Overbank Research Articles

Coupled channel–floodplain dynamics and resulting stratigraphic architecture viewed through a mass-balance lens

ABSTRACT Basin-wide accommodation production and associated sediment mass deposition exert fundamental controls on stratigraphic architecture, but the details of this relationship are not fully understood. This is because it is unknown how accommodation production directly influences morphodynamics both in terms of channel process (i.e., channel migration, channel avulsion) and floodplain process, both of which are themselves coupled dynamically and are critical to the nature of stratigraphic architecture. To address this, we expand on existing theory that links sediment mass balance and resultant stratigraphic architecture. We use two fan-delta experiments that each experience different rates of accommodation production to measure key surface morphometrics and subsurface sedimentary characteristics. Importantly, sediment was transported in bedload and suspension in these experiments, resulting in construction of strata characterized by channel bodies surrounded by overbank strata deposited from suspension fallout. From these data we use three key timescales to capture the overall behavior of the system when placed into mass-balance space: avulsion setup timescales (TA) and channel mobility timescales (TV) that define short-term surface autogenics, and an accretion timescale (TC) that incorporates longer-term deposition. We find that the ratio of both TC/TA and TC/TV are independent of accommodation production rate in mass-balance space, which supports a self-organized response of channel dynamics to environmental boundary conditions. The fraction of strata generated from key depositional environments largely supports this behavior, particularly for channel sand bodies that resulted in deposition from bedload transport. As such, our results suggest that channel-body density is independent of accommodation production rate in a mass-balance space. We found that, although contributing to a significant fraction of the basin strata, far-field overbank deposition rates are insensitive to accommodation production and that differences in autogenic timescales between experiments largely resulted from differences in channel deposition rates, highlighting the close coupling between channel dynamics and accommodation generation. More generally the observed self-organized response of surface morphodynamics to accommodation production in mass-balance space provides a process-based framework to explain the utility of balancing mass for the prediction of down-system sediment size fractionation and sedimentary architecture.

The heterogeneous geomorphological impact of an exceptional flood event and the role of floodplain vegetation

AbstractApplication of an integrated spatial approach combining several sources of remote sensing data to include both channel and floodplain morphological and sedimentological impacts has identified the geomorphological effects of three extreme flood events during a single flood season (2019–2020) along a 16‐km reach of the River Teme, UK. This combined approach allowed the assessment of in‐channel pattern development, incision and aggradation; lateral bank migration; and overbank sedimentation and scour by out‐of‐channel flows. Rates of change during the event period were compared with those in the previous 10 years. The approach also allowed the role of vegetation and cultivation, both bankside and out on floodplains, to be assessed with variations in the extent of riparian wood and channel slope driving contrasts in the extent of the response. The spatial impacts from such extreme events are highly localised, varied in kind, and can be considered for both rivers and floodplains together. Erosional effects were distinctively distributed and not simply contributions to ongoing meander development; channel aggradation was localised, and overbank sedimentation explicably patchy. In reaches without woody vegetation, differences in channel and floodplain slope, local floodplain relief as created by prior events, and the impact of man‐made structures were factors that drove variations in flood response. This study strongly underlines the role of continuous riparian vegetation in maintaining bank stability and constraining lateral channel migration, but also to the potential influence of floodplain vegetation and planting for ‘natural engineering’ in the context of floodplains as well as channels in comparable environments. Maintenance of riparian vegetation in the context of landowner and Natural England conflict and management of future flood risk is important, but also highlighted is the need to consider the role of hedgerows and wider planting for constraining soil and riverbank erosion during flood events.

