Rivers are important pathways for metal(loid) contamination in mining areas. The Kafue River flows through the Zambian Copperbelt with nearly a hundred-year history of Cu and Co mining. Nine cores down to 2.5 m deep were drilled in fluvial sediments along a 750-km long river section and analysed for grain size, elemental composition, and mineralogy using extraction tests and scanning electron microscopy with an aim to investigate the spatial and temporal contamination patterns. The silty and fine- to coarse grained sandy sediments were deposited in natural levees, semi-abandoned meanders, and channel bars. They are heavily polluted by Cu reaching ore grade (up to 1.9 %) and Co, with UCC-based enrichment factors (EF) as high as 704 and 60, respectively, which is more than an order of magnitude higher than the most severely impacted large European rivers, and slightly polluted by Pb, As, U and other elements. The main carriers of Cu are malachite, pseudomalachite, secondary Fe oxyhydroxides (ferrihydrite, goethite), sulphides, and Cu-bearing grains of kaolinite, chlorite, and mica. This Cu contamination is traceable (EF up to 13) in sediments 750 km downstream of the Kafue River inflow to the Copperbelt. The contaminated sediments are similar to 100 cm to similar to 220 cm thick and their average sediment accumulation rates similar to 12 to similar to 27 mm/yr indicating that the contaminated suspended particulate matter can be rapidly deposited along the river, representing a potential environmental hazard. Arsenic and Pb can be scavenged to Fe oxyhydroxides and accumulate in capillary fringe above groundwater level during early diagenesis.

Early diagenetic precipitation of red iron oxide (hematite) in most marine red beds (MRB) makes these sediments suitable archives for seafloor redox conditions. A composite succession of upper Frasnian to lower Famennian red pelagic limestones was studied at two sections in the Montagne Noire, South of France including the Coumiac base of the Famennian GSSP section containing the Upper and Lower Kellwasser (LKW and UKW) horizons of global dysoxia/anoxia. Data from facies analysis, gamma-ray spectrometry, magnetic susceptibility, Vis-diffuse reflectance and X-ray fluorescence spectroscopy with 5 to 25 cm resolution at the section were supplemented by optical and scanning electron microscopy, electron microprobe analysis and laser-ablation inductively coupled mass spectrometry of thin sections. Submicron hematite crystals in the red facies are closely associated with authigenic clays, pitted microspar, microstromatolites, microborings, and Frutexites microproblematica indicating a microbial control on its precipitation at or very close to the sediment–water interface. The hematite precipitation was driven by iron cycling accompanied by cycling of redox-sensitive elements (Mn, Cu, V, Mo, U) along (micro-)redox gradients within the sediments under oxic seafloor conditions, supported by low sedimentation rates. The red stratigraphic succession is punctuated by eight, 0.5 to 1.5 m thick horizons including the LKW and UKW, with non-red colours and elevated concentrations of redox-sensitive elements reflecting various stages of bottom dysoxia to anoxia. The horizons show a recurrence time of 0.85 Myr to 2.0 Myr and they are interpreted as repeated phases of seafloor dysoxia/anoxia due to vertical fluctuations of the oxygen minimum zone culminating during the Frasnian/Famennian crisis.

This study integrates sedimentological, petrographic, geochemical, and fluid-inclusion data to assess the factors influencing reservoir quality in the Lower Devonian Tadrart Sandstone of the central Ghadamis Basin. The study reveals that reservoir quality is strongly governed by depositional facies, which exert primary control on subsequent diagenetic processes. Eogenetic alterations include mechanical compaction, the development of mixed-layer illite-smectite and kaolinite, and early precipitation of Mg-poor siderite, which is attributed to meteoric water influx during relative sea-level fall. Mesogenetic alterations are characterized by chemical compaction, pervasive quartz overgrowth cementation, dickite formation, illitization, chloritization, crystallization of euhedral pyrite and a later generation of Mg-rich siderite. The data indicate that coarse-grained tidal channel sandstones (FA4) exhibit the best reservoir quality, with an average porosity of 12 % and permeability up to 480 mD (av. 127 mD). In contrast, fine-grained intertidal sandstones (FA2-FA3) show similar porosity (12 %) but very low permeability (<1 mD), whereas the mixed mud-sand intertidal facies (FA1) have the poorest properties (porosity 6 %; permeability <0.1 mD) and are more strongly affected by diagenesis. Fluid-inclusion microthermometry reveals homogenization temperatures up to 205 degrees C and high-salinity brines, indicating a deep burial (>4 km) followed by uplift and dilution by meteoric waters. These results demonstrate how integrating depositional facies analysis with reconstructed diagenetic pathways clarifies the evolution of reservoir heterogeneity and provides a predictive framework for assessing sandstone reservoirs in intracratonic basins.

