Geochemistry

The study was carried to determine the mineralogy of soils of different geomorphic units for providing the more detailed information needed to improve agricultural production in north-eastern part of Haryana. The soils of the study area were slightly acidic to strongly alkaline in reaction (6-9.4). The cation exchange capacity and electrical conductivity varied from 3.10-26.80 cmol (+) kg-1 and 0.16-1.20 dSm-1, respectively. In general, the soils were siliceous in nature with SiO2 ranging from 68.60 to 87.90 percent. The soil samples from surface and subsurface diagnostic horizons were studied through X-ray diffraction. In fine sand, quartz was the dominant mineral followed by feldspars, muscovite, hornblende, tourmaline, zircon, biotite, iron ores and sphene. In silt fraction, quartz was the dominant mineral followed by mica, feldspars, chlorite, kaolinite, interstratified and traces of smectite and vermiculite. Semi-quantitative estimation of clay fraction indicated that illite wa...

An X-ray absorption spectroscopy (XAS) study of the Fe local environment in natural amethyst (a variety of a-quartz, SiO 2 ) has been carried out. Room temperature measurements were performed at the Fe K-edge (7,112 eV), at both the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions. Experimental results were then compared with DFT calculations. XANES experimental spectra suggest Fe to occur mainly in the trivalent state, although a fraction of Fe 2? is identified. EXAFS spectra, on the other hand, reveal an unusual short distance for the first coordination shell: \Fe-O[ = 1.78(2) A ˚, the coordination number being 2.7(5). These results allow to establish that Fe replaces Si in its tetrahedral site, and that numerous local distortions are occurring as a consequence of the presence of Fe 3? variably compensated by protons and/or alkaline ions, or uncompensated. The formal valence of Fe, on the basis of both experimental and DFT structural features, can be either 4? or 3?. Taking into account the XANES evidences, we suggest that Fe mainly occurs in the trivalent state, compensated by protons, and that a minor fraction of Fe 4? is stabilised by the favourable local structural arrangement.

As the UK's National marine data centre, a key responsibility of the British Oceanographic Data Centre (BODC) is to provide data management support for the scientific activities of complex multidisciplinary long term research programmes. Since the initial cruise in 1995, the NERC funded Atlantic Meridional Transect (AMT) project has undertaken 18 north-south transects of the Atlantic Ocean. As the project has evolved there has been a steady growth in the number of participants, the data volume, complexity and the demand for data. BODC became involved in AMT in 2002 at the beginning of phase II of this programme and since then has provided continuous support to both the AMT and wider scientific community through rescue, quality control, processing and access to the data. The data management comprises a team of specialist data managers using a sophisticated infrastructure of software and hardware to manage, integrate and serve the physical, biological and chemical data. Here, we discuss the approach adopted, techniques applied and some guiding principles for management of large multi-disciplinary programmes.

The seismic stratigraphy of the western McMurdo Sound region has been reevaluated in response to the apparent 8 m y . discrepancy in the age of seismic units traced between the CRP-1 drillhole located off Cape Roberts and the CIROS-1 drillhole, located 70 km further south. All the available seismic reflection in the region, including new single and multi-channel seismic data recorded in the region in 1996 by RIV N B PALMER, have been compiled and reanalysed to develop a consistent interpretation of the seismic units in the region, using the seismic stratigraphy of . The interpretation has been based on the original interpretation of seismic units in the data recorded by the RIV S. P. LEE (Cooper & Davey, 1987) and has been traced across the region to the CRP-1 drillsite. A crucial correlation at the CRP-1 site is for the boundary between the Units V3 and V4. This unconformity lies at depth east of the drillsite and the associated reflection event has been traced to the CRP-l site in two ways; one directly across the Roberts Ridge, where it has to be traced through the seafloor multiple, and the second through deep water north of Roberts Ridge. The two correlation pathways result in a discrepancy of about 100 m where the unconformity intersects CRP-l. If the correlation across Roberts Ridge is correct then the strata equivalent to 3 18 m in CIROS-1 will, at the CRP-1 site, be 21 thick and the V 3 N 4 boundary lies 163 mbsf. If the alternative is correct then the equivalent strata at the CRP-1 site will have also reduced in thickness, but only to about 120 m, and the V3N4 boundary lies around 250 mbsf.

The Mersin ophiolite, represented by approximately 6-km-thick oceanic lithospheric section on the southern flank of the Taurus calcareous axis, formed in the Mesozoic Neo-Tethyan ocean some time during Late Cretaceous in southern Turkey. The ultramafic and mafic cumulates having over 3 km thickness consist of duniteBchromite, wehrlite, clinopyroxenite at the bottom and pass into gabbroic cumulates in which leucogabbro, olivine-gabbro and anorthosite are seen. Crystallization order is olivine (Fo 91-80 )Bchromian spinel (Cr8 60-80), clinopyroxene (Mg8 95-77 ), plagioclase ) and orthopyroxene (Mg8 68- 77 ). Mineral chemistry of ultramafic and mafic cumulates suggest that highly magnesian olivines, clinopyroxenes and absence of plagioclase in the basal ultramafic cumulates are in good agreement with products of high-pressure crystal fractionation of primary basaltic melts beneath an island-arc environment. Major, trace element geochemistry of the cumulative rocks also indicate that Mersin ophiolite was formed in an arc environment. Coexisting Ca-rich plagioclase and Forich olivine in the gabbroic cumulates show arc cumulate gabbro characteristics. Field relations as well as the geochemical data support that Mersin ophiolite formed in a supra-subduction zone tectonic setting in the southern branch of the Neo-Tethys in southern Turkey.

The coral reef ecosystems at Palau Island have attracted growing attention recently. However, there are still many uncertainties about the coral reef ecosystems there because the characteristics of nutrient dynamics and primary production are expected to be largely different between shallow fringing coral reefs distributed in the Southern Japan and barrier reefs with deeper lagoon at Palau Island. Especially, how physical parameters such as light intensity, current velocity and wave strength, which vary depending on the water depth, control the primary production and material transport in the lagoon area is not yet well known. In this study, we investigated nitrogen cycles in the lagoon system combining the observations and several process studies: 1) distribution of nutrients and dissolved organic nitrogen in the water column, 2) depth-dependent characteristics of the surface sediment such as particle size, organic matter contents and nutrient profiles in the porewater, 3) flux of ...

