Loess Layers Research Articles

Wildfire history and climatic change in the semi-arid loess tableland in the middle reaches of the Yellow River of China during the Holocene: Evidence from charcoal records

High-resolution macroscopic charcoal and sediment analysis was used to reconstruct fire history and environmental changes from three loess-paleosol profiles on the semi-arid loess tableland landscape during the Lateglacial period and the Holocene. Analysis of charcoal concentrations, influx, and the ratios of particle-size classes (from which changes in charcoal taphonomy over time are inferred) in the profiles show spatially coherent patterns of change that relate to regional variations in climate. Effective moisture variability on century to millennial timescales and regional differences in fuel availability appear to be the most important controls on fire from the Lateglacial period to the mid Holocene (12,000–3100 yr BP). Conversely, asynchronous fire patterns during the late Holocene appear to indicate regional and temporal variations as well as changing intensities of human activity. Land use intensified in the region during the late Holocene, when the climate became more arid, and a distinct increase in charcoal concentration then indicated an unprecedented increase in biomass burning. The increase in fire activity occurs in the recent loess layer (L0) and the surface soil (TS) consistent with the establishment of irrigated farming for cereal cultivation in the southern part of the study region about 3100 yr BP. Broad-scale land reclamation was extended to the loess tableland region about 2170–1730 yr BP (during the Qin-Han Dynasty period), and the rapidly decreasing charcoal concentration in the accumulated topsoil (at depths of less than 20 cm) at the CCY site since 1500 yr BP is consistent with the development of terrace farming in the northern part of the study region at that time. In summary, the evolution of fire history in the study profiles across the region is closely related to (1) gradients in humidity; (2) spatial and temporal variability in the distribution and intensity of human land use; and (3) the buildup of burnable biomass, among which there was a nonlinear complex relationship during the Holocene. Increased efforts to synthesize and analyze multiple paleo-environmental records and to combine these with multiproxy evidence are needed to understand wildfire history as well as human land use and social cultural development across the region in depth.

Iron mineralogical proxies and Quaternary climate change in SE-European loess–paleosol sequences

The loess–paleosol sequences Batajnica/Stari Slankamen (Serbia) and Mircea Voda (Romania) represent key archives for the climate and landscape development of the middle and lower Danube Basin during the last 700,000years. For deciphering the Quaternary climate evolution in these regions, the Batajnica/Stari Slankamen and Mircea Voda sites are for the first time studied by a multi-proxy approach based on iron mineralogical parameters. Changes in the iron mineralogical composition are identified and characterized by rock magnetic investigations, diffuse reflectance spectroscopy (DRS) and Munsell color based proxies. The results show that environmental conditions during mid- and early Middle Pleistocene interglacials were more favorable for hematite formation, suggesting a more oxidizing pedoclimate as in the more recent interglacials. This is also reflected in a gradual increase of the anhysteretic remanent magnetization vs. saturation isothermal remanent magnetization (ARM/SIRM) ratio. In the studied profiles changes in this ratio can be linked to a preferential hematitization of coarse-grained ferrimagnetica and relates to warmer climate conditions and a more extended estival dry period. At the same time, rock magnetic parameters indicate a preferential destruction of fine-grained magnetic particles in older paleosols resulting from seasonal excess moisture.A progressive cooling and decrease of rainfall during the Middle and Late Pleistocene is evidenced not only for interglacial pedocomplexes but also for glacial loess layers. This finding is in line with previously published proxy records of silicate weathering and clay formation at these sites and similar trends reported from other sites in the European steppe belt. Relating iron mineralogical proxies to paleopedological characteristics and proxies of silicate weathering, additionally a change in the seasonal pattern of the interglacial temperature and precipitation regime from a Mediterranean type to a steppe type climate is revealed, highlighting the potential of such a multi-proxy approach.Possible triggers for this paleoenvironmental evolution are discussed, as well, finally highlighting a “Quaternary uplift hypothesis”, which best could explain the inferred trend of cooling, aridification and increasing continentality. Accordingly, changes in atmospheric circulation and rain shadow effects induced by small-scale uplift of European mountain belts (Alps, Carpathians, Dinaric Alps) would provide a driving mechanism for the westward extension of the Eurasian steppe belt into Central and SE-Europe during the Quaternary.