Paleoecology and paleoenvironment of the Early Cretaceous theropod-dominated ichnoassemblage of the Los Corrales del Pelejón tracksite, Teruel Province, Spain

The earliest Cretaceous (mid-late Berriasian) tracksite Los Corrales del Pelejón is an important dinosaur trackway site in Teruel Province in Spain. The ichnoassemblage occurs in the Galve Formation (Galve sub-basin, Maestrazgo Basin) and comprises around 40 tracks assigned to theropods and ornithopods. In this paper, we undertake a paleoenvironmental analysis of the succession, which includes the overbank deposits of a fluvial environment, and discuss the implications of these findings for trackway preservation and orientation. The track-bearing unit is composed of fine- to very fine-grained, thinly bedded sandstone layers with wave ripples and traces of the Mermia ichnofacies, which were deposited as splay deposits within an ephemeral overbank pond. Two different theropod ichnotaxa (Megalosauripus cf. transjuranicus and Grallatoridae indet.) of three different size classes occur as small-, medium-, and large-sized tracks. The ornithopod tracks are classified as cf. Iguanodontipus isp. Five theropod trackways (M. cf. transjuranicus) show a bimodal orientation pattern with a similar orientation to NE-SW wave ripple crests, suggesting that these animals were walking parallel to the shoreline of the ephemeral overbank pond. Three of them walked in a similar subparallel orientation, but there is no evidence suggesting gregarious behavior as they have slightly different orientations and/or speed values. The Los Corrales del Pelejón site is an example of environmental influence on dinosaur behavior.

Vertebrate ichnology and palaeoenvironmental associations of Alaska’s largest known dinosaur tracksite in the Cretaceous Cantwell Formation (Maastrichtian) of Denali National Park and Preserve

ABSTRACT The Upper Cretaceous Cantwell Formation in Denali National Park and Preserve (DENA) preserves an abundant and diverse ichnofossil record of high latitude dinosaurs. Field-based investigations of the formation remain limited due to its wide areal extent and remoteness, leaving questions concerning its temporal and faunistic relationships to other units unaddressed. Here we describe the largest tracksite known in DENA and all of Alaska – a 7500 square metre outcrop of steeply dipping beds known as the Coliseum. The site exposes 66.3 metres of vertical section consisting of laterally extensive fine- to medium-grained sandstone, mudstone, calcareous shale, and bentonite. Vertebrate trace fossils include true tracks, transmitted tracks, natural casts, and trackways documented via handheld and UAV-assisted photogrammetry, enabling three-dimensional mapping of the site. Facies analysis reveals a depositional environment of crevasse splay and overbank deposits within a fluvial floodplain. U-Pb dating of bentonite collected from the site returned an age of 69.3 ± 0.9 Ma, improving the limited temporal constraints of the formation. We document several ichnotaxa, some new to the formation, representing ornithopods, ceratopsids, and large and small-bodied avian and non-avian theropods. The Coliseum provides a rare window into a high latitude, Late Cretaceous forested ecosystem deposited in a Greenhouse World.

Coupled channel-floodplain dynamics and resulting stratigraphic architecture viewed through a mass-balance lens

Basin-wide accommodation production and associated sediment mass deposition exert fundamental controls on stratigraphic architecture, but the details of this relationship are not fully understood. This is because it is unknown how accommodation production directly influences morphodynamics both in terms of channel process (i.e., channel migration, channel avulsion) and floodplain process, both of which are themselves coupled dynamically and are critical to the nature of stratigraphic architecture. To address this, we expand upon existing theory that links sediment mass balance and resultant stratigraphic architecture. We use two fan-delta experiments that each experience different rates of accommodation production to measure key surface morphometrics and subsurface sedimentary characteristics. Importantly, sediment was transported in bedload and suspension in these experiments, allowing for construction of strata characterized by channel bodies surrounded by overbank strata deposited from suspension fallout. From these data we use three key timescales to capture the overall behavior of the system when placed into mass balance space; avulsion setup timescales (TA) and channel mobility timescales (TV) that define short-term surface autogenics, and an accretion timescale (TC) that incorporates longer term deposition. We find that the ratio of both TC/TA and TC/TV are independent of accommodation production rate in mass-balance space, which supports a self-organized response of channel dynamics to environmental boundary conditions. The fraction of strata generated from key depositional environments largely supports this behavior, particularly for channel sand bodies that resulted in deposition from bedload transport. As such, our results suggest that channel body density is independent of accommodation production rate in a mass-balance space. We found that, although contributing to a significant fraction of the basin strata, far-field overbank deposition rates are insensitive to accommodation production and that differences in autogenic timescales between experiments largely resulted from differences in channel deposition rates, highlighting the close coupling between channel dynamics and accommodation generation. More generally the observed self-organized response of surface morphodynamics to accommodation production in mass-balance space provides a process-based framework to explain the utility of balancing mass for the prediction of down-system sediment size fractionation and sedimentary architecture.

