Characterisation of early Archaean chemical sediments by trace element signatures

Rare earth element (REE) plus yttrium (Y) patterns of modem seawater have characteristic features that can be used as chemical fingerprints. Reliable proxies for marine REE + Y chemistry have been demonstrated from a large geological time span, including Archaean banded iron formation (BIF), stromatolitic limestone, Phanerozoic reef carbonate and Holocene microbialite. Here we present new REE + Y data for two distinct suites of early Archaean (ca. 3.7-3.8 Ga) metamorphosed rocks from southern West Greenland, whose interrelationships, if any, have been much debated in recent literature. The first suite comprises mangetite-quartz BIF, magnetite-carbonate BIF and banded magnetite-rich quartz rock, mostly from the Isua Greenstone Belt (IGB). The REE + Y patterns, particularly diagnostic anomalies (Ce/Ce*, Pr/Pr*), are closely related to those of published seawater proxies. The second suite includes banded quartz-pyroxene-amphibole +/- garnet rocks with minor magnetite from the so-called Akilia Association enclaves (in early Archaean granitoid gneisses) of the coastal region, some 150 km southwest of the IGB. Rocks of this type from one much publicised and highly debated locality (the island of Akilia) have been identified by some workers [Nature 384 (1996) 55; Geochim. Cosmochim. Acta 61 (1997) 2475] as BIF-facies, and their C-13-depleted signature in trace graphite interpreted as a proxy for earliest life on Earth. However, REE + Y patterns of the Akilia Association suite (except for one probably genuine magnetite-rich BIF from Ugpik) are inconsistent with a seawater origin. We agree with published geological and geochemical (including REE) work [Science 296 (2002) 1448] that most of the analysed Akilia rocks are not chemical sediments, and that C-isotopes in such rocks therefore cannot be used as biological proxies. Application of the REE + Y discriminant for the above two rock suites has been facilitated in this study by the use of MC-ICP technique which yields a more complete and precise REE + Y spectrum than was available in many previous studies. (C) 2004 Elsevier B.V. All rights reserved.

Chemical characterization of earth's most ancient clastic metasediments from the Isua Greenstone Belt, southern West Greenland

New and published major and trace element abundances of elastic metasediments (mainly garnet-biotite-plagioclase schists) from the similar to 3.8 Ga Isua Greenstone Belt (IGB), southern West Greenland, are used in an attempt to identify the compositional characteristics of the protoliths of these sediments. Compositionally, the metasediments are heterogeneous with enrichment of LREE (La/Sm-chord = 1.1-3.9) and variable enrichment and depletion of HREE (Gd/Yb-chord = 0.8-4.3). Chondrite-normalized Eu is also variable, spanning a range from relative Eu depletion to enrichment (Eu/Eu* = 0.6-1.3). A series of geochemical and geological criteria provides conclusive evidence for a sedimentary origin, in disagreement with some previous studies that questioned the presence of genuine elastic metasediments. In particular, trace element systematics of IGB metasediments show strong resemblance to other well-documented Archaean clastic sediments, and are consistent with a provenance consisting of ultramafic, malic and felsic igneous rocks. Two schists, identified as metasomatized mafic igneous rocks from petrographic and field evidence, show distinct compositional differences to the metasediments. Major element systematics document incipient-to-moderate source weathering in the majority of metasediments, while signs of secondary K-addition are rare. Detailed inspection of Eu/Eu*, Fe2O3 and CIW (chemical index of weathering) relationships reveals that elevated iron contents (when compared to averages for continental crust) and strong relative enrichment in Eu may be due to precipitation of marine Fe-oxyhydroxides during deposition or diagenesis on the seafloor. Some of the IGB metasediments have yielded anomalous Nd-142 and W-182 isotopic compositions that were respectively interpreted in terms of early mantle differentiation processes and the presence of a meteorite component. Alternatively, W and possibly Nd isotopes could have been affected by thermal neutron capture on the Hadean surface. The latter process was tested in this study by analysis of Sm isotope compositions, which serve as an effective monitor for neutron capture effects. As no anomalous variation from terrestrial values was detected, we infer that isotope systematics (including W-182 and Nd-142) of IGB metasediments were not affected by neutron capture, but reflect decay of radioactive parent isotopes. Copyright (c) 2005 Elsevier Ltd.

