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Carbon and strontium isotope chemostratigraphy (255 δ13Ccarb and δ18O, and 130 87Sr/86Sr analyses of carbonate components in whole-rock samples) in combination with detailed mapping at 1:20,000 scale in part of the Fauske Nappe in the Rognan area, Nordland, have led to a major revision of what had previously been considered to represent a continuous lithostratigraphy spanning over 100 million years of geological time: from Cambrian to Silurian. This new work has indicated that the high-grade, barren, marble and siliciclastic succession occurs in a series of thrust sheets which have diverse apparent depositional ages ranging from Early Cryogenian to Early Silurian. The new data support earlier interpretations that the rocks of the Fauske Nappe were deposited along the carbonate platform and adjacent continental slope of the eastern margin of Laurentia during the Neoproterozoic to Early Palaeozoic time interval. Most of the thrust sheets were generated in Early Ordovician time during the earliest stages of the main phase of the Taconian orogeny, and then immediately overlain unconformably by a carbonate breccia and conglomerate unit, the Oynes formation, also of Early Ordovician age. Just one formation (Rognan formation) in the Fauske Nappe is younger, of Early Silurian age, with Sr- and C-isotopic data that are comparable to those in fossiliferous, Early Silurian, metalimestones farther north in Troms. These particular carbonate rocks are considered to have accumulated in a post-Taconian successor basin, prior to their transport during the Scandian orogeny into the Uppermost Allochthon of the Scandinavian Caledonides. [ABSTRACT FROM AUTHOR]

The central zone of the Miocene Štiavnica stratovolcano hosts several occurrences of Cu-Au skarn-porphyry mineralisation, related to granodiorite/quartz-diorite porphyry dyke clusters and stocks. Vysoká-Zlatno is the largest deposit (13.4 Mt at 0.52% Cu), with mineralised Mg-Ca exo- and endoskarns, developed at the prevolcanic basement level. The alteration pattern includes an internal K- and Na-Ca silicate zone, surrounded by phyllic and argillic zones, laterally grading into a propylitic zone. Fluid inclusions in quartz veinlets in the internal zone contain mostly saline brines with 31-70 wt.% NaCl eq. and temperatures of liquid-vapour homogenization (Th) of 186-575°C, indicating fluid heterogenisation. Garnet contains inclusions of variable salinity with 1-31 wt.% NaCl eq. and Th of 320-360°C. Quartz-chalcopyrite veinlets host mostly low-salinity fluid inclusions with 0-3 wt.% NaCl eq. and Th of 323-364°C. Data from sphalerite from the margin of the system indicate mixing with dilute and cooler fluids. The isotopic composition of fluids in equilibrium with K-alteration and most skarn minerals (both prograde and retrograde) indicates predominantly a magmatic origin (δO 2.5-12.3‰) with a minor meteoric component. Corresponding low δD values are probably related to isotopic fractionation during exsolution of the fluid from crystallising magma in an open system. The data suggest the general pattern of a distant source of magmatic fluids that ascended above a zone of hydraulic fracturing below the temperature of ductile-brittle transition. The magma chamber at ∼5-6 km depth exsolved single-phase fluids, whose properties were controlled by changing PT conditions along their fluid paths. During early stages, ascending fluids display liquid-vapour immiscibility, followed by physical separation of both phases. Low-salinity liquid associated with ore veinlets probably represents a single-phase magmatic fluid/magmatic vapour which contracted into liquid upon its ascent. [ABSTRACT FROM AUTHOR]

