Fluvial Sediment Samples Research Articles

Textural characteristics of fluvial sediments in the Kosi River Basin, Bihar, India

The fluvial sediment samples collected from the Kosi River Basin, Bihar were subjected to textural analysis. The textural parameters were computed using the appropriate phi values. Statistical metrics including mean, standard deviation, skewness, and kurtosis were estimated. From the findings, the mean size of river sand has been observed from medium to fine-grained nature (between 0.97 Φ and 2.72 Φ). Within the range of 0.50 Φ to 0.77 Φ, the standard deviation denotes a moderately well-sorted to moderately sorted nature. The sediment samples exhibit skewness values ranging from -0.344 Φ to 0.267 Φ. The Kurtosis varies between 0.86 Φ and 1.9 Φ, indicating a leptokurtic to mesokurtic nature. Thus, the statistical measures have revealed that sediments are dominant in the medium sand category, moderately well sorted, finely skewed, and fall under leptokurtic character. The bivariate plots constructed between the statistical metrics indicate the unimodal nature of sediments.

Assessment of hydrological, geological, and biological parameters of a river basin impacted by old Hg mining in NW Spain

Mercury (Hg) is a toxic metal that can cause adverse effects for the health of ecosystems. The Caudal River is one of the main rivers in the Asturias region (NW Spain), whose basin is highly anthropized, hosting several Hg mines, closed in the last century. Arsenic (As) is also found in the mineral paragenesis of the Hg deposits, posing a greater environmental risk. In the mining sites, remaining old facilities and tailings continue to release these elements into the environment. In this work, samples of fluvial sediments and water were taken, both in areas affected by anthropic activity and in pristine areas, in order to establish the background levels for the critical elements. The mineralogical study of the sediments, combined with EDS microanalysis, is useful to identify mineralogical traps such as Fe oxides or clays to retain the As. The As content in all sampled sediments is above the threshold effect levels (TEL), the possible effect range within which adverse effects occasionally occur, according to the Canadian Sediment Quality Guidelines for the Protection of Aquatic Life. This fact is related to a naturally high geochemical background in the basin, due to the existing mineral deposits. The PEL threshold (the probable effect range within which adverse effects frequently occur) is exceeded by more than an order of magnitude in the sediments downstream of the Hg mines. In these points, the As content in the water, exceeding 700 μg L−1 As, is also above the quality standard established in Spanish legislation. As a result, the Caudal River tributaries in the lower part of the basin do not reach a good ecological state, according to the Hydrological Planning Office, and in some cases their state is deficient, showing low richness and high dominance of macroinvertebrates. Although the concentrations decrease with distance from the source, these findings justify the low ecological quality of the affected watercourses.

Composition of Rare Earth Elements in Fluvial Sediments of the Lesser Zab River Basin, Northeastern Iraq: Implications for Tectonic Setting and Provenance

During the past few decades, rare earth elements (REEs) have gained enormous attention in geochemical studies worldwide as a result of their important role in the manufacturing of high-tech equipment. REEs in river sediment have been widely used for provenance determination and in geochemical studies of continental crust, rock and sediment environments, and anthropogenic pollution. This study aims to elucidate the origin and tectonic setting of Little Zab River Basin (LZRB) sediments by examining 23 fluvial sediment samples of rare earth elements (REEs) collected from both the primary river and the inter-sub-basin regions during the rainy or high-flow season. The ICP-MS method was employed to analyze all samples to identify and assess the compositions of REEs. A fraction of the river sediments, smaller than 2 mm, which is more representative and more homogeneous, was used to carry out geochemical analysis. REE concentrations in the Little Zab River (LZR) and the upper parts of the LZRB were generally higher than those in the lower parts. The concentration of REEs in nearly all samples was lower than that of the North American Shale Composite (NASC), and the Upper Continental Crust (UCC), except for the sub-basin sediment Sbs2, which was higher than these references; also, the sediment sample Zrs4 was slightly higher than NASC. Light rare earth elements (LREEs) display enrichment relative to heavy rare earth elements (HREEs) with a range between 7.15 μg/g and 12.37 μg/g for LZR samples and between 5.95 μg/g and 13.03 μg/g for the sub-basin samples. The REE discrimination diagrams, along with the chondrodite-normalized pattern of the studied sediments, confirm that the sediment is predominantly sourced from the alkaline basaltic unit of the late Cretaceous Walsh group of an arc tectonic affinity.

