Fluvial systems play a crucial role in coastal and riverine ecosystems, making it essential to understand their responses to sea level changes for preserving biodiversity and managing natural resources. The evolution ...Fluvial systems play a crucial role in coastal and riverine ecosystems, making it essential to understand their responses to sea level changes for preserving biodiversity and managing natural resources. The evolution of the modern Indus River Delta offers a rare opportunity to study the interplay between sea level fluctuations, tectonism, sediment supply, and the corresponding fluvial responses. This study employs the ‘SedSim' stratigraphic forward model to simulate the delta's evolution from 200 kyr to the next5 kyr, drawing on data from field observations, Landsat imagery, digital elevation models, and previous studies. The model consists of 205 layers, each representing a 1-kyr time step, covering the last two glacial-interglacial cycles. Between 200 kyr and 130 kyr, during a lowstand period, sedimentation on the delta plain continued due to partial flow from the Indus River. During the last interglacial(130–60 kyr), rising sea levels led to peak sediment deposition, characteristic of a highstand phase. From 60 kyr to 18 kyr, sea levels dropped to their lowest during the Last Glacial Maximum(LGM), resulting in extensive erosion and minimal deposition on the delta plain. From 18 kyr to the present, rapidly rising sea levels, coupled with intensified monsoon activity, increased sedimentation rates and triggered avulsion and aggradation processes. The model accurately predicted depositional thickness across the delta plain, indicating a maximum of ca. 200 m at the shoreline platform, ca. 175 m in the northeastern delta, and ca. 100 m in the central delta. The study underscores the delta's vulnerability to future sea level rise, which–at a projected rate of 1 m/kyr–could significantly influence the densely populated, low-lying delta plain. These findings offer valuable insights into the geomorphic evolution of the Indus Delta and emphasize the socioeconomic implications of sea level change, underscoring the importance of proactive management and adaptation strategies.展开更多
A macro-tidal tropical estuary with high fluvial discharge is characterized by both fragility and remarkable dynamism.This study utilizes the Salween River Delta(SRD)as a case example to examine the interplay between ...A macro-tidal tropical estuary with high fluvial discharge is characterized by both fragility and remarkable dynamism.This study utilizes the Salween River Delta(SRD)as a case example to examine the interplay between morphology and vegetation under similar tidal conditions.Our analysis of correlations and inferences revealed several significant trends in the SRD:(1)an overall expansion of land area and intertidal vegetation,with the most pronounced changes occurring in the eastern sector;(2)the predominance of river discharge influencing the southwestern and northern sectors,contrasted with the primary impact of storm surges in the eastern sector;and(3)three distinct causal relationships among estuarine morphology,vegetation,storm surges,and river discharge:a direct model where river discharge shapes estuarine morphology,a progressive model in which river discharge affects vegetation distribution,subsequently influencing estuarine morphology,and a hybrid model where storm surges directly impact vegetation and indirectly modify its distribution through changes in estuarine morphology.The stability of sediment supply and the role of intertidal vegetation are crucial for the continuous seaward advance,providing a vital foundation for the protection and development of estuarine deltas.展开更多
0 INTRODUCTION The Qilian Mountain Belt,at the forefront of the Tibetan Plateau's expansion,offers key insights into the plateau's tectonic deformation(Zuza et al.,2018;Zheng et al.,2010;Zhang et al.,2004;Tapp...0 INTRODUCTION The Qilian Mountain Belt,at the forefront of the Tibetan Plateau's expansion,offers key insights into the plateau's tectonic deformation(Zuza et al.,2018;Zheng et al.,2010;Zhang et al.,2004;Tapponnier et al.,2001;Meyer et al.,1998).The northwest-trending mountain ranges in the Qilian Shan(“Shan”means“Mountain”in Chinese)have significantly influenced this deformation(Zheng et al.,2013).展开更多
The geomorphological evolution of the Northeastern Tibetan Plateau （NETP） could provide valuable information for reconstructing the tectonic movements of the region. And the considerable uplift and climatic changes ...The geomorphological evolution of the Northeastern Tibetan Plateau （NETP） could provide valuable information for reconstructing the tectonic movements of the region. And the considerable uplift and climatic changes at here, provide an opportunity for studying the im- pact of tectonic and monsoon climate on fluvial morphological development and sedimentary architecture of fluvial deposits. The development of peneplain-like surface and related land- scape transition from basin filling to incision indicate an intense uplift event with morphologi- cal significance at around 10-17 Ma in the NETP. After that, incision into the peneplain was not continuous but a staircase of terraces, developed as a result of climatic influences. In spite of the generally persisting uplift of the whole region, the neighbouring tectonic blocks had different uplift rates, leading to a complicated fluvial response with accumulation terraces alternating with erosion terraces at a small spatial and temporal scale. The change in fluvial activity as a response to climatic impact is reflected in the general sedimentary sequence on the terraces from high-energy （braided） channel deposits （at full glacial） to lower-energy de- posits of small channels （towards the end of the glacial）, mostly separated by a rather sharp boundary from overlying flood-Ioams （at the glacial-interglacial transition） and overall soil formation （interglacial）. Pronounced incision took place at the subsequent warm-cold transi- tions. In addition, it is hypothesized that in some strongly uplifted blocks energy thresholds could be crossed to allow terrace formation as a response to small climatic fluctuations （10^3-10^4 year timescale）. Although studies of morpho-tectonic and geomorphological evolu- tion of the NETP, improve understanding on the impacts of tectonic motions and monsoonal climate on fluvial processes, a number of aspects, such as the distribution and correlation of peneplain and the related morphological features, the extent and intensity of tectonic move- ments influencing the crossing of climatic thresholds, leading to terrace development, need to be studied further.展开更多
Deposition of fluvial sandbodies is controlled mainly by characteristics of the system, such as the rate of avulsion and aggradation of the fluvial channels and their geometry. The impact and the interaction of these ...Deposition of fluvial sandbodies is controlled mainly by characteristics of the system, such as the rate of avulsion and aggradation of the fluvial channels and their geometry. The impact and the interaction of these parameters have not received adequate attention. In this paper, the impact of geological uncertainty resulting from the interpretation of the fluvial geometry, maximum depth of channels, and their avulsion rates on primary production is studied for fluvial reservoirs. Several meandering reservoirs were generated using a process-mimicking package by varying several con- trolling factors. Simulation results indicate that geometrical parameters of the fluvial channels impact cumulative pro- duction during primary production more significantly than their avulsion rate. The most significant factor appears to be the maximum depth of fluvial channels. The overall net-to-gross ratio is closely correlated with the cumulative oil production of the field, but cumulative production values for individual wells do not appear to be correlated with the local net-to-gross ratio calculated in the vicinity of each well. Connectedness of the sandbodies to each well, defined based on the minimum time-of-flight from each block to the well, appears to be a more reliable indicator of well-scale production.展开更多
The concept and characteristics of fluvial fan are elucidated through literature review and case analysis.Firstly,the concept and terminology of fluvial fan are introduced.Secondly,the progress and controversy on the ...The concept and characteristics of fluvial fan are elucidated through literature review and case analysis.Firstly,the concept and terminology of fluvial fan are introduced.Secondly,the progress and controversy on the formation mechanism,analysis methods and sedimentary models of fluvial fan are elaborated,and fluvial fan is compared with alluvial fan,river and lacustrine delta.Finally,ten identification signs of the fluvial fan are proposed.It is found through the study that development and scale of fluvial fan are affected by external factors such as climate,tectonic,provenance and wind field.The facies and lithofacies association inside the fan are controlled by the activity of the internal channel.It is pointed that fluvial fans are widely distributed in the world not only today but also in the geological history.The occurrence of fluvial fan will change the traditional continental deposition system dominated by alluvial fan-river-lacustrine.Meanwhile,the research of fluvial fan will be of great significance in the fields of sedimentology and oil and gas exploration.展开更多
The spatial distribution of valley setting （laterally-unconfined, partly-confined, or confined） and fluvial morphology in the source region of the Yangtze and Yellow Rivers is contrasted and analyzed. The source reg...The spatial distribution of valley setting （laterally-unconfined, partly-confined, or confined） and fluvial morphology in the source region of the Yangtze and Yellow Rivers is contrasted and analyzed. The source region of the Yangtze River is divided into 3 broad sections （I, II and III） based on valley setting and channel gradient, with the upstream and downstream sections being characterized by confined （some reaches partly-confined） valleys while the middle section is characterized with wide and shallow, laterally-unconfined valleys. Gorges are prominent in sections I and III, while braided channel patterns dominate section II. By contrast, the source region of the Yellow River is divided into 5 broad sections （sections I-V） based on valley characteristics and channel gradient. Sections I, II and IV are alluvial reaches with mainly laterally-unconfined （some short reaches partly-confined） valleys. Sections III and V are mainly confined or partly-confined. Greater morphological diversity is evident in the source region of the Yellow River relative to the upper Yangtze River. This includes braided, anabranching, anastomosing, meandering and straight alluvial patterns, with gorges in confined reaches. The macro-relief （elevation, gradient, aspect, valley alignment and confinement） of the region, linked directly to tectonic movement of the Qinghai-Tibet Plateau, tied to climatic, hydrologic and biotic considerations, are primary controls upon the patterns of river diversity in the region.展开更多
