Stratigraphic development of an Upper Jurassic deep marine syn‐rift succession,Inner Moray Firth Basin,Scotland     

Adam D. McArthur  Adrian J. Hartley  David W. Jolley 《Basin Research》2013,25(3):285-309

The stratigraphic development of an Upper Jurassic syn‐rift succession exposed at outcrop in the Inner Moray Firth Basin has been investigated using high‐resolution biostratigraphy and sedimentology. A continuous 970 m thick section, exposed in the hangingwall of the Helmsdale Fault was logged in detail. The succession spans 8 Ma and contains eight lithofacies types, which indicate deposition in a deep marine setting. Boulder beds contain large, angular clasts, with bed thicknesses typically >2 m and poor sorting suggesting deposition by debris flows. An inverse clast stratigraphy is observed; the oldest boulder beds contain sandstone clasts of Upper Old Red Sandstone (ORS) with younger debris flows containing clasts of Middle ORS calcareous siltstone. A marked change from siliciclastic to carbonate dominated sedimentation occurred during the Early Tithonian, interpreted primarily as a result of change in lithologies in the footwall catchment from sandstone to calcareous siltstone, which reduced supply of siliciclastic sediment. Secondary factors are identified as increased aridity in the Early Tithonian, which reduced sand supply from the hinterland and a third‐order Early Tithonian eustatic sea‐level rise, which trapped coarser clastic sediment within the hinterland. Biostratigraphy allows calculation of variations in sedimentation rates with recognition of: (1) an early rift phase characterised by sandy turbidite deposition, when sedimentation rates averaged 0.08 m/ky, (2) a rift climax phase from the Early Kimmeridgian where sedimentation rates increased steadily to a maximum of 0.64 m/ky in the Early Tithonian, with strata dominated by boulder scale clast‐supported debris flows and (3) a late stage of rifting from the mid Tithonian, where sedimentation rates decreased to 0.07 m/ky. Overall sedimentation rates are comparable to those of other deep marine rift basins. Unroofing a resistant lithology on the footwall of a rift has important implications for siliciclastic sediment supply in rift basins.  相似文献   

Perpendicular flow deviation in a magnetized counter-streaming plasma     

Y.-D. Jia  Y.J. Ma  C.T. Russell  H.R. Lai  G. Toth  T.I. Gombosi 《Icarus》2012,218(2):895-905

Charged dust exists in various regions in the Solar System. How this charged dust interacts with the surrounding plasma is not well understood. In this study we neglect the charging process and treat the charged dust as a fluid interacting with the ambient magnetized plasma fluid. The model reproduces the expected plasma deceleration with both positively charged and negatively charged dust, but a new effect arises. Negatively charged dust causes the magnetic field to bend in the direction of the convection electric field, while positively charged dust causes the opposite magnetic field bending. Consequently, the interaction does not only result in a perpendicular shift in the downstream current system, but also a rotation in these currents. We present quantitative results using the multi-fluid MHD code BATSRUS for both subsonic and supersonic interactions. We find that the same perpendicular bending exists for all counter-streaming interaction problems, independent of the shape of the dust cloud. The new model can be applied to plasma interaction studies including, but not limited to, charged dust particles in the solar wind, cometary plasma, the Enceladus plume, and active plasma releases, such as the Active Magnetospheric Particle Tracer Experiment (AMPTE) mission. The predicted behavior is consistent with observations at Enceladus.  相似文献   

The Radial Variation of Interplanetary Shocks in the Inner Heliosphere: Observations by <Emphasis Type="Italic">Helios</Emphasis>, MESSENGER,and STEREO     

H. R. Lai  C. T. Russell  L. K. Jian  X. Blanco-Cano  B. J. Anderson  J. G. Luhmann  A. Wennmacher 《Solar physics》2012,278(2):421-433