Calcite septarian concretions from the Permian Beaufort Group in the Maniamba Graben (NW Mozambique) allow controls on the composition and nature of diagenetic fluids to be investigated. The concretions formed in lacustrine siltstones, where they occur in spherical (1 to 70 cm in diameter) and columnar (up to 50 cm long) forms within three closely spaced, discrete beds totalling 2·5 m in thickness. Cementation began at an early stage of diagenesis and entrapped non-compacted burrows and calcified plant roots. The cylindrical concretions overgrew calcified vertical plant roots, which experienced shrinkage cracking after entrapment. Two generations of concretionary body cement and two generations of septarian crack infill are distinguished. The early generation in both cases is a low-Mn, Mg-rich calcite, whereas the later generation is a low-Mg, Mn-rich calcite. The change in chemistry is broadly consistent with a time (burial)-related transition from oxic to sub-oxic/anoxic conditions close to the sediment–water interface. Geochemical features of all types of cement were controlled by the sulphate-poor environment and by the absence of bacterial sulphate reduction. All types of cement present have δ13C ranging between 0‰ and −15‰(Vienna Peedee Belemnite, V-PDB), and highly variable and highly depleted δ18O (down to 14‰ Vienna Standard Mean Ocean Water, V-SMOW). The late generation of cement is most depleted in both 13C and 18O. The geochemical and isotopic patterns are best explained by interaction between surface oxic waters, pore waters and underground, 18O-depleted, reducing, ice-meltwaters accumulated in the underlying coal-bearing sediments during the Permian deglaciation. The invariant δ13C distribution across core-to-rim transects for each individual concretion is consistent with rapid lithification and involvement of a limited range of carbon sources derived via oxidation of buried plant material and from dissolved clastic carbonates. Syneresis of the cement during an advanced stage of lithification at early diagenesis is considered to be the cause of development of the septarian cracks. After cracking, the concretions retained a small volume of porosity, allowing infiltration of anoxic, Ba-bearing fluids, resulting in the formation of barite. The results obtained contribute to a better understanding of diagenetic processes at the shallow burial depths occurring in rift-bound, lacustrine depositional systems. [ABSTRACT FROM AUTHOR]

Abstract: A preliminary evaluation of compound-specific isotope analysis (CSIA) as a novel, alternative method for identifying source correlation compounds in soils contaminated with residual heavy or weathered petroleum wastes is presented. Oil-contaminated soil microcosms were established using soil (sandy-loam, non-carbonaceous gley) amended with ballast-, crude- or No.6 fuel oil. Microcosms were periodically sampled over 256days and δ13C values (which express the ratio of 13C to 12C) determined at each time point for five n-alkanes and the isoprenoid norpristane using gas chromatography–isotope ratio mass spectrometry (GC-IRMS). Although some temporal variation was observed, no significant temporal shifts in the δ13C values for the five n-alkanes were measured in all three oils. Isoprenoid isotope ratios (δ13C) appeared to be least affected by biotransformation, especially in the No.6 fuel oil. The research suggests that the δ13C of isoprenoids such as norpristane, may be of use as source correlation parameters. [Copyright &y& Elsevier]

A core retrieved from Lake Frassino (northern Italy) provided evidence of palaeohydrological change in this area during the last 14 ka. Lithological, malacological and, in particular, stable isotope composition of freshwater shells allowed the delineation of the main phases of lake evolution between the Lateglacial and Holocene. Lateglacial conditions were drier than the Holocene, although a wetter period was inferred before c. 14 ka. According to the oxygen isotope composition of freshwater shells, the Holocene showed a clear bipartition. The first part, which lasted from ∼ 9100 to 7000 yr BP, was drier and was followed by a rapid increase in humidity at ∼ 7000–6800 yr BP. Between ∼ 6800 and 5000 yr BP, there were wetter and more stable conditions, as indicated by smaller δ18O oscillations of Pisidium and Valvata shells. From c. 5000 to 2600 yr BP the record is characterized by larger fluctuations, which may indicate that short-term and particularly pronounced alternation of wet and dry periods occurred. [ABSTRACT FROM AUTHOR]