Petrographic composition and heavy minerals in modern river sand: A global database

AbstractIn the case of modern river sediments, source rocks, tectonic setting, and climatic and geomorphological conditions are fully known, diagenetic effects are by definition none, and physical and chemical processes during erosion, transport, and deposition can be investigated directly in any required detail. Their study thus provides the fundamental information needed to understand the impact of various controls on sediment generation and sediment routing systems in diverse geological settings. With the growing interest in source‐to‐sink sedimentary systems for economic purposes, researchers have focused more and more on modern environments, producing an ever‐increasing amount of compositional data on river sediments. To better integrate and utilize these large datasets, we systematically compiled a global database of 4,208 fluvial sediment samples compiled from 100 published papers, book chapters, and dissertations and included 3,747 petrographic and 1,943 heavy‐mineral analyses. The analysed samples are mostly located in Asia, Africa, Europe, and South America, with fewer examples from North America and Oceania. Each sample is complemented by metadata describing references, river name, geographic location, sampling date, analytical method, and grain size, so that samples can be grouped and filtered to meet different needs including comparison with other datasets.

A strontium isoscape of northern Australia

Abstract. Strontium isotopes (87Sr/86Sr) are useful to trace processes in the Earth sciences as well as in forensic, archaeological, palaeontological, and ecological sciences. As very few large-scale Sr isoscapes exist in Australia, we have identified an opportunity to determine 87Sr/86Sr ratios on archived fluvial sediment samples from the low-density National Geochemical Survey of Australia. The present study targeted the northern parts of Western Australia, the Northern Territory, and Queensland, north of 21.5∘ S. The samples were taken mostly from a depth of ∼60–80 cm in floodplain deposits at or near the outlet of large catchments (drainage basins). A coarse (<2 mm) grain-size fraction was air-dried, sieved, milled, and digested (hydrofluoric acid + nitric acid followed by aqua regia) to release total Sr. The Sr was then separated by chromatography, and the 87Sr/86Sr ratio was determined by multicollector inductively coupled plasma mass spectrometry. The results demonstrate a wide range of Sr isotopic values (0.7048 to 1.0330) over the survey area, reflecting a large diversity of source rock lithologies, geological processes, and bedrock ages. The spatial distribution of 87Sr/86Sr shows coherent (multi-point anomalies and smooth gradients), large-scale (>100 km) patterns that appear to be broadly consistent with surface geology, regolith/soil type, and/or nearby outcropping bedrock. For instance, the extensive black clay soils of the Barkly Tableland define a >500 km long northwest–southeast-trending unradiogenic anomaly (87Sr/86Sr <0.7182). Where sedimentary carbonate or mafic/ultramafic igneous rocks dominate, low to moderate 87Sr/86Sr values are generally recorded (medians of 0.7387 and 0.7422, respectively). Conversely, In proximity to the outcropping Proterozoic metamorphic basement of the Tennant, McArthur, Murphy, and Mount Isa geological regions, radiogenic 87Sr/86Sr values (>0.7655) are observed. A potential correlation between mineralization and elevated 87Sr/86Sr values in these regions needs to be investigated in greater detail. Our results to date indicate that incorporating soil/regolith Sr isotopes in regional, exploratory geoscience investigations can help identify basement rock types under (shallow) cover, constrain surface processes (e.g. weathering and dispersion), and, potentially, recognize components of mineral systems. Furthermore, the resulting Sr isoscape and future models derived therefrom can also be utilized in forensic, archaeological, palaeontological, and ecological studies that aim to investigate, for example, past and modern animal (including humans) dietary habits and migrations. The new spatial Sr isotope dataset for the northern Australia region is publicly available (de Caritat et al., 2022a; https://doi.org/10.26186/147473).