The Meguma Zone of southern Nova .Scotia is the most outboard lithotectonic terrane of the northeastern Appalachians. Peraluminous granitoid plutons doininate a late Devonian episode of magmatic activity, but minor mafic intrusive bodies of roughly the same age also occur in the Meguma Terrane. We propose to classify the granitoid plutons as: (i) Central Plutons, including the South Mountain Batholith, which are ca. 372 my old, late-to post-tectonic, predominantly unfoliated, emplaced into low-grade metamorphic host rocks, generally not spatially associated with mafic intrusions, exclusively peraluminous with polymetallic Sn-W-Mo-U greisen-and vein-doininated mineral deposits, and entirely crustally-derived (sub-Meguma Group source rocks and Meguma Group containination), that probably owe their origin to crustal thickening associated with the collision of the Meguma terrane against the Avalon terrane; and (ii) Peripheral Plutons, at the northeastern and southwestern extremities of the Meguma Zone, which may be slightly older (~3 76 my old), late-tectonic, moderately foliated, emplaced into higher-grade metamorphic host rocks, spatially associated with late Devonian mafic intrusions (LDMls), mostly peraluminous with only liinited Be-pegmatite Inineralization, and ofinixed derivation (sub-Meguma Group source rocks and mantle-derived mafic magmas), that probably owe their origin to the lower to mid-crustal emplacement of subduction-related mafic magmas intruded prior to the final emplacement of the Meguma terrane. This integration and synthesis of the field relations, geochronology, petrology, geocheinistry, and Inineralization for the felsic and mafic magmatism represents a new petrogenetic and tectonic paradigm for the Meguma Zone in the late Devonian.

Rutherford backscattering combined with channeling is used as a measure of the crystalline quality of thin films. For lattice mismatched structures the channeling spectrum implicitly contains the quantitative depth distribution of dislocation defects through a deconvolution analysis that takes into account the rate of dechanneling with depth. We describe a sputtering/depth profiling procedure to extract the defect density which tests this deconvolution procedure. It is shown that the analysis can severely underestimate the defect density at large depths. We show, by further analysis, that this discrepancy can be resolved when energy loss straggling is taken into account. The sputtering/defect profiling procedure is applied to the important system of GaAs grown onto Si.

The comprehensive study of intramountain basins located in the Coastal Cordillera of the continental emergent Andean forearc in Northern Chile, enables the better understanding of the nature and evolution of the upper crustal deformation during the Neogene and Quaternary. A case study is the extensive extensional half-graben Alto Hospicio basin. The basin is cut by the Coastal Cliff, which exposes the deformed Neogene basin fill. Also exposed are several structural systems, some of which affect Quaternary surfaces. The results of the integrated geophysical surveys (Electromagnetic Transient and Gravity) allow us to fully constrain the geometry of the Alto Hospicio basin and the lithological relationship between the subsurface geological units. The structural geology analysis assesses the deformation regimes affecting the faults present in the basin and surrounding area. Altogether evidence a change in the deformation regime from an EW extensional deformation during the Miocene-Pliocene to a NS compression in the Quaternary as is presented in this study. We suggest this deformation change is related to a small change in the convergence vector orientation during the Pliocene.

Phase relations, compositions, and modes of two natural primitive alkaline basalts were determined through experiments performed at 0.8 GPa, temperatures between 1000 and 1310 °C, and nominal water (H 2 O i ) contents varying from < 1 (natural water rock content) to 6 wt.%. The two natural samples used as starting material are high-Mg, moderate-K, alkaline

We have analysed the relationship between the volcanic substratum and magma body emplacement for the acid dome complexes of Latium, Central Italy. Our study shows that the volcanic edifices, which are mainly Pleistocene cryptodomes and related explosive products, were derived from mantle magmas contaminated by crustal materials. The Cimini, Tolfa and Cerite-Manziate dome complexes of Latium show the following characteristics: a shallow laccolith origin; emplacement in basins that have identical tectonic evolution and geological structure; the same magmatic composition and density contrast between magma and host rock; and geochronological data that are inconsistent with field evidence. In the Cimini and Tolfa dome complexes, the deformation induced by shallow intrusions was accompanied by ∼200 m uplift of the sedimentary cover. The estimated pluton infilling time for the Cimini and Tolfa domes is 10 2 years while the strain rate required to uplift their Pliocene overburden by 200 m is ε m ′ ∼ 10 -9 s -1 . The rapid evolution of the dome complexes is consistent with field data that show no relevant interruptions in the volcanic activity and no significant compositional changes in the volcanic products related to the extrusion of the domes. For the Cerite-Manziate dome complex, the minimal input rate of magma favoured a monogenetic style of volcanism, independent of the regional stress conditions.

Two syneruption lahar deposit successions from Quaternary Italian volcanoes are presented, displaying different facies associations interpreted to reflect different water sources. The lahar deposits associated with the White Trachytic Tuff Cupa (WTTC) ignimbrites from the Quaternary Roccamonfina volcano, located 150 km to the southeast of Rome, have been interpreted in terms of rain-generated lahars. The WTTC ignimbrites are made of more than 1 km 3 of loose pumice and lava lithic debris emplaced along the hyperbolic slope of the volcano at ca. 300 ka during an interglacial period characterised by mild and wet climate. The lahar deposits are organised in a coarseningupward, aggradational, and back-stepping succession of medium-to thick-bedded, progressively juvenile-poorer, noncohesive debris flow to fluvial deposits. Box-shaped channels cut the WTTC ignimbrites along the steep upper slopes. Channels are filled with lava lithic-rich fluvial to hyperconcentrated-flow sand and conglomerate, which are interpreted as lag deposits related to processes of bulking due to the removal of light pumice and ash debris from the upper slope. Along the lower slopes of the volcano and in the surrounding ring plains where the average slope inclination decreases to few degrees, lahars emplaced an aggradational succession of bedded, ash-rich, hyperconcentrated-flow deposits entirely derived from WTTC components. The succession coarsens upward with increasing presence of lava-rich conglomerate lenses, fluvial in origin, interpreted to record the progressive restoration through time of the drainage network. The succession is cut by incised gullies filled with polygenetic fluvial deposits which indicate the restoration of intererruption condition. By contrast, the ca. 23-ka, small-volume, Peperino Albano phreatomagmatic eruption from Colli Albani volcano, located 30 km to the southeast of Rome, emplaced a valleyponded, block and ash ignimbrite, which, along the western slope of the volcano, grades laterally into a single, farreaching, thick lahar deposit. The lahar deposit coarsens upward from coarse-ash, hyperconcentrated-flow deposit into a lithic-block-rich, debris-flow deposit. This lahar deposit has been interpreted to be directly derived from a pyroclastic flow and particularly related to the entrance of the pyroclastic flow into a pre-existing maar crater lake along the pyroclastic-flow path. The basal sand-size, hyperconcentrated-flow deposit is interpreted to represent early deposition from the fast frontal flood wave, whereas the coarse lithic-rich debris-flow deposit at the top may represent the rear of the lahar. The separation of the two facies can be related to processes of 'hydraulic sieving' operated by the lake water, which couples with ash particles, leaving behind the coarser fraction.

