Triassic palaeosols in the upper narrabeen group of New South Wales

Detailed study of palaeosols in the sea cliffs between Long Reef and Palm Beach, north of Sydney, has given a much clearer idea of the environment and climate of the area during the late Scythian to early Anisian portion of Triassic time.

At the base of the exposed succession, kaolinitic clayey soils with red B horizons were formed on volcanogenic sediments derived from the old Gerringong volcanic ridge to the east. The red Bald Hill Claystone consists largely of soil material, both in place and resorted. These were grey‐brown podzolic soils (ferrods) formed on well‐drained sites under coniferous forest. Humic gleys (fibrists) within the overlying Garie Formation were probably lowland catenary equivalents formed under Dicroidium, Voltziopsis, and equisetalean swamp woodland.

These soils were drowned by the relative rise of the Narrabeen lagoonal complex and the concomitant southward growth of sediments of the Gosford Delta. These sediments formed the lower Newport Formation, of clean quartz‐lithic sandstone and grey kaolinite‐illite shale, derived from an extensive source land to the north and west. The most widespread soils in the delta were gleyed podzolic soils (aquods) under Dicroidium heath. Younger soils of a similar type (alluvial soils or aquents) also supported Dicroidium heath in low‐lying areas and Pleuromeia meadows in interdistributary bays. On slightly more elevated areas a more oxidized gleyed podzolic soil (ochrept) developed. On clayey levees, grey clay soils (fluvents) formed under a Dicroidium flora locally dominated by Taeniopteris lentriculiformis.

Few palaeosols are preserved in the upper Newport Formation and Hawkesbury Sandstone because of the more frequent channel reworking of the floodplain during their deposition.

The dominance of podzols is compatible with a cool temperate climate.     

Late cainozoic environments of part of Northeastern South Australia∗

In the Lake Frome area of South Australia there is a sedimentary sequence of non‐marine (or possibly distant marginal marine) pale‐green to grey, fine elastics and carbonates (Namba Formation). The base of these deposits is Medial Miocene in age and they are overlain unconformably by Pleistocene (and ? Pliocene) sediments. The Miocene sequence is equivalent to the Etadunna Formation of the Lake Eyre Basin, and the clay mineralogy is similar.

Combining evidence from mineralogy, palynology, and vertebrate palaeontology, a warm high‐rainfall climate operating on a subdued topography is indicated for the lower part of the Miocene Lake Frome sequence. This caused the illite‐chlorite‐kaolinite suite of the largely Precambrian provenance to be transformed to smectite and randomly‐interstratified clay. A palygorskite‐dolomite assemblage accumulated in alkaline lakes of extreme marginal marine situation during periods of seasonal dry intervals superposed on the previous climate.

A change to illite‐dominated clay, stratigraphically about halfway up the sequence, occurred simultaneously with initial uplift of the Flinders Ranges. These ranges were previously represented by, at the most, a region of low hills. Uplift, without intervention of climatic change, is sufficient to alter the clay mineralogy by promoting increased leaching. Higher in the sequence, and correlated with the major phase of uplift in the Flinders Ranges, smectite re‐appears. In this case the clay suite is believed to have resulted from increased aridity. The smectite‐rich sediments accumulated above the water table in extensive fan and mud‐flow deposits.

The Neogene sequence records a major palaeogeographic change from low energy rivers, swamps, and lakes in a low relief terrain, probably connected to the sea, to a landscape approaching that of the present during Miocene‐Pliocene times. When the Pleistocene Millyera Formation accumulated, the landscape resembled the present, though the ancestral Lake Frome was larger, and rainfall higher.     

Surface geochemical and biogeochemical expression of base‐metal mineralization at Woodlawn,New South Wales,Australia

The presence of base‐metal mineralization at Woodlawn was first recognised early in 1968 when a roadside reconnaissance geochemical sampling survey, conducted over felsic volcanic rocks in the Goulburn‐Tarago area, encountered anomalous B horizon soils containing up to 200 ppm Cu, 800 ppm Pb and 300 ppm Zn. Regional soil thresholds have been determined at 50 ppm Cu, 90 ppm Pb and 50 ppm Zn. Chip samples from the subsequently located gossan revealed up to 2000 ppm Cu, 8000 ppm Pb and 2000 ppm Zn, 500 ppm Sn, 25 ppm Ag and 3000 ppm As.

