The smelters and the tree—an environmental story

Over the past 150 years a chestnut oak growing on a ridge above the Palmerton zinc smelters, Pennsylvania, USA, has recorded environmental changes. Changes in chemistry measured in a tree-ring core from this chestnut oak signal the start of smelting in the late 1800s, the change in ore feed during the 1920s and 1930s, and the positive impact of pollution abatement efforts. Since the cessation of smelting in the 1980s, many of the metal concentrations have returned to pre-smelter backgrounds. As evidenced by the Palmerton study, tree ring records can be used as a tool for environmental forensics.     

Assessing adaptive capacity within regional climate change vulnerability studies—an Alpine example

Adaptive capacity represents a crucial component in the assessment of a region’s vulnerability to climate change. The term adaptive capacity is only fuzzily defined, and determining it is difficult and often neglected in previous studies. In this paper, a newly developed adaptive capacity concept is introduced, with a respective indicator/criteria system and simple aggregation methods. The approach allows for adaptive capacity assessments at 3 levels of specificity (impact specific, sector specific and regional generic). The selection of indicators is tailor-made for Alpine regions, where the approach has been widely tested. The presented approach requires extended stakeholder involvement, namely for the evaluation of the indicators. The overall effort needed for its implementation remains reasonable. The outcome of the assessment exercise does not provide precise objective measurements, but remains an indicative estimation due to the fuzziness and complexity of the underlying concept. The conceptual approach is transferable to other mountain areas and beyond, the selection of indicators however is only valid for the Alpine region. The showcase presents results from the adaptive capacity assessment in the region of South Tyrol, where the method was carried out as part of a climate change vulnerability study. The outcomes indicate a number of issues that future actions could address in order to improve adaptive capacity in the region, namely in the field of prevention measures against meteorological extremes and natural hazards.     

Tectono-metallogenic systems — The place of mineral systems within tectonic evolution,with an emphasis on Australian examples

Tectono-metallogenic systems are geological systems that link geodynamic and tectonic processes with ore-forming processes. Fundamental geodynamic processes, including buoyancy-related processes, crustal/lithospheric thinning and crustal/lithospheric thickening, have occurred throughout Earth's history, but tectonic systems, which are driven by these processes, have evolved as Earth's interior has cooled. Tectonic systems are thought to have evolved from magma oceans in the Hadean through an unstable “stagnant-lid” regime in the earlier Archean into a proto-plate tectonic regime from the late Archean onwards. Modern-style plate tectonics is thought to have become dominant by the start of the Paleozoic. Mineral systems with general similarities to modern or geologically recent systems have been present episodically (or semi-continuously) through much of Earth's history, but most of Earth's present endowment of mineral wealth was formed during and after the Neoarchean, when proto- or modern-style plate tectonic systems became increasingly dominant and following major changes in the chemistry of the atmosphere and hydrosphere. Changes in the characteristics of some mineral systems, such as the volcanic-hosted massive sulphide (VHMS) system, reflect changes in tectonic style during the evolution towards the modern plate tectonic regime, but may also involve secular changes in the hydrosphere and atmosphere.Whereas tectono-metallogenic systems have evolved in general over Earth's history, specific tectono-metallogenic systems evolve over much shorter time frames. Most mineral deposits form in three general tectono-metallogenic systems: divergent systems, convergent systems, and intraplate systems. Although fundamental geodynamic processes have driven the evolution of these systems, their relative importance may change as the systems evolved. For example, buoyancy-driven (mantle convection/plumes) and crustal thinning are the dominant processes driving the early rift stage of divergent tectono-metallogenic systems, whereas buoyancy-driven processes (slab sinking) and crustal thickening are the most important processes during the subduction stage of convergent systems. Crustal thinning can also be an important process in the hinterland of subduction zones, producing back-arc basins that can host a number of mineral systems. As fundamental geodynamic processes act as drivers at some stage in virtually all tectonic systems, on their own these cannot be used to identify tectonic systems. Moreover, as mineral systems are ultimately the products of these same geodynamic drivers, individual mineral deposit types cannot be used to determine tectonic systems, although mineral deposit associations can, in some cases, be indicative of the tectono-metallogenic system.Ore deposits are the products of geological (mineral) systems that operate over a long time frame (hundreds of millions of years) and at scales up to the craton-scale. In essence, mineral systems increase the concentrations of commodities through geochemical and geophysical processes from bulk Earth levels to levels amenable to economic mining. Mineral system components include the geological (tectonic and architectural) setting, the driver(s) of mineralising processes, metal and fluid sources, fluid pathways, depositional trap, and post-depositional modifications. All of these components link back to geodynamic processes and the tectonic system. For example, crustal architecture, which controls the spatial distribution of, and fluid flow, within mineral systems, is largely determined by geodynamic processes and tectonic systems, and the timing of mineralisation, which generally is relatively short (commonly < 1 Myr), correlates with local and/or far-field tectonic events.The geochemical characteristics of many mineral systems are a consequence of their geodynamic and tectonic settings. Settings that are characterised by low heat flow and lack active magmatism produce low temperature fluids that are oxidised, with ore formation caused largely by redox gradients or the provision of external H₂S. The characteristics of these fluids are largely governed by the rocks with which they interact, rocks that have extensively interacted with the hydrosphere and atmosphere, both environments that have been strongly oxidised since the great oxidation event in the Paleoproterozoic. In settings characterised by high heat flow and active magmatism, ore fluids tend to be higher temperature and reduced, with deposition caused by cooling, pH neutralisation, depressurisation and fluid mixing. Again, the characteristics of these fluids are governed by rocks with which they interact, in this case more reduced magmatic rocks derived from the mantle or lower crust.     