1. Preservation assessment shows some well-preserved Ordovician trilobite eyes 2. Ordovician trilobite eyes yield  18 O values similar to Ordovician brachiopods 3. SIMS and clumped isotope results indicate diagenetic alteration of trilobites 4. Classic protocols to assess preservation may be inapt for most ancient carbonates

With the support of research projects focusing on sampling and data analysing of different varieties of chemical compounds, wavelength dispersive X-ray fluorescence (WDXRF) technique is commonly used in many research laboratories throughout the world wide to determine the elemental composition of various unknown samples. In the present study, first time we have employed polychromatic S8 TIGER WDXRF spectrometer to study the chemical state analysis in Cl Kα and Kβ 1,3 X-ray emission lines. A Voigt function is used to determine the central peak position of the K shell emission lines in all samples. From the present measurements, it is seen that both positive and negative shifts have been observed in Cl Kα (2.622 keV) and Kβ 1,3 (2.817 keV) emission peaks. It has been also seen that the effective charge, relative line-width and relative intensity ratio I(Kβ 1,3 /Kα) are found proportional with the chemical shift. Furthermore, a parabolic relation is also established between them.

Supposed or potential Devonian igneous rocks in the accretionary complex of southern Chile were investigated using sensitive high-resolution ion microprobe U-Pb dating of zircon, with Hf-and O-isotope analyses of selected grains. Ages of 384 ± 3 and 382 ± 2 Ma are confirmed for two igneous bodies (another having been previously dated at 397 ± 1 Ma). Detrital zircon ages in the host rocks, some associated with Devonian marine fossils, indicate maximum possible sedimentation ages of c. 330 -385 Ma. Devonian ages of 391 ± 10 and 374 ± 3 Ma for plutonic rocks at the western edge of the North Patagonian Massif are somewhat older than those of orthogneisses in the western flank of the Andes near Chaitén (361 ± 7 and 364 ± 2 Ma). O and Hf isotopes indicate that the Devonian intrusions in the accretionary complex crystallized from mantle-derived magmas, whereas those in the North Patagonian Massif show a strong crustal influence, corresponding to oceanic and continental margin subduction environments of magma genesis, respectively. Devonian zircon provenance in the accretionary complex was from the North Patagonian Massif and not from the mantle-derived intrusions, suggesting that the accretionary complex formed an integral part of the Gondwana margin during Devonian-Carboniferous times.

Several fluid circulation events are recorded in the Aquitaine Basin and the Chaînons Béarnais in the Pyrenean belt of southwestern France. Different fluid types are found in all locations studied. The main difference comes from the thermal peak event (rifting), which was more intense in the Chaînons Béarnais close to the exhumed mantle zone. In situ gas analysis associated of fluid inclusions and isotopic (C, O, H, S) analyses show that similar fluids are generated in both systems, although separated by deep structures, e.g. the North Pyrenean Frontal Thrust (NPFT). The Pyrenean tectonic history leads to the compartmentalization of fluid circulations.

Mafic and silicic dyke rocks, which occur in the Ag-U ore district of Jáchymov (Joachimsthal) in the Krušné hory (Erzgebirge) belong to kersantites, diorite porphyries, and granite porphyries, subordinately to spessartites. Dykes of minettes are located outside the district and penetrate the Nejdek-Eibenstock granitic massif. Mafic and silicic dykes exhibit diverse cross-cutting relationships and form in places composite dykes. Lamprophyres correspond to shoshonitic magmas with high abundances of compatible (Cr, Ni) and incompatible elements (Rb, Ba, P). All mafic dykes were affected by a postmagmatic alteration manifested by replacement of primary olivine and pyroxenes by amphibole, biotite and chlorite. Granite porphyries crystallized from leucocratic, weakly peraluminous, low-P magmas with moderate enrichments in Rb and depletions in Ca, Sr and Zr. By contrast, diorite porphyries are intermediate rocks containing 62-65 wt. % SiO 2 whose geological occurrence and major-element composition suggest origin by magma mixing involving lamprophyric and silicic melts, with simultaneous fractionation of biotite. The Th/U ratios in all dyke rocks correspond to chondritic and crustal values and demonstrate that whole-rock uranium contents were neither significantly increased nor affected by contemporaneous mineralization events. The stable isotope composition has been determined for whole rocks (O, C, S) and carbonate minerals (C, O). Wholerock δ 18 O values range between 1.6 to 7.8 ‰ SMOW and do not show any systematic variations with the rock types. The isotopic composition of carbonates is represented by the following values: δ 18 O = 19.6 to 25.0 ‰ SMOW and δ 13 C = -5.7 to -9.0 ‰ PDB. The high positive values of δ 18 O of carbonates are in a remarkable contrast to compositions of primary magmatic carbonates and indicate the carbonate formation during low-temperature hydrothermal event(s). Sulphides in kersantites and diorite porphyries yielded δ 34 S = 0.5 to 6.6 ‰ CDT, which document crustal in addition to mantle source of sulphur consistent with average value in the Saxothuringian crust (~ 5 ‰ CDT). Bulk magnetic susceptibility of dyke rocks shows a general decrease from mafic to silicic magmas in a sequence as follows: kersantites -500, minettes -350, diorite porphyries -350 and granite porphyries -50•10 -6 [SI]. Local increases up to 5000•10 -6 [SI] are due to accessory pyrrhotite in kersantites and diorite porphyries. Mafic dykes in the Western Krušné hory (Erzgebirge) are preferentially found within the Jáchymov-Gera tectonic zone and demonstrate spatial focusing of ascending mantle-derived melts. Such pathways may have served for transfer of ore-forming elements on the crustal scale by fluids of diverse origin.

An overview of the association between lamprophyric intrusions and rare-metal mineralizationGranite-related rare metal districts in orogenic settings are occasionally associated with lamprophyre dikes. We recorded 63 occurrences of lamprophyres in bimodal dike suites of about 200 granite bodies related to rare metal deposits. Most lamprophyres occur in Paleozoic and Mesozoic metallogenic provinces in the northern hemisphere. Lamprophyres which are associated with rare metal deposits are calc-alkaline (kersantites, minettes, spessartites) or more rarely alkaline lamprophyres (camptonites, monchiquites) which occur in the roof zone of complex granitic bodies as pre-granitic, intra-granitic, intra-ore or post-ore dikes. Most lamprophyres are spatially associated with dominant felsic dikes and/or with mafic dikes represented by diorites or diabases. Diorites and lamprophyres occasionally exhibit transitional compositions from one to another. Lamprophyres share common geochemical charact...