Fluvial deposits from the Middle Triassic Youfangzhuang Formation in Henan Province, China contain a low-diversity trace fossils. Vertical dwelling burrows of opportunists dominate in active channel, whereas horizonta...Fluvial deposits from the Middle Triassic Youfangzhuang Formation in Henan Province, China contain a low-diversity trace fossils. Vertical dwelling burrows of opportunists dominate in active channel, whereas horizontal deposit-feeding, grazing, and vertical dwelling burrows occur in overbank deposits. Seven recurrent ichnofabrics were distingushed. The Palaeophycus tubularis ichnofabric pre- serves below scour interface between two fluvial cycles. The Skolithos linearis ichnofabric forms in middle to high-energy, soft substrates in the middle and upper parts of active channel deposits under semi-arid climate. The Skolithos linearis-Planolites montanus ichnofabric occurs in the sediments just a little above the Skolithos linearis ichnofabric and is formed in middle-energy, soft substrates in the up- per part of active channel deposits. The Planolites montanus ichnofabric is mostly preserved in associa- tion with medium- to thick-bedded brown-red silty mudstones or siltstones in low-energy, perennial muddy bottom ponds in overbank settings. The Taenidium barretti ichnofabric is interpreted as peri- odically exposed ephemeral ponds or low-energy distal floodplain. The Skolithos isp. ichnofabric com- monly occurs in middle to high-energy firm ground of proximal foodplain or crevasse-splay deposits. The root trace iehnofabric occurs in the crevasse splay deposits. The presence of thin palaeosols and the abundance of calcretization in mudstones indicate a seasonal climate ranging from humid to semi-arid, with high temperature, rainfall, and well-defined dry and wet seasons.展开更多
The Huang Shui River, a main tributary of the Yellow River, crosses a series of tectonically subsided and uplifted areas that show different patterns of terrace formation. The distribution of fluvial terrace of the Hu...The Huang Shui River, a main tributary of the Yellow River, crosses a series of tectonically subsided and uplifted areas that show different patterns of terrace formation. The distribution of fluvial terrace of the Huang Shui River is studied through topographic and sedimentologic terrace mapping. Three terraces in the Haiyan Basin, four terraces in the Huangyuan Basin, 19 terraces in the Xi＇ning Basin （the four high terraces may belong to another river）, nine terraces in the Ping＇an Basin, five terraces in the Ledu Basin and 12 terraces in the Minhe Basin are recognized. Sedimentology research shows that the geomorphologic and sedimentological pattern of the Huang Shui River, which is located at the margin of Tibet, are different from that of the rivers at other regions. The formation process of the terrace is more complicated at the Huang Shui catchment： both accumulation terrace and erosion terrace were formed in each basin and accumulation terraces were developed in some basins when erosion terraces were formed in other basins, indicating fluvial aggradation may occur in some basins simultaneously with river incision in other basins. A conceptual model of the formation process of these two kinds of fluvial terraces at Huang Shui catchment is brought forward in this paper. First, the equilibrium state of the river is broken because of climatic change and/or tectonic movement, and the river incises in all basins in the whole catchment until reaching a new equilibrium state. Then, the downstream basin subsides quickly and the equilibrium state is broken again, and the river incises at upstream basins while the river accumulates at the subsidence basin quickly until approaching a new equilibrium state again. Finally, the river incises in the whole catchment because of climatic change and/or tectonic movement and the accumulation terrace is formed at the subsidence basin while the erosion terrace is formed at other basins. The existence of the accumulation terrace implied the tectonic subsidence in the sub-basins in Huang Shui catchment. These tectonic subsidence movements gradually developed from the downstream Minhe Basin to the upstream Huangyuan Basin. Dating the terrace sequence has potential to uncover the relationship between the subsidence in the catchment and the regional tectonic at the northeastern Tibetan Plateau.展开更多
The Alagxa Plateau, in the margin of the northeastern Tibetan Plateau, is one of the most important dust source areas in East Asia, and the widespread sandy desert in the area is important both as a reservoir and a so...The Alagxa Plateau, in the margin of the northeastern Tibetan Plateau, is one of the most important dust source areas in East Asia, and the widespread sandy desert in the area is important both as a reservoir and a source of eolian silty. The northeastern margin of the Tibetan Plateau is one of the most actively-growing mountain belt on earth, and has large amounts of debris, with masses of fine grained material, which were continuously mobilized and deposited in the Alagxa Plateau by rivers, forming broad alluvial fans. It is possible that the role of fluvial sediments as a source of silty dust in the Alagxa Plateau has been underestimated. In this study, we test this hypothesis by investigating the iron mineralogical and geochemical characteristics of the fluvial sediments and the surface material of the sandy desert in the Alagxa Plateau, and comparing them with paleo-eolian dust deposits(loess) in the adjacent Chinese Loess Plateau(CLP) to investigate the possible linkages among the fluvial sediments, sandy desert and the last glacial loess of the CLP. The results show that sandy desert typically have high contents of goethite, and high ratios of goethite to hematite, similar to the fluvial sediments in the Alagxa Plateau. Based on the major element characteristics, field investigations and the results of previous studies, we found a genetic link between the silt component of the fluvial sediments and the sandy desert in the Alagxa Plateau with high value of Gt(goethite) and similarity of the Gt/(Hm(hematite)+Gt) ratio. But the silt component of the sandy desert main come from the adjacent fluvial sediments. The iron mineralogical characteristics(χ(magnetic susceptibility), χARM(anhysteretic susceptibility), SIRM(saturation isothermal remanent magnetization) and SIRM_(AF100 mT)(SIRM demagnetized at 100 mT)) of the CLP samples overlap with those of the fluvial sediments in the Alagxa Plateau, but there is a mismatch with the sandy desert samples. This suggests that the fluvial sediments are the source of a large amount of silty material which could be transported to the CLP. Therefore, we conclude that the fluvial sediment in the Alagxa Plateau is an important source of eolian silt, which is deposited in downwind region, and that this source has been previously underestimated.展开更多
Mid-Cretaceous strata within the Tintina Trench, 3 km west of the community of Ross River, contain evidence of deposition in two distinct, alternating, fluvial settings. Coal-bearing, mud-dominated strata are commonly...Mid-Cretaceous strata within the Tintina Trench, 3 km west of the community of Ross River, contain evidence of deposition in two distinct, alternating, fluvial settings. Coal-bearing, mud-dominated strata are commonly associated with high-constructive sandy channel systems, with extensive overbank, levee and splay deposits. Channels are between 3 and 30 m wide and 0.4-7 m thick. They show repetitive development of side and in-channel bar-forms, as well as up-channel widening of the rivers by selective erosion of associated overbank and levee deposits. Levees extended for several hundred metres away from the channels. In this setting low-angle inclined stratification and epsilon cross stratification may reflect lateral migration of crevasse channels or small streams. The paucity of exposure prevents recognition of the channels as products of multiple channel anastomosed systems or single channel high-constructive systems. Gravel-dominated strata, inter-bedded with, and overlying coal-bearing units, are interpreted as deposits of wandering gravel-bed rivers, with sinuosity approaching 1.4. In most exposures they appear to be dominated by massive and thin planar-bedded granule to small pebble conglomerates, which would traditionally be interpreted as sheet-flood or longitudinal bar deposits of a high-gradient braided stream or alluvial fan. Architectural analysis of exposures in an open-pit shows that the predominance of flat bedding is an artefact of the geometry of the roadside exposures. In the pit the conglomerates are dominated by large scale cross stratification on a scale of 1-5.5 m. These appear to have developed as downstream and lateral accretion elements on side-bars and on in-channel bars in water depths of 2-12 m. Stacking of strata on domed 3rd order surfaces suggests development of longitudinal in-channel bar complexes similar to those observed in parts of the modern Rhone River system. Mudstone preserved in some of the channels reflects intervals of channel abandonment or avulsion. Minimum channel width is from 70 to 450 m.展开更多
