Sandy Deposits Research Articles

Exploring soil pedogenesis through frequency-dependent magnetic susceptibility in varied lithological environments

AbstractThe use of percent frequency-dependent magnetic susceptibility (χfd%) is well-established for detecting superparamagnetic (SP) components in fine-grained soils and sediments. This study employs χfd% as a direct indicator of pedogenetic processes in soils from the Moroccan Rif region. Three soil transects (T1, T2, and T3), each comprising four soil cores with depths reaching 100 to 120 cm, were sampled from distinct lithological formations within an area subject to moderate to intense erosion. A total of 272 soil samples were collected and analyzed using MS2 Bartington Instruments, providing values to calculate χfd% and identify ultrafine ferrimagnetic minerals (SP, < 0.03 μm). In Quaternary fluvial terraces (T1) soils, approximately 60% of the samples indicate a mixture of SP, multidomain (MD), and Single Stable Domain (SSD) magnetic grains, while 30% contained coarser MD grains. Only 10% of the samples exhibit predominantly superparamagnetic (SP) grains. Soils on marly substrates (T2) showed 90% of samples with a combination of SP, MD, and SSD, and just 10% had SP grains. In contrast, soils from Villafranchian sandy deposits displayed χfd% values exceeding 10% in over 50% of samples, indicating that almost all iron components consist of SP grains. Physico-chemical analyses of the soils in profiles T1, T2, and T3 reveal distinct characteristics, including variations in clay content, organic matter, nutrient levels, and proportions of free and total iron. These results are important for understanding soil evolution and pedogenesis, with profiles T1 and T3 showing advanced development marked by high mineral iron, clay, and organic matter content. In contrast, profile T2 reflects a weak stage, influencing nutrient availability and contributing to overall soil dynamics in the respective profiles. The results of this study suggest that magnetic susceptibilities in these samples primarily originate from pedogenetic sources, revealing significantly advanced pedogenesis compared to T1 and T2 soils. The findings of this study align with previous research on soil erosion and degradation in the region, demonstrating that soils developed on terraces and marly substrates are more degraded and less stable than those on sandy substrates. This study underscores the utility of magnetic susceptibility as a rapid and effective indicator for initial soil assessment and gauging the degree of pedogenesis.

The influence of soil factors on the different vegetation formations of the Dunas Park, Salvador, Bahia, Brazil

This article was conducted in a restinga ecosystem on quaternary sandy deposits of Parque das Dunas, Salvador, Bahia, Brazil; located north of Salvador, this area comprises a landscape formed by different edaphic gradients with varied vegetation formations. An edaphic characterization of the sections of these remnants was carried out to understand the influence of edaphic factors on the distribution of the plant composition of this environment. For this purpose, a transect was delimited perpendicular to the coastline. In this transect, 08 plots of 25x25m were implanted, 100m apart. In the Centre of each plot, a 1m wide and 60 cm deep trench was opened, where soil samples were collected to determine edaphic and granulometric parameters. These samples in each plot followed the distribution of the vegetation formations of this environment. It was found that the different water regimes and topography of the area influence the soil factors, which interferes with the distribution and heterogeneity of the vegetation. The highest levels of fine, very fine and medium sand fractions and calcium and phosphorus were found in the highest portions. These areas, with better drainage, have a higher plant density. There is a lower vegetation density with open sandbanks in lower areas, lower levels of fine, very fine and medium sand fractions, and lower nutrient retention. In these environments, some areas are partially flooded with adapted species. It was also found that most of the plots had a very acidic pH with the presence of exchangeable Al, which could indicate high nutrient unavailability. Thus, the sandbanks' soil conditions influence the vegetation's development, inducing the plant species to develop adaptive mechanisms to maintain their biological organization.

