Aeolian Sand Research Articles

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.

Reconstruction of Climate and Environmental Evolution in the Northeastern Tibetan Plateau Since the Holocene Based on Aeolian Sediments

Reconstruction of Climate and Environmental Evolution in the Northeastern Tibetan Plateau Since the Holocene Based on Aeolian Sediments

Middle to late Holocene climate change in the monsoon-dominated southeastern Tibetan Plateau and its relationship with human activity

Aeolian deposits on the southeastern Tibetan Plateau (SETP) can provide evidence of how prehistoric humans were influenced by climatic and environmental changes in high-altitude regions. We present the results of multi-proxy analyses of a middle–late Holocene aeolian section in the SETP, together with the probability density of the ages of various cultural sites within and around the study area. Quartz optically stimulated luminescence dating provides a reliable chronology for this section, and analyses of geochemical elements, color and grain size are used to reconstruct the pattern of climate change during the middle–late Holocene. The results suggest a trend of gradually decreasing moisture from the middle Holocene (∼6 ka) onwards, followed by a slight increase at ∼2 ka, which is supported by TraCE-21 ka simulation results. These changes were closely related to variation in the Indian summer monsoon (ISM) caused by decreasing Northern Hemisphere summer insolation and an increase in the Atlantic Meridional Overturning Circulation. The variations in dust activity are inversely related with moisture and there was a significant decrease in dust activity after ∼2 ka. The drought conditions during the 4.2 ka event recorded within the section appear to be a continuation of the trend of middle–late Holocene climatic deterioration, which is superimposed on a weakening trend of the ISM. The permanent human occupation of the study area after ∼2 ka corresponded to an interval of mild and wet climate when dust activity was relatively weak. An observed correlation between the intensity of human activity and dust storms suggests that the enhancement of human activities played a significant role in increasing the occurrence of dust storms. Overall, our results provide new insights into human-environmental interactions in the SETP.

Orbital forcing of aridity/humidity fluctuations in the Hexi Corridor and Alxa Plateau, NW China, during the last 1.8 million years

The processes controlling aridity/humidity variations in mid-latitude Asia dust source regions on orbital timescales are unclear. Both insolation and polar ice sheets can affect the climate at mid-latitudes, but determining their individual contributions is challenging. Here we present a compilation of paleoclimate data (the content of smectite and aeolian sand, and the proportion of the hydraulic component) from sites in the Hexi Corridor and Alxa Plateau, located at the junction of the regions influenced by the mid-latitude East Asian Monsoon (EAM) and the Westerlies. Our objectives were to determine the links between aridity/humidity variations in this region and Earth orbital forcing and changes in high-latitude ice sheets. We found that the aridity/humidity variations in the Hexi Corridor and Alxa Plateau were paced mainly by the long eccentricity cycle (∼400 ka), facilitating roughly coherent beat in changes of the mass accumulation rate (MAR) and the excursions of thick/coarse loess layers L1, L5, L9, L15 and L24 on the Chinese Loess Plateau. Additionally, spectral analysis of the paleoclimate data revealed that the expression of the Mid-Pleistocene transition (MPT) was spatially variable. A transition between the dominant periodicities in the western Hexi Corridor and Alxa Plateau occurred at ∼0.9 Ma, but in the eastern Alxa Plateau this transition occurred at ∼0.7 Ma. Our data compilation also demonstrates an interval of wet climate in the Hexi Corridor and Alxa Plateau after ∼0.34 Ma, which is consistent with paleoclimate records from loess deposits in Westerlies-dominated Central Asia. We attribute this to insolation forcing via complex internal feedbacks in the Southern Ocean, involving the enhancement of the Atlantic deep-water circulation, and the interplay between Indian Monsoon and the Westerlies. Overall, our findings highlight the importance of the Earth orbital control of aridity/humidity cycles on the boundary of the EAM and the Westerlies in mid-latitude Asia.