Accumulation occurs widely in fluvial processes.Accurately accounting for the effects of previous water and sediment conditions on accumulation is essential for studying riverbed evolution.In this study,to reveal the ...Accumulation occurs widely in fluvial processes.Accurately accounting for the effects of previous water and sediment conditions on accumulation is essential for studying riverbed evolution.In this study,to reveal the physical mechanisms of accumulation,various geometric observations of both the upstream and downstream reaches of dams on several typical fluvial channels were analyzed.The changes in water and sediment conditions were defined as external disturbances.Assuming that the probability of an external disturbance conforms to a Poisson distribution,and that the response intensity induced by an individual disturbance decays exponentially over time,a mathematical description of the accumulation of internal responses to external disturbances is given.Furthermore,a corresponding theoretical model for simulating the spatiotemporal readjustments of characteristic river variables is proposed based on stochastic theory.The proposed models are then applied to investigate spatiotemporal readjustment in the upper and lower reaches of dams following their construction.The results indicate that temporally,the vertical,lateral,and overall readjustment rates of the reaches are relatively fast in the early period following dam construction but then decrease rapidly over time.Accumulated riverbed degradation,channel width,and sedimentation continuously increase until a new dynamic equilibrium is reached.These phenomena reflect the representative accumulation characteristics of fluvial processes.Spatially,the erosion intensities in downstream reaches decrease nonlinearly along the channel until eventually diminishing.The unbalanced spatial distribution of erosion intensity arises from the system response characterized by propagation in space but decay over time,which is characteristic of accumulation phenomena after disturbances.The results of the developed model show that the spatiotemporal readjustments of the studied cross-sections and channel reaches can be accurately described by the unified theoretical formula derived herein.The model predictions show good agreement with observed field data with determination coefficients of 0.92,0.93,0.76,and 0.95 for vertical,lateral,longitudinal,and overall readjustments,respectively.The proposed theoretical models account for both the accumulation characteristics of fluvial processes and their spatial distributions.In demonstrating the proposed ap-proach,this study provides a theoretical basis and new calculation method for quantitatively describing the spatiotemporal readjustments of non-equilibrium fluvial channels following external disturbances.展开更多
The Nepal Himalayas is the source of many glacial and spring-fed river systems crisscrossing the mountainous terrain.There is an increasing recognition of small mountain rivers(SMRs)to have a significant combined expo...The Nepal Himalayas is the source of many glacial and spring-fed river systems crisscrossing the mountainous terrain.There is an increasing recognition of small mountain rivers(SMRs)to have a significant combined export of dissolved and particulate organic carbon to the global carbon flux.We analyzed fluvial sediments from two SMRs and compared the results with two large mountain rivers(LMRs)in Nepal.We investigated the organic matter(OM),its compositional variability,and seasonal export using a suite of lipid biomarkers,namely n-alkanes,n-alkanoic acids,n-alkanols,and sterols.The SMRs indicated a similarity in lipid distribution and were affected by a strong seasonal variability.The LMRs showed a distinct contrast in the distribution of lipids in suspended sediments.Bedload sediments in SMRs were derived from diverse sources with weak terrigenous dominance all-year-round compared to the suspended load.Functional lipids(n-alkanoic acids and n-alkanols)were the major constituents in SMR sediments,indicating better preservation.In contrast,n-alkane concentration dominated over other fractions in suspended sediments retrieved from LMRs.The biomarker trends differentiate SMRs from LMRs with lower transformed/degraded OM in SMRs.A common observation was the strong presence of even carbon compounds in short-chain n-alkanes in SMR bedload sediments and their predominance in suspended sediments in LMRs.Such an unusual trend is attributed to specific biomarker sources from the catchment and ongoing processes in fluvial systems.Topsoil colonized by fungal species under moist acidic conditions and autochthonous bacteria contributes to the organic matter pool in shallow SMRs.In LMRs,the contribution from thermally mature sedimentary hydrocarbons and the diagenetic reduction of nalkanoic acids to n-alkanes are additional contributors to the allochthonous carbon pool.The differences in lipid concentrations,their distribution,seasonality,and the size of rivers suggest differential preservation/degradation of the organic matter pool and their importance in contributing to the carbon budget.展开更多
The middle and lower reaches of the Tarim River are currently one of the main regions of ecological restoration in the arid areas of western China.Using the principles and method of landscape ecology,this study has ch...The middle and lower reaches of the Tarim River are currently one of the main regions of ecological restoration in the arid areas of western China.Using the principles and method of landscape ecology,this study has chosen the fluvial corridor landscape in the middle and lower reaches of the Tarim River,and discusses the region’s ecologically functional regionalization system and issues related to its practical classification.On this basis the corresponding regionalizing principles and standards were developed which were used to qualitatively divide the three main landscapes as the ecologically functional areas in the drainage basin.The paper has also analyzed the characteristic of the study areas,and has put forward the measures for its ecological restoration.展开更多
Based on detailed investigation of the modern sedimentation of the distributive fluvial system of Shule River and the data of unmanned aerial vehicle(UAV)aerial photography and satellite remote sensing,the sedimentary...Based on detailed investigation of the modern sedimentation of the distributive fluvial system of Shule River and the data of unmanned aerial vehicle(UAV)aerial photography and satellite remote sensing,the sedimentary characteristics and differences of distributive fluvial system in arid areas are analyzed.By comparing the changes in slope,river morphology and sedimentary characteristics in different sections from the apex to the toe,the distributive fluvial system of Shule River can be divided into three facies belts:"proximal","middle"and"distal".The proximal belt has the largest slope and strongest hydrodynamic condition,mainly appears as large-scale braided river deposits;the fluvial bars in this belt are mainly composed of gravels,the gravels have good roundness and certain directionality,and are medium-large boulders,with low sand content;the main microfacies in this belt are braided channel and flood plain.The middle belt with slope smaller than the proximal belt,is mainly composed of braided bifurcating river deposits.Due to branching and infiltration,this belt has weaker hydrodynamic conditions,so some of the distributive rivers dry up,appearing as ephemeral rivers.This belt has small lenticular sandbodies,fine to medium gravels,higher sand content,and mainly braided channel,flood plain and aeolian dune microfacies.The distal belt has the smallest slope and flat terrain,where the river begins to transform from braided river to meandering river,the sediment is mainly sand.Due to the influence of slope,this belt has weaker erosion toward source and stronger lateral erosion,and point bars developing around the edge of the active lobes.In this belt,the river is completely meandering,and the main microfacies are braided channel,meandering channel,flood plain,aeolian dune,lake and swamp.展开更多
Understanding controls on river planform changes can help to build predictive models for distributive fluvial systems,and then guide the oil and gas exploration.To do this we have undertaken a detailed investigation o...Understanding controls on river planform changes can help to build predictive models for distributive fluvial systems,and then guide the oil and gas exploration.To do this we have undertaken a detailed investigation of the modern Great Halten River distributive fluvial system from the Sugan Lake Basin,Qinghai,China.Unmanned aerial vehicle(UAV) photography,satellite remote sensing data and elemental analysis were used to determine differences in the sedimentary characteristics of the distributive fluvial system.From the apex to the toe,the changes in the slope,river morphology,sedimentary characteristics and element content in different regions were determined and three facies belts:“proximal”,“medial” and “distal” were identified.We found that the sedimentary structure and elemental content characteristics of each facies differ greatly.We compare the large-scale evolution of rivers from braided to meandering rivers,and the fine description of sedimentary characteristics in combination with each observation,we strengthen our overall understanding of the modern DFS from macro to micro scale.At the same time,we summarize the sedimentation model of the Great Halten River DFS,and our study provides a reference for establishing the sedimentary model in continental petroliferous basins.展开更多
