Pedogenic carbonates, found extensively in arid and semiarid regions, are important in revealing regional climatic and environmental changes as well as the carbon cycle. In addition, stable carbon and oxygen isotopic ...Pedogenic carbonates, found extensively in arid and semiarid regions, are important in revealing regional climatic and environmental changes as well as the carbon cycle. In addition, stable carbon and oxygen isotopic compositions of pedogenic carbonates have been used to rebuild paleoecology (biomass and vegetation) and to estimate paleotemperature and paleoprecipitation during past geological time. By utilizing the stable carbon and oxygen isotopic compositions (δ13C and (δ18O) of secondary nodules in Ustic Vertisols, this study looked into the climatic and environmental changes in the dry valleys of the Yuanmou Basin, Yunnan Province, in southwestern China. The results showed that during the early Holocene, a warm-humid or hot-humid climate existed in the Yuanmou Basin, but since then fluctuations in climate have occurred, with a dry climate prevailing. A highly significant correlation (r = 0.92, n = 9) between δ13C and δ18O values of carbonates illustrated that there had been a continual shifting between cold-humid and warm-dry climates in southwestern China including the Yuanmou Basin since the early Holocene.展开更多
The continent is the second largest carbon sink on Earth’s surface.With the diversification of vascular land plants in the late Paleozoic,terrestrial organic carbon burial is represented by massive coal formation,whi...The continent is the second largest carbon sink on Earth’s surface.With the diversification of vascular land plants in the late Paleozoic,terrestrial organic carbon burial is represented by massive coal formation,while the development of soil profiles would account for both organic and inorganic carbon burial.As compared with soil organic carbon,inorganic carbon burial,collectively known as the soil carbonate,would have a greater impact on the long-term carbon cycle.Soil carbonate would have multiple carbon sources,including dissolution of host calcareous rocks,dissolved inorganic carbon from freshwater,and oxidation of organic matter,but the host calcareous rock dissolution would not cause atmospheric CO2drawdown.Thus,to evaluate the potential effect of soil carbonate formation on the atmospheric p CO2level,different carbon sources of soil carbonate should be quantitatively differentiated.In this study,we analyzed the carbon and magnesium isotopes of pedogenic calcite veins developed in a heavily weathered outcrop,consisting of limestone of the early Paleogene Guanzhuang Group in North China.Based on the C and Mg isotope data,we developed a numerical model to quantify the carbon source of calcite veins.The modeling results indicate that4–37 wt%of carbon in these calcite veins was derived from atmospheric CO2.The low contribution from atmospheric CO2might be attributed to the host limestone that might have diluted the atmospheric CO2sink.Nevertheless,taking this value into consideration,it is estimated that soil carbonate formation would lower 1 ppm atmospheric CO2within 2000 years,i.e.,soil carbonate alone would sequester all atmospheric CO2within 1 million years.Finally,our study suggests the C–Mg isotope system might be a better tool in quantifying the carbon source of soil carbonate.展开更多
Few global syntheses of oxygen and carbon isotope composition of pedogenic carbonates have been attempted,unlike marine carbonates.Pedogenic carbonates represent in-situ indicators of the climate conditions prevailing...Few global syntheses of oxygen and carbon isotope composition of pedogenic carbonates have been attempted,unlike marine carbonates.Pedogenic carbonates represent in-situ indicators of the climate conditions prevailing on land.The δ^(18)O and δ^(13)C values of pedogenic carbonates are controlled by local and global factors,many of them not affecting the marine carbonates largely used to probe global climate changes.We compile pedogenic oxygen and carbon isotopic data(N=12,167)fromCretaceous to Quaternary-aged paleosols to identify potential trends through time and tie them to possible controlling factors.While discrete events such as the Paleocene-Eocene Thermal Maximum are clearly evidenced,our analysis reveals an increasing complexity in the distribution of the δ^(18)O vs δ^(13)C values through the Cenozoic.As could be expected,the rise of C4 plants induces a shift towards higherδ13C values during the Neogene and Quaternary.We also show that the increase in global hypsometry during the Neogene plays a major role in controlling the δ^(18)O and δ^(13)C values of pedogenic carbonates by increasing aridity downwind of orographic barriers.Finally,during the Quaternary,an increase of 3‰in δ^(18)O values is recorded both by the pedogenic carbonates and the marine foraminifera suggesting that both indicators may be used to track global climate signal.展开更多
Distribution of radionuclides in the soil samples, Infra-red stimulated luminescence dating techniques, elec-trical conductivity, pH measurements and grain size analysis of soils of the region between the Ganga and Ya...Distribution of radionuclides in the soil samples, Infra-red stimulated luminescence dating techniques, elec-trical conductivity, pH measurements and grain size analysis of soils of the region between the Ganga and Yamuna Rivers (in the Upper Gangetic plain) have been studied. Soil characteristics are highly sensitive to climate changes and the degree of soil development indicated by higher thicknesses of A-Horizons, solum and clay accumulation in b-horizon are higher during the periods 1.7 - 3.6 ka and 6.5 - 9.6 ka, marked by wet and warm climates (inferred from earlier studies), the former period being marked by higher degree of soil development than the later. Radionuclides are significantly in higher amounts in soils developed during the period 1.7 - 3.6 ka, thus indicating that this was the wettest and warmest period, so these radionuclides could be released by weathering of primary rocks and be preserved in sedimentary rocks deposited during that pe-riod.展开更多
lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai （35°N）, the Loess Plateau. Stable carbon isotopic ...lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai （35°N）, the Loess Plateau. Stable carbon isotopic composition indicates that （ ⅰ ） C<sub>4</sub> plants might be present at least by7.0 Ma; （ ⅱ ） C<sub>4</sub> plants expanded gradually between ～4.0 and ～3.2 Ma, and their biomass fraction was up to 50%; and （ ⅲ ） the biomass of C<sub>4</sub> vegetation since ～2.0 Ma seems to have been decreased to the level （about 20%） before 4.0 Ma. C<sub>4</sub> plant expansion at Lingtai cannot be fully understood with the 'global C<sub>4</sub> expansion' model because it occurred much later up to 3.0 Ma than in Pakistan, which indicates that some changes in the regional climatic system may also contribute to C<sub>3</sub>/C<sub>4</sub> shift except changes in atmospheric CO<sub>2</sub> concentrations and temperature. The latitudinal zone for C<sub>3</sub>/C<sub>4</sub> transition seems to move southwards slightly in East Asia, compared with the case in North America where 37°N is the ideal展开更多
Although Pleistocene red paleosols are widely distributed in South China, paleoenviron-mental interpretation has proved difficult because of intense weathering. Here we combine data from molecular fossil and magnetic ...Although Pleistocene red paleosols are widely distributed in South China, paleoenviron-mental interpretation has proved difficult because of intense weathering. Here we combine data from molecular fossil and magnetic properties to reconstruct a record of changes in pedogenic intensity for red paleosols in Southeast China. Depth distribution pattern of magnetic properties indicates that lower （higher） χ but higher （lower） values of HIRM （hard isothermal remanent magnetization） and SIRM （saturation isothermal remanent magnetization）/χ has tight relationship with the intensity of pedogenesis,especially the occurrence of well-developed net-like veins, which is absolutely responsible for the presence of anti-ferromagnetic minerals at the cost of fine-grained SP （superparamagnetic）/SD （single domain） ferrimagnetic minerals. The carbon distribution pattern of n-alkanes, n-alkanols, and n-alkanoic acids reflects the predominant contributions of microorganisms to the organic matter during pedogenesis, which provide direct evidence for strong microbial activities in response to theextremely hot-humid condition while white coarse net-like veins occurrence. Our results demonstrate that the presence of the enhanced East Asia summer monsoon has played a key role in the oxide-dominated weathering regime, and pedogenesis, and microbial activities. Changes in molecular ratios and magnetic properties are used to show that red paleosols have undergone three stages of soil formation in striking response to the evolution of the East Asia summer monsoon： （1） the most effective since the Middle Pleistocene; （2） moderately effective since 270 ka or so; （3） least effective since the last glacial. Our research provides important evidence to understand how red paleosols espond to global change since the Middle Pleistocene.展开更多
Soil inorganic carbon （SIC） stocks continuously change from the formation of pedogenic carbonates, a process requiring inputs of Ca2＋ and Mg2＋ ions. This study ranked the soil orders in terms of potential inorgani...Soil inorganic carbon （SIC） stocks continuously change from the formation of pedogenic carbonates, a process requiring inputs of Ca2＋ and Mg2＋ ions. This study ranked the soil orders in terms of potential inorganic carbon sequestration resulting from wet Ca2＋ and Mg2＋ deposition from 1994 to 2003 within the continental United States. The analysis revealed that average annual atmospheric wet deposition of Ca2＋ and Mg2＋ was the highest in the Central Midwest-Great Plains region, likely due to soil particle input from loess-derived soils. The soil orders receiving the highest total average annual atmospheric wet Ca2＋ and Mg2＋ deposition, expressed as potential inorganic carbon formation （barring losses from erosion and leaching）, were： 1） Mollisols （1.1 × 10^8 kg C）, 2） Alfisols （8.4 × 10^7 kg C）, 3） Entisols （3.8 × 10^7 kg C）, and 4） Aridisols （2.8 × 10^7 kg C）. In terms of area-normalized result, the soil orders were ranked： 1） Histosols （73 kg C km-2）, 2） Alfisols and Vertisols （64 kg C km-2）, 3） Mollisols （62 kg C km-2）, and 4） Spodosols （52 kg C kin-2）. The results of this study provide an estimate of potential soil inorganic carbon sequestration as a result of atmospheric wet Ca2＋ and Mg2＋ deposition, and this information may be useful in assessing dynamic nature of soil inorganic carbon pools.展开更多
Knowledge of soil carbon（C） distribution and its relationship with the environment can improve our understanding of its biogeochemical cycling and help to establish sound regional models of C cycling. However, such ...Knowledge of soil carbon（C） distribution and its relationship with the environment can improve our understanding of its biogeochemical cycling and help to establish sound regional models of C cycling. However, such knowledge is limited in environments with complex landscape configurations. In this study, we investigated the vertical distribution and storage of soil organic carbon（SOC） and soil inorganic carbon（SIC） in the 10 representative landscapes（alpine meadow, subalpine shrub and meadow, mountain grassland, mountain forest, typical steppe, desert steppe, Hexi Corridor oases cropland, Ruoshui River delta desert, Alxa Gobi desert, and sandy desert） with contrasting bioclimatic regimes in the Heihe River Basin, Northwest China. We also measured the 87 Sr/86 Sr ratio in soil carbonate to understand the sources of SIC because the ratio can be used as a proxy in calculating the contribution of pedogenic inorganic carbon（PIC） to total SIC. Our results showed that SOC contents generally decreased with increasing soil depth in all landscapes, while SIC contents exhibited more complicated variations along soil profiles in relation to pedogenic processes and parent materials at the various landscapes. There were significant differences of C stocks in the top meter among different landscapes, with SOC storage ranging from 0.82 kg C/m^2 in sandy desert to 50.48 kg C/m^2 in mountain forest and SIC storage ranging from 0.19 kg C/m^2 in alpine meadow to 21.91 kg C/m^2 in desert steppe. SIC contributed more than 75% of total C pool when SOC storage was lower than 10 kg C/m^2, and the proportion of PIC to SIC was greater than 70% as calculated from Sr isotopic ratio, suggesting the critical role of PIC in the C budget of this region. The considerable variations of SOC and SIC in different landscapes were attributed to different pedogenic environments resulted from contrasting climatic regimes, parent materials and vegetation types. This study provides an evidence for a general trade-off pattern between SOC and SIC, showing the compensatory effects of environmental conditions（especially climate） on SOC and SIC formation in these landscapes. This is largely attributed to the fact that the overall decrease in temperature and increase in precipitation from arid deserts to alpine mountains simultaneously facilitate the accumulation of SOC and depletion of SIC.展开更多