The first grid B horizon soil geochemical survey was conducted in 1968 over the gossan and surrounding area, and repeated with closer spaced sampling in the first half of 1970. The first survey delineated strong Cu (to 1000 ppm) and Pb (to 2500 ppm) anomalies coincident with the gossan zone, and intense hydromorphic zinc anomalies (to 3000 ppm) located down slope from the gossan in residual clay‐soils derived from dolerite bedrock. Threshold values have been determined at 140 ppm Cu, 700 ppm Pb and 580 ppm Zn. Ag and Sn in B horizon soils show pronounced anomalies coincident with the gossan and are suitable metals for geochemical target definition. Of fourteen trace elements determined in 1974 from B and C horizon soils on two lines across the ore zone Cu, Pb, Zn, Se, Ba, Sn and Ag show direct correlation with the mineralization, whereas Cd and Mn show moderate hydromorphic dispersion, having accumulated principally in clay soils derived from dolerite weathering. As, Sb and Bi, whilst responding over the ore zone, show elevated values in soils over hanging‐wall units; Ni and Co show maximum levels in soils over dolerite bedrock.

Bark and leaves of Acacia mearnsii, collected from a line across the gossan, contain anomalous levels of Cu, Pb, Zn, Sn and Ti near the ore zone, and weaker, but clearly anomalous Mn and Ni levels over dolerite bedrock. Both bark and leaves of Acacia mearnsii reflect the presence of concealed mineralization. The shrub Solanum linearifolium grows preferentially over and close to the Woodlawn ore zone, where it contains up to 840 ppm Cu, 250 ppm Pb, 7300 ppm Zn, 6 ppm Sn and 250 ppm Ti in leaf ash compared with levels of 200 ppm Cu, 2 ppm Pb, 400 ppm Zn, 0.8 ppm Sn and 60 ppm Ti in plants growing 1.5 km from the ore zone. This shrub has potential as an indicator of base‐metal mineralization.     

The geology and palaeohydrology of the Kow Swamp fossil hominid site,Victoria, Australia

During a lake‐full phase at the end of the Pleistocene Period, lacustrine silts and aeolian sands were deposited around the eastern margins of Kow Swamp. These sediments have yielded the remains of a large population of early Australian man, retaining certain archaic Homo erectus characteristics.

The lake‐lunette system in which the burials were made provides a geographically isolated situation for the examination of late Pleistocene and Holocene hydrological changes which have left their imprint on the sediments, soils and vegetation.     

Geochemical characteristics of stream sediments,sediment fractions,soils, and basement rocks from the Mahaweli River and its catchment,Sri Lanka

Geochemical variations in stream sediments (n = 54) from the Mahaweli River of Sri Lanka have been evaluated from the viewpoints of lithological control, sorting, heavy mineral concentration, influence of climatic zonation (wet, intermediate, and dry zones), weathering, and downstream transport. Compositions of soils (n = 22) and basement rocks (n = 38) of the catchment and those of <180 μm and 180–2000 μm fractions of the stream sediments were also examined. The sediments, fractions, soils and basement rocks were analyzed by X-ray fluorescence to determine their As, Pb, Zn, Cu, Ni, Cr, V, Sr, Y, Nb, Zr, Th, Sc, Fe₂O₃, TiO₂, MnO, CaO, P₂O₅ and total sulfur contents. Abundances of high field strength and ferromagnesian elements in the sediments indicate concentration of durable heavy minerals including zircon, tourmaline, rutile, monazite, garnet, pyriboles, and titanite, especially in <180 μm fractions. The sediments show strong correlation between Ti and Fe, further suggesting presence of heavy mineral phases containing both elements, such as ilmenite and magnetite. The basement rocks range from mafic through to felsic compositions, as do the soils. The river sediments lack ultrabasic components, and overall have intermediate to felsic compositions. Elemental spikes in the confluences of tributary rivers and high values in the <180 μm fractions indicate sporadic inputs of mafic detritus and/or heavy minerals to the main channel. Al₂O₃/(K₂O + Na₂O) and K₂O/Na₂O ratios of the sediments and LOI values of the soils correlate well with the climatic zones, suggesting intense weathering in the wet zone, lesser weathering in the intermediate zone, and least weathering in the dry zone. Low Sr and CaO contents and Cr/V ratios in stream sediments in the wet zone also suggest climatic influence. Fe-normalized enrichment factors (EFs) for As, Pb, Zn, Cu, Ni and Cr in stream sediments in the main channel are nearly all <1.5, indicating there is no significant environmental contamination. The chemistry of the sediments, rocks and the soils in the Mahaweli River are thus mainly controlled by source lithotype, weathering, sorting, and heavy mineral accumulation.     

