Evolution Of Fluvial Systems Research Articles

Structural geological surveys and improvement of tectonic understating of the Pre-Ordovician/Tertiary Graben boundary in vicinity of Nicolaus Copernicus Polar Station, Svalbard

Researchers around the globe are on a quest to develop solutions to mitigate and prevent global warming and climate change. This includes facilitating the switch to renewable energies. Assistant Professor Slawomir Jack Giletycz, Director of the Polar Research Station in Svalbard and part of the Structural Geomorphology Research Group, Department of Earth Sciences at National Central University in Taiwan, is interested in glacial retreat in Svalbard, Norway. As the Earth warms, glaciers are melting and land that was previously buried by glaciers is being exposed. By studying this land, researchers can glean new insights. For example, Giletycz and his collaborators are performing geological mapping of areas that have been recently exposed to subaerial conditions due to the glacial retreat. They are working to develop new geological maps and interpret tectonic and structural settings. The researchers are also investigating fluvial system development and surveying particular glaciers. They are using unmanned aerial vehicles to capture aerial images of entire glacier river systems and can use the images to build a digital surface model that can be used in applications such as QGiS or ArcGiS. In the long tem, they can monitor the development of glacier fluvial systems such as sediment discharge. Another focus for the researchers is conducting plaeocoast surveys of the Kaffiøyra plain in western Svalbard. Excitingly, the researchers are the first humans to study Svalbard in this way and, through this work, they will make significant contributions to geological mapping and underpin geology, tectonics and structures.

Unraveling the tectonic and climatic influences on River Erosion: A late Quaternary case from the Dongda River, northeast tibet

Rivers adjust their equilibrium profiles to base-level changes induced both by climatic fluctuations and tectonic movements. It is crucial, yet challenging, to differentiate their distinct roles in shaping the evolution of fluvial systems when both forces are involved. In contrast to the broader, regional-scale impact of climatic changes, the various tectonic deformation at local-scale can be recorded as various terrace deformation patterns. The Dongda River, located on the northeastern edge of the Tibetan Plateau, crosses active folds and thrusts, providing a unique opportunity to isolate the effects of climatic and tectonic forces. In this study, we identified five river terraces along Dongda River, designated as T1, T2, T3, T4a, and T4b, from lowest to highest. Radiocarbon and OSL dating results reveal abandonment ages of 4.2 ± 0.3 ka, 6.1 ± 0.5 ka, 12.4 ± 2.5 ka, 16.4 ± 0.2 ka, and 27.4 ± 2.5 ka, showing rhythmic alignment with climatic fluctuations since the late Pleistocene. Elevation profiles of the terraces demonstrate base-level aggradation at the footwall of the Fengle fault between T4a/b and T2, highlighting a tectonically dominated process of river incision at its hanging wall. Differential uplift rates were estimated to be 2.2 ± 0.3 mm/a at the North Qilian Shan hinterland, 1.1 ± 0.2 mm/a in the Huangcheng Basin, 0.2–0.4 mm/a in the Yangxiang Basin, and 1.1 ± 0.2 mm/a within the foreland fold-and-thrust belt of Dahuang Shan, respectively. In contrast, an accelerated incision rate (>1.8 mm/a) has been observed throughout the entire basin since the abandonment of T2, coinciding with the adjustments in the Asian monsoon and westerlies systems since the Mid-Holocene. This study provides insights into the complex interplay between climatic variability and tectonic activity in fluvial systems, enhancing our understanding of how these competing forces have shaped the evolution of the fluvial landscape over time.