Abstract: Carbon and oxygen isotope measurements of 66 samples from the 60m-thick variegated marble in the Upper Allochthon of the Norwegian Caledonides have a mean δ 13Ccarb of −8.4±0.9‰ (V-PDB), and a mean δ 18O of 20.2±2.2‰ (V-SMOW). The variegated marble is overlain by 150m-thick pale grey marble characterised by mean δ 13Ccarb of −6.5±0.8‰ (n =25) and underlain by dark grey marbles with a mean δ 13Ccarb of +4.8±1.1‰ (n =61). This tripartite unit of an poorly constrained age—but between Neoproterozoic and Early Silurian—discontinuously developed over a distance of 500km, is likely to represent one of the largest isotopically anomalous sedimentary carbonate formations yet reported. The marbles depleted in 13C beyond the canonical mantle value of −6‰ show no obvious evidence of post-sedimentary repartitioning of carbon isotopes. Several other carbonate formations deposited within approximately 680–540Ma time interval (Chenchinskaya, Nikolskaya and Torginskay in Siberia, Ingta in NW Canada, Shuram in Central Oman, Trezona and Wonoka in South Australia) are several hundred meters thick, developed over a distance of hundreds of kilometres, and all show a similar depletion in 13C beyond the mantle value, for reasons that are not well understood. The existence of these carbonates represents a challenging problem for our current understanding of global carbon geodynamics. Changes in the ratio of reduced/oxidised carbon sequestered in sediments, a methane hydrate release or ‘zero’ biological productivity, if applied separately, cannot explain carbon isotope characteristics and formation of these carbonates. We tentatively propose that several factors associated with unusual geodynamic and palaeoclimatic scenarios developed between 600 and 540Ma might have been involved in the extreme lowering of the isotopic composition of carbon entering the global Earth surface environment. This period was marked by the retreat of Neoproterozoic glaciers and break-up of the supercontinent Rodinia. The late-postglacial warming might have induced a massive release of methane hydrates extremely enriched in 12C. The ‘death’ of Rodinia was marked by unusually rapid (approximately 20cm/year) motion of newly formed continental plates suggesting vigorous mantle convection and an enhanced restructuring of the lowest compartments of the Earth. This could provide a flux of 12C-rich material from the isotopically light asthenosphere–mantle source (δ 13C=−25 to −15‰) to the surface. Considerable reconfiguration of the continental and sea areas of the Earth might have triggered enhanced weathering of previously deposited 12C-rich organic matter. In presenting this working hypothesis we also question the completeness of our understanding of the terrestrial carbon cycle, and the popular assumption that the isotopic composition of carbon entering the global Earth surface environment was always around −6‰. [Copyright &y& Elsevier]

Oxygen isotopic compositions of rubies and sapphires from 106 deposits worldwide, as well as heated natural corundum, have been measured in this study. Artificially heated corundums have the same oxygen isotopic composition as unheated material. The δ18O ratio of natural corundum is a good indicator of its geological environment of formation. The consistently restricted δ18O range found for each type of deposit is explained by host-rock buffering during fluid-rock interaction. The δ18O constrains the geological source of the major type of gem-quality rubies sold on the market and brings new insight to gems found in placers. High-quality blue sapphires from Kashmir, Andranondambo, and Sri Lanka have specific oxygen isotopic ranges, but they overlap those of Mogok in Myanmar. Combined with traditional gemology techniques, oxygen isotope analysis will contribute toward defining the origin of some commercial high-value blue sapphires, especially from Kashmir. [ABSTRACT FROM AUTHOR]