The palaeoclimatic significance of continental red beds (CRB) is the subject of a long-standing debate. The CRBs are strikingly often found in association with arid, aeolian sediments, humid fluvial sediments and palaeosols, reflecting variable climatic regimes. In this study, diffuse reflectance spectroscopy (DRS) is used in combination with facies analysis, petrology, bulk-rock and in-situ major and trace element geochemistry, and molybdenum stable isotopes to better understand the origin and distribution of the hematite pigment in a spectrum of PermoTriassic aeolian, fluvial and pedogenic facies of the Colorado Plateau, Utah. Their red colour is characterized by high (> 30) percentage of red-band (625-700 nm) reflectance in the DRS spectra and high hematite-to-goethite peak height ratios (1.5 to 5.7) from their first derivatives. Most hematite occurs in form of submicronic to micron-sized, platy crystals in altered biotite grains, clayey grain coatings, clayey matrix, pyrite framboid pseudomorphs, and as pore-filling cement. Hematite is most abundant in palaeosols, but also present in aeolian, sand dune and damp interdune deposits, fluvial channel-fill, sandy and gravelly bars, and floodplain deposits. Iron for the hematitization was supplied from reductive release of Fe2+ from biotite and clay minerals. The hematitization itself occurred under oxic conditions, associated with formation of kaolinite, mobilization of V, Mo, As, U, and fractionation of rare earth elements and Mo isotopes, especially in lateritic palaeosols. Hematitization during weathering, pedogenesis, transportation and early diagenesis, and reworking and redeposition of the red material by rivers and wind is thought to be the principal mechanism of the formation of red beds in the Colorado Plateau. The processes of hematitization and the fluvial-aeolian dynamics were controlled by alternation of wetter and drier periods likely caused by the Permo-Triassic Pangean mega-monsoonal climatic regime.

Continental red beds (CRB) are characteristic for their predominant red colour due to the widespread presence of ferric oxides (hematite or goethite) that might suggest distinctly oxygenated atmospheric conditions during their formation. Therefore, elemental and isotopic systematics of iron, a redox-sensitive element, can provide critical constraints on Fe cycling and possibly also palaeoredox conditions. However, our knowledge of the iron isotopic systematics (delta Fe-56) of CRB remains very limited. This prevents to evaluate whether these rocks are useful to trace past atmospheric oxygenation. To fill the gap, we present an extensive dataset of Fe elemental and isotopic data, paralleled by M & ouml;ssbauer and diffuse reflectance spectra, for classic Phanerozoic examples of CRB supplemented by the analyses of colour detrital grain coatings. The data reveal goethite as the principal phase within grey-green siliciclastic lithologies and detrital grain coatings. These samples show a positive correlation between Fe3+/Fe-T and delta Fe-56 (fine-grained lithologies) suggesting percolation of late-stage diagenetic fluids at variable redox and pH conditions connected with hematite dissolution. In contrast, the red facies are characterized by the predominance of hematite, largely variable Fe-T contents and delta Fe-56 values overlapping with those estimated for the upper continental crust. The overall lighter and more homogeneous delta Fe-56 values in Phanerozoic red beds compared to their Palaeoproterozoic (similar to 2.2 Ga) counterparts are consistent with more oxygenated atmosphere during the Phanerozoic. Therefore, the appearance of CRB may serve as an important marker of atmospheric oxygenation in the past.