Soils result from the interaction of five independent formation factors.If one factor varies,while the others remain constant,different soils can be produced.Herein,we demonstrated an opposing trend,wherein two soils ...Soils result from the interaction of five independent formation factors.If one factor varies,while the others remain constant,different soils can be produced.Herein,we demonstrated an opposing trend,wherein two soils were similar,despite considerable differences in all factors of soil formation.We sampled two Inceptisols(Oxic Dystrudepts) formed on different parent materials(gneiss vs.mica schist),climate(tropical altimontane vs.warmer,drier plateau),topography(1 650 m,45% slope vs.1 000 m,8% slope),time(rejuvenated vs.old,stable surface),and vegetation(rainforest vs.Cerrado savanna).The two soils had similar chemical properties,whereas the soil on mica schist had finer particle size distribution,lower porosity,and lower saturated hydraulic conductivity.These properties were related to a coarser blocky microstructure compared to the soil on gneiss.Both soils presented active mineral weathering and pronounced pedoplasmation,demonstrated by clay contents>300 g kg^(-1),although only the Dystrudept on gneiss possessed coarse rock fragments.The C horizons of both soils presented fragmented clay coatings suggestive of argilluviation,likely relict,because they were not observed in the B horizons.The similarities in many properties of the two Dystrudepts,despite contrasting factors of soil formation,suggest converging evolution and that soil classification at the subgroup level was efficient in grouping similar formative processes in tropical conditions.Moreover,this work revealed that similar pedogenic processes acting on different factors of soil formation can result in similar soil properties,at least for Inceptisols where further soil development is hindered by topographic limitations.展开更多
The geology, sediment and soil studies are important due to its significant impacts on agriculture, mining, constructions materials, industries, environment, ground water percolation, air pollution, surface and ground...The geology, sediment and soil studies are important due to its significant impacts on agriculture, mining, constructions materials, industries, environment, ground water percolation, air pollution, surface and ground water pollutions, earthquakes and geo-hazards in Afghanistan. In this research, we studied petrography, Sediment, tectonic structures, soil fraction selection by using hydrometer, sieving analysis, and geological mapping. Results show different kinds of metamorphic rocks of low grade and medium grade metamorphisms, Garnete mica Schist, Garnete Schist, Quarsite, different types of minerals among rocks. Further, type of sediment consisting residual angular (Autochthonous) and rounded (Allochthonous) transported by water, among sediments consisting Garnete, Gneiss, Schist, Quarsite, Biotite and consisting different type of sizes boulders, Cobble, Granule, Sand, Silt. Hydrometer analysis shows different types of soil clayey loam, sandy loam, silty loam. Moreover, Geological mapping shows complex tectonic structures like joints, cracks, faults, folds, anticline and syncline. The obtained<i> </i><span style="font-family:Verdana;">results suggest that the petrography, sediments and soil researches can be used efficiently for catchments of the Kabul Basin and other basins in Afghanistan.</span>展开更多
Apatite is the dominant phosphorus(P) mineral in early stages of soil development, and its redistribution as labile forms under pedogenesis controls terrestrial bioavailability. Quantitative distribution of labile for...Apatite is the dominant phosphorus(P) mineral in early stages of soil development, and its redistribution as labile forms under pedogenesis controls terrestrial bioavailability. Quantitative distribution of labile forms of P and apatite-P was examined in Pothwar Loess Plain, Pakistan where the degree of pedogenesis varied with relief. Four soil types, Typic Ustorthents(Rajar), Typic Calciustepts(Missa), Udic Calciustepts(Basal), and Udic Haplustalfs(Guliana), were sampled from three replicated locations at genetic horizon level. With the exception of total P value at surface, the mean total and apatite-P decreased towards the surface in Udic Haplustalfs and Udic Calciustepts where dicalcium and octacalcium phosphate increased toward surface. Iron(oxides and oxyhydroxides) adsorbed and occluded P forms were also in greater quantities in Udic Haplustalfs and increased toward the surface, whereas they were lowest and uniform in the Typic Ustorthents. Aluminum- and organic P correlated with soil organic matter. Apatite-P decreased exponentially with an increase in the sum of iron adsorbed and occluded P fractions, and fitted the equation M(x)= M0 [1- exp(-wx)] with r2= 0.996, where M(x)is the mean apatite-P concentration in solum, M0 is the apatite-P content in the loess sediments, x is the cumulative iron adsorbed and occluded P, and w is an empirical factor indicating the change rate of apatite-P in the loess. From the calculated apatite-P of 740 mg kg-1at the time of deposition, mean apatite-P loss was 60% in Udic Haplustalfs, 33% in Udic Calciustepts, 23% in Typic Calciustepts, and 8% in Typic Ustorthents. The transformation of soil P to labile forms was faster and deeper in level or slight depressions followed by gently sloping areas in wide plains, and was the least in the gullied land.展开更多
Fertile topsoil was added onto the surface of barren slope land in Three Gorges Reservoir region of China in an anthropogenic process known as the foreign soil reconstruction project. The main goal of this paper was t...Fertile topsoil was added onto the surface of barren slope land in Three Gorges Reservoir region of China in an anthropogenic process known as the foreign soil reconstruction project. The main goal of this paper was to reveal the influence of anthropogenic activities on pedogenic processes and soil classifications. Chemical weathering indices and comparative analysis were applied to discuss changes in geochemical compositions and weathering features of purplish soils(Cambisols) before and after the project. Results showed that:(1) The foreign soil reconstruction project slightly altered the major element composition of topsoil and improved the soil structure. Although the distributions of major elements in the original topsoil, original subsoil, foreign topsoil and newly constructed topsoil were all similar to that in upper continental crust, newly constructed topsoil was the most similar soil.(2) The chemical index of alteration was more sensitive than the weathering index of Parker at indicating chemical weathering status of purplish soil. The chemical weathering status of newly constructed topsoil was higher than that of the original topsoil and lower than that of foreign topsoil.(3) Anthropogenic activities may provide a promising new thought for the anthropogenic soil classification system. The scope and subgroups of Anthrosols should be extended and strengthened. Or there may be a need to combine Anthrosols and Technosols orders to create a new soil order. The results may be used for optimizing soil mellowing engineering activities and enriching the soil classification system.展开更多
