Development Of Alluvial Fans Research Articles

The early–middle Cambrian siliciclastic tide‐dominated succession in eastern Korea

AbstractThe basal Taebaek Group (Myeonsan and Myobong formations) illustrates second‐order transgression on the eastern Sino‐Korean Block during the early–middle Cambrian (Stage 3?–Wuliuan). The irregular palaeotopography of Precambrian basement led to the development of localised alluvial fans and fan deltas. As transgression continued, tidally influenced estuarine and associated shallow subtidal flats developed. Continued transgression resulted in a relatively deep subtidal environment, with postulated carbonate shoals serving as barriers. Stacking of facies indicates a general deepening‐upward trend, transitioning from terrestrial–nearshore to marine environments dominated by tidal effects. The study area subsequently experienced shallowing, leading to the emergence of tidal inlet and dune environments. Siliciclastic input was attenuated, facilitating the development of carbonate shoal complexes. The overall transgressive succession of the basal Taebaek Group aligns with similar sequences observed in the Sino‐Korean Block and western Laurentia, where the lowermost Cambrian strata which formed in various depositional environments on the uneven basement rocks were followed by extensive tide‐dominated siliciclastic successions. These successions were then overlain by epeiric carbonate platforms that developed synchronously across the area as siliciclastic input diminished with the continued transgression. This comparison demonstrates that the transgressive sequences in the Sino‐Korean Block and western Laurentia can be understood within a framework that explains how extensive Cambrian carbonate platforms initially developed due to a second‐order eustatic sea‐level rise during the Cambrian greenhouse period.

Facies analysis, architectural elements, and paleoenvironmental reconstruction of alluvial deposits of the low terraces and floodplains in the Middle Sebou river (Eastern Saïss foreland basin, Morocco)

This paper focuses on the study of the floodplain and low terrace deposits of the Middle Sebou Valley, which crosses the south-rif corridor and constitutes the eastern limit of the Saïss Basin. The study includes the identification of facies, the determination of architectural elements, the reconstruction of paleoenvironments, and the proposal of a model for deposit formation. The work is based on detailed sedimentological analysis of the deposits, focusing on lithology, grain size, primary sedimentary structures, and the types of contact between facies. Facies analysis identified 21 facies grouped into three associations corresponding to nine architectural elements whose identification was based on the study of their lateral and vertical profiles. The architectural elements identified include the channel (CH), gravel bars and bedforms (GB), sandy bedforms (SB), downstream accretion (DA), lateral accretion (LA), sediment gravity flows (SG), natural levee (LV), floodplain (FF), and abandoned channels and meanders (FF (CH)). The alluvium is organized into rhythmic and fining-up elementary sequences reflecting its deposition in different fluvial environments: alluvial fan, straight to slightly sinuous and braiding-tending fluvial environment, and meandering fluvial environment. Alluvial deposition is controlled by lithology, climate, and tectonics. Lithology and tectonics controlled the slope, the degree of valley confinement, the accommodation space, and the alluvial fan development. Climate controlled the flow regime, sediment dynamics, and the formation of paleosol and calcrete.

The Chaman and Paghman active faults, west of Kabul, Afghanistan: Active tectonics, geomorphology, and evidence for rupture in the destructive 1505 earthquake

The city of Kabul, Afghanistan, lies within the Kabul Block, which is bounded by the Sarobi, Gardez and Paghman fault, the northern extension of the Chaman fault, accommodating oblique convergence between the Indian and Eurasian plates. In this paper, we describe the geologic structure and tectonic geomorphology of the northeast-striking Paghman fault and a ∼10-km-long portion of the Chaman fault using a combination of field observations and remote sensing data, and assess evidence for rupturing in the 1505 historical earthquake. The Paghman fault is predominantly a left-lateral strike-slip fault with a minor dip-slip component along the eastern margin of the Paghman Mountains. The Chaman and Paghman faults displaces Paleogene to Quaternary units with clear displacement of recent deposits. Continuous left-lateral movement of the both faults have caused stream deflection, capturing, abandonment, and finally, incision of alluvial deposits inside the Kabul Basin. We identify several stages in the alluvial fan development and displacement that were once a continuous unit displaced left-laterally as a single fan but are now incised by beheaded and offset stream channels. An approximately 30-km-long active fault trace is identified with geomorphic evidence of recent faulting and vertical offset ∼0.5–3 m, which we interpret is related to the historical 1505 earthquake in the area along the Chaman and Paghman faults. Our observations indicate significant along-strike variations in faults trace geometry. The seismic event comprises several fault segments separated by discontinuities such as stepovers. The two faults have accumulated enough elastic strain to cause a larger earthquake since the 1505 quake.