Stable oxygen isotope analyses were obtained from fossil brachiopod shells from a shallow marine deposit of Upper Pleistocene age (approximately 80 ka) in New Zealand as part of a palaeoenvironmental investigation. Bulk analyses of entire shells of Calloria inconspicua yielded highly variable results (a range of 2.30‰), rendering these data of limited use as palaeoenvironmental proxies. Attempts to obtain consistent oxygen isotope values by removing areas of the brachiopod shell thought to be prone to oxygen isotope disequilibrium effects (‘vital effects’) revealed that the matching anterior portions of ventral and dorsal valves from the same individual (which were secreted at the same time) also yielded different oxygen isotope ratios. The dorsal valve δ18O values were higher and less variable than those obtained from the ventral valve of the same individual. The investigation was then extended to living representatives of the same species from a similar shallow water habitat from the South Island of New Zealand. The pattern of dorsal valves yielding higher and less variable oxygen isotope values than matching areas of the ventral valves was repeated in seven out of eight individuals investigated, although there was considerable variation in the absolute values from specimen to specimen. Contrary to common practice therefore, it seems that in this species it is the much thinner and lighter dorsal valve that provides a more consistent isotopic measurement. If converted into absolute temperature estimates, the dorsal valve measurements correspond to a temperature midway between the mean and maximum annual temperature experienced by this species in its present-day habitat, which may make it acceptable as a palaeoenvironmental indicator. The high level of variation between individuals (including an inferred temperature from one ventral valve above the mean maximum temperature experienced) indicates that a range of individuals needs to be investigated in any palaeoenvironmental investigation to avoid misleading interpretations. However, intra- and inter-specimen variation in isotopic composition may provide valuable palaeobiological information on growth rates, metabolism and possibly also pathological conditions in the past. [Copyright &y& Elsevier]

Magnesite forms a series of 1- to 15-m-thick beds within the ≈2·0 Ga (Palaeoproterozoic) Tulomozerskaya Formation, NW Fennoscandian Shield, Russia. Drillcore material together with natural exposures reveal that the 680-m-thick formation is composed of a stromatolite–dolomite–‘red bed’ sequence formed in a complex combination of shallow-marine and non-marine, evaporitic environments. Dolomite-collapse breccia, stromatolitic and micritic dolostones and sparry allochemical dolostones are the principal rocks hosting the magnesite beds. All dolomite lithologies are marked by δ13C values from +7·1‰ to +11·6‰ (V-PDB) and δ18O ranging from 17·4‰ to 26·3‰ (V-SMOW). Magnesite occurs in different forms: finely laminated micritic; stromatolitic magnesite; and structureless micritic, crystalline and coarsely crystalline magnesite. All varieties exhibit anomalously high δ13C values ranging from +9·0‰ to +11·6‰ and δ18O values of 20·0–25·7‰. Laminated and structureless micritic magnesite forms as a secondary phase replacing dolomite during early diagenesis, and replaced dolomite before the major phase of burial. Crystalline and coarsely crystalline magnesite replacing micritic magnesite formed late in the diagenetic/metamorphic history. Magnesite apparently precipitated from sea water-derived brine, diluted by meteoric fluids. Magnesitization was accomplished under evaporitic conditions (sabkha to playa lake environment) proposed to be similar to the Coorong or Lake Walyungup coastal playa magnesite. Magnesite and host dolostones formed in evaporative and partly restricted environments; consequently, extremely high δ13C values reflect a combined contribution from both global and local carbon reservoirs. A 13C-rich global carbon reservoir (δ13C at around +5‰) is related to the perturbation of the carbon cycle at 2·0 Ga, whereas the local enhancement in 13C (up to +12‰) is associated with evaporative and restricted environments with high bioproductivity. [ABSTRACT FROM AUTHOR]