The advantages of thermal methods for mineral-magnetic research of loess/paleosolsequences are illustrated in an introductory overview. When applying thermal methods, magnetiteand maghemite can be distinguished, somet...The advantages of thermal methods for mineral-magnetic research of loess/paleosolsequences are illustrated in an introductory overview. When applying thermal methods, magnetiteand maghemite can be distinguished, something which is difficult with field-dependentmeasurements at room temperature. Also, variable low-temperature oxidation that is related toclimate may be quantified. Thirdly, grain-size estimates pertaining to the whole superparamagneticrange can be inferred from LT warming experiments and to a lesser extent from variable chemicalalteration during heating. Application of mineral-magnetic techniques may lead to thedevelopment of quantifiable proxy parameters for paleoclimate.展开更多
Understanding of the role of atmospheric moisture and heat transport in the climate system of the Cretaceous greenhouse world represents a major challenge in Earth system science. Stable isotopic paleohydrologic data ...Understanding of the role of atmospheric moisture and heat transport in the climate system of the Cretaceous greenhouse world represents a major challenge in Earth system science. Stable isotopic paleohydrologic data from mid-Cretaceous paleosols in North America, from paleoequatorial to paleoArctic latitudes, have been used to constrain the oxygen isotope mass balance of the Albian hydrologic cycle. Over the range from 40°-50°N paleolatitude, sideritic paleosols predominate, indicating paleoenvironments with positive precipitation-evaporation （P-E） balances. Local exceptions occur on leeward side of the Sevier Orogen, where calcic paleosols in the wedge-top depozone record paleoenvironments with negative P-E balances in the orographic rain shadow. Stratigraphic sections in the Wayan Formation of Idaho （WF） were sampled from the wedge-top depozone. The units consist of stacked m-scale mudstone paleosols separated by m-scale sandstone-siltstone beds. Sections were sampled for organic carbon isotope profiles, and B-horizons from 6 well-developed paleosols were sampled for detrital zircons to determine maximum depositional ages. The first of these from the WF has produced a U-Pb concordia age of 101.0±1.1 Ma. This same WF section has produced a stratigraphic trend of upwardly decreasing δ18C values ranging from -24‰ upwards to -27‰ VPDB, suggesting correlation to the late Albian C15 C-isotope segment. Pedogenic carbonates from the WF principally consist of micritic calcite, with carbon-oxygen isotope values that array along meteoric calcite lines （MCLs） with δ18O values that range from -9.47‰ up to -8.39‰ VPDB. At approximately 42°N paleolatitude, these MCL values produce calculated paleoprecipitation values of-8.12‰ to -7.04‰ VSMOW, a range that is consistent with the estimates produced from other proxies at the same paleolatitudes across North America. These results indicate that despite the orographic rain shadow effect, the processes of meridional atmospheric moisture transport in this locale were similar to those in more humid mid-latitude paleoenvironments elsewhere in the continent.展开更多
In an attempt to provide more data about the mechanics of transition metal occurrence and translocation in soil environments, Fe-Mn concretions are separated from bulk samples of representative soil types and the elem...In an attempt to provide more data about the mechanics of transition metal occurrence and translocation in soil environments, Fe-Mn concretions are separated from bulk samples of representative soil types and the element contents are determined. The results are reported and discussed in the sense of environmental geochemistry in this article.展开更多
Pedogenic processes can explain the trends in magnetic susceptibility and soil magneticmineralogy of the Ljubljana Basin chronosequence. The chronosequence formed in predominantlycarbonate sandy gravel outwash terrace...Pedogenic processes can explain the trends in magnetic susceptibility and soil magneticmineralogy of the Ljubljana Basin chronosequence. The chronosequence formed in predominantlycarbonate sandy gravel outwash terraces ranging from 5 to 1800 ka. Magnetic susceptibilityenhancement can be attributed to the formation of secondary superparamagnetic （SP） and singledomain （SD） ferrimagnetic minerals in eluvial horizons. Magnetic minerals that form in illuvialhorizons are predominantly antiferromagnetic. Downward migration of pedogenic iron compoundswith clay （formation of ferri-argillans） causes thickening of the enhanced zone with soil age.In contrast to other published soil chronosequence studies, magnetic susceptibility values donot increase with soil-age （duration of pedogenesis）. Nevertheless, frequency dependence ofmagnetic susceptibility （FD%） and indices such as maximum eluvial magnetic susceptibility （MS）divided by minimum illuvial MS (Max. E / Min. IX<sub>lf</sub> and maximum eluvial MS minus minimumilluvial MS (Max. E -Min. IX<sub>lf</sub>) increase with the logarithm of soil age suggesting that the magneticmineral transformations continue with time, but that their rate decreases. These indices are usefulfor comparisons, and may be useful for age correlations. Hypothesis that magnetic susceptibilityenhancement and precipitation have a positive correlation seems to be valid until the precipitationexceeds the critical value of 100-150 cm/year. The critical value in different settings may dependon the temperature regime and on the yearly distribution of precipitation.展开更多
基金Project supported by the National Key Basic Research Support Foundation of China (No. G1998040800).