Overbank sedimentation and its influence on channel avulsion: examples of the Cretaceous Tando and Namyang basins in the mid-western part of the Korean Peninsula

Overbank sedimentation and its influence on channel avulsion: examples of the Cretaceous Tando and Namyang basins in the mid-western part of the Korean Peninsula

Geochemistry of the Lancang River (Upper Mekong River) overbank sediments: Implications for provenance, weathering and sedimentary characteristics

Large rivers originating from the Tibetan Plateau play a crucial role in sediment production and transportation and thus influence the ocean composition and global climate. This study focuses on the geochemical characteristics, including major, trace and rare earth elements of overbank sediments from the Lancang River (Upper Mekong), which drains southwest China and is one of the largest international rivers in Asia. We characterize sediment maturity and recycling, weathering and provenance in a typical, tectonically active cold-humid climate region. Lancang River (LR) sediments with an average chemical index of alteration (CIA) of 73 ± 6 and an average index of compositional variability (ICV) of 1.1 ± 0.6 suggest an intermediate mineralogy and chemical maturity corresponding to moderate weathering in a slightly warmer climate. The provenance of LR sediments is characterized by felsic source rocks, similar to the upper continental crust (UCC), followed by recycled sedimentary rocks, which were possibly derived from the Yidun, North Qiangtang (NQ) and Songpan-Ganzi (SGZ) terranes at upstream locations when the Lingcang basalt (LCB) provided mafic rocks for LR sediments. However, recycled materials have limited impacts on sediment maturity, as reflected by the degree of weathering. Highly physical weathering (erosion) has created a massive source for LR sediments due to active tectonics, while the impacts of climate on weathering processes have increased. Meanwhile, the overbank sediment in large rivers could be a good sampling medium for evaluating terrestrial weathering, provenance and sediment characteristics using geochemical evidence.

Paleoenvironmental reconstruction of the Permian coal beds in the Paraná Basin (Brazil): evidence from organic geochemical and sedimentological analyses

The Rio Bonito Formation (Paraná Basin) contains the thickest coal beds in Brazil, that are related to peat-swamp developed in coastal depositional systems during the early Permian. This study aims to understand the source of the coal organic matter and to distinguish depositional sub-environments along the coal-bearing interval from the southern border of the basin. The analysis was performed on sedimentological and stratigraphic data from 10 wells combined with organic petrology and geochemistry of the three coal beds. Samples were collected in different key beds from the SG-14 well, in different and strategic depths at the base (218.0 m), at the intermediate (209.0 m), and at the top (181.0 m) of the coal-bearing interval. The vitrinite reflectance measurements of the selected samples, Tmax values, C29 ααα 20 S/(20 S + 20 R) ratio, and the absence of peak Ts (and presence of peak Tm) revealed the organic matter in the coal-bearing interval is thermally immature, suggesting low burial depth for the Rio Bonito Formation in the study region. Maceral composition showed predominance of vitrinite and inertinite in the three coal samples. Rock-Eval pyrolysis data indicate that the coal beds are composed of type III kerogen in the three samples, while the biomarkers indicate type II-III kerogen mixtures. The n-alkane distribution profiles suggest dominance of terrestrial organic matter in the samples, with a possible marine contribution at the top of the coal-bearing interval. The pristane/phytane (Pr/Ph) and C27/C29 ααα20 R ratios (regular steranes) revealed sub-anoxic condition and land plants as major organic matter source for basal and intermediate parts of the coal-bearing interval. They also indicate an increased anoxic conditions and possible marine algal contribution toward the uppermost coal level. The presence of cone-in-cone-shaped structures (SG-07 well, depth 157.5 m) and Orbiculoidea fossils (SG-14 well, depth 192.5 m) are indicative of brackish water and support river-marine source mixtures at the top of the coal-bearing interval. The evolutive sedimentation model comprises four paleoenvironments for the Rio Bonito Formation along geological time, in which the basal part of the coal interval is interpreted as overbank deposits in a fluvial depositional system. On the other hand, the intermediate part of the coal-bearing interval was formed in bay-head delta, and the upper part was deposited in the central estuary, both in a tide- and wave-influenced estuarine context.

