Braided River Research Articles

Interferometric SAR Observation of Permafrost Status in the Northern Qinghai-Tibet Plateau by ALOS, ALOS-2 and Sentinel-1 between 2007 and 2021

With global warming, permafrost is undergoing degradation, which may cause thawing subsidence, collapse, and emission of greenhouse gases preserved in previously frozen permafrost, change the local hydrology and ecology system, and threaten infrastructure and indigenous communities. The Qinghai-Tibet Plateau (QTP) is the world’s largest permafrost region in the middle and low latitudes. Permafrost status monitoring in the QTP is of great significance to global change and local economic development. In this study, we used 66 scenes of ALOS data (2007–2009), 73 scenes of ALOS-2 data (2015–2020) and 284 scenes of Sentinel-1 data (2017–2021) to evaluate the spatial and temporal permafrost deformation over the 83,000 km2 in the northern QTP, passing through the Tuotuohe, Beiluhe, Wudaoliang and Xidatan regions. We use the SBAS-InSAR method and present a coherence weighted least squares estimator without any hypothetical model to calculate long-term deformation velocity (LTDV) and maximum seasonal deformation (MSD) without any prior knowledge. Analysis of the ALOS results shows that the LTDV ranged from −20 to +20 mm/year during 2007–2009. For the ALOS-2 and Sentinel-1 results, the LTDV ranged from −30 to 30 mm/year during 2015–2021. Further study shows that the expansion areas of permafrost subsidence are concentrated on braided stream plains and thermokarst lakes. In these areas, due to glacial erosion, surface runoff and river alluvium, the contents of water and ground ice are sufficient, which could accelerate permafrost subsidence. In addition, by analyzing LTDV and MSD for the different periods, we found that the L-band ALOS-2 is more sensitive to the thermal collapse of permafrost than the C-band sensor and the detected collapse areas (LTDV < −10 mm/year) are consistent with the GF-1/2 thermal collapse dataset. This research indicates that the InSAR technique could be crucial for monitoring the evolution of permafrost and freeze-thaw disasters.

Revised temporal and morphostratigraphic context for Clark Quarry: A late-Pleistocene, fluvially-reworked, Atlantic coast backbarrier deposit

Sediments along the Atlantic Coastal Plain (ACP) of North America have been the focus of numerous paleontological investigations and yielded a diverse array of vertebrate remains; yet the depositional environments associated with their preservation are poorly understood. In this study, we present a multidisciplinary analysis of the depositional environment at Clark Quarry, a late-Pleistocene, fossil-rich locality located within the ACP in Georgia, USA. Clark Quarry is currently positioned 15 km west of the Atlantic Ocean coast and lies within the Princess Anne Terrace, a 100–80 ka paleobarrier-island complex. Fossil-bearing sediments at Clark Quarry are interpreted to have been deposited as a low-energy, fluvial environment that subsequently reworked low-lying terrain of the Princess Anne Terrace backbarrier. Interpretations of digital elevation models (DEM) and infrared stimulated luminescence (IRSL) ages on K-rich feldspar sand grains indicate that this region was an estuarine zone backing (i.e., westward) the Princess Anne paleobarrier island that was subsequently reworked by fluvial activity 68–52 ka. These new interpretations, paired with additional radiocarbon ages from fossil carbonates and overlying soil horizons, indicate that radiocarbon samples may have been influenced by isotopic exchange and should be interpreted as minimum age estimates. Additionally, ground-penetrating radar (GPR) surveys in conjunction with DEM analysis may have captured the subsurface signature of a meandering fluvial system transitioning to a braided style, emphasizing the dynamic nature of this depositional environment. Non-preferential orientation of excavated long bones suggests multidirectional paleoflow, further suggesting a braided stream influence. When considered in conjunction, these data: 1) indicate that Clark Quarry represents a spatially and temporally resolved window into the late-Pleistocene ecosystem in southeastern North America, and 2) suggest that existing radiocarbon data from late-Pleistocene ACP localities should be considered with caution.