文摘Pedogenic carbonates, found extensively in arid and semiarid regions, are important in revealing regional climatic and environmental changes as well as the carbon cycle. In addition, stable carbon and oxygen isotopic compositions of pedogenic carbonates have been used to rebuild paleoecology (biomass and vegetation) and to estimate paleotemperature and paleoprecipitation during past geological time. By utilizing the stable carbon and oxygen isotopic compositions (δ13C and (δ18O) of secondary nodules in Ustic Vertisols, this study looked into the climatic and environmental changes in the dry valleys of the Yuanmou Basin, Yunnan Province, in southwestern China. The results showed that during the early Holocene, a warm-humid or hot-humid climate existed in the Yuanmou Basin, but since then fluctuations in climate have occurred, with a dry climate prevailing. A highly significant correlation (r = 0.92, n = 9) between δ13C and δ18O values of carbonates illustrated that there had been a continual shifting between cold-humid and warm-dry climates in southwestern China including the Yuanmou Basin since the early Holocene.
基金funded by the National Key Technology Program during the 13th Five-Year Plan Period (Grant No. 2016ZX05034001-007)National Natural Science Foundation of China (Grant No. 41772359)
文摘The continent is the second largest carbon sink on Earth’s surface.With the diversification of vascular land plants in the late Paleozoic,terrestrial organic carbon burial is represented by massive coal formation,while the development of soil profiles would account for both organic and inorganic carbon burial.As compared with soil organic carbon,inorganic carbon burial,collectively known as the soil carbonate,would have a greater impact on the long-term carbon cycle.Soil carbonate would have multiple carbon sources,including dissolution of host calcareous rocks,dissolved inorganic carbon from freshwater,and oxidation of organic matter,but the host calcareous rock dissolution would not cause atmospheric CO2drawdown.Thus,to evaluate the potential effect of soil carbonate formation on the atmospheric p CO2level,different carbon sources of soil carbonate should be quantitatively differentiated.In this study,we analyzed the carbon and magnesium isotopes of pedogenic calcite veins developed in a heavily weathered outcrop,consisting of limestone of the early Paleogene Guanzhuang Group in North China.Based on the C and Mg isotope data,we developed a numerical model to quantify the carbon source of calcite veins.The modeling results indicate that4–37 wt%of carbon in these calcite veins was derived from atmospheric CO2.The low contribution from atmospheric CO2might be attributed to the host limestone that might have diluted the atmospheric CO2sink.Nevertheless,taking this value into consideration,it is estimated that soil carbonate formation would lower 1 ppm atmospheric CO2within 2000 years,i.e.,soil carbonate alone would sequester all atmospheric CO2within 1 million years.Finally,our study suggests the C–Mg isotope system might be a better tool in quantifying the carbon source of soil carbonate.
文摘Few global syntheses of oxygen and carbon isotope composition of pedogenic carbonates have been attempted,unlike marine carbonates.Pedogenic carbonates represent in-situ indicators of the climate conditions prevailing on land.The δ^(18)O and δ^(13)C values of pedogenic carbonates are controlled by local and global factors,many of them not affecting the marine carbonates largely used to probe global climate changes.We compile pedogenic oxygen and carbon isotopic data(N=12,167)fromCretaceous to Quaternary-aged paleosols to identify potential trends through time and tie them to possible controlling factors.While discrete events such as the Paleocene-Eocene Thermal Maximum are clearly evidenced,our analysis reveals an increasing complexity in the distribution of the δ^(18)O vs δ^(13)C values through the Cenozoic.As could be expected,the rise of C4 plants induces a shift towards higherδ13C values during the Neogene and Quaternary.We also show that the increase in global hypsometry during the Neogene plays a major role in controlling the δ^(18)O and δ^(13)C values of pedogenic carbonates by increasing aridity downwind of orographic barriers.Finally,during the Quaternary,an increase of 3‰in δ^(18)O values is recorded both by the pedogenic carbonates and the marine foraminifera suggesting that both indicators may be used to track global climate signal.
文摘Distribution of radionuclides in the soil samples, Infra-red stimulated luminescence dating techniques, elec-trical conductivity, pH measurements and grain size analysis of soils of the region between the Ganga and Yamuna Rivers (in the Upper Gangetic plain) have been studied. Soil characteristics are highly sensitive to climate changes and the degree of soil development indicated by higher thicknesses of A-Horizons, solum and clay accumulation in b-horizon are higher during the periods 1.7 - 3.6 ka and 6.5 - 9.6 ka, marked by wet and warm climates (inferred from earlier studies), the former period being marked by higher degree of soil development than the later. Radionuclides are significantly in higher amounts in soils developed during the period 1.7 - 3.6 ka, thus indicating that this was the wettest and warmest period, so these radionuclides could be released by weathering of primary rocks and be preserved in sedimentary rocks deposited during that pe-riod.
