement of denudation and obstruction of northward moisture due to the uplift of the Qinghai-Tibet Plateau were responsible for the provenance of iUite and chlorite under weak chemical weathering. Though the Qinghai-Tibet Plateau reached a certain elevation by the mid-Miocene, yet the mid-Miocene widespread warming might have largely impacted the Gerze climate.展开更多
The present study investigated the incorporation of sugarcane bagasse ash(SCBA)in red ceramics,sintered in conventional oven and microwave oven,aiming to provide an alternative product,and a sintering process with hig...The present study investigated the incorporation of sugarcane bagasse ash(SCBA)in red ceramics,sintered in conventional oven and microwave oven,aiming to provide an alternative product,and a sintering process with higher energy efficiency in the production of red ceramics.The raw materials were characterized by XRF,XRD,thermogravimetry,particle size distribution and specific mass analyses.The specimens were shaped by extrusion in two different compositions,red clay and red clay with addition of 20%SCBA and sintered at temperatures from 700 to 1100℃.The conventional sintering occurred for 60 min with heating rate of 10℃/min.In the microwave oven the sintering occurred in a hybrid way,with heating rate of 50℃/min for 5,10 and 15 mins.After sintering the tests of linear shrinkage,compressive strength,water absorption,apparent porosity and apparent specific mass were performed.The addition of SCBA causes an increase in the values of water absorption and decreases the compressive strength and specific mass of the red ceramic.This occurs due to the creation of pores inside the material from the volatilization of organic matter present in the ashes.The sintering in microwave oven,when compared to conventional sintering,promotes an increase in the values of compressive strength and specific mass and reduction of water absorption values of ceramics,probably due to the refinement of the microstructure and the higher densification.Thus the incorporation of ashes can be partially compensated by a more efficient sintering.The use of SCBA and the sintering in microwave oven,showed to be viable alternatives in the development of a more sustainable and light material,promoting the management of waste,reduction in the consumption of raw materials and energy saving.展开更多
Natural clays have been used by man in infections of bacterial etiology, since the first historical registers. Our attention turned to a red-colored clay, known in the northeast of Brazil as “barro de louça”...Natural clays have been used by man in infections of bacterial etiology, since the first historical registers. Our attention turned to a red-colored clay, known in the northeast of Brazil as “barro de louça” (dish clay). These clays and other natural earth materials seem interesting to us, as the blockage of the liberation of toxins or inactivation, may be related to the interruption of infection cycles in the skin and mucous membranes. The adsorptive and absorptive properties of the mineral clays are well documented in the cure process of skin and gastrointestinal diseases. Susceptibility and bacterial tropism tests were carried out. The results were analyzed and interpreted according to the conventional microbiological protocol. The bacterial strains, Staphylococcus aureus, Escherichia coli e Pseudomonas aeruginosa, did not present a susceptibility profile to an isotonic solution of clay, but there was an increase of the bacterial tropism as the concentration of the isotonic solution was increased, being the minimal observed concentration of 100 mg/mL. Our aim is to document a type of red clay from the northeast of Brazil with possible attraction properties (Tropism) to bacteria and their toxins.展开更多
Two Red Clay profiles near Xi’ an and Xifeng were investigated in an attempt to determine magne-tostratigraphic and palaeoclimatic records. The results show that aeolian dust accumulation and the related East Asia pa...Two Red Clay profiles near Xi’ an and Xifeng were investigated in an attempt to determine magne-tostratigraphic and palaeoclimatic records. The results show that aeolian dust accumulation and the related East Asia palaeomonsoon system had begun by 6.5 Ma, and it is deduced that the Tibetan Plateau had reached a significant elevation at that time. The late Tertiary palaeoclimatic history of the Red Clay as reflected by magnetic susceptibility is reconstructed during the period of 6.5-2.5 Ma. Stepwise increase in susceptibility of aeolian dust accumulation appears to have a close correlation to the uplift processes of the Tibetan Plateau. The remarkable increase of aeolian dust accumulation at 3.2 Ma appears to be due to the influence of global ice volume on the East Asia monsoon. Palaeomonsoon variation during the late Tertiary as recorded in the Red Clay sequences from the Chinese Loess Plateau can be regarded as the product of a number of interacting factors, such as uplift of the Tibetan Plateau,展开更多