Stylolites are ubiquitous diagenetic products in carbonate rocks. They play a significant role in enhancing or reducing fluid flow in subsurface reservoirs. This study unravels the relationship between stylolite networks, carbonate microfacies, and the elemental geochemistry of Upper Cretaceous limestones of the Kometan Formation (shallow to moderately deep marine) in Northern Iraq. Stylolites exhibit diverse morphologies across mud- and grain-supported limestone facies. Statistical analyses of stylolite spacing, wavelength, amplitude, and their intersections and connectivity indicate that grain size, sorting, and mineral composition are key parameters that determine the geometrical properties of the stylolites and stylolite networks. Stylolites typically exhibit weak connectivity and considerable vertical spacing when hosted in packstone facies with moderate grain sorting. Conversely, mud-supported limestones, marked by poor sorting and high textural heterogeneity, host well-developed stylolite networks characterized by high amplitude and frequent intersections, indicating significant dissolution and deformation processes. Stylolites in mud-supported facies are closely spaced and present heightened amplitudes and intensified junctions, with suture and sharp-peak type. This study unveils that stylolites can potentially enhance porosity in the studied formation.

The thermal history of the Boskovice Basin in the SE Bohemian Massif remains a subject of debate, particularly regarding the extent and timing of thermal resetting in its sedimentary succession. Previous studies have suggested either prolonged burial-related heating or localised tectonothermal events as the dominant mechanism. To address this controversy, we apply apatite fission track (AFT) and zircon (U–Th)/He (ZHe) thermochronology to seven samples from the uppermost Carboniferous–lower Permian coal-bearing siliciclastic succession. The ZHe thermochronometry yielded Permian ages (297.7 ± 8.6 to 262.4 ± 7.9 My), whilst the AFT ages range from 187.3 My ± 14.2 to 120.8 ± 10.2. The AFT ages of all samples are much younger than their stratigraphic ages, indicating that they have been thermally reset. In contrast, the ZHe ages of some samples are only 10–30 My younger than the depositional age, whilst for the remaining samples, they coincide with the stratigraphic age. This means that only in some samples, the zircon grains have been reset, in which case they record a thermal event in the Middle–Late Permian. The unimodal distribution, relatively short mean lengths (13.25–12.30 µm) and low standard deviation values (1.4–1.1 μm) of the track lengths indicate that the Permian heating event was followed by prolonged residence in the AFT partial annealing zone during the Mesozoic and final Late Cretaceous–Cenozoic cooling phase, as shown by numerical thermal models. Thermal modelling using ZHe and AFT data has shown that the coalification of organic matter contained in the uppermost Carboniferous to lower Permian rocks occurred already in the Permian, when the Boskovice Basin sedimentary rocks experienced maximum paleotemperatures. Consequently, our results indicate the importance of Middle–Late Permian tectonics leading to inversion of the Boskovice Basin (273.7–262.4 My; Guadalupian) only 10–30 My after the end of sedimentation. Temperature evolution for BAC-1 sample from the Boskovice Basin.

This article focuses on the necessity to enhance the current understanding of the accumulation and fate of pesticides and pharmaceuticals (emerging pollutants) in abandoned meanders and adjacent river channel bars. The primary objective of this study is to conduct a comparative analysis of pollutant concentrations in both settings and to identify the driving factors of their deposition. The studied sites are situated within two distinct catchments of the Morava and Odra rivers in the eastern part of the Czech Republic. The most prevalent pesticides were identified as propiconazole, metazachlor and tebuconazole. For caffeine and pharmaceuticals, the peak concentrations exceeded 10 µg/kg. The other pharmaceuticals frequently detected in these sediments were carbamazepine, diclofenac and metoprolol. The polycyclic aromatic hydrocarbons and polychlorinated biphenyls, selected for comparison (hereafter referred to as ‘legacy pollutants’), reached high to extremely high levels due to their frequent use in the past or present. Pollutant assemblages differed between channel bars and abandoned meanders. The maximum concentrations of emerging pollutants have been observed to be generally higher in abandoned meanders; however, the relative occurrence of pollutants has been found to be higher in channel bars. Abandoned meanders are most vulnerable to contamination in the first years following the cut-off, due to the increased frequency of flooding during this period. Consequently, they pose a higher environmental risk. Older meanders contain residual concentrations of pollutants and can serve as long-term sinks for organic pollutants, thereby providing temporal patterns. Conversely, channel bars represent current contamination levels and thus indicate spatial trends.