On-site treatment of textile yarn dyeing effluents using an integrated biological–chemical oxidation process

This paper reports the results of the treatment of a yarn dyeing effluent using an integrated biological–chemical oxidation process. In particular, the biological unit was based on a sequencing batch biofilter granular sludge reactor (SBBGR), while the chemical treatment consisted of an ozonation step. Biological treatment alone was first performed as a reference for comparison. While biological treatment did not produce an effluent for direct discharge, the integrated process assured good treatment results, with satisfactory removal of chemical oxygen demand (up to 89.8 %), total nitrogen (up to 88.2 %), surfactants (up to 90.7 %) and colour (up to 99 %), with an ozone dose of 110 mg of ozone per litre of wastewater. Biomass characterization by fluorescence in situ hybridization has revealed that filamentous bacteria represented about 20 % of biomass (coherently with high sludge volume index values); thanks to its special design, SBBGR guaranteed, however, stable treatment performances and low effluent suspended solids concentrations, while conventional activated sludge systems suffer from sludge bulking and even treatment failure in such a condition. Furthermore, biomass characterization has evidenced the presence of a shortcut nitrification–denitrification process.     

Defining metamorphogenic mineral deposits —an introduction

Summary Early tentative hypotheses, that regional metamorphism may be genetically associated with the formation of mineral deposits are now reasonably confirmed, and the class of metamorphogenic mineral deposits is widely accepted. Two end member models define a range of possibilities occurring in nature: the prograde devolatilization model, and the retrograde leaching model. In the first, the mineralizing fluids are thought to have been generated and to have acquired their solute content within source rocks undergoing prograde metamorphism. Then they flow towards lower pressure zones, possibly accompanied by further reactions with country rocks. Finally, changes in the chemical or physical environment along the flow conduits potentially induce mineral precipitation. Retrograde leaching occurs after peak metamorphism, when a still-hot metamorphic complex is flooded and cooled by waters from outside; this will normally happen during uplift and extensional tectonics, and the resulting convection cells are open to the surface. Metamorphogenic deposits cannot be recognized as such in the field, where they appear as examples of epigenetic hydrothermal mineralization. Only the application of a broad spectrum of laboratory methods allows a correct genetic classification. It is expected that future research will increasingly quantify the evolution of metamorphic terranes through time, similar to modern basin analysis in petroleum geology.