Neotectonic impact on drainage development in the Eastern Himalayan foreland basin

The present study intends to divulge the complex drainage evolution in connection to neotectonic controls focusing the Jaldhaka and Raidak River interfluve on the eastern Himalayan Foreland Basin (HFB). It involves analysing the surface and sub-surface changes in the fluvial system's evolution with field and geospatial evidence bearing geomorphic markers, sediment analogy and channel morphological properties. The channel orientation, planimetry and the channel longitudinal process anomaly were attributed solely from the geospatial perspective as surface evidence of neotectonic controls. The results unveil an intense neotectonic control on channel development–from structurally guided channel avulsion that shaped the presently active course of the Torsa River to deformation-guided channel morphological changes. Moreover, relatively higher deflection angles, intense channel sinuosity and tight meandering bends forming along the structural elements symptomizes the structure-controlled drainage development in recent times. Furthermore, sediment analogy from deep well logs and shallow subsurface trenches was analysed to obtain subsidence-driven fluvial sequences and geochronology of sedimentary deformation in channel beds and floodplains. The Optically Stimulated Luminescence (with fading correction) technique-based determination of shallow sub-surface sediment's age indicates occurrences of palaeoseismic events between 1.6 ka (±0.1 ka) and 1.35 ka (±0.2 ka) as well as between 1.35 ka (±0.2 ka) and 1.14 ka (±0.1 ka) had resulted in channel bed sagging while stress impacted the formation of syn-sedimentary folding. The palaeoseismic events that led to relative subsidence are evident in upward sediment stacking (channel fill) sequences being observed at multiple trenches. The deep sub-surface staking of channel floor deposition lenses is also evident of basin subsidence that influenced channel oscillations of reoccupation type.

Exploring the influence of vegetated mid-channel bar on flow and turbulence in bifurcated channels: An experimental approach

The evolution of fluvial systems is greatly impacted by mid-channel bars, a typical morphodynamic process in natural rivers. Sometimes, the growth of vegetation over these bars complicates the morphological behaviour by interacting with the flow. It is therefore necessary to have a fundamental interpretation of the flow-turbulence structure around the mid-bar in presence of vegetation cover in order to understand braiding dynamics, still studies in this area are scarce. The present study investigates the process-form-vegetation-interaction through experimental investigation at a flume scale mid-channel bar model with different natural vegetation cover arrangements (paddy, leafy, and rigid stem). The flow-turbulence behaviour has been observed through the bifurcated channel using the three-dimensional Acoustic Doppler Velocimeter (ADV). Results showed that the longitudinal velocity component varies with the different vegetation cover, and it was highest with leafy vegetation (about 32%). Similarly, the Reynolds Stress and Turbulence Intensity were also observed to be higher in case of leafy vegetation. A unique pattern of flow-turbulence parameters was observed near the bar level, the lower canopy level, and the upper canopy level. Moreover, it was found that vegetation structure and its flexible nature influence both longitudinal velocity reduction and momentum transfer at and over the canopy, as well as the thickness of the shear layer region.

The Early Paleozoic sedimentary record in northeastern Brazil: Unravelling the sedimentary provenance and evolution of fluvial systems after the Western Gondwana assembly

The sedimentary units of the geographically isolated basins of NE Brazil are historically interpreted as coeval and part of the same depositional system that was ultimately responsible to the deposition of the first sedimentary sequence of the intracratonic Parnaíba Basin. We present the first integrated detrital zircon U-Pb age dataset from the Early Paleozoic basins of NE Brazil, providing new insights into the depositional evolution and erosional history after Western Gondwana assembly. The lowermost sedimentary units (Ipu, Cariri, and Tacaratu formations) of eleven NE Brazil sedimentary basins (Parnaíba, Araripe, Tucano-Jatobá, Lavras da Mangabeira, Fátima, São José do Belmonte, and Mirandiba) were analyzed by a multi-proxy approach aiming to propose new insights on the paleogeographic reconstruction and stratigraphic correlations. Sedimentary provenance data, together with paleocurrents measurements consistently towards NNW-NW, suggests that the primary source for all the Early Paleozoic sedimentary units of NE Brazil were elevated orogenic areas related to the Brasiliano Orogeny to the south of Borborema Province (e.g., Riacho do Ponta, Rio Preto, and Sergipano belts). Based on detrital zircon U-Pb ages, we position the beginning of sedimentation of these basins in the Ordovician. The U-Pb age spectra for all analyzed sedimentary successions are remarkably similar. The analysis of KDE plots, CA-DA gap curves, and (dis)similarity tests, reinforced the correlation and contemporaneity of all the Ordovician sedimentary successions of NE Brazil. The conceived paleogeography model points to deposition of all the analyzed successions in a ramp, slightly tilted towards NW, where continental-scale fluvial system drained Neoproterozoic orogenic areas (i.e., Brasiliano Orogeny) dispersing huge volumes of sediments towards Borborema Province interior.