Alüvyal Yelpazelerin Morfolojik Gelişimine Etki Eden Faktörler: Maymundağı Yelpazeleri Örneği

Alüvyal yelpazeler, akarsu sistemlerinin önemli bir parçasıdır ve jeomorfoloji alanında ilgi uyandırmaktadır. Bu makale, alüvyal yelpazelerin morfolojilerini etkileyen iklim koşulları, tektonizma ve taban suyu değişikliklerinden oluşan temel faktörler hakkında genel bir anlayış sunmayı amaçlamaktadır Alanyazından örneklerle alüvyal yelpazelerin morfolojik gelişiminde bu faktörlerin etkisi aktarılmaktadır. Makale aynı zamanda Acıgöl grabeninin kuzeybatısını sınırlayan, KD-GB doğrultusu güneyde D-B’ya dönen, Maymundağı fayının önünde depolanan alüvyal yelpaze istiflerinin morfolojik gelişimi hakkında bilgi vermektedir. Bu alanda D-B doğrultulu dağ önünde iç içe geçmiş iki farklı alüvyal yelpaze sistemi bulunmaktadır. Bu gelişim önceden Pleyistosen gölünün yüksek seviyesiyle ilişkilendirilmiş olsa da daha sonra yapılan çalışmalarda göl seviyesinde Geç Kuvaterner döneminde bu gelişimi etkileyecek bir yükselme olmadığı belirlenmiştir. Bu çalışmada morfolojik gelişimin yelpazenin alt kesiminde etkin olan faylanma sonucunda gerçekleştiği ortaya konulmuştur.

Reconstruction of the Late Miocene to Pliocene continental succession of Samos Island: Palaeoenvironmental implications for the Eastern Aegean domain

AbstractOn the Island of Samos (East Aegean region, Greece), two sedimentary basins are filled by thick continental series dated to the Late Miocene to Early Pliocene. A multidisciplinary study has been performed including (1) the definition of 21 sedimentary facies, (2) a review of the biological components and (3) carbon, oxygen and strontium stable isotope analyses. The succession is characterised by various depositional settings and hydrochemical compositions. Five main stages of basin evolution have been identified: (1) The Late Serravallian is marked by the development of alluvial fans and fan delta; (2) during the Lower Tortonian, isolated shallow lakes with variable salinity, from fresh to brackish, developed under warm and relatively humid conditions; (3) the Middle to Upper Tortonian is marked by the development of a large and deep lake with saline and alkaline waters, under colder and drier conditions; (4) the Latest Tortonian to Messinian period is represented by an ephemeral alluvial system, developed under a dry climate; (5) during the Zanclean, a palustrine and paludal wetland system, dominated by tufa carbonates, developed under moderately humid conditions. This succession is of particular interest for the reconstruction of the palaeoenvironmental evolution of the transition zone between the Mediterranean domain, and the Paratethys and circum‐Paratethys areas. The geochemical data and the presence of flora (diatoms) and fauna (gastropods) of marine affinity suggest transient ingressions of marine‐related water or groundwater inflows as early as the Lower Tortonian. The Samos succession records the complex interaction between the regional geodynamics and climate. The extensional regime of the Eastern Aegean zone generates subsidence, interrupted in the mid‐Tortonian (9 Ma) by a brief compressive event and a major exposure of the basins. Furthermore, the Late Miocene progressive aridification, followed by a change to a more humid climate (Pliocene) is also a major driver of the sedimentation.