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Das Erkenen metamorphogener Lagersätten-eine Einleitung

Zusammenfassung Frühe Beobachtungen über enge Zusammenhänge zwischen regionaler Metamorphose und Lagerstättenbildung wurden in jüngerer Zeit bestätigt, so daß die Klasse der metamorphogenen Lagerstätten nunmehr nahezu gesichert ist. Zwei verschiedene genetische Modelle bilden die Endglieder eines in der Natur vorkommenden Spektrums solcher Lagerstättenbildung: das Modell der prograden Devolatilisierung und das Modell einer retrograden Laugung. Im ersten Fall wurden die lagerstättenbildenden Fluide innerhalb eines Gesteinskörpers gebildet, während dieser eine prograde Metamorphose erlitt; gleichzeitig nahmen die Fluide ihre kennzeichnende Lösungsfracht auf. Danach fließen sie einem Druckgefälle folgend aus dem Bildungsraum ab, z.T. unter weiteren Reaktionen mit Nebengesteinen. Chemische oder physikalische Zustandsänderungen im Verlauf der Fließwege induzieren den Mineralabsatz. Retrograde Laugung hingegen findet statt, wenn ein noch heier metamorpher Komplex nach Durchlaufen der maximalen p/T-Bedingungen durch von außen zufließende Wässer geflutet und abgekühlt wird; dies wird gewöhnlich mit Aufstieg und Dehnungstektonik verbunden sein, weshalb die resultierenden Konvektionszellen zur Oberfläche offen sind. Metamorphogene Lagerstätten können nicht nur mit Feldmethoden als solche erkannt werden, da sie dort einfach als epigenetische hydrothermale Mineralisationen erscheinen. Nur die Anwendung eines breiten Spektrums geeigneter Labormethoden erlaubt eine richtige Zuordnung. Es wird erwartet, daß zukünftige Forschung dadurch wesentliche Fortschritte erzielt, daß die Entwicklung metamorpher Komplexe in Zeit und Raum quantitativ untersucht wird, ähnlich wie jene sedimentärer Becken in der modernen Erdölgeologie.

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This paper was presented at the IGCP 291 Project Symposium Metamorphic Fluids and Mineral Deposits, ETH Zürich, March 21–23, 1991.     

GRIDA3—a shared resources manager for environmental data analysis and applications

GRIDA3 (Shared Resources Manager for Environmental Data Analysis and Applications) is a multidisciplinary project designed to deliver an integrated system to forge solutions to some environmental challenges such as the constant increase of polluted sites, the sustainability of natural resources usage and the forecast of extreme meteorological events. The GRIDA3 portal is mainly based on Web 2.0 technologies and EnginFrame framework. The portal, now at an advanced stage of development, provides end-users with intuitive Web-interfaces and tools that simplify job submission to the underneath computing resources. The framework manages the user authentication and authorization, then controls the action and job execution into the grid computing environment, collects the results and transforms them into an useful format on the client side. The GRIDA3 Portal framework will provide a problem-solving platform allowing, through appropriate access policies, the integration and the sharing of skills, resources and tools located at multiple sites across federated domains.     

State power and environmental initiatives in China: Analyzing China’s green building program through an ecological modernization perspective

This paper applies the ecological modernization (EM) framework to analyze China’s green building program. EM focuses on the effective institutionalization of environmental objectives into respective political and economic systems, and thus provides valuable insights into the roles of the state and other stake holders in environmental regulation. Since the mid-2000s, the Chinese government has advanced an aggressive green building campaign, which is distinguished by its speed, scale, and evolution from one of voluntary participation to a top-down implementation through administrative hierarchies. While this has resulted in a remarkable growth of green building projects, questions remain about the effectiveness and sustainability of such a state-centered approach. Though interviews with officials, planners, architects, real estate developers, and property managers in several Chinese cities, data analysis of the green building stock, and surveys of architects, this paper analyzes Chinese green building patterns and situates such patterns among the contradictory motivations of different levels of government and their relationships to different stake holders. This research finds that the top-down state apparatus is not sufficient to overcome these contradictions and the profit motives of the property developers. However, many under-developed opportunities exist to leverage property developers, building professionals, and the public to engage in green building practices. In the end, I argue that the state must embrace reform to build flexible and collaborative movements with other parties with strong public participation. China’s ecological modernization process may feature a stronger state and faster changes, but it is not exempted from the need of political modernization.     

