Geochemical and petrographic characteristics of impactites and Cretaceous target rocks from the Yaxcopoil‐1 borehole,Chicxulub impact structure,Mexico: Implications for target composition     

Martin G. Tuchscherer  Wolf Uwe Reimold  Christian Koeberl  Roger L. Gibson 《Meteoritics & planetary science》2005,40(9-10):1513-1536

Abstract— We present major and trace element data as well as petrographic observations for impactites (suevitic groundmass, bulk suevite, and melt rock particles) and target lithologies, including Cretaceous anhydrite, dolomite, argillaceous limestone, and oil shale, from the Yaxcopoil‐1 borehole, Chixculub impact structure. The suevitic groundmass and bulk suevite have similar compositions, largely representing mixtures of carbonate and silicate components. The latter are dominated by melt rock particles. Trace element data indicate that dolomitic rocks represented a significant target component that became incorporated into the suevites; in contrast, major elements indicate a strong calcitic component in the impactites. The siliceous end‐member requires a mafic component in order to explain the low SiO₂ content. Multicomponent mixing of various target rocks, the high alteration state, and dilution by carbonate complicate the determination of primary melt particle compositions. However, two overlapping compositional groups can be discerned—a high‐Ba, low‐Ta group and a high‐Fe, high‐Zn, and high‐Hf group. Cretaceous dolomitic rocks, argillaceous limestone, and shale are typically enriched in U, As, Br, and Sb, whereas anhydrite contains high Sr contents. The oil shale samples have abundances that are similar to the North American Shale Composite (NASC), but with a comparatively high U content. Clastic sedimentary rocks are characterized by relatively high Th, Hf, Zr, As, and Sb abundances. Petrographic observations indicate that the Cretaceous rocks in the Yaxcopoil‐1 drill core likely register a multistage deformation history that spans the period from pre‐ to post‐impact. Contrary to previous studies that claimed evidence for the presence of impact melt breccia injection veins, we have found no evidence in our samples from a depth of 1347–1348 m for the presence of melt breccia. We favor that clastic veinlets occur in a sheared and altered zone that underwent intense diagenetic overprint prior to the impact event.  相似文献   

Sedimentology of a debris‐rich,perhumid valley glacier margin in the Rakaia Valley,South Island,New Zealand     

Olivia M. Hyatt  James Shulmeister  David J. A. Evans  Glenn D. Thackray  Uwe Rieser 《第四纪科学杂志》2012,27(7):699-712

The sedimentology and stratigraphy of a multi‐phase glaciation sequence dating to Marine Isotope Stage 6 in the Rakaia Valley, South Island, New Zealand, is presented. This outcrop presents an example of the depositional signature of an end member of temperate valley glaciation, where voluminous sediment supply in a tectonically active setting combines with high annual temperatures and low seasonality to generate significant year‐round glacifluvial activity. Such glacial systems produce geological–climatic units that are dominated by thick sequences of aggradational gravels and proglacial lake sediments trapped behind outwash heads during deglaciation. At Bayfields Cliff, outwash sequences record an oscillating glacier margin marked by a sequence of glacier‐fed, Gilbert‐type deltas. The deltas are cut by numerous small‐scale, syndepositional, normal faults indicating both loss of glacier support and melt‐out of buried ice. A larger‐scale thrust fault system reflects late‐stage ice overrun. Braid plain gravels and chaotic disturbed glacial lake sediments are also recorded. A notable feature of these systems is the virtual absence of till in an environment with much other evidence for proximal ice. Cumulatively we regard these sediment–landform associations as diagnostic of debris‐laden, perhumid, temperate valley glacier systems. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Observations of Comet 9P/Tempel 1 around the Deep Impact event by the OSIRIS cameras onboard Rosetta     

Horst Uwe Keller  Sonia Fornasier  Stubbe F. Hviid  Jörg Knollenberg  Miriam Rengel  Gabriele Cremonese  Detlef Koschny  Ekkehard Kührt  Holger Sierks  Cesare Barbieri  Hans Rickman  Michael F. A'Hearn  Maria-Antonella Barucci  Vania da Deppo  Björn J.R. Davidsson  Stefano Debei  Fritz Gliem  José J. Lopez Moreno  Giampiero Naletto  Angel Sanz Andrés 《Icarus》2007,187(1):87-103

The OSIRIS cameras on the Rosetta spacecraft observed Comet 9P/Tempel 1 from 5 days before to 10 days after it was hit by the Deep Impact projectile. The Narrow Angle Camera (NAC) monitored the cometary dust in 5 different filters. The Wide Angle Camera (WAC) observed through filters sensitive to emissions from OH, CN, Na, and OI together with the associated continuum. Before and after the impact the comet showed regular variations in intensity. The period of the brightness changes is consistent with the rotation period of Tempel 1. The overall brightness of Tempel 1 decreased by about 10% during the OSIRIS observations. The analysis of the impact ejecta shows that no new permanent coma structures were created by the impact. Most of the material moved with . Much of it left the comet in the form of icy grains which sublimated and fragmented within the first hour after the impact. The light curve of the comet after the impact and the amount of material leaving the comet ( of water ice and a presumably larger amount of dust) suggest that the impact ejecta were quickly accelerated by collisions with gas molecules. Therefore, the motion of the bulk of the ejecta cannot be described by ballistic trajectories, and the validity of determinations of the density and tensile strength of the nucleus of Tempel 1 with models using ballistic ejection of particles is uncertain.  相似文献   