Geochemical characteristics and environmental significance of Talede loess–paleosol sequences of Ili Basin in Central Asia

The loess–paleosol deposit in Central Asia is a sensitive indicator of the evolution of the quaternary paleoclimate in the Westerlies, providing insight into the quaternary climate history and its relationship with global climatic changes. Based on the geochemical analysis of elemental composition of densely sampled strata from Talede loess–paleosol sequence in the Ili Basin, the results showed that SiO2 had the highest major elements content, followed by Al2O3. The order of compositional abundance of major elements was generally as follows: SiO2 > Al2O3 > CaO > Fe2O3 > MgO > Na2O > K2O. Trace elements (i.e. Rb, Sr, Sc, Ni, Cu, Ga, Mo, Y, Pb, Th) in the paleosol layers (i.e. S 0, S m, S 1) and the loess layer of L 1 were enriched relative to underlain loess (L 2) horizons, except for the contents of Zr, Cs, Nd, and La in paleosol layers. All of geochemical proxies, such as enrichment factor, Rb/Sr ratio, eluvial coefficient (K i ) and chemical weathering index, display no obvious differentiation in the Talede loess–paleosol deposit. The results indicate that the weak chemical weathering, greater evaporation and low effective moisture in Ili Basin, are to a degree weaker than those in the China Loess Plateau and the climate was warm–dry during the interglacial period. In addition, the loess of Ili area is rich in schistose minerals and implies that the loess may come from the deserts of Central Asia and it may be closely related to the widespread aridification of Central Asia.

Engineering properties of compacted loesses as construction materials

Loess often causes some problems when they are naturally deposited, or when they are used as fill materials in the construction of embankments. In the case of constructing the embankment on a thick, naturally deposited loess layer, the collapsibility, or consolidation will be a critical issue to be considered. In contrast, when a loess is used as a fill material, compactability, stiffness (resilient modulus), and pumping problem induced by repeated traffic loadings should be accounted for. In this study, in order to evaluate the mechanical characteristics of Indiana loess for constructing embankments, the following laboratory tests were conducted on four loesses having different clay contents (10%, 20%, 25%, and 30%): the standard compaction test, the collapse potential test, the CRS consolidation test, the direct shear test, the resilient modulus test, as well as the soil index test. Test results show that the collapsible potential can be significantly improved by well-compacting the loess when it is used as a fill material. Based on the results of collapsible tests on four loesses having different clay contents (10%, 20%, 25%, and 30%), it has been found that the higher the silt content, the higher the collapse potential at the given density corresponding to the naturally-deposited condition. This implies that the amount of silt in Indiana loess is the most influential factor in terms of collapsibility. The results of direct shear tests show that the effect of clay contents does not have much influence on the friction angle and cohesion of the compacted loess materials used in embankments. Unlike the shear behavior, the resilient behavior of compacted loess materials is considerably affected by the clay content such that the loess with the largest silt content shows the lowest resilient modulus due to the pumping-like phenomenon induced by the repeated loading.

A long-term increasing aridification and cooling trend at the Chinese Loess Plateau during the Pliocene

The development of Asian aridification and cooling is a research hotspot nowadays. Loess-Red Clay sequence in the Chinese Loss Plateau provides an excellent terrestrial archive of such paleoclimatic evolution. This paper applied the magnetic “unmixing” technique to isolate the magnetic components of the Red Clay sequence for the first time. The Jiaxian section in the north edge of Chinese Loess Plateau is sensitive to paleoclimate changes because it is in the transitional zone of the monsoon and non-monsoon area. Systematic magnetic measurements and XRD analysis consistently indicate that the magnetic components of Red Clay are predominantly magnetite, maghemite and hematite. The strongly developed paleosols exhibit high content of soft magnetic minerals, higher Ms and Mrs, and lower Bc and Bcr. While the weakly developed paleosols and loess samples display the opposite features. With increasing alternating field, the contributions of soft components to SIRMx mT are cleaned gradually (SIRM is the saturation isothermal remanent magnetization; SIRMx mT represents the residual SIRM after alternating field demagnetization at x mT). The significant contributor to SIRM100 mT is hematite, an indication of the intensity of chemical weathering. Variations in the ratios of SIRM100 mT/SIRM, SIRM100 mT/SIRM60 mT, and SIRM100 mT/SIRM30 mT document a long-term up-section decreasing trend during the last 5–2.6 Ma, with similar trends to the long-term up-section increase in δ18O values of marine records. Decreased hematite content indicates weakened chemical weathering, which further implies an increasing aridification and cooling and a gradually weakened summer paleomonsoon mainly in the depositional area (Chinese Loess Plateau). In some loess layers, where hematite is mainly of aeolian origin, the mineral magnetic signals may indicate aridification and cooling in the Asian interior (source region). This long-term aridification and cooling trend is probably attributed to the comprehensive activity of ongoing global cooling, progressive uplift of the Tibetan Plateau and changes in land–sea distribution.

