Comparison of iron isotope variations in modern and Ordovician siliceous Fe oxyhydroxide deposits

Formation pathways of ancient siliceous iron formations and related Fe isotopic fractionation are still not completely understood. Investigating these processes, however, is difficult as good modern analogues to ancient iron formations are scarce. Modern siliceous Fe oxyhydroxide deposits are found at marine hydrothermal vent sites, where they precipitate from diffuse, low temperature fluids along faults and fissures on the seafloor. These deposits exhibit textural and chemical features that are similar to some Phanerozoic iron formations, raising the question as to whether the latter could have precipitated from diffuse hydrothermal fluids rather than from hydrothermal plumes. In this study, we present the first data on modern Fe oxyhydroxide deposits from the Jan Mayen hydrothermal vent fields, Norwegian-Greenland Sea. The samples we investigated exhibited very low δ56Fe values between -2.09‰ and -0.66‰. Due to various degrees of partial oxidation, the Fe oxyhydroxides are with one exception either indistinguishable from low-temperature hydrothermal fluids from which they precipitated (-1.84‰ and -1.53‰ in δ56Fe) or are enriched in the heavy Fe isotopes. In addition, we investigated Fe isotope variations in Ordovician jasper beds from the Løkken ophiolite complex, Norway, which have been interpreted to represent diagenetic products of siliceous ferrihydrite precursors that precipitated in a hydrothermal plume, in order to compare different formation pathways of Fe oxyhydroxide deposits. Iron isotopes in the jasper samples have higher δ56Fe values (-0.38‰ to +0.89‰) relative to modern, high-temperature hydrothermal vent fluids (ca. -0.40‰ on average), supporting the fallout model. However, formation of the Ordovician jaspers by diffuse venting cannot be excluded, due to lithological differences of the subsurface of the two investigated vent systems. Our study shows that reliable interpretation of Fe isotope variations in modern and ancient marine Fe oxyhydroxide deposits depends on comprehensive knowledge of the geological context. Furthermore, we demonstrate that very negative δ56Fe values in such samples might not be the result of microbial dissimilatory iron reduction, but could be caused instead by inorganic reactions.

Recent Increases in Atmospheric Concentrations of Bi, U, Cs, S and Ca from a 350-Year Mount Everest Ice Core Record

High-resolution major and trace elements (Sr, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu, Bi, U, Tl, Al, S, Ca, Ti, V, Cr, Mn, Fe, and Co) quantified in a Mount Everest ice core ( 6518 m above sea level) spanning the period 1650-2002 AD provides the first Asian record of trace element concentrations from the pre-industrial era, and the first continuous high-resolution Asian record from which natural baseline concentrations and subsequent changes due to anthropogenic activities can be examined. Modern concentrations of most elements remain within the pre-industrial range; however, Bi, U, and Cs concentrations and their enrichment factors (EF) have increased since the similar to 1950s, and S and Ca concentrations and their EFs have increased since the late 1980s. A comparison of the Bi, U, Cs, S, and Ca data with other ice core records and production data indicates that the increase in atmospheric concentrations of trace elements is widespread, but that enrichment varies regionally. Likely sources for the recent enrichment of these elements include mining, metal smelting, oil and coal combustion, and end uses for Bi, and mining and refinement for U and Cs. The source of the synchronous enrichment of Ca and S is less certain, but may be related to land use and environmental change.

A High-Resolution Record of Atmospheric Dust Composition and Variability Since Ad 1650 from a Mount Everest Ice Core

A Mount Everest ice core analyzed at high resolution for major and trace elements (Sr, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu, Bi, U, Tl, Al, S, Ca, Ti, V, Cr, Mn, Fe, Co) and spanning the period A. D. 1650- 2002 is used to investigate the sources of and variations in atmospheric dust through time. The chemical composition of dust varies seasonally, and peak dust concentrations occur during the winter-spring months. Significant correlations between the Everest dust record and dust observations at stations suggest that the Everest record is representative of regional variations in atmospheric dust loading. Back-trajectory analysis in addition to a significant correlation of Everest dust concentrations and the Total Ozone Mapping Spectrometer (TOMS) aerosol index indicates that the dominant winter sources of dust are the Arabian Peninsula, Thar Desert, and northern Sahara. Factors that contribute to dust generation at the surface include soil moisture and temperature, and the long-range transport of dust aerosols appears to be sensitive to the strength of 500-mb zonal winds. There are periods of high dust concentration throughout the 350-yr Mount Everest dust record; however, there is an increase in these periods since the early 1800s. The record was examined for recent increases in dust emissions associated with anthropogenic activities, but no recent dust variations can be conclusively attributed to anthropogenic inputs of dust.