ASSESSMENT OF THE QUALITY OF RIVER SEDIMENTS IN BASELINE NATIONAL MONITORING STATIONS OF 12 COUNTRIES IN THE DANUBE RIVER BASIN

Fluvial sediment samples (river bottom sediment, suspended sediment and active floodplain/overbank) were collected in 2 baseline stations of the Transnational Monitoring Network for each of the 12 countries in the Danube Basin Region: Austria, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, Hungary, Republic of Moldavia, Montenegro, Romania, Republic of Serbia, Slovakia and Slovenia, according to a harmonized methodology. The sediment samples were analyzed for selected hazardous substances (HSs): 8 metals, 8 polycyclic aromatic hydrocarbons (PAHs) and 6 pesticides in an accredited laboratory selected as reference laboratory, as well as in national laboratories. Risk ratios were computed in order to compare the results to the Environmental Quality Standards listed in the European Directives, to the national threshold values in the Danube Basin, and to other available international European and American quality standards, and the risk ratios were classified as background, alert and intervention values for readily evaluation. Results show widespread metal(oid) (As, Cd, Cu, Hg, Pb, and Zn) contamination in the Danube Basin, most often associated with historic mining. Concentration values of Ni and Cr exceeding the thresholds are caused by the geological background (ultrabasic and metamorphic rocks in Bosnia and Herzegovina, Republic of Serbia and Romania). Concentration values higher than the thresholds for some of the PAHs (e.g. Fluoranthene) and sometimes for Total PAHs were also noted almost in every countries, caused by industrial activities, wastewater discharges or navigation on the Danube River. Pesticides were below the detection limit or below the legislative intervention thresholds at all national baseline sampling sites.

OCTOPUS database (v.2)

Abstract. OCTOPUS v.2 is an Open Geospatial Consortium (OGC) compliant web-enabled database that allows users to visualise, query, and download cosmogenic radionuclide, luminescence, and radiocarbon ages and denudation rates associated with erosional landscapes, Quaternary depositional landforms, and archaeological records, along with ancillary geospatial (vector and raster) data layers. The database follows the FAIR (Findability, Accessibility, Interoperability, and Reuse) data principles and is based on open-source software deployed on the Google Cloud Platform. Data stored in the database can be accessed via a custom-built web interface and via desktop geographic information system (GIS) applications that support OGC data access protocols. OCTOPUS v.2 hosts five major data collections. CRN Denudation and ExpAge consist of published cosmogenic 10Be and 26Al measurements in modern fluvial sediment and glacial samples respectively. Both collections have a global extent; however, in addition to geospatial vector layers, CRN Denudation also incorporates raster layers, including a digital elevation model, gradient raster, flow direction and flow accumulation rasters, atmospheric pressure raster, and CRN production scaling and topographic shielding factor rasters. SahulSed consists of published optically stimulated luminescence (OSL) and thermoluminescence (TL) ages for fluvial, aeolian, and lacustrine sedimentary records across the Australian mainland and Tasmania. SahulArch consists of published OSL, TL, and radiocarbon ages for archaeological records, and FosSahul consists of published late-Quaternary records of direct and indirect non-human vertebrate (mega)fauna fossil ages that have been systematically quality rated. Supporting data are comprehensive and include bibliographic, contextual, and sample-preparation- and measurement-related information. In the case of cosmogenic radionuclide data, OCTOPUS also includes all necessary information and input files for the recalculation of denudation rates using the open-source program CAIRN. OCTOPUS v.2 and its associated data curation framework allow for valuable legacy data to be harnessed that would otherwise be lost to the research community. The database can be accessed at https://octopusdata.org (last access: 1 July 2022). The individual data collections can also be accessed via their respective digital object identifiers (DOIs) (see Table 1).

Using machine learning to improve predictions and provide insight into fluvial sediment transport

AbstractA thorough understanding of fluvial sediment transport is critical to addressing many environmental concerns such as exacerbated flooding, degradation of aquatic habitat, excess nutrients, and the economic challenges of restoring aquatic systems. Fluvial sediment samples are integral for addressing these environmental concerns but cannot be collected at every river and time of interest. Therefore, to gain a better understanding for rivers where direct measurements have not been made, extreme gradient boosting machine learning (ML) models were developed and trained to predict suspended sediment and bedload from sampling data collected in Minnesota, United States (U.S.), by the U.S. Geological Survey. Approximately 400 watershed (full upstream area), catchment (nearby landscape), near‐channel, channel, and streamflow features were retrieved or developed from multiple sources, reduced to approximately 30 uncorrelated features, and used in the final ML models. The results indicate suspended sediment and bedload ML models explain approximately 70% of the variance in the datasets. Important features used in the models were interpreted with Shapley additive explanation (SHAP) plots, which provided insight into sediment transport processes. The most important features in the models were developed to normalize streamflow by the 2‐year recurrence interval and quantify the rate of change in streamflow (slope), which helped account for sediment hysteresis. Generally, this study also showed a combination of mostly watershed and catchment geospatial features were important in ML models that predict sediment transport from physical samples. This study is a promising step forward in making fluvial sediment transport predictions using machine learning models trained by physically collected samples. The approach developed here can be used wherever similar datasets exists and will be useful for landscape and water management.

