Paleoclimatic implications of micromorphic features of Quaternary paleosols of NW Himalayas and polygenetic soils of the Gangetic Plains — A comparative study

Micromorphological examination of the paleosols (50–10 ka) developed in alluvial fan deposits of the NW Himalayas and the bordering polygenetic soils (mainly Holocene) of the Gangetic Plains has been used to differentiate the pedosedimentary features indicating climatic changes during late Quaternary time. The paleosols within rapidly aggrading sediments of the alluvial fans of the Dehradun valley resulted in response to the reduced rate of sedimentation and climatic changes and correspond to the MIS3 and MIS2 stages. Distinctive micromorphic features of these paleosols provided the details of the prevalent pedogenesis in response to the paleoclimatic changes during 50 ka. Microfabrics of these paleosols show reorganization of the pedality from massive and/or subangular blocky to platy and prismatic structures, strong to very strong mobilization of the plasma, different types of textural pedofeatures along with faunal activities. These pedofeatures are indicative of cold-humid climate with subsequent change to even colder but drier conditions during the last Glaciation. Comparison of the micromorphological characters of the paleosols of the NW Himalayas and the polygenetic soils of the Gangetic Plains show the same degree of soil development indicating 5–10 ka pedogenic intervals in alluvial fans of the Dehradun Valley. However, the difference in their pedofeatures is attributed to different pedogenic environments. The paleosols of the Dehradun Valley show predominance of the illuvial features with superposed impure silty clay on earlier clay pedofeatures and banded clay fabric features without any pedogenic calcium carbonate. The bordering Gangetic Plains are covered with polygenetic soils developed on stable surfaces and are < 13.5 ka. These surficial soils developed during the period marked by deglaciation and correspond to MIS1 stage. These are defined by the juxtaposition of different illuvial pedofeatures along with pedogenic calcium carbonate. This study suggests that formation of the paleosols in NW Himalayas was mainly controlled by warmer intervals during the last glaciation and the movement along the adjacent thrusts. While fluctuating climate punctuated with humid–semiarid–humid conditions played a major role during the formation of soils on the Gangetic Plains in Holocene that favoured illuviation, calcification and dissolution of pedogenic carbonates in the polygenetic soils.     

Establishing a Holocene sediment budget for the river Dijle

A Holocene sediment budget was constructed for the 758 km² Dijle catchment in the Belgian loess belt, in order to understand long-term sediment dynamics. Hillslope sediment redistribution was calculated using soil profile information from 809 soil augerings, which was extrapolated to the entire catchment using morphometric classes. As large parts of the forests within the catchment prove to have undergone little or no erosion since medieval times, a correction was applied for the presence of forests. Total Holocene erosion amounts 817 ± 66 Mt for the catchment, of which 327 ± 34 Mt was deposited as colluvium. This corresponds with a net Holocene soil erosion rate of 10.8 ± 0.8 × 10³ Mg ha^− 1 for the entire Dijle catchment. Alluvial deposits were studied through 187 augerings spread over 17 cross-valley transects. The total alluvial sediment deposition equals 352 ± 11 Mt or 42% of total eroded sediment mass. Results indicate that at the scale of a medium-sized catchment the colluvial sediment sink is as important as the alluvial sediment sink and should not be neglected. As a result the estimation of erosion through alluvial storage and sediment export would yield large errors. Dating of sediment units show an important increase in alluvial deposition from medieval times onwards, indicating the important influence of agricultural activities that developed from that period. Mean sediment export rates from the catchment for the last 1000–1200 years range between 0.8 and 1.3 Mg ha^− 1 a^− 1 and are consistent with present suspended sediment measurements in the Dijle. Erosion for agricultural land for this period is 9.2 ± 2.2 Mg ha^− 1 a^− 1. Sediment budgets for the various tributary catchments provide an insight in the sources and sinks of sediment at different scales within the catchment.     