Major tunnel valleys and sedimentation changes document extensive Early Pleistocene glaciations of the Barents Sea

Sedimentary records of Early Pleistocene (~2.6–0.8 Ma) glaciations are sparse on shelves, yet trough mouth fans on adjacent continental slopes provide a continuous record of ice-sheet and climate development throughout the Quaternary. Here, we interpret high-quality 3D seismic reflection data combined with borehole and chronostratigraphic information from a shelf-slope setting in the southwestern Barents Sea to study meltwater and sediment inputs to the deep ocean, focusing on the onset of Pleistocene glaciations. Sandy deposits were brought to the slopes of the high-latitude Bear Island Fan by a preglacial contourite-turbidite system from ⁓2.6–2.4 Ma. Muddy glacigenic debris flows document the first shelf-edge glaciation at ⁓2.4 Ma. From 1.78–0.78 Ma, muddy turbidity-current- and debris-flow-derived sediments were delivered from shelf to slope via six tunnel valleys measuring up to 12 km in width and 200 m in depth. These tunnel valleys and associated downslope deposits formed during the 41-kyr climate cycles of the Early Pleistocene, and evidence abundant channelized, meltwater discharges from these glaciations. Following the mid-Pleistocene transition to 100-kyr cycles, a change in the style of glaciation is suggested by a change in landform and facies associations consistent with a reduced meltwater contribution. This study shows that the Norwegian-Barents shelf was extensively glaciated in the Early Pleistocene, with a first shelf-edge glaciation from ~2.4 Ma.

Paleogeographic reconstruction and sedimentary evolution of tidal-dominated estuarine depositional systems: Insights from the campanian M1 sandstone formation, Oriente Basin, Ecuador

The Oriente Basin is a back-arc basin located east of the Ecuadorian Andes in South America. Evidence suggests that during the Cretaceous period, the basin's margins received a terrigenous shallow marine sedimentation. Due to regional variations in accommodation and depositional controlling factors near a shoreline, the sedimentary environments in the fluvial-marine transitional zones exhibit considerable variability. In this study, we analyzed the sedimentological characteristics of the M1 Sandstone Formation unit (∼83 Ma-72 Ma), which comprises a set of ancient estuarine deposits preserved in the northern part of the basin. We quantified the impact of mixed hydrodynamic processes on the distribution of tidal-dominated estuarine facies and discussed the development conditions and evolutionary processes of an estuarine formation under the background of persistent transgression. Core, well log, and seismic data provide evidence for reconstructing the tidal-dominated estuarine environment. In the core section, we identified 14 lithofacies and 7 major facies association types. The frequent occurrence of sedimentary structures associated with tidal currents indicates that tidal processes extensively reworked the deposits. The spatial distribution trends of facies associations reveal the evolution of mixed hydrodynamic conditions dominated by tidal processes in the estuary and allow us to divide the M1 Sandstone Formation into four depositional periods: the initial development, rapid development, decline, and the post-infilling open coast tidal flat development periods. Furthermore, through a systematic analysis of hydrodynamic conditions and sediment distributions, we identified multiple depositional centers in the tidal-dominated estuary influenced by different hydrodynamic processes. These correspond to the upstream fluvial-dominated tidal point bar depositional region, the middle mixed-energy depositional interaction zone, and the downstream tidal-dominated tidal sand bar depositional region. In these regions, the substantial accumulation of sandy deposits, represented by tidal sand bars, reflects the high accommodation space characteristic of tidal-dominated estuaries. Our findings indicate that the slow subsidence of a broad and gently sloping coastal topography, stable material transport, and sea level change dominated by marine transgression ensured the necessary accommodation for the development of the estuary in the M1 Sandstone Formation. The sedimentological study of the M1 Sandstone Formation provides a case for understanding the sedimentary evolution in fluvial-marine transitional zones.

Landsat Analysis of Terraced Thermokarst Lake Variability on Alaska's Coastal Plain

ABSTRACTThermokarst lakes are abundant across the Arctic landscape. Although they are largely understood to form due to thawing permafrost and subsidence, these lakes exist in a variety of forms, shapes, and sizes. Some lakes across the Arctic exhibit shallow subaqueous terraces. The terraces have previously been shown to maintain permafrost beneath them due to the presence of bedfast ice during most of the year, whereas a talik develops beneath the deeper central pool. However, the formation of these terraces and their prevalence across the Arctic are currently unknown. In this study, we mapped the locations of thermokarst lakes and their terraces in the Alaska coastal plain using Landsat imagery. We found that terraces are larger and more abundant in sandy deposits, occupying an average of 40% of the lake area, compared to 20% of the lake area in non‐sandy lithologies. Terraces are most often found on the eastern and western lake shorelines, likely associated with regional wind directions, forming on the long sides of northwest–southeast oriented lakes. We propose a conceptual model for terrace formation in sandy deposits that describes the growth of shallow littoral shelves that protect the eastern and western shorelines from erosion while allowing lake extension in the northwest and southeast directions. Finally, given the close association between bedfast ice, talik extent, and the shallow subaqueous terraces, we suggest that mapping of these relatively stable terraces may provide insights about talik extent across the Arctic coastal region. Continued warming and changes to lake ice regimes are likely to increase talik extent, which may be easily observable by temporal analysis of terrace abundance and extent in widely available remotely sensed imagery.