The fifth paleosol layer in the southern part of China's Loess Plateau and its environmental significance

Through field investigations, dark red–brown lumpy ferruginous argillans (LFAs) and an underlying weathered loess layer under the fifth layer (S5 paleosol) were discovered in the Guanzhong Plain in the southern part of the Loess Plateau in northwest China's Shaanxi Province. The ultramicrotexture of the LFAs and their mineral and chemical compositions were analyzed. Experimental results showed that mixed illite–smectite minerals comprise about 90% of the LFAs in mineral composition, with 40% SiO2 content and high Fe2O3 (about 10.0%) and Al2O3 (about 22.5%) contents in chemical composition. Neo-formed microcrystalline grains of clay minerals dominated the LFAs. The micromineral crystal grains in the LFAs were mainly plates with some degree of alignment, giving the argillans crystalline optical properties. Red LFAs and weathered loess layers under the S5, and the depth to which Fe2O3 and CaCO3 from the S5 have been removed, indicate that chemical weathering was much stronger when the paleosol layers formed than that at present. While the S5 paleosol was developed, a subtropical climate prevailed in the southern Loess Plateau, with a mean annual temperature and rainfall about 4 °C and 500 mm higher respectively than that at present. The adequacy in moisture in at least 4.2 m of the gravitational water zone during the formation of S5 was suitable for forest growth. During the warmest and moistest climate span of growth for 2.5 million years when S5 was formed, the Qinling Mountains lost its function as a climatic boundary between the subtropical and temperate zones of East Asia, when the summer air masses crossed the Qinling Mountains and reached the Guanzhong Plain, bringing rich precipitation.

CHARACTERISTICS OF MAJOR GEOCHEMICAL ELEMENTS OF TACHENG LOESS DEPOSITS IN XINJIANG AND ITS PALEOENVIRONMENTAL IMPLICATIONS

In this paper,we studied the characteristics of major geochemical elements and weathering intensity of the loess deposits at the Tacheng section,Xinjiang,northwest China.Results show that among the oxides of the major geochemical elements,SiO2,Al2O3,CaO,CO3,Fe2O3,MgO,K2O and Na2O occur in a decreasing order in the loess section.There is obvious differentiation of oxides in the palaeosol and loess layers and the average contents of Al2O3,Fe2O3 and CaO were markedly higher in paleosol layers.CaO,Fe2O3,MgO,and K2O were accumulated and Na2O,SiO2,Al2O3 depleted in the section compared to the upper continental crust(UCC).The oxides have different distribution pattern in loess and paleosols and some of the major geochemical elements exhibit different concentrations in the topsoils and the paleosols.Further analysis shows that the Tacheng section had experienced weak chemical weathering after deposition,which was similar to the Yili loess section but far weaker than the loess deposits in the Chinese Loess Plateau and the lower reaches of the Yangtze River.The differentiation of weathering degree between the loess and paleosol was also distinct,indicating that the paloesols have experienced stronger weathering process.However,the eluviation of paleosol layers was weaker than that of loess layers probably resulting from the decline of humidity during the period of pedogenesis.The heat-moisture pattern might exert important effect on the chemical weathering of loess/paleosol sequences in the arid area.