Development of gullies and sediment fans in last-glacial areas on the example of the Suwałki Lakeland (NE Poland)

The density of gully network in the Suwa?ki Lakeland (northeastern Poland) with typical last-glaciation relief is 0.2 km/km² on average and locally reaches 1.2 km/km². Most gullies are isolated but sporadically they create dendritic patterns. The larger gullies are developed along dellies (bowl-shaped, dry valleys) or melt-out valleys. The smaller and shorter gullies occur on the slopes of melt-out depressions and tunnel valleys. Ages of peat covered by fans at the mouths of larger gullies indicate that gully erosion started between 3520 ± 70 to 2240 ± 100 BP. Two different units build the fans and infilled the gullies. The older unit in the lower part of fans is up to 5 m thick, contains sand and gravel that generally originated from the bottom and bank erosion of the gullies and resembles alluvium. The younger unit, about 2–3 m thick, consists of colluvium. The fans at the mouths of smaller and shorter gullies are mainly built of colluvium. The maximal grain diameter in both units is similar, which testifies to a similar intensity of extreme rainfalls. The analysed sediments have different characteristics, which indicate that the source material and depositional changes are linked to forest clearance and farmland expansion starting in the 7th century AD and continuing in the Middle Ages.     

Spatial and temporal variability of sediment and dissolved loads from two alpine watersheds of the Lesser Himalayas

Estimation of sediment load from Himalayan basins is of considerable importance for the planning, designing, installation and operation of hydro-power projects, including management of reservoirs. In the present study, an assessment of physical and chemical load, sediment yield and erosion rate has been undertaken at eight different locations in the Sainj and Tirthan watersheds. The analysis revealed that the maximum load was transferred during the monsoon season. Moreover, the estimated average chemical erosion rate of the Sainj (83 t km^− 2 yr^− 1) and Tirthan (80 t km^− 2 yr^− 1) watersheds were higher than that of the Indian average (69 t km^− 2 yr^− 1) representing all the rivers. Both watersheds were eroding physically and chemically at a faster rate than that of the world global average erosion rate (185 t km^− 2 yr^− 1). The flattish nature of the channels in some segments of these watersheds showed a lower transport of sediments, where as the constricted segments having steep bed slopes increased the velocity of flow and the sediment transport rate. These findings have important implications for water resource management in the context of sediments mobilization, erosion, channel management, ecological functions and operation of the hydro-power projects in the Lesser Himalayan region.     

Long-term accumulation and material balance of organic matter in the soil of an effluent infiltration basin

The fate of organic matter (OM) in large-scale infiltration basins used for wastewater treatment by the soil aquifer treatment (SAT) system was investigated. Measured changes in the organic matter concentrations in the soil profiles of the infiltration basins and detailed long-term records of OM concentrations in the recharged effluent and in the observation wells and recovery wells water, were used to calculate OM material balances in the SHAFDAN wastewater treatment plant, serving the City of Tel-Aviv, Israel, since 1977. The average annual total organic matter (TOM) load delivered by the effluents to the soil was ~ 5 kg m^− 2 y^− 1. Soil OM concentrations increased from 0.11% in the pristine soil to ~ 0.8% and ~ 0.6%, in the 0-0.15 m and 0.15-0.30 m soil layers, respectively, after ~ 20 y of effluent recharge, but did not change significantly in the 1.80-2.10 m deep layer. The OM accumulation rates in the top two soil layers were fast initially, then declined slowly and the OM concentrations approached a steady state following 10-15 y of effluent recharge. This suggests that stabilization of the ‘active biofilm’ layer in the infiltration basins' soils is a relatively slow process. Material-balance calculations showed, that accumulated OM in the top 0-2.1 m soil layer amounted to only ~ 4% of the TOM added by the effluents during ~ 20 y of recharge. Along the flow pathway of the effluent through the vertical 50-100 m thick soil-sediment column, DOC concentrations decreased by 70-90% (from ~ 18.9 mg L^− 1 to ~ 3.7 mg L^− 1). Continued flow in the aquifer from the observation wells to the recovery wells further decreased DOC concentrations by about 50% (from ~ 3.7 to ~ 1.5 mg L^− 1).     

