Fluvial Sands Research Articles

Monsoon control on evolution of the western Indian aeolian landscape: Insights from U-Pb detrital zircon geochronology and Sr-Nd-Hf isotope studies of the Thar Desert sand dunes

Evolution of landscape is linked to the interplay of tectonics, lithology, and climate. To better understand the evolution of aeolian landscape of the western Indian subcontinent and its major driver/s, we carried out a quantitative provenance analysis of the sand dunes of Thar Desert and desert river Luni using whole rock Sr-Nd-Hf isotopes and detrital zircon U-Pb geochronology. Our findings show Himalayan origin for the Thar sands. River Indus consistently contributed about 30–40 % of the total dune sand across the desert. The sand dunes in the north and the west of the desert are dominated by sediments derived from the source rocks drained by Sutlej river and its tributary Beas river whereas the dunes of central Thar are dominated by sediments supplied by rocks drained by Jhelum, Ravi and Chenab rivers. Analysis of detrital zircon U-Pb age spectra of sediments from desert river Luni reveal that dune sand of southern Thar Desert forms nearly 80 % of its present-day sediment load. Notably, the Thar dune sands show remarkable compositional similarity to the early to middle Holocene Indus delta sediments suggesting shared source/s. Existing paleolimnological and climatic records suggest a wetter environment in the Thar during early to middle Holocene. This evidence coupled with compositional similarities between the Thar dunes and the Indus delta sediments from the same period, indicate a probable extension of the Indus-Sutlej floodplain into southeast Thar during that time. Subsequent aridification of the region in the late Holocene likely led to seasonal winds recycling this fluvial sand to form the present-day Thar dunes, and shaping the current aeolian landscape in western India.

Heavy Minerals Distribution and Provenance in Modern Beach and Fluvial Sands of the Betic Cordillera, Southern Spain

This study uses heavy detrital minerals to determine actualistic fluvial and beach sand provenance across the Betic Cordillera (Spain), along the coast from Almeria to Marbella. The Betic Cordillera, primarily composed of metamorphic rocks to the east, supply an assemblage dominated by almandine and graphite, with a longshore dispersal from Almeria to Malaga. Buergerite and hypersthene indicate the provenance of calcalkaline lavas east of Cabo de Gata. The western part of the Betic Cordillera, which comprises the Ronda Peridotite Complex, supplies a chromite and diopside assemblage, with a dispersal from Marbella to Algeciras. Considering these mineralogical suites, the effects of source rock compositions and weathering are evaluated. The heavy mineral species mirror the mineralogy of the source rocks of local outcrops and wider source terranes. The fluvial heavy mineral suites do not differ significantly from those in the beaches except for some unstable species. Unstable species such as olivine, pyroxene, and amphibole do not show evidence of loss because of elevated topography and semiarid climate, which do not affect heavy minerals. This contribution also evaluates the potential of some heavy detrital species as ideal pathfinders in searching for diamonds.

Reservoir Mud Releasing May Suboptimize Fluvial Sand Supply to Coastal Sediment Budget: Modeling the Impact of Shihmen Reservoir Case on Tamsui River Estuary

AbstractRegular release of sediment from reservoir has been increasingly adopted as a strategy for sustainable management. Here, we use a process‐based morphodynamic model to simulate the estuarine sediment dynamics impacted by turbidity current venting implemented by the Shihmen Reservoir during three typhoon events in 2008. Upon validation with the post‐event bathymetries, the model hindcasts reveal that mud releasing can be effective in mitigating reservoir siltation, yet may be a suboptimal strategy for alleviating coastal sediment deficit. A vast majority of the released muds were delivered through the estuary and exported to offshore by flood advection, wave dispersion, and tidal flushing. The flood‐driven sands, sourced mainly from downstream tributaries, were instead the major contributor to coastal sediment budget. However, mud mantling (covering and immobilizing sand deposits by the reservoir‐released muds) reduced sand availability and thus sand delivery to the coast. For the present case, 25% of the released muds were deposited along the way, presence of these mud covers reduced sand delivery by 15%, compared to a hypothetical scenario of clear‐water flood releases. The relative sand transport deficit is found to increase linearly with the degree of bed mud saturation, 1–D/R, with D/R the ratio of single‐event mud deposit to release. Given broad relevance to global reservoirs encountering the problems of siltation and coastal sediment deficit, our findings highlight that sustainable management needs to look beyond just a bulk amount of sediment, but it is critical to consider how different sediment fractions are interacting and impacted by human activities.

