Timing of igneous accretion,composition, and temporal relation of the Kassandra–Sithonia rift-spreading center within the eastern Vardar suture zone,Northern Greece: insights into Jurassic arc/back-arc systems evolution at the Eurasian plate margin     

Nikolay Bonev  Peter Marchev  Robert Moritz  Petyo Filipov 《International Journal of Earth Sciences》2015,104(7):1837-1864

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Benthic nutrient fluxes along the Laurentian Channel: Impacts on the N budget of the St. Lawrence marine system     

Benoît Thibodeau  Moritz F. Lehmann  Jacqueline Kowarzyk  Alfonso Mucci  Yves Gélinas  Denis Gilbert  Roxane Maranger  Mohammad Alkhatib 《Estuarine, Coastal and Shelf Science》2010

Water column concentrations and benthic fluxes of dissolved inorganic nitrogen (DIN) and oxygen (DO) were measured in the Gulf of St. Lawrence and the Upper and Lower St. Lawrence Estuary (USLE and LSLE, respectively) to assess the nitrogen (N) budget in the St. Lawrence (SL) system, as well as to elucidate the impact of bottom water hypoxia on fixed-N removal in the LSLE. A severe nitrate deficit, with respect to ambient phosphate concentrations (N*∼−10 μmol L⁻¹), was observed within and in the vicinity of the hypoxic bottom water of the LSLE. Given that DO concentrations in the water column have remained above 50 μmol L⁻¹, nitrate reduction in suboxic sediments, rather than in the water column, is most likely responsible for the removal of fixed N from the SL system. Net nitrate fluxes into the sediments, derived from pore water nitrate concentration gradients, ranged from 190 μmol m⁻² d⁻¹ in the hypoxic western LSLE to 100 μmol m⁻² d⁻¹ in the Gulf. The average total benthic nitrate reduction rate for the Laurentian Channel (LC) is on the order of 690 μmol m⁻² d⁻¹, with coupled nitrification-nitrate reduction accounting for more than 70%. Using average nitrate reduction rates derived from the observed water column nitrate deficit, the annual fixed-N elimination within the three main channels of the Gulf of St. Lawrence and LSLE was estimated at 411 × 10⁶ t N, yielding an almost balanced N budget for the SL marine system.  相似文献   

Mycological evidence of coprophagy from the feces of an Alaskan Late Glacial mammoth     

Bas van Geel  R. Dale Guthrie  Jens G. Altmann  Peter Broekens  Ian D. Bull  Fiona L. Gill  Boris Jansen  Aline M. Nieman  Barbara Gravendeel 《Quaternary Science Reviews》2011,30(17-18):2289-2303

Dung from a mammoth was preserved under frozen conditions in Alaska. The mammoth lived during the early part of the Late Glacial interstadial (ca 12,300 BP). Microfossils, macroremains and ancient DNA from the dung were studied and the chemical composition was determined to reconstruct both the paleoenvironment and paleobiology of this mammoth. Pollen spectra are dominated by Poaceae, Artemisia and other light-demanding taxa, indicating an open, treeless landscape (‘mammoth steppe’). Fruits and seeds support this conclusion. The dung consists mainly of cyperaceous stems and leaves, with a minor component of vegetative remains of Poaceae. Analyses of fragments of the plastid rbcL gene and trnL intron and nrITS1 region, amplified from DNA extracted from the dung, supplemented the microscopic identifications. Many fruit bodies with ascospores of the coprophilous fungus Podospora conica were found inside the dung ball, indicating that the mammoth had eaten dung. The absence of bile acids points to mammoth dung. This is the second time that evidence for coprophagy of mammoths has been derived from the presence of fruit bodies of coprophilous fungi in frozen dung. Coprophagy might well have been a common habit of mammoths. Therefore, we strongly recommend that particular attention should be given to fungal remains in future fossil dung studies.  相似文献   

The effects of vigorous mixing in a convective model of zonal flow on the ice giants     