The Skouries porphyry Cu±Au deposit, containing an indicated reserve of 206 Mt at 0.54% Cu and 0.80 g/t Au, is hosted by at least four hypabyssal monzonite±porphyry phases. In decreasing age, they are: (1) pink monzonite, (2) main monzonite, (3) intra-mineral monzonite, and (4) late-stage porphyry. Highgrade ore is directly associated with the main and intra-mineral monzonite phases. All intrusive phases are cut by late-stage monzonite dykes that are barren. The monzonites have porphyritic textures with phenocrysts of plagioclase, alkali feldspar and amphibole as well as apatite and titanite microphenocrysts in a ®ne-grained feldspar-dominated groundmass. Mineralized samples are aected to varying degrees by potassic alteration, ranging from weak biotite±magnetite disseminations, through cross-cutting veinlets of hydrothermal orthoclase, to zones with pervasive orthoclase ¯ooding. The high halogen contents of the Skouries intrusions are re¯ected in the high Cl and F concentrations of mica phases (up to 0.19 and 2.48 wt% respectively). The presence of magmatic magnetite in all intrusive phases implies high oxygen fugacities of the parental melts. All four monzonite phases have relatively evolved compositions, as re¯ected by their high SiO 2 , low MgO and low mg#, and variable but low contents of mantlecompatible elements such as V, Ni and Co. However, their mg# suggests increasing degrees of fractionation of the parental melts with decreasing age. Their high K 2 O (up to 5.8 wt%) and K 2 O/ Na 2 O ratios (>1), as well as their high Ce/Yb and Th/Yb ratios (>34 and >21 respectively), which are believed to have been unaected by alteration processes, are typical of alkaline rocks of the shoshonite association. Importantly, the Skouries intrusions are characterized by very high U and Th contents (up to 18.9 ppm and 62 ppm, respectively) that are consistent with accessory thorite and rare allanite in several samples. The high initial 87 Sr/ 86 Sr ratios (0.7082) for the Skouries intrusions suggest crustal contamination during emplacement. The use of geochemical discrimination diagrams assigns the rocks to a continental arc setting in accord with the interpretation of previous workers.

Ordered framboids from Devonian Chattanooga Shale (U.S.A.) and Rammelsberg Banderz (Germany) show a common orientation in any one sample. This observation was made using a stereographic method of reconstruction in which the lineations within the framboids were measured on each of three planes cut mutually at right angles from the rock samples. The explanation for this preferred orientation is not yet known, but it may originate from crystal-growth during compaction of the shales. Pyrit-,,Himbeeren" ans dem devonischen Chattanooga Shale (U.S.A.) und vom Rammelsberg Banderz zeigen bevorzugte Orientiernngen ihrer inneren Struktur (Figure ) gegeniiber der Sedimentschichtung. Diese Beobachtnngen sind in stereographischen Projektionen aufgezeichnet. Der Vorgang der Orientierung mag auf die Kristallisation der Pyrit-Netzwerke w/ihrend der Diagenese zuriickzufiihren sein.

Estimating sex on large assemblages of commingled skeletal human remains is challenging because it prevents the systemic observation of the skeleton and thus reduces the reliability of sex-ratio estimation. In order to tackle this problem, the applicability of sample-specific odontometric methods was assessed on the human skeletal remains from the Middle Neolithic cave necropolis of Bom Santo in Portugal. We present an approach that confirms some of the assumptions -the normal distribution of the data and the 1:1.5 sex ratio -indicated by for the application of sample-specific methods. These assumptions are often difficult to assess in archaeological samples and thus prevent the use of sample-specific methods. The mean bucco-lingual diameter of 51 lower right canine teeth was used as a cut-off point to discriminate between sexes within a sample from Bom Santo. Before that, Shapiro-Wilk statistics was used to confirm that the distribution of the data in a sample of 51 lower canine teeth was normal. In addition, the range and central tendency of the data were compared to other samples for which the sex of the individuals was known in order to confirm that those parameters were consistent with those of a sample presenting a balanced sex ratio. The canine sex estimations were then compared with the sex estimation obtained from mandibles where canine teeth were still in situ (n = 8). No clear disagreement between the two methods was found thus demonstrating good potential of this method for sex estimation and for the sex ratio estimation in commingled human skeletal remains. Results indicated that sex ratios in Room A and Room B at Bom Santo were quite different. This indicates that the two locations may have been used in a different way according to sex.

Bones submitted to heat experience structural and chromatic modifications. In particular, heat-induced bone warping and thumbnail fractures have been linked to the burning of fleshed and green bones -where the soft tissues have been removed from the bones soon after deathin contrast to dry bones. Those have been suggested as indicators of the state of the individual before being burned thus allowing inferences about the funerary behaviour of archaeological populations. A large sample of 61 skeletons submitted to cremation has been examined for the presence of both of these heat-induced features. Although uncommon, bone warping and thumbnail fractures were present in some of the skeletons demonstrating that its presence is not restricted to the burning of non-dried bones as generally believed. Rather than being an indicator of the presence of bones with soft tissues, bone warping seems to be more of an indicator of the preservation of collagen-apatite links which can be maintained on dry bones with low collagen deterioration. In addition, our results also do not confirm thumbnail fractures as an exclusive sign of the burning of bones with soft tissues. As a result, these heat-induced changes should be used with caution when trying to infer about the preburning state of an individual.

Amorphous Fe 0:55 Zr 0:45 films, having thickness of 400 nm, were grown on silicon substrates by co-deposition using ion beam sputtering. Limited surface roughness makes this system particularly suitable for fine-scale scanning force microscopy analysis and nano-indentation. The samples were irradiated with MeV C 60 clusters, and the surface morphology of single impacts was found to have a ''doughnut'' shape, i.e. hillocks having a central crater. Quantitative evaluation of the deformation was achieved by measuring their height and diameter. When C 60 projectiles deviate from normal incidence, a tail emerges along the direction of the incident beam. The height of the hillock and length of the tail are increasing with the incidence angle, and the magnitude of the deformation indicates that the damage mainly occurs due to a radial coherent mass transport outwards from the track core by a compression shockwave-like mechanism. The residual compressive in-plane stress, $)0.4 GPa for the as-deposited films, was found to notably influence the C 60 induced plastic deformations. Indeed, stress relaxation results in a marked decrease in height combined with a significant widening of the surface features. This ''flat'' surface morphology is attributed to an enhanced radial efficiency of the pressure pulse, owing to a significant reduction of the hardness of the amorphous film after stress relaxation. The overall picture outlined from our observations suggests that the surface damage induced by single MeV C 60 ions possibly is the signature of plastic deformation induced at large distances by an energetic radial pressure pulse. This unsteady shockwave allows the energy transfer outwards from the localised region along the ion path that experiences a sudden transient heating.