Palaeogeographic heterogeneity of large-amplitude changes in marine sedimentation rates during the Carnian Pluvial Episode (Late Triassic)

Major environmental changes marked the Carnian (Late Triassic), including global warming and enhanced hydrological cycling linked to multiple carbon cycle perturbations. These perturbations occurred in an interval called the Carnian Pluvial Episode (CPE), between the Julian 1–Julian 2 boundary and the base of the Tuvalian 2 (late early to middle late Carnian). The CPE is linked to pronounced changes in terrestrial and marine sedimentary basins, with abrupt switches in the sedimentation style and a widespread crisis of carbonate systems. In this study, we have quantified changes in sedimentation rate and the relative variations in sedimentation rate through well age-constrained successions spanning the CPE in different marine basins. Relative to background (pre-CPE) Julian 1 values, during the CPE interval sedimentation rates rose by 142%–3400% in the Julian 2, and then decreased in the Tuvalian 1 in the marine sequences of Western Tethys and Panthalassa. By contrast, in the successions of Eastern Tethys sedimentation rates dropped by 50%–100% across the CPE interval. In the Western Tethys, the high increases in sedimentation rates were coupled with a shift from prevailing carbonate to siliciclastic sedimentation, but a similar lithological shift is associated with a decrease in sedimentation rates in Eastern Tethys. In Panthalassa, higher Julian 2 sedimentation rates can be linked to mineralogical and geochemical evidence of increased input of aeolian dust under arid environmental conditions. The heterogenous changes in sedimentation rate across different basins/regions during the CPE interval indicate that sedimentation was likely controlled by the interplay of different, sometimes local phenomena such as synsedimentary tectonism, sea-level oscillations and climate. However, they could ultimately be related to palaeogeographically different responses to the pronounced environmental changes implied by the Carnian carbon cycle perturbations.

Mechanical transport revealed by optical textures of heavy minerals in aeolian sand: A case study in the Badain Jaran Desert, Northwestern China

Determining whether and to what extent the relative abundance of heavy minerals in original detrital assemblage has been modified by mechanical transport is beneficial for understanding regional historical climate changes and acquiring modern sediment provenance information. Utilizing the frequency of surface mechanical optical textures of heavy minerals may be an effective approach to address this question. However, the connection between the frequency surface mechanical optical textures of heavy minerals and the variations in the relative abundance of these minerals remains uncertain. In this study, 12 modern aeolian sand samples were collected from the Badain Jaran Desert in hyper arid region of northwestern China, characterized by weak weathering to analyze their relative contents of five major heavy minerals. Then, 3796 transparent heavy mineral grains were photographed under the parallel light of a polarizing microscope, and the frequency of 13 surface mechanical optical textures were calculated. The results reveal that the variations in the relative abundance of heavy minerals are substantially influenced by mechanical transport. The decrease in the relative abundance of heavy minerals with weak mechanical stability primarily attributed to mechanical collision. Conversely, the variations in the relative abundance of heavy minerals with strong mechanical stability are primarily influenced by mechanical abrasion. Therefore, mechanical transport impact on the relative abundance of heavy minerals in regions with weak chemical weathering. Establishing heavy mineral characteristic indices for provenance studies using the relative abundance of mechanically unstable minerals may not directly indicate transport distance but rather the strength of wind forces, which have significant potential in palaeo wind regime studies. This study expands the research field of sediment surface micromorphology and has potential applications in inferring past climate changes and determining modern sediment provenance.

Modelling the paleopedological development of loess/palaeosol sections using discriminant function analysis of compositional geoscience data, case study in Eastern Croatia

Previous studies on the mineralogical differentiation of Pleistocene loess/palaeosol sections focused on the description and source material of four loess/palaeosol sections located on the eastern border of Croatia along the Danube: Zmajevac, Zmajevac I, Erdut and Šarengrad. The authors demonstrated the decreasing influence of the Danube and the increasing influence of the rivers draining the Central Bosnian Mountains of the Dinaric Ophiolite Zone both important source areas for aeolian sediments at the southern edge of the Carpathian Basin that transport material from the Central Bosnian Mountains. The aim of this research is to identify the palaeoclimatic factors that influenced the pedogenetic development of the studied palaeosols. The model was created based on the research results of the same four loess/palaeosol sequences in Eastern Croatia. This model can also be applied in other locations to determine the influence of certain climatic factors on the degree of pedogenetic development of individual palaeosols. The loess/palaeosol sequences were divided into eight comprehensive groups (horizons) based on their genesis, degree of pedological development and/or position in the soil profiles. The explanation of the typical patterns occurring between the studied horizons is based on the construction of a Discriminant Function Model (DFM) resulting from the analysis of the compositional data (CoDa) of the geochemical (major and trace elements) and granulometric (grain size) data of the loess/palaeosols in combination with external variables such as weathering coefficients and chemical soil properties. In the final phase, the DFM was transformed from structural (mathematical) to functional (process) terms. This revealed that three main themes dominate the formation of Pleistocene loess/palaeosol sequences: 1) the separation of well-developed palaeosols from parent material; 2) the separation of automorphic palaeosols from hydromorphic soils exposed to post-pedogenic waterlogging conditions; and 3) the differentiation of horizons (soils and alluvium) formed by the redeposition (by water or mudflows) of previously deposited aeolian material, regardless of whether and to what extent it was exposed to post-sedimentary pedogenesis.

