Exploring the impact of diagenesis on (isotope) geochemical and microstructural alteration features in biogenic aragonite          下载免费PDF全文

Ann‐Christine Ritter  Vasileios Mavromatis  Martin Dietzel  Ola Kwiecien  Felix Wiethoff  Erika Griesshaber  Laura A. Casella  Wolfgang W. Schmahl  Jennifer Koelen  Rolf D. Neuser  Albrecht Leis  Dieter Buhl  Andrea Niedermayr  Sebastian F. M. Breitenbach  Stefano M. Bernasconi  Adrian Immenhauser 《Sedimentology》2017,64(5):1354-1380

For the Quaternary and Neogene, aragonitic biogenic and abiogenic carbonates are frequently exploited as archives of their environment. Conversely, pre‐Neogene aragonite is often diagenetically altered and calcite archives are studied instead. Nevertheless, the exact sequence of diagenetic processes and products is difficult to disclose from naturally altered material. Here, experiments were performed to understand biogenic aragonite alteration processes and products. Shell subsamples of the bivalve Arctica islandica were exposed to hydrothermal alteration. Thermal boundary conditions were set at 100°C, 175°C and 200°C. These comparably high temperatures were chosen to shorten experimental durations. Subsamples were exposed to different ¹⁸O‐depleted fluids for durations between two and twenty weeks. Alteration was documented using X‐ray diffraction, cathodoluminescence, fluorescence and scanning electron microscopy, as well as conventional and clumped isotope analyses. Experiments performed at 100°C show redistribution and darkening of organic matter, but lack evidence for diagenetic alteration, except in Δ₄₇ which show the effects of annealing processes. At 175°C, valves undergo significant aragonite to calcite transformation and neomorphism. The δ¹⁸O signature supports transformation via dissolution and reprecipitation, but isotopic exchange is limited by fluid migration through the subsamples. Individual growth increments in these subsamples exhibit bright orange luminescence. At 200°C, valves are fully transformed to calcite and exhibit purple‐blue luminescence with orange bands. The δ¹⁸O and Δ₄₇ signatures reveal exchange with the aqueous fluid, whereas δ¹³C remains unaltered in all experiments, indicating a carbonate‐buffered system. Clumped isotope temperatures in high‐temperature experiments show compositions in broad agreement with the measured temperature. Experimentally induced alteration patterns are comparable with individual features present in Pleistocene shells. This study represents a significant step towards sequential analysis of diagenetic features in biogenic aragonites and sheds light on reaction times and threshold limits. The limitations of a study restricted to a single test organism are acknowledged and call for refined follow‐up experiments.  相似文献   

Preparing a seismic hazard model for Switzerland: the view from PEGASOS Expert Group 3 (EG1c)   总被引：1，自引：0，他引：1  

Roger M. W. Musson  Souad Sellami  Wolfgang Brüstle 《Swiss Journal of Geoscience》2009,102(1):107-120

The seismic hazard model used in the PEGASOS project for assessing earth-quake hazard at four NPP sites was a composite of four sub-models, each produced by a team of three experts. In this paper, one of these models is described in detail by the authors. A criticism sometimes levelled at probabilistic seismic hazard studies is that the process by which seismic source zones are arrived at is obscure, subjective and inconsistent. Here, we attempt to recount the stages by which the model evolved, and the decisions made along the way. In particular, a macro-to-micro approach was used, in which three main stages can be described. The first was the characterisation of the overall kinematic model, the “big picture” of regional seismogenesis. Secondly, this was refined to a more detailed seismotectonic model. Lastly, this was used as the basis of individual sources, for which parameters can be assessed. Some basic questions had also to be answered about aspects of the approach to modelling to be used: for instance, is spatial smoothing an appropriate tool to apply? Should individual fault sources be modelled in an intraplate environment? Also, the extent to which alternative modelling decisions should be expressed in a logic tree structure has to be considered.  相似文献   

A model for multiphase flow and transport in porous media including a phenomenological approach to account for deformation—a model concept and its validation within a code intercomparison study     

Sandra Freiboth  Holger Class  Rainer Helmig  Tobias Graf  Wolfgang Ehlers  Viktoria Schwarz  Christos Vrettos 《Computational Geosciences》2009,13(3):281-300