The wind system responsible for transporting dust onto the Chinese Loess Plateau during the late Miocene and Pliocene is still unknown and recent investigations highlight many controversies. This report aims to invest...The wind system responsible for transporting dust onto the Chinese Loess Plateau during the late Miocene and Pliocene is still unknown and recent investigations highlight many controversies. This report aims to investigate spatiotemporal changes in grain-size and sedi- mentation rate of the Neogene Red Clay deposits in north China and to explore palaeoclimatic changes during the late Miocene and Pliocene, in particular the palaeowind system that trans- ported dust. Samples were collected from eight Red Clay sections on the Loess Plateau. Meas- urement and analysis show that there is a clear southward decrease in the mean grain-size index and in the coarse particle fraction (>20 μm). At Jiaxian site on the northern Loess Plateau, the average mean grain-size is around 20 μm, while at Lantian site in the south, the mean is around 9 μm. The coarse particle fraction >20 μm makes up 24.4% and 5.6%, at the two sites respec- tively. This distinct diversity of grain-size in the aeolian Red Clay deposit between the north and south indicate that the palaeodust was transported mainly by northerly low-level winds. The grain-size variations in the Red Clay deposits can also be divided into three stages (the lower, the middle and the upper interval): grain-size of the lower stage is significantly coarser than that of the middle stage, but finer than that of the upper stage. As a consequence, the intensity of pa- laeowind and desiccation of the dust source region during the late Miocene and Pliocene can be divided into three stages: 6.2―5.4 Ma, 5.4―3.5 Ma and 3.5―2.6 Ma. Strength of the palaeowind during the middle stage (5.4―3.5 Ma) is weaker than that of the previous and subsequent stages and the intensity of palaeowind during the latest stage (3.5―2.6 Ma) is stronger than that of the early time (6.2―5.4 Ma). Variations in the sedimentation rate of the Red Clay deposit can also be divided into three stages: the earlier, the middle and the later interval. The sedimentation rate of the earlier stage is higher than during the middle stage, but lower than during the later one. This is a clear indicator of changes in the palaeowind intensity and aridity in the dust source region and may be linked with global ice volume changes during the late Miocene and the Pliocene.展开更多
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 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 pe-dogenesis 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 eo-lian/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 envi-ronmental 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.展开更多
The Lower Pliocene of the Linxia Basin in Gansu Province is one of only a few representative sections for the Early Pliocene sedimentary records in northern China, and even in East Asia. Recently,abundant mammalian fo...The Lower Pliocene of the Linxia Basin in Gansu Province is one of only a few representative sections for the Early Pliocene sedimentary records in northern China, and even in East Asia. Recently,abundant mammalian fossils were found from the base of red clays of the Lower Pliocene Hewangjia Formation at Duikang in Guanghe County within this basin. Previously, the Pliocene mammals were sparsely found in China, and most were collected from fluvial and lacustrine deposits in the eastern Loess Plateau. Mammals from the widely distributed Pliocene Hipparion Red Clay are less in number.The known fossils from Duikang include 20 species and belong to the Shilidun Fauna. Their faunal components are similar to the Early Pliocene Gaozhuang Fauna from Ynshe, Shanxi. On the other hand, some taxa from Duikang have not been found in the Gaozhuang Fauna, are slightly more primitive in evolutionary level, and appeared mainly in the Late Miocene. As a result, the age of the Duikang fossils may be slightly earlier than that of the Gaozhuang Fauna and closer to the lower boundary of the Piiocene. The Duikang fossiliferons bed is 0.8 m above the top of the Late Miocene Linshu Formation, and the first occurrence of the three-toed horse Hipparion pater can be regarded as a biostratigraphical marker of the Miocene/Pliocene boundary. In conclusion, Duikang is an ideal candidate locality to establish as the stratotype of the lower boundary of the Chinese terrestrial Pliocene.展开更多
基金supported by the National Natural Science Foundation of China(Project No.41920104007 and 41772334).