Geochemical tools for the stratigraphic correlation of floodplain deposits of the Morava River in Strážnické Pomoraví, Czech Republic from the last millennium

The floodplain of the Morava River in Strá?nické Pomoraví, south-east Moravia, Czech Republic contains a very valuable record of regional environmental change, which goes back to several thousand years. Its interpretation has been limited by poor stratigraphic correlation and dating of the sediments. We present a geochemical solution to this challenge. We studied 8 outcrops of floodplain deposits from 4 localities along a 6 km long part of the current meander belt of the Morava River in Strá?nické Pomoraví using geochemical proxy analyses, magnetic susceptibility measurements, ¹⁴C dating of wood remnants, and sediment micromorphology. The proxy methods are based on elemental analysis (EDXRF) and analysis of the cation exchange capacity of clay minerals; granulometric analyses provided the basis for lithological and facies assignment of the sediments. Our geochemical and mineralogical interpretations have further been tested by microstratigraphically studying the optical properties of the fine fraction. Horizons older than about 3 centuries were ¹⁴C dated using wood remnants and the age of deposits from the last century was determined on the base of several proxies reflecting their industrial contamination by heavy metals and magnetic particles. The mean depositional rate over the period from about 1000 to about 1900 AD ranged from 0.2 to 0.6 mm y^− 1, depending on the sedimentary facies. The coeval lithological change in the majority of the studied sections indicated a change of the meander belt structure at between ~ 1200 AD and ~ 1600 AD probably as a consequence of changes of channel structure. The alluvial deposition in the 20th century was strongly affected by the river regulation.     

Reconstructing the paleotopography beneath the loess cover with the aid of an electromagnetic induction sensor

During the last glacial period (Weichselian), wind-blown loess was deposited over the undulating landscape of central Belgium, which had been formed in surfacing Tertiary marine sediments. Since valleys were filled up with a thicker loess layer than hill tops, the present topography is much smoother. This smoothing was enhanced by subsequent erosion processes. Reconstructing the paleolandscape at a detailed scale is almost impossible by conventional procedures based on soil augerings. Therefore, the use of the electromagnetic induction sensor, EM38DD, was evaluated as an alternative for mapping the depth to the Tertiary clay substrate. On our 2.7 ha study site, located in the loess belt of central Belgium, a strong non-linear relationship (R² = 0.86) was found between the apparent electrical conductivity (ECa), measured by the vertical dipole orientation of the EM38DD and the depth to a Tertiary clay substrate. These predictions were validated by independent observations of the depth to the Tertiary clay and a correlation coefficient of 0.83, with an average error of 0.22 m, was found. So, our dense ECa measurements (2 by 2 m resolution) allowed us to build a three-dimensionall surface of the depth to the Tertiary substrate, reconstructing the paleotopography beneath the loess cover. This paleotopography revealed distinct erosion patterns on the surface of the Tertiary clay. The continuity of these was confirmed by an analysis of surface flow patterns conducted on the reconstructed paleotopography. The non-invasive, time- and cost-effective electromagnetic induction sensor was found to offer new perspectives to reconstruct and analyse in detail the Quaternary paleotopography beneath the loess cover.     

Factors controlling the erosion rates in a semi-arid zone (Bardenas Reales,NE Spain)

Bardenas Reales is an erosive depression 415 km² in area located in the central-western part of the Ebro Depression. Tertiary sediments crop out in the margin of the basin whereas Quaternary sediments, Holocene in age, occur only in its centre. These Holocene sediments (clays and silts) are the result of the erosion and weathering of the Tertiary clays and are made up of 3 different stratigraphic units. Erosion is clearly the dominant process in the centre of the depression, generating gullies up to 10 km in long and 8 m deep. In order to analyse and quantify the erosion rates of the studied area, erosion was measured on two Soil Erosion Plots with volumetric and instrumental techniques that have been supplied for the last 12 years. The results show that the estimated erosion rates depend extrinsically on the used method and intrinsically on the time of the year in which they are measured. The most accurate values are those obtained by means of collector devices. The values obtained by the microtopographic profile gauge are overestimated, while the results of the measurement with erosion pins are clearly lower. The study area is located in a semi-arid environment, with two pluviometric maximums, in spring and autumn, associated with convective storms. In summer and winter, rainfall is related to Atlantic cyclonal fronts. Soil loss is significant during the pluviometric maximums when rainfall quantity and intensity are higher. During cyclonal periods, in contrast, water erosion is null or scarce and soil loss is related to mudflows. In addition, the erosion rates of each Holocene unit are different. The C2 Holocene unit has undergone greater erosion because of its physico-chemical properties. All the stratigraphic units have similar characteristics regarding Tertiary materials. Since 1993 the average erosion rate measured by the collector device on the Tertiary materials is 32 Mg ha^− 1 year^− 1 and 77 Mg ha^− 1 year^− 1 in the Holocene.     