Multiphase flow processes in unsaturated cohesive soils are often affected by deformation due to swelling and shrinking as a result of varying water contents. This paper presents a model concept which is denoted ‘phenomenological’ in terms of the processes responsible for soil deformation, since the effects of deformation on flow and transport are only considered by constitutive relations that allow an adaptation of the hydraulic properties. This new model is validated in a detailed intercomparison study with two state-of-the-art models that are capable of explicitly describing the processes relevant for the deformation. A ‘numerical experiment’ with a state-of-the-art reference model is used to produce ‘measurement data’ for an inverse-modelling-based estimation of the model input parameters for the phenomenological concept.  相似文献   

Estimation of the temporal autocorrelation structure by the collocation technique with an emphasis on soil moisture studies     

Simon Zwieback  Wouter Dorigo  Wolfgang Wagner 《水文科学杂志》2013,58(8):1729-1747

Abstract

The collocation technique has become a popular tool in oceanography and hydrology for estimating the error variances of different data sources such as in situ sensors, models and remote sensing products. It is also possible to determine calibration constants, for example to account for an off-set between the data sources. So far, the temporal autocorrelation structure of the errors has not been studied, although it is known that it has detrimental effects on the results of the collocation technique, in particular when calibration constants are also determined. This paper shows how the (triple) collocation estimators can be adapted to retrieve the autocovariance functions; the statistical properties as well as the structural deficencies are described. The coupling between the autocorrelation of the error and the estimation of calibration constants is studied in detail, due to its importance for analysing temporal changes. In soil moisture applications, such time variations can be induced, for example, by seasonal changes in the vegetation cover, which affect both models and remote sensing products. The limitations of the proposed technique associated with these considerations are analysed using remote sensing and in situ soil moisture data. The variability of the inter-sensor calibration and the autocovariance are shown to be closely related to temporal patterns of the data.

Editor D. Koutsoyiannis

Citation Zwieback, S., Dorigo, W., and Wagner, W., 2013. Estimation of the temporal autocorrelation structure by the collocation technique with an emphasis on soil moisture studies. Hydrological Sciences Journal, 58 (8), 1729–1747.  相似文献   

In situ N and C labelling of indigenous and plantation tree species in a tropical mountain forest (Munessa, Ethiopia) for subsequent litter and soil organic matter turnover studies     

Bruno Glaser  Marianne BeneschMichaela Dippold  Wolfgang Zech 《Organic Geochemistry》2012,42(12):1461-1469

We propose a novel pragmatic approach of in situ ¹⁵N and ¹³C isotope labelling of trees for subsequent litter decomposition and turnover studies under field conditions. Using this method the labelling of even large trees under natural conditions is possible and compared to tree labelling under artificial conditions in greenhouses the in situ approach is less expensive. ¹³C and ¹⁵N labelling were carried out simultaneously via photosynthesis by tree gassing with ¹³CO₂ and by stem injection of ¹⁵NH₄¹⁵NO₃. The aims of this study were: (i) to produce a sufficient quantity of labelled plant material for subsequent field incubation studies and (ii) to investigate the effectiveness and distribution of in situ ¹⁵N (¹⁵NH₄¹⁵NO₃) and ¹³C (¹³CO₂) labelling of Podocarpus falcatus, Croton macrostachys, Prunus africana and Cupressus lusitanica. The following targets need to be achieved: (i) Assuming almost natural litter fall conditions, enough labelled plant material must be produced in situ for the turnover experiment; (ii) intra-plant tracer enrichment shall be homogeneous; (iii) tracer enrichment should be comparable for different tree species; and (iv) tracer enrichment must be sufficient for subsequent litter turnover studies using the stable isotope approach. Our results clearly demonstrated that several kilograms of labelled plant material can be produced in situ. For many ecosystems, this amount is sufficient for a long term litter turnover experiment on a field scale under almost natural litter fall conditions. However, intra-plant label uptake of ¹³C and ¹⁵N was heterogeneous so that only leaves (litter) should be used for the turnover study. It could be shown that only a part of the labile C and N fraction in the leaves was labelled. Nevertheless, label uptake was sufficient for subsequent litter turnover studies.  相似文献   

Geochemically induced shifts in catabolic energy yields explain past ecological changes of diffuse vents in the East Pacific Rise 9°50'N area     