Influence of lake water pH and alkalinity on the distribution of core and intact polar branched glycerol dialkyl glycerol tetraethers (GDGTs) in lakes

Branched glycerol dialkyl glycerol tetraethers (GDGTs) are bacterial membrane lipids, ubiquitously present in soils and peat bogs, as well as in rivers, lakes and lake sediments. Their distribution in soil is controlled mainly by pH and mean annual air temperature, but the controls on their distribution in lake sediments are less well understood. Several studies have found a relationship between the distribution of branched GDGTs in lake sediments and average lake water pH, suggesting an aquatic source for them, besides that for soil transported to the lake via erosion. We sampled the surface water suspended particulate matter (SPM) from 23 lakes in Minnesota and Iowa (USA), that vary widely in pH, alkalinity and trophic state. The SPM was analyzed for the concentration and distributions of core lipid (presumed fossil origin) and intact polar lipid (IPL, presumed to derive from living cells) branched GDGTs. The presence of substantial amounts (18–48%) of IPL-derived branched GDGTs suggests that branched GDGTs are likely of autochthonous origin. Temperature estimates based on their distribution using lake-specific calibrations agree reasonably with water temperature at time of sampling and average air temperature of the season of sampling. Importantly, a strong correlation between the distribution of branched GDGTs and lake water pH was found (r² 0.72), in agreement with a predominant in situ production. An stronger correlation was found with lake water alkalinity (r² 0.83), although the underlying mechanism that controls the relationship is not understood. Our results raise the potential for reconstructing pH/alkalinity of past lake environments, which could provide important knowledge on past developments in lake water chemistry.     

Magnetic,geochemical and mineralogical properties of sediments from karstic and flysch rivers of Croatia and Slovenia

The aim of the present work was to investigate links between the low-field magnetic susceptibility (MS) and chemical and mineral composition of sediments from several Croatian and Slovenian rivers, as well as to determine possible anthropogenic influence on these sediments. MS measurements are a fast and simple method, which serves as a proxy for the estimation of pollution in different environmental systems. The investigated rivers are predominantly unpolluted rivers from Croatian and Slovenian karstic and flysch areas, which belong to the Adriatic or the Black Sea watersheds: the Dragonja, the Mirna, the Ra?a, the Ri?ana, the Reka, the Rak, the Cerkni?nica, the Unec and the Ljubljanica rivers. It was assumed that, due to their mostly unpolluted status, they could serve as a database for natural MS background values for this region. For comparison, several rivers and a lake from the Celje old metallurgic industrial area (Slovenia) were also investigated: the Savinja, the Hudinja, the Voglajna rivers and Slivni?ko Lake. They form a sub-basin of the Sava River drainage basin. Sediments of the clean karstic and flysch rivers showed extremely low MS values, with mass susceptibility values ranging from 0.58 × 10^?7 to 5.11 × 10^?7 m³/kg, and isothermal remanent magnetism (IRM) values ranging from 0.71 to 7.88 A/m. In the Celje industrial area, river sediments showed much higher MS values, with mass susceptibility values ranging from 1.31 × 10^?7 to 38.3 × 10^?7 m³/kg, and IRM values ranging from 0.91 to 100.42 A/m. The highest MS value was found in the Voglajna River at Teharje-?tore, a point which showed a significant number of anomalies of toxic metals in earlier investigations. Semiquantitative determination of relations between grain size and concentration of magnetite was performed using the Thompson-Oldfield method. X-ray diffraction (XRD) mineralogical analysis showed that sediments of the Celje area have mostly quartz as major mineral, with relatively small amount of carbonate minerals, while in sediments of karstic rivers carbonate minerals prevail. Statistically significant correlations were obtained between MS and Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Ba in the Slovenian karstic region and between MS and Cr, Fe, Co, Ni and Zn in flysch drainage basins. On the contrary, no correlation of MS and Hg content was obtained.     