Strain determination from three known stretches—an exact solution

In a domain of finite homogeneous deformation, the strain ellipse is uniquely specified by three linearly independent stretch measurements. An exact determination of the principal reciprocal quadratic stretches and principal directions is obtained by solving three simultaneous equations. The equations derived have important applications to the problem of constructing the strain ellipsoid from sectional data and to finite-element interpolation.     

Use of the 87Sr/86Sr isotopic ratio as an environmental tracer: an example of the application to the Fossil Forest of the Dunarobba (FFD) sedimentary system near Aviglano Umbro (Terni—Central Italy)

A recent discovery of Pliocene tree trunks (Taxodium, Glyptostrobus or Sequoia) perfectly preserved in the fluvial lacustrine sediments deposited in the old Tiberin Lake (near the town of Dunarobba, Central Italy) has led to the study of the conditions responsible for the trunks preservation. The present work has applied Sr isotope techniques to examine and confirm fluid migration in the different sediment types which cross the entire fluvial-lacustrine sequence. Based on the ⁸⁷Sr/⁸⁶Sr ratios measured in carbonate and in silicate fractions of samples collected from a bore hole (from 0 to 120 m) it is concluded that each sedimentary level has limited communication between zones and is characterised by different isotope values. This suggests that the intrinsic properties of these clays make them a good material for isolating waste, both for direct use and for a better buffer in other formations, possibly less secure, such as salt or granite. The results obtained in the present work have demonstrated some of the potential uses of the ⁸⁷Sr/⁸⁶Sr isotopic ratio as an environmental tracer for confirming results from some of the geotechnical (such as permeability) and geochemical parameters of these host sediments.     

Kinematic analysis of an en échelon—continuous vein complex

An array of sigmoidal tension gashes from the Idaho—Wyoming thrust belt changes laterally into a continuous vein. Detailed mechanical twin analysis was used to determine the strain variation in the optically and chemically homogeneous blocky calcite filling. In the continuous portion of the vein complex, the shortening axes are parallel to the vein boundary. However, the orientation of the shortening axes in the tip areas of the sigmoidal gashes are at an angle of approximately 35° to the vein boundary, and are parallel to the trend of the tips. Twinning patterns in the central portions of the gashes record two principal strain axes of shortening of nearly equal magnitude with the maximum perpendicular to the vein trend. Everywhere in the vein complex the orientation of the maximum extension axis is parallel to the twist axis of the gashes. The petrofabric strain results show that the vein filling has largely recorded local strains. The pattern of variation in orientation of the principal strains in the vein complex is in close agreement with the theoretically determined stress distribution in similar structures. Our results show that the sigmoidal gashes were formed at the leading edge of a propagating vein and that the sigmoidal shape reflects changes in the local strain field rather than a remote shear. The orientation of these local strains closely corresponds to the orientation of the local stresses.     

Application of Prognosticating Methods of Placer Gold Resources——Taking the Upper Regions of the Nenjiang River as an Example

On the basis of analysing and studyingthe mineralizing conditions and content ratinglaws, the authors infer the geology and oresnear old placers by applying the remote sens-ing technology and analogous method, and     

Namibia's orange river boundary — origin and reemerged effects of an inattentive colonial boundary delimination