Structural control on drainage pattern development of the western Taiwan orogenic wedge

AbstractStructural control on drainage patterns has long been suggested to play an important role in the development of fluvial systems, including their map pattern. Along the western Taiwan orogenic wedge, a prominent drainage pattern change is present, from predominantly orogen parallel drainages in the south to river systems that flow perpendicular to the long axis of the mountain belt in the north. Such change likely reflects the temporal evolutionary process as the Taiwan orogen propagates southward. We propose that the flow direction change of river systems is produced by the development of the fold‐and‐thrust belt on the pro‐wedge side of the mountain belt and is facilitated by drainage reorganization that includes abrupt drainage captures and more gradual divide movements, permitting drainage basins to attain a geometrically stable configuration with time. Our observations in Taiwan demonstrate not only how tectonic uplift is effective at modifying river patterns in the early stages of orogenic development but also how time and increased stream power encourage river networks to adjust to more effective patterns in mature mountain belts.

Sediment Load and Grain Size Controls on Channel Migration Patterns in Experimental Deltas

AbstractUnderstanding channel migration is essential in interpreting long‐term evolution of fluvial systems and their deposits. Using data from an experimental delta, we analyzed the kinematics of the upstream channel and assessed the relative dominance of continuous lateral channel migration versus abrupt changes (i.e., avulsions). Detailed investigation of channel centerline location at minute intervals reveals a short‐term correlation between the magnitude of migration rates measured at the same location and a spatial correlation that diminishes with distance between points. The main finding is that the channel migrates across the entire deltaic domain without large and abrupt lateral shifts but through continuous lateral migration at variable rates. Long periods of back and forth small moves are separated by short bursts of rapid lateral migration. This finding contradicts the default expectation that that aggrading systems are characterized by avulsions and suggests that highly mobile rivers tend to avulse less. We contrast this with another experiment conducted under similar conditions but with finer sediment supplied at a lower rate which shows drastically less lateral migration; the kinematics is instead dominated by periodic flow reconfiguration episodes akin to avulsions, an indication that channel migration‐style depends on the sediment load. The characteristics of these two experiments parallel two regions of the Mississippi River, the meandering and highly mobile alluvial plain and the less dynamic deltaic region, suggesting that bedload sediment deposition at the transition into backwater zone plays an important role in re‐shaping the river planform and migration style.

The Evolution of Ancient Fluvial Systems in Memnonia Sulci, Mars: Impact Crater Damming, Aggradation, and a Large Water Body on the Dichotomy?

AbstractThere is conflicting evidence for an ancient ocean which occupied the northern hemispheric basin on Mars. Along different regions of the dichotomy boundary, sediment fans have been interpreted as either forming into a large water body or a series of smaller paleolake basins. Here, we investigate fluvial systems in the Memnonia Sulci region of Mars, set along the dichotomy, which comprise erosional valley networks, paleolake basins, inverted channel systems, and sediment fans. We focus our analysis on the evolution of the upslope catchment and characterizing the ancient environment of a large, downslope basin, bound by the topographic dichotomy and the Medusae Fosse Formation. The catchment fluvial systems comprise highly degraded valley networks and show a complex history of incision and filling, influenced by paleolake basin overflow, impact crater damming, aggradation, and possibly a downstream water body. The morphology of the sediment fans is consistent with either fluvial fans or deltas and they form at discrete elevations, rather than a common elevation plane. Our analysis is consistent with the sediment fans forming into a series of paleolake basins set along the dichotomy, rather than into a large inner sea or ocean‐sized water body. The fluvial systems were likely active between the mid Noachian and early Hesperian periods. Our results demonstrate the complex, multi‐phase evolution of fluvial systems on ancient Mars and highlight the importance of regional and local studies when characterizing ancient regions of the dichotomy.