文摘lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai （35°N）, the Loess Plateau. Stable carbon isotopic composition indicates that （ ⅰ ） C<sub>4</sub> plants might be present at least by7.0 Ma; （ ⅱ ） C<sub>4</sub> plants expanded gradually between ～4.0 and ～3.2 Ma, and their biomass fraction was up to 50%; and （ ⅲ ） the biomass of C<sub>4</sub> vegetation since ～2.0 Ma seems to have been decreased to the level （about 20%） before 4.0 Ma. C<sub>4</sub> plant expansion at Lingtai cannot be fully understood with the 'global C<sub>4</sub> expansion' model because it occurred much later up to 3.0 Ma than in Pakistan, which indicates that some changes in the regional climatic system may also contribute to C<sub>3</sub>/C<sub>4</sub> shift except changes in atmospheric CO<sub>2</sub> concentrations and temperature. The latitudinal zone for C<sub>3</sub>/C<sub>4</sub> transition seems to move southwards slightly in East Asia, compared with the case in North America where 37°N is the ideal
基金supported by the National Natural Science Foundation of China(Nos.40502015,40872202,and40930210)the 111 Project of China(No.B08030)
文摘Although Pleistocene red paleosols are widely distributed in South China, paleoenviron-mental interpretation has proved difficult because of intense weathering. Here we combine data from molecular fossil and magnetic properties to reconstruct a record of changes in pedogenic intensity for red paleosols in Southeast China. Depth distribution pattern of magnetic properties indicates that lower （higher） χ but higher （lower） values of HIRM （hard isothermal remanent magnetization） and SIRM （saturation isothermal remanent magnetization）/χ has tight relationship with the intensity of pedogenesis,especially the occurrence of well-developed net-like veins, which is absolutely responsible for the presence of anti-ferromagnetic minerals at the cost of fine-grained SP （superparamagnetic）/SD （single domain） ferrimagnetic minerals. The carbon distribution pattern of n-alkanes, n-alkanols, and n-alkanoic acids reflects the predominant contributions of microorganisms to the organic matter during pedogenesis, which provide direct evidence for strong microbial activities in response to theextremely hot-humid condition while white coarse net-like veins occurrence. Our results demonstrate that the presence of the enhanced East Asia summer monsoon has played a key role in the oxide-dominated weathering regime, and pedogenesis, and microbial activities. Changes in molecular ratios and magnetic properties are used to show that red paleosols have undergone three stages of soil formation in striking response to the evolution of the East Asia summer monsoon： （1） the most effective since the Middle Pleistocene; （2） moderately effective since 270 ka or so; （3） least effective since the last glacial. Our research provides important evidence to understand how red paleosols espond to global change since the Middle Pleistocene.
基金Supported by the National Science Foundation of USA(No.0340534)the U.S.Department of Agriculture(Nos.SC-1700278,SC-1700452,and SC-1700462)
文摘Soil inorganic carbon （SIC） stocks continuously change from the formation of pedogenic carbonates, a process requiring inputs of Ca2＋ and Mg2＋ ions. This study ranked the soil orders in terms of potential inorganic carbon sequestration resulting from wet Ca2＋ and Mg2＋ deposition from 1994 to 2003 within the continental United States. The analysis revealed that average annual atmospheric wet deposition of Ca2＋ and Mg2＋ was the highest in the Central Midwest-Great Plains region, likely due to soil particle input from loess-derived soils. The soil orders receiving the highest total average annual atmospheric wet Ca2＋ and Mg2＋ deposition, expressed as potential inorganic carbon formation （barring losses from erosion and leaching）, were： 1） Mollisols （1.1 × 10^8 kg C）, 2） Alfisols （8.4 × 10^7 kg C）, 3） Entisols （3.8 × 10^7 kg C）, and 4） Aridisols （2.8 × 10^7 kg C）. In terms of area-normalized result, the soil orders were ranked： 1） Histosols （73 kg C km-2）, 2） Alfisols and Vertisols （64 kg C km-2）, 3） Mollisols （62 kg C km-2）, and 4） Spodosols （52 kg C kin-2）. The results of this study provide an estimate of potential soil inorganic carbon sequestration as a result of atmospheric wet Ca2＋ and Mg2＋ deposition, and this information may be useful in assessing dynamic nature of soil inorganic carbon pools.
基金supported by the National Natural Science Foundation of China(91325301,41130530,41371224,41601221)
文摘Knowledge of soil carbon（C） distribution and its relationship with the environment can improve our understanding of its biogeochemical cycling and help to establish sound regional models of C cycling. However, such knowledge is limited in environments with complex landscape configurations. In this study, we investigated the vertical distribution and storage of soil organic carbon（SOC） and soil inorganic carbon（SIC） in the 10 representative landscapes（alpine meadow, subalpine shrub and meadow, mountain grassland, mountain forest, typical steppe, desert steppe, Hexi Corridor oases cropland, Ruoshui River delta desert, Alxa Gobi desert, and sandy desert） with contrasting bioclimatic regimes in the Heihe River Basin, Northwest China. We also measured the 87 Sr/86 Sr ratio in soil carbonate to understand the sources of SIC because the ratio can be used as a proxy in calculating the contribution of pedogenic inorganic carbon（PIC） to total SIC. Our results showed that SOC contents generally decreased with increasing soil depth in all landscapes, while SIC contents exhibited more complicated variations along soil profiles in relation to pedogenic processes and parent materials at the various landscapes. There were significant differences of C stocks in the top meter among different landscapes, with SOC storage ranging from 0.82 kg C/m^2 in sandy desert to 50.48 kg C/m^2 in mountain forest and SIC storage ranging from 0.19 kg C/m^2 in alpine meadow to 21.91 kg C/m^2 in desert steppe. SIC contributed more than 75% of total C pool when SOC storage was lower than 10 kg C/m^2, and the proportion of PIC to SIC was greater than 70% as calculated from Sr isotopic ratio, suggesting the critical role of PIC in the C budget of this region. The considerable variations of SOC and SIC in different landscapes were attributed to different pedogenic environments resulted from contrasting climatic regimes, parent materials and vegetation types. This study provides an evidence for a general trade-off pattern between SOC and SIC, showing the compensatory effects of environmental conditions（especially climate） on SOC and SIC formation in these landscapes. This is largely attributed to the fact that the overall decrease in temperature and increase in precipitation from arid deserts to alpine mountains simultaneously facilitate the accumulation of SOC and depletion of SIC.