Landscape geomorphology and local‐riverine features influence Broad Whitefish ( Coregonus nasus ) spawning habitat suitability in Arctic Alaska

Landscape-level geomorphic processes influence the spatial and temporal arrangement of fish habitats in freshwater ecosystems and fishes move across riverscapes, selecting a suite of habitats to maximise fitness. Here, we explore the influence of geomorphology on stream channel attributes and assess Broad Whitefish (Coregonus nasus) spawning habitat potential in the Colville River in Arctic Alaska. Using high-resolution digital surface models (5 m2), we quantified the stream network extent and summarised channel habitat attributes continuously across the drainage network. Next, we developed an intrinsic potential (IP) model for Broad Whitefish by using geomorphic channel parameters previously understood to be associated with spawning habitats (channel width, median substrate size and channel braiding) to estimate the potential of streams across the Colville River watershed to provide spawning habitat. Our model results show the majority of habitat with high IP (≥0.6) was located within the braided sections of the main channel, which encompass >1548 km, but only 2% of the total channel network. The IP model was tested by tracking radio-tagged Broad Whitefish using aerial surveys. Prespawn fish moved into the watershed starting mid-July and mostly used habitat with moderate to very high IP in the middle and lower watershed. Several individuals were relocated in smaller multichannels with vegetated bars that contained very low IP (≤0.2), suggesting that other factors, such as hyporheic flow, may also influence spawning habitat selection. Our study demonstrates that IP modelling offers a useful method to quantify spawning habitat potential in data-poor riverscapes, providing useful information for managers to assess potential anthropogenic impacts and develop conservation plans to protect essential Broad Whitefish habitat.

Glaciofluvial sequences recording the Birrfeld Glaciation (MIS 5d\u20132) in the Bern area, Swiss Plateau

In this paper, we document that glaciofluvial gravel sequences and glacial till deposits that are exposed in the Müntschemier and Finsterhennen gravel pits (Swiss Plateau west of Bern) record three glacial advances during the Birrfeld Glaciation, which corresponds to the last glacial cycle. Sedimentological logging shows that both gravel pits expose deposits of glaciofluvial braided river systems. These sediments are overlain by a till that was deposited during the Last Glacial Maximum (LGM). The results of the provenance analysis imply that the sediments were mainly supplied by the Valais Glacier, which originated in the Central Alps. A minor contribution of the material was supplied by the Saane Glacier with sources in the northern parts of the Alps. In addition, the morphometric analysis particularly of quartzite clasts in the till deposits indicate that while some clasts (the angular ones) were eroded and transported by the Valais Glacier from the Central Alps to the depositional site, the majority of the quartzite constituents (the rounded ones) were most likely reworked from the Molasse bedrock or older gravels. This implies that a large fraction of the sediments in the Müntschemier and Finsterhennen gravel pits could represent recycled material from older fluvial gravels and conglomerates that were then reworked by the glaciers as they advanced to the foreland. Based on the sedimentological data and considering published and new optically stimulated luminescence (OSL) chronological data, we propose a landscape evolution scenario where the first glacial advance occurred during Marine Isotope Stage (MIS) 5d. The second glacier advance followed during MIS 4, while the last one during the Last Glacial Maximum (LGM), which corresponds to the MIS 2. The MIS 5d advance is recorded by the lowest unit of the Müntschemier gravel pit and consists of a fining upward sequence made up of an alternation of gravel and sand beds. The MIS 4 advance is recorded by the unit beneath the LGM till at Müntschemier and by the lowermost layer in the Finsterhennen gravel pit. It comprises an alternation of gravel and sand beds, which coarsens and thickens upwards. The LGM advance, finally, resulted in the deposition of amalgamated gravel beds at Finsterhennen, which ended with the construction of a till that is encountered on the top of both gravel pits. Sediments related to the interstadial conditions between MIS 5a and MIS 5b and MIS 3 were not encountered, which suggests that the warmer periods were characterised by non-deposition and/or erosion, which possibly resulted in the observed sedimentary hiatus. Although the chronological results are still preliminary, the available information allows us to suggest that during the Birrfeld Glaciation, the Valais lobe advanced several times to the Swiss Plateau. In addition, the facies associations imply that the eastward expansion of the Valais lobe during the MIS 5d and MIS 4 were most likely shorter than during the LGM.