VELOCITY AND EVOLUTION OF SHOCK WAVES IN SAND WITH INCREASING WATER CONTENT

Interest in the problems of shock wave propagation in saturated porous media is associated with studying seismic exploration issues, modeling the hummer effect during hydraulic fracturing, studying the water-gas impact on formations for the purpose of efficient oil production, etc. Experimental work on waves in bulk media is usually carried out in shock tubes. Traditionally, shock tubes are used to study the characteristics of the propagation of shock waves in various media, to analyze the wave properties of these media based on the speed of the shock waves and the change in the shape of the pulse along the passage of the first – main pulse. In a shock tube equipped with a section of bulk media, the wave is repeatedly reflected from the surface of the porous medium under study and the upper end of the tube. Re-reflected waves can be used to study changes in the environment that occurred under the influence of a shock wave, i.e. as probing pulses. In this article, sounding is understood as identifying acoustic properties (changing the shape of shock pulse diagrams and their velocities). This paper presents the results of experimental studies of the propagation of shock waves of small amplitude in sand with a volumetric content of liquid in the pore space from 0 to 40 %, and illustrates the influence of the presence of liquid in the pores on the shape of the main and probing pulses. The research was carried out using the Shock Tube installation, in the Laboratory of Experimental Hydrodynamics of the Mavlyutov Institute of Mechanics of Ufa Branch RAS. An increase in the speed of wave propagation was established with increasing water saturation of sand in the range from 0 to 40 %. An increase in the amplitude of reflected waves when passing through sand, the formation of peaks and stretching of pulses were discovered. The research results can be used in processing geophysical data to interpret seismograms of sandy deposits saturated with gas-liquid systems.

Effects of Local Scouring on Load-Bearing Behaviors of Monopile–Friction Wheel Hybrid Foundations on Sandy Deposit Soil under Lateral Loading

Effects of Local Scouring on Load-Bearing Behaviors of Monopile–Friction Wheel Hybrid Foundations on Sandy Deposit Soil under Lateral Loading

Millennial-scale fluctuations of palaeo-ice margin at the southern fringe of the last Fennoscandian Ice Sheet

Abstract. The paper presents the first terrestrial record of millennial-scale palaeo-ice margin oscillations at the southern fringe of the last Fennoscandian Ice Sheet (FIS) during the last glacial cycle. The study area is located in northern Poland close to the last FIS maximum limit. The chronology and dynamics of palaeo-ice margin oscillations at the southern fringe of the FIS are based on combined luminescence and 10Be surface exposure dating. Optically stimulated luminescence (OSL) was used to date sandy deposits (fluvioglacial sediments and aeolian deposits filling fossil periglacial wedges) intercalating basal till layers. The most likely age of the tills was constrained by Bayesian modelling of the sequence of OSL ages and lithostratigraphy. 10Be surface exposure dating was used on erratic boulders left during the final retreat of the last FIS and resting on the surface of glacial landforms. Our results, which are mainly based on OSL chronology and Bayesian modelling, indicate millennial-scale oscillations of the last FIS in northern Poland between ∼19 and ∼17 ka. The last FIS retreated and re-advanced over a relatively short period of time (2–3 ka), leaving lithostratigraphic records (basal tills) of three ice re-advances over a millennial-scale cycle: 19.2±1.1, 17.8±0.5 and 16.9±0.5 ka. Despite 10Be surface exposure ages obtained for 14 erratic boulders being poorly clustered, the main mode of age distribution occurs at ∼18 ka and indicates a possible signal of the ice sheet retreat after one of the re-advances. We explore the dynamics of these oscillations and compare the proposed cycles of the southern FIS advances and retreats with existing patterns of the last deglaciation and millennial-scale fluctuations of the last FIS inferred from marine records.