A stress and coping approach to organisational change: Evidence from three field studies

In this paper, a stress and coping perspective is used to outline the processes that determine employee adaptation to organisational change. A theoretical framework that simultaneously considers the effects of event characteristics, situational appraisals, coping strategies, and coping resources is reviewed, Three empirical investigations of organisational change that have tested various components of the model are then presented. In the first study, there was evidence linking event characteristics, situational appraisals, coping strategies and coping resources to levels of employee adjustment in a sample of pilots employed in a newly merged airline company. In a more focused test of the model with a sample of employees experiencing a restructuring process in their Organisation it was found that the provision of change-related information enhanced levels of efficacy to deal with the change process which, in turn, predicted psychological wellbeing, client engagement, and job satisfaction. In a study of managers affected by a new remuneration scheme, there was evidence to suggest that managers who received change-specific information and opportunities to participate in the change process reported higher levels of change readiness. Managers who reported higher levels of readiness for change also reported higher levels of psychological wellbeing and job satisfaction. These studies highlight ways in which managers and change agents can help employees to cope during times of organisational change.

Zinc deposits and related mineralization of the Burketown mineral field, including the world-class Century Deposit, Northern Australia: Fluid inclusion and stable isotope evidence for basin fluid sources

The stratiform Century Zn-Pb deposit and the discordant Zn-Pb lode deposits of the Burketown mineral field, northern Australia, host ore and gangue minerals with primary fluid inclusions that have not been affected by the Isan orogeny, thus providing a unique opportunity to investigate the nature of the ore-forming brines. All of the deposits are hosted in shales and siltstones belonging to the Isa superbasin and comprise sphalerite, pyrite, carbonate, quartz, galena, minor chalcopyrite, and minor illite. According to Pb model ages, the main ore stage of mineralization at Century formed at I575 Ma, some 20 m.y. after deposition of the host shale sequence. Microthermometry on undeformed, primary fluid inclusions hosted in porous sphalerite shows that the Zn at Century was transported to the deposit by a homogeneous, Ca2+- and Na+-bearing brine with a salinity of 21.6 wt percent NaCl equiv. delta D-fluid of the fluid inclusion water ranges from -89 to -83 per mil, consistent with a basinal brine that evolved from meteoric water. Fluid inclusion homogenization temperatures range between 74 degrees and 125 degrees C, which are lower than the 120 degrees to 160 degrees C range calculated from vitrinite reflectance and illite crystallinity data from the deposit. This discrepancy indicates that mineralization likely formed at 50 to 85 Mpa, corresponding to a depth of 1,900 to 3,100 m. Transgressive galena-sphalerite veins that cut stratiform mineralization at Century and breccia-filled quartz-dolomite-sphalerite-galena veins in the discordant Zn-Pb lodes have Pb model ages between 1575 and 1485 Ma. Raman spectroscopy and microthermometry reveal that the primary fluid inclusions in these veins contain Ca2+, Na+. but they have lower salinities between 23 and 10 wt percent NaCl equiv and higher delta D-fluid values ranging from -89 to -61 per mil than fluid inclusions in porous sphalerite from Century. Fluid inclusion water from sphalerite in one of the lode deposits has delta O-18(fluid) values of 1.6 and 2.4 per mil, indistinguishable from delta O-18(fluid) values between -0.3 to +7.4 per mil calculated from the isotopic composition of coexisting quartz, dolomite, and illite. The trend toward lower salinities and higher delta D-fluid values relative to the earlier mineralizing fluids is attributed to mixing between the fluid that formed Century and a seawater-derived fluid from a different source. Based on seismic data from the Lawn Hill platform and paragenetic and geochemical results from the Leichhardt River fault trough to the south, diagenetic aquifers in the Underlying Calvert superbasin appear to have been the most likely sources for the fluids that formed Century and the discordant lode deposits. Paragenetically late sphalerite and calcite cut sphalerite, quartz, and dolomite in the lode deposits and contain Na+-dominated fluid inclusions with much lower salinities than their older counterparts. The isotopic composition of calcite also indicates delta O-18(fluid) from 3.3 to 10.7 per mil, which is larger than the range obtained from synmineralization minerals, supporting the idea that a unique fluid source was involved. The absolute timing of this event is unclear, but a plethora of Pb model, K-Ar, and Ar-40/Ar-39 ages between 1440 and 1300 Ma indicate that a significant volume of fluid was mobilized at this time. The deposition of the Roper superbasin from ca. 1492 +/- 4 Ma suggests that these late veins formed from fluids that may have been derived from aquifers in overlying sediments of the Roper superbasin. Clear, buck, and drusy quartz in veins unrelated to any form of Pb-Zn mineralization record the last major fluid event in the Burketown mineral field and form distinct outcrops and ridges in the district. Fluid inclusions in these veins indicate formation from a low-salinity, 300 degrees +/- 80 degrees C fluid. Temperatures approaching 300 degrees C recorded in organic matter adjacent to faults and at sequence boundaries correspond to K-Ar ages spanning 1300 to 1100 Ma, which coincides with regional hydrothermal activity in the northern Lawn Hill platform and the emplacement of the Lakeview Dolerite at the time of assemblage of the Rodinia supercontinent.