This study investigates the mechanisms controlling the coloration of red beds of the Gercus Formation, which was deposited in a deltaic environment during the Eocene, and focusses on the dynamic interplay between depositional setting and diagenetic processes in shaping the distinct hues. A comprehensive multi-proxy methodology was employed, including facies analysis, quantitative color assessment using diffuse visible spectral reflectance (DRS), optical and electron microprobe microscopy, bulk-rock geochemistry (XRF and XRD), and in-situ geochemical analysis via laser-ablation ICP-MS. The results reveal that the spectrum of sediment hues, from red, to yellow-brown, gray-green, and gray, arise from the formation and distribution of Fe oxy/hydroxides, which are largely determined by sedimentary lithology, redox conditions, and diagenetic transformations. Sedimentation rates play a crucial role in regulating redox conditions and determining sediment coloration. Rapid sedimentation restricts oxygen exposure, fostering suboxic conditions that inhibit Fe oxidation, leading to gray-green sediments. Conversely, slower sedimentation allows for prolonged oxygen exposure, facilitating formation of Fe oxy/hydroxide and hematite, and resulting in red and yellow-brown sediments. Chlorite clay minerals are pivotal in transporting and supplying the Fe necessary for Fe oxy/hydroxide formation. Their transformation to chlorite-smectite mobilizes Fe either predepositionally or during eodiagenesis. In oxic environments, enhanced smectitization releases more Fe, preserving Fe oxy/hydroxides and promoting development of red sediment. In contrast, anoxic conditions suppress smectitization, dissolve predepositional Fe oxy/hydroxides, and produce non-red layers. Additionally, sediments with low clay content are unable to develop red coloration, even under oxic conditions, due to insufficient clay-mediated hematite formation, thereby retaining their original hues.

The processes responsible for reddening of Continental Red Beds (CRBs) and the relationship between color variation and paleoenvironmental conditions are presented focusing on a comprehensive multi-proxy study of Permian sediments in the Bohemian Massif, Czechia. The investigation incorporates facies analysis, quantitative color assessment using diffuse Vis-spectral reflectance (DRS), optical and electron microprobe microscopy, bulk- rock (XRF and XRD), and in-situ geochemistry (laser-ablation ICP-MS). Results indicate a progressive drying trend from the Cisuralian to Guadalupian series in studied continental red sediments. Different facies indicate the change of the sedimentary environment from a deep lacustrine environment (lower part of Rudn & iacute;k Member, Cisuralian) to a fluvial floodplain and eolian environment (Trutnov Formation, Guadalupian). Examination of the three major categories (white, gray-green and red sediments) identified in the studied continental red beds indicates that diagenetic alteration of clay minerals and biotite was the main source of iron fueling the growth of hematite responsible for their red color. Early diagenetic processes and paleoenvironmental conditions, particularly the oxidizing or reducing conditions play a key role in the red sediment formation. It is suggested that later diagenetic stages are incapable of coloring non-red, iron-rich sediments formed in deep anoxic lacustrine environments. Microbial activities and reducing fluids have been identified as the main factors in the formation of gray-green sediments forming distinct reduction zones. The reduction spots formed during the early stages of diagenesis (eodiagenesis), and they were likely never red. In contrast, reduction strips, initially exhibiting a red hue, underwent a color change during more advanced stages of diagenesis (mesodiagenesis). (c) 2024 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Surface analogues are suitable tools to link reservoir models to real facies but they require a robust outcrop -tosubsurface stratigraphic correlation. In this study, we correlate gamma -ray (GR), and porosity logs from nine wells drilled in the Cretaceous Kometan Formation, a prolific carbonate reservoir of northern Iraq, with geochemical logs from three sections representing surface analogues. The sections were sampled for microfacies, X-ray diffraction mineralogy, and element geochemistry using X-ray fluorescence spectrometry calibrated by ICP-MS data. Six microfacies composed of mudstones to packstones with planktonic, and benthic foraminifers were identified in outcrop, and interpreted as middle ramp, outer ramp, and basin deposits. The microfacies show increasing Al and K, and decreasing Ca concentration trends from the middle ramp to the basin settings. Their subsurface analogues are carbonates, marls and shales with benthic foraminifers, deposited in proximal, inner to middle ramp parts of the Kometan mixed carbonate-siliciclastic ramp system. The K + Al logs are correlated for 33 km, and the subsurface GR logs for over 100 km distance, but both reflect detrital admixture in biogenic carbonate. However, the outcrop- and subsurface log patterns show opposite vertical trends. The subsurface, inner ramp GR maxima in the middle Kometan, correlate with the outcrop K + Al minima jointly reflecting landwards and seawards shifts of the middle ramp carbonate factory during transgressions and regressions, respectively. The maxima and minima are interpreted as maximum regression (mrs) and maximum flooding surfaces (mfs) in the T-R sequence-stratigraphic model. Neutron -density and sonic logs indicate that the best reservoir quality is achieved in fractured pure carbonates, which are controlled by these T-R cycles. The results highlight the importance of elemental geochemistry in stratigraphic correlation of lithologically uniform sequences, and suggest that outcrop geochemistry can be correlated with well logs. (c) 2023 Elsevier B.V. All rights reserved.