Recommended Nomenclature for the Sapphirine and Surinamite Groups (Sapphirine Supergroup)

Minerals isostructural with sapphirine-1A, sapphirine-2M, and surinamite are closely related chain silicates that pose nomenclature problems because of the large number of sites and potential constituents, including several (Be, B, As, Sb) that are rare or absent in other chain silicates. Our recommended nomenclature for the sapphirine group (formerly-aenigmatite group) makes extensive use of precedent, but applies the rules to all known natural compositions, with flexibility to allow for yet undiscovered compositions such as those reported in synthetic materials. These minerals are part of a polysomatic series composed of pyroxene or pyroxene-like and spinel modules, and thus we recommend that the sapphirine supergroup should encompass the polysomatic series. The first level in the classification is based on polysome, i.e. each group within the supergroup Corresponds to a single polysome. At the second level, the sapphirine group is divided into subgroups according to the occupancy of the two largest M sites, namely, sapphirine (Mg), aenigmatite (Na), and rhonite (Ca). Classification at the third level is based on the occupancy of the smallest M site with most shared edges, M7, at which the dominant cation is most often Ti (aenigmatite, rhonite, makarochkinite), Fe(3+) (wilkinsonite, dorrite, hogtuvaite) or Al (sapphirine, khmaralite); much less common is Cr (krinovite) and Sb (welshite). At the fourth level, the two most polymerized T sites are considered together, e.g. ordering of Be at these sites distinguishes hogtuvaite, makarochkinite and khmaralite. Classification at the fifth level is based on X(Mg) = Mg/(Mg + Fe(2+)) at the M sites (excluding the two largest and M7). In principle, this criterion could be expanded to include other divalent cations at these sites, e.g. Mn. To date, most minerals have been found to be either Mg-dominant (X(mg) > 0.5), or Fe(2+)-dominant (X(Mg) < 0.5), at these M sites. However, X(mg) ranges from 1.00 to 0.03 in material described as rhonite, i.e. there are two species present, one Mg-dominant, the other Fe(2+)-dominant. Three other potentially new species are a Mg-dominant analogue of wilkinsonite, rhonite in the Allende meteorite, which is distinguished front rhonite and dorrite in that Mg rather than Ti or FC(3+) is dominant at M7, and an Al-dominant analogue of sapphirine, in which Al > Si at the two most polymerized T sites vs. Al < Si in sapphirine. Further splitting of the supergroup based on occupancies other than those specified above is not recommended.

Chemical Composition of Fresh Snow from Glaciar Marinelli, Tierra Del Fuego, Chile

A fresh-snow sampling campaign was conducted during the late austral summer of 2006 in the accumulation zone of Glaciar Marinelli, located in the Cordillera Darwin, Tierra del Fuego, Chile. Snow samples were analyzed for stable isotopes (delta(18)O, major soluble ions (Na', K', Ca, Mg, a NO(3)(-), SO(4)(2-), MS(-)) and major and trace elements (Na, Mg, Al, Fe, Ca, Sr, Cd, Cs, Ba, La, Ce, Pr, Dy, Ho, Er, Bi, U, As, Ti, V, Cr, Mn). The dominance of marine chemistry resembles that in studies from Patagonian glaciers. Snow chemistry was dominantly loaded by marine species (Cl(-), Na(+) and ssSO(4)(2-)), while contributions of crustal species (e.g. Al and Fe) were very low. Empirical orthogonal function analysis suggests two possible dust sources, one represented by Al and Fe and the other by La, Ce and Pr. Enrichment-factor calculations suggest the majority of elements are within average upper-crustal ratios, but major enrichments of Bi and Cd (hundreds of times) suggest possible anthropogenic sources. Linear correlation of delta(18)O and barometric pressure (r = 0.60, p < 0.007) suggests a potential 'amount effect' relationship between depleted delta(18)O ratios and stronger storm conditions (e.g. greater precipitation). The snow-chemistry records from Glaciar Marinelli are the first measured in Tierra del Fuego, the southernmost glaciated region outside Antarctica.