Debris‐flow fan development and geomorphic effects in alpine canyons under a changing climate

AbstractDebris flows in alpine environments are prone to occur in the context of global climate change (i.e., elevated air temperature and higher frequency of strong precipitation events). (Alluvial) Fans often develop at the outlet of tributaries after high‐intensity debris flows. Most debris‐flow fans in alpine canyon areas extend directly to the main river channel and become the forefront of the interaction between the tributary gully and the main river channel. Clarifying the development processes/dynamics, evolutionary mechanisms and driving factors of alluvial fans would shed light on understanding the geomorphological effects and genesis of river valleys in alpine canyon areas. Here, we report the development of debris‐flow fan at the outlet of the Tianmo Gully, a formerly hazard‐free but currently hazard‐active tributary of the Parlung Tsangpo Basin, Southeast Tibet, where debris flows have occurred frequently in the last two decades. Combining remote‐sensing images, DEM data, UAV aerial photography, RTK topographic survey and other fieldwork, the development processes and morphological characteristics of the Tianmo fan under the influence of four large debris flows were analysed. Both primary events (described as episodic debris‐flow events characterized by high‐magnitude mass movement) and secondary events (corresponding to perennial stream flow processes with much lower sediment concentrations) affected the development of the Tianmo fan. Episodic debris‐flow events drastically shape the macroscopic morphology of the fan, with rapid deposition and expansion of the fan body, whereas perennial stream flow processes slowly modulate the fan during the intermittent period between debris flows, mainly with gradual retrogressive incision and lateral migration of flow channel on the fan body. Influenced by the strong sediment‐transport process of debris flows and the alluvial fan development, the planform of the Parlung Tsangpo River evolved from a relatively narrow and single‐thread pattern to an alternating‐wide‐and‐narrow pattern, with a corresponding staircase‐like longitudinal profile.

Primary and secondary sedimentary processes in debris-flow-dominated alluvial fan deposits within karstic setting: An example from the Middle Atlas-Sais foreland basin transition zone, Morocco

The transition between the Middle Atlas and the Sais Basin contains a sequence of alluvial fans from the Plio-Quaternary period. These fans are mostly made up of debrites and are found resting unconformably on top of carbonate beds from the Jurassic Period. This location provides a key case study for investigating the primary processes of aggradation, as well as the secondary processes that alter alluvial fan deposits. Alluvial fans are developed through primary processes that occur intermittently over time, resulting in both active and inactive sectors. Internal and external organization of the deposits is, however, partially influenced by secondary processes that can cause mechanical, chemical, and/or biochemical changes, making the comprehension of alluvial fan development processes more complex. In this study, we investigated fan development processes by examining five lithostratigraphic logs and seven sedimentary facies in eight alluvial fans that have merged together. The findings indicate that debris flows were the main driver of fan development, with some contribution from sheet floods and mud-flows. In addition, the study suggests that secondary processes, including mechanical, chemical, biochemical, and diagenetic processes, have had a substantial impact on sediment deposition. The mechanical processes include brittle deformation, incision, reworking, and desiccation. On the other hand, the chemical and/or biochemical processes are evidenced by paleosol and calcrete development, as well as cementation, micritization, dissolution, development of porosity, oxidation, recrystallization, epigenesis, and neoformation. These processes would have been influenced by hydrological, hydrogeological and karstic factors, which are closely linked to the generally semi-arid climatic conditions punctuated by wet phases.

