Stages Of Soil Formation Research Articles

Soil morphological characteristics in the active volcanic toposequence zone at Tangkuban Parahu volcano, Indonesia

Soil formation in volcanic terrains presents a significant challenge due to the diverse physical and chemical properties imparted by volcanic activity, which are not yet fully understood. This study investigates the unique morphological characteristics of soil profiles within crater topography sequences at the Tangkuban Parahu Volcano, Indonesia. To address this gap, five representative sample profiles (I, II, III, IV, V) were analyzed. The Ratu Crater pathway topography was characterized by steep to very steep slopes. Detailed analysis identified three predominant soil layers, each with distinct features such as color, texture, porosity, and chemical composition, reflecting different stages of soil formation. At the highest elevation near the crater rim, Profile V was composed mainly of volcanic ash, with a loose structure, high porosity, and acidic pH, indicative of recent volcanic deposits. Profile III, at intermediate elevations, consisted of highly weathered soil with sandy loam textures and clear layer demarcations, suggesting prolonged soil development and consolidation. Profile I, at the lowest elevation, featured loamy sand with significant weathering and organic matter incorporation, indicating advanced soil development stages. The findings underscore the impact of volcanic activity on soil morphology, revealing distinct layers that correlate with various ages and developmental stages. Understanding these processes can inform agricultural practices.

Paleo-pedological record in loess deposits in the south of the East European plain, based on Beglitsa-2017 section study

Loess-paleosol sequences (LPSs) are one of the main components of the natural environment, which traces how the climate has changed in the past. The article discusses changes in the landscape and climatic conditions from the Middle Pleistocene to the present, identified by the results of the LPS of the Beglitsa-2017 section study. We obtained new data on soil cover change in the Late and Middle Pleistocene in the North-Eastern Azov region based on multi-proxy analysis with high-resolution sampling along the section. The first data on the polygenetic origin of the Salyn interglacial paleosol (MIS 5e) profile which developed according to the Gypsic Calcic Chernozems type in the interglacial optimum, was obtained. Still, in the last stage of soil formation, its type changed to the more arid Gypsic Chernozems (Arenic). During MIS 5c and MIS 5a, the paleosols developed in a more arid climate; their modern analogues may be Gypsic Kastanozems and Calcic Gypsisols, respectively. The period of MIS 3 in the study area is marked by severe cryo-arid conditions, which influenced the formation of incipient Calcic Gypsisols. The profiles of the Middle Pleistocene paleosols in the lower part of the LPS of the Beglitsa-2017 section were subject to gleying processes, which formed specific Gleysols or Stagnosols paleosols. The preliminary age of these paleosols corresponds to MIS 13/15 and 8/9. The MIS 7 paleosols are structurally similar to modern Calcic Kastanozems, currently distributed in the dry steppe zone. Reconstruction of the formation of the LPS paleosol cover in the Beglitsa-2017 section made it possible to trace the trend of changes in climatic conditions in the past. Climate aridity decreases in the interval between MIS 5e and MIS 1, and the maximum drought peaks were recorded in MIS 3 paleosols. Earlier, climate aridization intensified from MIS 13/15 and continued until MIS 7/6. The results will complement our understanding of the soil cover changing over time and will expand the reconstruction of climate change throughout the East European Plain.

PHYTOEXTRACTION OF HEAVY METALS BY HERBAL PLANTS ON TECHNOGENIC SOILS

The purpose of the work is to study the specifics of the natural restoration of vegetation on highly toxic embryozems (on the example of the technogenic dump from the large chemical production «Usoliekhimprom», Irkutsk region). It was shown that organo-accumulative embryozem is the first stage of soil formation and the beginning of plant colonization. The level of technogenic soils pollution with heavy metals was assessed by a set of indicators, based on them, organo-accumulative embryozems were classified as soils with an extremely dangerous level of pollution. It was found that the first pioneers on these embryozems were 9 aboriginal species of herbaceous plants: Melilotus albus Medikus., Melilotus officinalis (L.) Pall., Trifolium hybridum L., Trifolium repens L., Trifolium pratense L., Vicia cracca L., Medicago sativa L., Sonchus arvensis L., Chamerion angustifolium (L.) Scop. A number of their unique features allow them to grow in conditions of very strong soil pollution – this is a high level heavy metals accumulation in phytomass, good adaptation of mineral nutrition to hard growing conditions, an increase in biomass during the growing season, and the absence of visual signs of damage. The obtained results give every reason to recommend these herbaceous plants for use as phytoextractors of heavy metals on technogenic dumps.