The fluvial-tidal transition(FTT)is a complex depositional zone,where fluvial flow is modified by tides as rivers approach a receiving marine basin.Variations in the relative importance of tidal versus fluvial process...The fluvial-tidal transition(FTT)is a complex depositional zone,where fluvial flow is modified by tides as rivers approach a receiving marine basin.Variations in the relative importance of tidal versus fluvial processes lead to a distinctive distribution of sediments that accumulate on channel bars.The FTT generally consists of three broad zones:(1)a freshwater-tidal zone;(2)a tidally influenced freshwater to brackish-water transition:and(3)a zone of relatively sustained brackish-water conditions with stronger tides.A very common type of deposit through the fluvial-tidal transition,especially on the margins of migrating channels,is inclined heterolithic stratification(IHS).At present,a detailed account of changes in the character of IHS across the FIT of a paleo-channel system has not been reported,although a number of modern examples have been documented.To fill this gap,we quantitatively assess the sedimentology and ichnology of IHS from seven cored intervals in three geographic areas situated within the youngest paleovalley("A"Valley)in the Lower Cretaceous McMurray Formation of Alberta.Canada.We compare the data to trends defined along the FTT in the present-day Fraser River in British Columbia.Canada to interpret paleo-depositional position in the ancient fluvial-tidal channels.Analysis determined that the mean mudstone thickness is 8.2 cm in the southern study area(SA).Mean thickness increases to 11 cm in the central study area(CA),and decreases again to 4.4 cm in the northern study area(NA).The proportion of mudstone is 31%in SA,44%in CA,and 27%in NA.Thicknessweighted mean bioturbation intensity in sands varied from 0.29 in SA and CA.to 0.28 in NA.On the other hand,thickness-weighted mean bioturbation intensity(Bl)in mudstone increases from 1.46 in SA.to 1.77 in CA.and is 1.94 in NA.The ichnological diversity also increased from south to north.Sedimentological results show sinilar trends to those of the Fraser River,enabling the identification of a freshwater to brackish-water transition zone with tidal influence.The interpreted position of the transition is underpinned by the bioturbation intensity and trace-fossil diversity trends,indicating periodic brackish-water conditions throughout SA in the McMurray Formation during low river flow conditions.Together,these data suggest that a broad FTT existed in the"A"Valley,with fluvial-dominated channels to the south that experienced seasonal brackish-water inundation during base flow,and channels experiencing increasing brackish-water influence lying further north towards a turbidity maximun zone.The FIT zone appears to have extended for several hundred kilometers fron south to north.Based on the sedimentological and ichnological data,as well as estimations of lateral accretion rates,we refute the colmonly applied Mississippi River depositional analogue for McMurray Formation channels.Rather,we show that while not a perfect fit,the tidally influenced Fraser River shows much greater agreement with the depositional character recorded in McMurray Formation IHS.Future work on the McMurray system should focus on characterizing tide-dominatecl deltaic and estuarine systems,such as the Ganges-Brahmaputra,and on forward-modeling the evolution of tide-dominated and tideinfluenced river systems.展开更多
Coupling within fluvial systems relates to the connectivity between the various components of the system. It can be viewed at several scales from local scales of hillslopetochannel and reachtoreach coupling, to larger...Coupling within fluvial systems relates to the connectivity between the various components of the system. It can be viewed at several scales from local scales of hillslopetochannel and reachtoreach coupling, to larger scales of zonal coupling between the major functional zones of the fluvial system, and to the scale of regional coupling. Coupling influences how the system responds to environmental change and how the effects of environmental change are propagated through the system. This paper provides a review, based largely on previously published work, of the coupling concept, and how the effective temporal scales vary with the spatial scale of coupling. Local scale coupling is considered through the hillslope to channel coupling in the Howgill Fells, northwest England, observed over a 30year monitoring period, together with examples from badlands in Spain, and reachtoreach coupling on the River Dane, northwest England. At the zonal scale the relative influence of climatic and baselevel change on coupling through dryregion alluvial fans is considered on fan systems in Spain, Nevada, and UAE/Oman. For large scale regional coupling, the response of the Tabernas basin, southeast Spain to tectonic uplift, is examined. The factors influencing coupling mechanisms vary with temporal and spatial scales. At the hillslopetochannel scale the significant factors are the magnitude and frequency characteristics of sediment generation and removal mechanisms within the context of progressive morphological change. Effective timescales range from the individual event to decadal timescales. At the zonal scale, that of alluvial fans, the significant factors are climatic change, and particularly in the appropriate morphological setting, baselevel change. Effective timescales are of the order of hundreds to thousands of years. At the regional scale, the response to tectonic uplift may take >100 ka to be transmitted through the drainage basin.展开更多
The Yellow River is usually assumed to record tectonic activities and climatic changes;however,a systematic study was lack in the sedimentology,stratigraphy,geomorphology and geochronology for the entire Yellow River ...The Yellow River is usually assumed to record tectonic activities and climatic changes;however,a systematic study was lack in the sedimentology,stratigraphy,geomorphology and geochronology for the entire Yellow River though various geologic scholars have conducted numerous works in individual basins.This review focused on well-preserved fluvial terrace sequences that formed along this river on northeastern(NE)Tibetan Plateau and Ordos Block over the past 2.6 Ma.After comparing numerous initial incision ages at different segments along the Yellow River,we found out that the youngest initial incision may occur at ca.150 ka at the Longyang Gorge.The Yellow River may transit from multiple separated endorheic drainages to an entire external drainage after 150 ka,which may cause differentiations in the apparent incision rates before and after 150 ka;thus apparent net incision rates were calculated respectively for the Yellow River before 150 ka and the drainage network post 150 ka.Apparent net incision rates prior to 0.15 Ma were calculated as 0.15,0.29,0.10,0.12 and 0.03 mm/a respectively in Tongde-Xunhua,Lanzhou-Linxia basins,Heishan,Jinshan and Fenwei-Sanmen Gorges in this review,which mainly reflected Kunhuang-Gonghe Tectonic Event,generated by the Indo-Asian collision and diminishing as the NE Tibetan Plateau eastward extruding at ca.1.8-0.15 Ma.Apparent net incision rates post 0.15 Ma were calculated respectively for NE Tibetan Plateau and Ordos Block,considering their different base level.On NE Tibetan Plateau,four fluvial degradational phases were identified between ca.105~70,53~40,25~16 and 12~6 ka associated with terrace levels respectively,at average elevations of 96,40,20 and 10.5 meters above the current river level(m arl)within a range of 5~96 m arl;and four broad periods in the last 150 ka on Ordos Block:possibly marine oxygen isotope stage(MIS)5,ca.118 to 72 ka,most of MIS 3,ca.44~28 ka,transition from LGM to last deglacial ca.20 to 16 ka,and 4~3 ka at average elevations of 67.5,26,19 and 11.5 m arl.These degradational phases post 0.15 Ma were associated with multiple processes including enhanced fluvial discharge with an increase in monsoonal precipitation and/or melt water in deglaciation.展开更多
Evidence from lithology, foraminiferal assemblages, and high-resolution X-ray fluorescence scanning data of core SFK-1 indicates tidally influenced paleo-fluvial sedimentation during the last glacial maximum (LGM) on ...Evidence from lithology, foraminiferal assemblages, and high-resolution X-ray fluorescence scanning data of core SFK-1 indicates tidally influenced paleo-fluvial sedimentation during the last glacial maximum (LGM) on the outer shelf of the East China Sea. The paleo-fluvial deposits consist of river channel facies and estuarine incised-valley-filling facies. Different reflections on the seismic profile across core SFK-1 suggest that the river channels shifted and overlapped. River channel deposition formed early in the LGM when sea level fell and the estuary extended to the outer shelf. Channel sediments are yellowish- brown in color and rich in foraminifera and shell fragments owing to the strong tidal influence. Following the LGM, the paleo-river mouth retreated and regressive deposition of estuarine and incised-valley-filling facies with an erosion base occurred. The river channel facies and estuarine incised-valley-filling facies have clearly different sedimentary characteristics and provenances. The depositional environment of the paleo-river system on the wide shelf was reconstructed from the foraminiferal assemblages, CaCO3 content and Ca/Ti ratio. The main results of this study provide further substantial constraints on the recognition of late Quaternary stratigraphy and land-sea interactions on the ECS shelf.展开更多
基金the Science and Technology Innovation Project of the Laoshan Laboratory (No. LSKJ202203402)the Major Research Project on the Tethys Geodynamic System from the National Science Foundation of China (No. 92055204)。
文摘Fluvial systems play a crucial role in coastal and riverine ecosystems, making it essential to understand their responses to sea level changes for preserving biodiversity and managing natural resources. The evolution of the modern Indus River Delta offers a rare opportunity to study the interplay between sea level fluctuations, tectonism, sediment supply, and the corresponding fluvial responses. This study employs the ‘SedSim' stratigraphic forward model to simulate the delta's evolution from 200 kyr to the next5 kyr, drawing on data from field observations, Landsat imagery, digital elevation models, and previous studies. The model consists of 205 layers, each representing a 1-kyr time step, covering the last two glacial-interglacial cycles. Between 200 kyr and 130 kyr, during a lowstand period, sedimentation on the delta plain continued due to partial flow from the Indus River. During the last interglacial(130–60 kyr), rising sea levels led to peak sediment deposition, characteristic of a highstand phase. From 60 kyr to 18 kyr, sea levels dropped to their lowest during the Last Glacial Maximum(LGM), resulting in extensive erosion and minimal deposition on the delta plain. From 18 kyr to the present, rapidly rising sea levels, coupled with intensified monsoon activity, increased sedimentation rates and triggered avulsion and aggradation processes. The model accurately predicted depositional thickness across the delta plain, indicating a maximum of ca. 200 m at the shoreline platform, ca. 175 m in the northeastern delta, and ca. 100 m in the central delta. The study underscores the delta's vulnerability to future sea level rise, which–at a projected rate of 1 m/kyr–could significantly influence the densely populated, low-lying delta plain. These findings offer valuable insights into the geomorphic evolution of the Indus Delta and emphasize the socioeconomic implications of sea level change, underscoring the importance of proactive management and adaptation strategies.