Paleoenvironmental interpretation of multiple soil–loess sequence at Milford Reservoir,northeastern Kansas

A loess/soil section near the Republican River in northeastern Kansas includes three superposed soils/paleosols in at least three superposed loess units, including Peoria Loess (PL), the Gilman Canyon Formation (GCF), and Loveland Loess (LL), The GCF coincides with a composite soil with a 1.3 m thick, buried organic-rich (A) horizon that yields AMS radiocarbon ages from 30.3 to 22.4 ka (or 35.7 to 26.9 ka when calibrated) that overlies a 1.6 m oxidized B horizon complex. The B subhorizons stratigraphically and morphologically resemble the “reddish pedocomplex” described elsewhere in Kansas and Illinois that dates between about 69 and 35 ka. The upper LL yields a TL age of about 136 and 130 + 30 ka. Thus, PL, the GCF, and LL were probably deposited mainly during the late Wisconsinan, middle Wisconsinan, and Illinoian (∼ Oxygen Isotope Stages (OIS) 2, 3, and 6, or about 12 to 24, 24 to 60, and 130 to 188 ka, respectively). Soils 1, 2, and 3, then formed mainly during OIS stages 1, 3, and 5, respectively, or about 12 to 12, 60 to 60, and 73 to 130 ka.     

Phosphorus and iron erosion from non-vegetated sites in a post-mining landscape,Lusatia, Germany: Impact on aborning mining lakes

Particulate phosphorus (P) can be transported via soil erosion in overland flow to waters, where it provides a long-term source of P for aquatic biota, and can accelerate freshwater eutrophication. Hence, knowledge of P sources is important for good environmental management. However, data on P, and related Fe, losses from various structures of a post-mining landscape are lacking. A year-long monitoring, and ten short rainfall simulations on plot scale, at ridges and rills and a combination of them, revealed high erosion from bare lignite mining dumps at Schlabendorf-North, Lusatia, Germany. The mean annual soil erosion rate from the year-long monitoring site was 18 × 10⁶ kg km^− 2 yr^− 1, corresponding to 0.034 g m^− 2 min^− 1. The erosion rates were lowest at rill plots (1.9–4.4 g m^− 2 min^− 1), intermediate at ridge plots (14.3–37.1 g m^− 2 min^− 1), and highest at a combined rill and ridge plot (48.7–63.4 g m^− 2 min^− 1). These differences in extent were due to small scale differences in morphology and extreme water repellency. The hydrophobicity leads to very low infiltration, thus generating surface runoff even at low rainfall intensities. Loss rates of P and Fe, as deduced from the year-long erosion rate, were 470–650 kg km^− 2 yr^− 1, and 37.9 × 10³–71 × 10³ kg km^− 2 yr^− 1 respectively. However, these P inputs from lignite mining dump erosion, consisting of P-poor (17–90 μg g^− 1) tertiary spoil materials, into aborning mining lakes, are negligible since they are accompanied by high Fe inputs, which favour an efficient P co-precipitation in the water column.     