Towards developing sediment quality assessment guidelines for aquatic systems: An Australian perspective

Sediment at the sediment‐water interface of natural and man‐made waterways forms an integral part of the ecosystem because it is affected by a continuous flux of physical, chemical and biological components between the sediment, interstitial water and the overlying water column. Aquatic sediments contain records of past and present urban and rural runoff, chemical discharges and spills. In recent years sediment quality has received increasing attention following identification of the role of sediment as both a sink for pollutants and as a contaminant source with potential impacts on the quality of receiving waters. Research has indicated that the processes leading to remobilization of contaminated sediments in upstream reaches of a waterway may, through time, exert a significant influence on water quality in the downstream reaches. This, together with the cumulative effects due to contaminant input from point and non‐point source discharges, have dramatic effects on water quality and thus on ecosystem structure and functioning.

The problems associated with elevated concentrations of many hazardous organic and inorganic compounds have resulted in the establishment of aquatic sediment quality criteria and management guidelines in many overseas countries, with the objectives being the reduction and elimination of adverse environmental effects and human health risks associated with contaminated sediments. Whereas more than 70% of the Australian population is clustered around the coastal waterways, little is known about the role of sediments as a repository of environmental pollutants and/or as a source of adverse impacts on water quality and the health of our rivers. The paucity of knowledge on the quality of aquatic sediment highlights the need for the development of coherent guidelines for sediment quality assessment and management of contaminated sites, which are consistent with Australian environmental conditions and land use features.

A comparative evaluation of sediment quality information from eight coastal rivers along the east coast of Australia, presented in this paper, indicates the possibility for establishing a framework for regional sediment quality assessment. This may be achievable by using textural and compositional attributes of bottom sediments in depositional areas to develop databases on the loading and concentration trends of nutrients and contaminants. Regional variability in sediment quality determinants are shown to reflect the influence of catchment hydrology, lithology and land use on nutrient and contaminant concentration trends. Locally, the loading and partitioning behaviour of sediment‐bound contaminants is largely controlled by the nature and the extent of interactions occurring at the sediment‐water interface within individual depositional units.

The concept of ‘Sediment Effect Zone’ is introduced to provide a compartmental approach to the characterization of aquatic sediments and depositional environments in different hydrologic zones. This approach offers a rational basis for follow‐up chemical and biological assessments to establish sediment quality standards and management guidelines. Because of the complex influences of environmental, methodological and statistical factors on defining the sediment variability, the need for implementing proper quality control measures from early stages of design of a sediment quality assessment program is highlighted.     

Geochemical and Microbiological Analysis of Sambe Hot Springs,Shimane Prefecture,Japan

Microbiological contribution to the formation of the manganese deposits in Sambe hot springs, Shimane, was investigated in combination with water chemistry, characterization of sediments and microbial community structure. Analysis of bacterial and fungal community structure based on DNA extracted from a Mn‐oxidizing enrichment culture indicated close matches with Pseudomonas putida, Phoma sp. and Plectosphaerella cucumerina, all Mn‐oxidizing microorganisms. These sediments were poorly crystalline and formed at neutral pH values, which is characteristic of biogenic precipitates. The EPMA results demonstrated a positive correlation between Mn and Ba contents in well‐crystalline Mn oxide grains. Substantial Ba contents were observed inside Mn oxide grains. These findings indicated that Ba contents in sediments are influenced by not only aqueous Ba²⁺ concentrations but also crystallinity of biogenic birnessite. Barium would be incorporated in birnessite during biomineralization.     

A reassessment of late glacial – Holocene diatom oxygen isotope record from Lake Baikal using a geochemical mass‐balance approach

We present a new palaeoenvironmental record of hydrological variability in Lake Baikal, based on re‐modelled δ¹⁸O_diatom values of diatom silica (δ¹⁸O_modelled), where the residual contaminants are identified and compensated for using electron optical imaging and whole‐sample geochemistry. δ¹⁸O_modelled interpretations are based on the balance between rivers with high δ¹⁸O values and rivers with low δ¹⁸O values. Isotopic variability is related to latitudinal differences in precipitation which feed these rivers. The δ¹⁸O_modelled record suggests that rather moist conditions prevailed in the Lake Baikal region during the latter stages of the Younger Dryas. Throughout the Holocene, episodes of low δ¹⁸O_modelled values are, in general, in good agreement with increases in percentage haematite‐stained grains in North Atlantic sediments (indicative of ice‐rafted debris events). Rivers with southerly catchments dominate fluvial input especially between c. 3.3 and 2 cal ka BP, concurrent with high precipitation in the Lake Baikal region. Copyright © 2011 John Wiley & Sons, Ltd.     