Pore structures with rich nanopores and permeability in tight gas reservoirs are poorly understood up to date. Advanced techniques are needed to be employed to accurately characterize pore structures, especially tiny pores which include micron and nanopores. In this study, various experimental techniques such as scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) T 2 , nitrogen adsorption method, and NMR cryoporometry (NMRC) are combined to interrogate the complex pore systems of the tight gas reservoir in the Linxing formation, Ordos Basin, China. Results show that tight gas sandstones are primarily comprised of residual interparticle and clay-dominated pores. Clay and quartz are two dominate minerals while pyrite occupies a nontrivial amount as well. The permeability of tight gas sandstones is very low, exhibiting an extremely poor positive correlation with porosity. While pore types and relative pore contents are more influential factors on the permeability, accurate characterization of pore size distribution is critical for the permeability of tight gas sandstones. Therefore, complementary characterization methods are carried out, indicating that neither small pores with radii < 100 nm (around peak 1 in NMR T 2 distribution) nor large pores with radii > 5 μm (around peak 3 in NMR T 2 distribution) control the permeability by analyzing the connectivity of the pores in various size ranges, but rather pores averaging approximately 350 ± X nm (around peak 2 in NMR T 2 distribution) have sufficient connectivity to host and transmit hydrocarbons. The pore size of tight gas sandstones is dominated by the clay-rich mineral assemblage. The study shows that the NMRC technique can be a very promising method, especially when referred to as a promising "roadmap" on how to interrogate tight formations such as the tight gas sands or even shale especially for the nanopore characterization.

Triple oxygen isotope (δ17O and δ18O) values of high- and low-temperature altered oceanic crust and products of basalt alteration experiments were measured to better constrain ocean isotope compositions in deep time. The data define an array of δ18O and Δ′17O (Δ′17O=δ′17O − λRL × δ′18O + γ) values from mantle values toward 1‰ and −0.01‰, respectively, with a λ of ~0.523. The altered oceanic crust data were used to construct a model for estimating δ18O-Δ′17O values of the ancient oceans if the continental weathering flux (FCW) and/or hydrothermal oceanic crust alteration flux (FHT) changed through time. A maximum lowering of 7‰ and 4‰, respectively, is achieved in the most extreme cases. The δ18O value of the ocean cannot be raised by more than 1.1‰. Eclogites from the Roberts Victor kimberlite (South Africa), with a protolith age of 3.1 Ga, have δ18O-Δ′17O values that precisely overlap with those of the modern altered oceanic crust, suggesting that the Archean oceans had similar iso...

Heterogeneous oxygen isotope compositions of plagioclase from the Boehls Butte anorthosite include some of the most oxygen-18–depleted values (to −16 per mil) reported for plagioclase in meta-igneous rocks and indicate high-temperature ( T &gt; 500°C) isotopic exchange between plagioclase and nearly pristine meteoric fluid. Retrograde reaction-enhanced permeability assisted influx of meteoric-hydrothermal fluids into the deep-seated anorthosite. Isotopic gradients of about 14 per mil over 600 micrometers in single crystals require short-lived (about 10 4 years) diffusional exchange of oxygen and locally large effective water:rock ratios, followed by rapid loss of water and cessation of oxygen diffusion in the anorthosite.

The kinetics of the breakdown reaction dolomite = periclase + calcite + CO 2 were investigated using cores of dolomitic marble. Two samples of Reed Dolomite from southwestern Nevada were cut into cylinders approximately 4 × 6 mm in size. The cores were sealed in gold capsules with isotopically enriched water (H 2 18 O or HD 18 O 0.5 16 O 0.5 ). The samples were heated in a cold-seal hydrothermal apparatus to 650-750 °C at 100 MPa for durations ranging from 2-59 days. The cores were then sectioned and examined by EPMA, XRD, and SIMS techniques. All experiments showed some amount of reaction regardless of duration or temperature. Reaction products occurred mainly along grain boundaries, fractures within grains, and along sample edges. Ion images and isotope-ratio analysis indicated that reaction products exchanged with inÞ ltrating ß uids. Reaction rates were calculated from measured extents of reaction, which were determined from automated EPMA modes. At 700 °C, we measured reaction rates ranging from 3.8 × 10 -14 to 2.3 × 10 -12 mol/mm 2 •s. The extent of reaction is proportional to the square root of time, suggesting a diffusion-controlled process. A shrinking-core model for the dolomite breakdown reaction Þ ts the grain-size data, suggesting that diffusion of H 2 O and CO 2 through the mantle of reaction products controlled the rate. Apparent activation energies for that diffusion are ~283 ± 32 kJ/mol for coarse-grained samples and ~333 ± 36 kJ/mol for Þ ne-grained samples. Initial reaction occurred relatively fast near the surface of dolomite grains, but continued diffusion through the reaction products ultimately controlled the rate of dolomite breakdown.

Anomalously high porosities up to 30% at burial depth of >3000 m along with varying amounts and types of carbonate cements occur in the fluvial channel sandstone facies of the Triassic Skagerrak Formation, Central Graben, Norway. However, porosities of the Skagerrak Formation are lower in the Norwegian sector than in the UK sector. In this study, petrographic analysis, core examination, scanning electron microscopy, elemental mapping, carbon and oxygen isotope, fluid inclusion and microgeometry analysis are performed to determine the diagenesis and direct influence on reservoir quality, with particular focus on the role played by carbonate cementation. The sandstones are mainly fine-grained lithicarkosic to sub-arkosic arenites and display a wide range of intergranular volumes (2.3% to 43.7% with an average of 23.6%). Porosity loss is mainly due to compaction (av. 26.6%) with minor contribution from cementation (av. 12.1%). The carbonate cements are patchy in distribution (from trace to 20.7%) and appear as various types e.g. calcretes (i.e. calcareous concreted gravels), poikilitic sparite and sparry ferroan dolomite, and euhedral or/and aggregated ankerite/ferroan dolomite crystals. This study highlights the association of carbonate precipitation, with the remobilisation of carbonate from intra-Skagerrak calcretes during early burial stage i.e. <500 m. During deeper burial, compaction is inhibited by carbonate cements, resulting high intergranular volume of up to 32% and 29% for fine-and medium-grained sandstones, respectively. Carbonate cement dissolution probably results from both meteoric water flow with CO 2 during shallow burial, and organic CO 2 and carboxylic acid during deep burial. The maximum intergranular volume enhanced by dissolution of early carbonate cements is calculated to 8% and 5% for fine-and mediumgrained sandstones, respectively. Compaction continues to exert influence after dissolution of carbonate cements, which results in a loss of ~6 % intergranular volume for fine-and medium-grained sandstones. Reservoir quality of the Norwegian sector is poorer than that of the UK sector due to a lower coverage of clay mineral coats e.g. chlorite, later and deeper onset of pore fluid overpressure, lower solubility of carbonate compared to halite, and a higher matrix content.