Cenozoic reorganization of fluvial systems in eastern China: Sedimentary provenance of detrital K-feldspar in Taiwan

Cenozoic passive margin sediments in Taiwan provide an important natural archive to reconstruct drainage reorganization in eastern China. In this study, we used Pb isotope compositions of detrital K-feldspar to investigate the sedimentary provenance of Cenozoic strata in Taiwan and to constrain fluvial system evolution in eastern China. Eocene to lower Oligocene sandstones in Taiwan are characterized by radiogenic K-feldspar grains (206Pb/204Pb>18.4), indicating that the eastern Cathaysia Block served as the dominant sediment contributor. In contrast, a late Oligocene sample has a Pb isotopic character indistinguishable from that of the Gan River, a major tributary of the Yangtze River. This provenance change is interpreted as the result of headward (westward) migration of the paleo-Min River to the Wuyishan (Wuyi Mountains) during the late Oligocene. Miocene deposits are enriched in relatively unradiogenic K-feldspar (206Pb/204Pb<17.0) which can be reliably traced back to the Dabie and Sulu orogenic belts. Since the early Miocene, the paleo-Yangtze River, mainly draining the Yangtze Craton and the Dabie orogenic belt, delivered a large volume of detritus to the East China Sea Shelf Basin and also to the proto-Taiwan region.

Nonclimatic and extrabasinal processes controlled pedogenesis in paleosols of the Paleocene Nacimiento Formation, New Mexico, USA

AbstractPaleosols can represent intervals of nondeposition in sedimentary packages and are used with increasing frequency as proxies for paleoenvironmental conditions during basin filling. However, the complexities of factors both internal and external to pedogenesis require consideration of paleosols in any basin or sedimentary package in a broader context than is often assumed. With this in mind, we measured and analyzed pedogenic features, stratigraphic position, geochemical composition, and petrography of paleosols in the Nacimiento Formation to gain insight into the paleoenvironmental conditions of the early Paleocene in the San Juan Basin. During this interval, the San Juan Basin was located in middle northern latitudes (~40°N) and saw rapid terrestrial siliciclastic sedimentation related to Laramide tectonism. Evidence from earlier researchers suggests that prevailing climate conditions during Nacimiento Formation deposition were warm and humid. We used morphological properties of paleosols to categorize paleosols into pedotypes indicative of distinct pedogenic conditions. The general stratigraphic distribution of these pedotypes shows an up-section increase in soil drainage conditions through the Nacimiento Formation that cannot be correlated with known climate changes. We suggest that fluvial system evolution was the major control on pedogenic conditions. We investigated Nacimiento Formation paleosols with widely used paleosol geochemical climate analyses, which provided paleoclimate estimates that are in disaccord with independently derived estimates. We show that in alluvial depositional systems with source areas in weathered sedimentary rocks, these analyses can be difficult to interpret and likely lead to estimates that do not reflect true pedogenic conditions during the postdepositional near-surface alteration of sediments. Petrographic analysis of Nacimiento Formation paleosols showed that some likely formed under semiarid to subhumid conditions that allowed pedogenic accumulation and illuviation of smectite clays yet did not substantially chemically alter primary detrital plagioclase feldspar grains in paleosol B horizons. The paleosols of the Nacimiento Formation, when analyzed at the basin scale, show that sedimentary aggradational processes can overpower climate processes in creation of a sequence of paleosols in a stratigraphic section. In addition, the incorporation of clays from sedimentary rocks in a basin's source area can drastically skew the geochemical signatures and therefore interpretations of paleosols in that basin.