文摘Red clay landslides are widely distributed worldwide,resulting in severe loss of life and property.Although rainfall-induced red clay slopes have received extensive attention,the role of cracks in the evolutionary process of red clay slopes and their connection to failure mechanisms is still poorly understood.A comprehensive approach integrating field investigation,laboratory tests,and numerical simulations was conducted to study the 168 red clay landslides in Xinshao County,China.The results show that red clay is prone to forming cracks at high moisture content due to its low swelling and high shrinkage properties.The failure mode of red clay slopes can be summarized in three stages:crack generation,slope excavation,and slope failure.Furthermore,the retrospective analysis and numerical simulations of the typical landslide in Guanchong indicated that intense rainfall primarily impacts the shallow layer of soil within approximately 0.5 m on the intact slope.However,cracks change the pattern of rainfall infiltration in the slope.Rainwater infiltrates rapidly through the preferential channels induced by the cracks rather than uniformly and slowly from the slope surface.This results in a significant increase in both the depth of infiltration and the saturated zone area of the cracked slope,reaching 3.8 m and 36.2 m^(2),respectively.Consequently,the factor of safety of the slope decreases by 13.4%compared to the intact slope,ultimately triggering landslides.This study can provide valuable insights into understanding the failure mechanisms of red clay slopes in China and other regions with similar geological settings.
文摘This research aimed at testing the viability of using Sorghum Stalk Ash (SSA) as a partial replacement of lime in the stabilization of red clay soils for road subgrade construction. Red clay soils have been identified as highly expansive soils, which are affected by both climatic conditions and loading patterns. The consideration of both traffic loading patterns and climatic effects on these soils has been taken into account. A penetration test of 2.5 mm has been used on both pure red soils and stabilized soils at 10% and 15% partial replacement of lime with SSA and showed an improvement in the CBR of stabilized red clay soils up to 11.6%. Again, the PI of stabilized soils at 15% partial replacement of lime reduced up to 11.2%. The results obtained on both CBR and PI of these red clay soils are within the recommended values for the effective subgrade required for laying both permanent and flexible pavements. As a result, a recommendation of making use of SSA to lower the quantities of lime and its costs used in the stabilization of highly expansive soils have been tested through this research. However, further research on a more percentage partial replacement of lime to improve the PI of these soils to below 10% while keeping the CBR levels within the road construction regulations is welcomed.
基金Chinese Postdoctoral Fund and Natural Scienced Found of Shandong Province(No.93E0157)
文摘Coagulation of red tide organism cells with clays is discussed in theory and the effects of some fac-tors on it are studied.A quantitative model is presented which describes how the coagulation varies withpH in solution.According to the model,within the pH-range between pH<sub>zpc<sub>a</sub></sub>and pH<sub>zpc<sub>b</sub></sub>,V<sub>R</sub> is negativeand the coagulation is strong and strongest at pH=(pH<sub>zpc<sub>a</sub></sub>+pH<sub>zpc<sub>b</sub></sub>)/2.It is also demonstrated that whenthe diameter of clay particles is close to that of cells,the collision probability is low,resulting in weakercoagulation.The model results have been corroborated by experiments and so are scientific and theoreticalbases for application.
基金supported by the National Basic Research Program of China(973 Program)(No. 2009CB421008)111 Project(No.B07011)Program for Changjiang Scholars and Innovative Research Team in University(PCSIRT)
文摘Red clay type gold deposits,located in the south of China,are situated not only in orogenic belts,but also in inner cratons,where climate is tropical-subtropical with clear arid and humid.The lateritic weathering crust often can be divided into five zones,including topsoil,siliceous duricrust zone,multi-color zone(or red clay zone in some deposits),pallid zone and saprolite zone from surface to the base rock,several of which are absent in some deposits.The base rocks are composed mainly of carbonate rocks with minor clastic rocks,intermediate-basic volcanic rocks and intermediate-acid and alkalic intrusions.The orebodies are mainly located in the multi-color zone with part of them in the pallid and saprolite zones.The ore sources include orebodies of Carlin-type gold deposits and porphyry gold deposits,as well as gold-rich base rocks.The red clay type gold deposits experienced early-stage endogenic gold mineralization and laterization during the Tertiary and Quaternary.The areas with endogenic gold deposits,especially Carlin-type gold deposits and porphyry gold deposits in karst depressions on the plateau,structual erosional platforms in the middle-lower mountains,and intermountain basins in southern China are well worth studying to trace red clay type gold deposits.