Morphological and architectural evolution of submarine channels: An example from the world's largest submarine fan in the Bay of Bengal

The characteristics and evolution of different types of channel-complex sets (CCSs) have long attracted attention from both academia and the oil industry. 3D seismic data from the world's largest submarine fan in the Bay of Bengal allow the exploration of morphology, architecture, and evolution of a Pleistocene submarine channel system from inception to abandonment. Four types of architectural elements are recognized, including feeder and distributary channel-complex set (CCS), levees, bend cutoffs, and incised and unincised crevasse splays. Three types of CCSs are recognized: (1) erosional non-leveed CCSs with the lowest values of channel width (W), thickness (T), and cross-sectional area (Ca) (mean values of W = 153 m, T = 20 m, and Ca = 2613 m2); (2) graded CCSs with the highest values of W, T and Ca (mean values of W = 745 m, T = 89 m, and Ca = 49183 m2); (3) aggradational leveed CCSs with intermediate values of W, T and Ca (mean values of W = 476 m, T = 56 m, and Ca = 21968 m2). Graded CCSs and aggradational leveed CCSs have overbank levees, crevasse splays and bend cutoffs, whereas erosional non-leveed CCSs lack these features. Such architectural difference in overbank deposits suggests a channel evolution pattern of initial incision (erosional non-leveed CCSs) and then aggradation (graded and aggradational leveed CCSs), resulting in a pattern of incision-to-aggradation channel evolution. An increase-then-decrease in channel morphometrics (represented by W, T, and Ca) from erosional non-leveed CCSs with the lowest mean values of W, T, and Ca, to graded CCSs with the highest mean values of W, T, and Ca, and finally to aggradational leveed CCSs with the intermediate mean values of W, T, and Ca suggest that the incision-to-aggradation channel evolution is related to waxing-then-waning energy cyclicity. Submarine channel turbidity flows during the waxing energy phase became progressively more energetic and increasingly more erosional, producing erosional non-leveed CCSs. Instead, submarine channel turbidity flows during the waning energy phase were more diluted and increasingly more depositional, thereby producing aggradational leveed CCSs. The phase of peak environmental energy was most likely accompanied by most energetic turbidity currents, resulting in graded CCSs. Results and observations from the current study contribute to a better understanding of architectural complexity and evolution of submarine channels.

Catchment and in-channel sources in three large Eurasian Arctic rivers: Combining monitoring, remote sensing and modelling data to construct Ob', Yenisey and Lena rivers sediment budget

This paper presents a comparative study of fluvial sediment budgets for the largest Siberian rivers of Northern Eurasia - Ob', Yenisey and Lena which cover over 14 % of the Eurasia continent. Each component of the sediment budget was assessed using an independent approach. The Revised Universal Soil Loss Equation model (RUSLE) was used to calculate catchment erosion based on the GMTED 2010 DEM with a resolution of 250 m. Channel erosion was quantified through automatic image decoding integrated with riverbank elevation estimated from ArcticDEM and hydromorphological 1D modeling of streamflow depths, whereas sediment yield was assessed based on a combination of long-term suspended sediment load monitoring at the outlet gauging stations and bed load estimates. Large differences between total (catchment and riverbank) erosion (1622 Mt year−1 for the Ob', 898 Mt year−1 for the Yenisey, 1218 Mt year−1 for the Lena) and yearly sediment export (58.2 Mt year−1 for the Ob', 32.5 Mt year−1 for the Yenisey and 38.6 Mt year−1 for the Lena) suggest that catchment, in-channel and overbank sediment sinks and storage dominate the sediment budget. The throughflow from the sources to the sea is less than 4 % of the suspended sediment inflow (total erosion). This data enhances the knowledge of the sediment delivery rates in large river systems. Over ∼96 % decline of sediment transport compared to catchment total erosion is explained by storage in various buffer zones of the catchment and river network including mainly hillslopes, as well as reservoirs and floodplains.