The role of bedrock and climate for the Late Quaternary erosive-depositional behavior of an intraplate tropical river: The Tietê River case, southeastern Brazil

The evolution of fluvial systems has been related to tectonics and climate controls across various spatiotemporal scales. Despite the growing efforts to investigate the effects of those controls in the fluvial dynamics, there is a lack of studies in intraplate tropical regions. Here, we applied geomorphological, sedimentological, and optically stimulated luminescence dating (OSL) techniques to investigate the effects of climate and tectonic factors on the evolution of the Upper and Middle Tietê River during the late Quaternary, especially concerning alluvial aggradation and terraces formation. The Tietê River is one of the most important rivers of southeast Brazil, flowing from crystalline steep to sedimentary low-relief intraplate terrains, in an area with evidence of Cenozoic tectonics and under tropical monsoon climate. We recognized one fluvial terrace level in the Upper Tietê valley and a sequence of seven terraces, from 2 to 105 m above the channel level, in the Middle Tietê. These terraces are formed by thin deposits (<10 m), composed of sandy and gravelly sediments. The terraces of the Upper Tietê and the high and intermediate terrace levels of the Middle Tietê River are strath, while the low terraces of the middle reach are cut-and-fill. Lithological shifts and structural features of the watershed terrain play a strong control in the occurrence and distribution of these terrace levels. The Serra de Paranapiacaba, a regional knickzone, hinders the lowering of the base level and the river incision to upstream, limiting the formation and preservation of terraces in high topographic levels in the Upper Tietê. The formation of seven terrace levels in the Middle Tietê River was controlled by the combination of low erosion resistance of the lithological substrate and high stream power and coarse bedload that increased the erosion efficiency of the channels. Thus, the influence of intraplate tectonics on the fluvial landscape is restricted to passive controls by exhumated basement structures from older tectonic events. OSL dating of sedimentary deposits in different terrace levels indicate five periods of aggradation in the Middle Tietê valley since 18 ka: 17.7 ± 1.7 ka; 9.8 ± 1.0 to 8.6 ± 0.8 ka; 7.1 ± 0.7 to 5.8 ± 0.5 ka; 4.2 ± 0.4 to 3.1 ± 0.3 ka; and 0.6 ± 0.06 ka. The results indicate that changes in the activity of the South American Monsoon System induced changes in vegetation cover and water discharge in the river valleys of southeastern Brazil over the past 18 ka. The aggradation periods are correlated with drier environmental conditions and sparser vegetation. In contrast, valley incision occurred under transitions to wetter environmental conditions and was potencialized by vegetation recovery. Therefore, climate-induced changes in the water discharge were the main allogenic control on the late Quaternary landscape evolution.

Where will widening occur in an outwash braidplain? A new approach to detecting controls on fluvial lateral erosion in a glacierized catchment (north‐western Spitsbergen, Svalbard)