Timing and Kinematics of late Cenozoic Strike-slip Faults in the Western Tibetan Plateau: New Constraints from Provenance Analysis and Detrital Thermochronology

The activities of the three large strike-slip fault systems—the Karakoram, the Karakax, and the Longmu Co-Guozha Co faults—located in the western Tibetan Plateau have induced the intense exhumation of the Karakoram and the southern Western Kunlun ranges. However, the histories of these faults remain debated or loosely constrained, partly due to the restricted access to bedrock samples and associated comprehensive analyses. The application of detrital provenance analysis and detrital thermochronology to sediments can provide valuable information on the locations, crystallization timing, and exhumation of the source terranes of the sediments, thereby shedding light on tectonic histories. This study utilizes modern fluvial sand to obtain exhumation information on the Karakoram and the southern Western Kunlun ranges and to reconstruct the history of the major faults. We achieve this through provenance analysis (heavy-mineral analysis and detrital zircon UPb dating) and detrital apatite fission-track dating. Our results reveal widespread Paleogene rock exhumation across the western Tibetan Plateau and focused mid-Miocene (ca. 15–12 Ma) exhumation along the Karakoram and the southern Western Kunlun ranges. Moreover, the Karakoram Range experienced renewed exhumation at ca. 7 Ma. Through an integration of our results and regional geological evidence, we suggest that the focused mid-Miocene exhumation reflects the initiation of the Karakoram and the Karakax faults; the subsequent ca. 7 Ma exhumation episode of the Karakoram Range indicates a regional kinematic reorganization due to the initiation of the Longmu Co-Guozha Co Fault. We propose that the middle and late Miocene strike-slip faulting in the western Tibetan Plateau was driven by the oblique underthrusting of the Indian lithosphere.

Assessment of Fertility Dynamics and Nutritional Quality of Potato Tubers in a Compost-Amended Mars Regolith Simulant.

Mars exploration will foresee the design of bioregenerative life support systems (BLSSs), in which the use/recycle of in situ resources might allow the production of food crops. However, cultivation on the poorly-fertile Mars regolith will be very challenging. To pursue this goal, we grew potato (Solanum tuberosum L.) plants on the MMS-1 Mojave Mars regolith simulant, pure (R100) and mixed with green compost at 30% (R70C30), in a pot in a cold glasshouse with fertigation. For comparison purposes, we also grew plants on a fluvial sand, pure (S100) and amended with 30% of compost (S70C30), a volcanic soil (VS) and a red soil (RS). We studied the fertility dynamics in the substrates over time and the tuber nutritional quality. We investigated nutrient bioavailability and fertility indicators in the substrates and the quality of potato tubers. Plants completed the life cycle on R100 and produced scarce but nutritious tubers, despite many critical simulant properties. The compost supply enhanced the MMS-1 chemical/physical fertility and determined a higher tuber yield of better nutritional quality. This study demonstrated that a compost-amended Mars simulant could be a proper substrate to produce food crops in BLSSs, enabling it to provide similar ecosystem services of the studied terrestrial soils.