Phosphorus in soils and fluvial sediments from a Cerrado biome watershed under agricultural expansion.

Over the past decades, lands alongside Gurguéia River have witnessed rapid expansion of soybean agriculture which has increased soil degradation and affected nutrient concentration in sediment, especially phosphorus (P). The present study aimed to quantify the P concentration in soils under different land uses (i.e., croplands, grasslands, and cerrado) and fluvial sediments (suspended sediment, channel bank, and riverbed sediments), assessing pollution over the main watercourse in cerrado biome Gurguéia watershed, located in Piauí State, Brazil. In total, 136 compositesoil samples at a depth of 0-5cm, under different land uses, as well as 51 composite fluvial sediment samples were collected over the watershed. The land use change from native cerrado had resulted in an increase of total phosphorus (TP) whose concentration was higher in cropland areas, followed by suspended sediment, channel bank, and riverbed sediments. This high concentration in cropland areas resulted from phosphate fertilizer inputs. The transfer of phosphorus to water bodies was evidenced, since an increase of TP was observed in suspended sediment, channel bank and riverbed sediments. Mineralogical signatures in sediments were identified by X-ray diffraction analysis which showed the occurrence of kaolinite, illite, smectite, iron oxides, and other minerals in lesser proportions. The presence of 1:1 minerals was higher in riverbed sediments and downstream sampling points, while 2:1 minerals were present in higher proportions in suspended sediment and channel bank sediment, as well as at the upstream and middle sampling points. This finding shows that land use change from cerrado to cropland due to soybean agriculture expansion might increase P discharges from terrestrial to aquatic environments, with sediments being the major carrier of this element.

Stirred not shaken; critical evaluation of a proposed Archean meteorite impact in West Greenland

Large meteorite impacts have a profound effect on the Earth's geosphere, atmosphere, hydrosphere and biosphere. It is widely accepted that the early Earth was subject to intense bombardment from 4.5 to 3.8 Ga, yet evidence for subsequent bolide impacts during the Archean Eon (4.0 to 2.5 Ga) is sparse. However, understanding the timing and magnitude of these early events is important, as they may have triggered significant change points to global geochemical cycles. The Maniitsoq region of southern West Greenland has been proposed to record a ∼3.0 Ga meteorite impact, which, if confirmed, would be the oldest and only known impact structure to have survived from the Archean. Such an ancient structure would provide the first insight into the style, setting, and possible environmental effects of impact bombardment continuing into the late Archean. Here, using field mapping, geochronology, isotope geochemistry, and electron backscatter diffraction mapping of 5,587 zircon grains from the Maniitsoq region (rock and fluvial sediment samples), we test the hypothesis that the Maniitsoq structure represents Earth's earliest known impact structure. Our comprehensive survey shows that previously proposed impact-related geological features, ranging from microscopic structures at the mineral scale to macroscopic structures at the terrane scale, as well as the age and geochemistry of the rocks in the Maniitsoq region, can be explained through endogenic (non-impact) processes. Despite the higher impact flux, intact craters from the Archean Eon remain elusive on Earth.

Climatic zonation complicated the lithology controls on the mineralogy and geochemistry of fluvial sediments in the Heihe River basin, NE Tibetan Plateau

Knowledge of the composition of modern fluvial sediments is important for understanding the combined effect of lithology and climatic factors on the erosion and sedimentation within drainage basins, However, this information is incomplete in arid and semiarid environments. In this study, 37 modern fluvial sediment samples were collected from the Heihe River and its major tributaries, in the NE Tibetan Plateau, and for analyses of heavy minerals, trace and rare earth elements (REEs) and grain size. The main aim was to explore the influence of erosion, transport and deposition processes on sediment composition, and to define appropriate provenance indicators specific to these rivers. Along the Heihe River, the amount of unstable minerals is abundant and not changing, these result suggests that chemical weathering plays only a minor role. The composition of six sediment samples obtained from the upper-middle reaches of Heihe River are influenced by hydrodynamic sorting processes, which resulted in enrichment of heavy minerals. In addition, the mineralogical and geochemical compositions lead to different conclusions regarding the contributions from tributaries to the sediments in the middle-lower reaches of the Heihe River. This may reflect the occurrence of contrasting hydrodynamic conditions in Heihe River and its tributaries which result in the transport of different size fractions. Moreover, the <63 μm fraction of the sediments from the Heihe River basin has been affected by inputs of eolian dust, which means that this fraction is less influenced by the rock types within the sediment source areas than is the case for the other size fractions. Therefore, we conclude that the sand fraction is more suitable for source to sink analysis of fluvial sediments within this and comparable environments. In the upper areas of the Fengle River basin, the combination of low temperature, sparse vegetation coverage and high precipitation have resulted in intense erosion. This case reminds us to note the effect of the climatic zonation on the provenance analysis in arid regions.