Alluvial development during climate fluctuations depicted with spectral decomposition of the Middle Triassic to Lower Jurassic post‐rift succession in the Horda Platform (Norway) and the impact on reservoir properties

AbstractFor the first time, this study presents interpretations of alluvial fans in spectral decomposition RGB Blends, analysed in seismic time slices from the Middle Triassic to Lower Jurassic stratigraphical interval of the Horda Platform (northern North Sea). The time slices record a shifting alluvial fan front, fluvial variability, uplift and erosion and reveals depositional elements that may set the common conception of the geological development of this area during the Early–Middle Mesozoic up for discussion. Results show that the Upper Triassic Lunde Formation in the eastern margin of the Horda Platform was characterized by the deposition of coalesced alluvial fans. A variable extent of the fan front through the Upper Triassic is linked to interplaying allogenic factors: uplifted source areas in the aftermath of Early–Middle Triassic rifting determined sediment availability; climate transitioning from arid to semi‐humid, with increasingly fluctuating precipitation, controlled sedimentation, and run‐off; provenance dictated bulk sedimentology and affected prevailing alluvial processes. An overall retreat of the fan system through the Late Triassic coincided with a significant change in landscape characteristics at the transition into the overlying Statfjord Group. Uplift and initial tilting of the Horda Platform caused landscape degradation and the formation of plateaus and incised valleys, contemporaneous with increased humidity and marine transgression, forming estuaries. The shift in depositional style has implications for reservoir properties, creating complexity and heterogeneity in terms of facies distribution and connectivity, which may benefit potential CO2 storage. Upper Triassic alluvial fan development in the Horda Platform (northern North Sea) depicted through spectral decomposition of seismic time slices Enhanced level of seismic stratigraphic interpretation with RGB blending Impact of allogenic factors on alluvial depositional development Implications of alluvial variability on reservoir properties

Using Multisensor Earth Observation Data to Understand the Development of the Kourtéré Kori Alluvial Fan and Its Impact on the Hydrology of the Niger River

The Niger River (NR) is threatened with silting up due to the evolution of alluvial fans (AFs) in the Niamey region. The most significant is the Kourtéré AF. This study aims to map the spatial extent of this AF and analyze its progression and impact on the NR using a machine learning algorithm such as support vector machine on Landsat and Sentinel-2 images from between 1985 and 2021. Sentinel-1 data were then used to generate a digital terrain model at 10 m resolution through the Interferometric Synthetic Aperture RADAR (InSAR) technique to understand the Kourtéré watershed hydrology. Results show that the AF area increased from 55.19 ha in 1985 to 303.86 ha in 2003 and 237.18 ha in 2021. The AF has invaded a section of the NR since 2000 and began to invade its main bed in 2016. More than 73.71 ha of NR were converted into AF between 1985 and 2016. The flow direction of the NR has been disturbed by changes in AF, making it easier to overflow at flows much lower than previously. The Kourtéré watershed is dominated by a dense network of gullies with a Sediment-Transport Index of 424.4, which facilitates significant sediment transport into the AF and NR and leads to its silting up.

Facies architecture of the Plio-Quaternary alluvial fan deposits from south-eastern margin of the Saïss foreland basin (Morocco): Paleoclimatic and neotectonic implications

Eight Plio-Quaternary alluvial fans from south-eastern margin of the Saïss foreland basin were the subject of a thorough sedimentological study based upon detailed facies analysis. This study allowed distinguishing 16 sedimentary facies. The typology of the latter, their spatial distribution and sedimentary organization afforded the classification of the studied fans into three groups. Group 1 is dominated by non-cohesive debris flow and cohesive to very poorly-sorted blocky conglomerate deposits that are associated with silt-clayey and calcrete. The setting up of the deposits of this group occurred in a tectono-karstic depression whereby a WNW progradation of the deposits and an important incision into the previous consolidated deposits would have been controlled. Group 2 is characterized by a predominance of the muddy fraction, presumably linked to the large surface area of the watershed and the river activity. Group 3 is dominated by coarse deposits with rare mudflows interpreted to be the direct consequence of an important neotectonic activity which is expressed by localized incremental pulses of the Agourai-El Hajeb-Ain Cheggag faults system and Middle Atlas directional faults (i.e., NE-SW) along toe fan during the Plio-Quaternary period. Groups 2 and 3 are also characterized by deposits whose the related processes are dominated by cohesive and non-cohesive debris flows, mud-rich debris, channelized debris flows and non-cohesive flows, hyper-concentrated flows and sheet-flood flows. The morphogenesis of these alluvial fans and the emplacement of their deposits are neotectonic- and climate-controlled. Tectonics have played a major role in the rejuvenation of the Middle Atlas relief and, through controlling the base-level, created the space available for the establishment and development of alluvial fans onto the south-eastern margin of the Saïss basin. This extensive tectonics has resulted in normal faultings and layer tiltings. The climate played an important role in the formation of facies by controlling (i) the mechanical properties of paleoflows, (ii) sedimentary dynamics and (iii) the formation of paleosols and calcrete.