黄土高原不同侵蚀类型区侵蚀产沙强度变化及其治理目标

为了确定黄土高原不同侵蚀类型区的治理目标,采取"水文—地貌法",利用98个水文站控制区和234个侵蚀产沙单元,在分析其不同治理阶段土壤侵蚀产沙变化特征与减沙幅度,不同侵蚀强度面积的变化及其空间分布的基础上,提出了未来20a黄土高原主要流失区的区域治理目标:土壤流失量控制在3.60×108 t左右,土壤侵蚀模数1 300 t/(km2.a)左右。其中,黄土峁状丘陵沟壑区为3 000t/(km2.a),黄土梁状丘陵沟壑区为2 000t/(km2.a),干旱黄土丘陵沟壑区为2 000t/(km2.a),黄土平岗丘陵沟壑区为1 000t/(km2.a),风沙黄土丘陵沟壑区为1 000t/(km2.a),黄土山麓丘陵沟壑区为1 000t/(km2.a),森林黄土丘陵沟壑区为300t/(km2.a),黄土高塬沟壑区为1 500t/(km2.a),黄土残塬沟壑区为3 000t/(km2.a),黄土阶地区为500t/(km2.a),风沙草原区为500t/(km2.a),高原土石山区为100t/(km2.a)。未来20a黄土高原的治理重点区域为黄土峁状丘陵沟壑区(2.20×104 km2)、干旱黄土丘陵沟壑区(1.50×104 km2)、黄土高塬沟壑区(8 600km2)、黄土梁状丘陵沟壑区(4 600km2)。     

Simulating badland erosion with KINEROS2 in a small Mediterranean mountain basin (Vallcebre,Eastern Pyrenees)

The Ca l?Isard catchment (1.32 km²), a sub-basin of the Vallcebre experimental catchments, yields large amounts of sediments (about 580 Mg km^− 2 year^− 1) that are produced in relatively small but very active eroded areas (badlands). Several lines of evidence suggest that there is a delay between sediment production, caused by intense summer rainstorms, and sediment transport, occasioned by the main floods produced by large precipitation events following wet antecedent conditions. First, a calibration–validation exercise was carried out with sediment yield data obtained using containers provided with slot divisors in a badlands micro-catchment (1240 m²). Then, the model was applied to the main badlands areas in the Ca l?Isard sub-catchment for a 4-year period and the simulated sediment yields were compared with the records at the gauging station. The test was performed with the Generalized Likelihood Uncertainty Estimation (GLUE) approach for assessing the uncertainty associated with model predictions, which assumes that many parameter sets can give acceptable simulations. The results demonstrated the capacity of KINEROS2 to simulate badland erosion, although it showed limited robustness. A clear temporal mismatch between erosion and sediment transport and the relevance of sediment stores in the catchment were confirmed, while the total weights of sediment were generally under-predicted. The limited suitability of the area used for calibration or the role of sediment sources not simulated in the approach may account for this shortcoming.     

Reductive transformation of pentachlorophenol on the interface of subtropical soil colloids and water

Ten soil colloids were obtained from three kinds of Fe-rich (> 50 g kg^− 1) subtropical soil parent materials (Basalt, Sandshale, and Quaternary Period Red Earth) collected in nine sites in Guangdong of China. Effect of the Fe-rich soil colloids and adding Fe(II) and oxalic acid on reductive dechlorination transformation of pentachlorophenol (PCP) were studied on colloids interfaces of reaction suspension. Mineralogical properties and specific surface area of the soil colloids were characterized by X-ray powder diffraction and Brunauer-Emmett-Teller (BET) methods, respectively. A series of reductive experiments were designed to determine PCP transformation and chloride ion release, and to calculate rate constant (k values) of pseudo first-order kinetics. Our results showed that reductive transformation of PCP occurred with k values from 0.007 to 0.057 d^− 1, and relevant chloride was released in the suspension of the ten soil colloids. Soil colloid developed from Basalt presented higher transformation rates (0.040-0.057 d^− 1) than that from Sandshale (0.007-0.033 d^− 1) and Quaternary Period red earth (0.012 d^− 1). Two paddy soil colloids developed from Sandshale (0.032-0.033 d^− 1) were more active than other three Sandshale soil colloids (0.007-0.011 d^− 1). The k values were significantly and positively correlated to the BET surface area (P < 0.01, n = 10). Addition of oxalic acid (0.022-0.231 d^− 1) or Fe(II) (0.029-0.256 d^− 1) into suspension of soil colloids gave arise to increase by 1.2-9.4 times in the k values. The release of chloride ion was simultaneously elevated. The enhancement of oxalic acid or Fe(II) on reductive transformation of PCP was attributed to increase of surface-bound Fe(II), which possess high reductive reactivity. The k values adding 1.0 mM oxalic acid were significantly and positively correlated to BET surface area and soil pH (P < 0.01), while k values adding 1.0 mM Fe(II) were related to total Fe (P < 0.001). The results may give new insight to understand the contribution of PCP abiotic reductive transformation in subtropical and tropical soils, and also in permeable reactive barriers.     