MAGNETIC PROPERTY AND DOMINATING FACTORS OF THE LOESS AT NORTHERN PIEDMONT OF TIANSHAN,XINJIANG

We carried out systemic rock-magnetic investigations on the loess/paleosol sequence at the northern piedmont of the Tianshan Mountain,Xinjiang.Results show that the main magnetic minerals of this sequence are magnetite,maghaemite,haematite,and the main magnetic grain size of magnetic minerals are PSD and MD.The magnetic susceptibility of the loess layer in the Tianshan Mountains is higher than that of paleosoil,which is different from the loess in Loess Plateau.Magnetic susceptibility of the sediments is controlled by native ferrimagnetic minerals from source.Fine grain magnetic materials produced by pedogenic progress make limited contribution to magnetic susceptibility of the loess.

Лессы верхнего плейстоцена опорного разреза Ложок (юг Западной Сибири), динамика природной среды и климата

Лессы верхнего плейстоцена опорного разреза Ложок (юг Западной Сибири), динамика природной среды и климата

Difference Analysis of Loess Seismic Subsidence between <i>In Situ</i> Experiment and Laboratory Test

Seismic subsidence of loess is a kind of disaster induced by strong ground motion in loess area, while seldom example of this subsidence was found in long time study, usually instead of laboratory test. An explosion ground motion in a typical loess field was designed to verify seismic subsidence of loess with natural condition and laboratory test of loess seismic subsidence was conducted in China. The result proved seismic subsidence of loess could be induced by explosion ground motion, while the maxmuim settlement of 3.3cm in the case of experiment is much less than 53cm with a moderate or strong dynamic stress in laboratory due to an incomplete seismic subsidence of loess in this field. The seismic subsidence of toper loess layers is less than the below in the field test although it is opposite to in laboratory test due to closer distance between the below layers and explosion shots.

The magnetic properties of Serbian loess and its environmental significance

This paper reports a loess-paleosol sequence located in the Danube River basin, Serbia, which formed at least since the latest part of the early Pleistocene, and before the paleomagnetic B/M boundary. Various magnetic parameters of the Serbian V-L1-V-S4 loess-paleosol sequence have been measured and analyzed in the Titel Loess Plateau. These parameters show a very similar magnetic behavior compared with that of the Chinese loess. There is a general positive relationship between magnetic susceptibility (χ) and pedogenesis. The main contributors to χ are the magnetic grains of SP (superparamagnetic) and SD (single domain) magnetic domains, while MD (multi domain) contributes only a small percentage. The difference in χ between loess and paleosol mainly is caused by pedogenesis. The very fine magnetic minerals increase gradually with increasing soil development (from loess to soil), and they lead to higher χ. The thermomagnetic curves show thatmagnetic minerals in the loess layers are magnetite and maghemite, both providing a major contribution to χ. In contrast the paleosol layers mainly are composed of magnetite, with almost no or a very small amount of maghemite, as implied by a reversible thermomagnetic behavior. This indicates that pedogenic conditions during V-S3 and V-S4 strong soil development have resulted in maghemite that is no longer stable, and has been resolved or converted to other stable phase minerals. This likely indicates that soil moisture during V-S3 and V-S4 development exceeded a critical condition of maghemite stability.

Integrating heterogeneous landscape characteristics into watershed scale modelling

Abstract. Two versions of the SWAT-model with different dominating runoff generation processes have been applied. One version comprises the original available SWAT version where only the basic input data are used. In the second version SWAT has been modified, by the integration of an impermeable layer at the subbasin level, in order to better reflect the boundary between soil and bedrock that results in increased lateral flow in low mountain ranges. As well, since conventional German soil maps do not describe soil horizons beyond 2 m depth, we also added a 4 m fixed depth in the lowland areas in order to reflect the deep loess deposits in this region. The decision for the location of the impermeable and the additional loess layer was based on a GIS analysis of additional geologic information. This study revealed that both model versions produced acceptable and comparable results regarding the evaluated goodness of fit measures. The GLUE analysis showed that the SWAT model set up with additional information about the distribution of impervious soil layers and the loess depth in the lowlands produced the highest simulation quality and the lowest uncertainty. Moreover, SWAT II version was able to better represent the spatial extend of the dominating runoff processes best. This leads to the conclusion that the SWAT II version is better suited for scenario analysis than the original model version.