Conclusion From the above and beside the securing of water rights for the national mining industry, the irrigation clusters scattered as if pearls along the Orange River's N bank are of an obviously unrenouncable significance for the Namibian agricultural production. In any case, it is clearly of utmost importance for Windhoek to secure the possession of the N flood plain by a boundary accord to be reached as soon as possible. This should determine as a minimal solution the border line finally along the low water mark, or, certainly more advantageous for the country, following the rivers median line. Even more so because, in spite of the high costs this would entail due to the lack of infrastructure in the inaccessible Orange gorge, the future extending potential of the irrigation schemes on the N bank are be estimated at least on 7800 ha (Otzen 1989) which is six times the developed irrigation area at the present stage and more than the actual overall Namibian irrigated cultivation area.In order to strengthen the claim to all areas presently disputed between the Republics of Namibia and South Africa and backed by several in international law not binding UN General Assembly resolutions, the Windhoek Constitutional Assembly resolved Article 1 (4) of the new Namibian constitution: The national of Namibia shall consist of the whole of territory recognised by the international community through the organs of the United Nations as Namibia, including the enclave, harbour and port of Walvis Bay, as well as the off-shore islands of Namibia, and its southern boundary shall extend to the middle of the Orange River. Secret negotiations have been taking place since 21st March 1990 but as in the case of the much disputed possession of Walvis Bay, the Republic of South Africa cannot be forced to accept the low water line or the now constitutionally claimed median line as the revised Orange River boundary. South Africa remains internationally unsuable and the small Namibia is presently unable to put pressure on the leading regional power. On the contrary, such a substantial revision of the failures of the late German colonial administration seems only be attainable, if it all, after a phase of positive development in Windhoek, so to be recognised by Pretoria, which then could be result in a voluntary surrender of the South African claim to the N bank to seal then hopefully reached good neighbourly relations between the Republic of South Africa and the recently emerged Republic of Namibia.     

Assessment of aquifer vulnerability to contamination in Khanyounis Governorate, Gaza Strip—Palestine, using the DRASTIC model within GIS environment

Groundwater is a very important natural resource in Khanyounis Governorate (the study area) for water supply and development. Historically, the exploitation of aquifers in Khanyounis Governorate has been undertaken without proper concern for environmental impact. In view of the importance of quality groundwater, it might be expected that aquifer protection to prevent groundwater quality deterioration would have received due attention. In the long term, however, protection of groundwater resources is of direct practical importance because, once pollution of groundwater has been allowed to occur, the scale and persistence of such pollution makes restoration technically difficult and costly. In order to maintain basin aquifer as a source of water for the area, it is necessary to find out, whether certain locations in this groundwater basin are susceptible to receive and transmit contamination. This study aims to: (1) assess the vulnerability of the aquifer to contamination in Khanyounis governorate, (2) find out the groundwater vulnerable zones to contamination in the aquifer of the study area, and (3) provide a spatial analysis of the parameters and conditions under which groundwater may become contaminate. To achieve that, DRASTIC model within geographic information system (GIS) environment was applied. The model uses seven environmental parameters: depth of water table, net recharge, aquifer media, soil media, topography, impact of vadose zone, and hydraulic conductivity to evaluate aquifer vulnerability. Based on this model and by using ArcGIS 9.3 software, an attempt was made to create vulnerability maps for the study area. According to the DRASTIC model index, the study has shown that in the western part of the study area the vulnerability to contamination ranges between high and very high due to the relatively shallow water table with moderate to high recharge potential, and permeable soils. To the east of the previous part and in the south-eastern part, vulnerability to contamination is moderate. In the central and the eastern part, vulnerability to contamination is low due to depth of water table. Vulnerability analysis of the DRASTIC Model indicates that the highest risk of contamination of groundwater in the study area originates from the soil media. The impact of vadose zone, depth to water level, and hydraulic conductivity imply moderate risks of contamination, while net recharge, aquifer media, and topography impose a low risk of aquifer contamination. The coefficient of variation indicates that a high contribution to the variation of vulnerability index is made by the topography. Moderate contribution is made by the depth to water level, and net recharge, while impact of vadose zone, hydraulic conductivity, soil media, and Aquifer media are the least variable parameters. The low variability of the parameters implies a smaller contribution to the variation of the vulnerability index across the study area. Moreover, the “effective” weights of the DRASTIC parameters obtained in this study exhibited some deviation from that of the “theoretical” weights. Soil media and the impact of vadose zone were the most effective parameters in the vulnerability assessment because their mean “effective” weights were higher than their respective “theoretical” weights. The depth of water table showed that both “effective” and “theoretical” weights were equal. The rest of the parameters exhibit lower “effective” weights compared with the “theoretical” weights. This explains the importance of soil media and vadose layers in the DRASTIC model. Therefore, it is important to get the accurate and detailed information of these two specific parameters. The GIS technique has provided an efficient environment for analysis and high capabilities of handling large spatial data. Considering these results, DRASTIC model highlights as a useful tool that can be used by national authorities and decision makers especially in the agricultural areas applying chemicals and pesticides which are most likely to contaminate groundwater resources.     

