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This study aims to evaluate the level of metallic pollution in the recent sediments of the Zoubia area (Aïn Kechera) in north-east of Algeria. The method used for this assessment involves sediments sampling and the determination of heavy metal concentrations. The study estimated the level of metallic pollution in the sediments by calculating several pollution indexes, including the contamination factor (CF), the enrichment factor (FE), the geo-accumulation index (Igeo), the individual ecological risk index (), the potential ecological risk (RI) and statistical analysis of the data. The study monitored seven trace metals: cadmium (Cd), chromium (Cr), nickel (Ni), lead (Pb), zinc (Zn) and copper (Cu). The results indicate an enrichment of Cd, Pb, Zn, and Cu in all samples. However, Ni, Co, and Cr levels are below those of the continental crust (background). The geo-accumulation index values for Co, Ni, and Cr are negative in all samples. On the other hand, positive geo-accumulation index values were observed for Cd, Pb, Zn, and some Cu samples (B1, B2, B3, and B4) with individual ecological risks of less than 40 for Cd, (94.48-119.21) for Zn, and (80.23-135.4) for Cu, respectively. This indicates low risk for Cd and high risk for Zn and Cu. The results indicate that Pb poses a significant ecological risk (537.4-842.05) and may have adverse effects on human health. The most significant pollutants, in order of increasing risk, are Pb, Cu, Zn, and Cd. [ABSTRACT FROM AUTHOR]

The production of cysts by dinoflagellates can be part of the life cycle of some species, improving their survival under adverse environmental conditions; cyst germination may explain the recurrence of algal blooms in some cases. In order to evaluate the germination rates of Pyrodinium bahamense, its cysts were retrieved from surface sediments collected in San José Lagoon, SW Gulf of California, and germination assays were carried out through the cysts incubation under two contrasting light and nutrient concentration conditions. Also, to evaluate cysts viability, we isolated P. bahamense cysts and other dinoflagellate species from different depth layers of a 210Pb-dated sediment core (~100 years) to examine their germination for 20 days. Germination rates were higher under light (28–56%) than in darkness (23–34%); there were indications that the nutrient-enriched media was more effective in promoting germination than seawater. Furthermore, germination was observed in cysts isolated from all selected core depths, even those corresponding to ~100 years. These results demonstrate that cysts remain viable for long periods, and P. bahamense cysts germinate in any light and nutrient conditions. The results of this research provide relevant information to understand its physiology and complex population dynamics. This species should be closely monitored in the area in the context of climate change, as current natural conditions are likely to change.

The production of cysts by dinoflagellates can be part of the life cycle of some species, improving their survival under adverse environmental conditions; cyst germination may explain the recurrence of algal blooms in some cases. In order to evaluate the germination rates of Pyrodinium bahamense, its cysts were retrieved from surface sediments collected in San José Lagoon, SW Gulf of California, and germination assays were carried out through the cysts incubation under two contrasting light and nutrient concentration conditions. Also, to evaluate cysts viability, we isolated P. bahamense cysts and other dinoflagellate species from different depth layers of a 210Pb-dated sediment core (~100 years) to examine their germination for 20 days. Germination rates were higher under light (28–56%) than in darkness (23–34%); there were indications that the nutrient-enriched media was more effective in promoting germination than seawater. Furthermore, germination was observed in cysts isolated from all selected core depths, even those corresponding to ~100 years. These results demonstrate that cysts remain viable for long periods, and P. bahamense cysts germinate in any light and nutrient conditions. The results of this research provide relevant information to understand its physiology and complex population dynamics. This species should be closely monitored in the area in the context of climate change, as current natural conditions are likely to change. [ABSTRACT FROM AUTHOR]

The paleoenvironmental reconstruction of Aveiro Lagoon is being carried out based on the sedimentological, paleoecological, geochemical and mineralogical characterization of sediment samples collected systematically in the lagoon. This paper presents results concerning the changes in the chemical and mineralogical composition of the fine fraction (

The main aim of this research is to define the mineralogical composition of recent sediments deposited around the Al-Teeb river basin in eastern Missan, trying to determine the provenance or the source of these sediments. The study area represents the southeastern edge of the Mesopotamian Plain and is part of it. Quaternary deposits cover most of the area. It is clayey with old sea and river deposits and part of aeolian deposits. These sediments cover 95% of the study area, while the older rocks, which date back to the Tertiary (Late Miocene – Pliocene), exposed in the area east and northeast of the Al-Teeb area, made up hills which back to the undifferentiated Pliocene Mukdadiya and Bai-Hassan formations. The light components of these sediments consist mainly of quartz, feldspars (potash and plagioclase feldspar), sedimentary rock fragments (carbonate rock fragments, chert rock fragments, evaporates fragments), igneous rock fragments, and metamorphic rock fragments The heaviest minerals are opaque, amphiboles, pyroxenes, chlorite, epidotes, biotite, garnet, muscovite, zircon, kyanite, staurolite, and rutile. These sediments are typically formed by sedimentary rocks (single or many cycles), low and high-rank metamorphic rocks, acidic and basic igneous rocks, and pegmatite rocks. The high percentage of opaque heavy minerals in clastic sediment refers to unstable clastic sediments. The stability issue to the areas during the study shows that there are significant variances over the several places, indicating dissimilar sources and types of source rocks. [ABSTRACT FROM AUTHOR]

We address the role of the Congo River sediment dispersal in exporting and trapping organic carbon into deep offshore sediments. Of particular interest is the Congo submarine canyon, which constitutes a permanent link between the terrestrial sediment sources and the marine sink. The Congo River delivers an annual sediment load of ~40 Tg (including 2 Tg of C) that feed a mud-rich turbidite system. Previous estimates of carbon storage capacity in the Congo turbidite system suggest that the terminal lobe complex accounts for ~12% of the surface area of the active turbidite system and accumulates ~18% of the annual input of terrestrial particulate organic carbon exiting the Congo River. In this paper, we extend the approach to the whole active turbidite depositional system by calculating an average burial of terrestrial organic matter in the different environments: canyon, channel, and levees. We estimate that between 33 and 69% of terrestrial carbon exported by the Congo River is ultimately trapped in the different parts of turbidite system and we evaluate their relative efficiency using a source to sink approach. Our carbon budget approach, which consider annual river discharge versus offshore centennial accumulation rates, indicates that about half of the total particulate organic matter delivered yearly by the Congo River watershed escapes the study area or is not correctly estimated by our deep offshore dataset and calculations. [ABSTRACT FROM AUTHOR]