Quantifying early mineral weathering reactions in serpentinite bedrock

Understanding early chemical reactions that initiate weathering in cohesive bedrock is crucial to predicting porosity development, nutrient availability, and trace element mobility in later stages of soil formation. We seek to characterize incipient chemical weathering in serpentinite bedrock containing primarily serpentine and augite from a former quarry on Little Deer Isle, ME, USA. Bedrock and a small amount of overlying soil were sampled along a quarry face to a depth of 6 m and analyzed using SEM, XRD, XRF, and electron microprobe for chemistry and primary and secondary mineralogy to determine chemical and mineralogical changes as a function of depth.Extensive chemical and mineralogical evidence of both dissolution and precipitation extend approximately 1 m into the bedrock. Approximately 50% of Ca is depleted to 1 m in the bedrock; additionally, we observed weathering textures including dissolution pits and denticulated edges within augite in the top 0.5 m of bedrock. Although serpentine shows evidence of weathering in the soils, we see minimal evidence of chemical or textural serpentine weathering within the bedrock. We observed small quantities of secondary Fe–Mn-(oxyhydr)oxides and possible Cr-bearing smectite, although analytical methods made clay identification difficult. The presence of barite and possible Cu-bearing secondary minerals along existing fracture networks suggests mobilization and reprecipitation to depths of 4 m. Based on both chemical and mineralogical evidence, it is likely that the dissolution of augite controls porosity development within the weathering profile. Augite dissolution along dissolution pits, denticulated fractures, and grain boundaries contributes to secondary porosity during incipient weathering of the bedrock, promoting further weathering of augite and accessory minerals and eventual dissolution and disaggregation of serpentine. This is confirmed by calculated field weathering rates for augite.

Differentiation of Soil Processes by Stages of Soil Formation in the Regions of a Dry Climatic Belt

Differentiation of Soil Processes by Stages of Soil Formation in the Regions of a Dry Climatic Belt

EVOLUTION OF IRRIGATED SOILS "CENTRAL FERGANA" UNDER THE INFLUENCE OF ANTHROPOGENIC FACTORS

It is known that the study of the historical development of soils is an important task in determining the direction of changes in their cross-section and thereby developing a system of integrated measures to address many issues, such as their conservation and productivity, improvement and rational use. The historical development of soils means that the already developed full-profile soils change in connection with the evolution of the whole natural environment. In this case, one genetic type or type of soil can pass to another genetic type or type. As a result, the characteristics of the previous soil formation stage in the soil profile gradually begin to fade or transform, and new characters are formed in accordance with the new stage of soil formation.

Phosphorus dynamics during early soil development in a cold desert: insights from oxygen isotopes in phosphate

Abstract. At the early stages of pedogenesis, the dynamics of phosphorus (P) in soils are controlled by microbial communities, the physicochemical properties of the soil and the environmental conditions. While various microorganisms involved in carrying out biogeochemical processes have been identified, little is known about the actual contribution of microbial processes, such as organic P hydrolysis and microbial P turnover, to P cycling. We thus focused on processes driven by microbes and how they affect the size and cycling of organic and inorganic soil P pools along a soil chronosequence in the Chamser Kangri glacier forefield (Western Himalayas). The rapid retreat of the glacier allowed us to study the early stages of soil formation under a cold arid climate. Biological P transformations were studied with the help of the isotopic composition of oxygen (O) in phosphate (δ18OP) coupled to sequential P fractionation performed on soil samples (0–5 cm depth) from four sites of different age spanning 0 to 100–150 years. The P bound to Ca, i.e., 1 M HCl-extractable P, still represented 95 % of the total P stock after approximately 100 years of soil development. Its isotopic composition was similar to the parent material at the most developed site. Primary phosphate minerals, possibly apatite, mostly comprised this pool. The δ18OP of the available P and the NaOH-extractable inorganic P instead differed from that of the parent material, suggesting that these pools underwent biological turnover. The δ18OP of the available P was mostly controlled by the microbial P, suggesting fast exchanges occurred between these two pools possibly fostered by repeated freezing–thawing and drying–rewetting cycles. The release of P from organic P becomes increasingly important with soil age, constituting one-third of the P flux to available P at the oldest site. Accordingly, the lighter isotopic composition of the P bound to Fe and Al oxides at the oldest site indicated that this pool contained phosphate released by organic P mineralization. Compared to previous studies on early pedogenesis under alpine or cold climate, our findings suggest a much slower decrease of the P-bearing primary minerals during the first 100 years of soil development under extreme conditions. However, they provide evidence that, by driving short-term P dynamics, microbes play an important role in controlling the redistribution of primary P into inorganic and organic soil P pools.