EARLY HOLOCENE OXYGEN ISOTOPE CHRONOLOGIES (11,267–6420 CAL BP) FROM ICE WEDGE AT CHARA, TRANSBAIKALIA

ABSTRACTAccelerator mass spectrometry radiocarbon (AMS 14C) dating was used for determining the age of wedge ice. It has been found that between 11,270 and 6420 cal BP, or the Greenlandian and Northgrippian stages of the Holocene, ice wedges grew syngenetically in sandy deposits with gravel in the Chara River valley. The variations of δ18O values in the ice wedges are about 8‰, from –25.5‰ to –18.8‰. Based on the stable isotope composition of ice wedges, paleotemperature reconstructions revealed that the mean January temperature was as low as –38°C during the coldest periods of the early half of the Holocene and as high as –28°C during the warmer periods.

Experimental investigation of dynamic behaviour of pile-supported bridges in sandy deposits

This paper presents the results of centrifuge tests performed on reinforced concrete (RC) pile–supported simply supported girder bridge models in non-liquefiable (unsaturated) and liquefiable (saturated) slightly inclined sandy soil sites. The main objectives were to investigate the dynamic response characteristics of RC pile–supported simply supported girder bridges in non-liquefiable and liquefiable soils, examine the mechanisms causing beam collapse and damage to pile–pier yielding, and verify the effectiveness of cable restrainers. The centrifuge tests were conducted in non-liquefiable and liquefiable sites, each consisting of a three-span RC pile–supported simply supported girder bridge model and a control model with a superstructure equipped with a cable restrainer. First, the dynamic characteristic parameters of the soil and structural models in both sites were obtained. Subsequently, the conventional test results were interpreted, including the excess pore pressure ratio, acceleration, and displacement. The analysis included examining the moment demand of the pile–pier structure and seismic damage mechanisms. Finally, a correlation analysis was performed to evaluate the inertial and kinematic effects on the moment demand of the pile–pier structure. The results show that the acceleration response after soil liquefaction at the inclined sites is amplified unilaterally in the downslope direction and spikes appear. The liquefiable foundation is displaced to the downslope. However, major earthquake induces foundation displacement, and liquefaction leads to a longer duration and more significant soil displacement. The installation of cable restraints significantly increased the acceleration response of the superstructure. Still, it effectively reduced the relative displacement of the superstructure and prevented the beam from collapsing. Soil liquefaction decreases the bending moment of the pile–pier structure, and the cable restrainer causes the damage mode of the pile–pier structure to shift from the pile head to the pier bottom. In the non-liquefiable scenario, the bending moment demand at the pile head has a more significant influence on the inertial effect. Additionally, using the cable restrainer system can increase the kinematic effect after liquefaction. The test results can be used to validate numerical models and provide a reference for pile foundation design.

Revisiting a proof of concept in quartz-OSL bleaching processes using sands from a modern-day river (the Séveraisse, French Alps)

Conditions of sediment transport and deposition in highly dynamic fluvio-glacial environments enhance incomplete bleaching of luminescence signals during sunlight exposure. Whatever the geomorphic context or application, partial bleaching has been widely reported and remains a methodological limitation for application of Optically Stimulated Luminescence (OSL) dating methods, potentially resulting in sediment-burial age overestimation. This study focuses on the highly dynamic Séveraisse River (SW French Alps) where modern-day alluvial sands of a braided reach were sampled to assess the degree of quartz-OSL partial bleaching associated with superficial pre- and post-deposition geomorphic processes. Our original approach combines (i) a photogrammetry-based survey, (ii) sediment grain-size analysis, and (iii) measurements of both portable OSL luminescence signals and conventional quartz OSL equivalent doses in modern superficial (from 0.1 to 1 cm) and sub-surface (up to 30 cm) alluvial sands exposed to sunlight for at least 19 days. Our results show high but spatially variable residual luminescence signals at the surface, measured in all grain-size fractions with both the portable luminescence reader (≥5 x106 cts/g) and conventional quartz-OSL doses (≥80 Gy), even within the uppermost millimetres of the exposed alluvial surface. Our data thus highlight poor luminescence bleaching in the Séveraisse's modern sands, during both pre-depositional transport and post-depositional exposure. In addition, our study reveals, for the first time, the significant sunlight attenuation over a few millimetres within modern alluvial sediments, perhaps conditioned by dark sand grains, and/or by superficial blanketing by silts (i.e. waning flow stage) that leads to a porosity decrease and very low sunlight penetration. We suggest the occurrence of a critical sediment layer (i.e. only a few mm thick) that could play a key role in bleaching processes for alluvial surfaces, with strong implications for our understanding of residual doses in braided systems' sandy deposits and the dynamics of such alluvial surfaces.