Loess-paleosol sequence at Korshiv (Ukraine): Chronology based on complementary and parallel dating (TL, OSL), and litho-pedosedimentary analyses

The paper concerns the issues of age as well as lithological and pedological development of the loess-paleosol sequence available for direct research at the Korshiv site in the Volhynian Upland (West Ukraine). For dozens of identical samples, a series of comparative laboratory TL dating (Gdańsk, Lublin) and OSL dating (Gliwice) was performed, supplemented by the physicochemical and micromorphological analyses. Due to the different dating techniques used in individual laboratories, the details of their methodology were also presented. The resulting series of dates confirmed the lithological and pedostratigraphic diagnosis of the sediments during the last two loess-forming cycles. Additionally, the age of the loess layer at the base of the available sequence was established. It was defined as loess L5 and correlated with MIS 12. The resulting age of the mineral substrate in different laboratories shows considerable similarity (upper sequence), but also clear differences (lower part). The OSL dates were younger than the TL dates. Two high-rank fossil soil complexes investigated in the profile represent MIS 7 and 5. For the Eemian-Early Weichselian pedocomplex (S1), the tripartite structure of the younger paleosol represents Early Weichselian Glaciation (MIS 5.4-5.1). The dates helped to conclude that there is a possibility of stratigraphic separateness of the Dubno soil (MIS 3). The whole youngest sedimentary sequence is dated from 20 to 14 ka and correlates well with the period when the Last Glacial ice sheet advanced during its main stadial in Poland.

Reconstruction of the late Quaternary paleoenvironments of the Nussloch loess paleosol sequence, Germany, using n-alkane biomarkers

This study contributes to the paleoenvironmental reconstruction of the loess–paleosol sequence of Nussloch, Germany, by using n-alkanes as plant leaf-wax-derived lipid biomarkers. We found that n-alkane patterns and concentrations in the Saalian loess and the last interglacial Eemian paleosol of Nussloch point to very strong degradation and prevailing deciduous vegetation. Degradation effects in the overlying paleosols and loess layers are less pronounced and allow for the application of an end-member mixing model to estimate vegetation changes semi-quantitatively. Our findings highlight the potential for the interpretation of degradation-corrected n-alkane ratios. n-Alkane modelling results for loess layers, paleosols and an in-filled paleochannel dated to ~60–32ka suggest that up to ~50% of the n-alkanes were derived from deciduous trees or shrubs. This finding is in agreement with the abundant occurrence of wood fragments and indicates a highly variable and dynamic landscape dominated by tundra shrubland. On the other hand, deciduous trees or shrubs did not contribute significantly to the soil organic matter in the late Weichselian loess layers and the intercalated Gelic Gleysols (~32–18ka).

Glacial outburst floods and loess sedimentation documented during Oxygen Isotope Stage 4 on the Columbia Plateau, Washington State

Stratigraphy and age control of late Pleistocene loess, associated glacial outburst flood deposits and flood-cut unconformities in the Channeled Scabland, Washington State, United States, indicate a significant Cordilleran ice sheet advance during marine Oxygen Isotope Stage 4. Glacial outburst flood deposits from stage 2 (classic Bretz flood deposits, ca 21 to 13 ka) and related features in the Channeled Scabland overlie a widespread layer of loess that contains buried soils and the Mount St. Helens set C tephra (ca 46 ka). This loess in turn overlies deposits of the penultimate episode of giant outburst floods and an unconformity cut by those floods. Regional trends in the thickness, texture, and overall composition of the older loess are strikingly similar to those from the youngest loess, known to be derived from stage 2 flood deposits. We conclude that the older loess also is derived from fine-grained flood deposits. Luminescence ages, tephrochronology, and soil development rates indicate that the bulk of deposition of the older loess occurred during stage 3, following glacial outburst flooding marked by a regional flood-cut unconformity. The apparent cyclical pattern of cold-climate buried soils, flood deposits, and thick loess accumulations demonstrate that sediment supply renewed by flood episodes is a major control on accumulation of loess on glacial timescales.