基金the Brazilian funding agencies Capes/Fapemig(No.23038.008715/2012-21)Fapemig(No.CAG PPM 00132/14)Conselho Nacional de Pesquisa(No.303840/2014-5)
文摘Soils result from the interaction of five independent formation factors.If one factor varies,while the others remain constant,different soils can be produced.Herein,we demonstrated an opposing trend,wherein two soils were similar,despite considerable differences in all factors of soil formation.We sampled two Inceptisols(Oxic Dystrudepts) formed on different parent materials(gneiss vs.mica schist),climate(tropical altimontane vs.warmer,drier plateau),topography(1 650 m,45% slope vs.1 000 m,8% slope),time(rejuvenated vs.old,stable surface),and vegetation(rainforest vs.Cerrado savanna).The two soils had similar chemical properties,whereas the soil on mica schist had finer particle size distribution,lower porosity,and lower saturated hydraulic conductivity.These properties were related to a coarser blocky microstructure compared to the soil on gneiss.Both soils presented active mineral weathering and pronounced pedoplasmation,demonstrated by clay contents>300 g kg^(-1),although only the Dystrudept on gneiss possessed coarse rock fragments.The C horizons of both soils presented fragmented clay coatings suggestive of argilluviation,likely relict,because they were not observed in the B horizons.The similarities in many properties of the two Dystrudepts,despite contrasting factors of soil formation,suggest converging evolution and that soil classification at the subgroup level was efficient in grouping similar formative processes in tropical conditions.Moreover,this work revealed that similar pedogenic processes acting on different factors of soil formation can result in similar soil properties,at least for Inceptisols where further soil development is hindered by topographic limitations.
文摘The geology, sediment and soil studies are important due to its significant impacts on agriculture, mining, constructions materials, industries, environment, ground water percolation, air pollution, surface and ground water pollutions, earthquakes and geo-hazards in Afghanistan. In this research, we studied petrography, Sediment, tectonic structures, soil fraction selection by using hydrometer, sieving analysis, and geological mapping. Results show different kinds of metamorphic rocks of low grade and medium grade metamorphisms, Garnete mica Schist, Garnete Schist, Quarsite, different types of minerals among rocks. Further, type of sediment consisting residual angular (Autochthonous) and rounded (Allochthonous) transported by water, among sediments consisting Garnete, Gneiss, Schist, Quarsite, Biotite and consisting different type of sizes boulders, Cobble, Granule, Sand, Silt. Hydrometer analysis shows different types of soil clayey loam, sandy loam, silty loam. Moreover, Geological mapping shows complex tectonic structures like joints, cracks, faults, folds, anticline and syncline. The obtained<i> </i><span style="font-family:Verdana;">results suggest that the petrography, sediments and soil researches can be used efficiently for catchments of the Kabul Basin and other basins in Afghanistan.</span>
基金Supported by the Higher Education Commission,Pakistan
文摘Apatite is the dominant phosphorus(P) mineral in early stages of soil development, and its redistribution as labile forms under pedogenesis controls terrestrial bioavailability. Quantitative distribution of labile forms of P and apatite-P was examined in Pothwar Loess Plain, Pakistan where the degree of pedogenesis varied with relief. Four soil types, Typic Ustorthents(Rajar), Typic Calciustepts(Missa), Udic Calciustepts(Basal), and Udic Haplustalfs(Guliana), were sampled from three replicated locations at genetic horizon level. With the exception of total P value at surface, the mean total and apatite-P decreased towards the surface in Udic Haplustalfs and Udic Calciustepts where dicalcium and octacalcium phosphate increased toward surface. Iron(oxides and oxyhydroxides) adsorbed and occluded P forms were also in greater quantities in Udic Haplustalfs and increased toward the surface, whereas they were lowest and uniform in the Typic Ustorthents. Aluminum- and organic P correlated with soil organic matter. Apatite-P decreased exponentially with an increase in the sum of iron adsorbed and occluded P fractions, and fitted the equation M(x)= M0 [1- exp(-wx)] with r2= 0.996, where M(x)is the mean apatite-P concentration in solum, M0 is the apatite-P content in the loess sediments, x is the cumulative iron adsorbed and occluded P, and w is an empirical factor indicating the change rate of apatite-P in the loess. From the calculated apatite-P of 740 mg kg-1at the time of deposition, mean apatite-P loss was 60% in Udic Haplustalfs, 33% in Udic Calciustepts, 23% in Typic Calciustepts, and 8% in Typic Ustorthents. The transformation of soil P to labile forms was faster and deeper in level or slight depressions followed by gently sloping areas in wide plains, and was the least in the gullied land.
