Recent Developments in Quasilinear Cosmic Ray Particle Acceleration Theories     

Reinhard Schlickeiser  Rami Vainio 《Astrophysics and Space Science》1998,264(1-4):457-469

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The remote determination of the mean kinetic temperature of planets and satellites having a negligible atmosphere     

Reinhard Beer 《Icarus》1974,23(3):445-453

A novel method, called the crossover technique, has been devised for the remote determination of the surface temperature of planets, satellites, and asteroids having a negligible atmosphere. The method is discussed using new spectra of Mars as an example, and it is shown how it might be extended to other solar system objects. The accuracy of the method, both absolutely and in comparison to other methods, is also considered.  相似文献   

Magnitude,Scale, and Dynamics of the 2020 Mei-yu Rains and Floods over China※     

Ambrogio VOLONTé  Mark MUETZELFELDT  Reinhard SCHIEMANN  Andrew G.TURNER  Nicholas KLINGAMAN 《大气科学进展》2021,38(12):2082-2096

Large parts of East and South Asia were affected by heavy precipitation and flooding during early summer 2020. This study provides both a statistical and dynamical characterization of rains and floods affecting the Yangtze River Basin (YRB). By aggregating daily and monthly precipitation over river basins across Asia, it is shown that the YRB is one of the areas that was particularly affected. June and July 2020 rainfall was higher than in the previous 20 years, and the YRB experienced anomalously high rainfall across most of its sub-basins. YRB discharge also attained levels not seen since 1998/1999. An automated method detecting the daily position of the East Asian Summer Monsoon Front (EASMF) is applied to show that the anomalously high YRB precipitation was associated with a halted northward progression of the EASMF and prolonged mei-yu conditions over the YRB lasting more than one month. Two 5-day heavy-precipitation episodes (12?16 June and 4?8 July 2020) are selected from this period for dynamical characterization, including Lagrangian trajectory analysis. Particular attention is devoted to the dynamics of the airstreams converging at the EASMF. Both episodes display heavy precipitation and convergence of monsoonal and subtropical air masses. However, clear differences are identified in the upper-level flow pattern, substantially affecting the balance of airmass advection towards the EASMF. This study contextualizes heavy precipitation in Asia in summer 2020 and showcases several analysis tools developed by the authors for the study of such events.  相似文献   

New insights into Late Pleistocene glacial and postglacial history of northernmost Ungava (Canada) from Pingualuit Crater Lake sediments     

Hervé Guyard  Guillaume St-Onge  Reinhard Pienitz  Pierre Francus  Bernd Zolitschka  Garry K.C. Clarke  Sonja Hausmann  Veli-Pekka Salonen  Patrick Lajeunesse  Grégoire Ledoux  Michel Lamothe 《Quaternary Science Reviews》2011,30(27-28):3892-3907

The Pingualuit Crater was formed by a meteoritic impact ca. 1.4 million years ago in northernmost Ungava (Canada). Due to its geographical position near the center of successive North American ice sheets and its favorable morphometry, the Pingualuit Crater Lake (water depth = 246 m) promises to yield a unique continuous sedimentary sequence covering several glacial/interglacial cycles in the terrestrial Canadian Arctic. In this paper, we suggest the existence of a subglacial lake at least during the Last Glacial Maximum (LGM) by hydraulic potential modeling using LGM ice-surface elevation and bed topography derived from a digital elevation model. These results support the hypothesis that the bottom sediments of the Crater Lake escaped glacial erosion and may contain a long-term continental sedimentary sequence. We also present the stratigraphy of a 9 m-long core retrieved from the deep basin of the lake as well as a multiproxy reconstruction of its deglacial and postglacial history. The base of the core is formed by very dense diamicton reflecting basal melt-out environments marking the end of subglacial conditions at the coring site. The overlying finely laminated silt are related to the onset of proglacial conditions characterized by extremely low lacustrine productivity. Infra Red Stimulated Luminescence and AMS ¹⁴C dating, as well as biostratigraphic data indicate sediment mixing between recent (e.g. Holocene) and much older (pre- to mid-Wisconsinan) material reworked by glacier activity. This process prevents the precise dating of these sediments that we interpret as being deposited just before the final deglaciation of the lake. Two finer grained and organic-rich intervals reflect the inception of lacustrine productivity resulting from the cessation of glacial meltwater inputs and ice-free periods. The lower organic interval corresponds to the early postglacial period (6850–5750 cal BP) and marks the transition between proglacial and postglacial conditions during the Holocene Thermal Maximum, while the uppermost organic-rich core section represents late Holocene sediments (～4200–600 cal BP). The organic intervals are separated by a basin-scale erosive slide occurring around 4200 cal BP and likely related to 1) a seismic event due to the glacio-isostatic rebound following the last deglaciation or 2) slope instabilities associated with rapid discharge events of the lake.  相似文献   

Palaeolimnological conditions inferred from fossil diatom assemblages and derivative spectral properties of sediments in thermokarst ponds of subarctic Quebec,Canada     

Frédéric Bouchard  Reinhard Pienitz  Joseph D. Ortiz  Pierre Francus  Isabelle Laurion 《Boreas: An International Journal of Quaternary Research》2013,42(3):575-595