Albian sedimentation in western Atlas, Morocco

Detailed study of field sections and extensive ammonite collection allowed to specify the sedimentary evolution and age of the Albian series of the Western Atlas (Morocco). After a significant hiatus of earliest Albian age, the Albian transgression began in the late Douvilleiceras leightonense Zone with partly clastic deposits. A transgressive pulse gave way to clayey marl deposits (Douvilleiceras mammillatum Zone), which evolved upward to partly carbonate, laminated deposits of late early Albian to earliest middle Albian age (Lyelliceras pseudolyelli to early Lyelliceras lyelli zones). A major hiatus that encompassed most of the middle Albian, was followed by a new transgression marked first by sandy deposits (Dipoloceras cristatum and Pervinquiria pricei zones), and then by clayey marl and limestone nodules (Pervinquieria inflata Zone). A sharp sea level fall (late Pervinquieria inflata to early Pervinquieria fallax zones) led to the development of a shallow marine carbonate shelf (Kechoula Formation). A last transgressive pulse allowed deposition of outer shelf clayey marls (Pervinquieria rostrata to Arrhaphoceras briacensis (?) zones), interrupted near the Albian-Cenomanian boundary by a sea level fall and hiatus. Anoxic to disoxic conditions are recorded in the latest early Albian and the late Albian, which correlate with the Leenhardt and Breistroffer levels, respectively. Correlations with Albian successions in North Africa and southern Europe suggest a mainly eustatic origin for the most important sedimentary discontinuities, although the late Albian sea-level drop may be tectonically enhanced.

Gravity tectonics controls on reservoir-scale sandbodies: Insights from 3D seismic geomorphology of the canyons buried in the upper slope of the Eastern Niger delta basin

High-resolution 3D seismic data analysis was integrated with a calibrated well and biostratigraphy data to present the first overview of a buried Pleistocene canyon system on the upper slope of the eastern Niger Delta, the Galabor Canyon. Attribute maps of specific horizons allow documenting the changing morphologies and infill lithologies of two main branches of the canyon through two stages of activity separated by a reference horizon dated at 0.99 Ma based on well calibration. At the upper slope, growth faults dissect the canyon heads, the catchment of which encroaches a network of valleys incised on the outer shelf. The canyon fill is composed of muddy channels and mass-transport deposits, largely derived from the collapse of canyon walls and sand-rich bodies forming a tract sourced by shelf-edge deltas at the outlet of the incised valleys. High-density turbiditic processes likely control the distribution of sand bodies along the canyon, ranging from tributary fans on the upper slope to 6 km-wide meander belts on the middle slope. The sandy deposits accumulate in minibasins formed along the canyon path, downstream of the subsiding hanging wall of the growth faults and upstream of shale ridges that damp the flow in the canyon. These results show that canyons can be major targets for sand reservoir exploration on the upper slope of large muddy deltas.

Sand liquefaction in simple shear tests

Liquefaction is a phenomenon marked by a rapid loss of soil strength and stiffness, which generally occurs in loose saturated sandy deposit during earthquake because of the generation of excess pore water pressure. Several experimental researches concluded that liquefied soil behaves as a fluid during ground movement, but after the earthquake motion ceases, due to the dissipation of excess pore water pressure, the liquefied soil recovers its initial stiffness and returns to behave as a solid. Liquefaction resistance of sandy soil can be studied by means of Cyclic Simple Shear (CSS) test or Cyclic Triaxial (CTX) tests. While CTX tests are widely used in liquefaction studies due to their simplicity, CSS tests are more representative of stress conditions produced during an earthquake by simulating the continuous rotation of the principal stress axes. In this research the preliminary results of CSS tests carried out with confining rings on the sandy samples retrieved in the South of Sicily are reported. The apparatus is described in detail. All samples used were obtained from the same type of Italian sand by using same preparation method to minimize the number of factors influencing the results. Moreover, all tests were conducted by a single operator. All experimental results are reported in the plane cyclic resistance ratio (CRR) and number of cycles where liquefaction occurs (Nliq) in order to assess the liquefaction phenomenon.