文摘There is fine and uniform clay with aluminous and ferrous cementation in the red clay found in Guigang, Guangxi. It has the characteristics of shrinkage outwardly, rigid upper but soft lower and well grown fissure. In addition there are engineering characteristics such as high water content, low compactness and low compressibility, high strength and high contractility but slight expansibility. This paper discusses the red clay's engineering characteristics and its change regulation with depth by analyzing changes in the red clay's grain size composition, mineralogical constitution, and chemical composition.
基金This work is supported by the National Natural Science Foundation of China(Grant Nos.52068027,51668018,51768021).
文摘Completely weathered phyllite(CWP)soil is a kind of special soil with high swell potential,while red clay is a special soil with high shrinkage.This means that these two kinds of special soils are usually not suitable for direct use as subgrade fill.To reduce the swell index of the CWP soil and the shrinkage of red clay at the same time,it was proposed to blend the CWP soil with red clay to improve their basic characteristics.A series of swell index tests and dry-wet cycle tests of the blended soils have been carried out at varying blending ratios,compaction coefficients and moisture contents.The test results show that the free swell index of the blended soil decreases with the increase of red clay,moisture content and compaction coefficient,respectively.The fissure density of the blended soil first decreases and then increases with the blending ratio,with the lowest being zero when the blending ratio is ranging from 20%to 40%.Through particle microscopic analysis and elemental composition analysis,it is found that the neutralization effect,the dilution effect of swell minerals,and the partition effect of coarse particles play an important role in restraining expansion and shrinkage deformation of the blended soil.Based on the liquid limit requirement of Chinese Railway Design Code(TB 10001-2016),the optimal blending ratio of red clay has been proposed to be 50%.Compared with the CWP soil,the free load swell index of the blended soil is reduced by 45.0%and the fissure density is reduced by 99.3%compared with that of red clay.Therefore,it is feasible to improve the CWP soil by blending it with red clay at an optimal ratio of 50%by using the neutralization effect of the expansion of CWP and shrinkage of red clay.
基金This study was supported by the State Key Laboratory Project of China(Grant No.KF2020-12)the Yunnan Education Department Project of China(Grant Nos.2020Y0175 and 2020J0240).
文摘To explore an environmentally friendly improvement measure for red clay,the function and mechanism of xanthan gum biopolymer and polypropylene fibers on the strength properties of red clay were investigated by unconfined compressive strength and scanning electron microscopy tests.The test results demonstrated that the contents and curing ages of xanthan gum had significant influences on the unconfined compressive strength of red clay.Compared with untreated soil,1.5%xanthan gum content was the optimal ratio in which the strength increment was between 41.52 kPa and 64.73 kPa.On the other hand,the strength of xanthan gum-treated red clay increased,whereas the ductility decreased with the increase in curing ages,indicating that the xanthan gum-treated red clay started to gradually consolidate after 3 days of curing and stiffness significantly improved between 7 and 28 days of curing.The results also showed that the synergistic consolidation effects of the xanthan gum–polypropylene fibers could not only effectively enhance the strength of red clay but also reduce the brittle failure phenomenon.The strengths of soil treated with 2.0%xanthan gum-polypropylene fibers were 1.9–2.41 and 1.12–1.47 times than that of red clay and 1.5%xanthan gum-treated clay,respectively.The results of study provide the related methods and experiences for the field of ecological soil treatment.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.41201008,41371032 and 41371206)
文摘Increasing interest in recent years has focused on vermicular red clay(VRC) in southern China due to its controversial sedimentary environment and provenance. Grain size is a useful way to determine sedimentary environment and provenance. Fisher Linear Discriminant Analysis(LDA) is a common and widely used method for multivariate statistical analysis. Based on a proper training sample set, the LDA can be used to discuss the sediment provenance. In this study, grain size data for 77 Malan loess samples and 41 floodplain deposit samples were used as a training sample set to deduce a Fisher linear discriminant function. Then, 299 VRC samples from 6 Quaternary red clay profiles were analyzed using the discriminant function. Grain size parameters and microscopic images of quartz grains separated from the VRC were evaluated in detail to determine the VRC sedimentary environment in south China. The results show that VRC profiles can be classified into two regions: the Chiang-nan Hilly Region and Wuyi Mountains Region. The VRC samples in the Chiang-nan Hilly Region originated from eolian dust deposits. This VRC is characterized by a higher content of fine particles(<20 μm) and lower average transport kinetic energy than loess in a C-M plot. The quartz grain sizes and microscope images of this VRC suggest that it could be a polyphyletic mixture of far-sourced and nearsourced eolian deposits. The far-sourced eolian deposits share similar provenance with Xiashu loess and were transported by the East Asian winter monsoon. The near-sourced eolian deposits were dust emitted from the adjacent floodplain. In the Wuyi Mountains Region, the rugged topography weakened the dustfall and strengthened the reconstructive effect of hydrodynamic forces during the Quaternary glacial periods. The VRC in this region was reworked strongly by water and retained typical hydraulic characteristics no matter the source.