Thermokarst ponds are widespread in arctic and subarctic regions, but little is known about their temporal evolution prior to human observations. This paper presents a pioneer biostratigraphic study conducted at a subarctic site with limnologically contrasted ponds located on the eastern shore of Hudson Bay, Canada. Fossil diatom and visible near infrared (VNIR) derivative spectral analyses were performed on short sediment cores, confirming the occurrence of three distinct stratigraphic facies as already inferred from an anterior sedimentological study: a lacustrine upper facies (UF) and a marine lower facies (LF), separated by an organic‐rich/peat transitional zone (TZ). Diatoms were almost absent from LF, but increased significantly in both TZ and UF. Identified diatom taxa were mainly benthic species (e.g. genera Fragilaria, Pinnularia), and their down‐core distribution appeared to be related to dissolved organic carbon (DOC) and possibly pH conditions. Diatom‐inferred DOC showed a decreasing trend towards the surface (potentially associated with an increase in pH), inverse to the general trend in this region, suggesting the action of other mechanisms on DOC, such as exhaustion of external inputs from limited catchments and the role of discontinuous peat layers (former surfaces of permafrost mounds) during the initial stages of pond formation. These bryophilous substrates in aerophilic habitats probably controlled diatom community composition. The combination of diatom and VNIR data revealed similar trends between (i) opal (amorphous silica) and diatom abundances; (ii) eukaryotic/prokaryotic algae ratio and anoxia or hypoxia in bottom waters; and (iii) limonite (iron oxide) and redox conditions in surface sediments. These findings indicate that diatom community changes and pond limnological evolution in the recent past were controlled mainly by autogenic processes (e.g. local vegetation/soil development, peat accumulation and erosion), rather than by allogenic forcing mechanisms (e.g. precipitation and temperature, geochemical leaching of the surrounding glaciomarine sediments).  相似文献   

Macroscopically‐Zoned Grandite from the Garnetite Skarn of Meka Presedla (Kopaonik Mountain,Serbia)     

Pavle Tan?i?  Predrag Vuli?  Reinhard Kaindl  Bernhard Sartory  Radovan Dimitrijevi? 《《地质学报》英文版》2012,86(2):394-405

The macroscopically-zoned grandite from the garnetite skarn of Meka Presedla (Kopaonik Mountain, Serbia) was studied with optical microscopy, electron microprobe analysis (EMPA), Fourier transform infra-red (FT–IR), and Raman methods. The EMPA results indicate that the main core–rim compositional variations (Ca2.93–2.97Mn0.05–0.06Mg0.00–0.01Al1.14–1.26Fe3+0.72–0.83Ti0.00–0.02Si2.97–3.02O12) slightly differ along the zones, showing evidence for a quasi-cyclic alternation of the oscillatory zoning nature. Among this, considerable variation is observed only by the Al–Fe3+ substitutions in the octahedral site. The EMPA also indicate that the grandite zones compositionally vary, mostly within ±1 and ±2 mol% of the homogeneity level range, that is, Grs64±1Adr36±1Sps2 (A), Grs62±1Adr38±1Sps2 (B), Grs59±2Adr40±2Sps2 (C), Grs58±2Adr41±2Sps2 (D), and Grs58±1Adr41±1Sps2 (E). Therefore, the investigated garnet can be considered as relatively highly homogeneous. The majority of compositions lie within the narrow miscibility region of 0.58±2相似文献   

The impact of diagenetic fluid–rock reactions on Rotliegend sandstone composition and petrophysical properties (Altmark area, central Germany)     

Dieter Pudlo  Viktor Reitenbach  Daniel Albrecht  Leonhard Ganzer  Ulrich Gernert  Joachim Wienand  Bernd Kohlhepp  Reinhard Gaupp 《Environmental Earth Sciences》2012,67(2):369-384

In the framework of the German R&D joint project CLEAN (CO₂ large-scale enhanced gas recovery in the Altmark natural gas field), Rotliegend reservoir sandstones of the Altensalzwedel block in the Altmark area (Saxony-Anhalt, central Germany) have been studied to characterise litho- and diagenetic facies, mineral content, geochemical composition, and petrophysical properties. These sands have been deposited in a playa environment dominated by aeolian dunes, dry to wet sand flats and fluvial channel fills. The sediments exhibit distinct mineralogical, geochemical, and petrophysical features related to litho- and diagenetic facies types. In sandstones of the damp to wet sandflats, their pristine red colours are preserved and porosity and permeability are only low. Rocks of the aeolian environment and most of the channel fill deposits are preferentially bleached and exhibit moderate to high porosity and permeability. Although geochemical element whole rock content in these rocks is very similar, element correlations are different. Variations in porosity and permeability are mainly due to calcite and anhydrite dissolution and differences in clay coatings with Fe-bearing illitic-chloritic composition exposed to the pore space. Moreover, mineral dissolution patterns as well as compositions (of clays and carbonate) and morphotypes of authigenic minerals (chlorite, illite) are different in red and bleached rocks. Comparison of the geochemical composition and mineralogical features of diagenetically altered sandstones and samples exposed to CO₂-bearing fluids in laboratory batch experiments exhibit similar character. Experiments prove an increase in wettability and water binding capacity during CO₂ impact.  相似文献   