基金National Natural Science Foundation of China,No.41906148,No.42271086Rejuvenating Yunnan Talents Support Plan Young Talent Program,No.XDYC-QNRC-2023-0322。
文摘A macro-tidal tropical estuary with high fluvial discharge is characterized by both fragility and remarkable dynamism.This study utilizes the Salween River Delta(SRD)as a case example to examine the interplay between morphology and vegetation under similar tidal conditions.Our analysis of correlations and inferences revealed several significant trends in the SRD:(1)an overall expansion of land area and intertidal vegetation,with the most pronounced changes occurring in the eastern sector;(2)the predominance of river discharge influencing the southwestern and northern sectors,contrasted with the primary impact of storm surges in the eastern sector;and(3)three distinct causal relationships among estuarine morphology,vegetation,storm surges,and river discharge:a direct model where river discharge shapes estuarine morphology,a progressive model in which river discharge affects vegetation distribution,subsequently influencing estuarine morphology,and a hybrid model where storm surges directly impact vegetation and indirectly modify its distribution through changes in estuarine morphology.The stability of sediment supply and the role of intertidal vegetation are crucial for the continuous seaward advance,providing a vital foundation for the protection and development of estuarine deltas.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(No.2019QZKK0901)the State Key Laboratory of Earthquake Dynamics(No.LED2023B04)+1 种基金the National Natural Science Foundation of China(Nos.42272242,W2411033,W2521003)the Science and Technology Plan of Gansu Province(No.22JR11RA088)。
文摘0 INTRODUCTION The Qilian Mountain Belt,at the forefront of the Tibetan Plateau's expansion,offers key insights into the plateau's tectonic deformation(Zuza et al.,2018;Zheng et al.,2010;Zhang et al.,2004;Tapponnier et al.,2001;Meyer et al.,1998).The northwest-trending mountain ranges in the Qilian Shan(“Shan”means“Mountain”in Chinese)have significantly influenced this deformation(Zheng et al.,2013).
基金Foundation： National Natural Science Foundation of China, No.41522101 National Key Research and Development Program, No.2016YFA0600500 Dutch-Chinese Exchange Program
文摘The geomorphological evolution of the Northeastern Tibetan Plateau （NETP） could provide valuable information for reconstructing the tectonic movements of the region. And the considerable uplift and climatic changes at here, provide an opportunity for studying the im- pact of tectonic and monsoon climate on fluvial morphological development and sedimentary architecture of fluvial deposits. The development of peneplain-like surface and related land- scape transition from basin filling to incision indicate an intense uplift event with morphologi- cal significance at around 10-17 Ma in the NETP. After that, incision into the peneplain was not continuous but a staircase of terraces, developed as a result of climatic influences. In spite of the generally persisting uplift of the whole region, the neighbouring tectonic blocks had different uplift rates, leading to a complicated fluvial response with accumulation terraces alternating with erosion terraces at a small spatial and temporal scale. The change in fluvial activity as a response to climatic impact is reflected in the general sedimentary sequence on the terraces from high-energy （braided） channel deposits （at full glacial） to lower-energy de- posits of small channels （towards the end of the glacial）, mostly separated by a rather sharp boundary from overlying flood-Ioams （at the glacial-interglacial transition） and overall soil formation （interglacial）. Pronounced incision took place at the subsequent warm-cold transi- tions. In addition, it is hypothesized that in some strongly uplifted blocks energy thresholds could be crossed to allow terrace formation as a response to small climatic fluctuations （10^3-10^4 year timescale）. Although studies of morpho-tectonic and geomorphological evolu- tion of the NETP, improve understanding on the impacts of tectonic motions and monsoonal climate on fluvial processes, a number of aspects, such as the distribution and correlation of peneplain and the related morphological features, the extent and intensity of tectonic move- ments influencing the crossing of climatic thresholds, leading to terrace development, need to be studied further.
文摘Deposition of fluvial sandbodies is controlled mainly by characteristics of the system, such as the rate of avulsion and aggradation of the fluvial channels and their geometry. The impact and the interaction of these parameters have not received adequate attention. In this paper, the impact of geological uncertainty resulting from the interpretation of the fluvial geometry, maximum depth of channels, and their avulsion rates on primary production is studied for fluvial reservoirs. Several meandering reservoirs were generated using a process-mimicking package by varying several con- trolling factors. Simulation results indicate that geometrical parameters of the fluvial channels impact cumulative pro- duction during primary production more significantly than their avulsion rate. The most significant factor appears to be the maximum depth of fluvial channels. The overall net-to-gross ratio is closely correlated with the cumulative oil production of the field, but cumulative production values for individual wells do not appear to be correlated with the local net-to-gross ratio calculated in the vicinity of each well. Connectedness of the sandbodies to each well, defined based on the minimum time-of-flight from each block to the well, appears to be a more reliable indicator of well-scale production.
基金Supported by the China National Science and Technology Major Project(2017ZX05009-002)
文摘The concept and characteristics of fluvial fan are elucidated through literature review and case analysis.Firstly,the concept and terminology of fluvial fan are introduced.Secondly,the progress and controversy on the formation mechanism,analysis methods and sedimentary models of fluvial fan are elaborated,and fluvial fan is compared with alluvial fan,river and lacustrine delta.Finally,ten identification signs of the fluvial fan are proposed.It is found through the study that development and scale of fluvial fan are affected by external factors such as climate,tectonic,provenance and wind field.The facies and lithofacies association inside the fan are controlled by the activity of the internal channel.It is pointed that fluvial fans are widely distributed in the world not only today but also in the geological history.The occurrence of fluvial fan will change the traditional continental deposition system dominated by alluvial fan-river-lacustrine.Meanwhile,the research of fluvial fan will be of great significance in the fields of sedimentology and oil and gas exploration.
基金National Natural Science Foundation of China, No.41001008 No.51209010+1 种基金 International Science ＆ Technology Cooperation Program of China, No.2011DFA20820 No.2011DFG93160Acknowledgements Gary Brierley gratefully acknowledges support from a Visiting Professorship awarded by the Chinese Academy of Sciences.