基金This work is supported by the National Natural Science Foundation of China(Grant Nos.52068027,51668018,51768021).
文摘Completely weathered phyllite(CWP)has the characteristics of difficult compaction,low shear strength after compaction and large settlement after construction.The traditional improvement method using a single agent of red clay or cement for CWP satisfies the subgrade requirements for ordinary railway,but cannot meet the requirements of immediate strength and long-term post-construction settlement of high-speed railway at the same time.A series of experimental investigations were undertaken for the blended CWP soils,with three additives used.The first additive was red clay,the second was cement and the third was a combination of both red clay and cement at various portions.Results of consolidation test and shear strength test carried out for the treated CWP soils show that:1)The effect of cement on improving the compression modulus of CWP is much better than that of red clay;2)The settlement of an embankment of 10 m high formed by blended soil of CWP with 3%cement can be controlled within 15 mm,while the settlement will be 25.15 mm for the same embankment of blended soil of CWP with 40%red clay;3)The shear strength and ultimate bearing capacity of CWP improved by red clay are much better than those of 5%cement;4)The ultimate bearing capacity of CWP improved by 40%red clay is 3.42 times of that by 3%cement and 2.95 times by 5%cement.Furthermore,the bearing capacity of CWP when improved by red clay can meet railway subgrade requirements immediately after compaction,while cement improved CWP needs a curing time of 1 day or longer.This is an impediment to rapid construction process.The improvement mechanism of red clay is mainly filling effect and grading improvement effect,while the improvement mechanism of cement is mainly hardening reaction,which produces high strength material to cement.It is found that 40%red clay and 3%cement treated CWP,which is considered to be optimum,can meet the subgrade requirements of both immediate bearing capacity and long-term post-construction settlement for the high-speed railway.
基金co-supported by the National Natural Science Foundation of China(grants No.41421002, 41372037,41372036,41372020 and 41002052)
文摘Objective Aeolian sediments on the Chinese Loess Plateau contain some of the best continental archives of palaeoclimate change in the Late Cenozoic. The consensus that alternating MS in loess-paleosols in China was due to the strengthening and weakening of the East Asian palaeomonsoon provides an excellent climate record when correlated with global ice volume. Significantly, new basal dates from the red clay underlying the loess-paleosol sequence indicate that wind-blown dust began to accumulate on the Chinese Loess Plateau at least 22 million years ago. There are differences of opinion,
文摘In this study, a new composite ceramic material using a red clay matrix with different amount of clinker from the cement industry has been developed. The aim is to valorize some natural resources such as red clay and sub-products from the cement industry as clinker in order to develop new materials for industrial and/or catalytic uses. Raw materials were grounded in order to reduce the particle size and obtain a homogeneous slip. The samples were mixed and compressed into pellets and undergo a heat treatment up to 1100℃. Geotechnical characterization has been carried out. Firing proprieties (shrinkage, water absorption, and mechanical resistance to the inflection) were measured. The composition of the ceramic material was investigated by X-ray diffraction, XRF, SEM and EDS methods. The incorporation of clinker in the ceramic composite material up to 50 wt% exhibits good behaviors (physical and mechanical proprieties) and can be used as a ceramic product.