Michael Hentscher  Wolfgang Bach 《Geochemical transactions》2012,13(1):1-11

The East Pacific Rise (EPR) at 9°50'N hosts a hydrothermal vent field (Bio9) where the change in fluid chemistry is believed to have caused the demise of a tubeworm colony. We test this hypothesis and expand on it by providing a thermodynamic perspective in calculating free energies for a range of catabolic reactions from published compositional data. The energy calculations show that there was excess H₂S in the fluids and that oxygen was the limiting reactant from 1991 to 1997. Energy levels are generally high, although they declined in that time span. In 1997, sulfide availability decreased substantially and H₂S was the limiting reactant. Energy availability dropped by a factor of 10 to 20 from what it had been between 1991 and 1995. The perishing of the tubeworm colonies began in 1995 and coincided with the timing of energy decrease for sulfide oxidizers. In the same time interval, energy availability for iron oxidizers increased by a factor of 6 to 8, and, in 1997, there was 25 times more energy per transferred electron in iron oxidation than in sulfide oxidation. This change coincides with a massive spread of red staining (putative colonization by Fe-oxidizing bacteria) between 1995 and 1997. For a different cluster of vents from the EPR 9°50'N area (Tube Worm Pillar), thermodynamic modeling is used to examine changes in subseafloor catabolic metabolism between 1992 and 2000. These reactions are deduced from deviations in diffuse fluid compositions from conservative behavior of redox-sensitive species. We show that hydrogen is significantly reduced relative to values expected from conservative mixing. While H₂ concentrations of the hydrothermal endmember fluids were constant between 1992 and 1995, the affinities for hydrogenotrophic reactions in the diffuse fluids decreased by a factor of 15 and then remained constant between 1995 and 2000. Previously, these fluids have been shown to support subseafloor methanogenesis. Our calculation results corroborate these findings and indicate that the 1992-1995 period was one of active growth of hydrogenotrophic communities, while the system was more or less at steady state between 1995 and 2000.  相似文献   

Drinking water production from surface water sources in the tropics: Brasília DF,Brazil     

Ekaterina Vasyukova  Wolfgang Uhl  Fuad Braga  Claudia Simões  Tânia Baylão  Klaus Neder 《Environmental Earth Sciences》2012,65(5):1587-1599

Drinking water production at three waterworks was evaluated with respect to variable weather conditions in the Brasília Distrito Federal. Results of the investigation revealed that seasonal variations in rainfall play an important role in influencing the quality of the surface water sources used for drinking water production in the district. In most surface sources, particles and apparent colour are likely to originate from erosion during rain events. This represents the primary challenge facing waterworks, notably when the raw water qualities of the sources to be treated at one facility differ by one order of magnitude, as well significantly varying from one season to the next. Treatment efficiencies in terms of turbidity, apparent colour and dissolved organic carbon (DOC) removal were evaluated. Drinking water quality was found to be significantly influenced by raw water quality at all considered treatment plants. With regard to DOC removal, treatment was most efficient in waterworks which treated raw water with high percentages of biopolymers and humics. Most dissolved organics were removed by coagulation. Finally, conclusions are drawn on how to better cope with challenges facing drinking water production in a tropical climate. The first of these recommendations is the introduction of online turbidity and dissolved organic matter monitoring in order to optimise the coagulation process for the removal of these two parameters. A combination of different coagulants could also be considered for this process. Additional more sophisticated improvements to process stability, such as determination of floc characteristics, introduction of artificial neural networks or the eventual upgrade of the treatment train using membrane filtration, are also suggested.  相似文献   

Catabolic and anabolic energy for chemolithoautotrophs in deep-sea hydrothermal systems hosted in different rock types     

Jan P. Amend  Thomas M. McCollom  Wolfgang Bach 《Geochimica et cosmochimica acta》2011,75(19):5736-5748