Characterisation of a Natural Quartz Crystal as a Reference Material for Microanalytical Determination of Ti, Al, Li, Fe, Mn, Ga and Ge

A natural smoky quartz crystal from Shandong province, China, was characterised by laser ablation ICP-MS, electron probe microanalysis (EPMA) and solution ICP-MS to determine the concentration of twenty-four trace and ultra trace elements. Our main focus was on Ti quantification because of the increased use of this element for titanium in- quartz (TitaniQ) thermobarometry. Pieces of a uniform growth zone of 9 mm thickness within the quartz crystal were analysed in four different LA-ICP-MS laboratories, three EPMA laboratories and one solution-ICP-MS laboratory. The results reveal reproducible concentrations of Ti (57 ± 4 lg g-1),Al (154 ± 15 lg g-1), Li (30 ± 2 lg g-1), Fe (2.2 ± 0.3 lg g-1), Mn (0.34 ± 0.04 lg g-1), Ge (1.7 ± 0.2 lg g-1) and Ga (0.020 ± 0.002 lg g-1) and detectable, but less reproducible, concentrations of Be, B, Na, Cu, Zr, Sn and Pb. oncentrations of K, Ca, Sr, Mo, Ag, Sb, Ba and Au were below the limits of detection of all three techniques. The uncertainties on the average concentration determinations by multiple techniques and laboratories for Ti, Al, Li, Fe, Mn, Ga and Ge are low; hence, this quartz can serve as a reference material or a secondary reference material for microanalytical applications involving the quantification of trace elements in quartz.

Benchmarking the simulation of Cr isotope fractionation

A benchmark problem set consisting of four problem levels was developed for the simulation of Cr isotope fractionation in 1D and 2D domains. The benchmark is based on a recent field study where Cr(VI) reduction and accompanying Cr isotope fractionation occurs abiotically by an aqueous reaction with dissolved Fe 2+ (Wanner et al., 2012., Appl. Geochem., 27, 644–662). The problem set includes simulation of the major processes affecting the Cr isotopic composition such as the dissolution of various Cr(VI) bearing minerals, fractionation during abiotic aqueous Cr(VI) reduction, and non-fractionating precipitation of Cr(III) as sparingly soluble Cr-hydroxide. Accuracy of the presented solutions was ensured by running the problems with four well-established reactive transport modeling codes: TOUGHREACT, MIN3P, CRUNCHFLOW, and FLOTRAN. Results were also compared with an analytical Rayleigh-type fractionation model. An additional constraint on the correctness of the results was obtained by comparing output from the problem levels simulating Cr isotope fractionation with the corresponding ones only simulating bulk concentrations. For all problem levels, model to model comparisons showed excellent agreement, suggesting that for the tested geochemical processes any code is capable of accurately simulating the fate of individual Cr isotopes.

Superspace description of wagnerite-group minerals (Mg,Fe,Mn) 2 (PO 4 )(F,OH)

Reinvestigation of more than 40 samples of minerals belonging to the wagnerite group (Mg, Fe, Mn)2(PO4)(F,OH) from diverse geological environments worldwide, using single-crystal X-ray diffraction analysis, showed that most crystals have incommensurate structures and, as such, are not adequately described with known polytype models (2b), (3b), (5b), (7b) and (9b). Therefore, we present here a unified superspace model for the structural description of periodically and aperiodically modulated wagnerite with the (3+1)-dimensional superspace group C2/c(0[beta]0)s0 based on the average triplite structure with cell parameters a [asymptotically equal to] 12.8, b [asymptotically equal to] 6.4, c [asymptotically equal to] 9.6 Å, [beta] [asymptotically equal to] 117° and the modulation vectors q = [beta]b*. The superspace approach provides a way of simple modelling of the positional and occupational modulation of Mg/Fe and F/OH in wagnerite. This allows direct comparison of crystal properties.