PHASING FEATURES OF THE SOIL-FORMING PROCESS IN AGROCHERNOZEMS OF WATERSHED PLATEU IN THE CENTRAL PART OF PODILLIA

The development of the paleosoils during the warm stages (thermochrons) of the Pliocene and Pleistocene, being reflected in the structure of soil-loess and red-brown formations of Ukraine, is characterized by a clear regularity. This is manifested in the formation of complex soil layered constructions (pedocomplexes) reflecting the chronological stages of pedogenesis. Agrochernozems of watershed plateu in the central part of Podillia, formed on the loess rocks of the Late Pleistocene age, also show this general regularity of Pliocene-Pleistocene soil formation. Contrasting changes in the physic-geographical conditions of pedolitogenesis in the ancient Holocene (late glacial) and evolutionary trend of soil formation during the following Holocene periods lasting for 10–8 thousand years led to the formation of a two-stage Holocene soil layering on the plakor lands of the region, represented by chernozem-type soils. Morphological signs of staged soil formation are concentrated in one genetic profile, which, along with the sign of anthropization of landscapes and soil formation significantly complicates the detailed identification of soils and their historical and genetic analysis. The early stage of the local soil formation history is recorded in these soils in the form of solid-phase products of soil-forming processes (puppets, soil wormholes, coprolites, moles drains). These relict pedogenic formations are located in the lower part of the soil profile of agrochernozems. In general, in the soil profile of agrochernozems on the watershed plateu in the central part of Podillia the morphologically hidden stages of soil formation are noticeable, which is typical of the first half of the Holocene thermochron. The soil of the initial stage of pedogenesis correlates with the horizon of the mole loess P(h)k and the lower part of the transitional brown-colour horizon Phk or PhI. The humus profile of the plakor agrochernozems has soil characteristics of the early optimal stage, which lasted for 7–8 thousand years from the preboreal to the late subatlantic. There are no pedogenic signs of other stages of development of the pedocomplex. So, modern day soils of this region (agrochernozems) are polygenetic two-stage formations that have not reached the status of full-fledged pedocomplex. Key words: evolution; pedogenesis; agrochernozem; Holocene; stages of soil formation; pedocomplex; Podillіa.

Metabolomic Profiling of Biolayers on the Surface of Marble in Nature and Urban Environment. Case Study of Karelia and St. Petersburg

The formation of biolayers of various taxonomic and biochemical composition occurs on the rock surfaces under various environmental conditions. The composition of metabolites in various types of biolayers on the marble surface in natural outcrops and urban environment was studied. Metabolome profiling was fulfilled by GC-MS. It was found that communities in urban environment are much less biochemically diverse than in a quarry. The seasonal differences in metabolite network between samples dominate over taxonomic ones in biolayers with predomination of algae and cyanobacteria and in biolayers with predomination of fungi. The biolayers of different stage of soil formation are less susceptible to seasonal variability.