Unusual textural and chemical characteristics of disseminated dolomite in Upper Jurassic shelf sediments of the North Sea have provided the basis for a proposed new interpretation of early diagenetic dolomite authigenesis in highly bioturbated marine sandstones. The dolomite is present throughout the Franklin Sandstone Formation of the Franklin and Elgin Fields as discrete, non-ferroan, generally unzoned, subhedral to highly anhedral ‘jigsaw piece’ crystals. These are of a similar size to the detrital silicate grains and typically account for ≈5% of the rock volume. The dolomite crystals are never seen to form polycrystalline aggregates or concretions, or ever to envelop the adjacent silicate grains. They are uniformly dispersed throughout the sandstones, irrespective of detrital grain size or clay content. Dolomite authigenesis predated all the other significant diagenetic events visible in thin section. The dolomite is overgrown by late diagenetic ankerite, and bulk samples display stable isotope compositions that lie on a mixing trend between these components. Extrapolation of this trend suggests that the dolomite has near-marine δ18O values and low, positive δ13C values. The unusual textural and chemical characteristics of this dolomite can all be reconciled if it formed in the near-surface zone of active bioturbation. Sea water provided a plentiful reservoir of Mg and a pore fluid of regionally consistent δ18O. Labile bioclastic debris (e.g. aragonite, Mg-calcite) supplied isotopically positive carbon to the pore fluids during shallow-burial dissolution. Such dissolution took place in response to the ambient ‘calcite sea’ conditions, but may have been catalysed by organic matter oxidation reactions. Bioturbation not only ensured that the dissolving carbonate was dispersed throughout the sandstones, but also prohibited coalescence of the dolomite crystals and consequent cementation of the grain framework. Continued exchange of Mg2+ and Ca2+ with the sea-water reservoir maintained a sufficient Mg/Ca ratio for dolomite (rather than calcite) to form. Irregular crystal shapes resulted from dissolution, of both the dolomite and the enclosed fine calcitic shell debris, before ankerite precipitation during deep-burial diagenesis. [ABSTRACT FROM AUTHOR]

Late Pleistocene and Holocene archaeological deposits from the central Mediterranean regions contain abundant terrestrial gastropod shell remains. Stable isotope studies of their shell carbonate are valuable proxies for various aspects of climate and environmental change such as temperature, hydrological sources and balance, as well as vegetation. Here we present stable carbon and oxygen isotope data of snail shells from several archaeological deposits in the western Mediterranean (Iberian, Italian Peninsula and Sicily). Isotope ratios differ remarkably between the Late Pleistocene, Holocene and modern shells. The results can be interpreted in terms of hydrological variations and changes in vegetation over time. Fossil shells offer the opportunity to examine the effects of past climate change on local and regional environments. [ABSTRACT FROM AUTHOR]

Oxygen isotope studies were carried out across units of a Neoproterozoic nappe system, south of Sa˜o Francisco Craton. A temperature decrease toward the base of the system is found, consistent with a previously recognized inverted metamorphic pattern. The tectonic contact of the basal unit and the reworked southern Sa˜o Francisco craton show a steep temperature gradient, suggesting that low temperature thrusting acted as the dominant tectonic process. The contrasts between the δ18O values of the Treˆs Pontas-Varginha and Carmo da Cachoeira nappes and the differences among the samples and minerals are consistent with the preservation of sedimentary isotopic composition during metamorphism. The small differences in the δ18O values between the undeformed and the deformed calc-silicate samples (∼1.6‰) suggest that the δ18O value of mylonitization fluids was close to that which equilibrated with the metamorphic assemblage. The distinct δ18O values of metapelitic and calc-silicate samples and the great temperature difference from one type to the other indicate that no large-scale fluid interaction processes occurred during metamorphism. Oxygen isotopic estimations of both Treˆs Pontas-Varginha undeformed rocks and Carmo da Cachoeira unaltered equivalents indicate δ18O values of up to 18‰. Comparison between these values and those from the ‘basement’ orthogneisses (8.3–8.5‰) indicates the latter are not sources for the metapelites. [Copyright &y& Elsevier]

Loess deposits have been described in the past for the upper section of Buca Dei Corvi succession (Central Italy). In this paper the deposits were re-analysed to clarify the depositional environment and to attempt a paleoclimate reconstruction. Two radiocarbon dates on pedogenic carbonate constrain the ages to the Late Glacial, and are consistent with previous OSL dating of the top of the succession. The non-marine mollusc assemblage shows typical character of cold and dry climatic conditions, testified by strong oligotypical composition. Mineralogy and geochemistry of the sediments indicate the abundant presence of exotic quartz mineral which can be explained only by wind transport. Probably, wind transport was also responsible of deposition of carbonate which then dissolved and re-precipitated producing pedogenic concretions. Stable isotopes ( 13 C/ 12 C and 18 O/ 16 O ratios) of the concretions are consistent with a climate drier than present conditions, with an environment characterized by sparse vegetation. [ABSTRACT FROM AUTHOR]