Seasonal habitat use by warmwater fishes in a braided river, southwestern Japan: effects of spatiotemporal thermal heterogeneity

Seasonal habitat use by warmwater fishes in a braided river, southwestern Japan: effects of spatiotemporal thermal heterogeneity

The effect of riparian pool‐riffles on the hydrochemistry of hyporheic habitats: The River Esk, Yorkshire, UK

AbstractEuropean Union Water Framework Directive (WFD) (2000/60/EC) waterbody statuses are often derived from the assemblage of mixed‐taxon organisms found within bed sediments. Yet no routine water chemistry samples are taken from riverbed substrate, despite many interstitial species being dependant on specific physicochemical conditions. This paper examines water and nutrient exchanges between stream and substrate, the hyporheic zone, and the consequent alteration to the chemistry of interstitial and in‐stream waters, which in turn leads to small‐scale but significant changes in habitat. Bed topography, principally a pool‐riffle sequence, was surveyed and hydraulically sampled to examine the hyporheic flow pathways generated between the stream, substrate, and groundwater—creating an ecotone. Hyporheic zone, in‐stream and groundwater hydrochemistry, and hydraulic measures were assessed at a braided woodland river reach using a dense monitoring approach. The findings demonstrate that through a 23‐m pool‐riffle sequence, where water infiltrates at the riffle‐head and subsequently exfiltrates at the riffle‐tail, there is a 5% reduction in mean in‐stream nitrate‐N and a 73% reduction in hyporheic zone concentration. When calcium‐enriched riffle‐tail exfiltrate meets riffle‐runoff water that is turbulently oxygenated from riffle‐flow, an interstitial redoxcline is created. Dissolved oxygen nocturnally drops, with photosynthetic rate reduction, which causes hyporheic nitrate‐N to double its daytime concentration. The results are related to the Yorkshire River Esk freshwater pearl mussels, Margaritifera margaritifera Linnaeus (1758), a declining endangered species. At present, scant monitoring of interstitial hydrochemistry and diurnal change across stream and substrate occurs.

Study on Sedimentary Facies and Reservoir Characteristics of Paleogene Sandstone in Yingmaili Block, Tarim Basin

Block Yingmai 7 is structurally located in the western segment of the southern margin of the Kuqa Depression in the Tarim Basin. In the foreland basin, huge continental Mesozoic and Cenozoic strata have been deposited. In recent years, the Paleogene bottom sandstone section has been the main oil and gas exploration horizon. In order to further improve the oil and gas exploration effect of the Paleogene bottom sandstone in the study area and improve the accuracy of reservoir prediction, based on the related theory of sedimentology and petrology, this paper analyzes and studies the cores obtained by drilling in the Paleogene through laboratory core analysis experiments. The study shows that the Paleogene bottom sandstone is a braided river delta sedimentary system, and the sedimentary microfacies are mainly underwater distributary channels. The sandstone type is mainly light gray lithic feldspar fine sandstone, the sandstone debris particle sorting degree is medium-good, and the roundness is sub-edge-sub-circular. The microscopic characteristics of the reservoir are large pore throat radius, low displacement pressure, mainly intergranular pores, and good pore connectivity. It is a thin-layered mesoporous, medium-permeable, large-throat, and strongly heterogeneous reservoir. Finally, a classification evaluation table of reservoirs in block Yingmai 7 is established, and it is considered that the reservoirs of types I and II are enriched areas of oil and gas resources. The research results provide evidence for the prediction of oil and gas reservoirs.