基金the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (Grant No. 2012BAD05B06)
文摘Fertile topsoil was added onto the surface of barren slope land in Three Gorges Reservoir region of China in an anthropogenic process known as the foreign soil reconstruction project. The main goal of this paper was to reveal the influence of anthropogenic activities on pedogenic processes and soil classifications. Chemical weathering indices and comparative analysis were applied to discuss changes in geochemical compositions and weathering features of purplish soils(Cambisols) before and after the project. Results showed that:(1) The foreign soil reconstruction project slightly altered the major element composition of topsoil and improved the soil structure. Although the distributions of major elements in the original topsoil, original subsoil, foreign topsoil and newly constructed topsoil were all similar to that in upper continental crust, newly constructed topsoil was the most similar soil.(2) The chemical index of alteration was more sensitive than the weathering index of Parker at indicating chemical weathering status of purplish soil. The chemical weathering status of newly constructed topsoil was higher than that of the original topsoil and lower than that of foreign topsoil.(3) Anthropogenic activities may provide a promising new thought for the anthropogenic soil classification system. The scope and subgroups of Anthrosols should be extended and strengthened. Or there may be a need to combine Anthrosols and Technosols orders to create a new soil order. The results may be used for optimizing soil mellowing engineering activities and enriching the soil classification system.
文摘The advantages of thermal methods for mineral-magnetic research of loess/paleosolsequences are illustrated in an introductory overview. When applying thermal methods, magnetiteand maghemite can be distinguished, something which is difficult with field-dependentmeasurements at room temperature. Also, variable low-temperature oxidation that is related toclimate may be quantified. Thirdly, grain-size estimates pertaining to the whole superparamagneticrange can be inferred from LT warming experiments and to a lesser extent from variable chemicalalteration during heating. Application of mineral-magnetic techniques may lead to thedevelopment of quantifiable proxy parameters for paleoclimate.
基金a contribution of IGCP Project 609 "Climate-environmental deteriorations during greenhouse phases:Causes and consequences of short-term Cretaceous sea-level changes "
文摘Understanding of the role of atmospheric moisture and heat transport in the climate system of the Cretaceous greenhouse world represents a major challenge in Earth system science. Stable isotopic paleohydrologic data from mid-Cretaceous paleosols in North America, from paleoequatorial to paleoArctic latitudes, have been used to constrain the oxygen isotope mass balance of the Albian hydrologic cycle. Over the range from 40°-50°N paleolatitude, sideritic paleosols predominate, indicating paleoenvironments with positive precipitation-evaporation （P-E） balances. Local exceptions occur on leeward side of the Sevier Orogen, where calcic paleosols in the wedge-top depozone record paleoenvironments with negative P-E balances in the orographic rain shadow. Stratigraphic sections in the Wayan Formation of Idaho （WF） were sampled from the wedge-top depozone. The units consist of stacked m-scale mudstone paleosols separated by m-scale sandstone-siltstone beds. Sections were sampled for organic carbon isotope profiles, and B-horizons from 6 well-developed paleosols were sampled for detrital zircons to determine maximum depositional ages. The first of these from the WF has produced a U-Pb concordia age of 101.0±1.1 Ma. This same WF section has produced a stratigraphic trend of upwardly decreasing δ18C values ranging from -24‰ upwards to -27‰ VPDB, suggesting correlation to the late Albian C15 C-isotope segment. Pedogenic carbonates from the WF principally consist of micritic calcite, with carbon-oxygen isotope values that array along meteoric calcite lines （MCLs） with δ18O values that range from -9.47‰ up to -8.39‰ VPDB. At approximately 42°N paleolatitude, these MCL values produce calculated paleoprecipitation values of-8.12‰ to -7.04‰ VSMOW, a range that is consistent with the estimates produced from other proxies at the same paleolatitudes across North America. These results indicate that despite the orographic rain shadow effect, the processes of meridional atmospheric moisture transport in this locale were similar to those in more humid mid-latitude paleoenvironments elsewhere in the continent.
文摘In an attempt to provide more data about the mechanics of transition metal occurrence and translocation in soil environments, Fe-Mn concretions are separated from bulk samples of representative soil types and the element contents are determined. The results are reported and discussed in the sense of environmental geochemistry in this article.
文摘Pedogenic processes can explain the trends in magnetic susceptibility and soil magneticmineralogy of the Ljubljana Basin chronosequence. The chronosequence formed in predominantlycarbonate sandy gravel outwash terraces ranging from 5 to 1800 ka. Magnetic susceptibilityenhancement can be attributed to the formation of secondary superparamagnetic （SP） and singledomain （SD） ferrimagnetic minerals in eluvial horizons. Magnetic minerals that form in illuvialhorizons are predominantly antiferromagnetic. Downward migration of pedogenic iron compoundswith clay （formation of ferri-argillans） causes thickening of the enhanced zone with soil age.In contrast to other published soil chronosequence studies, magnetic susceptibility values donot increase with soil-age （duration of pedogenesis）. Nevertheless, frequency dependence ofmagnetic susceptibility （FD%） and indices such as maximum eluvial magnetic susceptibility （MS）divided by minimum illuvial MS (Max. E / Min. IX<sub>lf</sub> and maximum eluvial MS minus minimumilluvial MS (Max. E -Min. IX<sub>lf</sub>) increase with the logarithm of soil age suggesting that the magneticmineral transformations continue with time, but that their rate decreases. These indices are usefulfor comparisons, and may be useful for age correlations. Hypothesis that magnetic susceptibilityenhancement and precipitation have a positive correlation seems to be valid until the precipitationexceeds the critical value of 100-150 cm/year. The critical value in different settings may dependon the temperature regime and on the yearly distribution of precipitation.