Continental red beds are coloured by secondary Fe(III)-oxy-hydroxides (mainly hematite) which makes them excellent archives of ancient near-surface redox conditions. However, colour is often treated as a subjective physical property, and opinions differ widely as to the environment and timing of colouration of the red beds. This study utilizes diffuse spectral reflectance to address the degree of reddening (hematitization) of the Siluro-Devonian Old Red Sandstone representing a dryland fluvial system with abundant palaeo-Vertisols, coinciding with the period of land colonization by vascular plants. The hematitization was studied along with the stratigraphy, facies, pedogenic features, petrology, element and Molybdenum isotope geochemistry. The mudstones and palaeosols are typically red while sandstones are often grey. The red colouration corresponds to approximately 30 to 36% of red band (625 to 700 nm) reflectance and high hematite to goethite ratios. The red sediments contain hematitized biotite, submicronic hematite in mudstone and sandstone matrix, and hematite cement in calcretes. The hematitization was synchronous with formation of pedogenic mudcracks, Vertic slickensides, calcretes, reduction spots, sometimes hydrodynamic reworking, and accompanied by local (grain-scale) depletion in Fe(II), enrichment in Fe(III), and mobilization of U, V, As, Cu, Zn and Mo. It is estimated that the hematite growth was rapid (several hundred to thousand years) but the average sedimentation rates were low (approximately 3 to 10 cm/kyr). Erosion led to development of reactivation surfaces separating layers with contrasting hematite content and geochemistry. It is suggested that high rates of pedogenesis and low sedimentation rates favour the reddening and may represent an important control on the formation of continental red beds. Limited levels of soil waterlogging, and the published delta 13C values (-9 to -12 parts per thousand Vienna Pee Dee Belemnite) of the pedogenic carbonate, might reflect the changes in the nature of the soil biomantle during the early Devonian land colonization by vascular plants.

Understanding the spatial variation in lithology is crucial for characterizing reservoirs, as it governs the distribution of petrophysical characteristics. This study focuses on predicting the lithology of carbonate rocks (limestone, argillaceous limestone, marly limestone, and marl) within the Kometan Formation, Khabbaz Oil Field, Northern Iraq, using well logs. Precise lithology prediction was achieved by applying multivariate regression method on neutron, sonic, and density logs. Gamma-ray and elemental concentrations from bulk-rock X-ray fluorescence spectroscopy were employed to identify clay minerals, paleoenvironments, and quantify the shale content. The results indicate that the Kometan Formation predominantly comprises limestone, marl, marly limestone, and argillaceous limestone in the middle section. The middle part exhibits a higher shale content compared to the lower and upper parts. A statistically significant correlation (R2 = 0.83–0.85) between described and predicted lithology was established. The model with a higher coefficient of determination (0.85) was tested for further predictions in other wells in the Kirkuk Oil Field. This research can be valuable for lithological and petrophysical characterization of carbonate reservoirs and electrofacies analysis, particularly in situations where core data is unavailable.