AbstractThe dynamics of fluvial system evolution depend on fluvial processes and their driving forces associated with climatic variations, which affect changes in the morphology of river channels and floodplains. Neither channel slope and morphology, nor the properties of fluvial sediment have previously been considered as determinants of active braidplain widening on outwash plains (formed from valley/alpine glaciers and confined by pre‐existing topography) in the High Arctic region and in the forefields of retreating glaciers. Factors determining widening of braidplain activity of the Waldemar River outwash (north‐western Spitsbergen, Svalbard) were analysed on the basis of geomorphological, sedimentological, glaciological and meteorological research, and indicate significant multiple correlations between meltwater discharge, precipitation, braidplain width, morphology of the braided channel and the textural features of braidplain deposits. The capability of multivariate adaptive regression splines to detect these relationships was described, and threshold values were identified. The results indicate that the rate of active braidplain widening is proportional to the meltwater outflow in proglacial rivers, which can decrease despite a growing rate of glacial ablation. A proposed model enables us to predict zones of braidplain prone to widening activity in the High Arctic (humid) outwash fans and plains as well as fans developed in arid intermountain basins. The necessary conditions to activate braidplain widening processes were (1) spatial changes in the outwash feeding system due to glacier terminus retreat and (2) crossing the thresholds in passive factors (S and d50) controlling lateral erosion intensity. As a result, the braidplain reached a new dynamic equilibrium, in which high‐magnitude–low‐frequency extreme meltwater discharges were of particular importance in terms of braidplain dynamics and are the dominant controls on the pattern of distributary channels.

Early Pleistocene drainage pattern changes in Eastern Tibet: Constraints from provenance analysis, thermochronometry, and numerical modeling

The geometry and evolution of fluvial systems are thought to be related to surface uplift. In eastern Tibet, rivers exhibit peculiar drainage patterns but how these patterns were established and their connection with the plateau uplift are still under debate. Here, we use detrital zircon U-Pb dating, bedrock (U-Th)/He thermochronometry, topographic analysis and numerical modeling to explore the paleo-drainage pattern of the Dadu and Anning Rivers, eastern Tibet. Our detrital data indicate that the Pliocene sources of sediments to the Anning River are different from the modern ones and they include a source similar to that of the modern Dadu River, implying a paleo-connection between the Dadu and the Anning Rivers and a subsequent cutoff of this connection after the deposition of the Pliocene sediments. Bedrock thermochronometric data along the Dadu River reveal rapid cooling at ∼10 Ma and a possible enhanced cooling at ∼2 Ma, which we interpret as a response to the regional plateau uplift in eastern Tibet and to the Dadu-Anning capture, respectively. Combined with topographic analysis and numerical modeling, our results indicate an Early Pleistocene capture between the Dadu and Anning Rivers, resulting in the changes in the sediment sources of the Anning River, enhanced incision of the Dadu, and the transience of the Dadu River profile. The Dadu-Anning capture is related to the motion along the active sinistral strike-slip Daliangshan fault that locally disrupts the river network. This event does not date the plateau uplift; rather, it indicates how river reorganization can effectively enhance river incision and affect landscape development independently from regional-scale uplift.

Major advances in studies of the physical geography and living environment of China during the past 70 years and future prospects

The natural environment provides material essentials for human survival and development. The characteristics, processes, regional differentiation and forcing mechanisms of the elements of the natural environment (e.g. geomorphology, climate, hydrology, soil, etc.) are the main objects of research in physical geography. China has a complex natural environment and huge regional differentiation and therefore it provides outstanding reserach opportunities in physical geography. This review summarizes the most important developments and the main contributions of research in the physical geography and human living environment in China during the past 70 years. The major topics addressed are the uplift of the Tibetan Plateau and the evolution of its cryosphere, the development of fluvial systems, the acidification of the vast arid region of the Asian interior, variations in the monsoon and westerly climate systems on multiple timescales, the development of lakes and wetlands, the watershed system model, soil erosion, past human-environment interactions, biogeography, and physical geographic zonality. After briefly introducing international research developments, we review the history of research in physical geography in China, focusing on the major achievements and major academic debates, and finally we summarize the status of current research and the future prospects. We propose that in the context of the national demand for the construction of an ecological civilization, we should make full use of the research findings of physical geography, and determine the patterns and mechanisms of natural environmental processes in order to continue to promote the continued contribution of physical geography to national development strategies, and to further contribute to the theory of physical geography from a global perspective.