Active deep-sea hydrothermal vents are hosted by a range of different rock types, including basalt, peridotite, and felsic rocks. The associated hydrothermal fluids exhibit substantial chemical variability, which is largely attributable to compositional differences among the underlying host rocks. Numerical models were used to evaluate the energetics of seven inorganic redox reactions (potential catabolisms of chemolithoautotrophs) and numerous biomolecule synthesis reactions (anabolism) in a representative sampling of these systems, where chemical gradients are established by mixing hydrothermal fluid with seawater. The wide ranging fluid compositions dictate demonstrable differences in Gibbs energies (ΔG_r) of these catabolic and anabolic reactions in three peridotite-hosted, six basalt-hosted, one troctolite-basalt hybrid, and two felsic rock-hosted systems. In peridotite-hosted systems at low to moderate temperatures (<∼45 °C) and high seawater:hydrothermal fluid (SW:HF) mixing ratios (>10), hydrogen oxidation yields the most catabolic energy, but the oxidation of methane, ferrous iron, and sulfide can also be moderately exergonic. At higher temperatures, and consequent SW:HF mixing ratios <10, anaerobic processes dominate the energy landscape; sulfate reduction and methanogenesis are more exergonic than any of the aerobic respiration reactions. By comparison, in the basalt-hosted and felsic rock-hosted systems, sulfide oxidation was the predominant catabolic energy source at all temperatures (and SW:HF ratios) considered. The energetics of catabolism at the troctolite-basalt hybrid system were intermediate to these extremes. Reaction energetics for anabolism in chemolithoautotrophs—represented here by the synthesis of amino acids, nucleotides, fatty acids, saccharides, and amines—were generally most favorable at moderate temperatures (22-32 °C) and corresponding SW:HF mixing ratios (∼15). In peridotite-hosted and the troctolite-basalt hybrid systems, ΔG_r for primary biomass synthesis yielded up to ∼900 J per g dry cell mass. The energetics of anabolism in basalt- and felsic rock-hosted systems were far less favorable. The results suggest that in peridotite-hosted (and troctolite-basalt hybrid) systems, compared with their basalt (and felsic rock) counterparts, microbial catabolic strategies—and consequently variations in microbial phylotypes—may be far more diverse and some biomass synthesis may yield energy rather than imposing a high energetic cost.  相似文献   

Late Cambrian deformation in the Lesser Himalaya     

Om N. Bhargava  Wolfgang Frank  Rufus Bertle 《Journal of Asian Earth Sciences》2011,40(1):201-212

The Tons Valley, situated in the central-easternmost part of the Himachal Lesser Himalaya, adjoining the Garhwal Himalaya, shows geological features suggestive of a strong pre-Tertiary deformational episode. The Paleoproterozoic Dharagad Group, overlain by the Mesoproterozoic Deoban and Neoproterozoic Simla groups rest as a thrust sheet over the Middle Cambrian Chilar Formation, which occurs as windows and also as tectonic slivers within the thrust sheet designated as the Dharagad Thrust Sheet (DTS). The mineral lineation, inclination of tectonic slivers and overturned beds suggest that the DTS was translated from the NE. The westernmost and southwesternmost leading edges of the DTS are exposed at Subathu and Morni WNW and WSW respectively of the Tons Valley. The position of the leading edges of the DTS vis-à-vis the windows in the Tons Valley suggest a minimum translation of about 50 km for the DTS. The Simla Group at Subathu and the Deoban at Morni, forming parts of the DTS, constitute basement for the Thanetian–Lutetian Subathu Formation of the Himalayan Foreland Basin (HFB). This stratigraphic relationship unambiguously demonstrates that the Simla and the Deoban Groups, forming leading edges of the allochthonous DTS, were already translated and emplaced at Subathu and Morni before the creation of the HFB in which the deposition commenced with the Subathu Formation in Thanetian. It implies that the DTS was translated from the NE to the present position at Subathu and Morni in pre-Thanetian time. There is no direct evidence to constrain the age of the thrusting.In view of regional regression in Late Cambrian, a distinct angular unconformity between the Cambrian and the overlying Ordovician, Early Paleozoic metamorphism and extensive development of Early Paleozoic granites and their rapid exhumation, a Late Cambrian age is suggested for the DTS thrusting. Not only the direction of movement of the DTS is same as that of the Tertiary thrust sheets but also Cambrian folds are co-axial with the Tertiary folds. This strange coincidence shows that similar kinematic field existed during two tectonic events. A ridge, like the present Central Crystalline Axis, was elevated between the Tethyan and Lesser Himalayan basins, which contributed zircons of the Early Cambrian age to both basins.  相似文献   

<Emphasis Type="Italic">Scombroclupea occidentalis</Emphasis> sp. nov. (Clupeiformes,Teleostei) from the Cenomanian (Cretaceous) Plattenkalk deposits of NE Mexico     

Samuel Giersch  Eberhard Frey  Wolfgang Stinnesbeck  Christina Ifrim  José Manuel Padilla Gutierrez 《Swiss Journal of Geoscience》2011,104(1):73-84

A new species of the clupeid genus Scombroclupea is described from the Upper Cretaceous (Cenomanian) Plattenkalk locality “Loma la Mula” in Coahuila, northeastern Mexico. The material provides new osteological data for the genus, which clarify its systematic position. The Mexican Scombroclupea points to an occurrence of the genus in the western Tethys and indicates a vicariant event between S. macrophthalma from Lebanon and Croatia and the new species described herein. The analysis of the functional morphology of Scombroclupea supports the reconstruction of an oscillatory locomotion mode in this genus.  相似文献