UNLOCKING THE ARCHITECTURE OF THE COLONIZATION WINDOW: ICHNOFABRICS FROM UPPER CRETACEOUS TIDE-INFLUENCED MEANDER-LOOP DEPOSITS

ABSTRACT Studies dealing with the colonization window typically emphasize two major features: duration (short term vs. long term) and frequency of colonization (episodic vs. continuous). However, our understanding of tide-influenced meander loops requires consideration of an additional feature, the architecture of the colonization window, which comprises not only the spatial dimension and geometry of the colonization surface, but also its evolution through time. Tide-influenced meander-loop systems show a heterogeneous trace-fossil distribution that reflects the variety of processes operating along the point-bar and overbank colonization surfaces. Ichnofabric analysis of tide-influenced meander-loop deposits from the Upper Cretaceous Tremp Formation (Pyrenees, Spain) provides valuable insights into the sedimentary and ichnological dynamics of these marginal-marine systems and allows the importance of stratal geometry controlling the colonization window to be evaluated. Six ichnofabrics are identified in point bars and associated overbank deposits. These ichnofabrics differ in bioturbation index (e.g., higher in the upper part than the lower-middle parts of point bars), preservation of primary sedimentary fabric (typically preserved in the lower-middle parts of point bars), inferred behavior and trophic types (e.g., dominance of dwelling or feeding structures in the lower-middle and upper parts of point bars, respectively), and other features such as depth of penetration, ichnotaxonomic composition, presence or absence of root trace fossils and/or mottling, or number of superimposed suites. The key environmental factor controlling the nature and distribution of ichnofabrics is the morphology of the point-bar lateral-accretion surfaces and their evolution through time. The architecture of the colonization window is here linked to the helicoidal flow and discharge changes in meandering channels, and the successive development of lateral accretion units with time.

Chemical Weathering Rates of Soils Developed on Eocene Marls and Sandstones in a Mediterranean Catchment (Istria, Croatia)

Physical and chemical weathering, together with biological and biochemical processes, form soil from bedrock and strongly influence the chemical composition of natural waters. Erosive processes, primarily through the agents of running water and wind, remove the products of weathering from catchments. The aim was to determine the chemical weathering of minerals because of changes in land-use and natural forestation in two small neighboring catchments of the rivers Argilla and Bazuja. Agricultural land-use practice is very intense in the Argilla catchment, while the Bazuja catchment’s arable land is mostly abandoned, with progressive forestation. Chemical weathering in soils and sediments was evaluated with the aid of bulk chemistry analysis focused on major elements, trace elements, and zirconium. Weathering indices, mass balance, and strain were calculated. The abandonment of arable land and intense forestation in the Bazuja catchment caused increased chemical weathering with the loss of base cations (Ca and Mg) and enrichment of conservative elements (Zr and Ti) in surface horizons. EIC and MTF values are positive (enrichment) in areas with agricultural activities, while forested areas show negative values (loss). A comparison of the oldest and youngest parts of the overbank sediment profiles in the swallow hole zone and stream sediments shows that chemical and mechanical weathering in the Bazuja catchment was similar to present weathering in the Argilla catchment, while agriculture was active in the Bazuja catchment. The integrated knowledge gained in small catchment studies can be broadly applicable to larger systems.