The Application of Weighted Logistic Regression Model in Prediction of Porphyry Copper Deposit——take Zharma—Sawur metallogenic belt,China—Kazakhstan border area,as an example

加权Logistic回归是基于GIS成矿预测的主要方法之一,其模型是不同于线性模型的一种类型.它具有强大的空间分析功能、适用性强、不受任何独立条件的约束、预测结果更可靠,因此在矿产资源评价研究中得到了很多地质学家的青睐.以矿床模型和成矿理论为基础,加权Logistic回归分析模型在成矿预测中的应用主要包括三部分:加权Logistic回归模型的建立及其应用、成矿有利度综合评价、成矿远景区圈定.本文以中国—哈萨克斯坦边境地区扎尔玛—萨吾尔成矿带斑岩型铜矿为例,探讨了基于GIS的加权Logistic回归模型在成矿预测中的应用.     

Paleomagnetism of the Jurassic Transantarctic Mountains revisited — Evidence for large dispersion of apparent polar wander within less than 3 Myr

The Transantarctic mountains predominantly consist of Jurassic continental flood basalts (Kirkpatrick) and sills (Ferrar) emplaced during the earliest phase of the break-up of Pangea. Published ages, based on a variety of geochronological methods all agree rather well and cluster around 180 Ma suggesting emplacement during a rather short time interval of not more than 3 Myr. Paleomagnetic studies, mostly carried out between the 60s and 90s of the last century, however, yield two well defined but significantly different groups of paleomagnetic pole positions plotting either in intermediate latitudes (A) or at latitudes exceeding 60°S (B). Pole positions belonging to group A are generally interpreted to be of primary origin whereas the significance of group B poles remains unclear. Here we report new data from the Kirkpatrick basalts of Northern Victoria Land, Antarctica, where 157 oriented paleomagnetic samples were taken, covering about 800 m of stratigraphy and 23 volcanic flows in Gair Mesa (73.4666°S; 162.8666°E). After removal of a steep magnetic overprint with rather low coercivities straight linear segments of exclusively normal polarity trending toward the origin of projection are identified in 151 samples from 22 sites. Maximum unblocking temperatures do not exceed 580 °C and maximum coercivities not 60 mT. The resulting mean virtual geomagnetic pole (VGP) for the Gair Mesa plots at 66.4°S; 227.7°E (α₉₅ of 6.2°, k = 25.7) comparable to group B poles. Reflecting light microscopy reveals that the magnetic inventory of all samples analyzed is dominated by magnetite showing shrinking cracks and broad ilmenite lamellae, the latter being diagnostic for high temperature oxidation. Analysis of the distribution of the 22 pole positions obtained here shows that secular variation has successfully been averaged (S_b = 15.9°) suggesting that the rocks studied here have recorded the time averaged geomagnetic field during early mid Jurassic times. Based on these new results we postulate that both clusters A and B of pole positions reflect primary magnetizations and that the Kirkpatrick basalts of Gair Mesa have been emplaced in a rather short normal polarity time interval of 3 Myr. If our reasoning is correct, the apparent polar wander path for the latest early Jurassic might be more complex than previously thought. Whether this complexity is evidence for massif True Polar Wander remains speculative.     