Tectonic movements of the Yanshan-Himalayan period in the northern Longmenshan and their impact on tight gas accumulation of the Shaximiao formation in the Qiulin structure, China

The Jurassic strata constitute a focal area for recent exploration and development of tight gas reservoirs in the western Sichuan Basin. This study investigates the Jurassic Shaximiao Formation in the northern Longmenshan in the Western Sichuan basin, focusing on tight gas reservoirs. The research integrates core and outcrop observations, seismic interpretations, and burial history analyses to understand hydrocarbon source rocks, sedimentation, reservoir characteristics, and structural characteristics. The impact of Yanshan-Himalayan tectonic movements on tight gas reservoir accumulation in the Shaximiao Formation is dissected, primarily around the Qiulin structure. The Western Sichuan Depression basin’s formation is influenced by gravitational gliding tectonics, which can be classified into the ‘Three Zones and One Belt,’ with Longmenshan in the frontal belt. Burial history analysis reveals distinct processes in the foreland belt and the depression basin. In the Qiulin area, gas reservoirs in the Shaximiao Formation are mainly charged by source rocks from the Xujiahe Formation. Tectonic movements play a significant role in creating favorable reservoirs and conditions for hydrocarbon migration and preservation. Natural gas accumulation is primarily controlled by fault connectivity to hydrocarbon sources and effective reservoir thickness. Gravitational sliding tectonics have shaped a fluvial-lacustrine environment for the Shaximiao Formation, with fluvial sand bodies acting as favorable reservoir zones. Small-scale normal faults formed by tectonic movements serve as conduits for natural gas migration. The research findings are of significant guidance for the exploration and development of tight oil and gas resources in western Sichuan basin.

Integrated seismic-stratigraphic, sedimentological and petrophysical approaches for characterizing the reservoir potential of early Cretaceous Alam El Bueib formation in the Meleiha concession of North Western Desert, Egypt

The Early Cretaceous late syn-rift sediments of Alam El Bueib Formation host potential, however poorly-explored reservoir targets in the north Western Desert of Egypt. The controls on depositional evolution and architecture of Alam El Bueib sedimentary facies, as well as the influence of depositional attributes on reservoir facies heterogeneity, are poorly constrained. Therefore, this study integrates seismic, sedimentological, and petrophysical data from Meleiha concession in the north Western Desert to build evolutionary models for Alam El Bueib succession and predict the architecture of the potential reservoir facies. Several channel systems were observed with a notable upward transition from complex-filled to flat-filled channels. The complex-filled channels correspond to the early highstand tidally-influenced estuarine, deltaic/estuarine sediments of Alam El Bueib-IV and Alam El Bueib-IIIG units. Matruh canyon and Alam El Bueib-IIIG fluvial sand bars were developed during a phase of forced regression, and the canyon was infilled by hemiplegic mudstones during the Late Valanginian sea level rise. The late highstand and lowstand facies of Alam El Bueib-IIIG unit present the main fluid flow conduits. The minimal degree of reservoir heterogeneity occurs in the lowstand amalgamated fluvial sandstone bars, whereas lateral and vertical reservoir heterogeneity increases in the deltaic/estuarine and estuarine successions of Alam El Bueib-IIIG and Alam El Bueib-IV, respectively. The lateral compartmentalization of the Alam El Bueib-IIIG fluvial facies against Alam El Bueib Matruh canyon shales produced excellent stratigraphic traps that should be tracked throughout the entire north Western Desert.

Seismic simulation and attribute analysis of Jurassic fluvial reservoirs in the P6 region, Xinjiang

Fluvial reservoirs are crucial for oil and gas exploration. In the Jurassic formations of Chepaizi anticline, ancient channels can be identified based on seismic facies similar to incised valleys. This study focuses on three key issues. Firstly, it aims to demonstrate the capability of spectral decomposition interpretation in distinguishing ancient channels. Secondly, it aims to prove that the incised valleys in the Jurassic formations of Chepaizi are ancient channels. Thirdly, given that the Jurassic is a new layer for oil and gas exploration in the region, it aims to identify the distribution of ancient channel and conglomerate. To address these issues, we conducted a seismic wave forward simulation study on channels and used spectral decomposition to interpret seismic data. The results show that: (1) Spectral decomposition can differentiate channels of different thicknesses, where low-frequency components correspond to thick channels and high-frequency components correspond to thin channels. (2) Using multi-attribute and multi-parameter fusion method can identify the fluvial sand body boundary. (3) The width of the channel in P6 area ranges from 400 to 1700 m, with an area of 78 km2. The fluvial sand bodies are generally distributed along the slopes. Few sandstones and conglomerates are distributed at the bottom of the channel. We conclude that further exploration should focus on the fluvial channel delta in the southeast of the study area.