Jonathan Aurnou  Moritz Heimpel 《Icarus》2007,190(1):110-126

Previous studies have used models of three-dimensional (3D) Boussinesq convection in a rotating spherical shell to explain the zonal flows on the gas giants, Jupiter and Saturn. In this paper we demonstrate that this approach can also generate flow patterns similar to those observed on the ice giants, Uranus and Neptune. The equatorial jets of Uranus and Neptune are often assumed to result from baroclinic cloud layer processes and have been simulated with shallow layer models. Here we show that vigorous, 3D convection in a spherical shell can produce the retrograde (westward) equatorial flows that occur on the ice giants as well as the prograde (eastward) equatorial flows of the gas giants. In our models, the direction of the equatorial jet depends on the ratio of buoyancy to Coriolis forces in the system. In cases where Coriolis forces dominate buoyancy, cylindrical Reynolds stresses drive prograde equatorial jets. However, as buoyancy forces approach and exceed Coriolis forces, the cylindrical nature of the flow is lost and 3D mixing homogenizes the fluid's angular momentum; the equatorial jet reverses direction, while strong prograde jets form in the polar regions. Although the results suggest that conditions involving strong atmospheric mixing are responsible for generating the zonal flows on the ice giants, our present models require roughly 100 and 10 times the internal heat fluxes observed on Uranus and Neptune, respectively.  相似文献   

Architecture of Upper Cretaceous rhyodacitic hyaloclastite at the polymetallic Madneuli deposit,Lesser Caucasus,Georgia     

Nino Popkhadze  Robert Moritz  Vladimer Gugushvili 《Central European Journal of Geosciences》2014,6(3):308-329

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A new degree-2190 (10 km resolution) gravity field model for Antarctica developed from GRACE,GOCE and Bedmap2 data     

Christian Hirt  Moritz Rexer  Mirko Scheinert  Roland Pail  Sten Claessens  Simon Holmes 《Journal of Geodesy》2016,90(2):105-127

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Petrology,geochemistry and U–Pb geochronology of magmatic rocks from the high-sulfidation epithermal Au–Cu Chelopech deposit,Srednogorie zone,Bulgaria     

Isabelle Chambefort  Robert Moritz  Albrecht von Quadt 《Mineralium Deposita》2007,42(7):665-690

The Chelopech deposit is one of the largest European gold deposits and is located 60 km east of Sofia, within the northern part of the Panagyurishte mineral district. It lies within the Banat–Srednegorie metallogenic belt, which extends from Romania through Serbia to Bulgaria. The magmatic rocks define a typical calc-alkaline suite. The magmatic rocks surrounding the Chelopech deposit have been affected by propylitic, quartz–sericite, and advanced argillic alteration, but the igneous textures have been preserved. Alteration processes have resulted in leaching of Na₂O, CaO, P₂O₅, and Sr and enrichment in K₂O and Rb. Trace element variation diagrams are typical of subduction-related volcanism, with negative anomalies in high field strength elements (HFSE) and light element, lithophile elements. HFSE and rare earth elements were relatively immobile during the hydrothermal alteration related to ore formation. Based on immobile element classification diagrams, the magmatic rocks are andesitic to dacitic in compositions. Single zircon grains, from three different magmatic rocks spanning the time of the Chelopech magmatism, were dated by high-precision U–Pb geochronology. Zircons of an altered andesitic body, which has been thrust over the deposit, yield a concordant ²⁰⁶Pb/²³⁸U age of 92.21 ± 0.21 Ma. This age is interpreted as the crystallization age and the maximum age for magmatism at Chelopech. Zircon analyses of a dacitic dome-like body, which crops out to the north of the Chelopech deposit, give a mean ²⁰⁶Pb/²³⁸U age of 91.95 ± 0.28 Ma. Zircons of the andesitic hypabyssal body hosting the high-sulfidation mineralization and overprinted by hydrothermal alteration give a concordant ²⁰⁶Pb/²³⁸U age of 91.45 ± 0.15 Ma. This age is interpreted as the intrusion age of the andesite and as the maximum age of the Chelopech epithermal high-sulfidation deposit. ¹⁷⁶Hf/¹⁷⁷Hf isotope ratios of zircons from the Chelopech magmatic rocks, together with published data on the Chelopech area and the about 92-Ma-old Elatsite porphyry–Cu deposit, suggest two different magma sources in the Chelopech–Elatsite magmatic area. Magmatic rocks associated with the Elatsite porphyry–Cu deposit and the dacitic dome-like body north of Chelopech are characterized by zircons with ɛHf_T90 values of ∼5, which suggest an important input of mantle-derived magma. Some zircons display lower ɛHf_T90 values, as low as −6, and correlate with increasing ²⁰⁶Pb/²³⁸U ages up to about 350 Ma, suggesting assimilation of basement rocks during magmatism. In contrast, zircon grains in andesitic rocks from Chelopech are characterized by homogeneous ¹⁷⁶Hf/¹⁷⁷Hf isotope ratios with ɛHf_T90 values of ∼1 and suggest a homogeneous mixed crust–mantle magma source. We conclude that the Elatsite porphyry–Cu and the Chelopech high-sulfidation epithermal deposits were formed within a very short time span and could be partly contemporaneous. However, they are related to two distinct upper crustal magmatic reservoirs, and they cannot be considered as a genetically paired porphyry–Cu and high-sulfidation epithermal related to a single magmatic–hydrothermal system centered on the same intrusion.  相似文献   