ОБ УЧАСТИИ ГЕТЕРОТРОФНЫХ МИКРООРГАНИЗМОВ В НАЧАЛЬНОМ ПОЧВООБРАЗОВАНИИ НА ОТХОДАХ АГЛОМЕРАЦИИ ЖЕЛЕЗНЫХ РУД

The results of studies of the development of heterotrophic microorganisms in embryosemes formed on the sand waste of iron ore agglomeration in Western Siberia are presented. At the initial stage of soil for-mation, low values of actual acidity and very low humus values were found in the initial embryosemes. It is established that such habitats are phytiotoxic, which is confirmed by data on the germination of seeds and the growth of seedlings: oats, oilseed radish and white mustard. It is proved that heterotrophic micro-organisms are adapted to life in embryos. Azotobacteria retain vital activity, thanks to toxin and mucus formation, and actively multiply. Micromycetes exhibit dimorphism-yeast and mycelial growth types, which expands the possibilities of their vegetative reproduction and population preservation. It was re-vealed that organo-accumulative embryos are the most viable for plants and microorganisms. For the first time, the glow of mold fungi and Azotobacter under cereal plants and pine plantations was recorded. It is suggested that the emission of light energy, the presence of oxidases of microorganisms and plant lignin contribute to humification in an oligotrophic environment

Pedostratigraphy and chronology of the Late Pleistocene for the extra glacial area in the Central Russian Upland (reference section Aleksandrov quarry)

New results on stratigraphy and chronology, obtained on the basis of OSL and 14C-dating of paleosols, sediments, and cryogenic deformations in the Aleksandrov quarry situated at the Central Russian Upland, are discussed. Due to the location of the site in a paleodepression, the section presents various stages of soil formation, cryogenesis and sedimentation starting from the Mikulino interglacial to the middle last glacial time. The studied sequence is well preserved and one of the most detailed soil-sedimentary terrestrial archives within Eastern Europe. It reflects climatic variations comprising the timespan from the marine isotopic stage (MIS) 5e to MIS 3. At the base of the paleodepression the pedogenetic stages are extraordinary detailed. Distinct paleosols are alternating with erosion-accumulative stages, forming the Ryshkovo pedolitocomplex during the Mikulino interglacial. During the Early Valdai time two interstadial paleosols were developed, and the Middle Valdai section comprises two main interstadial paleosols as well. In general, interstadial paleosols of the Late Valdai time are absent in the studied quarry. For the first time, the chronological boundaries of the MIS 5e interglacial are recorded and thus, the duration of soil formation could be determined from 12 to 15 thousand years. Furthermore, stages of periglacial conditions during the Early, Middle and Late Valdai time were dated. The obtained ages form the base for a chronostratigraphic framework, which was correlated with those of the loess-paleosol archives of Eastern, Central, and Western Europe.

Soil and Environmental Conditions at the Oroshaemoe Neolithic–Eneolithic Archeological Site in the Lower Volga Region

The results of interdisciplinary research conducted at the Eneolithic archeological site Oroshaemoe (5–7 ka BC) in Saratov oblast are presented. The studied soils are calcareous light chestnut soils (Eutric Cambisols (Loamic, Protocalcic, Ochric)); in the archeological excavation, they are human-modified and contain various artifacts. A set of pedological, paleopedological, paleoclimatic, and paleobotanical methods and radiocarbon dating have been applied. Information on alternation of the periods of humidization and aridization of the territory, stages of soil formation and sedimentation, and on the vegetation cover in the Holocene at the archeological site has been obtained and refined. According to our data, periodic alternation of more humid and more arid conditions has taken place since 7245 ± 60 BP. The stages of aridization were accompanied by the short-term sedimentation related to the activation of eolian processes. Loesslike sediments deposited during these stages are archeologically sterile (do not contain artifacts) and are relatively thin in comparison with the cultural layers separating them. The stages of humidization were marked by more active sedimentation accompanied by soil formation. The obtained data suggest that the past 5000 years have been the period of some humidization of climatic conditions. Preliminary estimates of sedimentation and soil formation rates in the Holocene in the study area attest to their considerable fluctuations. Thus, the rate of soil formation varied from 35 to 0.8 cm per century. The results of this study allow us to refine paleoclimatic reconstructions for the considered area. Periodic changes in the environmental conditions during the Holocene affected the life of the tribes, patterns of human settling, and regional and, possibly, global migration processes. The reconstruction of natural and climatic features of the archeological site and its comparison with published data attest to the uneven paleogeographic situation in the Lower Volga region. It is argued that the chronology of landscape and climatic changes during the Holocene as presented in the publications for the southern arid regions of the East European Plain needs to be revised and made more detailed.