文摘The red clay in Chenzhou, Hunan province is mostly in unsaturated state. Simply applying the mechanical properties that derived from classic saturated soil mechanics often leads to slope failures in this region. In order to study the shear strength characteristic of unsaturated red clay in Chenzhou and to explore a shear strength equation that can be easily applied in engineering practice, a series of triaxial tests of saturated and unsaturated red clay samples were performed using the regular triaxial testing apparatus. The testing results show that the peak strength of red clay drops slightly before the moisture content of 30% but decreases sharply after that. The friction angle of red clay under unsaturated state is basically equal to the effective friction angle under saturated state, while the cohesion of unsaturated red clay is far much bigger than that of saturated one, which indicates that the matric suction makes a great contribution to the cohesion. By fitting the testing results with appropriate curves, the relationships between total strength parameters and with moisture content were obtained. The total increases logarithmically before the moisture content of 35% then decreases linearly, while decreases cubically with increasing moisture content.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research(STEP)Program(Grant Nos.2019QZKK0704&2019QZKK0101)the National Natural Science Foundation of China(Grant Nos.42272221&41772167)+1 种基金the State Key Laboratory of Loess and Quaternary Geology(Grant No.SKLLQG1905)the Central University Research Foundation,Chang’an University(Grant Nos.300102272901)。
文摘Reflectance spectroscopy is rapid,inexpensive,and non-destructive and can provide important information about the mineralogy of rocks and sediments.We measured the reflectance spectroscopy of Miocene red clay deposits on the northeastern margin of the Tibetan Plateau,with the aim of developing a rapid methodology for detecting paleoclimatic changes.We obtained visible/near-infrared(VNIR)and short-wave infrared(SWIR)spectroscopy data from the red clay in the Jianzha Basin,and analyzed their relationship with independent paleoclimatic records,including mineral contents and environmental magnetic parameters.The results show that the VNIR parameters,including D500,D900,R500,and R900(where D and R represent the depth and reflectance of the absorption peaks around 500 and 900 nm,respectively)are temperature-sensitive and correlated with the magnetic susceptibility,frequency-dependent magnetic susceptibility,and the marine δ^(18)O record.The results of frequency-domain analysis of the VNIR parameters show that they reflect climate change on orbital timescales.SWIR parameters,such as AS1400,D1400/D1900 and D1900(where AS represents the asymmetry of the absorption peaks around1400 nm),are correlated with the illite and montmorillonite content,and they are sensitive to the weathering intensity.The spectral parameters of the eolian red clay in the Jianzha Basin reflect regional climatic changes caused by the uplift of the Tibetan Plateau at~8.5 Ma and global climatic cooling at~7.2 Ma,and thus they are applicable as both regional and global paleoenvironmental indicators.
基金financially supported by the Independent Research Project Foundation of State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan (No. GBL11307)the Key Project Foundation of China Geological Survey (No. 1212011121261)the National Natural Science Foundation of China (Nos. 41272053 and 41072030)
文摘This study collected the early Oligocene to middle Miocene sediments from the Gerze Basin of Tibet, and used X-Ray diffraction (XRD) and Scanning Electron Microscope (SEM) to discuss their clay mineralolgy, clay indices, better understand the clay mineralogy and its paleoclimatic significance. The results show that clay minerals of the Gerze Basin sediments are mainly composed of iilite and chlorite, with minor amounts of smectite and kaolinite, and their relative content varies along the section. Variations of relative contents and clay indices suggest that the Gerze Basin has experienced three-stage evolution of paleoclimate: I ) high ilUte and chlorite contents, with fluctuant smectite and low (I+Ch)/(K+S) ratio, indicative of a dominant seasonal arid climate from the early Oligoeene to late Oligocene; Ⅱ) higher illite and chlorite contents and larger (I+Ch)/(K+S) ratio but absence of kaolinite, indicating a colder and drier climate from the late Oligocene to early Miocene; Ⅲ) high iilite and chlorite contents with fluctuant (I+Ch)/(K+S) ratios and occasional occurrence of kaolinite, suggesting that the climate became warmer and more humid compared with that of stage Ⅱ in the mid-Miocene. These conclusions were also reinforced by the clay morphology, which suggests that physical weathering dominated in stage Ⅱ, while relatively strong chemical weathering was dominant in stages Ⅰ and Ⅲ Clay minerals of the sediments mainly consist of illite and chlorite, indicating that the source rock played a significant role in clay origin. It is inferred that global cooling and the enhancement of denudation and obstruction of northward moisture due to the uplift of the Qinghai-Tibet Plateau were responsible for the provenance of iUite and chlorite under weak chemical weathering. Though the Qinghai-Tibet Plateau reached a certain elevation by the mid-Miocene, yet the mid-Miocene widespread warming might have largely impacted the Gerze climate.