A Multifaceted Approach for Determining Sediment Provenance to Coastal Shipping Channels

Maintenance dredging for shipping channels is required to maintain safe and efficient navigational channels and berths in ports around the world. Sediment that refills dredged channels can enter ports via alluvial transport of eroded materials from upstream and adjacent catchments, from marine transport due to tidal currents and wind driven currents and from longshore drift. Identifying the provenance of sediment infilling navigational channels allows port operators to mitigate and manage sediment transport, potentially reducing dredging requirements and costs. Further, understanding sediment sources can inform options for beneficial reuse or disposal of dredged sediments. A multi-faceted approach was used to assess whether sediment provenance in the Port of Gladstone could be characterized. A combination of particle size analysis, rare earth element composition, carbon stable isotope ratios, strontium isotopes, and beryllium-7 radioisotopes was employed. Samples were collected at accumulation locations within the navigational channel. Potential sediment sources were sampled from sites of longshore drift to the south of the Port of Gladstone, and intertidal sand and mud representative of transport from currents. Fluvial sediment samples were collected during dry and wet season conditions and from the three main local catchments. Potential source sediment samples yielded identifiable differences with respect to rare earth elements, while beryllium-7 isotope analysis indicated recent deposition of sediments from mudflats or catchment within the channels. The approach used here provided insights into the source of recently deposited sediments to the dredged channels, enabling managers to make informed decisions on mitigation and management strategies.

Contribution of fluorite mining waste to mercury contamination in coastal systems.

Samples from 13 beaches along the northern Spanish coast, a region with a history of heavy industries, were first screened to identify signs of pollution. High concentrations of Hg and Ba on Vega beach were found, both elements belong to the fluorite ore paragenesis, mined in the surroundings. Samples of beach and fluvial sediments, and nearby soils were collected in Vega beach area to address potential Hg pollution, fate and sources. Most samples showed a similar pollutants fingerprint to that of beach samples, especially those taken from white dunes, registering notable Hg concentrations. Hg was enriched in the finer fractions, and overall the main input was attributed to the mining waste discharged along the coast in the past. Although a specific risk assessment and study of the submerged sediments are advisable for this area, Hg bioavailability and methylation were low, thus indicating that this metal poses a reduced environmental risk.

OCTOPUS: an open cosmogenic isotope and luminescence database

Abstract. We present a database of cosmogenic radionuclide and luminescence measurements in fluvial sediment. With support from the Australian National Data Service (ANDS) we have built infrastructure for hosting and maintaining the data at the University of Wollongong and making this available to the research community via an Open Geospatial Consortium (OGC)-compliant web service. The cosmogenic radionuclide (CRN) part of the database consists of 10Be and 26Al measurements in modern fluvial sediment samples from across the globe, along with ancillary geospatial vector and raster layers, including sample site, basin outline, digital elevation model, gradient raster, flow-direction and flow-accumulation rasters, atmospheric pressure raster, and CRN production scaling and topographic shielding factor rasters. Sample metadata are comprehensive and include all necessary information for the recalculation of denudation rates using CAIRN, an open-source program for calculating basin-wide denudation rates from 10Be and 26Al data. Further all data have been recalculated and harmonised using the same program. The luminescence part of the database consists of thermoluminescence (TL) and optically stimulated luminescence (OSL) measurements in fluvial sediment samples from stratigraphic sections and sediment cores from across the Australian continent and includes ancillary vector and raster geospatial data. The database can be interrogated and downloaded via a custom-built web map service. More advanced interrogation and exporting to various data formats, including the ESRI Shapefile and Google Earth's KML, is also possible via the Web Feature Service (WFS) capability running on the OCTOPUS server. Use of open standards also ensures that data layers are visible to other OGC-compliant data-sharing services. OCTOPUS and its associated data curation framework provide the opportunity for researchers to reuse previously published but otherwise unusable CRN and luminescence data. This delivers the potential to harness old but valuable data that would otherwise be lost to the research community. OCTOPUS can be accessed at https://earth.uow.edu.au (last access: 28 November 2018). The individual data collections can also be accessed via the following DOIs: https://doi.org/10.4225/48/5a8367feac9b2 (CRN International), https://doi.org/10.4225/48/5a836cdfac9b5 (CRN Australia), and https://doi.org/10.4225/48/5a836db1ac9b6 (OSL &amp;amp; TL Australia).