The 210Pb-based method allows for absolute age determination in recent sediments on the centennial scale. The most common sedimentary scenarios involve ideal deposition without any further redistribution. The conventional models apply to such conditions by adding specific assumptions that allow analytical formulations: constant flux (CF), constant initial concentration (CIC), and constant flux with constant sedimentation (CFCS). The χ-mapping models are presented as a novel methodological approach. They generate a large number (105 to 106) of potential solvers, consisting of sets of n (the number of slices in the core) values of initial activity concentrations, A 0 , and sedimentation rates, w. Empirical data serve to attract the solver that minimizes a χ function after encountering the best sorting along the core of the A 0 and w values. The specific assumptions of the above models are reformulated in terms of the statistical distributions of A 0 and w. The performance of the χ-mapping versions is demonstrated with a set of cores from the literature with independent chronologies. The main advantages compared to known analytical formulations are: i) χ-mapping provides a more robust fitting method. ii) It overcomes the problem of age reversals often found in the CIC model. iii) The CF model successfully applies to cores with unsteady and/or incomplete inventories. iv) The TERESA model (time estimates from random entries of sediments and activities), without analytical counterpart, is the only model that can manage continuous trends of change in the fluxes of unsupported 210Pb. The work discusses the conditions for compensating model errors in the chronologies, and the use of the palaeorecords of fluxes, A 0 and w. The methodology can be extended to other assumptions (models) and provides novel and insightful views on the 210Pb-based dating of recent sediments. • χ-mapping is a novel methodology for 210Pb-dating models CF, CFCS and CIC. • Empirical data attracts the best solution from clouds of ∼105 solvers minimizing χ. • Model assumptions formulated in terms of statistical distributions of A 0 and SARs. • The performance is demonstrated with real cores with independent chronologies. • The advantages with respect to classical methods are highlighted. [ABSTRACT FROM AUTHOR]

The lake Kolakkudi represents a small, isolated and fresh water lake situated in southern part of TamilNadu, India and it surrounded by fluvial placer deposits of garnet rich sands. In the study area to obtain information about rare earth elements (REEs) of core sediments and conceded sediment composition and distribution of rare earth elements as well as surrounding soil was investigated. The concentration of REEs in core sediments varies from 0.42 to 49.1 ppm. The higher REE content in the core sediments samples from various locations whichsignificance the plethora of clay and/or quartz with less significant effect caused by sedimentary sorting. According to the difference in the levelsof the rare earth elements, the rare earth elements normalized patterns and associated fractionation parameters (SLREE/SHREE, (La/Yb)N, and (NdYb) N) showed similarities between the lake sediments and the surrounding clays, confirming a widespread influence of nearby local lithology on the lake sediment composition. On the other hand, the results of the statistical analysis suggest the contribution of both clay rich soils and garnet rich sands in the lake sediments to the total content of rare earth elements. [ABSTRACT FROM AUTHOR]

• Combined presence of salt and water in a sediment leads to acid reaction during Rock-Eval analysis. • This acid reaction precedes usual thermal decomposition of carbonates. • Early decomposition of carbonates leads to a shift in Rock-Eval peak CO 2 temperatures. • Rock-Eval CO 2 peak shift leads respectively to over/underestimation of mineral/organic carbon. • Samples should be thoroughly rinsed before Rock-Eval analysis and interpretation. The amount of CaCO 3 in sediments and/or sedimentary rocks is usually measured by calcimetry while the nature of the carbonates is determined by X-ray diffraction. Recently, a carbonate recognition method based on the results of Rock-Eval pyrolysis was proposed in 2014 by Pillot et al. [ 1 ]. Rock-Eval pyrolysis is also widely used for the characterization of recent sediments. However, later in 2015 Baudin et al. [ 2 ] noticed that some of the characteristics of recent sediments tended to produce different results from those of more classical Rock-Eval analyses, causing bias in interpretations. In this study, the thermal stability of fossil and recent marine carbonated sediments was analyzed to identify differences in carbonate decomposition and to underline the importance of accounting for them in Rock-Eval analyses. The state of calcite preservation in recent marine sediments and sedimentary rocks at temperatures between 400 °C and 600 °C was characterized using different techniques (calcimetry, XRD, SEM imaging, etc.) for better interpretation of data obtained with Rock-Eval. Our results highlight a clear difference in the range of calcite decomposition temperatures during Rock-Eval analysis: between 550 °C and 775 °C for bulk clayey hemipelagic sediments versus 650 °C–840 °C after the same sediments were rinsed to get rid of the salt. During heating, water and hydroxide anions are released from clay minerals and react with salt crystals to form acid vapor. This acid vapor reacts with carbonates to produce CO 2. The chemical decomposition of carbonate starts at temperatures that are lower than the typical range of decomposition temperatures, leading to overestimation of mineral carbon content (overestimation of the S5 peak) and to underestimation of organic carbon content (underestimation of the S4CO 2 peak) with the Rock-Eval method. In the absence of clay minerals, such as in recent marine pure carbonate oozes, there is no evidence for this effect. It is therefore essential to prepare and rinse recent clay-rich carbonated sediment samples before Rock-Eval analysis to avoid misinterpretation. [ABSTRACT FROM AUTHOR]