The continental red beds, encompassing a broad spectrum of genetic types, can serve as important palaeoclimatological and palaeoenvironmental archives. The origin of sediment colouration is a complex process involving abiotic processes (e.g., breakdown of original and precipitation of newly-formed minerals), which, together with biogenic factors, lead to mobilisation of redox-sensitive elements and precipitation of Feand Mn(oxy)hydroxides. There is still discussion about the interpretation of the continental red beds as palaeoclimatological archives or the colour patterns reflecting ancient redox gradients. The layers coloured in red, yellow or black can be found in the Quaternary glaciofluvial sediments in the Czech Republic. We are using a combination of field study with multi-spectral petrophysical, petrological and geochemical analyses to investigate the mechanism and timing of the origin of coloured coatings in glaciofluvial sediments, and causes of cycling of Fe, Mn, and other redox sensitive elements and isotopes. The results show that both syndepositional and early diagenetic processes are responsible for the origin of colour patterns in the Quaternary glaciofluvial sediments. The stable molybdenum and iron isotope fractionation is primarily driven by the breakdown of the primary Fe and Mn-bearing silicates and the precipitation of the secondary Feand Mn-(oxy)hydroxides, such as goethite and birnessite. These precipitates are the main components of colouring coatings on the detrital grains and are able to bind other redox-sensitive elements, such as Cu, As, Mo, U, and REEs. The textural patterns and geochemistry suggest that the colour features were developed in the time range of decades to several thousand years after the deposition along ancient subsurface redox gradients due to changes in groundwater flow associated with primary lithology, glaciotectonics, and seasonal changes in the active layer of permafrost. The coatings show morphological features (rods, botryoids) and geochemical signatures (e.g., increased P contents) suggesting involvement of microorganisms to their precipitation. (c) 2024 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

This article focuses on the need to improve current knowledge of sedimentation and erosion processes in small reservoirs using the example of the Pochen reservoir (Czech Republic). We combined data from sediment cores with unmanned aerial vehicle imaging and ground-penetrating radar survey data. The results show a distinct sediment distribution, grain-size gradient, petrophysical properties, and geochemistry. Sediment thickness increases in the proximal-to-distal direction (from the inflow to the dam) with frequent erosion near the inflow, especially during floods. This contributed to the sediment relocation towards distal sites with a tendency towards downstream accretion. After reservoir flushing, sedimentation processes were replaced by drawdown-enhanced erosion. Considerable erosion occurred along a temporary drawdown channel, resulting in headward erosion and channel incision. Lateral erosion resulted in drawdown-channel widening. The most extensive lateral erosion took place in the middle part of the reservoir, where the channel created a complex multichannel-branched system.

ABSTRACTModern fluvial deposits can be affected by early diagenetic element mobilization at redox boundaries between oxygenated and oxygen‐free zones near the groundwater level. The visible product of redox transformation of Fe is the sediment colour. Distinct red and black sediment layers have been studied in eight shallow (<4.2 m depth) sections in the floodplain of Morava River, Czechia. The aim was to investigate the composition, origin, rates of formation and stratigraphic significance of the red strata using bulk‐rock analytical methods, radiocarbon dating, optical and scanning electron microscopy coupled with in situ (energy‐dispersive X‐ray scanning electron microscopy and laser ablation inductively coupled plasma mass spectrometry) geochemistry. The coloured layers, in places well‐cemented, developed in permeable sands and gravels above the water table, close to the boundary with overlying less permeable floodplain sandy silts. Their colour is due to Fe and Mn oxyhydroxides (goethite, haematite, todorokite and birnessite) coatings of framework grains. Black, Mn‐rich layers occur stratigraphically higher than the red, Fe‐rich ones. The coatings are a few‐hundred microns thick at maximum, often botryoidal, composed of alternating Fe‐rich and Mn‐rich laminae enriched in As, Mo, Sb, P, Cu and U. The coatings formed under suboxic conditions due to Fe and Mn oxyhydroxide cycling, driven partly by microbial activity, at the groundwater‐related redox boundary which resulted in the distinct vertical arrangement of the black and red layers. Being markedly enriched in As bound to Fe‐oxyhydroxides and exposed to fluctuating redox conditions, the coloured strata can potentially release As to groundwater and represent serious environmental hazards. Radiocarbon ages suggest that the groundwater‐type red beds can occur extremely quickly, over a few hundred years. It is assumed that, under suitable circumstances, this reddening can be preserved in the rock record, and represent a specific model for the development of continental red beds.