Initiation and Development of the Late Cenozoic Uplift of Daluo Mountains, Northeastern Margin of the Tibetan Plateau

AbstractDaluo Mountains lie at front of the arcuate tectonic belt at the northeastern margin of the Tibetan Plateau, and are the landform boundary zone between the active Tibetan Plateau and the stable North China Craton. Studying of the late Cenozoic uplift evolution of Daluo Mountains is important for understanding the expansion mechanism of the northeastern margin of the Tibetan Plateau and its influence on the western North China Craton. In this study, the late Cenozoic uplift of Daluo Mountains is constructed from the development of the late Cenozoic alluvial fan around Daluo Mountains. The entire sedimentary sequence and framework of the fan was revealed by the newly obtained drilling core data. The cosmogenic nuclide, optically stimulated luminescence, and detrital zircon U‐Pb dating results provide new evidences for discussion about the initial timing of the late Cenozoic uplift of Daluo Mountains and the key stages of uplift during the Pleistocene. The late Cenozoic alluvial fan at front of Daluo Mountains overlies a set of fluvial‐facies strata; therefore, development of the alluvial‐fan marks the start of late Cenozoic uplift of Daluo Mountains. The timing of this event can be constrained to ∼4.64 Ma. Two extensive gravel layers (dated to ca. 0.76–0.6 Ma and ∼0.05 Ma) developed during the Pleistocene, indicating two episodes of considerable uplift. This study provides a new time scale for the uplift and expansion of the arcuate tectonic belt at the northeastern margin of the Tibetan Plateau.

A method to detect abrupt shifts in river channel position using a Landsat‐derived water occurrence record

AbstractThe lateral migration of river channels is an important control on the evolution of alluvial fans, deltas, and floodplains. Lateral migration consists of both gradual riverbank migration and abrupt shifts in location due to avulsions or cutoffs. Methods exist to measure bank migration, but abrupt shifts in position are rarely considered or are not emphasized. Here we describe a new method using Landsat‐derived water occurrence images that primarily focuses on detecting when a channel has abruptly shifted position, either from avulsion or cutoff. The method does not assume any a priori model of channel geometry or evolution. Within a given area of interest, binary channel images created from the fluvial water occurrence record are stacked through time. Then a channel shift intensity, , is created by estimating the number of possible ending times for fluvial water voxels (a point in three‐dimensional space) in the stacked occurrence record. The number of possible end‐times for fluvial water voxels within a given region of the occurrence record reveals the likelihood that a reach of a river underwent an abrupt channel shift during the observation period. We present the results of this analysis for a 194 481 km2 region of the Amazonian basin. Follow‐up validation found three avulsions and 270 cutoffs within regions identified by this method. We show that areas above a threshold contain an avulsion or cutoff with high probability. This highlights the method's potential to detect and quantify abrupt channel shifts at the basin scale. The method also successfully distinguishes between abrupt channel movement and complex braiding behaviour. As this method is applicable to any binary water‐masked time series images, future applications of this method have the potential to provide insight into the controls and spatial variance of avulsions and cutoffs across a variety of scales.