Abstract Radiometric dating was a revolutionary contribution to the study of sedimentary processes. Empirical data from varved sediments show that unsupported 210Pb (210Pb exc) fluxes vary over time while they statistically correlate with sediment accumulation rates (SAR). This contradicts the basic assumption of the Constant Rate of Supply (CRS) model, which is the most widely used technique for recent sediments. This work is aimed at assessing the CRS model-errors by quantifying the effects on chronologies of various patterns of temporal variability of fluxes. Results are discussed through applications with synthetic and real cores for which and independent varve chronology or a set of reference dates are available. Periodic harmonic and random fluctuations in fluxes tend to cancel out positive and negative deviations in CRS ages, but they produce spurious variability in SARs. Persistent changes in fluxes lead to cumulated and unacceptable deviations of the CRS ages, which cannot be satisfactorily compensated by the use of a piecewise CRS model. The raw and piecewise CRS models can still be powerful tools of widespread use when the conditions for their applicability are well understood. The paper shows how the analysis of clusters in the 210Pb exc vs mass depth profile, along with the estimation of equivalent constant fluxes pre and post-dating a known reference date, are powerful methods to prevent misapplications of the CRS model. [ABSTRACT FROM AUTHOR]

Bacterial reactions are one of the major processes that control nutrient cycles in sediments. The aim of this study was to trace the bacterial biomarkers (hopanes) to understand early diagenetic processes in tropical mangrove dominant brackish sediments over modern timescales. Hopane homologues were examined by gas chromatography-mass spectrometry (GC-MS). The results suggested that hopane concentrations were high in Bolgoda Lake surface sediments (average ± SD = 1336.5 ng/g TOC ± 748.7) compared to mangrove mud cores (676.4 ng/g TOC ± 268.5). Therefore, the variation of bacterial biomasses can be controlled by the available reactive organic matter type and depositional environments (sulfate concentration). Total hopane concentrations gradually declined with the depth in core samples. In addition, total hopane concentrations showed moderate and weak correlations with organic matter types in upper (0-60 cm) and lower (> 60 cm) sedimentary successions, respectively. These features in core samples suggest the formation of geohopanoids during diagenesis. The variations of C31 hopane isomerisation ratio suggest the minor influence of reworking bacterial biomarkers in the upper sedimentary succession. Therefore, C31 22S (αβ) hopane distribution can indicate soil acidity (chemical origin) in the mangrove dominant swamp. [ABSTRACT FROM AUTHOR]

Conventional 210Pb-dating models use assumptions on sedimentary conditions that allow for analytical formulations. The novel χ-mapping models use numerical methods to generate and test a large number (∼106) of potential solvers. Empirical data (excess 210Pb vs. mass depth profile) serve to attract the solver that minimizes the χ function (the attractor), and it has been assumed that it also defines the most likely chronology. This work aims to test this assumption in a deep way. In synthetic and varved sediments, the performance of each solver can be quantified through a parameter ξ a accounting for the deviation of the model and the true ages. This work studies the complex relationships between χ and ξ a using the constant flux (χ-CF) and the constant sediment accumulation rate (CSAR) models, which operate in a parametric 3D space. The full mapping of the 3D χ function serves to find the absolute minimum, for the graphical representation of the complex topology of the attractors , which is model-specific, and for plotting clouds of chronological lines from solvers with varying χ values. The minimum value of ξ a (the best chronology) is achieved for a wide range of χ values, including the region of the absolute minimum. In complex cases, tiny changes in χ can result in quite different chronologies. Alternative attractors that include a reference date and an objective function are studied. The results provide guidelines for strengthening the 210Pb-based chronologies. • χ-CF and CSAR are 210Pb-dating models for sediments using a χ function as attractor. • The minimum χ gives the best fit to data but the best chronology may be uncertain. • Plotting the topology of the attractor and clouds of chronologies are helpful tools. • Defining attractors including time marks makes simpler the solution. • The study uses synthetic and varved sediments and helps strengthen the 210Pb-dating. [ABSTRACT FROM AUTHOR]

The 210Pb-based method aims at determining the absolute age of recent sediments on the centennial scale. A family of models assumes that at the sediment-water interface the flux of unsupported 210Pb (210Pb exc), F , relates to its initial activity concentration, A o , and the mass sedimentation rate, w , as: F = A o w. Additional specific assumptions that allow for analytical formulations of the models are: i) constant A o (CIC), constant F (CF), and constant F with constant w (CFCS). A model with constant w (CSAR) was suggested for completeness but never used because of the lack of a suitable analytical formulation. The TERESA model assumes random and independent variability for A o and w , described by normal distributions. It systematically generates a large number (∼105) of potential solutions, whose performance for fitting the empirical 210Pb exc profile is quantified through the χ-function. This work aims to adapt the above methodology to formulate the χ-mapping version of the CSAR model. The performance of the model is evaluated with a set of synthetic and real cores for which an independent chronology is available. CSAR is able to capture the mean sedimentation rate from the 210Pb exc data and provides reliable chronologies and paleorecords of A o , useful for tracking past changes in sedimentary conditions. CSAR provides an interesting different perspective for researchers working with 210Pb-based dating of recent sediments. • A210Pb-dating model assuming constant sedimentation rate is solved for first time. • The CSAR model uses the novel methodology of χ-mapping. • Empirical data attracts the best solution from clouds of ∼105 solvers minimizing χ. • The performance is demonstrated with real cores with independent chronologies. [ABSTRACT FROM AUTHOR]

Abstract The present paper is devoted to throw more light on the geological study of recent surface sediments of a small North African reservoir, as well as, the influence of mother country rocks on these sediments which hasn't been thoroughly studied before. The studied sediments have been confirmed to be mostly derived from Ethiopian sources as indicated by the calculated mineralogic indices, where higher pyroxene index (I Pyr = 62.07) was recorded. The Ethiopian Plateau and the local contribution from the surrounding country rocks (Aswan granites, Nubia Sandstone, basement rocks and some volcanic basaltic islands) played the principle role on the distribution of heavy and clay minerals to such sediments. [ABSTRACT FROM AUTHOR]