The Paks loess-paleosol sequence: A record of chemical weathering and provenance for the last 800 ka in the mid-Carpathian Basin

The Paks loess-paleosol sequence is one of the most important terrestrial records of Middle and Late Pleistocene environmental changes in East Central Europe, spanning the last ca. 0.8Ma. While geochemical proxies demonstrate a general decreasing chemical weathering trend over the last 0.8Ma in the Carpathian Basin, mineralogy and derived indices reflect intensifying physical erosion. In theory, the observed chemical weathering trend can be accounted for both by enhanced input of relatively unweathered material and by climate deterioration during the Quaternary, as the proxies such as CIA are not capable of distinguishing between pre- and post-depositional weathering. Enhanced physical erosion of the source areas, driven by tectonism, and resulting increased sedimentation of fresh mineral dust at the depositional site are demonstrated by increasing dolomite, illite and chlorite contents and sme/ill, sme/(ill+chl) ratios from older to younger sediments in the profile, together with increasing thickness of loess layers towards the youngest part of the sequence. At the same time, constant smectite contents (30–40%) in paleosols appear to disprove progressive aridization of interglacials through time and suggest that the duration of pedogenesis played an important role in determining soil types. Further, the increasing proportion of inherited phyllosilicates (illite and chlorite) would, in theory, raise the possibility that the decreasing values of chemical weathering indices are just artifacts of enhanced physical erosion and resulting increased dust deposition by a dilution effect. The above findings highlight the fact that the general view on chemical weathering is oversimplistic, as its ‘equation’ includes two basic variables, tectonism and time beyond climate and the interplay of these equally important factors will eventually determine its final value. To get a better grasp of these processes needs further data (more age control in loess profiles, data on uplift in and around sedimentary basins) and more sophisticated proxies, as the mineralogical data presented here can be considered only semiquantitative.Regarding the provenance of sediments in the Paks profile, geochemical data demonstrate that felsic rocks dominated the source areas and there have been only very little variations in provenance over the last ca. 0.8Ma. Significant contributions from mafic/ultramafic rocks to the sediments can be ruled out as revealed by lower abundances of ferromagnesian trace elements. The appearance of amphiboles and high dolomite contents suggest that loess material was at least partly sourced from local rocks and geochemical data reveal a genetic link between floodplain sediments and loess deposits.

Climatic control of magnetic granulometry in the Mircea Vodă loess/paleosol sequence (Dobrogea, Romania)

A detailed rock-magnetic investigation of loess/palaeosol samples from the section at Mircea Vodă (Dobrogea Plateau, Romania) is presented. Investigation of climatic control on magnetic granulometry used several grain-size and concentration-dependent proxies (magnetic susceptibility and its frequency dependence, anhysteretic remanent magnetization, isothermal remanent magnetization, hysteresis properties and FORC distributions) and an unmixing model for isothermal remanent magnetization curves. The paleosol layers in the Mircea Vodă sequence experienced significant pedogenic alteration, resulting in high amounts of ultrafine grained SP, grains at SP/SD threshold, stable SD grains and PSD magnetite/maghemite grains. The loess layers in the Mircea Vodă sequence are dominated by MD and/or PSD oxidized magnetite probably of aeolian origin. The unmixing model for IRM curves shows the presence of three components with different coercivities. The soft (∼21 mT) and medium (∼42 mT) coercivity components are produced by pedogenesis during interglacial and interstadial periods. The hard coercivity component (∼60 mT) is of aeolian origin, being dominant in loess layers.

Luminescence dating of Chinese loess beyond 130 ka using the non-fading signal from K-feldspar

A multi-elevated-temperature post-IR IRSL (MET-pIRIR) protocol, which utilizes the IRSL signals measured by progressively increasing the stimulation temperature from 50 to 300 °C in a step of 50 °C, was applied to date the potassium-rich feldspar (K-feldspar) extracts from loess samples at the Luochuan section of the Chinese Loess Plateau. It was observed that the MET-pIRIR ages obtained at elevated-temperatures (250 and 300 °C) are consistent with independent chronological control for the samples from the first loess layer (L1) to the third paleosol layer (S3), which correspond to the marine isotope stages (MIS) 2–9. Our results indicate that the MET-pIRIR protocol can provide reliable ages for the Chinese loess up to ∼300 ka. The results suggest that the MET-pIRIR signal measured at 250 and 300 °C gives the most reliable ages for older samples (>130 ka). For samples below L3, the natural MET-pIRIR signals measured at high temperatures reach the saturation level in dose response curves, suggesting a dating limit of ∼300 ka for the Luochuan loess section.