Evolution of the Holocene alluvial fan of the River Stryi in the foreland of the Eastern Carpathians (Western Ukraine)

The research reconstructs the development of the alluvial fan of the River Stryi in the Holocene and dates the phases of increased river activity and their correlation with other valleys in the upper Dniester and Vistula river basins. The age of the palaeochannels and the stratigraphy of alluvial fills are based on radiocarbon dating supported by the results of palynological analyses. The oldest (fossil) palaeochannel of the Stryi was dated to the Younger Dryas. The large-radius meander was abandoned at the end of the Boreal Phase during the period of flood intensification at about 8700 BP. The uneven top of the gravels (cut by palaeotroughs of a depth ranging from 2 to 4 m) indicates that during periods of increased discharges (Younger Dryas, end of the Boreal Phase, late Atlantic and beginning of the Subboreal) the troughs were cut and filled with channel sands. From the beginning of the Subboreal Phase (5400-5300 BP), aggradation of the valley bottom has been predominant, which is manifested not only by the overbuilding of the floodplain but also by the gradual elevation of the channel. The accumulation of sandy-silty overbank sediments dated to about 8300, 5400 and 2800 BP correlates well with the beginning of humid phases and floods in the upper Vistula and upper Dniester basins as well as floods recorded in lakes in the northern foreland of the Alps.

Using a post-glacial terrace sequence to better understand landscape evolution and paleohydrology in the eastern San Juan Mountains, USA

Terraces provide a unique record of environmental change as they form due to changes in sediment supply and hydrology. In the upper Rio Grande drainage, terraces are post-glacial in age and have not been impacted by tectonics during that period. As such, these terraces are the result of changes to the fluvial system since glaciers retreated. We mapped four terrace units across two sections of the upper Rio Grande. We then examined soil profiles on terrace units, described the sedimentology, and dated the terraces where possible. Our findings indicate that the upper terrace (FT1) formed as an outwash terrace during glaciation and that incision began immediately after glaciers had melted around 12.1 ka. Two intermediate terraces likely formed during brief pauses in post-glacial incision as aggradation of the lowest terrace (FT4, 7–14 m below FT1) had already begun by 9.6 ka. Cumulic soils and fine-grained sediment on FT4, combined with radiocarbon ages, indicate that FT4 aggraded consistently in both rivers throughout the Holocene. Specifically, overbank deposits emplaced during decadal-scale flooding have allowed FT4 to aggrade consistently since 9.6 ka. The main channel appears to have been stable throughout the entire Holocene given that it is pinched between fine-grained deposits. Previous work indicates that other authors have noted similar landforms although they seem to be underreported in the literature. The timing of terrace formation differs from that in nearby headwater streams, indicating that headwater systems are more responsive to hillslope processes while larger trunk streams appear to receive sediment from upstream. Apparent differences in flooding between the two basins may indicate that basins with water managed by reservoirs may flood the FT4 surface less often, thereby highlighting the impact of water management on both fluvial hydrology and sediment storage.

Using the colour of recent overbank sediment deposits in two large catchments to determine sediment sources for targeting mitigation of catchment-specific management issues

The effective management of sediment losses in large river systems is essential for maintaining the water resources and ecosystem services they provide. However, budgetary, and logistical constraints often mean that the understanding of catchment sediment dynamics necessary to deliver targeted management is unavailable. This study trials the collection of accessible recently deposited overbank sediment and the measurement of its colour using an office document scanner to identify the evolution of sediment sources rapidly and inexpensively in two large river catchments in the UK. The River Wye catchment has experienced significant clean-up costs associated with post-flood fine sediment deposits in both rural and urban areas. In the River South Tyne, fine sand is fouling potable water extraction and fine silts degrade salmonid spawning habitats. In both catchments, samples of recently deposited overbank sediment were collected, fractionated to either <25 μm or 63-250 μm, and treated with hydrogen peroxide to remove organic matter before colour measurement. In the River Wye catchment, an increased contribution from sources over the geological units present in a downstream direction was identified and was attributed to an increasing proportion of arable land. Numerous tributaries draining different geologies allowed for overbank sediment to characterise material on this basis. In the River South Tyne catchment, a downstream change in sediment source was initially found. The River East Allen was identified as a representative and practical tributary sub-catchment for further investigation. The collection of samples of channel bank material and topsoils therein allowed channel banks to be identified as the dominant sediment source with an increasing but small contribution from topsoils in a downstream direction. In both study catchments, the colour of overbank sediments could quickly and inexpensively inform the improved targeting of catchment management measures.