The Congo River, the second largest river in the world, is a major source of organic matter for the deep Atlantic Ocean because of the connection of its estuary to the deep offshore area by a submarine canyon which feeds a vast deep-sea fan. The lobe zone of this deep-sea fan is the final receptacle of the sedimentary inputs presently channelled by the canyon and covers an area of ~2500 km². The quantity and the source of organic matter preserved in recent turbiditic sediments from the distal lobe of the Congo deep-sea fan were assessed using Rock-Eval pyrolysis analyses. Six sites, located at approximately 5000 m water-depth, were investigated. The mud-rich sediments of the distal lobe contain high amounts of organic matter (~3.5 to 4% Corg), the origin of which is a mixture of terrestrial higher-plant debris, soil organic matter and deeply oxidized phytoplanktonic material. Although the respective contribution of terrestrial and marine sources of organic matter cannot be precisely quantified using Rock-Eval analyses, the terrestrial fraction is dominant according to similar hydrogen and oxygen indices of both suspended and bedload sediments from the Congo River and that deposited in the lobe complex. The Rock-Eval signature supports the 70% to 80% of the terrestrial fraction previously estimated using C/N and δ 13 C org data. In the background sediment, the organic matter distribution is homogeneous at different scales, from a single turbiditic event to the entire lobe, and changes in accumulation rates only have a limited effect on the quantity and quality of the preserved organic matter. Peculiar areas with chemosynthetic bivalves and/or bacterial mats, explored using ROV Victor 6000, show a Rock-Eval signature similar to background sediment. This high organic carbon content associated to high sedimentation rates (> 2 to 20 mm.yr −1 ) in the Congo distal lobe complex implies a high burial rate for organic carbon. Consequently, the Congo deep-sea fan represents an enormous sink of terrestrial organic matter when compared to other turbiditic systems over the world. [ABSTRACT FROM AUTHOR]

Geochemical data (total organic carbon-TOC content, δ 13 Corg, C:N, Rock-Eval analyses) were obtained on 150 core tops from the Angola basin, with a special focus on the Congo deep-sea fan. Combined with the previously published data, the resulting dataset (322 stations) shows a good spatial and bathymetric representativeness. TOC content and δ 13 Corg maps of the Angola basin were generated using this enhanced dataset. The main difference in our map with previously published ones is the high terrestrial organic matter content observed downslope along the active turbidite channel of the Congo deep-sea fan till the distal lobe complex near 5000 m of water-depth. Interpretation of downslope trends in TOC content and organic matter composition indicates that lateral particle transport by turbidity currents is the primary mechanism controlling supply and burial of organic matter in the bathypelagic depths. [ABSTRACT FROM AUTHOR]

The vertical distributions of bulk and molecular biomarker composition in samples from a ca. 156 cm sediment core from Lake Ichkeul were determined. Bulk analysis (Rock-Eval pyrolysis, carbonate, lipid extraction) and molecular analysis of saturated fractions were used to characterize the nature, preservation conditions and input of sedimentary organic matter (OM) to this sub-wet lake environment. The sediments are represented mainly by gray-black silty-clay facies where the carbonate (CaCO 3 ) content varies in a range of 10–30% dry sediment. Rock-Eval pyrolysis revealed a homogeneous total organic carbon (TOC) content of ca. 1% sediment, but with down core fluctuation, indicating different anoxic conditions at different depths and material source variation. The values show three periods of relative enrichment, exceeding ca. 1%, at 146-134 cm, 82 cm and 14-0 cm depth. The low Hydrogen Index (HI) values [<119 mg hydrocarbon (HC)/g TOC)] were characteristic of continental Type III OM. The T max values in the range 415–420 °C were characteristic of immature OM at an early diagenetic stage. The distributions of n -alkanes (C 17 to C 34 ), isoprenoid (iso) alkanes (pristane and phytane), terpanes and steranes showed that the OM is a mixture of marine algal and bacterial source and emergent and floating higher plant origin. In addition, the distributions, as well as several biomarker ratios ( n -alkanes, iso-alkanes/ n -alkanes), showed that the OM is a mixture of immature and mature. Significant downcore fluctuation was observed in the molecular composition. This indicates intense microbial activity below ca. 50 cm core depth under an anoxic and brackish environment. [ABSTRACT FROM AUTHOR]

Based on samples collected from two mountain lakes named as Lacs Paponoun located in the Cameroon Highlands (Africa), an assemblage of chrysophycean stomatocysts was investigated using scanning electron microscopy. Twenty stomatocysts are reported and described following the guidelines of the International Statospore Working Group (ISWG). Eleven cysts are described as new morphotypes. The present study documents the largest assemblage of chrysophycean stomatocysts from the recent sediments in tropical Africa detected so far. Additionally, it provides new data on global diversity of chrysophycean stomatocysts. [ABSTRACT FROM AUTHOR]

This work presents mineralogical, geochemical and Pb isotope compositions of heavy metals from overbank sediments of the Amapari river and its tributaries, in the region of Serra do Navio, central Amapá. The sediments are mainly composed of quartz, kaolinite, gibbsite and muscovite, displaying a large geochemical and Pb isotopic heterogeneity. The geochemical results indicate high contents of heavy metals and that the sediments underwent the same processes of enrichment for all investigated metals. The metals are mainly associated to Fe-minerals, while clay minerals are not relevant for the concentration of those metals. The variation of Pb isotopic compositions permitted to define an isochron in the 207Pb/204Pb vs. 206Pb/204Pb diagram with an age of 2169 ± 140 Ma, indicating that the sediments came essentially from the surrounding Paleoproterozoic units (supracrustal rocks and associated granitoids), without any significant contribution from the units of the Archean basement. Metal contents and sample locations do not show any relationships with the major mining prospects in the area.