文摘The present study investigated the incorporation of sugarcane bagasse ash(SCBA)in red ceramics,sintered in conventional oven and microwave oven,aiming to provide an alternative product,and a sintering process with higher energy efficiency in the production of red ceramics.The raw materials were characterized by XRF,XRD,thermogravimetry,particle size distribution and specific mass analyses.The specimens were shaped by extrusion in two different compositions,red clay and red clay with addition of 20%SCBA and sintered at temperatures from 700 to 1100℃.The conventional sintering occurred for 60 min with heating rate of 10℃/min.In the microwave oven the sintering occurred in a hybrid way,with heating rate of 50℃/min for 5,10 and 15 mins.After sintering the tests of linear shrinkage,compressive strength,water absorption,apparent porosity and apparent specific mass were performed.The addition of SCBA causes an increase in the values of water absorption and decreases the compressive strength and specific mass of the red ceramic.This occurs due to the creation of pores inside the material from the volatilization of organic matter present in the ashes.The sintering in microwave oven,when compared to conventional sintering,promotes an increase in the values of compressive strength and specific mass and reduction of water absorption values of ceramics,probably due to the refinement of the microstructure and the higher densification.Thus the incorporation of ashes can be partially compensated by a more efficient sintering.The use of SCBA and the sintering in microwave oven,showed to be viable alternatives in the development of a more sustainable and light material,promoting the management of waste,reduction in the consumption of raw materials and energy saving.
文摘Natural clays have been used by man in infections of bacterial etiology, since the first historical registers. Our attention turned to a red-colored clay, known in the northeast of Brazil as “barro de louça” (dish clay). These clays and other natural earth materials seem interesting to us, as the blockage of the liberation of toxins or inactivation, may be related to the interruption of infection cycles in the skin and mucous membranes. The adsorptive and absorptive properties of the mineral clays are well documented in the cure process of skin and gastrointestinal diseases. Susceptibility and bacterial tropism tests were carried out. The results were analyzed and interpreted according to the conventional microbiological protocol. The bacterial strains, Staphylococcus aureus, Escherichia coli e Pseudomonas aeruginosa, did not present a susceptibility profile to an isotonic solution of clay, but there was an increase of the bacterial tropism as the concentration of the isotonic solution was increased, being the minimal observed concentration of 100 mg/mL. Our aim is to document a type of red clay from the northeast of Brazil with possible attraction properties (Tropism) to bacteria and their toxins.
基金Project supported by the National Natural Science Foundation of China and the Foundation of Xi'an Laboratory of Loess and Quatemary Geology,Chinese Academy of Sciences
文摘Two Red Clay profiles near Xi’ an and Xifeng were investigated in an attempt to determine magne-tostratigraphic and palaeoclimatic records. The results show that aeolian dust accumulation and the related East Asia palaeomonsoon system had begun by 6.5 Ma, and it is deduced that the Tibetan Plateau had reached a significant elevation at that time. The late Tertiary palaeoclimatic history of the Red Clay as reflected by magnetic susceptibility is reconstructed during the period of 6.5-2.5 Ma. Stepwise increase in susceptibility of aeolian dust accumulation appears to have a close correlation to the uplift processes of the Tibetan Plateau. The remarkable increase of aeolian dust accumulation at 3.2 Ma appears to be due to the influence of global ice volume on the East Asia monsoon. Palaeomonsoon variation during the late Tertiary as recorded in the Red Clay sequences from the Chinese Loess Plateau can be regarded as the product of a number of interacting factors, such as uplift of the Tibetan Plateau,
基金supported by the National Natural Science Foundation of China(Grant Nos.49902009 and 40202005)the Outstanding Overseas Chinese Scholars Fund of the Chinese Academy of Sciences(Grant No.2003-1-7).