文摘The spatial distribution of valley setting （laterally-unconfined, partly-confined, or confined） and fluvial morphology in the source region of the Yangtze and Yellow Rivers is contrasted and analyzed. The source region of the Yangtze River is divided into 3 broad sections （I, II and III） based on valley setting and channel gradient, with the upstream and downstream sections being characterized by confined （some reaches partly-confined） valleys while the middle section is characterized with wide and shallow, laterally-unconfined valleys. Gorges are prominent in sections I and III, while braided channel patterns dominate section II. By contrast, the source region of the Yellow River is divided into 5 broad sections （sections I-V） based on valley characteristics and channel gradient. Sections I, II and IV are alluvial reaches with mainly laterally-unconfined （some short reaches partly-confined） valleys. Sections III and V are mainly confined or partly-confined. Greater morphological diversity is evident in the source region of the Yellow River relative to the upper Yangtze River. This includes braided, anabranching, anastomosing, meandering and straight alluvial patterns, with gorges in confined reaches. The macro-relief （elevation, gradient, aspect, valley alignment and confinement） of the region, linked directly to tectonic movement of the Qinghai-Tibet Plateau, tied to climatic, hydrologic and biotic considerations, are primary controls upon the patterns of river diversity in the region.
基金supported by the National Natural Science Foundation of China (No. 41072003)the Fostering Foundation of Henan Polytechnic University for the Excellent Ph. D Dissertation (No. 2011011001)
文摘Fluvial deposits from the Middle Triassic Youfangzhuang Formation in Henan Province, China contain a low-diversity trace fossils. Vertical dwelling burrows of opportunists dominate in active channel, whereas horizontal deposit-feeding, grazing, and vertical dwelling burrows occur in overbank deposits. Seven recurrent ichnofabrics were distingushed. The Palaeophycus tubularis ichnofabric pre- serves below scour interface between two fluvial cycles. The Skolithos linearis ichnofabric forms in middle to high-energy, soft substrates in the middle and upper parts of active channel deposits under semi-arid climate. The Skolithos linearis-Planolites montanus ichnofabric occurs in the sediments just a little above the Skolithos linearis ichnofabric and is formed in middle-energy, soft substrates in the up- per part of active channel deposits. The Planolites montanus ichnofabric is mostly preserved in associa- tion with medium- to thick-bedded brown-red silty mudstones or siltstones in low-energy, perennial muddy bottom ponds in overbank settings. The Taenidium barretti ichnofabric is interpreted as peri- odically exposed ephemeral ponds or low-energy distal floodplain. The Skolithos isp. ichnofabric com- monly occurs in middle to high-energy firm ground of proximal foodplain or crevasse-splay deposits. The root trace iehnofabric occurs in the crevasse splay deposits. The presence of thin palaeosols and the abundance of calcretization in mudstones indicate a seasonal climate ranging from humid to semi-arid, with high temperature, rainfall, and well-defined dry and wet seasons.
基金supported by the National Natural Science Foundation of China(Grant no.40901002 and 40325007)the 985 project to Nanjing University and the CAS-KNAW PhD project(05-PhD-10)
文摘The Huang Shui River, a main tributary of the Yellow River, crosses a series of tectonically subsided and uplifted areas that show different patterns of terrace formation. The distribution of fluvial terrace of the Huang Shui River is studied through topographic and sedimentologic terrace mapping. Three terraces in the Haiyan Basin, four terraces in the Huangyuan Basin, 19 terraces in the Xi＇ning Basin （the four high terraces may belong to another river）, nine terraces in the Ping＇an Basin, five terraces in the Ledu Basin and 12 terraces in the Minhe Basin are recognized. Sedimentology research shows that the geomorphologic and sedimentological pattern of the Huang Shui River, which is located at the margin of Tibet, are different from that of the rivers at other regions. The formation process of the terrace is more complicated at the Huang Shui catchment： both accumulation terrace and erosion terrace were formed in each basin and accumulation terraces were developed in some basins when erosion terraces were formed in other basins, indicating fluvial aggradation may occur in some basins simultaneously with river incision in other basins. A conceptual model of the formation process of these two kinds of fluvial terraces at Huang Shui catchment is brought forward in this paper. First, the equilibrium state of the river is broken because of climatic change and/or tectonic movement, and the river incises in all basins in the whole catchment until reaching a new equilibrium state. Then, the downstream basin subsides quickly and the equilibrium state is broken again, and the river incises at upstream basins while the river accumulates at the subsidence basin quickly until approaching a new equilibrium state again. Finally, the river incises in the whole catchment because of climatic change and/or tectonic movement and the accumulation terrace is formed at the subsidence basin while the erosion terrace is formed at other basins. The existence of the accumulation terrace implied the tectonic subsidence in the sub-basins in Huang Shui catchment. These tectonic subsidence movements gradually developed from the downstream Minhe Basin to the upstream Huangyuan Basin. Dating the terrace sequence has potential to uncover the relationship between the subsidence in the catchment and the regional tectonic at the northeastern Tibetan Plateau.
基金supported by the National Natural Science Foundation of China (41401046)the Fundamental Research Funds for the Central Universities (lzujbky-2016-264, lzujbky-2016-bt01)
文摘The Alagxa Plateau, in the margin of the northeastern Tibetan Plateau, is one of the most important dust source areas in East Asia, and the widespread sandy desert in the area is important both as a reservoir and a source of eolian silty. The northeastern margin of the Tibetan Plateau is one of the most actively-growing mountain belt on earth, and has large amounts of debris, with masses of fine grained material, which were continuously mobilized and deposited in the Alagxa Plateau by rivers, forming broad alluvial fans. It is possible that the role of fluvial sediments as a source of silty dust in the Alagxa Plateau has been underestimated. In this study, we test this hypothesis by investigating the iron mineralogical and geochemical characteristics of the fluvial sediments and the surface material of the sandy desert in the Alagxa Plateau, and comparing them with paleo-eolian dust deposits(loess) in the adjacent Chinese Loess Plateau(CLP) to investigate the possible linkages among the fluvial sediments, sandy desert and the last glacial loess of the CLP. The results show that sandy desert typically have high contents of goethite, and high ratios of goethite to hematite, similar to the fluvial sediments in the Alagxa Plateau. Based on the major element characteristics, field investigations and the results of previous studies, we found a genetic link between the silt component of the fluvial sediments and the sandy desert in the Alagxa Plateau with high value of Gt(goethite) and similarity of the Gt/(Hm(hematite)+Gt) ratio. But the silt component of the sandy desert main come from the adjacent fluvial sediments. The iron mineralogical characteristics(χ(magnetic susceptibility), χARM(anhysteretic susceptibility), SIRM(saturation isothermal remanent magnetization) and SIRM_(AF100 mT)(SIRM demagnetized at 100 mT)) of the CLP samples overlap with those of the fluvial sediments in the Alagxa Plateau, but there is a mismatch with the sandy desert samples. This suggests that the fluvial sediments are the source of a large amount of silty material which could be transported to the CLP. Therefore, we conclude that the fluvial sediment in the Alagxa Plateau is an important source of eolian silt, which is deposited in downwind region, and that this source has been previously underestimated.
基金NSERC,Lithoprobe(Snorcle) and the Government of the Yukon for providing support for this research
文摘Mid-Cretaceous strata within the Tintina Trench, 3 km west of the community of Ross River, contain evidence of deposition in two distinct, alternating, fluvial settings. Coal-bearing, mud-dominated strata are commonly associated with high-constructive sandy channel systems, with extensive overbank, levee and splay deposits. Channels are between 3 and 30 m wide and 0.4-7 m thick. They show repetitive development of side and in-channel bar-forms, as well as up-channel widening of the rivers by selective erosion of associated overbank and levee deposits. Levees extended for several hundred metres away from the channels. In this setting low-angle inclined stratification and epsilon cross stratification may reflect lateral migration of crevasse channels or small streams. The paucity of exposure prevents recognition of the channels as products of multiple channel anastomosed systems or single channel high-constructive systems. Gravel-dominated strata, inter-bedded with, and overlying coal-bearing units, are interpreted as deposits of wandering gravel-bed rivers, with sinuosity approaching 1.4. In most exposures they appear to be dominated by massive and thin planar-bedded granule to small pebble conglomerates, which would traditionally be interpreted as sheet-flood or longitudinal bar deposits of a high-gradient braided stream or alluvial fan. Architectural analysis of exposures in an open-pit shows that the predominance of flat bedding is an artefact of the geometry of the roadside exposures. In the pit the conglomerates are dominated by large scale cross stratification on a scale of 1-5.5 m. These appear to have developed as downstream and lateral accretion elements on side-bars and on in-channel bars in water depths of 2-12 m. Stacking of strata on domed 3rd order surfaces suggests development of longitudinal in-channel bar complexes similar to those observed in parts of the modern Rhone River system. Mudstone preserved in some of the channels reflects intervals of channel abandonment or avulsion. Minimum channel width is from 70 to 450 m.