Another Simple Method of Spectral Correction to Obtain Robust Eddy-Covariance Results   总被引：3，自引：0，他引：3  

Uwe Spank  Christian Bernhofer 《Boundary-Layer Meteorology》2008,128(3):403-422

The eddy-covariance method is the state-of-the-art tool to measure mass and energy fluxes, though many measuring systems (particularly closed-path systems) show strong spectral attenuation that causes significant underestimates of actual mass fluxes. The standard way to correct these underestimates is to use theoretically derived transfer functions. Practical implementation has shown that the attenuation, especially of closed-path systems, is underestimated by this method, even when the additional tube damping is considered. This paper introduces and tests three alternative site-specific and hardware specific correction methods based on spectral analysis, which typically enhance—additionally to the classical correction—the calculated mass fluxes based on closed-path analysers, as their inevitable tubing and the filters used cause additional flow attenuation. Two of the three methods are based on a site-specific and hardware specific transfer functions, the third uses direct comparison of cospectra. Primarily the methods based on transfer functions proved to be easy-to-handle once established for the specific set-up and measurement site. They represent practical and robust methods to correct for spectral attenuation.  相似文献   

Long-term ice sheet–climate interactions under anthropogenic greenhouse forcing simulated with a complex Earth System Model     

Miren Vizcaíno  Uwe Mikolajewicz  Matthias Gröger  Ernst Maier-Reimer  Guy Schurgers  Arne M. E. Winguth 《Climate Dynamics》2008,31(6):665-690

Several multi-century and multi-millennia simulations have been performed with a complex Earth System Model (ESM) for different anthropogenic climate change scenarios in order to study the long-term evolution of sea level and the impact of ice sheet changes on the climate system. The core of the ESM is a coupled coarse-resolution Atmosphere–Ocean General Circulation Model (AOGCM). Ocean biogeochemistry, land vegetation and ice sheets are included as components of the ESM. The Greenland Ice Sheet (GrIS) decays in all simulations, while the Antarctic ice sheet contributes negatively to sea level rise, due to enhanced storage of water caused by larger snowfall rates. Freshwater flux increases from Greenland are one order of magnitude smaller than total freshwater flux increases into the North Atlantic basin (the sum of the contribution from changes in precipitation, evaporation, run-off and Greenland meltwater) and do not play an important role in changes in the strength of the North Atlantic Meridional Overturning Circulation (NAMOC). The regional climate change associated with weakening/collapse of the NAMOC drastically reduces the decay rate of the GrIS. The dynamical changes due to GrIS topography modification driven by mass balance changes act first as a negative feedback for the decay of the ice sheet, but accelerate the decay at a later stage. The increase of surface temperature due to reduced topographic heights causes a strong acceleration of the decay of the ice sheet in the long term. Other feedbacks between ice sheet and atmosphere are not important for the mass balance of the GrIS until it is reduced to 3/4 of the original size. From then, the reduction in the albedo of Greenland strongly accelerates the decay of the ice sheet.  相似文献   

Impact of data assimilation of glider observations in the Ionian Sea (Eastern Mediterranean)   总被引：1，自引：0，他引：1  

Srdjan Dobricic  Nadia Pinardi  Pierre Testor  Uwe Send 《Dynamics of Atmospheres and Oceans》2010

Glider observations of temperature, salinity and vertically averaged velocity in the Ionian Sea (Eastern Mediterranean Sea), made in the period October 2004–December 2004, were assimilated into an operational forecasting model together with other in situ and satellite observations. The study area has a high spatial and temporal variability of near surface dynamics, characterized by the entrance of the Atlantic Ionian Stream (AIS) into the Northern Ionian Sea. The impact of glider observations on the estimation of the circulation is studied, and it is found that their assimilation locally improves the prediction of temperature, salinity, velocity and surface elevation fields. However, only the assimilation of temperature and salinity together with the vertically averaged velocity improves the forecast of all observed parameters. It is also found that glider observations rapidly impact the analyses even remotely, and the remote impacts on the analyses remain several months after the presence of the glider. The study emphasizes the importance of assimilating as much as possible all available information from gliders, especially in dynamically complex areas.  相似文献   

Seasonal to interannual climate predictability in mid and high northern latitudes in a global coupled model   总被引：3，自引：2，他引：1  