Holocene Soil Evolution in South Siberia Based on Phytolith Records and Genetic Soil Analysis (Russia)

Dark, coniferous hemiboreal forests in the south of West Siberia are located in the Holocene forest-steppe ecotone, where natural environmental conditions have been quite dynamic. This dynamic environment resulted in the contrasting evolution of regional soil cover and the development of unique soil profiles with the second humus horizon. The second humus horizon is assumed to be a relic from the dark-humus soil formation stage in the mid-Holocene. This article draws conclusions about changes in regional environmental conditions by analysing data from a geochemically interrelated coevolutionary soil series, obtained by using a combination of conventional soil studies, phytolith analyses, and accelerator mass spectrometry (AMS) dating of phytolith-occluded carbon (PhytOC) and humic acids. The results showed that, in general, phytocenoses changed from mire-meadow vegetation towards forest vegetation via the meadow stage. However, these stages had different durations, depending on the soil catenary position. The topographical divergence of soil phytolith profiles reflects the relief effect on the development of specific soil type combinations, accounting for the major elements of the regional mid-Holocene soil cover. The leading elementary soil-forming processes were humus accumulation and hydrogenic accumulation of calcium carbonates. In the hilltop site of Endocalcic Stagnic Albic Luvisols, the evolutionary changes were shown by the shift from the meadow phytocenosis (Calcic Stagnic Chernozem) to the forest phytocenosis. In the midslope site, the environment was more humid from the start, favouring a phytocenosis with features of the meadow-mire type. The shift from the meadow-mire environment (with Spodic Chernic Gleysols) to the forest type environment with leading profile-forming processes, acid hydrolysis and lessivage, was gradual, occurring via the meadow stage with Calcic Stagnic Chernozem. In the toeslope site (Calcic Stagnic Greyzemic Epidystric Umbrisols), the meadow-mire stage (with Spodic Chernic Gleysols) was succeeded by the forest stage of soil formation. The AMS-dating of PhytOC estimated that the dark-humus stage of soil formation began 6.5–5.7 years calBC. Despite the observed slight translocation of phytoliths down soil profiles and phytolith solubilisation, phytolith analysis can be used to reconstruct shifts in the soil formation environment for surface Holocene palaeosols.

Trends of Soil Processes in Natural Landscapes of Mountain and Piedmont Provinces of Dagestan

Data of long-term researches for revealing the trend of modern processes of soil formation and degradation in the mountain and piedmont provinces of Dagestan are given. The aim of the researches was to study the modern soil-erosion and ecologic-ameliorative status of the soil cover and changes in the naturalresource potential of slope lands under the effect of natural and anthropogenic factors over a 50-year period. A strong effect of exogenic and endogenic factors on slope ecosystems results in development of erosion and degradation processes. The soil cover is formed under conditions of intensive geomorphologic, geochemical, and biological processes. The increasing anthropogenic load and climate aridization exert a strong effect on their dynamics. The comparison of data of earlier soil-erosion survey with modern ones shows great changes in the spatial pattern of eroded soils. The areas of noneroded lands became two times smaller over the period of studies. There is a tendency for a decrease in the areas of brown forest soils of a hydromorphic type of soil formation and for enlargement in the area of semihydromorphic and automorphic brown and chestnut soils. A great diversity of soil–plant cover in the areas with vertical zonality is related to differences in slope aspects, topography, and steepness. Soil evolution is characterized by a trend from hydromorphic and semihydromorphic to automorphic stages of soil formation.