Geological and trace element evidence for a marine sedimentary environment of deposition and biogenicity of 3.45 Ga stromatolitic carbonates in the Pilbara Craton, and support for a reducing Archaean ocean

Bedded carbonate rocks from the 3.45 Ga Warrawoona Group, Pilbara Craton, contain structures that have been regarded either as the oldest known stromatolites or as abiotic hydrothermal deposits. We present new field and petrological observations and high-precision REE + Y data from the carbonates in order to test the origin of the deposits. Trace element geochemistry from a number of laminated stromatolitic dolomite samples of the c. 3.40 Ga Strelley Pool Chert conclusively shows that they precipitated from anoxic seawater, probably in a very shallow environment consistent with previous sedimentological observations. Edge-wise conglomerates in troughs between stromatolites and widespread cross-stratification provide additional evidence of stromatolite construction, at least partly, from layers of particulate sediment, rather than solely from rigid crusts. Accumulation of particulate sediment on steep stromatolite sides in a high-energy environment suggests organic binding of the surface. Relative and absolute REE + Y contents are exactly comparable with Late Archaean microbial carbonates of widely agreed biological origin. Ankerite from a unit of bedded ankerite–chert couplets from near the top of the stratigraphically older (3.49 Ga) Dresser Formation, which immediately underlies wrinkly stromatolites with small, broad, low-amplitude domes, also precipitated from anoxic seawater. The REE + Y data of carbonates from the Strelley Pool Chert and Dresser Formation contrast strongly with those from siderite layers in a jasper–siderite–Fe-chlorite banded iron-formation from the base of the Panorama Formation (3.45 Ga), which is clearly hydrothermal in origin. The geochemical results, together with sedimentological data, strongly support: (1) deposition of Dresser Formation and Strelley Pool Chert carbonates from Archaean seawater, in part as particulate carbonate sediment; (2) biogenicity of the stromatolitic carbonates; (3) a reducing Archaean atmosphere; (4) ongoing extensive terrestrial erosion prior to ∼3.45 Ga.

Empirical evidence showing the relationships between three approaches for pollution control

Willingness to pay models have shown the theoretical relationships between the contingent valuation, cost of illness and the avertive behaviour approaches. In this paper, field survey data are used to compare the relationships between these three approaches and to demonstrate that contingent valuation bids exceed the sum of cost of illness and the avertive behaviour approach estimates. The estimates provide a validity check for CV bids and further support the claim that contingent valuation studies are theoretically consistent.

Initiation of fungal epizootics in diamondback moth populations within a large field cage: proof of concept for auto-dissemination

Adult diamondback moths (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), inoculated with the fungus Zoophthora radicans, were released within a large field cage containing DBM-infested potted broccoli plants. Larvae and pupae on exposed and caged control plants were examined on five occasions over the next 48 days for evidence of Z. radicans infection. Infected larvae were first detected on exposed plants 4 days after the initial release of adults, and after 48 days the infection level reached 79%. Aerially borne conidia were a factor in transmission of the fungus. Infection had no effect on possible losses of larval and adult cadavers due to scavengers in field crops. In a trial to measure the influence of infection on dispersal, twice as many non-infected as infected males were recaptured in pheromone traps, although the difference in cumulative catch only became significant 3 days after release of the males. In a separate experiment, when adult moths were inoculated with Beauveria bassiana conidia and released into the field cage, DBM larvae collected from 37 of 96 plants sampled 4 days later subsequently died from B. bassiana infection. The distribution of plants from which the infected larvae were collected was random, but the distribution of infected larvae was clustered within the cage. These findings suggest that the auto-dissemination of fungal pathogens may be a feasible strategy for DBM control, provided that epizootics can be established and maintained when DBM population densities are low.