A mid–late Holocene flood record from the alluvial reach of the Mahi River, Western India

Flooding of rivers in India is linked with the peak monsoons. Investigating the linkage between monsoonal patterns and flood history of various rivers is therefore of fundamental importance in the Indian context. In the present study, the slackwater deposits in the alluvial reaches of the Mahi river basin, western India have been documented. These occur in the ravines incised during the early Holocene on an alluvial surface comprising sediments of Late Pleistocene age. The slackwater deposits occur at elevations up to 20 m from the present river level and extend to about 500 m inland. The carbonate rich sediments forming the ravine cliffs have provided bank stability and the dissections in the ravines have helped in the accumulation of slackwater deposits due to backflooding of the floodwater from the main channel. Recent gullies have incised the sediments and exposed deposits related to major flood events. The best exposures of slackwater deposits have been observed at Dodka. The sediment succession of the slackwater deposits is dominated by bedsets and laminasets of silt and sand separated by colluvial sediments. Four events of flood deposition occurred during the mid to late Holocene. Two units of slackwater deposits, SWD 2 and 4 have been dated by IRSL at 4.6 ± 1 ka and 1.7 ± 0.5 ka. The stratigraphy of these deposits indicates that the first two slackwater units (SWD1 and SWD2) have resulted due to flooding in a regime of intense monsoon. The other two units, however, represent extreme high magnitude floods in a period of low average precipitation.     

Holocene evolution of floodplain soils and landscapes in the Kulikovo field area

The lithostratigraphic, radiocarbon, macro- and micromorphological, particle-size, and other analyses have been applied to reconstruct the Holocene evolution of soils and landscapes on the high- and mediumlevel floodplains of the Nepryadva River in the Kulikovo field area. It is shown that the soils buried within the thickness of alluvial sediments on the high- and medium-level floodplains were formed in different times and had their own evolution patterns; the polygenetic nature of these soils is demonstrated. The development of floodplain landscapes in the Holocene was affected by the long-term climatic fluctuations. The bed of the high floodplain was formed during the Late Valdai glacial stage. The beginning of the development of an intricate sequence of buried soils and sediments of the floodplain dates back to the Boreal period. This pedosedimentary sequence in the studied area can be referred to as the Kulikovo sequence. In the course of its formation, the pedogenic stages with a predominant development of soils alternated with the lithogenic stages of active alluviation and deposition of colluvial deposits from adjacent slopes on the floodplain.     

Characterization of relict Late Pleistocene and Early Holocene paleosols buried in wedge-shaped structures on the southern coast of the Finnish Gulf

The physical and physicochemical properties and morphogenetic characteristics of the buried soddy gleyic and gleyed paleosols developed from the glaciolacustrine loamy sediments on the southern coast of the Finnish Gulf in the Late Pleistocene and Early Holocene (12–9 ka, calibrated) are considered. It is shown that the morphology and properties of these paleosols sharply differ from those of the enclosing gravelly sands deposited in the ancient basins. The latter substrates serve as the major type of soil-forming materials for the modern surface soils. The studied paleosols fill wedge-shaped structures dissecting the gravelly sediments. Their profiles are well preserved, though their normal horizontal orientation is disturbed; large soil blocks were displaced into the open wedges. The presence of these soils attests to the fact that the initial soil cover in the studied region was formed in the Late Glacial epoch soon after the retreat of the glacial sheet. The good degree of preservation of the paleopedogenic information recorded in the profiles of these paleosols is of great value for the paleoenvironmental reconstructions.     

Loessic silt deposits in the Western Himalayas: Their sedimentology, genesis and age

Loess is abundant in the foreland basins of the Himalayas. However, it is poorly developed within the intermontane basins of the western Himalayas and Karaloram. Selected sections were studied from the Swat Himalaya and the Karakoram Mountains. Fieldwork and sedimentological analysis including grain size, mineralogy and microfabric showed that the loessic sediments have been reworked and some have undergone weak pedogeneses. These silts are not true loess, rather a “loessic colluvium”. Thermoluminescence (TL) dates from the loessic sediments in sections from the Swat valley provided younger ages than earlier workers had suggested. This is consistent with reworking of the loess in these areas. It is concluded that care must be taken when using loessic silts for TL in similar mountainous terranes.     