Karst Rock Relief of Qara and White Desert (Western Desert of Egypt)

The karst rock relief clearly reveals the ways in which the karst surface and caves have been shaped and how they have developed. The oldest traces are the rock features of old karst caves, which were formed under climate conditions entirely different from the current ones, i.e., in the Pleistocene, and which have been dry for a longer period of time. Today, the wind is the prevailing factor in shaping the rock on the surface and in the karst of the White Desert near Farafra in particular, where we can witness the development of an entire range of wind rock features which helps us sort and classify them logically. However, in the wadis near the Qara Oasis a unique rock relief is forming, in which traces of water flow and dissolution of the rock under the sandy deposits are utterly predominant. The rainfall volume is low, however, the heavy rainfall events lasting short periods of time are enough to shape the less resistant rock. The rock features dominating the walls are co-shaped by dissolution and aeolian erosion. Crust forms on those parts of the rock surface that come in contact with water. The bare surfaces, on the other hand, are carved out by the wind. In the places where the crust has flaked off, the wind carves out cups.

Origin of the Badar Sand Field and the late pleistocene tectonic movements in the Tunka depression, the Baikal Rift Zone, Eastern Siberia

The Badar Sand Field is a geomorphological phenomenon representing a dome structure that dominates the topography of the subsiding Tunka Depression in the SW Baikal Rift. Many interpretations of its origin, including tectonic uplift, have been proposed, but the question remains open. We propose a new model to explain its genesis, based on a thorough analysis of both new and previously published geomorphological and sedimentological data. We suggest that the accumulation of the Badar Sand Field occurred in two stages: aquatic and aeolian. The lower part of the sandy deposits accumulated during the long-term existence of a landslide-dammed paleolake within the Tunka Depression. The upper part was formed after the drainage of the paleolake due to aeolian redeposition of sands. New results of OSL-dating from the vertical 40-m geological cross-section “Badar” showed that the accumulation of lake sediments occurred in the period 24–15 thousand years ago (MIS2). Based on the analysis of satellite images, we modeled the paleolake and determined that it arose as a result of landslides that dammed the antecedent section of the Irkut river valley in the Elovsky Spur. The analysis of the Irkut river terraces showed the absence of tectonic uplift within the Tunka Depression in the Holocene. The incision of the Irkut River at 40–90 m into the Badar dome occurred as a result of the restoration of equilibrium in the longitudinal profile of the river due to changes in sedimentation conditions in the post-glacial period.

Effects of local scouring on the bearing capacity of monopile-wheel composite foundations in sandy deposit

The monopile-friction wheel composite foundation is an innovative offshore wind turbines (OWTs) foundation type for its good bearing properties and anti-erosion advantages. The local scouring is a non-negligible challenge by moving surrounding soils away till even some engineering disasters. To explore this kind of unfavorable effects, we model the response of scouring to the bearing capacity of the composite foundation by means of laboratory flume tests. Furthermore, the influence of different loading sequences (i.e., T→H or H→T) is considered, and the failure envelopes are also obtained. On this basis, a 3D finite element model is established to investigate the impact of key scouring parameters and different loading point heights on the bearing capacity. The conclusions are as follows: local scouring can significantly reduce the bearing capacity; the scouring depth has the most significant effect, followed successively by the scouring angle and extent; compared with pure horizontal foundations, the ultimate torsional bearing capacity of the foundations under the combined T→H loading sequence decreases by about 1.95%–11.1%, while the horizontal bearing capacity under the combined H→T loading sequence decreases by about 0.82%–1% compared with pure torsional foundations; the loading point height has noticeable effects on the lateral resistance for the composite foundation.

DEVELOPMENT OF A REFERENCE TRANSECT BASED ON GPR DATA FOR WETLANDS IN THE SOUTHEASTERN PART OF THE ONEGA LOWLAND<a href="#FN2"><sup>2</sup></a>

The post-glacial development of the Lake Onega coast, together with modern processes, creates conditions for the formation of complex coastal ecosystems that may be vulnerable to possible climate change and anthropogenic impacts. Such systems include wetlands extending along the eastern and southern coasts of Lake Onega. The area of a special interest is near the mouth of the Andoma River, as it combines the influence of the riverbed processes of a large river, the dynamics of the coast of Lake Onega, and peat lands development. The aim of the research was a detailed study of the structure of the Holocene deposits in the lake-river interval on the northern bank of the Andoma River, which reflects the stages of formation and variability of the natural conditions of the lakeside lowland. A reference transects including 4,800 m long GPR profile, supplemented with boreholes was created. The complex study of GPR cross-section and peat cores revealed the internal structure of the peat bog. A plateau-like uplift of the mineral base of the bog, framed by rupture zones with accompanying watercourses, was found. This area is considered as a deformation formed because of glacial dislocations or because of neotectonic deformations. Besides the main structural elements, local erosion incisions accompanied by sandy deposits, which could be confined to the buried paleochannels of the Andoma River, were found at the top of the limno-alluvial sediments. Analysis of the complex transect together with a vegetation description showed a difference in biological and environmental conditions zones, which contribute to biological diversity of the study site. In the future, the reference transects development provides a basis for the initial identification of vulnerabilities and long-term monitoring of the ecological transformation of ecosystems.