Studies of recent environmental perturbations often rely on data derived from marine sedimentary records. These records are known to imperfectly inscribe the true sequence of events, yet there is large uncertainty regarding the corrections that should be employed to accurately describe the sedimentary history. Here we show in recent records from the Gulf of Aqaba, Red Sea, how events of the abrupt disappearance of the planktonic foraminifer Globigerinoides sacculifer , and episodic deposition of the artificial radionuclide 137 Cs, are significantly altered in the sedimentary record compared to their known past timing. Instead of the abrupt disappearance of the foraminifera, we observe a prolonged decline beginning at core depth equivalent to ∼30 y prior to its actual disappearance and continuing for decades past the event. We further observe asymmetric smoothing of the radionuclide peak. Utilization of advection–diffusion–reaction models to reconstruct the original fluxes based on the known absolute timing of the events reveal that it is imperative to use a continuous function to describe bioturbation. Discretization of bioturbation into mixed and unmixed layers significantly shifts the location of the modeled event. When bioturbation is described as a continuously decreasing function of depth, the peak of a very short term event smears asymmetrically but remains in the right depth. When sudden events repeat while the first spike is still mixed with the upper sediment layer, bioturbation unifies adjacent peaks. The united peak appears at an intermediate depth that does not necessarily correlate with the timing of the individual events. In a third case, a long lasting sedimentary event affected by bioturbation, the resulting peak is rather weak compared to the actual event and appears deeper in the sediment column than expected based on the termination of the event. The model clearly shows that abrupt changes can only endure in the record if a thick sediment layer settled on the sediment–water interface at once or if bioturbation rates decreased to very low values for a prolonged period of time. In any other case smearing by bioturbation makes an abrupt event appear to have started shortly before the real timing and end long after its true termination. [ABSTRACT FROM AUTHOR]

Knowledge of sedimentation rates in lakes is required to understand and quantify the geochemical processes involved in scavenging and remobilization of contaminants at the Sediment-Water Interface (SWI). The well-known 210 Pb excess ( 210 Pb ex ) method cannot be used for quantifying sedimentation rates in uranium-enriched catchments, as large amounts of 210 Pb produced by weathering and human activities may dilute the atmospheric 210 Pb. As an alternative dating method in these cases, we propose an original method based on 232 Th decay series nuclides. This study focuses on an artificial lake located in a granitic catchment downstream from a former uranium mine site. The exponential decay of 228 Ra excess ( 228 Ra ex ) with depth in two long cores yields sedimentation rates of 2.4 and 5.2 cm yr −1 respectively. These sedimentation rates lead to the attribution of the 137 Cs activity peak observed at depth to the Chernobyl fallout event of 1986. The 228 Ra ex method was also applied to two short cores which did not display the 137 Cs peak, and mean sedimentation rates of 2.1 and 4.0 cm y −1 were deduced. The proposed method may replace the classical radiochronological methods ( 210 Pb ex , 137 Cs) to determine sedimentation rates in granitic catchments. [ABSTRACT FROM AUTHOR]

The Paraíba do Sul River (PSR) is a medium-sized river that flows through the Minas Gerais, São Paulo and Rio de Janeiro Brazilian states the three most developed states in Brazil. Industrial parks and cities have historically been established along the river basin. The waters of PSR are used in agriculture, industry and human consumption of over 20 million people, including Rio de Janeiro City. Furthermore, the river receives effluent from these activities: agricultural runoff, industrial waste, and domestic sewage. Therefore, PSR has been considered polluted, particularly by heavy metals. In order to assess heavy metals in bottom sediments grains of the PSR, to infer their elemental composition, and to characterize individual sediment grains morphology, a non-destructive methodology - X-ray microanalyses (Scanning Electron Microscope coupled to Energy Dispersive X-rays Spectrometer/SEM/EDS) - was used. Heavy metals - Cr, Mn, Ni, Cu, Zn, Zr, Ag, Ba, Au, La, Ce, Nd, Th, Y, Sn, Os and Pb – were detected by SEM/EDS in bottom sediment grains from PSR, predominantly in grains with equivalent diameter ≤10 μm. They occurred as silicates, oxides (hydro-oxides), sulfides, carbonates, sulfates, phosphates and chlorides. All detected heavy metals occurred as, at least, one kind of soluble metal compound, mainly due to ionic exchange from silicates, with the exception of Ag, which was chloride, sulfate or metallic as Os, Au and Pb. These results corroborate heavy metal PSR pollution and food chain risk, considering that near-shore continental shelf is free of heavy metals contamination. Our results also give support to the hypothesis that the PSR estuary can act as a trap for these elements. [ABSTRACT FROM AUTHOR]

Makirina Cove was formed by the Holocene sea-level rise whichcaused a marine ingression into the depression formed within Albian–Cenomanian dolomites at approximately 4.5 ka B.P. At present, MakirinaCove represents an restricted, stressed, shallow-marine (ecosystem characterized by varying seawater temperatures (0–35°C)as well as fluctuating salinities (up to 41‰) affected by seasonallyenhanced evaporation, continuous freshwater supply through on-shoreand submarine springs associated with the coastal karst area and surface run-off episodes. These environmental conditions have beenconducive to high primary production of organic matter resulting inthe formation of organic-rich deposits which contain up to 5 wt.% oforganic carbon. Up to the present times, 3.5 m of sediments have beendeposited indicating a relatively high sedimentation rate estimated at0.75 m/1.0 ka in the northern central part of the Cove.The sediments are being deposited mostly as poorly sortedclayey–sandy silts. The distribution and concentration of most of thechemical elements is dependant on the mineralogical composition andgranulometric features of the Makirina sediments, which show valuesmore or less similar to those from the Central Adriatic. Accordingly,there is a positive correlation with Al and K concentrations increasingoff-shore and with the depth being associated with increasing concentrations of clay minerals within the clay fraction. The same holdstrue for concentrations of some trace elements, especially Mo and Sewhich is consistent with the distribution pattern of sulphides.Selenium is preferentially enriched in authigenic pyrite and itis probably the major source of Se in the Makirina Cove sediments.The concentrations of Ca, Mg and Sr decrease off-shore and they arelinked to the composition of the surrounding carbonate rocks. Thesaturation indices show that the water is supersaturated with respectto carbonates enabling the precipitation of authigenic amorphous orcrystalline carbonate phases from the pore water in the upper segmentof the sediment column. According to the oxygen isotopic (δ18O) composition,molluscs precipitated their carbonate shells mostly duringwarmer periods (May to November) at or near isotopic equilibriumwith their ambient waters. The carbon isotopic δ13C composition ofmollusc carbonate shells is environmentally affected due to oxidationand decomposition of organic matter as well as influxes of fresh waterinto the Cove, indicating their formation out of the predicted isotopicequilibrium with atmospheric CO2. Palynological and organic carbonisotopic (δ13C) composition shows that the sedimentary organic matter(SOM) is 70–90% lipid- and hydrogen-rich and on average 2/3 marinederived (mainly phytoplankton, bacteria and marine macrophytes) and1/3 terrestrially derived (mainly woody tissue). The variations in composition of SOM have been noted as a function of the distance fromthe shore. The type and the preservation state of SOM and pyrite aswell as the measurements of Eh, pH, total alkalinity, dissolved inorganiccarbon (DIC) and the enrichment of redox-sensitive trace elements,indicate oxygen-depleted depositional conditions and that thesediment is highly reductive even in the uppermost segment at thesediment/water interface. According to the results obtained from theapplied methods, the features of Makirina sediments strongly reflectthe given depositional conditions within this restricted, stressed, shallow-marine environment where these organic-rich sediments originate,and may therefore serve as a calibration standard in further investigations