Textures, provenances and structures of sediment in the inner shelf south of Shandong Peninsula, western South Yellow Sea

Although many studies have been performed on the mud wedge in the distal part of the Yellow River subaqueous delta, little is known about the southwestern terminus of the Yellow River mud wedge in the inner shelf of the Southern Yellow Sea (SYS). We use ∼3000 km of high-resolution subbottom seismic profiles, 147 surficial sediment samples, as well as 30 fluvial sediment samples to study sediment textures, provenance and structures in the inner shelf in western SYS. Our results show that sediment in the inner shelf south of Shandong Peninsula can be categorized into multiple types, including sand, silt, sandy silt, muddy sand, mud, gravel mud and others. About 60% of the study area is covered by silt and sandy silt. Assuming a finer texture of sediment from Yellow River and a relatively coarser one for sediment from local small rivers, our results reveal at least two contrasting sediment sources. East of the Laoshantou Headland, on the southern coast of the peninsula, the sediment is mainly from the Yellow River. Holocene sediment deposition reaches about 15 m thickness in water depths of ∼10 m. The homogeneous surficial sediment pattern is mainly controlled by the Yellow Sea Coastal Current, the Yellow Sea Warm Current, as well as local currents. However, west of Laoshantou Headland, sediment from local small rivers draining the peninsula plays a more important role. Over there the Holocene mud wedge is no more than 5-m thick, and is re-worked by strong tides and longshore currents. The seaward extension of Laoshantou Headland the southern peninsula seems to act as an effective sediment trap, aiding the accumulation of sediment carried by longshore currents. This new study delineates the western boundary of Yellow River subaqueous delta and helps better quantify sediment budget in the Yellow Sea. It also shed light on the sedimentation interplay of large rivers with local small rivers on many epicontinental shelves and passive margins around the world.

Identifying the degree of luminescence signal bleaching in fluvial sediments from the Inner Mongolian reaches of the Yellow River

Abstract The partial bleaching of the luminescence signal prior to deposition results in age overestimation, and can be a problem in delineating fluvial evolution within an OSL chronological framework. The Inner Mongolian reaches of the Yellow River are characterised by a high sediment load and complex sources of sediments. To test the incomplete bleaching occurring in this type of environment, the residual doses and the luminescence signal characteristics of different particle size fractions from 14 modern fluvial sediment samples were investigated. Furthermore, 26 OSL ages derived from drilling cores were compared with 11 radiocarbon ages. Our results show that the residual equivalent doses principally range between 0.16 and 0.49 Gy for silt grains, and between 0.35 and 3.72 Gy for sand grains of modern samples. This suggests that medium-grained quartz has been well bleached prior to deposition, and is preferable to coarse-grained quartz when dating fluvial sediments in this region. The results also show that the De values of coarse-grained fractions display a stronger correlation with distance downstream. In addition, a comparison of OSL and radiocarbon ages from drilling cores establishes further confidence that any initial bleaching of these sediments was sufficient. As a result, we believe that the studied fluvial samples were well bleached prior to deposition.

The relationship between environmental factors and magnetic susceptibility in the Ili loess, Tianshan Mountains, Central Asia