CAUSES OF THERMAL SUFFOSION ATTENUATION ON THE BESTYAKH TERRACE OF THE LENA RIVER, CENTRAL YAKUTIA

This paper presents the results of thermal suffosion study in the Ulakhan-Taryn Creek valley, Central Yakutia, where intrapermafrost groundwater is discharged. Interpretation of satellite images and analysis of field data from landscape surveys, electrical resistivity tomography studies and ground temperature observations were used to determine the factors contributing to the attenuation of thermal suffosion in sandy deposits of the IV (Bestyakh) terrace of the Lena River. Successional stages of revegetation in the accumulation zones of sands washed off by subsurface flow were examined. Vegetation succession was found to modify geocryological conditions in the groundwater discharge area, sometimes leading to its complete freezing. Conditions favorable both for permafrost aggradation and degradation may develop, depending on the landscape type. Ground temperature data indicate that the active layer thickness in sands at a thermal suffosion site covered by sparse pine forest is 3.5 m, while the mean annual permafrost temperature at the depth of zero annual amplitude is –0.2°С. In 2014, a subaerial talik began to form at this site, the bottom of which lowered from 3.5 m down to 6.0 m. At a larch site with tussocks, the active layer thickness is within 0.5–0.8 m and the mean annual permafrost temperature is about –2.0°С. An ERT survey provided information on the current permafrost and groundwater conditions, where groundwater discharge has ceased. A scenario is proposed describing the changes in the discharge area caused by permafrost disturbance above an aquifer. Formation of an underground cavity and collapse of the overlying permafrost layer resulting in characteristic depressions and sinkholes at the surface promote ground freezing in the discharge zone. Mechanical blocking the flow paths reduces the flow velocity promoting the restoration of permafrost and cutting off the area of soil removal by thermal suffosion. Further on, this attenuates the thermal suffosion. Its active phase can shift spatially due to thawing the pore ice in the permafrost in contact with the confined aquifer, widening soil voids and forming new flow pathways. Thus, attenuation of thermal suffosion on the Bestyakh Terrace of the Lena River results from the combination of internal (impeded flow) and external (vegetation succession) factors.

Heinrich Stadial 1 continental sand dunes and Middle to Late Holocene paleosol sequences in SE Iberia: Implications for human occupation and site formation processes

Continental aeolian sandy deposits are common in the semi-arid Mediterranean biomes of the Iberian Peninsula. Very few studies, however, have addressed their chronology, formation, and evolution. In this work, we present the interdisciplinary study of the Villena dune field (SE Iberian Peninsula) for which sand dune-paleosol sequences spanning the Last Glacial to the Late Holocene have been documented. The surface area of the Villena dune field and the dune morphology were mapped using LIDAR elevation data. Three different stratigraphic sequences were analyzed through geochronology (OSL and AMS C14), micromorphology,soil chemistry, grain size and X-ray powder diffraction. The formation of the Villena dune field was OSL dated between 16.3 ± 0.6 and 14.97 ± 0.5 ka during the Heinrich Stadial 1 (HS1). Deflation, diffuse floods and runoff processes led to the removal of GS-1 and Early Holocene sediments from the stratigraphic sequences. Subsequently, discontinuous polycyclic soil sequences developed on the dune top sections from the Middle to the Late Holocene. Three main pedogenetic processes linked to palaeoenvironmental shifts –organic matter accumulation, calcium carbonate redistribution and periglacial features– were documented in two soil sequences registered in the stratigraphies investigated, which also included sedimentary hiatuses. Our work identified for the first time: (i) the formation of continental dune deposits spanning the HS1 on the Iberian Mediterranean region; (ii) sedimentary dynamics helping to understand Early to Late Holocene archaeological site formation processes in this area; and (iii) periglacial features dated the Little Ice Age.