The two major sources of collisionless shocks in the solar wind are interplanetary coronal mass ejections (ICMEs) and stream interaction regions (SIRs). Previous studies show that some SIR-associated shocks form between Venus and Earth while most form beyond 1 AU. Here we examine the high-resolution magnetometer records from Helios 1 and 2 obtained between 0.28 and 1 AU and from MESSENGER obtained between 0.3 and 0.7 AU to further refine our understanding as to where, and in what context, shocks are formed in the inner solar system. From Helios data (Helios 1 from 1974 to 1981 and Helios 2 from 1976 to 1980), we find there were only a few shocks observed inside the orbit of Venus with the closest shock to the Sun at 0.29 AU. We find that there is a strong correlation between shock occurrence and solar activity as measured by the sunspot number. Most of the shocks inside of the orbit of Venus appear to be associated with ICMEs. Even the ICME-associated shocks are quite weak inside the orbit of Venus. By comparing MESSENGER and STEREO results, from 2007 to 2009, we find that in the deep solar minimum, SIR-driven shocks began to form at about 0.4 AU and increased in number with heliocentric distance.  相似文献   

Flybys in the planar, circular, restricted, three-body problem     

Stefano Campagnola  Paul Skerritt  Ryan P. Russell 《Celestial Mechanics and Dynamical Astronomy》2012,113(3):343-368

An analysis is presented of gravity assisted flybys in the planar, circular, restricted three-body problem (pcr3bp) that is inspired by the Keplerian map and by the Tisserand- Poincaré graph. The new Flyby map is defined and used to give insight on the flyby dynamics and on the accuracy of the linked-conics model. The first main result of this work is using the Flyby map to extend the functionality of the Tisserand graph to low energies beyond the validity of linked conics. Two families of flybys are identified: Type I (direct) flybys and Type II (retrograde) flybys. The second main result of this work shows that Type I flybys exist at all energies and are more efficient than Type II flybys, when both exist. The third main result of this work is the introduction of a new model, called ??Conics, When I Can??, which mixes numerical integration and patched conics formulas, and has applications beyond the scope of this work. The last main result is an example trajectory with multiple flybys at Ganymede, all outside the linked-conics domain of applicability. The trajectory is computed with the pcr3bp, and connects an initial orbit around Jupiter intersecting the Callisto orbit, to an approach transfer to Europa. Although the trajectory presented has similar time of flight and radiation dose of other solutions found in literature, the orbit insertion ??v is 150 m/s lower. For this reason, the transfer is included in the lander option of the Europa Habitability Mission Study.  相似文献   

Episodic recharge and climate change in the Murray-Darling Basin, Australia   总被引：1，自引：0，他引：1  

Russell S. Crosbie  James L. McCallum  Glen R. Walker  Francis H. S. Chiew 《Hydrogeology Journal》2012,20(2):245-261

In semi-arid areas, episodic recharge can form a significant part of overall recharge, dependant upon infrequent rainfall events. With climate change projections suggesting changes in future rainfall magnitude and intensity, groundwater recharge in semi-arid areas is likely to be affected disproportionately by climate change. This study sought to investigate projected changes in episodic recharge in arid areas of the Murray-Darling Basin, Australia, using three global warming scenarios from 15 different global climate models (GCMs) for a 2030 climate. Two metrics were used to investigate episodic recharge: at the annual scale the coefficient of variation was used, and at the daily scale the proportion of recharge in the highest 1% of daily recharge. The metrics were proportional to each other but were inconclusive as to whether episodic recharge was to increase or decrease in this environment; this is not a surprising result considering the spread in recharge projections from the 45 scenarios. The results showed that the change in the low probability of exceedance rainfall events was a better predictor of the change in total recharge than the change in total rainfall, which has implications for the selection of GCMs used in impact studies and the way GCM results are downscaled.  相似文献   

Olivine or impact melt: Nature of the “Orange” material on Vesta from Dawn     

Lucille Le Corre  Vishnu Reddy  Nico Schmedemann  Kris J. Becker  David P. O’Brien  Naoyuki Yamashita  Patrick N. Peplowski  Thomas H. Prettyman  Jian-Yang Li  Edward A. Cloutis  Brett W. Denevi  Thomas Kneissl  Eric Palmer  Robert W. Gaskell  Andreas Nathues  Michael J. Gaffey  David W. Mittlefehldt  William B. Garry  Holger Sierks  Christopher T. Russell  Carol A. Raymond  Maria C. De Sanctis  Eleonora Ammanito 《Icarus》2013