Facies analysis and palaeoclimatic significance of ironstones formed during the Eocene greenhouse     

Walid Salama  Mortada El Aref  Reinhard Gaupp 《Sedimentology》2014,61(6):1594-1624

Lower and middle Eocene ironstone sequences of the Naqb and Qazzun formations from the north‐east Bahariya Depression, Western Desert, Egypt, represent a proxy for early Palaeogene climate and sea‐level changes. These sequences represent the only Palaeogene economic ooidal ironstone record of the Southern Tethys. These ironstone sequences rest unconformably on three structurally controlled Cenomanian palaeohighs (for example, the Gedida, Harra and Ghorabi mines) and formed on the inner ramp of a carbonate platform. These palaeohighs were exposed and subjected to subaerial lateritic weathering from the Cenomanian to early Eocene. The lower and middle Eocene ironstone sequences consist of quiet water ironstone facies overlain by higher energy ironstone facies. The distribution of low‐energy ironstone facies is controlled by depositional relief. These deposits consist of lagoonal, burrow‐mottled mud‐ironstone and laterally equivalent tidal flat, stromatolitic ironstones. The agitated water ironstone facies consist of shallow subtidal–intertidal nummulitic–ooidal–oncoidal and back‐barrier storm‐generated fossiliferous ironstones. The formation of these marginal marine sequences was associated with major marine transgressive–regressive megacycles that separated by subaerial exposure and lateritic weathering. The formation of lateritic palaeosols with their characteristic dissolution and reprecipitation features, such as colloform texture and alveolar voids, implies periods of humid and warm climate followed major marine regressions. The formation of the lower to middle Eocene ironstone succession and the associated lateritic palaeosols can be linked to the early Palaeogene global warming and eustatic sea‐level changes. The reworking of the middle Eocene palaeosol and the deposition of the upper Eocene phosphate‐rich glauconitic sandstones of the overlying Hamra Formation may record the initial stages of the palaeoclimatic transition from greenhouse to icehouse conditions.  相似文献   

Structural investigations of the two polymorphs of synthetic Fe-cordierite and Raman spectroscopy of hexagonal Fe-cordierite     

Udo Haefeker  Reinhard Kaindl  Peter Tropper  Hannes Krüger  Volker Kahlenberg  Maria Orlova 《Mineralogy and Petrology》2014,108(4):469-478

The crystal structures of synthetic hexagonal and orthorhombic Fe-cordierite polymorphs with the space groups P6/mcc and Cccm were refined from single-crystal X-ray diffraction data to R _{1, hex}?=?3.14 % and R _{1, ortho}?=?4.48 %. The substitution of the larger Fe²⁺ for Mg leads to multiple structural changes and an increase of the unit cell volumes, with a, c (hex)?=?9.8801(16) Å, 9.2852(5) Å and a, b, c (ortho)?=?17.2306(2) Å, 9.8239(1) Å, 9.2892(1) Å in the end-members. Furthermore Fe incorporation results in an increase of the volumes of the octahedra, although the diameters of the octahedra in direction of the c-axis decrease in both polymorphs. X-ray powder diffraction analysis indicates a high degree of Al/Si ordering in the orthorhombic polymorph, the Miyashiro distortion index is ~0.24. Estimations of site occupancies based on the determined tetrahedral volumes result in the following values for hexagonal Fe-cordierite: ~73 % Al for T₁ and ~28 % Al for T₂. For the first time Raman spectroscopy was performed on the hexagonal Fe-cordierite polymorph. In the hexagonal Fe-cordierite polymorph most Raman peaks are shifted towards lower wavenumbers when compared with the Mg-end-member.  相似文献   

Natural electromagnetic radiation (EMR) and its application in structural geology and neotectonics   总被引：2，自引：0，他引：2  

Reinhard O. Greiling  Hennes Obermeyer 《Journal of the Geological Society of India》2010,75(1):278-288

Natural electromagnetic radiation (EMR) impulses are emitted from rocks under stress. Electromagnetic emission may start during crystal deformation prior to and during the nucleation phase of nanocracks. The emission direction is either parallel with or normal to the crack surfaces. The EMR magnetic component is measured by the sensor or aerial of an instrument, the Cerescope, at frequencies from 5 to 50 kHz. Measurements at the surface show directions of recent stresses remarkably well. A calibration of EMR intensity in terms of stress magnitude is possible in tunnels, where the overburden pressure can be calculated. Two examples from the Upper Rhine Graben and NW India show EMR line measurements. In both cases, stress concentrations at fault or bedding surfaces can be detected. These surfaces can be regarded as tectonically active. Two further examples of EMR determinations in tunnels give more detailed information on the regional stress field. The example from the Swiss Jura fold-and-thrust belt shows directional results, with different directions beneath and above the regional detachment horizon at the base of the belt. The example from central Scandinavia shows a late Caledonian shear zone as a boundary between two recent stress domains, and gives absolute values of stress.  相似文献