基金National Natural Science Foundation of China,No.91547204National Key Resarch and Development Program of China,No.2016YFC0402500,No 2017YFC0404303。
文摘Accumulation occurs widely in fluvial processes.Accurately accounting for the effects of previous water and sediment conditions on accumulation is essential for studying riverbed evolution.In this study,to reveal the physical mechanisms of accumulation,various geometric observations of both the upstream and downstream reaches of dams on several typical fluvial channels were analyzed.The changes in water and sediment conditions were defined as external disturbances.Assuming that the probability of an external disturbance conforms to a Poisson distribution,and that the response intensity induced by an individual disturbance decays exponentially over time,a mathematical description of the accumulation of internal responses to external disturbances is given.Furthermore,a corresponding theoretical model for simulating the spatiotemporal readjustments of characteristic river variables is proposed based on stochastic theory.The proposed models are then applied to investigate spatiotemporal readjustment in the upper and lower reaches of dams following their construction.The results indicate that temporally,the vertical,lateral,and overall readjustment rates of the reaches are relatively fast in the early period following dam construction but then decrease rapidly over time.Accumulated riverbed degradation,channel width,and sedimentation continuously increase until a new dynamic equilibrium is reached.These phenomena reflect the representative accumulation characteristics of fluvial processes.Spatially,the erosion intensities in downstream reaches decrease nonlinearly along the channel until eventually diminishing.The unbalanced spatial distribution of erosion intensity arises from the system response characterized by propagation in space but decay over time,which is characteristic of accumulation phenomena after disturbances.The results of the developed model show that the spatiotemporal readjustments of the studied cross-sections and channel reaches can be accurately described by the unified theoretical formula derived herein.The model predictions show good agreement with observed field data with determination coefficients of 0.92,0.93,0.76,and 0.95 for vertical,lateral,longitudinal,and overall readjustments,respectively.The proposed theoretical models account for both the accumulation characteristics of fluvial processes and their spatial distributions.In demonstrating the proposed ap-proach,this study provides a theoretical basis and new calculation method for quantitatively describing the spatiotemporal readjustments of non-equilibrium fluvial channels following external disturbances.
基金This work was supported by the funding provided by Ventenskapsådet(Grant No.2016-05642)to JR.
文摘The Nepal Himalayas is the source of many glacial and spring-fed river systems crisscrossing the mountainous terrain.There is an increasing recognition of small mountain rivers(SMRs)to have a significant combined export of dissolved and particulate organic carbon to the global carbon flux.We analyzed fluvial sediments from two SMRs and compared the results with two large mountain rivers(LMRs)in Nepal.We investigated the organic matter(OM),its compositional variability,and seasonal export using a suite of lipid biomarkers,namely n-alkanes,n-alkanoic acids,n-alkanols,and sterols.The SMRs indicated a similarity in lipid distribution and were affected by a strong seasonal variability.The LMRs showed a distinct contrast in the distribution of lipids in suspended sediments.Bedload sediments in SMRs were derived from diverse sources with weak terrigenous dominance all-year-round compared to the suspended load.Functional lipids(n-alkanoic acids and n-alkanols)were the major constituents in SMR sediments,indicating better preservation.In contrast,n-alkane concentration dominated over other fractions in suspended sediments retrieved from LMRs.The biomarker trends differentiate SMRs from LMRs with lower transformed/degraded OM in SMRs.A common observation was the strong presence of even carbon compounds in short-chain n-alkanes in SMR bedload sediments and their predominance in suspended sediments in LMRs.Such an unusual trend is attributed to specific biomarker sources from the catchment and ongoing processes in fluvial systems.Topsoil colonized by fungal species under moist acidic conditions and autochthonous bacteria contributes to the organic matter pool in shallow SMRs.In LMRs,the contribution from thermally mature sedimentary hydrocarbons and the diagenetic reduction of nalkanoic acids to n-alkanes are additional contributors to the allochthonous carbon pool.The differences in lipid concentrations,their distribution,seasonality,and the size of rivers suggest differential preservation/degradation of the organic matter pool and their importance in contributing to the carbon budget.
基金supported by the National Natural Science Foundation of China (40271011)
文摘The middle and lower reaches of the Tarim River are currently one of the main regions of ecological restoration in the arid areas of western China.Using the principles and method of landscape ecology,this study has chosen the fluvial corridor landscape in the middle and lower reaches of the Tarim River,and discusses the region’s ecologically functional regionalization system and issues related to its practical classification.On this basis the corresponding regionalizing principles and standards were developed which were used to qualitatively divide the three main landscapes as the ecologically functional areas in the drainage basin.The paper has also analyzed the characteristic of the study areas,and has put forward the measures for its ecological restoration.
基金Supported by the National Natural Science Foundation of China(41772094)National Science and Technology Major Project(2016ZX05027-002-007)。
文摘Based on detailed investigation of the modern sedimentation of the distributive fluvial system of Shule River and the data of unmanned aerial vehicle(UAV)aerial photography and satellite remote sensing,the sedimentary characteristics and differences of distributive fluvial system in arid areas are analyzed.By comparing the changes in slope,river morphology and sedimentary characteristics in different sections from the apex to the toe,the distributive fluvial system of Shule River can be divided into three facies belts:"proximal","middle"and"distal".The proximal belt has the largest slope and strongest hydrodynamic condition,mainly appears as large-scale braided river deposits;the fluvial bars in this belt are mainly composed of gravels,the gravels have good roundness and certain directionality,and are medium-large boulders,with low sand content;the main microfacies in this belt are braided channel and flood plain.The middle belt with slope smaller than the proximal belt,is mainly composed of braided bifurcating river deposits.Due to branching and infiltration,this belt has weaker hydrodynamic conditions,so some of the distributive rivers dry up,appearing as ephemeral rivers.This belt has small lenticular sandbodies,fine to medium gravels,higher sand content,and mainly braided channel,flood plain and aeolian dune microfacies.The distal belt has the smallest slope and flat terrain,where the river begins to transform from braided river to meandering river,the sediment is mainly sand.Due to the influence of slope,this belt has weaker erosion toward source and stronger lateral erosion,and point bars developing around the edge of the active lobes.In this belt,the river is completely meandering,and the main microfacies are braided channel,meandering channel,flood plain,aeolian dune,lake and swamp.
基金supported by the National Natural Science Foundation of China (Nos.41772094 and 42130813)。
文摘Understanding controls on river planform changes can help to build predictive models for distributive fluvial systems,and then guide the oil and gas exploration.To do this we have undertaken a detailed investigation of the modern Great Halten River distributive fluvial system from the Sugan Lake Basin,Qinghai,China.Unmanned aerial vehicle(UAV) photography,satellite remote sensing data and elemental analysis were used to determine differences in the sedimentary characteristics of the distributive fluvial system.From the apex to the toe,the changes in the slope,river morphology,sedimentary characteristics and element content in different regions were determined and three facies belts:“proximal”,“medial” and “distal” were identified.We found that the sedimentary structure and elemental content characteristics of each facies differ greatly.We compare the large-scale evolution of rivers from braided to meandering rivers,and the fine description of sedimentary characteristics in combination with each observation,we strengthen our overall understanding of the modern DFS from macro to micro scale.At the same time,we summarize the sedimentation model of the Great Halten River DFS,and our study provides a reference for establishing the sedimentary model in continental petroliferous basins.