Environmental magnetic and geochemical characteristics of Chennai coastal sediments,Bay of Bengal,India

In this study, environmental magnetic, heavy metal and statistical analyses were conducted on 21 surface sediments collected from Chennai coast, India, to examine the feasibility of heavy metal pollution using magnetic susceptibility. The Chennai coastal sediment samples are dominated by ferrimagnetic minerals corresponding to magnetite-like minerals. The percentage of frequency dependent magnetic susceptibility reflects the presence of super-paramagnetic/single domain magnetic minerals in Chennai harbour, Cooum and Adayar rivers sediments. High pollution load index in sample E1, E2, CH7, C11, C12 and A16 is mainly due to anthropogenic activities such as, harbour activities, Cooum and Adayar rivers input and industrial effluent. Factor analysis shows that the magnetic concentration dependent parameters (χ, χ _ARM and SIRM) covary with the heavy metal concentrations, suggesting that the input of magnetic minerals and heavy metals in Chennai coastal sediments are derived from the same anthropogenic sources. Strong correlation obtained between pollution load index (PLI) and concentration dependent parameters (χ, χ _ARM and SIRM) for the polluted samples with magnetic susceptibility excess of 50×10^− 8 m³kg^− 1. Significant correlations between heavy metals and magnetic susceptibility point out the potential of magnetic screening/monitoring for simple and rapid proxy indicator of heavy metal pollution in marine sediments.     

Evaluation of secondary compression of sands and silts from CPTU

The estimate of secondary compression behaviour of sandy and silty deposits is not routinely taken into account in the classical settlement calculation, due to its generally limited contribution to the total amount of strains. However, such soils exhibit a non-negligible time-dependent behaviour and the prediction of their long-term response may sometimes be important.

This paper explores the capability of the piezocone test as an effective tool to estimate the one-dimensional secondary compression characteristics of sands and silts. The approach is mainly based on the observation that frictional response essentially governs both secondary compression of granular soils and cone resistance, hence it seems reasonable to establish a valid correlation among them.

The study uses part of the field data assembled over the last years at the Treporti Test Site (Venice, Italy), within an extensive research project aimed at analysing the stress-strain-time response of the predominantly silty sediments forming the Venetian lagoon subsoil.

Empirical, site-specific correlations for estimating the secondary compression coefficient from cone resistance are proposed. The regression analyses indicate that the estimate is slightly improved if the cone resistance-based correlations include a variable accounting for the different pore pressure response associated to the drainage conditions around the advancing cone.     

Geochemistry of large river suspended sediments: silicate weathering or recycling tracer?

This study focuses on the major and trace element composition of suspended sediments transported by the world’s largest rivers. Its main purpose is to answer the following question: is the degree of weathering of modern river-borne particles consistent with the estimated river dissolved loads derived from silicate weathering?In agreement with the well known mobility of elements during weathering of continental rocks, we confirm that river sediments are systematically depleted in Na, K, Ba with respect to the Upper Continental Crust. For each of these mobile elements, a systematics of weathering indexes of river-borne solids is attempted. A global consistency is found between all these indexes. Important variations in weathering intensities exist. A clear dependence of weathering intensities with climate is observed for the rivers draining mostly lowlands. However, no global correlation exists between weathering intensities and climatic or relief parameters because the trend observed for lowlands is obscured by rivers draining orogenic zones. An inverse correlation between weathering intensities and suspended sediment concentrations is observed showing that the regions having the highest rates of physical denudation produce the least weathered sediments. Finally, chemical and physical weathering are compared through the use of a simple steady state model. We show that the weathering intensities of large river suspended sediments can only be reconciled with the (silicate-derived) dissolved load of rivers, by admitting that most of the continental rocks submitted to weathering in large river basins have already suffered previous weathering cycles. A simple graphical method is proposed for calculating the proportion of sedimentary recycling in large river basins. Finally, even if orogenic zones produce weakly weathered sediments, we emphasize the fact that silicate chemical weathering rates (and hence CO₂ consumption rates by silicate weathering) are greatly enhanced in mountains simply because the sediment yields in orogenic drainage basins are higher. Hence, the parameters that control chemical weathering rates would be those that control physical denudation rates.     