Arsenic (As) is commonly sequestered at the sediment–water interface (SWI) in mining-impacted lakes through adsorption and/or co-precipitation with authigenic iron (Fe)-(oxy)hydroxides or sulfides. The results of this study demonstrate that the accumulation of organic matter (OM) in near-surface sediments also influences the mobility and fate of As in sub-Arctic lakes. Sediment gravity cores, sediment grab samples, and porewaters were collected from three lakes downstream of the former Tundra gold mine, Northwest Territories, Canada. Analysis of sediment using combined micro-X-ray fluorescence/diffraction, K-edge X-ray Absorption Near-Edge Structure (XANES), and organic petrography shows that As is associated with both aquatic (benthic and planktonic alginate) and terrestrially derived OM (e.g., cutinite, funginite). Most As is hosted by fine-grained Fe-(oxy)hydroxides or sulfide minerals (e.g., goethite, orpiment, lepidocrocite, and mackinawite); however, grain-scale synchrotron-ba...

Arsenic (As) is commonly sequestered at the sediment-water interface (SWI) in mining-impacted lakes through adsorption and/or co-precipitation with authigenic iron (Fe)-(oxy)hydroxides or sulphides. The results of this study demonstrate that the accumulation of solid-phase organic matter (OM) in near-surface sediments also influences the mobility and fate of As in sub-Arctic lakes. Sediment gravity cores, sediment grab samples, and porewaters were collected from three lakes downstream of the former Tundra gold mine, Northwest Territories. Analysis of sediment using combined micro-X-ray fluorescence/diffraction, K-edge X-ray Absorption Near-Edge Structure (XANES), and organic petrography shows that As is associated with both aquatic (benthic and planktonic alginate) and terrestrially-derived OM (cutinite; funginite). Most As is hosted by fine-grained Fe-(oxy)hydroxides or sulphide minerals ( e.g., goethite, orpiment, lepidocrocite, mackinawite); however, grain-scale synchrotron-based...

The Hudson Bay sedimentary basin was overlooked geologically until two decades ago. Recent efforts to understand the palaeogeothermal history of this basin have led to the evaluation of fluid inclusion microthermometry, apatite fission track, organic matter reflectance and Rock–Eval analyses. Although apatite fission track and organic maturity indicators tend to show relatively low maximum burial temperatures (60–80°C), evidence of potential oil slicks on the sea surface and oil and gas shows in offshore wells have been reported across Hudson Bay. Fluid inclusion microthermometry in a carbonate mound sequence suggests homogenization temperatures of 118 ± 25 and 93 ± 10°C for recrystallized synsedimentary marine calcite and late pore-filling burial calcite, respectively. This sequence provides an interesting geological framework to test the application of clumped isotope thermometry against independent geothermometers. Here, we present clumped isotope data acquired on the late calcit...

The Late Devonian Besa River Formation is an organic-rich shale sequence in Liard Basin, northeastern British Columbia, Canada, with significant natural gas reserves. High-resolution elemental geochemistry of three long continuous cored intervals of the Besa River Formation was used to better understand the paleodepositional environment of organic-rich intervals in this thick marine shale. The studied core intervals were divided into five chemostratigraphic units based on organic and inorganic geochemical proxies. The highest total organic carbon (TOC) content (up to 13 wt.%) was identified in the upper part of the Patry member (Unit III) within the Liard Basin. During the deposition of Unit III, low clastic influx and euxinic bottom conditions mostly contributed to the high accumulation of organic carbon. Moreover, a high productivity and organic influx may have increased organic-rich basinal sediments, which further depleted the seawater column oxygen content in the presence of a ...

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This study investigates diagenetic and geochemical processes that control the regional distribution and formation of sulfate minerals (i.e., anhydrite and barite) in the Early Triassic Montney tight gas siltstone reservoir in the Western Canadian Sedimentary Basin (WCSB). Petrographic observations revealed two generations of early and late anhydrite and barite cement with distinct regional occurrence. The early anhydrite cement is dominantly present in northeastern BC (low H 2 S concentration zone), while late-stage anhydrite and barite cement and fracture-and vug-filling anhydrite are dominant in western Alberta (high H 2 S concentration zone). The δ 34 S and δ 18 O variations of late anhydrite and barite in the studied samples suggest a mixing isotopic signature of Triassic connate water and Devonian evaporites as two major origins of sulfate-rich fluids to the Montney Formation. The isotopic composition of early anhydrite cement in both areas suggests sulfate-rich fluids largely originated from modified Triassic connate water, sulfide oxidation process, and/or basinal brines. In contrast, the late diagenetic anhydrite and barite cement as well as fracture-and vug-filling anhydrite from high H 2 S concentration zone represents a mixed isotopic signature of Triassic connate water and a significant contribution of Devonian evaporites. The similar isotopic composition of the late-stage anhydrite and barite cement as well as fracture-and vug-filling anhydrite in western Alberta with Devonian evaporites isotopic signature further supports the major role of deep-seated fault/fracture systems in the supply of sulfate-rich fluids. We propose that sulfate-bearing fluids were sourced from the dissolution of underlying Devonian evaporites and migrated through deepseated fracture networks up to the Montney Formation.