Genetic variation for carbon isotope discrimination in sunflower: Association with transpiration efficiency and evidence for cytoplasmic inheritance

Plants accumulate isotopes of carbon at different rates because of discrimination against C-13 relative to C-12. In plants that fix carbon by the C-3 pathway, the amount of discrimination correlates negatively with transpiration efficiency (TE) where TE is the amount of dry matter accumulated per unit water transpired. Therefore, carbon isotope discrimination (Delta) has become a useful tool for selecting genotypes with improved TE and performance in dry environments. Surveys of 161 sunflower (Helianthus spp.) genotypes of diverse origin revealed a large and unprecedented range of genetic variation for Delta (19.5-23.8parts per thousand). A strong negative genetic correlation (r(g)) between TE and Delta (r(g) = -0.87, P < 0.001) was observed in glasshouse studies. Gas exchange measurements of field grown plants indicated that Delta was strongly correlated with stomatal conductance to water vapor (g), (r(g) 0.64, P < 0.01), and the ratio of net assimilation rate (A) to g, (r(g) = 0.86, P < 0.001), an instantaneous measure of TE. Genotype CMSHA89MAX1 had the lowest TE (and highest Delta) of all genotypes tested in these studies and low yields in hybrid combination. Backcrossing studies showed that the TE of this genotype was due to an adverse effect of the MAX1 cytoplasm, which was inherited from the diploid perennial H. maximiliani Schrader. Overall, these studies suggested that there is an excellent opportunity for breeders to develop sunflower germplasm with improved TE. This can be achieved, in part, by avoiding cytoplasms such as the MAX1 cytoplasm.

Correlations between the satellite-derived seasonal cycle of phytoplankton biomass and aerosol optical depth in the Southern Ocean: Evidence for the influence of sea ice

The relationship between the production of dimethylsulfide (DMS) in the upper ocean and atmospheric sulfate aerosols has been confirmed through local shipboard measurements, and global modeling studies alike. In order to examine whether such a connection may be recoverable in the satellite record, we have analyzed the correlation between mean surface chlorophyll (CHL) and aerosol optical depth (AOD) in the Southern Ocean, where the marine atmosphere is relatively remote from anthropogenic and continental influences. We carried out the analysis in 5-degree zonal bands between 50 degrees S and 70 degrees S, for the period ( 1997 - 2004), and in smaller meridional sectors in the Eastern Antarctic, Ross and Weddell seas. Seasonality is moderate to strong in both CHL and AOD signatures throughout the study regions. Coherence in the CHL and AOD time series is strong in the band between 50 degrees S and 60 degrees S, however this synchrony is absent in the sea-ice zone (SIZ) south of 60 degrees S. Marked interannual variability in CHL occurs south of 60 degrees S, presumably related to variability in sea-ice production during the previous winter. We find a clear latitudinal difference in the cross correlation between CHL and AOD, with the AOD peak preceding the CHL bloom by up to 6 weeks in the SIZ. This suggests that substantial trace gas emissions ( aerosol precursors) are being produced over the SIZ in spring ( October - December) as sea ice melts. This hypothesis is supported by field data that record extremely high levels of sulfur species in sea ice, surface seawater, and the overlying atmosphere during ice melt.

Evidence of altered prefrontal-thalamic circuitry in schizophrenia: An optimised diffusion MRI study

MRI diffusion tensor imaging (DTI), optimized for measuring the trace of the diffusion tensor, was used to investigate microstructural changes in the brains of 12 individuals with schizophrenia compared with 12 matched control subjects. To control for the effects of anatomic variation between subject groups, all participants' diffusion images were non-linearly registered to standard anatomical space. Significant statistical differences in mean diffusivity (MD) measures between the two groups were determined on a pixel-by-pixel basis, using Gaussian random field theory. We found significantly elevated MD measures within temporal, parietal and prefrontal cortical regions in the schizophrenia group (P > 0.001), especially within the medial frontal gyrus and anterior cingulate. The dorsal medial and anterior nucleus of the thalamus, including the caudate, also exhibited significantly increased MD in the schizophrenia group (P > 0.001). This study has shown for the first time that MD measures offer an alternative strategy for investigating altered prefrontal-thalamic circuitry in schizophrenia. (c) 2006 Elsevier Inc. All rights reserved.