The Burela deposit is the largest kaolin deposit in Spain, mined for more than 50 years, the product being mainly used for porcelain. Kaolin is dominantly associated with Lower Cambrian felsites, interbedded with quartzites, micaschists and metapelites (Cándana Series), and was strongly folded during the Variscan orogeny. Kaolin layers were ductile and incompetent materials among more competent ones, producing many slides with a diastrophic appearance. Consequently, kaolin outcrops are morphologically very variable– i.e. pockets – and interlayered between metapelites and/or quartzites, resulting in complication for prospection and mining. The kaolin consists mainly of kaolinite, tubular halloysite, and spherical allophane along with quartz and minor illite. The content of kaolin minerals reaches up to 90% in the finer fractions (< 2 μm and < 1 μm). Geochemical analyses of trace and REE show a close relationship between kaolin and associated rocks. Two kaolin types can be differentiated: (i) massive, associated to felsite; and (ii) related to metapelite. A temperature range from 15 to 35 °C, with an average of approximately 28 °C was calculated on the basis of the isotopic signatures (δ 18 O, δD) for the kaolin materials. This scatter suggests that if continental weathering was involved in the kaolin formation on the lower side of the temperatures, it was not the only process, especially for kaolin associate with felsites and metapelites. The higher temperatures are indicative of a hydrothermal auto-metamorphic alteration, followed by a folding of the series that induced an apparently chaotic kaolin distribution with a combined continental weathering superimposed on the previous low-temperature hydrothermal felsite transformation. [ABSTRACT FROM AUTHOR]

The margins of mainland Europe, and especially those areas coming under the influence of North Atlantic weather systems, are ideally placed to record changing palaeoclimates. Cores from an infilled lake basin at Crudale Meadow in Mainland, Orkney, revealed basal deposits of calcareous mud (‘marl’) beneath sedge peat. Stable isotope, palynological and molluscan analyses allowed the establishment of palaeoenvironmental changes through the Devensian Lateglacial and the early Holocene. The δ 18 O marl record exhibited the existence of possibly four climatic oscillations in the Lateglacial (one of which, within event cf. GI-1c, is not often commented upon), as well as the Preboreal Oscillation and other Holocene perturbations. The cold episodes succeeding the Preboreal Oscillation were demarcated conservatively and one of these (event C5, ∼11.0 ka) may have previously been unremarked, while the putative 9.3 and 8.2 ka events seem not to produce corresponding palynologically visible floristic changes. The events at Crudale Meadow are consistent with those recorded at other sites from Britain, Ireland and elsewhere, and can be correlated with isotopic changes shown by the Greenland ice cores. The multi-proxy approach enriches the environmental reconstructions from the site, although the synchronicity of the response of the various proxies is sometimes equivocal, depending upon the time period concerned, taphonomy, and the nature of the deposits. The site may contain the most northerly Lateglacial isotope record from northwest Europe, and it has yielded one of the best archives for the demonstration of abrupt early Holocene events within Britain. [ABSTRACT FROM AUTHOR]