Numerical Simulations of Confined Braided River Morphodynamics: Display of Deterministic Chaos and Characterization Through Turbulence Theory

AbstractIn this paper, we utilize a numerical morphological simulation approach to study braiding channel dynamics under steady flow. We conduct 11 different runs in a laboratory configuration, with each initial condition featuring a unique small‐amplitude perturbation pattern of the bed topography. From these infinitesimal initial differences, braided channels evolve into patterns that are macroscopically different and unique to each run, thus showing sensitive dependence on the initial condition and hence a chaotic behavior. Leveraging the analogy of braiding and fluid turbulence put forward by Paola (1996), by introducing a Reynolds‐type decomposition of bed elevations into a reference and a fluctuating component we characterize braided channel dynamics through statistics of bed fluctuations. We observe that, over the simulation time frame, braiding is not statistically homogeneous, but is stationary in a spatially averaged sense. We prove that braiding is anisotropic and extract two distinct length scales associated with the correlations of bed fluctuations in the streamwise and cross‐channel direction. We observe that, under the time averaging window that yields stationary braiding, braiding shows hints of ergodic behavior, as the time statistics of one run converge to the ensemble statistics computed across all the other runs.

Lithologic Hydrocarbon Accumulations in the Upper Jurassic Kalazha Formation in the Foreland Slope, the South Marginal Junggar Basin, Northwest China

The foreland slope in the south marginal Junggar Basin (SMJB) is geologically favorable for mass lithologic oil and gas reservoir accumulation. Based on outcrops, thin sections, individual-well facies, and cross-well stratigraphic correlation, the stratigraphic distribution and features of the Upper Jurassic Kalazha Formation were investigated in the SMJB. There are two sedimentary sources in the southwest and southeast Kalazha Formation, which thin out from south to north and vanish in the northern slope. Fan deltas occur in the southwest, and braided river deltas occur in the southeast. Kalazha reservoir rocks and sedimentary facies were predicted using joint 2D and 3D seismic impedance inversion. According to the overall analysis, the Kalazha Formation in the foreland slope is favorable for hydrocarbon accumulation, considering structural highs as the destination of long-term hydrocarbon migration and the updip wedge-out zone in the north with potential lithologic traps. The accumulation model was established with source rocks, reservoir rocks, caprocks, and migration systems for the lithologic hydrocarbon reservoirs in the Kalazha Formation in the SMJB. As per the model and regional stratigraphic and structural features, Kalazha lithologic hydrocarbon reservoirs mainly formed in the annular updip wedge-out zone in the foreland slope. Our deliverables may provide useful information for mass lithologic hydrocarbon accumulation in the foreland slope and deep to ultra-deep hydrocarbon exploration in the SMJB.

Planform changes and alterations of longitudinal connectivity caused by the 2019 flood event on the braided Brahmaputra River in Assam, India

The longitudinal connectivity of rivers facilitates the downstream transfer of discharge and sediment. Any alterations to this component can potentially impair/block sediment movement, resulting in deposition and planform alterations. This effect is more enhanced in braided rivers, which usually convey large sediment volumes. In this study, we use Graph Theory to analyze the impact of a big flood event (July 2019 flood) on the channel planform configuration of the Brahmaputra River in the eastern Indian state of Assam. The in-betweenness centrality and structural sediment connectivity of the nodes (channel confluences/diffluences) and links were computed using different indices. The node accessibility was enumerated using the Shimbel Index. Sedimentographs were devised to simulate the likely sediment outflow volumes and its duration in the post-flood scenario. Our results reveal that significant changes in the channel planform were caused by this flood event, which repositioned mid-channel and bank-attached bar deposits and realigned the river's entwined multiple threads. These engendered alterations in the existing channel bifurcations and inter-node connections, thereby impacting on how the sediment was transferred and its pathways. The enumerated accessibility index and simulated sediment volumes reflected the above changes, with reach-wise variations apparent in these aspects. This study helps comprehend the flood-induced planform morphological changes in braided streams, which has implications for navigation. The framework used here can also be applied to assess other braided rivers.