The influence of aeolian sand on the mechanical properties of cement stabilized crushed stone

The utilization of aeolian sand resources for road construction is a specific measure to develop green and low-carbon transportation, and also conforms to the concept of green and sustainable development of roads in China. Based on this, the feasibility of using aeolian sand as a substitute for fine aggregate for cement stabilized graded crushed stone was explored, and the effects of different aeolian sand dosages on the unconfined compressive strength, bending and flexural strength, and splitting strength of cement stabilized crushed stone mixtures were studied. The results indicate that the addition of aeolian sand has a significant deterioration effect on the mechanical properties of cement stabilized graded crushed stone mixtures. The larger the amount of aeolian sand added, the more severe its impact on the mixture. Therefore, controlling the amount of aeolian sand within 6 % can meet the mechanical performance requirements. To ensure the large-scale utilization of aeolian sand resources, future research can comprehensively consider the shrinkage characteristics, durability, and water stability of cement stabilized crushed stone mixtures, and further recommend the maximum dosage of aeolian sand.

East Asian monsoon and westerly jet driven changes in climate and surface conditions in the NE drylands of China since the Late Pleistocene

The East Asian summer monsoon (EASM) is a major component of the global climate yet, the causes for the past spatiotemporal variability of EASM rainfall, its interactions and impacts remain unresolved. Here we use the Sr–Nd isotopes and rare earth elements composition of dust in a peat record from northeast (NE) China to investigate the relationship between aeolian dust, the East Asian monsoon and Westerly Jet (WJ) over East Asia since the Late Pleistocene (14 cal ka BP). The NE drylands of China dominate the dust fraction (Hunshandake, Horqin; 44–88%) with a contribution from the deserts of NW China (Badain Jaran, Tengger, Taklamakan; 10–44%), suggesting an influence of the WJ. Dust deposition varied during the Holocene, displaying a minimum between 8.0 and 6.0 cal ka BP and two peaks at 5.8–3.8 and 1.7–0.3 cal ka BP. Changes in dust flux are opposite to the East Asian winter monsoon intensity profile, suggesting a limited influence of the winter monsoon. The EASM appears to have played a more significant role in the dust cycle, with increasing dust fluxes corresponding with lower EASM precipitation. Variations in dust flux from NE drylands display shifts reflecting changes in EASM precipitations and dune activity along the EASM margin, where the dust originates from. To account for the influence of the WJ, we propose that the meridional position and intensity of the WJ also affected dust emission in the drylands’ region. A more northward position of the WJ allows the EASM front further north, generating more precipitations over the NE drylands, reducing the extent of arid areas, and resulting in less dust emission from dune activity, while the opposite occurs with a strong, more southerly WJ. Anthropogenic activities are likely to have had an increasing impact on the dust cycle over the late Holocene. Nevertheless, the presence of inconsistencies in records, coupled with a simultaneous decline in climatic conditions (mainly precipitations) during the same timeframe, hinders the precise assessment of the influence of human activities on dust emissions in the region.