Torben Koenigk  Uwe Mikolajewicz 《Climate Dynamics》2009,32(6):783-798

The upper limit of climate predictability in mid and high northern latitudes on seasonal to interannual time scales is investigated by performing two perfect ensemble experiments with the global coupled atmosphere–ocean–sea ice model ECHAM5/MPI-OM. The ensembles consist of six members and are initialized in January and July from different years of the model’s 300-year control integration. The potential prognostic predictability is analyzed for a set of oceanic and atmospheric climate parameters. The predictability of the atmospheric circulation is small except for southeastern Europe, parts of North America and the North Pacific, where significant predictability occurs with a lead time of up to half a year. The predictability of 2 m air temperature shows a large land–sea contrast with highest predictabilities over the sub polar North Atlantic and North Pacific. A combination of relatively high persistence and advection of sea surface temperature anomalies into these areas leads to large predictability. Air temperature over Europe, parts of North America and Asia shows significant predictability of up to half a year in advance. Over the ice-covered Arctic, air temperature is not predictable at time scales exceeding 2 months. Sea ice thickness is highly predictable in the central Arctic mainly due to persistence and in the Labrador Sea due to dynamics. Surface salinity is highly predictable in the Arctic Ocean, northern North Atlantic and North Pacific for several years in advance. We compare the results to the predictability due to persistence and show the importance of dynamical processes for the predictability.  相似文献   

Major and trace elements in German bottled water,their regional distribution,and accordance with national and international standards     

Manfred Birke  Uwe Rauch  Bodo Harazim  Hans Lorenz  Wolfgang Glatte 《Journal of Geochemical Exploration》2010

The market for mineral water has been growing steadily over the last few years. Germany is the country with the highest number of bottled mineral water brands (908 bottled water samples from 502 wells/brands were analyzed). The per capita consumption of mineral water in Germany in 2003 was 129 L. A wide range of values of one to seven orders of magnitude was determined for 71 elements in the bottled water samples analyzed by ICP-QMS, ICP-AES, IC, titration, photometric, conductometric and potentiometric methods. A comparison of the element concentrations and the legal limits for both bottled and tap water (EU, Germany, US EPA, WHO) shows that only 70% of the 908 mineral water samples fulfill the German and EU drinking water (i.e., tap water) regulations for all parameters (not including pH) for which action levels are defined. Nearly 5% of the bottled water samples not fulfill the German and EU regulations for mineral and table water. Comparison of our results with the current German and European action levels for mineral and table water shows that only 42 of the bottled water samples exceed the limits for one or more of the following elements: arsenic, nitrate, nitrite, manganese, nickel and barium concentrations. Ten of the bottled water samples contain uranium concentrations above the 10 μg/L recommended limit.  相似文献   

An integrated zircon geochronological and geochemical investigation into the Miocene plutonic evolution of the Cyclades, Aegean Sea, Greece: Part 1: Geochronology   总被引：1，自引：1，他引：0  

Robert Bolhar  Uwe Ring  Charlotte M. Allen 《Contributions to Mineralogy and Petrology》2010,160(5):719-742

We use 369 individual U–Pb zircon ages from 14 granitoid samples collected on five islands in the Cyclades in the Aegean Sea, Greece, for constraining the crystallisation history of I- and S-type plutons above the retreating Hellenic subduction zone. Miocene magmatism in the Cyclades extended over a time span from 17 to 11 Ma. The ages for S-type granites are systematically ~2 million years older than those for I-type granites. Considering plutons individually, the zircon data define age spectra ranging from simple and unimodal to complex and multimodal. Seven of the 14 investigated samples yield more than one distinct zircon crystallisation age, with one I-type granodiorite sample from Mykonos Island representing the most complex case with three resolvable age peaks. Two samples from S-type granites on Ikaria appear to have crystallised zircon over 2–3 million years, whereas for the majority of individual samples with multiple zircon age populations the calculated ages deviate by 1–1.5 million years. We interpret our age data to reflect a protracted history involving initial partial melting at deeper lithospheric levels, followed by crystallisation and cooling at shallower crustal levels. Our study corroborates published research arguing that pluton construction is due to incremental emplacement of multiple magma pulses over a few million years. Assuming that multiple age peaks of our 14 samples can indeed serve to quantify time spans for magmatic emplacement, our data suggest that Aegean plutons were constructed over a few million years. Our tectonic interpretation of the U–Pb ages is that the S-type granites resulted from partial melting and migmatisation of the lower crust, possibly starting at ~23 Ma. The I-type granites and associated mafic melts are interpreted to reflect the magmatic arc stage in the Cyclades starting at ~15 Ma.  相似文献   

Families of first kind periodic solutions of the spatial and planar elliptic restricted three-body problem with collision     

Lúcia Brandão Dias  Claudio Vidal 《Celestial Mechanics and Dynamical Astronomy》2010,106(4):339-370

We consider a restricted three-body problem where the primaries are moving in an elliptic collision orbit and the infinitesimal mass moves in a three dimensional space. This paper is devoted to prove analytically the existence of several families of symmetric periodic solutions as continuation of Keplerian circular orbits. In our approach the perturbing parameter is related with the energy of the primaries.  相似文献