The purpose of this paper was to examine to which extent the abundance and distribution of certain biological markers may be used for the identification of oil-type pollutants in recent sediments and ground waters. The samples were taken from the area of the Oil Refinery Pančevo (alluvial formation of the Danube River). The organic matter of the investigated samples was isolated using an extraction method with chloroform. The group composition and usual biological markers were analyzed in the obtained extracts. n-Alkanes and acyclic isoprenoids, pristane and phytane were analyzed using gas chromatographie (GC) analysis of saturated hydrocarbons. Polycyclic alkanes of the sterane and terpane type were analyzed using gas chromatography-mass spectrometry (GC-MS), i.e. by analyzing the carbamide non-adduct of the total alkane fraction (Single Ion Monitoring SIM-technique). The obtained results indicate that n-alkanes can be used for the identification of oil-type pollutants (for example, if the oil-pollutant is biodegraded or present in very low concentrations), and steranes and triterpanes can be used as very reliable indicators of oil-type pollution in recent sediments and ground waters.

Transformation of organic matter (OM) in Holocene sediments of Lake Ochki (southern coast of Lake Baikal) at the early stages of diagenesis has been studied using pyrolytic methods of Rock Eval (RE-pyrolysis) and pyrolysis-gas chromatography-mass spectrometry (Pyr-GC-MS). OM has been analyzed in lacustrine sediments and their main producers, phytoplankton and zooplankton. Data on the distribution of hydrocarbon-biomarkers in sediments indicate an uninterrupted influx of terrigenous OM and transformation of OM precipitated by microorganisms. The analysis of molecular composition of pyrolysates makes it possible to assume a sharp change of sedimentation conditions in the upper part of sedimentary sequence (0-60 cm). It is shown that the macromolecular aliphatic kerogen structure begins to form in incoherent sediment at the very early stages of diagenesis. [ABSTRACT FROM AUTHOR]

Rock–Eval pyrolysis, a widely used petroleum screening technique developed primarily for ancient sedimentary rocks and kerogens, has been increasingly applied to the characterization of recent lacustrine or marine sediments. However, as illustrated by results from various authors and by the analysis of recent sediments from various areas, the thermally labile character of recent organic matter (OM), the presence of poorly crystallized mineral (e.g. carbonate) and the eventual presence of salts (NaCl, sulfate) might perturb detection of the pyrolysis effluent. The aim here was to outline the problems generated by such perturbation and to demonstrate that specific operating conditions are needed for proper analysis of recent marine sediments. A modified Rock–Eval pyrolysis program, starting at lower temperature (180 °C) with a heating rate of 30 °C/min, is proposed as a standard mode for the analysis of recent OM in order to avoid misleading interpretation of Rock–Eval data and make possible the inter-comparison of results whatever the Rock–Eval device used. [ABSTRACT FROM AUTHOR]

After half a century, the use of unsupported 210 Pb ( 210 Pb exc ) is still far off from being a well established dating tool for recent sediments with widespread applicability. Recent results from the statistical analysis of time series of fluxes, mass sediment accumulation rates (SAR), and initial activities, derived from varved sediments, place serious constraints to the assumption of constant fluxes, which is widely used in dating models. The Sediment Isotope Tomography (SIT) model, under the assumption of non post-depositional redistribution, is used for dating recent sediments in scenarios in that fluxes and SAR are uncorrelated and both vary with time. By using a simple graphical analysis, this paper shows that under the above assumptions, any given 210 Pb exc profile, even with the restriction of a discrete set of reference points, is compatible with an infinite number of chronological lines, and thus generating an infinite number of mathematically exact solutions for histories of initial activity concentrations, SAR and fluxes onto the SWI, with these two last ranging from zero up to infinity. Particularly, SIT results, without additional assumptions, cannot contain any statistically significant difference with respect to the exact solutions consisting in intervals of constant SAR or constant fluxes (both being consistent with the reference points). Therefore, there is not any benefit in its use as a dating tool without the explicit introduction of additional restrictive assumptions about fluxes, SAR and/or their interrelationship. [ABSTRACT FROM AUTHOR]