Specific features of accumulation of humus in technozems under poplar plantations in the conditions of the Western Donbass

Specific features of accumulation of humus in technozems under poplar plantations in the conditions of the Western Donbass

Pedogenesis Dan Klasifikasi Tanah Yang Berkembang Dari Dua Formasi Geologi Dan Umur Bahan Erupsi Gunung Tangkuban Perahu

The efforts to utilize the agricultural land need a proper understanding of the soil characteristics. The soil characteristics themselves are influenced by the factors that regulate and control the soil forming and pedogenesis processes. The main soil forming factors in this study was the different ages and composition of parent materials from the eruption of Mt. Tangkuban Parahu in West Java. This research was done to comprehend the pedogenesis and to figure out the soil classifications that developed in two geological formations (Qyd and Qvu) and two ages of eruption (Holocene and Pleistocene) of Mt. Tangkuban Parahu. The study was conducted in Ciater, Subang Regency and Jatinangor, Sumedang Regency in West Java Province. The study consisted of four stages: preparation, field survey and soil sampling, laboratory analysis and presenting the report. The results showed that Pedon of Jatinangor consisted of three different stratifications of ages. The clay mineralogical composition was dominated by kaolinite, whereas mineralogical composition of the sandy fractions (heavy fractions) was augite-hypersthene. Pedon of Ciater also consists of three different stratifications of age. The clay mineralogical composition was dominated by allophane, while mineralogical compositions of the sandy fractions (heavy fractions) were green amphibole-hypersthene in the overlying horizons and amphibole-augite in the underlying horizons. The stage of soil formation on both pedon were cambic or viril. The soil classification according to Soil Taxonomy were Acrudoxic Durudands, medial over loamy-skeletal, isohyperthermic in Ciater Pedon and Fluventic Eutrudepts, fine, kaolinitic, isohyperthermic in Jatinangor Pedon.Key words: slow sand filter, activated carbon, silica sand, sand, gravel, zeolite

Exogenous processes and soil formation within a small river basin of Western Transbaikalia in the second half of the Holocene

We determined the sequence of formation of deposits on the first terrace above the Tarbagataika river floodplain, and a change of the sedimentation and soil-formation stages for the last 7 kyr. We reconstructed the accumulation dynamics of the sediment layer and calculated the mean sediment accumulation rates for different time intervals. The phases of intensification of erosion-accumulation and aeolian processes were recorded. The study revealed the main stratigraphic boundaries reflecting the fundamental changes of the settings of sedimentation: 7 cal. kyr BP, a change of riverbed sedimentation for floodplain sedimentation; 5.4 cal. kyr BP, intensification of erosion-accumulation processes due to climate aridization on the Atlantic-Subboreal boundary, and active input of erosion products to the floodplain; 4 cal. kyr BP, active filling of the river valley with horizontally layered polygenetic fine-grained sands and sandy loams containing intercalations of humic warps in conditions of the overlapped (built-up) floodplain with an increase in humidification in the middle of the Subboreal period and, as a consequence, an increase in the height of floods; 3.4 cal. kyr, the layer under investigation leaves the floodplain regime of sedimentation and accumulation of aeolian-deluvial deposits, and 1 cal. kyr, intensification of erosion-accumulation processes due to climatic and anthropogenic changes. We reconstructed the chronology and specific features of the pedogenesis stages which record the phases of temporal cessation of floodplain and slope sedimentation on the study territory. The results obtained are in good agreement with data on the hydraulicity of rivers, the stages of soil formation and on the manifestation of exogenous processes on the territories of Russia and Mongolia.

Стадії ґрунтотворення підвісних ґрунтів Верховинського вододільного хребта Українських Карпат