ASSESSMENT OF RIVER SEDIMENT QUALITY ACCORDING TO THE EU WATER FRAMEWORK DIRECTIVE IN LARGE RIVER FLUVIAL CONDITIONS. A CASE STUDY IN THE LOWER DANUBE RIVER BASIN

Increase of pollution of surface water and water sediments with hazardous substances (HSs) in the Danube River Basin requires implementation of systematic monitoring and evaluation of the sediment quality. The present study is focused on the ’South Danube’ Test Area (SDTA) that covers parts of the Lower Danube Basin in Romania, Serbia and Bulgaria. The SD area represents an extended region where Danube reaches its largest widths and depths and where pollution (industrial, mining, agricultural, waste etc.) from tributaries and land is supposed to accumulate in the sediments. Sampling of river bottom sediment (BS), suspended sediment (SS) and overbank (floodplain) sediment at two layers (0-5 cm in the top layer (FS TS) and 40-50 cm in the bottom layer (FS BS)), was carried out at 11 locations in order to analyze the concentration and distribution of 8 metal(oid)s (Cu, Pb, Zn, Cd, Hg, Ni, Cr, As), 6 polycyclic aromatic hydrocarbons (PAHs) and 6 pesticides as hazardous substances. The 2013/39/EU Directive and EU Water Framework Directive standards were used to sediment quality assessment. As a whole, the concentrations of heavy metals in the sediments are comparatively low and are around the normal values for soils. On the other hand, some sampling sites and sediment types have high or very high metal concentrations which exceed intervention levels. Our study well recognizes mining pollution sources in the Danube tributaries Borska Reka, Timok, Ogosta, Malak Iskar and Iskar from past and/or recent mining activity. This pollution is limited to the Danube tributaries and around their confluences into the Danube River. The concentration of heavy metals is strongly diluted in the Danube River and drops around normal values. The studied sediments reveal low concentrations of PAHs. Only fluoranthene content is higher in most of the sediment types and sampling sites on the Danube River, but exceeds the interventional level only at Pristol and at Hârșova. Our results show that the sediments in the Danube River are more polluted with PAHs than its tributaries. The identified organic compounds are assumed to be generated during incomplete or low temperature combustion processes or during road transportation and/or the navigation on the Danube River.

Architectural Model of a Dryland Gravel Braided River, based on 3D UAV Oblique Photogrammetric Data: A Case Study of West Dalongkou River in Eastern Xinjiang, China

AbstractThree‐dimensional unmanned aerial vehicle (UAV) oblique photogrammetric data were used to infer mountainous gravel braided river lithofacies, lithofacies associations and architectural elements. Hierarchical architecture and lithofacies associations with detailed lithofacies characterizations were comprehensively described to document the architectural model, architectural element scale and gravel particle scale. (1) Nine lithofacies (i.e., Gmm, Gcm, Gcc, Gci, Gcl, Ss, Sm, Fsm and Fl) were identified and classified as gravel, sand and fine matrix deposits. These are typical depositional features of a mountainous dryland gravel‐braided river. (2) Three architectural elements were identified, including channel (CH), gravel bar (GB) and overbank (OB). CH can be further divided into flow channel and abandoned channel, while GB consists of Central Gravel bar (CGB) and Margin Gravel bar (MGB). (3) The gravel bar is the key architectural element of the gravel braided river, with its geological attributes. The dimensions of GBs and their particles are various, but exhibit good relationships with each other. The grain size of GB decreases downstream, but the dimensions of GB do not. The bank erosion affects the GB dimensions, whereas channel incision and water flow velocity influence the grain size of GB. The conclusions can be applied to the dryland gravel braided river studies in tectonically active areas.