Assessing functional characteristics of a braided river in the Qinghai-Tibet Plateau, China

Functional characteristics of braided rivers with very high elevations (>3400 m) located in the Qinghai-Tibet Plateau, China provide unique insight into fully understanding global braided river functioning, but have not yet been explored because of their remote locations and harsh physiographic conditions. In this study, we unveiled these characteristics at the reach spatial scale over three decades in one of these braided rivers, the Upper Lancang River (ULR). Using Google Earth Engine resources and a specific selection of Landsat images obtained between 1989 and 2018 during the dry season (November to early May when water levels were low and comparable over years), we analyzed water area, extracted flowing and non-flowing channels, active channel widths (unvegetated bars and water channels), and calculated lateral shifting rates of the main channel for 13 sub-periods. We also developed an empirical method for estimating vegetated areas in the selected years. We found that (1) this braided system is partly controlled by peak flows and flood durations and the braiding activity evolved through time according to braided planform characteristics, (2) braiding intensity is high during low discharges, suggesting that the ULR is a very well-connected braided system with groundwater, but we observed higher braiding activity in spring than in fall, suggesting other factors than groundwater recharge also control non-flowing channel occurrence, and (3) the ULR supports a vegetation mosaic that is dynamic at a multi-year scale with period of declines that can be caused by scouring and rapid growth in an optimal recruitment window. These findings lead to our interpretation of vegetation behavior and surficial water – groundwater interactions, which needs future field validation.

Sedimentary characteristics and sand-body distributions in the Lower Permian He 8 Member, Ordos Basin, China

The Lower Permian He 8 Member (P1h8) in the Ordos Basin is a typical producing zone of tight lithologic gas reservoirs. Analyses of sedimentary characteristics, electrofacies, and sand-body distributions of P1h8, conducted on modern fluvial deposits, outcrops, cores, and well logs, revealed that braided rivers that developed in the Lower P1h8 and Upper P1h8 are characterized by meandering river. Within these fluvial deposits, the procedure consists of analyzing high-resolution sequence stratigraphy and sedimentary dynamics defined from calibrated logging curve signatures and depositional studies. According to modern and ancient fluvial deposits, we have developed a process-based sedimentary conceptual model for interpreting and predicting the distribution and geometries of sand bodies in braided and meandering deposits. The main sand body of the braided river system was bars and channel fill deposits. The braided river sand bodies are distributed over multiple vertical superimpositions and overlapping horizontal connections. The meandering river sand bodies are mainly point-bar deposits, which are bead-shaped and exhibit scattered development in the vertical direction. This comparison indicates that there were significant differences between braided and meandering deposystems. The sand bodies in the Lower P1h8 were multidirectionally connected and primarily distributed in a stacked pattern. In contrast, the sand bodies in the Upper P1h8 were distributed in an isolated manner, and fine grains (mud and silt) were deposited between the sand bodies with poor connectivity. We interpreted the fluvial deposits that control the distributions of the sand body of the He8 Member in the eastern Sulige gas field and constructed a corresponding prediction model of a braided-meandering reservoir. This model will promote understanding of the extent of fluvial deposits and sand-body distribution of P1h8, thus elucidating hydrocarbon-bearing sand units of the Ordos Basin for future exploration.