Coastal compartments: the role of sediment supply and morphodynamics in a beach management context

Coastal compartments provide a hierarchical framework to manage beaches and coastal ecosystems in Australia. This study examines the individual behaviour of three adjacent beaches within Shoalhaven Bight, a secondary compartment on the south coast of New South Wales (NSW). The Shoalhaven River discharges intermittently into the northernmost of the beaches, and a fluvial component is detectable within beach and foredune sands. The distribution and orientation of headlands constrains dispersal of fluvial sediments, and results in lower wave-energy conditions further south, implying limited sand transport from one beach, or tertiary compartment, to another. Two years of monthly subaerial surveys across ten different profiles and modelled storm-wave conditions during the major storms, were used to compare the response of beach volume and shoreline position. The greatest changes in volume were observed near Shoalhaven Heads and the northern ends of Culburra and Warrain-Currarong beaches. Results indicate the distinct individual response of neighbouring beaches over the two-year period, in contrast to general trends in beach behavior that might be inferred from long-term regional monitoring programs. However, they also demonstrate the limitations of short-term observations in comparison to those longer-term studies. The NSW beach systems of are some of the best understood in the world in terms of regional behaviour, as a consequence of several decades of surveys on key beaches. However, more focused local monitoring programs may be needed to establish detailed coastal sand transport, and an understanding of intermittent delivery of fluvial sand and longshore inputs and outputs, within and between different compartments.

Evidence of Potential Organo-Mineral Interactions during the First Stage of Mars Terraforming

Future space missions to Mars will depend on the development of bioregenerative life support systems. Mars regolith contains most of the nutrients needed for plant growth, but not organic matter (OM). Although Mars simulants have been deeply characterized and tested as growing media, no data are available about their possible modification occurring during terraforming, including the interaction of exogeneous OM with iron (Fe) oxides, particularly abundant in Mars regolith. The aim of this study was to investigate the mineral transformation and the OM evolution occurring in the early stages of the terraforming process. Potato was grown for 99 days on Mojave Mars Simulant MMS-1, alone (R100) and mixed with a compost 70:30 v:v (R70C30), and on a fluvial sand, alone (S100) and mixed with compost (S70C30), for comparison. Bulk (BK) and potato tubero/rhizo-sphere (RH) soils were fractionated to obtain particulate OM (POM) and mineral-associated OM (MAOM). Bulk samples and corresponding fractions were characterized for total nitrogen and organic carbon (C) and analyzed by Fe K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Organic C increased by 10 and 25 times in S70C30 and R70C30, respectively, compared to S100 and R100. Most of the organic C accumulated in the POM fraction of both growing substrates, while its content in the MAOM was 3 times higher in R70C30 than in S70C30. No significant differences between BK and RH were found. Finally, ferrihydrite mediated exogenous OM stabilization in regolith-based substrates, while Fe(III)-OM complexes were detected exclusively in sand-based growing media. Understanding mechanisms and testing potential sustainable practices for creating Mars regolith similar to terrestrial soil will be fundamental to sustain food crop production on Mars.

Holocene estuary infill leads to coastal barrier initiation from fluvial sand supply in southeastern Australia