NMR-based analysis of fractal characteristics of the pore structure of fully aeolian sand concrete under carbonation-dry-wet cycles

The evolution law of the pore structure of concrete is important for the study of concrete durability. To study the quantitative relationship between pore structure and macroscopic mechanics of aeolian sand concrete(ASC) under carbonation-dry-wet cycle(DWCs), the fractal characteristics of ASC under carbonation DWCs were analyzed by means of nuclear magnetic resonance(NMR) technology. The results showed that the carbonization product CaCO3 filled the pores and the compressive strength of ASC increased as the carbonization time increasing. When the DWCs was 0 times, the compressive strength of C1 and C2 groups increased by 9% and 13.6%, respectively, compared with C0. The compressive strength of C0 and C1 groups reached the maximum value when the DWCs was 40 times, while the C2 group reached the maximum value when the DWCs was 20 times. Compared with C0, the compressive strength of C1 and C2 increased by only 4% and 6%, respectively, after 100 DWCs. The fractal dimension Dmax reflected the proportion of harmless and multiple harmful pores in the damaged ASC. The fractal dimension Dmax was proportional to the proportion of harmless pores, and the correlation coefficient was 0.9303. The fractal dimension Dmax was inversely proportional to the proportion of harmful pores, and the correlation coefficient was 0.9565. The macroscopic mechanical properties were mainly affected by harmless pores and harmful pores, while the influence of less harmful pores and harmful pores was weak. This study will provide a theoretical justification for the use of ASC in practical engineering.

Foreign Experience Review on Engineering Protection of Seashores and Hillslopes

Introduction. During design, construction and operation of buildings and structures in the coastal areas there arises a serious problem of engineering protection of coasts and hillslopes from the dangerous geological processes, which include the coastal erosion, underflooding of territories, hillslope erosion, gravitational (slope) processes, such as intensification of landslides, etc. These processes often result in significant economic damage usually related to the non-recoverable loss of valuable coastal territories, deformation of buildings and structures, damage and destruction of the objects of transport and engineering infrastructure. In this regard, the study of the advanced foreign experience in engineering protection of the coastal areas and the evaluation of the possibility of it to be implemented in Russia is a relevant scientific and engineering task.Materials and methods. To prepare the review, the following data was used: field observation data with photographic evidences of the objects of engineering protection of seashores and hillslopes obtained by the authors during a business trip to the People's Republic of China (PRC) in October–November 2023; study and analysis of literature sources in the subject area, including the methods and technologies implemented in the Netherlands, Japan, the USA, Great Britain, Italy; summary and systematisation of the coastal protection methods for further development of their classification and evaluation of the possibility of implementing thereof in the Russian Federation.Research results. The main principles of design, the advanced methods and technologies of coastal protection used in China have been defined. They include: construction of the multi-level protective structures, such as the multiple-row breakwaters of special shape in combination with the stepped retaining walls, the vertical walls consisting of the driven piles, anchoring and spray-concrete covering of the slopes in combination with the metal meshes; terracing in combination with the retaining reinforced concrete (horizontal and vertical) crossbeams; the sloping wave-absorbing reinforced concrete surfaces; the meshy structures and fences combating the Aeolian processes, etc.The main methods used in the Netherlands, Japan, the USA and Italy for comprehensive protection of the large territories have been defined. Such as: the network of dams, weirs, wave breakers, coast paving, regulation of the flows by water locks and barriers, creation of the artificial protective islands; artificial replenishment with sand; creation of the green spaces along the coast; forming the dunes — natural or artificial hills of sand or pebbles located along the coast; creation of the concrete structures, stone jetties, floating constructions and even artificial reefs.The importance of management was emphasised, including the early warning systems for storms and tsunamis, weather and marine condition monitoring systems, as well as dissemination of the warning messages and evacuation plans among the population in the areas of potential threat.Discussion and conclusion. Based on the results of the review, the main conclusions were formulated. The recommendations were given on the possible ways of improving the coastal protection of the Caucasian Black Sea Coast and other coastal areas of the Russian Federation based on the advanced foreign experience.

Contribution of Asian dust into the sediment budget of the Parece Vela Basin over the last 1 Ma: Implications for the climate change in East Asia

By quantifying the deposition of Asia-derived dust in the Western Pacific Ocean it is possible to constrain the consequences of climate change in East Asia. However, the rates of eolian dust deposition and its transport mechanism in the low-latitude Pacific remain uncertain. Core CP19 recovered sediment dating from ∼1 Ma to the present in the Parece Vela Basin (PVB). In this study we present bulk-rock major and trace element geochemistry, and Sr and Nd isotopic compositions from this sediment. The results reveal that these clastic sediments are a mixture of volcanic materials derived from the adjacent island arcs and eolian dust material originating from the arid regions of East Asia. Within the PVB, the proportion of Asian dust in the detrital sediment ranges from 30% to 50%, with an average of 44%. The majority of the dust originated from Eastern Asian deserts. Sr and Nd isotopes indicate that there is a significant increase in the overall proportion of eolian dust in the PVB starting at ∼0.64 Ma, influenced by an enhanced East Asian winter monsoon. In contrast, strengthening of the East Asian summer monsoon led to a decrease in the proportion of the eolian dust from the Ordos deserts. The notable alteration in eolian dust flux to the PVB corresponds to an abrupt intensification of aridity and monsoon climate in the East Asian continent at ∼0.64 Ma, caused by the Middle Pleistocene Climate Transition.