Dataset of "Using a dense seismic array to study fluvial processes in a braided river reach under flood conditions"

Dataset of "Using a dense seismic array to study fluvial processes in a braided river reach under flood conditions"

Morphodynamic processes in a large gravel-bed braided channel in response to runoff change: a case study in the Source Region of Yangtze River

Morphodynamic processes in a large gravel-bed braided channel in response to runoff change: a case study in the Source Region of Yangtze River

From desert to monsoon: irreversible climatic transition at\u2009~\u200936\xa0Ma in southeastern Tibetan Plateau

Although there is increasing evidence for wet, monsoonal conditions in Southeast Asia during the late Eocene, it has not been clear when this environment became established. Cenozoic sedimentary sequences constrained by radiometrically dated igneous rocks from the Jianchuan Basin in the southeast flank of Tibetan Plateau now provide a section whose facies and climatic proxies determine this evolution. Semi-arid conditions had dominated the region since Paleocene controlled by the northern sub-tropical high pressure system, culminating in mid Eocene when desert dunes developed. From 36 Ma, the basin began to accumulate swamp sediments with coals, together with synchronous braided river deposits and diversified pollen assemblages, indicating significant increase in precipitation. This remarkable transition from dry to wet conditions precedes the Eocene/Oligocene boundary at 34 Ma, thus excluding general global cooling as the prime driver. We propose that uplift of Tibetan Plateau might have reached a threshold elevation by that time, operating through thermal and dynamic forcing, causing the inception or significant intensification of monsoonal rains to penetrate into this downwind locality.

Changes of Divergence and Confluence Relationship Between Dongting Lake and the Yangtze River After the Operation of the Three Gorges Project and Its Impact on the Waterway Depth

Human activities and climate change have profoundly changed the hydrological and geomorphological evolutionary processes and trends of rivers and lakes, which, in turn, has affected the utilization of their waterway depth. This study chose the Dongting Lake–Jingjiang confluence of the Changjiang River (Yangtze Rvier), since the operation of the Three Gorges Project, the split ratio of water and the sediment distribution of the three outlets of Dongting Lake—that is, Songzikou, Taipigkou, and Ouchikou—have continued to decrease. Along with the decreasing flow of Dongting Lake, the relative increase in the runoff of the Jingjiang reach and the increase in riverbed erosion intensity have increased the relative height difference between Jingjiang and Dongting Lake, intensifying the reduction of the split ratio of water and the sediment distribution of the three outlets. The riverbed erosion of the Jingjiang reach has created a promising foundation for an increase in the waterway dimensions. However, the length of the reach not meeting the requirements of 4.5× 200 m (water depth × width) is 18.4 km, of which the length in the river-lake confluence is 12.6 km, accounting for 68.35% of the total length of obstructed navigation. Furthermore, at the reach (Zhicheng–Dabujie reach) affected by the first outlet (Songzikou), a 4.5-m flume has been formed, but its width is less than 200 m. Moreover, the “steep slope and rapid current” phenomenon is clear, and it affects the safety of ships. At the reach (Taipingkou reach) affected by the second outlet, the shrinkage of the bottomland, and the intersecting braided river channels make the low-flow routes unstable, the water depth being less than 4.5 m. At the reach (Tianxingzhou–Ouchikou reach) affected by the third outlet, the shoreline of the reach has collapsed and retreated significantly. Additionally, beach erosion and the downstream movement of cut banks have caused the downstream waterway width at the reach to be reduced to less than 200 m or formed shoals with a water depth of less than 4.5 m. Owing to the jacking effect of the lake’s outflow backwater, the flow rate of the reach (Xiongjiazhou–Chenglingji reach) affected by the confluence of Dongting Lake decreased, creating a shoal with a water depth of less than 4.5 m in the navigation waterway. The results of this study have guiding significance for understanding the changes of channel conditions and the improvement of channel scale in the intersection area of rivers and lakes.