Abstract: Diagnostic molecular ratios and compound-specific 13C and 14C analyses were used to identify n-alkane sources in surface sediments collected along a transect from an urbanized estuary draining a peat-rich catchment (Tyne, UK). The most abundant homologues were generally C29 or C31, and the carbon preference index (CPI; 1.8 to 6.4) and average chain length (ACL; 28.5 to 29.5) of C25–C33 n-alkanes became progressively lower in samples closer to the mouth of estuary. δ 13C signatures of C19–C31 n-alkanes ranged from −37.1 to −29.3‰ and in general became more depleted with increasing carbon number. Δ14C values for C21 (−945 to −738‰) were significantly more depleted compared to C29 (−591 to −65‰) and C31 (−382 to −96‰), pointing to a much higher component of fossil (i.e., 14C-free) carbon in the shorter homologue. The radiocarbon contents for these three n-alkanes decreased toward the North Sea, which in conjunction with an up to 4‰ seaward 13C-enrichment in C29 and C31 and seaward decreases in CPI and ACL pointed to petrogenic hydrocarbon contamination in lower estuarine sediments. Independent 13C and 14C mass balances used to calculate the relative proportions of modern (i.e., plant wax) and fossil (i.e., petrogenic) n-alkanes yielded similar results and demonstrated that mixing with marine-derived organic matter (OM) or microbial degradation during estuarine transport led to a seaward decline in modern, longer-chain homologues, resulting in an increasingly larger fossil carbon contribution toward the mouth of estuary. The ability to clearly distinguish anthropogenic from natural inputs suggests that compound-specific radiocarbon analysis can successfully delineate the age of terrigenous OM delivered to the coastal zone even near historically polluted systems such as the Tyne. [Copyright &y& Elsevier]

Abstract: High-sulfidation (HS) epithermal systems have elements in common with passively degassing volcanoes associated with high T, acid fumarole fields or acid crater lakes. They are considered to form in two stages, the first of which involves advanced argillic alteration resulting from intense, strongly acidic fluid–rock interaction. The La Fossa hydrothermal system (Vulcano Island) represents a classic example of such an active HS system and can be considered as a modern analogue of this early stage of alteration, resulting in a core of intense silicic (90–95% pure SiO2) alteration surrounded by alunitic alteration zones. This paper focuses on a geochemical and stable isotope study of the surficial alteration facies of Vulcano – particularly the horizon characterized by strong silicic alteration – and on deep seated xenoliths ejected during the last eruption of La Fossa volcano (1888–90) that can be considered as representative of fragments of the deep conduit system of La Fossa volcano. Using directly measured temperatures at the sites of sampling, we have calculated fluid composition in isotopic equilibrium with the alteration products. The large range of measured silica δ 18O (12.3 to 29‰) reflects the wide range of formation temperatures (80–240 °C). The fluid compositions calculated for intense silicic alteration vary from −0.9 to +6.5‰. These are significantly heavier than local meteoric water (−6‰), and are consistent with derivation from the condensation of high-temperature fumarolic gases, dominated by magmatic fluids and rich in acid gases (SO2, H2S, HCl, HF), into shallow groundwaters of meteoric origin, with dynamically variable ratios of fumarolic steam/meteoric water. The calculated δ 18O and δD of water in equilibrium with alunite also suggest the mixing of magmatic and meteoric waters for the fluids involved in the genesis of advanced argillic alteration facies. The calculated δ 18O of water in equilibrium with hedenbergitic clinopyroxene, found in a veinlet in a metasomatized xenolith is +8.9‰. This value cannot reasonably result from water–rock interaction between the host volcanic rocks and surface water. Instead, it most likely represents a fluid (brine) exsolved from magma, which was responsible for high temperature metasomatism in the deep conduit system. [Copyright &y& Elsevier]