Dynamics of the aeolian landform at the coastal geosite of Parangtritis sand dune area, Yogyakarta

In 2014, Kelud, an active volcano in East Java, ejected ashes (hereafter termed KA; Kelud ash) that reportedly reached as far as Central Java and the Special Region of Yogyakarta (DIY). The KA deposits are observable in, among others, the coastal sand dune area in Parangtritis. Due to the active aeolian process, the KA layers can be found at different depths five years after the eruption. Thus, the KA can be used as a marker of the post-2014 aeolian activities at the Parangtritis dune, which was once classified as a degraded land and later recognized as a coastal geosite, ultimately allowing us to calculate the volume and sand transport rate. The research surveys performed at 25 points discovered volcanic ash layers at 1 cm to 26 cm below the surface. At some observed points, the ash deposits were found on the surface and continuously transported. This research observed an area of 60,000 m2 with an average of 8.5 cm thick sand layers lying above the KA layer. Based on the calculation, the total volume of the transported sand at the Parangtritis sand dune from 2014 to 2019 was approximately 5,100 m3. This volume is considerably small owing to various obstacles in the transport zones. Based on the five-year dynamic of the sand dune, this study suggested that restoration needs to be conducted immediately particularly in eliminating vegetation barriers to maintain the sediment balance (erosion-transport-sedimentation) of the coastal sand dune area.

Effect of pedestrian trampling on aeolian sand dynamics on beach surfaces: An experimental study

Wind tunnel experiments and measurements with the Portable In-Situ Wind Erosion Laboratory (PI-SWERL) were conducted to investigate the effect footprints on a sandy beach have on aerodynamic roughness, physical roughness, and the wind erosion threshold. Footprints parallel and footprints perpendicular to the wind were tested, for bare feet and walking shoes, for a lighter (63 kg) and a heavier (75 kg) person. The data were compared to a flat undisturbed surface, which served as control. Results show that footprints have a significant effect on aerodynamic roughness and on the wind erosion threshold. Aerodynamic roughness is higher, and the wind erosion threshold lower, for footprints parallel to the wind compared to footprints perpendicular to the wind, for footprints produced with bare feet compared to footprints produced by walking shoes, and for footprints made by a heavier person compared to footprints made by a lighter person. The differences with an undisturbed flat surface, for which aerodynamic roughness is small and the wind erosion threshold high, were found to be substantial. Of the measured physical roughness parameters of the footprints, surface area of the imprint showed the highest correlation with aerodynamic roughness. The effect of the volume and the average depth of the imprint on aerodynamic roughness was much smaller or even not statistically significant. The PI-SWERL measurements also suggested that on dry sandy surfaces foot imprints may rapidly disintegrate, even when the wind is only slightly above the erosion threshold. This study shows that when wind erosion models are used to describe and predict the initial phase of wind erosion on sandy beaches, the process of trampling with footprints should at least be considered.