Fluid salinities obtained by infrared microthermometry of opaque minerals: Implications for ore deposit modeling — A note of caution     

Robert Moritz   《Journal of Geochemical Exploration》2006,89(1-3):284

Infrared microthermometry of opaque minerals has revealed that temperatures of phase changes vary with the infrared light source intensity, resulting in an overestimate of fluid salinities and an underestimate of homogenization temperatures. Failing to recognize this analytical artifact during infrared microthermometry may result in meaningless geological models. A fluid inclusion investigation on enargite from a high-sulfidation epithermal deposit is used as an example to document this. Fluid salinities obtained during an early investigation ranged between 6.3 and 20.4 wt.% NaCl, which were interpreted as intense boiling or as evidence for the involvement of a magmatic brine during ore formation. Fluid inclusion salinities obtained with improved analytical settings, i.e. low light intensities, fall between 1.1 and 1.7 wt.% NaCl and are in better agreement with fluid salinities obtained in quartz from similar deposits, and recent modeling suggesting vapor transport of Au and Cu from deep porphyry-Cu environments to shallower high-sulfidation epithermal deposits.  相似文献   

Rapid biotic molecular transformation of fulvic acids in a karst aquifer   总被引：2，自引：0，他引：2  

Florian Einsiedl  Norbert Hertkorn  Moritz Frommberger  Boris P. Koch 《Geochimica et cosmochimica acta》2007,71(22):5474-5482

The study of molecular transformation processes of dissolved organic carbon (DOC) in the environment significantly contributes to a better understanding of the global biogeochemical organic matter cycle. In an oxic karst groundwater system, in which the most powerful abiotic DOC degradative reactions, photodegradation and metal-mediated redox chemistry, are at best marginal contributors, a near complete turnover of fulvic acids (FAs) has been observed within decades (∼60 years). Depletion of oxygen for a very extensive range of aliphatic and aromatic carbon chemical environments has been confirmed as well as the formation of novel classes of compounds, suggesting a major contribution from biotic processes. From these results we infer that FAs must be perceived as a rather active participant in the global carbon cycle. Molecular-level alterations of such magnitude and rapidity on such short-time scales ought to be considered as widespread in the processing of “refractory” DOC in the environment.  相似文献   

Modelling nitrogen and oxygen isotope fractionation during denitrification in a lacustrine redox-transition zone   总被引：1，自引：0，他引：1  

Moritz F. Lehmann  Peter Reichert  Alberto Barbieri 《Geochimica et cosmochimica acta》2003,67(14):2529-2542

The stable isotope composition (δ¹⁵N and δ¹⁸O) of nitrate was measured during Summer 1999 in the anaerobic hypolimnion of eutrophic Lake Lugano (Switzerland). Denitrification was demonstrated by a progressive nitrate depletion coupled to increasing δ¹⁵N and δ¹⁸O values for residual nitrate. Maximum δ¹⁵N and δ¹⁸O values amounted to 27.2 and 15.7‰, respectively.¹⁵N and ¹⁸O enrichment factors for denitrification (ε) were estimated using a closed-system model and a dynamic diffusion-reaction model. Using the Rayleigh equation (closed-system approach), we obtained ε values of −11.2 and −6.6‰ for nitrogen and oxygen, respectively. The average ε values derived using the diffusion-reaction model were determined to be −20.7 ± 3.8 for nitrogen and −11.0 ± 1.7 for oxygen. Both N and O isotope fractionation appeared to be lower when denitrification rates where high, possibly in association with high organic carbon availability. In addition, variations in the isotope effects may be attributed to the variable importance of sedimentary denitrification having only a small isotope effect on the water column. The combined measurement of N and O isotope ratios in nitrate revealed that coupled nitrification-denitrification in the open-water was of minor importance. This is the first study of nitrogen and oxygen isotope effects associated with microbial denitrification in a natural lake. Moreover, this study confirms the high potential of δ¹⁸O of nitrate as a valuable biogeochemical tracer in aquatic systems, complementing nitrate δ¹⁵N.  相似文献