The Paleoproterozoic Lomagundi-Jatuli positive δ13C excursion in sedimentary carbonates represents an event whose magnitude and duration is unique in Earth history, although precise absolute chronology of this event remains poorly constrained. In northeastern Fennoscandia, an ∼1300-m-thick sedimentary-volcanic succession of the Pechenga Greenstone Belt records decline of this isotopic excursion. Zircons from sedimentary rocks that occur within the decline have yielded 207Pb/206Pb dates at 2058 ± 2 Ma (±6 Ma including U decay constant uncertainties) and provide the first maximum age constraint on the termination of the Lomagundi-Jatuli event. Combined with existing constraints, these data indicate an ∼140 m.y. interval characterized by 13C-rich carbonate accumulation. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates δ13C and δ18O variations in the shells of modern brachiopods representing all extant groups of calcite-precipitating brachiopods, collected live from 8 locations. SEM examinations determined the ultrastructural characteristics of each species prior to isotope analyses. δ13C and δ18O analyses of shell carbonate were carried out with samples representing disparate morphological features and ultrastructural shell layers of both ventral and dorsal valves. Generally, δ18O values from the fibrous secondary or prismatic tertiary shell layers of the articulated Terebratulida and Rhynchonellida species were in oxygen isotopic equilibrium with ambient seawater. Isotopic temperatures extrapolated from these values are close to measured annual mean seawater temperatures. δ18O values were relatively unaffected by shell specialisation. The only exception was Antarctic species Liothyrella uva, which did not have a complete tertiary shell layer typical of this genus and had δ18O values of the innermost layer strongly correlated with δ13C and mostly not in oxygen isotopic equilibrium with ambient seawater. With the exception of the rhynchonellid Notosaria nigricans, the outer primary layer material was depleted in δ13C and δ18O and highly variable. Inclusion of this material even as part of a whole shell sample could lead to misinterpretation of seawater temperature, therefore only fossil secondary layer material should be used. The anomalous articulated thecideidine brachiopod Thecidellina barretti is composed of mainly primary shell material and was not in oxygen isotope equilibrium. δ18O values from the laminar secondary layer material of the inarticulated Craniida are highly variable. Therefore, these species are not recommended for use as palaeoenvironmental proxies. This study suggests caution when employing fossil brachiopod shells with similar ultrastructures to modern craniid and thecideidine brachiopods. The carbon isotope composition is highly variable in all of the brachiopods studied. Analysis of samples from specialised regions of the secondary shell layer show a pattern of depletion in 13C relative to non-specialised secondary material. The carbon isotope variability is independent of δ18O and is repeated in most of the articulated species regardless of geographical location. This is possibly a vital effect produced by metabolic prioritisation. [Copyright &y& Elsevier]

The age structure and stable isotope composition of a stalagmite (CC1) from an upland cave in central-western Italy were studied to investigate regional response to global climatic changes. Four growth phases are constrained by 28 thermal ionization and multi-collector inductively coupled plasma mass spectrometry Th–U ages and reveal intermittent deposition through the period between Marine Isotope Stage (MIS) 11 and 3 (∼380 and ∼43 kyr). Most of the growth took place between ∼380 and ∼280 kyr, a period punctuated briefly by a hiatus in deposition through the glacial maximum of MIS 10. Growth was terminated abruptly at 280 kyr just prior to the MIS 8 glacial maximum. With a present-day chamber temperature of 7.5 °C, the timing of hiatuses close to these glacial maxima point to freezing conditions at the time. No deposition was recorded through the entirety of MIS 7 and most of MIS 6, whilst two minor growth phases occurred at ∼141–125 and ∼43 kyr. Growth at 141 kyr indicates temperatures >0 °C at a time when MIS 6 ice volumes were close to their maximum. High stable carbon isotope (δ13C) values (−2.8‰ to +3.1‰) throughout the stalagmite''s growth reflect a persistently low input of biogenic CO2, indicating that the steep, barren and alpine-like recharge area of today has been in existence for at least the last ∼380 kyr. During MIS 9, the lowest δ13C values occur well after maximum interglacial conditions, suggesting a lag in the development of post-glacial soils in this high-altitude karst. The stable oxygen isotope (δ18O) trends match the main structural features of the major climate proxy records (SPECMAP, Vostok and Devils Hole), suggesting that the δ18O of CC1 has responded to global-scale climate changes, whilst remarkable similarity exists between CC1 δ18O and regional sea-surface temperature reconstructions from North Atlantic core ODP980 and southwest Pacific marine core MD97-2120 through the most detailed part of the CC1 record, MIS 9–8. The results suggest that CC1 and other stalagmites from the cave have the potential to capture a long record of regional temperature trends, particularly in regards to the relative severity of Pleistocene glacial stages. [Copyright &y& Elsevier]