基金The Natural Sciences and Engineering Research Council of Canada and Carbon Management Canada funded the rock record portion of this study
文摘The fluvial-tidal transition(FTT)is a complex depositional zone,where fluvial flow is modified by tides as rivers approach a receiving marine basin.Variations in the relative importance of tidal versus fluvial processes lead to a distinctive distribution of sediments that accumulate on channel bars.The FTT generally consists of three broad zones:(1)a freshwater-tidal zone;(2)a tidally influenced freshwater to brackish-water transition:and(3)a zone of relatively sustained brackish-water conditions with stronger tides.A very common type of deposit through the fluvial-tidal transition,especially on the margins of migrating channels,is inclined heterolithic stratification(IHS).At present,a detailed account of changes in the character of IHS across the FIT of a paleo-channel system has not been reported,although a number of modern examples have been documented.To fill this gap,we quantitatively assess the sedimentology and ichnology of IHS from seven cored intervals in three geographic areas situated within the youngest paleovalley("A"Valley)in the Lower Cretaceous McMurray Formation of Alberta.Canada.We compare the data to trends defined along the FTT in the present-day Fraser River in British Columbia.Canada to interpret paleo-depositional position in the ancient fluvial-tidal channels.Analysis determined that the mean mudstone thickness is 8.2 cm in the southern study area(SA).Mean thickness increases to 11 cm in the central study area(CA),and decreases again to 4.4 cm in the northern study area(NA).The proportion of mudstone is 31%in SA,44%in CA,and 27%in NA.Thicknessweighted mean bioturbation intensity in sands varied from 0.29 in SA and CA.to 0.28 in NA.On the other hand,thickness-weighted mean bioturbation intensity(Bl)in mudstone increases from 1.46 in SA.to 1.77 in CA.and is 1.94 in NA.The ichnological diversity also increased from south to north.Sedimentological results show sinilar trends to those of the Fraser River,enabling the identification of a freshwater to brackish-water transition zone with tidal influence.The interpreted position of the transition is underpinned by the bioturbation intensity and trace-fossil diversity trends,indicating periodic brackish-water conditions throughout SA in the McMurray Formation during low river flow conditions.Together,these data suggest that a broad FTT existed in the"A"Valley,with fluvial-dominated channels to the south that experienced seasonal brackish-water inundation during base flow,and channels experiencing increasing brackish-water influence lying further north towards a turbidity maximun zone.The FIT zone appears to have extended for several hundred kilometers fron south to north.Based on the sedimentological and ichnological data,as well as estimations of lateral accretion rates,we refute the colmonly applied Mississippi River depositional analogue for McMurray Formation channels.Rather,we show that while not a perfect fit,the tidally influenced Fraser River shows much greater agreement with the depositional character recorded in McMurray Formation IHS.Future work on the McMurray system should focus on characterizing tide-dominatecl deltaic and estuarine systems,such as the Ganges-Brahmaputra,and on forward-modeling the evolution of tide-dominated and tideinfluenced river systems.
文摘Coupling within fluvial systems relates to the connectivity between the various components of the system. It can be viewed at several scales from local scales of hillslopetochannel and reachtoreach coupling, to larger scales of zonal coupling between the major functional zones of the fluvial system, and to the scale of regional coupling. Coupling influences how the system responds to environmental change and how the effects of environmental change are propagated through the system. This paper provides a review, based largely on previously published work, of the coupling concept, and how the effective temporal scales vary with the spatial scale of coupling. Local scale coupling is considered through the hillslope to channel coupling in the Howgill Fells, northwest England, observed over a 30year monitoring period, together with examples from badlands in Spain, and reachtoreach coupling on the River Dane, northwest England. At the zonal scale the relative influence of climatic and baselevel change on coupling through dryregion alluvial fans is considered on fan systems in Spain, Nevada, and UAE/Oman. For large scale regional coupling, the response of the Tabernas basin, southeast Spain to tectonic uplift, is examined. The factors influencing coupling mechanisms vary with temporal and spatial scales. At the hillslopetochannel scale the significant factors are the magnitude and frequency characteristics of sediment generation and removal mechanisms within the context of progressive morphological change. Effective timescales range from the individual event to decadal timescales. At the zonal scale, that of alluvial fans, the significant factors are climatic change, and particularly in the appropriate morphological setting, baselevel change. Effective timescales are of the order of hundreds to thousands of years. At the regional scale, the response to tectonic uplift may take >100 ka to be transmitted through the drainage basin.
基金supported by the National Natural Science Foundation of China(Grant No.41472155),Grant No.ZR2022QD083,LYHZW202248 and NSFC 417644073Cultivating Young Talents in the Universities of Shandong Province(LUJIAOKEHAN2021-51,granted to L.Yu)。
文摘The Yellow River is usually assumed to record tectonic activities and climatic changes;however,a systematic study was lack in the sedimentology,stratigraphy,geomorphology and geochronology for the entire Yellow River though various geologic scholars have conducted numerous works in individual basins.This review focused on well-preserved fluvial terrace sequences that formed along this river on northeastern(NE)Tibetan Plateau and Ordos Block over the past 2.6 Ma.After comparing numerous initial incision ages at different segments along the Yellow River,we found out that the youngest initial incision may occur at ca.150 ka at the Longyang Gorge.The Yellow River may transit from multiple separated endorheic drainages to an entire external drainage after 150 ka,which may cause differentiations in the apparent incision rates before and after 150 ka;thus apparent net incision rates were calculated respectively for the Yellow River before 150 ka and the drainage network post 150 ka.Apparent net incision rates prior to 0.15 Ma were calculated as 0.15,0.29,0.10,0.12 and 0.03 mm/a respectively in Tongde-Xunhua,Lanzhou-Linxia basins,Heishan,Jinshan and Fenwei-Sanmen Gorges in this review,which mainly reflected Kunhuang-Gonghe Tectonic Event,generated by the Indo-Asian collision and diminishing as the NE Tibetan Plateau eastward extruding at ca.1.8-0.15 Ma.Apparent net incision rates post 0.15 Ma were calculated respectively for NE Tibetan Plateau and Ordos Block,considering their different base level.On NE Tibetan Plateau,four fluvial degradational phases were identified between ca.105~70,53~40,25~16 and 12~6 ka associated with terrace levels respectively,at average elevations of 96,40,20 and 10.5 meters above the current river level(m arl)within a range of 5~96 m arl;and four broad periods in the last 150 ka on Ordos Block:possibly marine oxygen isotope stage(MIS)5,ca.118 to 72 ka,most of MIS 3,ca.44~28 ka,transition from LGM to last deglacial ca.20 to 16 ka,and 4~3 ka at average elevations of 67.5,26,19 and 11.5 m arl.These degradational phases post 0.15 Ma were associated with multiple processes including enhanced fluvial discharge with an increase in monsoonal precipitation and/or melt water in deglaciation.
基金Supported by the National Natural Science Foundation of China (Nos.41040041,41206053,41225020,and 41076018) the Continental Shelf Drilling Program (No.GZH201100202)the China Geological Survey(Nos.1212010611301 and GZH200800501)
文摘Evidence from lithology, foraminiferal assemblages, and high-resolution X-ray fluorescence scanning data of core SFK-1 indicates tidally influenced paleo-fluvial sedimentation during the last glacial maximum (LGM) on the outer shelf of the East China Sea. The paleo-fluvial deposits consist of river channel facies and estuarine incised-valley-filling facies. Different reflections on the seismic profile across core SFK-1 suggest that the river channels shifted and overlapped. River channel deposition formed early in the LGM when sea level fell and the estuary extended to the outer shelf. Channel sediments are yellowish- brown in color and rich in foraminifera and shell fragments owing to the strong tidal influence. Following the LGM, the paleo-river mouth retreated and regressive deposition of estuarine and incised-valley-filling facies with an erosion base occurred. The river channel facies and estuarine incised-valley-filling facies have clearly different sedimentary characteristics and provenances. The depositional environment of the paleo-river system on the wide shelf was reconstructed from the foraminiferal assemblages, CaCO3 content and Ca/Ti ratio. The main results of this study provide further substantial constraints on the recognition of late Quaternary stratigraphy and land-sea interactions on the ECS shelf.