Mangrove development on a remote volcanic island in the South Atlantic

Sueste Bay, in the Fernando de Noronha archipelago (FNA), contains the only mangrove area among the oceanic islands of the South Atlantic. This work aims to reconstruct this mangrove's evolution during the Holocene based on a morphostratigraphic study integrated with palynological and multi-elemental geochemical data, temporally calibrated with radiocarbon dating. The data obtained indicated that, around 8000 to 7000 cal yr BP, well-developed Rhizophora and Laguncularia mangroves established over altered rocks of the Quixaba (phonolites, lamprophyres, basanites, trachyandesites and basalts) and Remédios (basanites, melilite and melanophelinites) Formation, under rising relative sea level, about 2 to 3 m below present. This period was the last record of Rhizophora in the FNA. From 6000 to 3600 cal yr BP, the lagoon system was eroded and significantly retrograded, under rising RSL during at least part of time, leaving clay pebbles scattered in the lower/upper shoreface deposit as the only record of its reworking. This process limited mud/mixed flats near the mouth of the Maceió River. Under a relative stability of RSL from 3600 cal yr BP to the present, a progradation of coastal facies, including beach/foredunes ridges, occurred and allowed the development of the modern lagoon system over swales between aeolian sand ridges. Mangroves were only observed during modern times but in environmental conditions very different from those of the previous occurrence. Indeed, Laguncularia coexists with several invasive plants within the narrow mixed flats associated with a small and almost filled tidal creek, whose siltation may be a product of the artificial damming of the Maceió River to supply public water to the archipelago. This study highlights the complex interactions between natural processes, sea-level changes, and human activities in shaping the coastal evolution of the Fernando de Noronha archipelago over the Holocene.

Mechanical Properties of Aeolian Sand Concrete Made from Alkali-Treated Aeolian Sand and Zeolite Powder.

The aim of this study is to promote the application of the excited zeolite powder (ZP)with aeolian sand powder (ASP) in the field of aeolian-sand concrete (ASC) production. This study utilises NaOH to treat composite cementitious materials containing aeolian sand and zeolite powders, which were used to replace 50% of the cement in aeolian-sand concrete (ASC). Production of alkali-inspired cement-based windswept concrete(AAZC).The mechanical properties of treated ASC considerably improved, especially when the NaOH dosage was 4% by mass. After curing this sample (denoted as AAZC-4) for 28 d, its compressive strength improved by 17.2%, and its split tensile increased by 16.3%. Potassium feldspar and montmorillonite in zeolite powder and SiO2 in the sand were decomposed by OH- and combined with other elements to generate various silicate gels and A-type potassium zeolite crystals inside the concrete. Microscopic examination showed that the gels and crystals intertwined to fill the pores, decreasing (increasing) the percentage of large (small) pores, thus optimising the pore structure. This substantially improved the mechanical properties of ASC. Freeze-thaw salt-intrusion tests showed that the extent of mass loss, degree of damage and loss of compressive strength of AAZC-4 were similar to those of ordinary concrete but were reduced by 36.8%, 19% and 52.1%, respectively, compared with those of ASC. Therefore, AAZC-4 has a sustainable working performance in chloride-ion permeable environments in cold and arid areas.

A quantitative study on the terrestrial input to the tropical Northeast Atlantic

Eolian dust and riverine discharge are identified as two key components of terrestrial input to the oceans. They supply micronutrients to the oceans and modify marine carbon biogeochemistry and global climate through dust-land-ocean interactions. However, it is challenging to accurately constrain regional terrestrial inputs in the past, with currently available models and geochemical proxies. The present study utilizes sedimentary wtCaCO3% records to estimate lithogenic fluxes. The depth-dependance of CaCO3 preservation in the Holocene and Last Glacial Maximum (LGM) sediments in two major basins of the tropical Northeast Atlantic Ocean is described using a carbonate dissolution model. Results show that during the LGM, reduced dust deposition and slight drops of fluvial input are found in the Canary Basin and Cape Verde margins, respectively. To supplement, carbonate deposition during the LGM indicates that the deep subtropical Northeast Atlantic is seized by more sluggish deep waters relative to today.

Mid‐Air Collisions Control the Wavelength of Aeolian Sand Ripples

AbstractThe wavelength of aeolian sand ripples increases with wind velocity, but the cause for this increase remained unclear until now. Using numerical simulations, we find that the relationship between the wind strength and the initial wavelength disappears without mid‐air collisions, which means that mid‐air collisions crucially contribute to the initial wavelength of ripples. As wind strength increases, the average hop length of non‐colliding particles decreases. Affected by the bed surface topography and the non‐uniform mid‐air colliding probability along the wavy surface, non‐colliding particles cause a surface modulated erosion/deposition flux. The first order contribution of the flux fluctuation destabilizes the original bed surface and has a wind‐dependent phase shift with respect to the surface profile. This phase shift leads to an initial wavelength that increases with wind velocity. Based on these findings we derive the scaling law for the initial wavelength of aeolian sand ripples, which agrees well with experimental results. A weak non‐linear relationship between ripple wavelength and wind velocity has been found, especially for large wind strengths.