Purpose: The main goal of this work was to determine the pyrogenic carbon (PyC) distribution in surficial sediments for the last 40 km of the Guadiana River (SW Iberian Peninsula). In addition, the changes in the contribution of terrestrial and marine organic matter (OM) sources and their relationship with the PyC contents were assessed. Materials and methods: Sediments were collected from 22 stations within the lower course of the Guadiana River. All the samples were analyzed for total organic carbon (TOC), total nitrogen (TN), organic carbon to nitrogen atomic ratios (C/N), and stable carbon isotope ratio (δC) as indicators of changes in the sources of OM. PyC was determined according to the chemo-thermal oxidation method (CTO-375). Results and discussion: TOC ranged from 0.25 to 2.37 %dw. The greatest TOC contents were located in sediments collected at the middle estuary. The C/N values ranged from 7.7 to 12.7, with slight relative increase in the marine input compared to pre-Alqueva times. Similar C/N ranges are representative of native soil OM, lacustrine OM, and local sedimentary OM. The δ C values of the sediment samples ranged from -25.0 to -27.6 ‰ illustrating a signature of C higher plants, marsh-plants, lacustrine plants, and freshwater algae present in the area of study and in the forests located upstream. PyC ranged between 0.17 and 0.74 gkg, with the highest contents measured in samples located close to urbanized areas. Sediments collected at the middle estuary, within a rural area, showed the lowest proportions of PyC relative to the percent of TOC (≤4 % TOC). The negative relationship between PyC to TOC ratio and TOC contents confirmed the selective preservation of PyC to degradation in the sedimentary OM of the Guadiana estuary. The carbon isotope composition of the final material after applying the CTO-375 method (hereafter called δC) was ˂-30 ‰, suggesting that the PyC fraction was mainly composed of a mixture of fossil fuels and C-charred biomass. Nevertheless, selective loss of the less recalcitrant OM fractions due to degradation and/or chemical alteration might contribute to lighter carbon isotope values of PyC. Conclusions: Geochemical data showed that sedimentary OM was composed of a mix of different OM sources, with a slight increase in the marine input after the Alqueva dam went into operation. The PyC content was higher close to urbanized areas of the Guadiana River estuary. The selective preservation of PyC in the sedimentary OM of the Guadiana estuary was observed. [ABSTRACT FROM AUTHOR]

This study investigates the influence of organic matter (OM) on the historical variations of Hg in sediments from two closely-situated Canadian Arctic lakes, prior to the advent of Hg pollution inputs. Because of variable landscape evolution in the Mackenzie River Delta over the past 1-3 millennia, the lakes provide distinctly different histories of OM sources, types, and degree of aquatic productivity (i.e., depositional environments). They also differ significantly in their pre-1900 Hg concentration profiles. When labile, kerogen-like carbon ('S2') from aquatic sources (diatoms and other unicellular algae) increased between 750 and 1900 A.D. in the more productive lake (Nesbitt), Hg concentrations also increased by ca. 50%. In contrast, S2 carbon concentrations in the nearby organic-poor lake (Big Lake) were several-times lower than in Nesbitt and decreased over the past millennium, while Hg concentrations showed no trend probably reflecting the stable input of clastic material from tundra soils. The contrast between lakes suggests that OM derived from unicellular algae is more effective at scavenging Hg than OM from terrestrial plants or aquatic macrophytes, possibly because of a higher content of labile, sulphur-rich compounds, high particle surface area and its dispersion throughout the water column. The results indicate that, in the absence of anthropogenic Hg inputs, increasing phytoplankton productivity and Hg scavenging alone can lead to significant increases in the Hg content of lake sediments. This finding is consistent with the hypothesis that increasing lake productivity because of climate warming during the twentieth century has confounded the interpretation of recently increasing Hg levels in northern lake sediments as being unequivocally due to anthropogenic Hg deposition. This study also suggests that sedimentary TOC by itself is a poor and sometimes misleading indicator of possible changes in the source and quality of OM in aquatic systems, which can have a major impact on Hg concentrations in sediments. [ABSTRACT FROM AUTHOR]

Abstract: The concentrations of Cu, Zn, Cr, Ni, Pb, As, Mn and Co were determined by Inductively Coupled Plasma–Mass Spectrometry both in recent sediments from different locations of the Huelva littoral (SW Iberian Peninsula) and in their humic acid (HA) fractions in order to evaluate distribution and binding capacity of those trace elements to HAs. In addition, elemental composition (C, N, S) and δ 13C values were determined to appraise the sources of organic matter in the area. This study involved the comparison of selected samples taken from different environments including the estuary of the Guadiana River, the main fluvial system of the region, the Tinto and Odiel estuary system and the proximal shelf. Significant positive correlations were found among Cu, Zn, As and Pb in bulk sediments, suggesting a common origin of all of those elements: the mining activities and pyrite deposits located hinterland. On the other hand, results for Cr, Co and Ni pointed to the basic rocks from the low basin of the Guadiana River as their main source. Elemental (C, N) and isotopic (δ 13C) composition of sediments indicated a significant contribution of autochthonous plankton in coastal shelf sediments, whereas estuarine and riverine sediments showed a major contribution of terrestrial biomass. Geochemical values for their corresponding HAs suggested a greater terrestrial contribution in the sedimentary OM of the coastal shelf sediments than in bulk sediments, which evidenced the influence of coastal currents and sediment fluxes. Humic acids sequester considerable amounts of Cu and Zn contributing to reduce the bioavailability of these contaminants. [Copyright &y& Elsevier]

Abstract: Study of the Holocene sediments of Lake Beloe (West Siberia) in the depth range 0–137 cm gave an insight into the transformation of organic matter (OM) at the early stages of diagenesis. Analysis of OM was performed by pyrolytic methods (Rock Eval and pyrolysis + chromato-mass spectrometry). It showed that the macromolecular aliphatic structure of the kerogen and the precursors of sterane and hopane geomoleculessterenes and hopenesform at the early stages of diagenesis. We suggest that macrophytes and bacteria are the main sources of OM for the lacustrine sediments. [Copyright &y& Elsevier]