Rare earth elements in fine-grained sediments of major rivers from the high-standing island of Taiwan

Thirty-eight sediment samples from 15 primary rivers on Taiwan were retrieved to characterize the rare earth element (REE) signature of fluvial fine sediment sources. Compared to the three large rivers on the Chinese mainland, distinct differences were observed in the REE contents, upper continental crust normalized patterns and fractionation factors of the sediment samples. The average REE concentrations of the Taiwanese river sediments are higher than those of the Changjiang and Huanghe, but lower than the Zhujiang. Light rare earth elements (LREEs) are enriched relative to heavy rare earth elements (HREEs) with ratios from 7.48 to 13.03. We found that the variations in (La/Lu)_UCC–(Gd/Lu)_UCC and (La/Yb)_UCC–(Gd/Yb)_UCC are good proxies for tracing the source sediments of Taiwanese and Chinese rivers due to their distinguishable values. Our analyses indicate that the REE compositions of Taiwanese river sediments were primarily determined by the properties of the bedrock, and the intensity of chemical weathering in the drainage areas. The relatively high relief and heavy rainfall also have caused the REEs in the fluvial sediments from Taiwan to be transported to the estuaries down rivers from the mountains, and in turn delivered nearly coincidently to the adjacent seas by currents and waves. Our studies suggest that the REE patterns of the river sediments from Taiwan are distinguishable from those from the other sources of sediments transported into the adjacent seas, and therefore are useful proxies for tracing the provenances and dispersal patterns of sediments, as well as paleoenvironmental changes in the marginal seas.     

Investigating the origin of Pb pollution in a terrestrial soil–plant–snail food chain by means of Pb isotope ratios

Lead isotope ratios were used to trace the origin of Pb in a soil–plant (Urtica dioica)–snail (Cepaea nemoralis) food chain in two polluted locations in the floodplains of the rivers Meuse and Rhine (Biesbosch National Park) and one reference location in the Netherlands. Lead isotope ratios and concentrations were determined in soil, litter, plant leaves, snails, rainwater and airborne particulate matter. Anthropogenic Pb in the soils of all locations was found to be derived from deposition of Pb polluted river sediments. Discharging rivers influenced the reference location before being reclaimed from the sea. The river sediment contains anthropogenic Pb from various sources related to industrial activities in the hinterland of the rivers Meuse and Rhine. Lead in the atmosphere contributed substantially to Pb pollution and Pb transfer in plant leaves and snails in all locations. Lead pollution in plant leaves and snails can be explained from a mixture of river sediment-Pb and atmospheric Pb from various transfer routes that involve low concentrations.     

Natural variations of δSi ratios during progressive basalt weathering, Hawaiian Islands

Silicon stable isotopes can be used to trace the biogeochemical pathways of Si as it moves from its continental sources to its sink in ocean sediments. Along the way, Si is incorporated into clay minerals, taken up by plants where it forms plant opal, and leached into rivers, the major land-to-ocean conduit. Compared to igneous rocks, the waters that drain continents are enriched in heavy Si isotopes, but the mechanisms that control fractionation have not been elucidated. We studied Si isotope fractionation along a 4 million yr basaltic soil chronosequence on the Hawaiian Islands. Using the natural context of these samples in combination with laboratory experiments, we demonstrate that the isotopic composition of dissolved Si in weathering systems is determined by the combined effects of rock disintegration, clay mineral neosynthesis, and Si biocycling. Weathering preferentially releases ²⁸Si into solution, whereas secondary mineral formation preferentially removes ²⁸Si from solution. In humid environments, leached soils have lost large amounts of this soluble Si, thus creating a net loss of ³⁰Si from the entire soil system. As soils develop and greater fractions of Si reside in neoformed clay minerals, δ³⁰Si_{bulk soil} values change progressively toward more negative values; basalt δ³⁰Si values are about −0.5‰, but older soils have δ³⁰Si values up to −2.5‰. The difference between the solid and solution δ³⁰Si values remains more or less constant with progressive weathering, and therefore, soil water from older soils has a more negative δ³⁰Si composition. In the upper horizons of the Hawaiian soils, this weathering-driven δ³⁰Si shift is modified by the addition of unweathered primary minerals via dust, carrying δ³⁰Si values of about −0.5‰, and by biocycling of Si via plants, producing negative δ³⁰Si values in phytoliths and positive δ³⁰Si values in soil solutions derived from upper horizons. Due to the high concentrations of dissolved Si in these near-surface layers, rivers have more positive δ³⁰Si values than predicted based on the weathering status of the lower horizons. When combined with published δ³⁰Si values from large rivers worldwide, we find that the results from Hawaii point to weathering control of Si isotopes delivered to the oceans, and thus, to an important continent-ocean linkage that warrants further investigation.     