Three-dimensional control of alluvial fans by rock uplift in an extensional regime: Aydın Range, Aegean extensional province

Tectonics imparts a first-order control on the overall morphology of alluvial fan systems in extensional settings by influencing sediment flux and accommodation space, while other factors such as climate, catchment lithology, and fault footwall characteristics are secondary. Previous alluvial fan modeling studies have focused on the link between the three-dimensional development of alluvial fans and rock uplift, however, despite the potential influence of tectonics on the overall three-dimensional morphology of alluvial fans, the controlling mechanisms, as well as their relative importance, remain largely unquantified in a natural setting with a targeted source-to-sink approach. Here, we examine 45 alluvial fans and their catchments along the southern mountain front of the Aydın Range, delimited by segmented normal faults in the western Anatolia Extensional Province, to quantify the role of rock uplift. We quantify river incision rates and catchment-wide erosion rates together with a series of topographic analyses across the southern flank of the Aydın Range as a proxy for rock uplift. Our results indicate that the spatial distribution of thicker and steeper alluvial fans fit well with higher rock uplift rates along the strike of the mountain front. In contrast, a lower uplift rate is responsible for prograding alluvial fans with decreasing thickness and gradients. Also, our data shows that alluvial fan thickness compared to other alluvial fan metrics strongly associated with the pattern of the rock uplift. This study demonstrates a field-based, quantitative linkage between three-dimensional alluvial fan morphology and rock uplift which has significant implications for improving alluvial fan models and understanding how alluvial fans respond to tectonics in extensional regions.

Machine learning-based identification for the main influencing factors of alluvial fan development in the Lhasa River Basin, Qinghai-Tibet Plateau

Machine learning-based identification for the main influencing factors of alluvial fan development in the Lhasa River Basin, Qinghai-Tibet Plateau

Characterizing the trend of channel braiding of a tropical transboundary river using spatial growth component analysis and ARIMA model

Channel braiding is one of the fundamental fluvial processes in the context of sediment-energy nexus. The present study intends to simulate the channel braiding pattern of a tropical river (Jaldhaka River) on the Himalayan foreland plains. The grain size of the bed material in the Jaldhaka River decreases with distance from the mountain front, as does the surface gradient from the piedmont plains to the northern alluvial plains accompanied by the development of alluvial fans. Such assemblage results in multiple facets of hydro-geomorphic controls on channel planform dynamicity. This study is one of the pioneering attempts to characterize the spatial and temporal trend of channel braiding in any river running through the foreland region of the Sikkim-Bhutan Himalayas. The type of channel braiding is determined by the three indices – (1) Braiding Index (BI*), (2) Channel Count Index (BI), and (3) Channel Length Index (Pt), in cases where no gradual and uniform trend of development has been seen.The spatial allometric growth of the channel braiding and time series association using the ARIMA model was examined on the twenty stretches of the river. The results depict nonuniformity in planform development with distance downstream during a 30-year time span (1990–2020). The nature of the planform value distribution concerning all three applied indices has projected a polynomial trend where certain intermediate channel segments break the general trend of the braiding intensity with downstream distance. Since the downstream braiding intensity of the Jaldhaka River hasn't decreased either linearly or exponentially, we were unable to find any significant relationship of it with surface gradient. The nature and association of the channel braiding of the Jaldhaka River point towards the influence of local controls (e.g. river terracing on the upper part and faultline controls in the middle part) on channel planform dynamicity. The prediction of channel braiding for 2030 and 2050 coupled with the model fitted with RMSE, and BIC bears great significance in revealing the future bar growth which may be useful for the different planners and stakeholders concerned with the river basin development.