A morphodynamic approach to coastal evolution involves recognition of internal thresholds, feedbacks and boundary conditions and should underpin coastal management. The Holocene evolution of the Bega River estuary and Tathra Beach coastal barrier was examined integrating existing sediment cores and radiocarbon dating, airborne terrestrial and marine Lidar and OSL dating. Sediment coring reveals the Bega River estuary began infilling with fluvial sand once sea levels stabilised at or near their present elevation. Radiocarbon dating suggests a prograding fluvial delta reached the coast approximately 4000–2250 years BP. Barrier deposition commenced ~3200 years ago coinciding with the arrival of fluvial sand at the coast. Shoreline progradation of the Tathra barrier occurred at 0.15 m/year from ~3200 years to present forming a sequence of ~17 foredune ridges which were each active for an average of ~190 years. In the past ~500 years, a sand spit has restricted the entrance of the Bega River estuary to the northern end of the embayment. The infill of the Bega River estuary over the Holocene represents an internal morphodynamic threshold or tipping point, which then enabled coastal barrier deposition as fluvial sand reached the coast. The coastal system approaches another threshold as the Tathra embayment infills, and sediment may be transported northward out of the embayment. At Tathra Beach, the positive sediment budget which resulted in barrier progradation is approximately 0.55 m3/m/year. This signal is masked on the yearly to decadal scale by fluctuations in beach volume an order of magnitude greater (5–20 m3/m/year depending on the timeframe examined). Thus longer-term datasets of beach change or reconstructions from the geological record are needed to underpin management decisions which will impact shorelines decades or centuries into the future.

Source-to-sink controls on modern fluvial sands in the Pantanal back-bulge basin (Brazil)

Sedimentological processes are underexplored in retro-arc basin segments of source-to-sink systems, particularly in the distal back-bulge depozone. The extant Pantanal Basin of Latin America is a large sub-tropical continental back-bulge for which the boundary conditions on riverine sedimentation (tectonics, climate, phytogeography) are reasonably understood. Here, we use a new database of riverbed sand samples (n = 97) to investigate the modern provenance of the Pantanal Basin. Petrographic analysis of grain-mounted thin sections and Gazzi-Dickinson point counting were used to assess the framework composition of the sands, and a pour point analysis based on geographic information systems (GIS) defined the hinterland geological environment for each sample. Six provenance domains were defined: (a) lowlands, (b) Amazon craton, (c) Rio Apa craton, (d) plateau, (e) South Paraguay Belt, and (f) North Paraguay Belt. Most Pantanal samples are quartzose non-orogenic detritus (Qt88\F5\L7). Rivers draining the Paraguay Belt highlands carry more lithic grains derived from carbonate parent rocks. The occurrence of plagioclase grains is rare. However, river sands where >30% of the total assemblage was K-feldspar were present downstream of foliated metamorphic outcrops of the Rio Apa craton. Sand relatively rich in fine K-feldspar grains in the medial Taquari River megafan were attributed to channel avulsion, incision, and reworking of floodplain deposits. Statistical analysis suggests that bedrock lithology and average annual rainfall are important controls on fluvial sands in the Pantanal Basin, with watershed slope, temperature, and dilution playing secondary roles in the spatial distribution of dominant grain types. This study provides new actualistic data that aim to improve interpretations of the geological record.

Relict and Modern Sediments on the Continental Shelf of the Northern South China Sea: A Reconsideration

AbstractUnderstanding the temporal‐spatial patterns of modern and relict sediments is of importance for assessing changes in the Quaternary environment and sea‐level. Sedimentological and geochemical data is presented, along with in situ shell‐based accelerator mass spectrometry 14C ages of 30 samples from the surface sediments on the northern shelf of the South China Sea (NSSCS). The authors’ data show that the NSSCS surface sediments exhibit considerable diversity in composition. Modern sediments are primarily constrained to the NW inner shelf, which is fed by fluvial sands sourced from Coastal South China river systems and dominated by the Pearl River Estuary delivery. The transport and discharge of the terrestrial sediments to the NSSCS is highly influenced by the Guangdong Longshore Current and its secondary cyclonic eddies. Relict sediments dominated by well‐sorted, medium‐ and coarse‐grained sands were identified in the NW Shenhu and NW Dongsha areas of the outer NSSCS. The sedimentology and geochemistry of the relict sediments imply that they were deposited in a dry and cold environment either during the low sea levels of the late Pleistocene (∼40 ka) or the early Holocene (∼10 ka). To the east, the Taiwan Shoal and vicinity are dominated by a sand mixture, at which the relict sediments were reworked by terrigenous supply and modern hydrodynamic environment due to the compound action of the Guangdong Longshore Current, seasonal cyclones, and Kuroshio Intrusion. The present isobaths of ∼−90 m in the NSSCS might be the reflective of the early Holocene coastal delta or the last glacial maximum shoreline.