NASA’s Dawn mission observed a great variety of colored terrains on asteroid (4) Vesta during its survey with the Framing Camera (FC). Here we present a detailed study of the orange material on Vesta, which was first observed in color ratio images obtained by the FC and presents a red spectral slope. The orange material deposits can be classified into three types: (a) diffuse ejecta deposited by recent medium-size impact craters (such as Oppia), (b) lobate patches with well-defined edges (nicknamed “pumpkin patches”), and (c) ejecta rays from fresh-looking impact craters. The location of the orange diffuse ejecta from Oppia corresponds to the olivine spot nicknamed “Leslie feature” first identified by Gaffey (Gaffey, M.J. [1997]. Icarus 127, 130–157) from ground-based spectral observations. The distribution of the orange material in the FC mosaic is concentrated on the equatorial region and almost exclusively outside the Rheasilvia basin. Our in-depth analysis of the composition of this material uses complementary observations from FC, the visible and infrared spectrometer (VIR), and the Gamma Ray and Neutron Detector (GRaND). Several possible options for the composition of the orange material are investigated including, cumulate eucrite layer exposed during impact, metal delivered by impactor, olivine–orthopyroxene mixture and impact melt. Based on our analysis, the orange material on Vesta is unlikely to be metal or olivine (originally proposed by Gaffey (Gaffey, M.J. [1997]. Icarus 127, 130–157)). Analysis of the elemental composition of Oppia ejecta blanket with GRaND suggests that its orange material has ∼25% cumulate eucrite component in a howarditic mixture, whereas two other craters with orange material in their ejecta, Octavia and Arruntia, show no sign of cumulate eucrites. Morphology and topography of the orange material in Oppia and Octavia ejecta and orange patches suggests an impact melt origin. A majority of the orange patches appear to be related to the formation of the Rheasilvia basin. Combining the interpretations from the topography, geomorphology, color and spectral parameters, and elemental abundances, the most probable analog for the orange material on Vesta is impact melt.  相似文献   

Vesta's mineralogical composition as revealed by the visible and infrared spectrometer on Dawn     

M. Cristina De Sanctis  Eleonora Ammannito  M. Teresa Capria  Fabrizio Capaccioni  Jean‐Philippe Combe  Alessandro Frigeri  Andrea Longobardo  Gianfranco Magni  Simone Marchi  Tom B. McCord  Ernesto Palomba  Federico Tosi  Francesca Zambon  Francesco Carraro  Sergio Fonte  Y. J. Li  Lucy A. McFadden  David W. Mittlefehldt  Carle M. Pieters  Ralf Jaumann  Katrin Stephan  Carol A. Raymond  Christopher T. Russell 《Meteoritics & planetary science》2013,48(11):2166-2184

The Dawn spacecraft mission has provided extensive new and detailed data on Vesta that confirm and strengthen the Vesta–howardite–eucrite–diogenite (HED) meteorite link and the concept that Vesta is differentiated, as derived from earlier telescopic observations. Here, we present results derived by newly calibrated spectra of Vesta. The comparison between data from the Dawn imaging spectrometer—VIR—and the different class of HED meteorites shows that average spectrum of Vesta resembles howardite spectra. Nevertheless, the Vesta spectra at high spatial resolution reveal variations in the distribution of HED‐like mineralogies on the asteroid. The data have been used to derive HED distribution on Vesta, reported in Ammannito et al. (2013), and to compute the average Vestan spectra of the different HED lithologies, reported here. The spectra indicate that, not only are all the different HED lithologies present on Vesta, but also carbonaceous chondritic material, which constitutes the most abundant inclusion type found in howardites, is widespread. However, the hydration feature used to identify carbonaceous chondrite material varies significantly on Vesta, revealing different band shapes. The characteristic of these hydration features cannot be explained solely by infalling of carbonaceous chondrite meteorites and other possible origins must be considered. The relative proportion of HEDs on Vesta's surface is computed, and results show that most of the vestan surface is compatible with eucrite‐rich howardites and/or cumulate or polymict eucrites. A very small percentage of surface is covered by diogenite, and basaltic eucrite terrains are relatively few compared with the abundance of basaltic eucrites in the HED suite. The largest abundance of diogenitic material is found in the Rheasilvia region, a deep basin, where it clearly occurs below a basaltic upper crust. However, diogenite is also found elsewhere; although the depth to diogenite is consistent with one magma ocean model, its lateral extent is not well constrained.  相似文献   