Mineralogical composition of the clay fraction and micromorphology of the Middle and Late Pleistocene loesses and paleosols in the center of the East European Plain

The mineralogical composition of the clay fraction and microfabrics of the cryogenic soil-loess sequences of the Middle and Late Pleistocene ages have been studied near the northern boundary of loess sediments on the East European Plain. Poorly ordered mixed-layered mica-smectitic minerals with different portions of smectitic layers predominate in the clay fraction; di-and trioctahedral hydromicas occupy the second place. The clay fraction also contains chlorite, clay-size quartz grains, and feldspars. Individual smectite is present in some of the samples. Interstadial chernozem-like paleosols are specified by the higher content of clay, the maximum concentration of smectitic layers in the mixed-layered minerals, and the presence of individual smectite. The clay fraction in the profiles of interglacial paleosols is sharply differentiated: in the eluvial part, it is depleted of smectite and enriched in kaolinite, hydromica, and clay-size quartz. These features allow us to suppose that interglacial paleosols were subjected to podzolization processes. According to the mineralogical indices, Middle Pleistocene paleosols can be differentiated into those subjected to lessivage (the Kamenskii interglacial paleosol) and podzolization (the Inzhavin interglacial paleosol).     

Deep infiltration through a sandy alluvial fan in semiarid Niger inferred from electrical conductivity survey,vadose zone chemistry and hydrological modelling

In semiarid southwestern Niger, most of the groundwater recharge is indirect and occurs through endoreic ponds. Elsewhere in the landscape, there is no evidence of deep infiltration, with a possible exception for gullies and alluvial fans on sandy slopes. In order to verify this hypothesis, a detailed geophysical and geochemical survey was conducted on a large, representative mid-slope fan (6 ha). At this site, distributed hydrological modelling conducted over the encompassing endoreic catchment (190 ha) showed high losses of runoff water by infiltration. Electromagnetic mapping and 2-D electrical imaging survey were used to investigate the 35 m deep vadose zone; in addition, 8 boreholes were drilled following the geophysical survey to constrain the interpretation. Variations in apparent electrical conductivity measured in boreholes appear to be mainly linked with changes in the soil solution mineralization. An extrapolation throughout the area shows that apparent electrical conductivity of the ground is systematically lower below channels; this suggests localised leaching through the unsaturated zone. A physically-based, 2-D distributed hydrologic model was used to estimate the amount of surface water loss by infiltration for the 1992–2002 period. Depending on year, infiltrated volumes range from 1000 to 24 000 m³. This represents between 5% and 16% of the runoff that reaches the final outlet of the basin, an endoreic valley bottom pond where recharge to the aquifer has been shown to occur. Because leaching of the vadose zone is observed down to a depth of 10 m below channels, episodic groundwater recharge through sandy mid-slope fans is highly probable during rainy years.     

Contribution to the paleolimnology of lake Valencia, Venezuela: Seismic stratigraphy

Lake Valencia is situated in a graben at 402 m a.s.l. in northern South America. The lake is slightly larger than 300 km² and the basin area is approximately 2750 km². Observations during the last two centuries suggest that the lake level has oscillated significantly. It is thought that the lake originated during the Quaternary, but its age may be as old as the Late Tertiary. Acoustic reflection profiles (UNIBOOM) indicate that, to the depth reached, the subsurface seismic stratigraphy consists of three units (Units I, II and III) separated by prominent reflectors. A 7.43 m core was obtained in the central part of the lake which reached approximately the base of Unit I. Sedimentological, palynological, and radiocarbon analyses indicate that Unit I is a Holocene lacustrine deposit, and that in the Late Pleistocene the lake either did not exist or was greatly reduced. Units II and III probably represent similar older lacustrine units. The stratigraphy is interrupted by Late Pleistocene-Holocene faulting. Clastic lenses were found near the base of Unit I, above the reflector which separates it from Unit II, in the eastern seismic profiles. These are interpreted as Early Holocene fluvio-lacustrine sediments which were deposited subaerially or as deltas.