Focussed cave formation on the rising limb of a phreatic loop beneath a river – The Potholes, southeastern Australia

At the Buchan karst in southeastern Australia, Early Devonian carbonates contain >700 caves and karst-related features. The Potholes, in the northern part of the karst, is a densely cavernous area with >100 caves and 60 dolines over only ~0.8 km2. The caves here are predominantly vertical and the roofs commonly show smooth upward steps, indicative of having formed by rising groundwater. Because of sea level fluctuations during the Early Devonian, the limestone at The Potholes forms a tongue that lenses out to the south and is overlain and underlain by relatively insoluble marl. Mapping of fluvial sands and gravels and valley-filling basalt shows that in the Paleogene, the limestone lay beneath a broad, southwards-flowing river valley. Cave development occurred along phreatic loops within the limestone underneath the riverbed, and the upwards limbs of these phreatic loops were focussed into a small area where the limestone lensed out. The concentrated upwards groundwater flow, which connected to springs in the riverbed, resulted in intense cave development within a restricted area, where the groundwater exploited many different pathways within the limestone. The Potholes caves developed entirely beneath the riverbed, and are notable in that numerous caves fed multiple resurgences rather the more common situation world-wide of a single passage connecting to a resurgence. Both these characteristics reflect the unique geological configuration of the site, and show how karst development is determined by the particular arrangement of soluble limestone beds.Dissolution of The Potholes caves could have begun in the mid-Cretaceous, when uplift increased the gradient of the ancestral river flowing over the limestone, driving groundwater flow through phreatic loops beneath the river, and terminated when the caves were drained following a second uplift in the mid-Pliocene. This demonstrates the antiquity of cave formation in this part of Australia.

Temporal Variability of Fluvial Sand Composition: An Annual Time Series From Four Rivers in SW Germany

AbstractThe sampling of fluvial sediment is subject to many sources of uncertainty, for example, time and location, and the number of samples collected. It is nevertheless commonly assumed that a sample taken at one time and location provides a somewhat averaged compositional signal. Any spatial or temporal variability of this signal is often neglected. This study investigates how the composition of bed load sand changes over an observation period of 1 year in four river basins with differing bedrock geology in southwestern Germany. Up to 12 bulk sediment samples were taken at the same locations using the same approach and analyzed for their granulometry and geochemistry. The results indicate that (a) different grain sizes yield different compositions due to source rock composition and hydraulic sorting effects, (b) bulk sediment composition changes temporally due to changing grain‐size distribution, and (c) compared to the bulk sample, the composition of narrow grain sizes is temporally more stable but nevertheless has an average variability of 15%. Because heavy mineral‐bound elements such as Zr have the highest variability, we relate a major component of compositional variability to temporally varying heavy mineral concentrations in response to hydrodynamic processes. Mixing modeling demonstrates that the fluvial sand faithfully reflects its catchment geology and that the sediment sources do not change substantially during the observation period, even during a flooding event. We conclude (a) that the causes for compositional variability may be disentangled using chemical and granulometric time series data and (b) that narrow grain sizes yield representative source rock contributions.