The first generation of star-forming haloes     

Darren S. Reed  Richard Bower  Carlos S. Frenk  Liang Gao  Adrian Jenkins  Tom Theuns  Simon D. M. White 《Monthly notices of the Royal Astronomical Society》2005,363(2):393-404

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Imaging the heterogeneity of mineral surface reactivity using Ag(I) and synchrotron X-ray microscopy     

J. E.?AmonetteEmail author  S. M.?Heald  C. K.?Russell 《Physics and Chemistry of Minerals》2003,30(9):559-569

Microscopic-scale imaging of reduced zones on the surfaces of minerals can be achieved by reaction with dilute Ag(I) solutions and subsequent analysis using synchrotron X-ray microscopy (XRM) above the Ag K-edge (25.5 keV). The principal reductant is Fe(II), but other reductants such as sulfide may contribute. Reduced zones may exist instrinsically, as in the structure of biotite and augite, or may be generated by reaction with chemical agents such as dithionite or treatment with sulfate-reducing bacteria (SRB). We demonstrate the method on flakes of specular hematite and biotite, as well as on thin sections of different rocks (arfvedsonitic granite, oolitic hematite, diabase, and quartz conglomerate) treated with SRB, and discuss possible artifacts that can occur. To our knowledge, this is the only microscopic technique that can image Fe(II) zones on the surface of an Fe-bearing mineral with monolayer sensitivity.  相似文献   

Metamorphic ore remobilization in the Hällefors district, Bergslagen, Sweden: constraints from mineralogical and small-scale sulphur isotope studies     

Thomas Wagner  Erik Jonsson  Adrian J. Boyce 《Mineralium Deposita》2005,40(1):100-114

The marble- and metavolcanic-hosted Pb–Zn–(Ag–Sb–As) deposits of the Hällefors district, located in the Palaeoproterozoic Bergslagen ore province, south central Sweden, comprise both stratabound sulphides and discordant, Ag-rich sulphide–sulphosalt veins. The complex sulphide–sulphosalt assemblages of the Alfrida-Jan Olof mines at Hällefors were investigated by a combination of ore microscopy, electron-microprobe analysis, and in situ laser sulphur isotope analysis. The massive ore is characterized by positive and homogeneous ³⁴S (+1.4 to +2.7 V-CDT), whereas vein-hosted sulphides and sulphosalts exhibit similar, but generally less positive to slightly negative ³⁴S (–0.6 to +2.0). Comparison of the observed ore mineral assemblages with calculated phase equilibria in the system Fe–As–S–O–H and isotopic fractionation as a function of temperature, oxygen fugacity and pH indicates that the vein-type mineralization was formed from relatively reduced and rather alkaline hydrothermal fluids. At these reduced conditions, fractionation of ³⁴S via changes of fO₂ is insignificant, and thus the isotopic signatures of the vein minerals directly reflect the composition of the sulphur source. We therefore conclude that the vein-type ore essentially inherited the sulphur isotope signature from the pre-existing massive sulphides via metamorphic remobilization at approximately 300–400°C and 2–3 kbar. Scales of remobilization observable are on the order of about 5 mm to 30 cm. Overall, the sulphide–sulphosalt assemblages from the Alfrida-Jan Olof mines exhibit ³⁴S values which are comparable to a majority of metasupracrustal-hosted deposits in the Bergslagen province, thereby suggesting a common origin from ca. 1.90–1.88 Ga volcanic-hydrothermal processes.Editorial handling: S. Nicolescu  相似文献