Small headwater stream evolution in response to Lateglacial and Early Holocene climatic changes and geomorphological features in the Saint-Gond marshes (Paris Basin, France)

The study focuses on river dynamics and vegetation changes during the last Glacial-Interglacial transition from a headwater stream located in the eastern part of the Paris Basin. We adopt a spatial multiproxy approach combining image analyses, geophysical surveys, sedimentary and pollen record analyses to document the impact of Lateglacial climate changes and geomorphological features on vegetation and fluvial dynamics in the small Boitet catchment (ca. 20 km2). Our results show that the sedimentary record is organized into six successive alluvial sequences reflecting changes in discharge and channel morphology in response to short phases of climate oscillations during the Lateglacial and Early Holocene periods. The Boitet alluvial sequences present some similarities with other NW European rivers that are interpreted as large-scale fluvial system evolution to climate changes. However, some local differences have also been highlighted partly related to the upstream position of the catchment. Among them, two distinctive features of the Boitet catchment are 1) the preservation of the Oldest Dryas deposits, which have been rarely described in this area, and 2) the recognition of multichannel river dynamics during the Oldest Dryas and Younger Dryas. We demonstrate that the fluvial evolution is firstly triggered by climate changes and that land surface features may also influence specifically upstream areas revealing contrasting responses of the river system.

Alluvial channel response to environmental perturbations: fill-terrace formation and sediment-signal disruption

Abstract. The sensitivity of fluvial systems to tectonic and climatic boundary conditions allows us to use the geomorphic and stratigraphic records as quantitative archives of past climatic and tectonic conditions. Thus, fluvial terraces that form on alluvial fans and floodplains as well as the rate of sediment export to oceanic and continental basins are commonly used to reconstruct paleoenvironments. However, we currently lack a systematic and quantitative understanding of the transient evolution of fluvial systems and their associated sediment storage and release in response to changes in base level, water input, and sediment input. Such knowledge is necessary to quantify past environmental change from terrace records or sedimentary deposits and to disentangle the multiple possible causes for terrace formation and sediment deposition. Here, we use a set of seven physical experiments to explore terrace formation and sediment export from a single, braided channel that is perturbed by changes in upstream water discharge or sediment supply, or through downstream base-level fall. Each perturbation differently affects (1) the geometry of terraces and channels, (2) the timing of terrace cutting, and (3) the transient response of sediment export from the basin. In general, an increase in water discharge leads to near-instantaneous channel incision across the entire fluvial system and consequent local terrace cutting, thus preserving the initial channel slope on terrace surfaces, and it also produces a transient increase in sediment export from the system. In contrast, a decreased upstream sediment-supply rate may result in longer lag times before terrace cutting, leading to terrace slopes that differ from the initial channel slope, and also lagged responses in sediment export. Finally, downstream base-level fall triggers the upstream propagation of a diffuse knickzone, forming terraces with upstream-decreasing ages. The slope of terraces triggered by base-level fall mimics that of the newly adjusted active channel, whereas slopes of terraces triggered by a decrease in upstream sediment discharge or an increase in upstream water discharge are steeper compared to the new equilibrium channel. By combining fill-terrace records with constraints on sediment export, we can distinguish among environmental perturbations that would otherwise remain unresolved when using just one of these records.

Response of a mountain‐foreland fluvial system to an advancing ice sheet, southern Poland

In this paper, fluvial deposits of Middle Pleistocene age in the mountain‐foreland area of southern Poland (Eastern Sudetes and Western Carpathians) are studied in order to document the evolution of fluvial systems during the coldest stages of glacial periods when the Scandinavian Ice Sheet advanced far to the south. The focus is on fluvial response to climate change and glacial impact on river system behaviour. Also considered is the tectonic uplift of the mountain part of river catchments and its potential influence on the style of fluvial sedimentation in the fore‐mountain area. Three drainage basins that were active during the Elsterian and Saalian glaciations are investigated. Facies analyses are carried out on thick successions of braided river deposits covered with till or glaciolacustrine sediments, which result in a reconstruction of the fluvial activity synchronous with the ice‐sheet advance. The results suggest that fluvial activity declined prior to ice‐sheet advance into the fore‐mountain area. This climatically induced change is directly recorded in alluvial successions by upward‐decreasing bed thicknesses and grain sizes. River longitudinal profiles were shortened in front of the advancing ice sheet. The base level of the studied rivers, created by the ice‐sheet margin, rose in parallel with glacial advance. As a result, the successive reaches of rivers (degradational, transitional, aggradational) underwent shortening and moved upstream within the catchments. Moreover, tectonically induced local increases of river slopes may have influenced the depositional processes.