Sedimentary characteristics of sandy braided river deposits and factors controlling their deposition: A case study of the lower Shihezi Formation in the northern ordos basin, China

Fluvial sandstones have been identified as significant reservoirs due to their importance in global hydrocarbon exploration. The current study investigated the sedimentary characteristics and temporal evolution of sandy braided river systems as well as the factors controlling their deposition in the Lower Shihezi Formation (H1-1 to H1-4 sub-member) of the Xinzhao area in the northern Ordos Basin using well logs, core intervals, whole rock geochemical data, and other measured reservoir parameters. Within the braided river deposits, five architectural elements were identified: multistory braided channel, single-story braided channel, sandy braid bar, overbank, and floodplain. The evolution of architectural elements in the Lower Shihezi Formation is closely related to paleoclimatic conditions and tectonic activity. Climate influences sediment accumulation through its effect on terrestrial detrital input, and tectonism influences stacking patterns and architectural style by influencing subsidence rates and accommodation changes. High sediment deliveries and high-energy hydrodynamic conditions in warm and humid climates, combined with low subsidence rates and low accommodation/sediment supply (A/S) ratios, can result in the formation of highly amalgamated braided channels and braid bars as well as complex vertical stacking patterns and aggradational processes in the H1-2 and H1-3 sub-members. Conversely, the dry and hot climates, high subsidence rates and associated high A/S ratios are responsible for the low detrital influx input, stacking of isolated sand bodies, and high preservation of overbank and floodplain deposits in the H1-4 sub-member. Considering the accommodation-based systems tracts, we contend that climate and tectonism both have a significant impact on the evolution and architectural styles of sandy braided river deposits. It is suggested that climates control the stacking pattern of fluvial sand bodies during high accommodation systems tracts, whereas both climates and accommodation spaces influence architectural styles and the degree of sand body amalgamation during low accommodation systems tracts. Considering the thick, highly amalgamated sand bodies with better reservoir properties and high vertical and lateral connectivity in the H1-2 and H1-3 sub-members, we posit that these stacked multistory sand bodies should be the preferential targets for hydrocarbon exploration. The findings of this study can further elucidate the architectural styles and factors that influence the deposition of sandy braided river systems under complex tectonic and climatic conditions.

Fluvial‐Aeolian Interaction and Compositional Variability in the River‐Fed Yarlung Tsangpo Dune System (Southern Tibet)

AbstractRiver‐fed dune fields characterized by relatively low quartz content are much more common on Earth than generally assumed, and the aeolian dune field system in the Yarlung Tsangpo (Upper Brahmaputra) river catchment is considered a typical example. As one of the highest‐altitude fluvial‐aeolian systems on Earth, the dune fields in different wide tracts of the Yarlung Tsangpo valley, made of sand entirely blown from the adjacent river bed, provides an excellent natural laboratory in which to investigate the diverse factors controlling textural and compositional changes induced by aeolian processes. To this aim, the textural (grain‐size, roundness) and compositional (petrography, heavy minerals) properties of multiple size classes of fluvial and aeolian sands were quantified. The results show that sediment composition is markedly controlled by grain size, with greater intrasample than intersample variability. Grain‐size controlled compositional differences cannot be exclusively ascribed to hydraulic‐sorting effects. Independent of their density or shape, quartz, sedimentary rock fragments, zircon, apatite, and epidote grains are observed to be on average smaller than feldspars, volcanic rock fragments, and pyroxenes. This indicates that the original size of minerals in source rocks also played a significant role, limiting their availability in finer (e.g., garnet) or coarser (e.g., apatite) classes. In the river‐fed dune system, the lower content of phyllosilicates and higher grain roundness could represent useful criteria to distinguish aeolian from fluvial sand. The efficient aeolian abrasion of river‐fed sediments on the Tibetan Plateau may be an effective mechanism for the production of dust deposited as vast loess covers during the Quaternary.

Sedimentary Facies of the Cimanuk River Delta on the North Java Coastal Area and Its Geotechnical Properties