It was found out that suspended soils in Verkhovyna Dividing Range in Ukrainian Carpathians are intrazonal ones and are formed near dense sandstones outcrops in Krosnenska zone provided excess moisture of flushing type of water regime. Suspended soils are located within the mountain-forest and subalpine zones under moss lichen communities. They form habitats ranging from 0.1 to 1.0 square meter, oval and oblong shaped with the highest capacity of organic horizon in the central part with gradual reduction to the periphery. Suspended soils in Ukrainian Carpathians were mentioned for the first time in writings of Professor A. Zrazhevskyi. Formation of suspended soils in dense sandstones within Verkhovyna Dividing Range can occur in two ways: initial (primary) soil development and settlement of moss lichen communities from adjacent soil areas. Main stages of formation of soils under research are detected analyzing the succession of plant communities and morphological features of each section. Initial stage begins with the settlement of alga, bacteria, fungi, actinomyces, lichens (crustose and foliose) in centres of soil formation and formation of humified layer of dark gray colour up to 2 cm thick. Moss settlement on the developed organo-mineral layer and formation of organic (peat) horizon marks the beginning of development stage. Soils under research with formed organic horizon up to 10 cm thick are to be classified as initial suspended soils. The development stage is accompanied by accumulation of defunct organic remains (peat formation) and expansion of organic horizon (Td+T). Soils formed in Krosnenska zone in mild wind-blown sandstones with organic horizon more than 10 cm thick are at the stage of equilibrium functioning. It is advisable to define these soils as peat-suspended soils. Suspended soils are not represented in the nomenclature list of soils of Ukraine, that encourages conducting more detailed research on their classification. Patterns of distribution of soils under research and stages of soil formation were found out. Key words: Verkhovyna Diving range, suspended soils, the formation of peat, genesis, stages of soil formation.

Pedogenetic interpretations of particle-size distribution curves for an alpine environment

The Qilian Mountains are generally capped by a productive silty soil layer wherever the environment allows. As Holocene loess is prevalent across the Qilian Mountains, we assume that at least some of these fine sediments are derived from loess deposition and that soils across the region may be genetically linked. To test these hypotheses, nine pedons in different landscapes within a typical alpine watershed of the Qilian Mountains were sampled. We also collected fine earth samples from glacier surfaces and crevices of glacial debris in the moraine zone. The particle-size distribution (PSD) is used as a proxy for identifying aeolian fractions in soils. The PSD curves of all of the fine-earth fractions examined are polymodal, although three modal sizes of roughly 16μm, 35μm and 80μm are found in almost all sediments in varying proportions. These modal sizes have been identified as three sources of aeolian sediments in different transport systems. The composition and thickness of loess sediments are related to local site conditions and may be related to the paleoenvironmental history of the site. Clastic debris and vegetation cover serve as dust traps during different stages of soil formation in this alpine environment, and soils grow upward with accumulating loess sediment. Our study demonstrates that PSD curves can be used to determine the origins (and especially aeolian origins) of soils. Furthermore, this study provides insight into the pedology, ecology and paleoenvironmental history of loess-affected ecosystems in alpine areas of the Qinghai-Tibetan Plateau.

A detailed paleomagnetic and rock-magnetic investigation of the Matuyama-Brunhes geomagnetic reversal recorded in the tephra-paleosol sequence of Tlaxcala (Central Mexico)

Geomagnetic reversals are global phenomena, for about 50 years the paleomagnetists attempted to acquire as many detailed records as possible using the magnetic memory of sediments and lava flows. Yet, transitional field behavior remains poorly characterized largely because of sporadic aspect of volcanic eruptions. In some specific cases, paleosols such as those developed from alluvial or aeolian sediments, may also record the variations of the Geomagnetic Field across the polarity changes. Here, we report a detailed paleomagnetic and rock-magnetic investigation on some radiometrically dated chromic luvisols located in Central Mexico carrying detrital or chemical remanent magnetization. The research was developed in order i) to demonstrate the primary origin of the magnetic remanence and ii) to show that paleosoils are good candidates to provide a high resolution record of the behavior of geomagnetic field during reversals. The lower part of the paleosoil sequence shows a clearly defined reverse polarity magnetization followed by geomagnetically unstable transitional field and ended by normal polarity remanence. Our AMS and rock magnetic data suggest that magnetization is acquired during the initial stage of soil formation in context of active volcanic activity since magnetic fabric is essentially sedimentary and reverse and normal polarity paleodirections are almost antipodal. Titanomagnetites are identified as main magnetic carriers of rock-magnetic measurements including thermomagnetics and hysteresis cycles. We propose that the transition recorded in this study correspond to the B-M boundary, considering the K-Ar datings available at the sequence bottom and that the chromic luvisols are potentially good recorders of the paleosecular variation. The identification of the B-M boundary within the studied sequence has fundamental significance for improving the chronological scale of Tlaxcala paleosol-sedimentary sequence and its correlation with the global proxies.