How the Quaternary climatic change affects present hydrogeological system on the Chinese Loess Plateau: A case study into vertical variation of permeability of the loess–palaeosol sequence

Abstract This article systematically investigated permeability, porosity, carbonate mass percentage, and magnetic susceptibility of representative loess–palaeosol layers (from L1 to S4) on the Chinese Loess Plateau, based on analysing a sequence on the Luochuan Yuan (tableland) as a case study. The results of in situ permeability measurements illustrate that average infiltration rate of loess layers is higher than that of palaeosol layers, and that average time for the loess layers to reach quasi-steady infiltration is longer than that of palaeosol layers. In addition, loess layers have higher porosity than palaeosols on average, and it is suggested as a major reason why the loess layers have a higher permeability on average, despite complex nature of different types of the interspaces. Higher porosity (i.e. more interspaces for storing moisture/water) of the loess layers is largely determined by lower intensity of pedogenesis of loess, which is in turn ascribed to the colder/drier palaeoclimatic conditions. The difference of permeability between loess and palaeosol layers facilitates the loess units more likely to be aquifers. In this regard, the Quaternary climatic change theory can make a contribution to hydrogeology of the Chinese Loess Plateau, and the regional climatostratigraphy can be regarded as a baseline for local water resource positioning and revegetation in such a semi-arid area.

Incorrect when uncorrected: Reconstructing vegetation history using n-alkane biomarkers in loess-paleosol sequences – A case study from the Saxonian loess region, Germany

This study aims at contributing to the reconstruction of the paleoenvironment of the Saxonian loess region by investigating sedimentary n-alkanes as plant leaf-wax derived biomarkers in two loess-paleosol sequences (LPSs), namely the Gleina and the Rottewitz LPSs.The Weichselian paleosols are characterised by n-alkane concentration maxima when compared to the loess layers. When this coincides with high odd-over-even predominances (OEPs), this points not only to increased n-alkane input and/or production but also to increased n-alkane preservation in the soils, namely in gleysols with water-logged edaphic conditions. By contrast, the buried cambisols reveal low OEPs, indicating accelerated degradation under aerobic edaphic conditions. The n-alkane concentrations in the truncated Eemian Interglacial paleosol are very low. This reflects the removal of the formerly n-alkane-enriched Eemian topsoil, low n-alkane input into the Bt-Sd-horizon (subsoil horizon of the Eemian luvisol) and/or strong soil organic matter mineralization. Four investigated n-alkane ratios show distinct variations during the Weichselian, tempting inferences of vegetation changes in terms of varying contributions of tree/shrub-derived (dominated by nC27 or nC29) versus grass-derived (dominated by nC31 or nC33) n-alkanes. However, using the OEP as a proxy for degradation and considering that n-alkane ratios are prone to degradation effects, the above interpretation is very likely incorrect. Degradation can account for most variability of the n-alkane ratios.Applying an endmember model based on a modern n-alkane reference dataset allows estimating the contribution of tree/shrub- versus grass-derived n-alkanes semi-quantitatively. These modelling results suggest that both the Gleina and the Rottewitz LPSs were formed under prevailing grassland. Minor contributions of trees/shrubs are only likely for the Gleinaer Soil Complex in Rottewitz LPS, for the top of a Brown Gleysol in Gleina LPS and the Holocene soil. The Weichselian vegetation changes as inferred from the uncorrected n-alkane ratios are not confirmed. Overall, the n-alkane results support the idea that the Gleinaer Soil Complex in Gleina and Rottewitz LPS, respectively, are not identical but rather are chronostratigraphic equivalents. More favourable regional climatic conditions presumably occurred in the southwesterly exposed Rottewitz locality and allowed tree/shrub vegetation to grow during favourable periods of the Weichselian. A major shortcoming of the n-alkane biomarker method is that only vegetation changes of deciduous woodland to grassland and vice versa can be reconstructed, because coniferous trees exhibit, by two to three orders of magnitude, lower n-alkane concentrations.