文摘The wind system responsible for transporting dust onto the Chinese Loess Plateau during the late Miocene and Pliocene is still unknown and recent investigations highlight many controversies. This report aims to investigate spatiotemporal changes in grain-size and sedi- mentation rate of the Neogene Red Clay deposits in north China and to explore palaeoclimatic changes during the late Miocene and Pliocene, in particular the palaeowind system that trans- ported dust. Samples were collected from eight Red Clay sections on the Loess Plateau. Meas- urement and analysis show that there is a clear southward decrease in the mean grain-size index and in the coarse particle fraction (>20 μm). At Jiaxian site on the northern Loess Plateau, the average mean grain-size is around 20 μm, while at Lantian site in the south, the mean is around 9 μm. The coarse particle fraction >20 μm makes up 24.4% and 5.6%, at the two sites respec- tively. This distinct diversity of grain-size in the aeolian Red Clay deposit between the north and south indicate that the palaeodust was transported mainly by northerly low-level winds. The grain-size variations in the Red Clay deposits can also be divided into three stages (the lower, the middle and the upper interval): grain-size of the lower stage is significantly coarser than that of the middle stage, but finer than that of the upper stage. As a consequence, the intensity of pa- laeowind and desiccation of the dust source region during the late Miocene and Pliocene can be divided into three stages: 6.2―5.4 Ma, 5.4―3.5 Ma and 3.5―2.6 Ma. Strength of the palaeowind during the middle stage (5.4―3.5 Ma) is weaker than that of the previous and subsequent stages and the intensity of palaeowind during the latest stage (3.5―2.6 Ma) is stronger than that of the early time (6.2―5.4 Ma). Variations in the sedimentation rate of the Red Clay deposit can also be divided into three stages: the earlier, the middle and the later interval. The sedimentation rate of the earlier stage is higher than during the middle stage, but lower than during the later one. This is a clear indicator of changes in the palaeowind intensity and aridity in the dust source region and may be linked with global ice volume changes during the late Miocene and the Pliocene.
基金Australian Research Council and Macquarie University Research (Grant No. 9208.0056), also partly supported by Chinese Academy of Sciences (KZ951-A1-402), the State Science and Technology Committee (95-YL1-40) and National Natural Science Foundation of Ch
文摘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 pe-dogenesis 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 eo-lian/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 envi-ronmental 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.
基金supported by the Ministry of Science and Technology of China (2006FY120300 and 2006CB806400)the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-120, Q09)the National Natural Science Foundation of China (40730210), and the All-China Stratigraphic Commission
文摘The Lower Pliocene of the Linxia Basin in Gansu Province is one of only a few representative sections for the Early Pliocene sedimentary records in northern China, and even in East Asia. Recently,abundant mammalian fossils were found from the base of red clays of the Lower Pliocene Hewangjia Formation at Duikang in Guanghe County within this basin. Previously, the Pliocene mammals were sparsely found in China, and most were collected from fluvial and lacustrine deposits in the eastern Loess Plateau. Mammals from the widely distributed Pliocene Hipparion Red Clay are less in number.The known fossils from Duikang include 20 species and belong to the Shilidun Fauna. Their faunal components are similar to the Early Pliocene Gaozhuang Fauna from Ynshe, Shanxi. On the other hand, some taxa from Duikang have not been found in the Gaozhuang Fauna, are slightly more primitive in evolutionary level, and appeared mainly in the Late Miocene. As a result, the age of the Duikang fossils may be slightly earlier than that of the Gaozhuang Fauna and closer to the lower boundary of the Piiocene. The Duikang fossiliferons bed is 0.8 m above the top of the Late Miocene Linshu Formation, and the first occurrence of the three-toed horse Hipparion pater can be regarded as a biostratigraphical marker of the Miocene/Pliocene boundary. In conclusion, Duikang is an ideal candidate locality to establish as the stratotype of the lower boundary of the Chinese terrestrial Pliocene.