10Be dating of the Kuitun River terraces in the northern Chinese Tian Shan foreland: Insights into fluvial evolution and tectonic shortening pattern

Characterizing active deformation of a piedmont structure is particularly helpful for understanding the dynamics of deformation of its adjacent active orogenic belt. This work focuses on fluvial geomorphology of the Kuitun River, which flows northwards out of the high mountains and perpendicularly cuts the E-W-striking Dushanzi anticline, a structure of the outermost fold-and-thrust belt in the northern Chinese Tian Shan foreland. Four episodes of alluvial fan development (fans F1–F4, sequentially younger in abandonment age) were identified. Based on the fluvial geomorphological framework constructed by these four alluvial fans, six terraces (terraces T1–T6, sequentially increasing height above the riverbed) were then defined. The topographic analyses and 10Be dating of these alluvial landforms show that the Kuitun River originally flowed northwestwards before at least 80 ka. Subsequent rock uplift caused by fold growth could have resulted in an eastward deflection, after which the river began to flow northeastwards to construct fan F2. At ~67 ka, accumulation of fan F2 ended, and the Kuitun River deflected westwards to flow northwards and began to construct fan F3. The final stabilization of the Kuitun River channel occurred at ~13 ka due to intense river incision forced by climate change, when the river began to incise a 200-m deep canyon and form a flight of strath terraces flanking the valley. By using geomorphic surfaces as the references, the Late Pleistocene and Holocene shortening rates of the Dushanzi anticline were estimated to be 0.71 + 0.17/−0.16 mm/yr (over the past ~67 kyr) and 1.6 + 0.39/−0.37 mm/yr (over the past 13 kyr), respectively. When combined with the long-term shortening rate of ~0.44 mm/yr since initiation of fold growth, it is inferred that the Dushanzi anticline likely experienced an acceleration of deformation during the late Quaternary. With respect to the entire orogenic belt, both fluvial geomorphic records and GPS surveys indicate that most of N-S crustal shortening (likely >70%) across the Tian Shan has been absorbed in the piedmonts of the range, a typical active orogenic belt in the interior of Asia.

Alluvial fan development during the Holocene in the Qu'Appelle Valley, Saskatchewan

Alluvial fan sediments contain valuable information on environmental change and anthropogenic influences, and function as an archive of landscape development. The purpose of this paper is to describe the analysis of the sedimentary information from core samples taken from two alluvial fans in the Saskatchewan prairies. The analysis assessed grain size, organic matter content, and microfossil presence to identify periods of accumulation and stabilization. Parker, Beavers, and Product weathering indices were used to analyze the modern source soil samples and the borehole cores to determine weathering/leaching conditions. The bed‐load transport sediments showed a higher leaching intensity whereas lower leaching was revealed for periods of stability, silt sheet flows, and sand sheet flows. The Beavers Index was not only a strong indicator of a bed‐load transport layer, but also of calcium accumulation zones marking alluvial fan surface stability. The large Dolomite/Calcite ratio marking the calcium accumulation zones was used for correlation between the two alluvial fan sites on a regional scale. A comparison of the stratigraphy of the two alluvial fans documents that a relationship exists between agriculture and an increase in erosion.

Glacier-Induced Alluvial Fan Development on the Northeast Tibetan Plateau Since the Late Pleistocene

The origin of alluvial fans at the drainage basin or the margins of the arid sedimentary basin on the northeastern Tibetan Plateau (NETP) has been a focus of debate among scientific communities. Extensive alluvial fans had developed in the mountain-basin systems of this region during the late Pleistocene. Based on geomorphic/stratigraphic studies and the optically stimulated luminescence (OSL) chronology, we investigated numerous alluvial sequences in the drainage basin of the coupled mountain-basin system on the NETP. Sedimentologic analyses showed that these alluvial sediments mainly comprise crudely meter and decimeter beds of fanglomerate and sandy lenticles, which occasionally contain boulders in the thinner layers. OSL dating results showed that the alluvial sediments were mainly developed during the late MIS 5, MIS 3, and Last Glaciation and Deglaciation (maximum aggradations), while little had occurred during the early Holocene. Comparing our ages and their probability density curves with those of glacial advances from the northeastern/eastern TP, the consistency of both records during different stages since the late Pleistocene suggested that the development of alluvial fans was driven by glacier activities, which yielded abundant outwash, feeding alluvial aggradations. Based on this finding, together with results of previous studies, we argued that the dynamics of alluvial geomorphic processes had a paleoclimatic origin rather than surface uplifts. Further studies indicated that the precipitation of glaciations originated from the ISM northward intrusion during the late MIS 5, MIS 3, and Holocene; however, it was mainly influenced by the westerlies during the Last Glaciation and Deglaciation. Therefore, the development of alluvial fans on the NETP represents coupling signals of the ISM and the westerlies on the interglacial–glacial cycle timescales. The coupling evolution of glacier activities and alluvial aggradations in the drainage basins of mountain-basin systems on the NETP provides a model for assessing the linkages between regional geomorphic processes and atmospheric circulations on hemispheric scales.