Characterization of seismic information entropy attributes of braided river delta sedimentary microfacies for the upper Shaximiao formation in the Wubaochang area, northeastern Sichuan Basin, China

Characterization of seismic information entropy attributes of braided river delta sedimentary microfacies for the upper Shaximiao formation in the Wubaochang area, northeastern Sichuan Basin, China

A Numerical Study on Bank Erosion of a Braided Channel: Case Study of the “Tangail and Manikganj Districts Along the Brahmaputra River”

Brahmaputra River comprises the characteristics of a braided channel and suspended sediment-dominant river. Frequent changes in the river course have led to severe bank erosion. In particular, Tangail and Manikganj districts have recently become bank erosion-prone areas. To predict vulnerable locations based on bank erosion, we aimed to understand the behavior of the braided channel by conducting a numerical simulation and satellite data analysis in this study. We employed a depth-integrated 2-D numerical model for water and sediment transport, which was originally proposed by Takebayashi et al. and modified by Harada et al. by introducing a new treatment of suspended sediment. In addition, bathymetry data were created using a series of satellite data information to successfully conduct the simulation. In this study, we focused on two aspects. The first point is the skewing of flow discharge along multiple channels, which belongs to the area of interest, as a large-scale phenomenon. The second point is changing the local geometry of the sand bar and changing the flow pattern, as a small-scale phenomenon. To consider the two different scales, we employed the computation domain as an entire channel. Our results indicate that the numerical model is successfully verified using satellite data information, and the two-scale phenomena are successfully described. Regarding the large-scale phenomenon, our results indicate that the distribution of higher flow rates activates various geomorphological changes, including riverbed evolution, channel changes, and bank erosion. On the other hand, small-scale phenomena, such as the rapid appearance of sand bars and changes in the water course, are directly related to bank erosion.

Reconstructing the depositional history of Pleistocene fluvial deposits based on grain size, elemental geochemistry and in-situ 10Be data

Constraining depositional phases in braided river deposits can be challenging if only based on sedimentology or geochronology. In this paper, we explored how different data sources can provide complementary information on the depositional history of Pleistocene fluvial deposits. The study was realized on the Zutendaal gravels that outcrop in Northeastern Belgium. In an 8 m high exposure of gravel sheets, we collected bulk samples that were processed for grain size, elemental geochemistry and cosmogenic radionuclides. After dry sieving, we derived the D10, D50, D90, gravel and sand content. From the elemental geochemistry of the bulk samples, we calculated the Ti/Zr and Cr/Zr ratios as proxies for provenance, the Al2O3/SiO2 and Ba/Sr ratios for hydrolysis, and the MnO, Fe2O3 concentrations and the Fe2O3+MnOAl2O3 ratio for oxidation. The 10Be concentration-depth profiles are informative to identify phases of landscape stability characterized by depositional hiatuses. To verify the existence of any aberrant variation in 10Be concentration associated to provenance, the in-situ 10Be concentrations were contrasted with provenance and weathering indices. Differences in grain size, elemental geochemistry and in-situ 10Be between sedimentary units were evaluated based on Mann-Whitney tests, while Spearman correlation tests informed us on the co-variation between data sources. The outcrop in the Zutendaal gravels contains three depositional units with significant differences in grain size and chemical weathering extent, and representing distinct 10Be accumulation phases. The absence of correlation between provenance and oxidation proxies indicates that weathering is essentially intraformational or post-depositional. Sedimentary hiatuses were identified based on fining upward sequences and 10Be concentration-depth profiles, whereby local deviation in 10Be concentration at the top of the fining upward sequence provided information on the duration of the hiatus. The case study illustrates how co-variations in weathering, provenance, granulometry indices and 10Be concentration are informative for the depositional history of fluvial sediments, and landscape stability during the Pleistocene.