The paper is focused on some results obtained during the interval 2006 - 2009, concerning the bottom sediments fingerprinting in 10 main lakes of the Danube Delta (DD), using a composite magnetic susceptibility (MS; k)-lithological tracer. However, some remarks to the previous data obtained within the last three decades are also done. The bottom sediments were collected with "van Veen"-type grab samplers. "Confined" vs "dynamic" vs "intermediate" deltaic environments are compared and defined by particular magnetic fingerprints recovered from lake sediments. The "dynamic environments", usually placed close to the influx points of the master canals or connected by relatively short canals to the main DD branches, are reflected by intermediate and high MS values, which are assigned to k classes III, IV and V of the MS scale achieved by the authors (Rădan & Rădan, 2007). The "confined environments", situated far from the Danubian supplies and from the direct riverine inputs, are characterised by a low intensity MS fingerprint, that is assigned to the lower k classes I and II, whereas the "intermediate" category is defined by k classes II and III. A distribution model points out the composition changes of the DD lake sediments, as the distance related to the Danubian source increases: the greater the distance to the source, the richer the sediments in organic matter and poorer in detrital mineral material. Several correlation coefficients (r) were calculated, e.g. related to k vs TOM (Organic matter), k vs CAR (Carbonate fraction), k vs (TOM+CAR) and k vs SIL (siliciclastic/mineral fraction). In addition to all these data, the diagrams showing the vertical distribution of the MS values for four sediment cores taken from three DD lakes are presented. The results demonstrate the abilities of the magnetic susceptibility as a lake sediments fingerprinting tool used for integrated lithological, hydrosedimentary and environmental-geoecological studies in deltaic lakes. [ABSTRACT FROM AUTHOR]

Abstract: The particulate organic matter in <63 µm surface sediments from the Mackenzie River and its main tributaries was studied using Rock-Eval pyrolysis and organic petrology. The organic matter in the sediments is dominated by refractory residual organic carbon (RC) of mainly terrigenous nature, as indicated by abundant inertinite, vitrinite, and type III kerogen. Sediments from the tributaries contained significantly more algal-derived organic matter than from the main channel of the river, highlighting the importance of low-energy system dynamics in the tributaries, which allows modest algal production, more accumulation, and better preservation of autochthonous organic matter. This is particularly true for tributaries fed by lacustrine systems, which showed the highest S1 and S2 fractions, and consequently higher total particulate organic carbon (POC) in the basin. Organic petrology of the sediment samples confirms abundant liptinitic materials (i.e., fat-rich structured algae, spores and pollen, cuticles, and resins). Forest fire and coal deposits are also confirmed to contribute to the basin. Assuming that suspended and fine surfacial sediments have a similar OC composition, the Mackenzie River is estimated to deliver a total POC flux of 1.1 Mt C/yr to its delta, of which 85% is residual carbon with liptinitic OC (S1+S2) and S3 accounting for another 9% and 6%, respectively. [Copyright &y& Elsevier]

The distribution, abundance and diversity of modern dinoflagellate cyst assemblages were investigated in sediments from the inshore seas of southern Chile (43°08′–54°55′ S) at eight sites from April 2004 to January 2005. A total of 24 cyst types were recorded, of which 12 and five were identified at the species and genus levels, respectively. Dinoflagellate cysts were recorded from all sampling sites, but they differed in total abundance (15–270 cysts ml-1) and diversity index (H′ 0.88–2.40). Heterotrophic dinoflagellate cysts assigned to heterotrophic species were the most abundant trophic form, with 418 cysts ml-1, representing 55% of the total cyst abundance. Cluster analysis based on the abundance of dinoflagellate cyst species indicated that sampling sites were segregated into three groups likely to be related to the proportion of autotrophic vs. heterotrophic species cysts and the total abundance of cysts at each site. Distinctive cyst species composition differences among sampling sites may allow inferences about local nutrient and feeding dynamics within the water column. [ABSTRACT FROM AUTHOR]

The paleoenvironmental reconstruction of Aveiro Lagoon is being carried out based on the sedimentological, paleoecological, geochemical and mineralogical characterization of sediment samples collected systematically in the lagoon. This paper presents results concerning the changes in the chemical and mineralogical composition of the fine fraction (<63 μm) and the clay fraction (<2 μm) in sediment samples from Aveiro Lagoon, mainly collected from the lower intertidal plain and sub tidal deposits located along the Mira, Ílhavo and Ovar channels. A zonography of the lagoon was established based on the parameters analyzed. The results show that the surface and near-surface sediments of Aveiro Lagoon trap relatively large quantities of trace metals, such as Cu, Pb, Co, Ni, Cd, Zn, Fe, Mn and Cr, considered to be partially adsorbed, particularly on silty and clayey particles, and co- precipitated on Fe and Mn oxyhydroxide forms precipitated in the topmost layers of sediments. Series of statistically significant relationships were established between trace metal concentrations and clay content and semi-quantitatively determined clay mineral species in the sediments. [ABSTRACT FROM AUTHOR]

The World''s largest peripheral foreland basin, developed in front of the rising Himalaya, incorporates a sedimentary pile on the order of 104 m in thickness. Temporal variation in the heavy mineral record exists in the northwestern Himalayan Foreland succession due to a change in the composition of the hinterland. This study was conducted in order to correlate the heavy minerals occurring in sedimentary rocks with those of the present day small rivers/streams flowing exclusively either in the Higher Himalaya or in the Lesser Himalaya. The present study confirms some of the earlier views demonstrating temporal variation in the heavy minerals in the Cenozoic Himalayan Foreland sequences. In addition, their correlation with the heavy minerals of recent river-deposited sediments help in identifying exact sources which became positive areas due to tectonic rising of the Himalaya at different stages.The results suggest that the heavy mineral suites were mainly contributed from the low- to medium-grade metamorphic provenance at the initial stages and from the high-grade metamorphic provenance at the later stage of foreland sedimentation. This may be associated with the shifting of the channel pattern from axial to transverse as mountain chains grown in width over time. Also, Higher Himalayan Baspa river sediments contain staurolite and kyanite, in addition to tourmaline, epidote, garnet and other minor heavy minerals whereas Bhuzas stream sediments contain sillimanite in addition to staurolite, kyanite, tourmaline, epidote and garnet. Similarities in the heavy minerals exclusively derived from the Higher/Lesser Himalaya, and the Cenozoic heavy minerals of the Himalayan Foreland in the Jammu area suggest that staurolite is a contribution of the hinterland during the earlier stage and kyanite is a contribution of the Higher Himalaya during the later stage. Among the three mineral markers, the sillimanite-bearing suite was derived at a still later stage from the Lesser Himalaya and/or Higher Himalaya due to successive emplacement of the thrust sheets. [Copyright &y& Elsevier]