Integration of data constraints and potential field modelling — an example from southern lower saxony,Germany

Most of interpretational tasks in geophysics require an interdisciplinary knowledge and integration of information from comprehensive data bases. Towards this end a combination of different geophysical surveys employing seismics, gravity and magnetics, provides new insights into the structures and tectonic evolution of natural deposits together with geological and petrological studies. No doubt, any interdisciplinary approach is essential for numerical modelling of these structures and the processes acting on it. The interpretation of garvity and magnetics by 3D modelling requires data from other independent sources, due to the ambiguity of these methods.In close cooperation with geologists and computer scientists we are developing an object oriented model of the southern rim of the Northwest German Basin which consists of information from industry wells, stratigraphy and geophysical parameters (e.g. density and susceptibility). GOCAD is used for geometrical modelling purposes, IGMAS handels the interactive modifications of geophysical model parameters and geometry. Both modelling programs are supported by an object oriented data base system which will guarantee the consistency of data and models.Combined interpretations of the southern basin are presented and show, how the information from different geo-disciplines is visualized in order to ease the modelling process.     

Evaluation of Trends and Changes in the Gulf of Gdańsk Ecosystem—an Integrated Approach

An integrated trend assessment was conducted for the Gulf of Gdańsk (GoG), Baltic Sea for the period 1994–2010 to describe changes and potentially important drivers of the ecosystem. We found changes in the biota, including an increase in open sea taxa (flatfish, sprat and cod), a decrease in typical coastal species such as eelpout and lumpfish and an increase in primary production. The analyses further suggest that changes in the food web were driven by a combination of anthropogenic pressures (e.g., nutrient loadings and fisheries) and possible interactions with climatic disturbance. Our analyses show that significant changes occurred in the GoG ecosystem between 1994 and 2010. The primary drivers and mechanisms of these changes are discussed. We describe this alteration of the GoG within the context of similar temporal patterns identified in adjacent areas.     

Fluctuations in late Neoproterozoic atmospheric oxidation — Cr isotope chemostratigraphy and iron speciation of the late Ediacaran lower Arroyo del Soldado Group (Uruguay)

Oxygenation of the Earth's atmosphere occurred in two major steps, near the beginning and near the end of the Proterozoic Eon (2500 to 542 Ma ago), but the details of this history are unclear. Chromium isotopes in iron-rich chemical sediments offer a potential to highlight fine-scale fluctuations in the oxygenation of the oceans and atmosphere and to add a further dimension in the use of redox-sensitive tracers to solve the question regarding fluctuations of atmospheric oxygen levels and their consequences for Earth's climate. We observe strong positive fractionations in Cr isotopes (δ⁵³Cr up to + 5.0‰) in iron-rich cherts and banded iron formation horizons within the Arroyo del Soldado Group (Ediacaran; Uruguay) that can be explained by rapid, effective oxidation of Fe(II)-rich surface waters. These fluctuations are correlated with variations in ratios of highly reactive iron (Fe_HR) to total iron (Fe_tot) which indicate a predominance of anoxic water columns (Fe_HR/Fe_tot > 0.38) during the onset of oxidation pulses. We favor the scenario by which isotopically heavy Cr(VI) entered the basin after pulses of oxidative weathering on land and in which Fe(II) accumulated in the water column. Neodymium isotopes reveal that these oxygenation pulses were followed by increased influxes to the basin of continental crust-derived detrital components of Paleoproterozoic (Nd T_DM model ages = 2.1–2.2 Ga) provenance typical of the Rio de la Plata Craton. The association of positive δ⁵³Cr–ferruginous (Fe_HR/Fe_tot > 0.38) stratigraphic intervals with low-diversity acritarch assemblages dominated by Bavlinella faveolata strongly support models postulating a stratified, eutrophic Neoproterozoic ocean. Thus, even within a few million years of the Precambrian–Cambrian boundary, paleoceanographic conditions resembled more those of Paleoproterozoic oceans than Phanerozoic and present oceans. This highlights the sheer magnitude of ecological changes at the Precambrian–Cambrian transition, changes which ultimately led to the demise of the Precambrian world and the birth of the metazoan-dominated Phanerozoic.     

Petrogenesis and geodynamics of plagiogranites from Central Turkey (Ekecikdağ/Aksaray): new geochemical and isotopic data for generation in an arc basin system within the northern branch of Neotethys

International Journal of Earth Sciences - In the Late Cretaceous, throughout the closure of the Neotethys Ocean, ophiolitic rocks from the İzmir–Ankara–Erzincan ocean branch were...