Geochemistry of minerals in CRP sediment cores from the Ross Sea, Antarctica

Sixty-four volcanic chists, sandstones and tephras between 5.95 and 618.19 meters below sea floor (mbsf) in the Cape Roberts Project cores 2 and 2A cores (CRP-2/2A) were examined for Cenozoic and Mesozoic volcanic components, using optical and Scanning Electron Microscopy. Minerals and glass shards in a selection of samples were analysed by electron microprobe fined with an EDAX detector. Laser-Ablation ICP-Mass-Spectrometry (ICP-MS) was used to determine rare earth elements and 14 additional trace elements in glass shards, pyroxenes and feldspars in order to pin-point the onset of McMurdo Volcanic Group (MVG) activity in the stratigraphic column. Pumices in tephra layers of peralkaline phonolite composition in Unit 7.2 -between 108 and 114 mbsf - were also analysed for trace elements by ICP-MS. This tephra unit is not reworked and its isotopic age (21.44 ± 0.05 Ma) is the age of deposition. The height of the eruptive column responsible for the deposition of the tephra was probably less than 8 km; the source was local, probably within 30 km from the drill site. Phonolite of unit 7.2 of CRP-2/2A has no direct petrogenetic relation with the peralkaline trachyte in the tephra-enriched layer of CRP-1 at 116.55 mbsf. Volcanic clasts and sand grains (glass shards, aegirine-augite, anorthoclase) related to Cenozoic activity of MVG were observed only starting from Unit 9.8, where they are dated at 24.22 ± 0.06 Ma at c. 280 mbsf. In this unit the lowest- occurring basaltic glass shard is found at 297.54 mbsf. Sampled McMurdo volcanics are generally vesicular and vary in composition from alkali basalt to trachyte and peralkaline phonolite. By contrast, below 320 mbsf, aphyric or slightly-porphyritic volcanic clasts become more abundant but they are all non-vesiculated, pigeconite and ilmenite-bearing basalts and dolerite of tholeiitic affinity. These rocks are considered to be related to lava flows and associated intrusions of Jurassic age (Kirkpatrick basalts and Ferrar dolerite). As in CRP-1, McMurdo volcanics appear to derive from a variety of lithologics. Besides glaciers, a dominant role of wind transportation from exposed volcanic rocks may be inferred from the contemporary occurrence of glass shards of different compositions at depths above 297.54 mbsf. These data confirm that the onset of magmatic activity in southern Victoria Land is considerably delayed (by about 24 Ma) with respect to northern Victoria Land.

Major elements and trace ferrides in deep sea cores obtained during the Swedish Deep-Sea Expedition in 1947-1948

Samples from sediment cores collected during the Swedish Deep-Sea Expedition 1947-1948 have been analyzed in the Geochemical laboratory of the Geological Survey of Sweden. Most samples were placed at our disposal by Professor Hans Pettersson, leader of the expedition mentioned. For complementary studies, samples from the Atlantic and Indian oceans were included in our investigation and the samples placed at our disposal by Professor B. Kullenberg, Göteborg. From the Tyrrhenian Sea we got samples from Professor E. Norin, Uppsala.

Concentrations of metals and POPs in liver tissue of wild sea bird chicks from the Norwegian arctic region

Lysosomal membrane stability, lipofuscin (LF), malondialdehyde (MDA), neutral lipid (NL) levels, as well as halogenated organic compounds (HOCs), Cr, Cd, Pb and Fe concentrations were analyzed in liver of black-legged kittiwake (BK), herring gull (HG), and northern fulmar (NF) chicks. There were significant species differences in the levels of NL, LF and lysosomal membrane stability. These parameters were not associated with the respective HOC concentrations. LF accumulation was associated with increasing Cr, Cd and Pb concentrations. HG presented the lowest lysosomal membrane stability and the highest. LF and NL levels, which indicated impaired lysosomes in HG compared to NF and BK. Lipid peroxidation was associated with HOC and Fe2+ levels. Specific HOCs showed positive and significant correlations with MDA levels in HG. The study indicates that contaminant exposure can affect lysosomal and lipid associated parameters in seabird chicks even at low exposure levels. These parameters may be suitable markers of contaminant induced stress in arctic seabirds.

The Cenomanian/Turronian Boundary Event at ODP Hole 103-641A

Drilling at ODP Site 641 (on the western margin of Galicia Bank, off northwestern Spain) revealed a thin, but pronounced, interval of black shale and gray-green claystone. Our high-resolution study combines the sedimentology, micropaleontology (palynomorphs and others), organic and inorganic geochemistry, and isotopic values of this layer to demonstrate the distinct nature of the sediment and prove that the sequence represents the local sedimentary expression of the global Cenomanian/Turonian Oceanic Anoxic Event (OAE) of Schlanger and Jenkyns (1976), Arthur and Schlanger (1979), and Jenkyns (1980), also called the Cenomanian/Turonian Boundary Event (CTBE). The most striking evidence is that the strong positive d13C excursion characterizing the CTBE sequences in shallow areas can be traced into a pronounced deep-sea expression, thus providing a good stratigraphic marker for the CTBE in various paleosettings. The isotopic excursion at Site 641 coincides with an extremely enriched trace metal content, with values that were previously unknown for the Cretaceous Atlantic. Similar to other CTBE occurrences, the organic carbon content is high (up to 11%) and the organic matter is of dominantly marine origin (kerogen type II). The bulk mineralogy of the CTBE sediments does not differ significantly from the general trend of Cretaceous North Atlantic sediments (dominance of smectite and zeolite with minor amounts of illite and scattered palygorskite, kaolinite, and chlorite); thus, no evidence for either increased volcanic activity nor a drastic climatic change in the borderlands was found. Results from Site 641 are compared with the CTBE section found at Site 398, DSDP Leg 47B (Vigo Seamount at the southern end of the Galicia Bank).