A celebration of the twentieth anniversary of the Fluvial Archives Group (FLAG)

The Fluvial Archives Group (FLAG) was founded in 1996 to bring together researchers looking at the development of fluvial systems over multiple timescales and global spatial scales. Fluvial archives of various types are important not just because they provide insights into past landscape dynamics, e.g., driven by climate or crustal processes, but also because they frequently contain fossil or archaeological material for which they provide stratigraphic control. Since 1996, FLAG has evolved from a research group of the British Quaternary Research Association into an organisation with around 500 members in over 20 countries. The research group held 12 biennial meetings, comprising both presentations and field excursions, as well as multiple themed sessions at international conferences. These had resulted by 2017 in 19 journal special issues, all fully detailed by Cordier et al. (2017). The goals of FLAG are: provision of a community for discussion of key issues concerning fluvial archives, including organising the aforementioned biennial discussion/field meetings, sessions at relevant international conferences, and special issues of journals; continued promotion of the value of fluvial archives by means of readily accessible published information; and coordination of activity with other research groupings with overlapping interests, e.g., by co-convening sessions and collaborating on publications.

Identification of the architecture and evolution of fluvial system using seismic geomorphology: A case study from Gulf of Thailand

This study attempts to identify fluvial architecture and document channel and channel belt dimensions of central Pattani Basin within Upper Miocene to Holocene interval by using seismic geomorphology and well log data. Many seismic attributes such as RMS, sweetness, semblance and spectral decomposition were computed to map channel morphology. Forty (40) horizon/time slices were analyzed to understand evolution of channel systems within the zone of interest. We measured key channel parameters to quantify channel morphology. Amplitude spectra of spectral decomposition and sweetness are found to be the most useful attributes. Image quality can be enhanced if semblance is combined with other attributes by adjusting the opacity level. Different fluvial styles are identified in different parts of the study area including high sinuosity system with broad meander belt, sand filled channel, low sinuosity distributary system and broad incised fluvial system with tributary valleys. The study interval can be divided into five periods based on channel morphology. Period 1 (900–700 ms) has moderate to high sinuosity channels in lower part, while in the upper part; it has low sinuosity systems. High sinuosity channel features representing well-developed meander belt dominated in Period 2 (700–600 ms). Period 3 (600–450 ms) comprised of wide and low sinuosity channels associated with coal deposition. Period 4 (450–250 ms) is characterized by possible marine deposition during high sea level with occasional fluvial intervene. Period 5 (250–100 ms) is represented by highly sinuous broad fluvial systems deposited within incised valley. Such variation in the fluvial styles would serve as a warning as to a rather simplistic assumptions on the channel scale and styles during reservoir modeling.

Specific Exogenetic (External) and Endogenetic (Internal) Effects on Fluvial System Evolution

A collection of papers appears under the title “Special External Effects on Fluvial System Evolution” in the journal, Quaternary. This is a new Special Issue under the aegis of the Fluvial Archives Group (FLAG), illustrating the recent progress made in paleo-fluvial research. These papers highlight the high complexity of the external forcing of fluvial dynamics, and especially, the combined results of several interfering variables. In addition, it appears that the study of fluvial archives cannot be limited to the general and direct effects of external variables, but it also has to include the indirect influences that are regionally variable.