Variability of the metal content of flood deposits

Fresh flood deposits were sampled in the flood-plains of two river systems, the River Meuse, with a catchment area of 33,000 km² and the River Geul, with a catchment area of 3,000 km². As a result of industrial and mining activities, both rivers have a history of severe metal pollution, especially with zinc, lead, and cadmium. The flood deposits of both rivers are heterogeneous mixtures of contaminated bottom sediments (with relatively long residence times in the river) and clean sediments derived from soil erosion on agricultural cropland (with very short residence times). An additional source of sediment is formed by erosion of older, locally highly contaminated streambank deposits. These older sediments are polluted as a result of solid waste disposal containing metalliferous ore and tailings in the sand fraction. This is especially the case in the River Geul, which drains an old zinc and lead mining area. The metal content of the Meuse sediments, however, originates largely from liquid industrial wastes and occurs mainly in the clay fraction. For this reason, the positive correlation between textural composition, organic matter content, and heavy metal concentration, which is often reported, was not observed, and normalization of the metal content was not possible. Nevertheless, a clear decrease of contamination was noticed along the River Geul; this trend was absent along the River Meuse. An attempt has been made to model the longitudinal decay pattern for each of the investigated havey metals.     

U–U–Th disequilibria and timescale of sedimentary transfers in rivers: Clues from the Gangetic plain rivers

This study uses ²³⁸U–²³⁴U–²³⁰Th disequilibria in river sediments in order to constrain the transfer times of sediments in alluvial plains of rivers from Himalaya and the Gangetic plain. From the observed distributions we infer sediment transfer times of about 100 ka in the Gangetic plain for rivers taking their source in the Himalayan chain, and longer transfer of about 160–250 ka for foothill-fed rivers. This difference is probably related to the difference in the sediment transport dynamics of these two types of rivers.     

Basalt weathering and trace elements migration in the boreal Arctic zone

Chemical weathering of basalts in the Putorana Plateau, Central Siberia, has been studied by combining chemical and mineralogical analysis of solids (rocks, soils, river sediments and suspended matter) and fluid solution chemistry in order to quantify CO₂ consumption and to assess the major factors controlling basic rock weathering under permafrost-dominated taiga climate. The chemical status of  40 major and trace elements (TE) in pristine boreal rivers and interstitial solutions of permafrost soils has been investigated using in-field ultrafiltration procedure. This revealed strong relationships between concentration of TE and that of major inorganic components of colloids, i.e., Fe or Al. Decomposing plant litter and permafrost thawing are considered important sources of most major and trace elements in Arctic rivers during summertime.     

Post‐deposition diffusion of 137Cs in lake sediment: Implications for radiocaesium dating

Peak activities of radiocaesium (¹³⁷Cs) in lake sediments have frequently been used to infer the ages of sediments deposited in the 1960s (¹³⁷Cs derived from nuclear bomb testing) or in 1986 (Chernobyl derived ¹³⁷Cs). Records of the vertical distribution of ¹³⁷Cs in sediments can thus be used to provide accurate dates for a critical period in which palaeoecological reconstructions often overlap contemporary monitoring data. However, knowledge regarding how the distribution of ¹³⁷Cs in sediments is affected by post‐depositional processes is limited to interpretations based on the ¹³⁷Cs distribution in sediments sampled at a single given date. This study assesses the extent to which the ¹³⁷Cs record in annually laminated (varved) lake sediments is affected by post‐depositional diffusion, using 11 archived sediment cores sampled between 1986 and 2007. The sediment record reveals how Chernobyl ¹³⁷Cs incorporated into the 1986 varve diffused downwards in the core at a decreasing rate over time, whereas the surface sediments continued to receive inputs of ¹³⁷Cs mobilized from the catchment soils or lake margin. In spite of these processes, all cores post‐dating the Chernobyl accident had a clear and well‐resolved peak in the 1986 varve, justifying the use of this feature as a fixed chronostratigraphic feature. Because of the very high levels of Chernobyl fallout at this site, downwards migration of Chernobyl ¹³⁷Cs has, however, completely masked the nuclear weapons ¹³⁷Cs fallout peak that had been clearly preserved in the 1964 varve of a pre‐Chernobyl core sampled just three weeks before the Chernobyl accident. In consequence, the weapons fallout marker is likely to be of little use for determining ¹³⁷Cs dates in areas strongly affected by high levels of Chernobyl fallout.