Red colouring in marine red beds (MRB) is commonly attributed to deposition and early diagenesis under specific redox conditions. Therefore, the MRB can be considered time-specific facies. However, since red colouring is a sub-jective criterion, it is difficult to establish a colour limit for the MRB in the scale from grey to yellow, orange, pink to red. Using spectral reflectance, carbonate petrology, bulk-rock and in-situ geochemistry data from three sections of Ordovician orthoceratite carbonates of South China, we addressed the question whether the incipient reddening in the pink carbonates was associated with similar redox changes and palaeoceanographic conditions like in the MRB. The yellowish grey to greyish orange pink (Munsell Rock Colour Chart) carbonates with low concentrations of he-matite (< 0.01 %) are transitional from goethite-bearing grey to hematite-enriched true MRB. The red-coloured skel-etal interiors, microstromatolites, nodules and filamentous microborings suggest an extensive microbial activity which was accompanied by precipitation of authigenic aluminosilicates (clays). We hypothesize that the microbial clay precipitation is an important intermediate step in Fe transformation from its primary sources to hematite in the MRB. The carbonate deposition was followed by early diagenetic, shallow-subsurface REE fractionation, and Fe\\Mn (+Mo, U and V) redox cycling along microbially controlled redox microgradients. The geochemical redox signature of the pink carbonates is very similar to the MRBs of Devonian and Ordovician age. They were deposited under sim-ilar palaeoenvironmental conditions on a deeper shelf inhabited by skeletal heterotrophs, with reduced rates of or-ganic matter burial and slow sedimentation rates. The sedimentation of the pink carbonates and MRBs seem to randomly coincide with the coeval global sea-level changes and delta 13Ccarb fluctuations suggesting that the local controls of sediment colour override the global ones.(c) 2022 Elsevier B.V. All rights reserved.

Dam reservoirs are complex depositional systems, which provide barriers to natural sediment transport along river courses. In addition, reservoir sedimentation causes serious problems in their operational management. Given the wide variability of reservoir bottom shapes, total volumes of stored water, river discharges, sediment loads and sediment textures, universal depositional models are difficult to achieve for dam reservoirs. This article focuses on the need to improve current understandings of sedimentation processes, and thorough spatial particle size distribution in dam reservoirs. To achieve this aim, sonar and ground penetrating radar surveys were combined with high-resolution stratigraphic data from 44 short sediment cores in two valley-type reservoirs, Sec and Krizanovice, part of a reservoir cascade in the Chrudimka River, which is a left-hand tributary of the Labe River (Czech Republic). Sonar survey was used to construct bathymetric maps and bottom reflection intensity images. The results showed topography inherited from pre-reservoir times and a good degree of correspondence between bottom reflection intensity and grain size. The sedimentation patterns exhibit distinct proximal-to-distal and transversal changes in sediment facies and grain size. Pre-reservoir and present morphologies have substantially shaped sediment accumulation. Spatial grain size sorting is a function of travel distance within reservoirs, which is conditioned by their bended and narrow geometry, as well as by reservoir management. Two stages of reservoir sedimentation are recognised. The initial stage was characterised by the filling of local depressions, which were overlain by the second stage, typified by continuous and horizontally deposited sediments. Relatively low sediment accumulation rates (from 0.2 to 1.06 cm/year) are the consequence of reservoir characteristics (capacity and associated accommodation space) and factors at a basin scale (low discharge, geology and land-use). Slow reduction of reservoir capacity was observed. The calculated trap efficiency is very high in the Sec Reservoir and much lower in the K.ri.zanovice Reservoir. The main factor controlling trap efficiency is reservoir capacity and shape combined with low inflow. Ultimately, the trap efficiency change over time because of varying reservoir capacity due to seasonal water level fluctuation and varying hydrologic conditions. Due to the slow silting of the reservoir, the trap efficiency has decreased only slightly. Aside from general trends, some specific features exist for every reservoir based on local geometry and reservoir management strategy. This implies that an innovative approach combining map, sonar and geophysical surveys with core data is required to develop better facies models and to optimise sediment management strategies.