Magnetostratigraphy of the Cenozoic Lulehe section in the Qaidam Basin: Implications for the tectonic deformationon the northeastern Tibetan Plateau

<p indent="0mm">The Qaidam Basin is the largest Cenozoic basin located on the northeastern margin of the Tibetan Plateau. The extremely thick Cenozoic sedimentary strata in the basin recorded regional tectonic deformation and associated climate change when the Tibetan Plateau grew outward to its margins. The Cenozoic strata in the Qaidam Basin have been historically subdivided into seven primary stratigraphic units: The Lulehe, Xia Ganchaigou, Shang Ganchaigou, Xia Youshashan, Shang Youshashan, Shizigou, and Qigequan formations. Although many studies have been performed in recent decades, the Qaidam Basin’s inception, development and extinction are still unclear, which requires more work, such as high-resolution magnetostratigraphies. This paper focuses on the Lulehe section, which is the type section of the Lulehe Formation on the northern margin of the Qaidam Basin. The Lulehe section encompasses the Lulehe to Shizigou Formations, and the section was previously estimated to have been initially deposited 52 Ma. We collected paleomagnetic samples from 2041 sites in the Lulehe section to establish magnetic polarity sequences of the section. Constrained by the regional stratigraphic correlation, the recognized magnetic polarity sequences of the Lulehe section were anchored to chrons C12n–C3n.4n (31–5 Ma). Our correlation places the age of the Lulehe Formation at 30.9–23.7 Ma, suggesting that the onset of sediment accumulation in the Qaidam Basin occurred ca. 31 Ma. Overlying the Lulehe Formation, the Xia Ganchaigou Formation was deposited from 23.7 to18.1 Ma, the Shang Ganchaigou Formation spans from 18.1 to 12.9 Ma, the Xia Youshashan Formation spans from 12.9 to 9.9 Ma, the Shang Youshashan Formation spans from 9.9 to 6.9 Ma, and Shizigou Formation is younger than 6.9 Ma. To characterize the sedimentary environments of strata within the Lulehe section, we undertook a detailed stratigraphic analysis. At the bottom of the section, the Lulehe Formation is characterized by alluvial facies (30.9–23 Ma). Upward, the Xia Ganchaigou Formation and Shang Ganchaigou Formation (23–13 Ma) are interpreted to have formed in braided river, meandering river, and lacustrine environments. The sedimentary environments of the Xia Youshashan Formation and Shang Youshasahn Formation are interpreted as delta-fan and braided river facies. An abrupt sedimentary environmental change from lacustrine to delta-fan occurred ca. 13 Ma in the Lulehe section. This lithofacies change in the section may represent tectonic deformation of the South Qilian Shan in the northern Qaidam Basin. From ca. 11 Ma, coarse-grained clasts significantly increased upward in the section, and the sedimentary environment changed to braided river. This phenomenon suggests that the northern Qaidam Basin fault system propagated southward to the region adjacent to the Lulehe section. At the top of the Lulehe section, the Shizigou Formation is characterized by an alluvial fan system. Sediment accumulation rates in the Lulehe section from ca. 31 to ca. 5 Ma were calculated based on the Lulehe magnetostratigraphy. We found that the Lulehe section almost maintained a stable accumulation rate from ca. 31 to ca. 15 Ma with an accumulation rate of 170.6 m/Ma. From ca. 15 Ma, the accumulation rate in the study area increased significantly to 271.2 m/Ma, and the accumulation rate in the section decreased slightly to 204.3 m/Ma from 11 Ma. The variations in the accumulation rate ca. 15 and ca. 11 Ma in the Lulehe section are consistent with the sedimentary environment changes ca. 13 and ca. 11 Ma. The increase in the sedimentation rate ca. 15 Ma again suggests that the northern Qaidam Basin fault system began to be active. The decrease in the sedimentation accumulation rate ca. 11 Ma indicates that the Lulehe section was involved in tectonic deformation related to southward propagation of the northern Qaidam Basin fault system, which may have reduced the accommodation space in the Lulehe region on the northern basin margin. Overall, our results indicate that the Qaidam Basin experienced two-stage tectonic deformation beginning ca. 31 Ma and subsequently ca. 15 Ma. The Oligocene (31 Ma) deformation led to the formation of the Qaidam Basin. The northern basin margin has been intensively deformed by anticlines and synclines as a result of fault thrusting since the middle Miocene.