Dilution by inert, refractory organic carbon can have a significant impact on the hydrocarbon potential of source rocks. In this study, a correction of total organic carbon, based on petrographic observations, is proposed to give a better indication of hydrocarbon generation potential. This correction shows that although the Second White Specks Formation is an excellent hydrocarbon source rock, hydrogen index and total organic carbon are influenced by dilution from refractory organic carbon of various sources. The results show that a higher degree of dilution occurs within the Belle Fourche Formation than the Second White Specks Formation. This dilution can have a significant impact on the hydrocarbon potential of the rock. Volumetric calculation of the inert carbon fraction using organic petrographic methods provides a semi quantitative method to correct total organic carbon values for the refractory organic carbon dilution effect. Incorporation of the dilution corrected organic carbon value in hydrogen index calculations allows a greater understanding of source rock hydrocarbon potential. This method provides better differentiation of the small scale variation between micro-facies and formation, as observed in the Second White Specks and Belle Fourche formations, than traditional bulk geochemical methodologies and previously proposed correction methodologies. Degree of dilution, either through transport of recycled allochthonous or autochthonous reworking of organic matter in-situ is highly variable and represents a significant challenge in the characterization of heterogeneous source rocks. This study investigates the organic petrology and geochemistry of a sediment core from the thermally immature area of the Upper Cretaceous Second White Specks Formation and Belle Fourche Formation. Reflectance and relative abundance of three maceral groups (bituminite, alginite, and refractory organic carbon macerals) showed significant organic matter compositional differences between micro-facies in the Second White Specks Formation. A change is also observed in organic matter composition from the upper part of the Belle Fourche Formation to the Second White Specks Formation. These compositional changes represent shifts in sediment source, sea floor oxygen levels, and depositional energy levels. These changes can be episodic, as observed between micro-facies, or longer time scale trends, as observed between the studied formations.

Incipient warming of peatlands at high latitudes is expected to modify soil drainage and hence the redox conditions, which has implications for Fe export from soils. This study uses Fe isotopes to assess the processes controlling Fe export in a range of Icelandic soils including peat soils derived from the same parent basalt, where Fe isotope variations principally reflect differences in weathering and drainage. In poorly weathered, well-drained soils (non-peat soils), the limited Fe isotope fractionation in soil solutions relative to the bulk soil (Δ 57 Fe solution-soil = -0.11 ± 0.12 ‰) is attributed to proton-promoted mineral dissolution. In the more weathered poorly drained soils (peat soils), the soil solutions are usually lighter than the bulk soil (Δ 57 Fe solution-soil = -0.41 ± 0.32 ‰), which indicates that Fe has been mobilised by reductive mineral dissolution and/or ligand-controlled dissolution. The results highlight the presence of Fe-organic complexes in solution in anoxic conditions. An additional constraint on soil weathering is provided by Si isotopes. The Si isotope composition of the soil solutions relative to the soil (Δ 30 Si solution-soil = 0.92 ± 0.26 ‰) generally reflects the incorporation of light Si isotopes in secondary aluminosilicates. Under anoxic conditions in peat soils, the largest Si isotope fractionation in soil solutions relative to the bulk soil is observed (Δ 30 Si solution-soil = 1.63 ± 0.40 ‰) and attributed to the cumulative contribution of secondary clay minerals and amorphous silica precipitation. Si supersaturation in solution with respect to amorphous silica is reached upon freezing when Al availability to form aluminosilicates is limited by the affinity of Al for metal-organic complexes. Therefore, the precipitation of amorphous silica in peat soils indirectly supports the formation of metal-organic complexes in poorly drained soils. These observations highlight that in a scenario of decreasing soil drainage with warming high latitude peatlands, Fe export from soils as Feorganic complexes will increase, which in turn has implications for Fe transport in rivers, and ultimately the delivery of Fe to the oceans.

The initiation of Northern Hemisphere glaciation in the subarctic North Pacific at ∼2.73 Ma was marked by an abrupt cessation of high opaline accumulation, considered to result from an increased stratification of the water column that should have led to higher utilization of nutrients in the surface ocean. We present a new stable Si isotope‐based record of Si utilization that is hard to reconcile with this model. A drop in 30Si/28Si by 0.4‰ at 2.73 Ma is coincident with an increase in bulk N isotope composition. The contrasting utilization records cannot have been both caused by a hydrographic change alone. Excluding a change in the Si:N export ratio, these results either imply a relative increase in silicic acid supplied to the surface waters or a change in its Si isotope composition. While it is impossible to distinguish between these two possibilities, both imply a regional or global change in the Si biogeochemical cycle, potentially caused by an enhanced storage of Si in the und...

Direct dating of fossil coral reefs using the U-series chronometer provides an important independent test of the Milankovitch orbital forcing theory of climate change. However, well-dated fossil corals pre-dating the last interglacial period (>130 thousand years ago; ka) are scarce due to, (1) a lack of sampling localities, (2) insufficient analytical precision in U-series dating methods, and (3) diagenesis which acts to violate the assumption of closed-system U-series isotopic decay in fossil corals. Here we present 50 new high-precision U-series age determinations for fossil corals from Henderson Island, an emergent coral atoll in the central South Pacific. U-series age determinations associated with the Marine Isotope Stage (MIS) 9 interglacial and MIS 7.5 interstadial periods are reported. The fossil corals show relatively little open-system U-series behaviour in comparison to other localities with fossil coral reefs formed prior to the last glacial cycle, however, open-system U-series behaviour is still evident in most of the dated corals. In particular, percent-level shifts in the [ 230 Th/ 238 U] act composition are observed, leading to conventional U-series ages that are significantly younger or older than the true sample age. This open-system U-series behaviour is not accounted for by any of the open-system U-series models, indicating that new models should be derived. The new U-series ages reported here support and extend earlier findings reported in , providing evidence of prolific coral reef development on Henderson Island at $320 ka, most likely correlated with MIS 9.3, and subsequent reef development at $307 ka during MIS 9.1, while relative sea-level was potentially $20 m lower than during MIS 9.3. The U-series ages for additional well-preserved fossil corals are suggestive of minor reef development on Henderson Island during MIS 7.5 (245-230 ka) at 240.3 ± 0.8 and 234.7 ± 1.3 ka. All U-series observations are consistent with the Milankovitch theory of climate change, in terms of the timing of onset and termination of the dated interglacial and interstadial periods. The best preserved samples also suggest that the oceanic 234 U/ 238 U during MIS 9 and MIS 7.5 was within five permil of the modern open ocean composition.