The mechanisms of the magnetic susceptibility (MS) enhancement of loess from Arid Central Asia (ACA) have received much attention recently. Consensus varies about factors controlling the magnetic properties as well as the environmental implications, and much effort needs to be gone into how surface processes affect the MS. In this study, we collected 214 topsoil, near‐surface loess, and fluvial sediment samples covering different elevations, climatic conditions, and vegetation from the Ili Valley in eastern ACA and analysed their magnetic properties and composition to investigate the factors influencing MS. Redundancy analysis (RDA) was employed to assess the relationship between environmental indicators and environmental factors. Our results show that (a) the concentration of pedogenic magnetic particles in the Ili loess and topsoils is limited. χlf is higher in loess but lower in paleosol, mainly attributable to changes in wind intensity; (b) the mean χfd, χfd%, and χlf values of topsoil are lower in the desert steppe and forest–meadow zones, but highest in the montane steppe zone, and are not positively associated with vegetation coverage and the intensity of pedogenic processes; and (c) elevation exerts the most important impact on topsoil χfd and χfd%, while χlf is influenced more by temperature than precipitation. (d) The magnetic enhancement could be mainly attributed to wind velocity; we also should consider elevation and other factors such as local material, climatic conditions, and distance to the dust source when interpreting the paleoclimatic or paleoenvironmental significance of magnetic parameters.

Feldspar flotation as a quartz-purification method in cosmogenic nuclide dating: A case study of fluvial sediments from the Pamir

Cosmogenic nuclide (CN) dating relies on specific target minerals such as quartz as markers to identify geologic events, including the timing of landscape evolution. The presence of feldspar in sediment samples poses a challenge to the separation of quartz and affects the chemical procedures for extracting the radioactive CNs 10Be and 26Al. Additionally, feldspar contamination reduces the 26Al/27Al ratio, thus hinders the accurate determination of 26Al by accelerator mass spectrometry (AMS). Using fluvial sediment samples from Central Asia, which contain 16–50 weight percent (wt.%) of feldspar, we show that the standard physical separation and chemical cleaning-up procedures for quartz-enrichment reduces the feldspar content to only 9–47?wt.%. We present a new froth flotation mineral-separation device and procedure that allows for very effective quartz enrichment before CN chemistry. Our flotation cell, which has a volume of 600?cm3, is built of borosilicate glass, holds up to 90?g of sample, and achieves quartz and feldspar separation in =2?h for very feldspar-rich samples. We trace the stepwise enrichment of quartz to 95–100% purity with our procedure by X-ray diffraction analysis.

Sources, transport and deposition of terrestrial organic material: A case study from southwestern Africa

Abstract Southwestern Africa's coastal marine mudbelt, a prominent Holocene sediment package, provides a valuable archive for reconstructing terrestrial palaeoclimates on the adjacent continent. While the origin of terrestrial inorganic material has been intensively studied, the sources of terrigenous organic material deposited in the mudbelt are yet unclear. In this study, plant wax derived n-alkanes and their compound-specific δ13C in soils, flood deposits and suspension loads from regional fluvial systems and marine sediments are analysed to characterize the origin of terrestrial organic material in the southwest African mudbelt. Soils from different biomes in the catchments of the Orange River and small west coast rivers show on average distinct n-alkane distributions and compound-specific δ13C values reflecting biome-specific vegetation types, most notably the winter rainfall associated Fynbos Biome of the southwestern Cape. In the fluvial sediment samples from the Orange River, changes in the n-alkane distributions and compound-specific δ13C compositions reveal an overprint by local vegetation along the river's course. The smaller west coast rivers show distinct signals, reflecting their small catchment areas and particular vegetation communities. Marine surface sediments spanning a transect from the northern mudbelt (29°S) to St. Helena Bay (33°S) reveal subtle, but spatially coherent, changes in n-alkane distributions and compound-specific δ13C, indicating the influence of Orange River sediments in the northern mudbelt, the increasing importance of terrigenous input from the adjacent western coastal biomes in the central mudbelt, and contributions from the Fynbos Biome to the southern mudbelt. These findings indicate the different sources of terrestrial organic material deposited in the mudbelt, and highlight the potential the mudbelt has to preserve evidence of environmental change from the adjacent continent.

Petrology and Geochemistry of Late Intermediate Period Ceramics, Southern Peru

Multiple petrological and geochemical analytical techniques revealed significant similarities in element and mineral distribution between the 47 ceramic samples from Chillo (southern coast, Peru), a Late Intermediate Period (ad 1000–1400) archaeological site. The similarity indicates a common raw material source. The analytical results of Holocene fluvial sediment samples, Cretaceous clay layers and fired and non-fired bricks, only eliminated the Cretaceous clay layers as a potential source material. Applying Raman spectroscopy, the red and violet colour of the slip is due to hematite, the yellow colour to a mixture of hematite, graphite and gypsum, and the black colour is either graphite or jacobsite.