Formation, mechanism and significance of alluvial‐dammed lakes in Golmud River catchment, north‐eastern Qinghai‐Tibetan Plateau

AbstractThis study investigated a series of dammed lakes and downstream‐adjacent alluvial fans in the upstream to middle reaches of the Golmud River in the eastern Kunlun Mountain, on the north‐eastern Qinghai‐Tibetan Plateau (QTP). An optically stimulated luminescence (OSL) chronology shows the sediments of five dammed lakes developed from c. 45–40, 30–25, 18–14, and 12–8 ka, corresponding to MIS 3b, late MIS 3a, Last Deglaciation, and early Holocene, respectively. The remote sensing data show these dammed lakes have a total area of 109.4 km2, with the lake volume of more than 4.0 km3. Symmetric alluvial fans from north–south tributary valleys produced OSL ages of c. 61–52, 42–31, 26–20, and 16–10 ka, corresponding to glaciation periods: the MIS 3c and MIS 3a, MIS 2, and the Last Deglaciation. This suggests that glacial activity is responsible for the alluvial fan development, where dammed rivers occurred first, but lake formation did not take place synchronously until later periods of strong hydrologic activity, resulting from northward intrusions of the Indian summer monsoon (ISM) or glacier melt. Thus, the blocking pattern is that river valleys were dammed during periods of glacial activity and lakes formed during wet periods. The lake formation and subsequent drainage may have resulted in: (i) impeded headwater incision and strengthening of downstream dissection; (ii) enriched the halite and potash in the distal Qarhan Salt Lake through hydrologic and hydrochemical processes of abundant water input, the salt lake expansion, salt redissolution from playa and final resedimentation during later dry periods. The alluvial‐dammed lake pattern in the mountain‐basin systems of eastern Kunlun Mountain offers a model for assessing the linkages between monsoon dynamics, geomorphic processes and distal salt lake evolutions in other arid regions.

Climatically- and tectonically-controlled development of the late quaternary alluvial fan in the north piedmont of Zhongtiao Shan (ZTS), north China

The evolution of alluvial fans is controlled by the tectonic setting and climatic fluctuations. This study focused on the Lidian alluvial fan in the northern piedmont of Zhongtiao Shan, north China, to study the fluvial responses to paleoenvironmental changes since the late Last Glacial Maximum. In combination with series of accelerator mass spectrometry (AMS) 14C dating data on fan sediments, sedimentary analyses indicated that the primary fan accumulation was controlled by episodic millennium-scale debris and sheet flood flow related aggradation during 13.3–13.0, 12.7–11.3, 6.2–4.5, and 4.5–2.8 cal ka BP. Between the accumulation periods, the fan process was dominated by aeolian paleosol-and-loess sequence development and the reworking of fan clasts. Considering regional hydraulic conditions and sediment flux, we proposed that the millennium-scale episodic debris flow related fan aggradation during 13.3–13.0, 12.7–11.3, and 4.5–2.8 cal ka BP was controlled by high-volume sediment influx of the permafrost and physical weathering during cold events. The millennium-scale sheet flood-dominated fan aggradation event during 6.2–4.5 cal ka BP was related to the abrupt coarsening and high sediment yield forced by tectonic uplift. We also suggest that the scattered distributed channelized floods and debris backfilling sediments within the fine-grain layers indicate that the deposition of irregular fan lobe accumulation coincided with hydraulic shifts over shorter temporal scales.