The r-process only nuclide 247 Cm decays to 235 U with a characteristic half-life of ϳ16 million years. 247 Cm is presently extinct, but offers considerable potential as a short-lived r-process chronometer, providing constraints on the time interval between the last r-process nucleo-synthetic event and the formation of the solar system. The existence of "live" 247 Cm in the early solar system should be manifested today as variations in 235 U/ 238 U, provided Cm was chemically fractionated from U when solids formed in the early solar system. Using multiple-collector ICPMS and a high-purity mixed 233 U-236 U spike to monitor instrumental mass fractionation, we are able to resolve variations in 235 U/ 238 U at the 1-2 epsilon level (2 M ; 1 epsilon ϭ 1 part in 10,000) on sample sizes consisting of 20 ng of uranium. Data can be acquired on smaller (Ͻ10 ng) samples with Ϯ2-3 epsilon 2 uncertainties. Uranium isotopic measurements and U, Nd and Sm concentrations were acquired on bulk samples of a suite of carbonaceous chondrites, unequilibrated and equilibrated ordinary chondrites and eucrites, for which conflicting results had previously been obtained. Our results show no well-resolved excursions in 235 U/ 238 U away from the terrestrial value at the ϳ2 epsilon level, and constrain the amount of 247 Cm-produced excess 235 U atoms to less than ϳ1 ϫ 10 8 atoms per gram of chondritic meteorite, with respect to terrestrial 235 U/ 238 U. Large (permil-level) anomalies in 235 U/ 238 U could, however, be artificially generated in the ordinary chondrites during laboratory processing. Therefore, U may be more susceptible to isotopic fractionation during chemical processing than previously recognized, and may reconcile some of the highly conflicting 235 U results reported by previous workers for chondritic meteorites. Our results indicate that a timescale of ϳ1-2 ϫ 10 8 years between the last actinide producing r-process event and the formation of the solar system may not be unreasonable based on the 247 Cm-235 U system. However, this conclusion is far from robust at this stage because the only bulk meteorites analysed that display strong Nd/U fractionation are highly metamorphosed chondrites that may have experienced a protracted history of redistribution and re-equilibration. The search for "live" 247 Cm in the early solar system can now be extended to early-formed condensates and mineral phases displaying strong Cm-U fractionations.

We present some of the first analyses of the stable isotopic composition of dissolved silicon (Si) in groundwater. The groundwater samples were from the Navajo Sandstone aquifer at Black Mesa, Arizona, USA, and the Si isotope composition of detrital feldspars and secondary clay coatings in the aquifer were also analyzed. Silicon isotope compositions were measured using high-resolution multi-collector inductively coupled mass spectrometry (HR-MC-ICP-MS) (Nu1700 & NuPlasma HR). The quartz dominated bulk rock and feldspar separates have similar d 30 Si of À0.09 ± 0.04& and À0.15 ± 0.04& (±95% SEM), respectively, and clay separates are isotopically lighter by up to 0.4& compared to the feldspars. From isotopic massbalance considerations, co-existing aqueous fluids should have d 30 Si values heavier than the primary silicates. Positive d 30 Si values were only found in the shallow aquifer, where Si isotopes are most likely fractionated during the dissolution of feldspars and subsequent formation of clay minerals. However, d 30 Si decreases along the flow path from 0.56& to À1.42&, representing the most negative dissolved Si isotope composition so far found for natural waters. We speculate that the enrichment in 28 Si is due to dissolution of partly secondary clay minerals and low-temperature silcretes in the Navajo Sandstone. The discovery of the large range and systematic shifts of d 30 Si values along a groundwater flow path illustrates the potential utility of stable Si isotopes for deciphering the Si cycling in sedimentary basins, tracing fluid flow, and evaluating global Si cycle.

It has been proposed that silicon (Si) isotopes are fractionated during weathering and biological activity leading to heavy dissolved riverine compositions. In this study, the first seasonal variations of stable isotope compositions of dissolved riverine Si are reported and compared with concomitant changes in water chemistry. Four different rivers in Switzerland were sampled between March 2004 and July 2005. The unique high-resolution multi-collector ICP-MS Nu1700, has been used to provide simultaneous interference-free measurements of 28 Si, 29 Si and 30 Si abundances with an average limiting precision of ± 0.04‰ on δ 30 Si. This precision facilitates the clarification of small temporal variations in isotope composition. The average of all the data for the 40 samples is δ 30 Si = + 0.84 ± 0.19‰ (± 1σ SD ). Despite significant differences in catchment lithologies, biomass, climate, total dissolved solids and weathering fluxes the averaged isotopic composition of dissolved Si in each river is strikingly similar with means of + 0.70 ± 0.12‰ for the Birs,+0.95 ± 0.22‰ for the Saane,+ 0.93 ± 0.12‰ for the Ticino and + 0.79 ± 0.19‰ for the Verzasca. However, the δ 30 Si undergoes seasonal variations of up to 0.6‰. Comparisons between δ 30 Si and physico-chemical parameters, such as the concentration of dissolved Si and other cations, the discharge of the rivers, and the resulting weathering fluxes, permits an understanding of the processes that control the Si budget and the fate of dissolved Si within these rivers. The main mechanism controlling the Si isotope composition of the mountainous Verzasca River appears to be a two component mixing between the seepage of soil/ground waters, with heavier Si produced by clay formation and superficial runoff associated with lighter Si during high discharge events. A biologically-mediated fractionation can be excluded in this particular river system. The other rivers display increasing complexity with increases in the proportion of forested and cultivated landscapes as well as carbonate rocks in the catchment. In these instances it is impossible to resolve the extent of the isotopic fractionation and contributed flux of Si contributed by biological processes as opposed to abiotic weathering. The presence of seasonal variations in Si isotope composition in mountainous rivers provides evidence that extreme changes in climate affect the overall composition of dissolved Si delivered to the oceans. The oceanic Si isotope composition is very sensitive to even small changes in the riverine Si isotope composition and this parameter appears to be more critical than

Techniques for the purification of Si for the determination of its natural stable isotopic composition have in the past been based on the requirements for gas-source mass-spectrometry, rather than MC-ICPMS. For high precision analyses by MC-ICPMS it is essential to have very pure solutions and in this paper a new technique is presented for the separation and purification of Si from natural samples to improve the determination of isotope ratios. A method has been optimised based on alkaline fusion followed by ion-exchange chromatography. The application to natural samples, such as river water samples and silicate mineral/rock samples is demonstrated. Alkali fusion avoids the use of hydrofluoric acid (HF), which introduces difficulties for the determination of Si isotope ratios using MC-ICPMS. By eliminating HF a 30-40% increase in sensitivity is achieved as well as a marked enhancement of mass bias stability leading to a factor of 2 improvement in reproducibility. The cation-exchange method enables processing of very small samples (3.6 μg Si) and a rapid and effective separation of Si from other cationic species. The overall recovery of Si during the entire procedure is better than 98% and no Si isotope fractionation is generated. Matrix tests demonstrate that this method is suitable for silicates, and that typical sulphate and nitrate abundances of river waters have no effect on measured Si isotope composition. The latter aspect is vital for analysis of river waters since the technique does not separate dissolved Si (silicic acid) from ambient anionic species. Overall, the new method presents a faster, safer and more reliable way to measure Si isotopes via MC-ICPMS.