Changes in the stratigraphic architecture as the response to the Upper Cretaceous tectonic and climatic interplay in the Sanfranciscana Basin, Brazil

During the Cretaceous, the Brazilian Intracratonic Sanfranciscana Basin was characterised by fluvial and aeolian deposition, whose facies, palaeosols, and stratigraphic architecture indicate significant changes in tectonics and climate. This work proposes a low-frequency sequence stratigraphic model, using the facies and palaeosols distribution as the stratigraphic proxy for identifying variations in the accommodation space, sediment supply, and their relationship with the tectonic and climatic events. The Unconformity U-0 was generated by the extensional tectonic processes during the Gondwana breakup in the Early Cretaceous and marked the initial continental sedimentation. The Lower Cretaceous Sequence SF1 overlies this unconformity, constituted by fluvial and lacustrine deposits. From south to north, the unconformity U-1 truncates the top of the Lower Cretaceous Sequence SF1 and the Precambrian basement, respectively. Overlaying Unconformity U-1 are the Upper Cretaceous volcanic rocks, fluvial, and aeolian deposits of the Sequence SF2. Because of the vertical and lateral changes, Sequence SF2 is divided into two sequences, SF2A and SF2B, separated by the regional Unconformity U-2, representing climatic and tectonic changes in the basin. During the late stage of sedimentation of Sequence SF1, the ratio between accommodation (A) and sediment supply (S) was positive in the south and negative in the basin's north. The evolution of Sequence SF2A records a negative A/S ratio, followed by an abrupt change to a positive A/S ratio in Sequence SF2B, leading to the genesis of the regional erosive surface of Unconformity U-2. Sequence SF2B also records increased humidity from arid climatic conditions, marked by the 3D regional distribution of facies and palaeosols, linked to the climatic changes detected in South America for the Late Cretaceous.

Quantitative facies analysis of a fluvio-aeolian system: Lower Triassic Buntsandstein Group, eastern France

Understanding the factors that control the temporal and spatial evolution of the Lower Triassic Buntsandstein Group, eastern France, is important not just for palaeoenvironmental reconstruction but also because it is an important reservoir for the lithium-rich geothermal brines in the Upper Rhine Graben region. The interval of interest in this study, the Lower Grès Vosgien Formation (LGV), is made up of c. 200 m of clastic deposits of mixed fluvial and aeolian origin. Given the proximity between the outcrops and the areas of mineral and heat exploration, this region offers a unique opportunity for quantitative analysis and correlation between outcrops and reservoirs. The LGV is the thickest Formation in the Buntsandstein Group. However, hitherto, no detailed architectural analysis has been published to reveal the controlling factors of its depositional elements. In this study, high-resolution facies analysis was applied to thirteen outcrops, and a core, to quantify fluvial and aeolian depositional architectures, and to comprehend palaeoenvironmental conditions during their deposition. Two facies associations were identified. The fluvial channel facies association, composed mainly of sandstones deposited in poorly confined, occasionally ephemeral channels, corresponds to 93 % of the total thickness. The analysis of >800 sets of strata characterised by lower-, transitional-, and upper-flow regime sedimentary structures, distributed within different architectural elements, enabled the distinction of temporal and spatial variabilities, and an estimate of fluvial palaeohydraulic characteristics. The wind- and water-laid facies association, which accounts for 7 % of the total thickness, records an architecture controlled by a fluctuating water-table level, and ephemeral floods. Results revealed that aeolian dunes and sand sheets accumulated in distinct temporal moments. The vertical trends, recorded in the core, indicate an upward increase in the frequency of intercalations between the two facies associations, and a decrease in the occurrences of thicker cross-bedded sandstone sets of fluvial origin, which, associated with the overall retrogradational stacking pattern of the LGV, is interpreted as the preserved record of a large distributive fluvial system (DFS). The occurrence of laterally extensive aeolian deposits, overlying fluvial deposits, is often associated by authors with periods of relatively more arid conditions at a regional scale. However, evidence indicates channel belt avulsion as an alternative interpretation for the establishment of the two facies associations. The findings enhance the knowledge about the depositional controlling factors in braided fluvial and aeolian systems, and improve predictive models that account for reservoir heterogeneity in accumulated successions of this type.