Tectonic setting, provenance, depositional, and paleo-climatic conditions of the late quaternary subcrop sediments of the southeastern coastal region of the Bengal basin

This is a systematic attempt to depict the genetic evolution of the Late Quaternary sediments of the southeastern (SE) coastal region of the Bengal basin regarding paleotectonic settings, sedimentation, provenance, paleo-climatic conditions, weathering condition and age. The study has considered multiple attributes such as, lithology/lithofacies, sedimentary features/records, major oxides, clay minerals, foraminifera, and radiocarbon dating. The lithological characters along with associated clay minerals confirmed that a Pleistocene paleosol horizon (over-bank deposits) of warm-humid nature is commonly encountered immediately on top of the sub-crop bed-rock in the area overlain by Holocene fluvio-marine sediments of the same nature. The lithofacies, foraminiferal assemblages, and sedimentary structures of the analyzed samples suggest that the Holocene sediments have been presumably deposited in a fluvio-marine condition after the Last Glacial Maximum (LGM) due to the transgression of the sea. Geochemically, the sediments are classified as Fe-rich shale, shale, and wake and primarily intermediate to felsic orogen provenance. These are possibly derived from intense weathered sources from the upheaval of Himalayan ranges of both active continental margin and Island Arc paleotectonic setting. The plot of the Index of Compositional Variability versus the Chemical Index of Alteration indicates that the sediments seemingly experienced intense weathering associated with warm and humid climatic conditions. The sedimentation rates of the area vary from place to place and layer to layer due to the complex delta-building process. The reconstructed Relative Sea Level Curve reveals that presumably, the sea level has reached its current position after the LGM. The deduction possibly will facilitate the (1) reconstruction of Late Quaternary coastal evolution after LGM, (2) support for future urbanization, land use plans, etc., and (3) also be helpful for international researchers to understand the possible sources of sediment input in the area from the complex interplay of the Indian-, Eurasian- and Myanmar-plates.

Some Potentially Toxic Elements (Pb, Zn, As, Cd, Cu, Ni, and Cr) in Overbank Sediments of Smaller Water Courses from the Drina River Basin (Republic of Serbia)

Some Potentially Toxic Elements (Pb, Zn, As, Cd, Cu, Ni, and Cr) in Overbank Sediments of Smaller Water Courses from the Drina River Basin (Republic of Serbia)

Půdní vývoj v nivě řeky Dyje v předpolí hradby hradiska Pohansko u Břeclavi

This work provides comprehensive information on soil development on the floodplain of the river Thaya in the area of the foreland of the Early Mediaeval agglomeration of Pohansko near Břeclav. We evaluated the basic properties of late Holocene soils and their genesis, assessed the influence of humans and identified particular soil-forming processes based on a combination of selected physical (grain-size distribution, magnetic susceptibility), chemical (Fe, Mn, P, Ca, soil pH) and biochemical analyses (total organic carbon and soil organic matter) as well as micromorphological observations. Our research revealed three autochthonous soils: two buried soils and one recent soil. All the soils were identified as Gleyic Fluvisols developed from overbank deposits and affected by intensive oxidation-reduction processes. The A horizons of the soils evolved by the formation and accumulation of humus. The upper buried Fluvisol certainly evolved during the 9th and 10th centuries (presence of Great Moravian sherds). However, its pedogenesis possibly started much earlier and ended later. Despite the presence of macroscopic evidence of human activities in this soil, there is no evidence of any anthropic influence on soil formation processes. The basal buried Fluvisol developed even before the Great Moravian settlement. Nevertheless, due to a lack of dating, the exact age of this soil cannot be determined at this stage of our study. Future research focused on dating will advance our understanding of the Holocene dynamic and development of the palaeoenvironment.