Understanding the sedimentary facies and their engineering properties in the Cimanuk river delta is very important to support the regional infrastructure development and the environmental assessment of the north Java coastal area. This research is aimed to characterize the sedimentary facies association and its geotechnical properties of the Cimanuk delta, Indramayu, West Java. Methods included geotechnical boring and Cone Penetration Tests with pore water measurement (CPTu). The results show that the subsurface condition of the Cimanuk delta comprises several sedimentary facies development and boundaries, namely the delta plain, delta front, and prodelta. The delta plain consists of the fluvial channel sands and marsh-lagoon; the delta front consists of beach ridge, and the prodelta is of clay to silt thickening towards the northeast. The fluvial channel consists of fluvial sand and silt, dense and hard with SPT N value of 30 and cone resistance, qc of 2,000-10,000 kPa. The beach ridge comprises beach sand and sandy silt, loose to very dense, with qc value of 500-16,000 kPa and SPT N value of 30. The delta plain sandy silt has a variable consistency from very soft to hard with SPT N value of 1-37, and qc value of 300- 4,900 kPa. The prodelta clay and silt consist of very soft to medium consistency, with qc value of 200- 3,000 kPa and SPT N value of 1-8. The prodelta clay-silts engineering properties are very soft to a soft consistency. When development occurs in the marsh-lagoon and prodelta facies, particular caution must be taken. The vertical, lateral, and spatial sedimentary facies and their geotechnical properties can provide information for spatial planning in the coastal region.

Sorption and desorption of naphthenic acids on reclamation materials: Mechanisms and selectivity of naphthenic acids from oil sands process water

This study investigated the application of materials peat-mineral mix (PT) and Pleistocene fluvial sands from different location (PF-1 and PF-2) obtained from surface mining of oil sands as sorbents of naphthenic acids (NAs) from oil sands process water (OSPW). To understand the sorption properties and mechanisms of NAs in the materials, sorption and desorption studies were performed using decanoic acid (DA) and 5-phenylvaleric acid (PVA). Additionally, the removal efficiency was evaluated using real OSPW to understand the effect of NA structure on sorption. Equilibrium of DA and PVA was reached at 2 days for PT, and 3 and 6 days for PF materials, respectively. Langmuir isotherm best fitted the equilibrium data. Maximum sorption capacities for DA and PVA were, respectively, 16.8 × 103 and 104 mg/kg for PT, 142.9 and 81.3 mg/kg for PF-1, and 600 and 476.2 mg/kg for PF-2. Hydrophobic interactions, hydrogen bonding, and π−π interaction were the main sorption mechanisms. Desorption of model compounds from post-sorption materials was not observed for 14 days. The removal of NAs from real OSPW ranged from 20 to 54%. PT is the most promising sorbent of NAs from OSPW because it partially removed NAs with a wide range of molecular weights and structures at very low dosage. Sorption of NAs was affected by the total organic carbon of the materials, emphasizing the hydrophobic interaction as an important sorption mechanism. The results suggest that some mobility of NAs is expected to take place if the reclamation materials come in contact with OSPW, which might occur in an oil sands reclamation landscape.

Which is the dominant source for the aeolian sand in the Badain Jaran Sand Sea, Northwest China: Fluvial or gobi sediments?

Fluvial and gobi sediments play significant roles in the formation of modern sand seas and their evolution. However, little is known about their respective source contributions, especially in quantitative terms. In the present study, we selected the Badain Jaran Sand Sea in Northwest China to quantitatively identify the sediment sources. To achieve this goal, we collected Heihe River sand and gobi sediments (Ejin gobi and the Beida–Yabrai gobis) as the potential sand sources. We performed provenance identification based on robust geochemical indicators, and found that both of these potential sources provided sand materials to the sand sea. Our quantitative analysis based on novel fingerprinting methods, namely consensus ranking (CR) and consistent tracer selection (CTS), suggested that the gobi sediments supplied more sand than the fluvial sand, accounting for 76.85 % and 23.15 % of the total (goodness of fit is 95.8 ± 3.89), respectively. Therein, the Ejin gobi was the dominant source for most regions of the sand sea (63.17 ± 21.43 %), but the Heihe River mainly fed sand source to the southern part of the sand sea (23.15 ± 18.66 %) and the Beida–Yabrai gobis provided the most sand to regions near the fan (13.68 ± 11.49 %). The source supply areas largely control above contribution difference. Our results demonstrate the critical role of gobi sediments for sand accumulation of the Badain Jaran Sand Sea.