Magnetic fabric and strain in Miocene volcanics in the southern margin of the Bükk Mountains, Hungary     

R  bert Bord  s 《Physics of the Earth and Planetary Interiors》1992,70(3-4):205-213

The magnetic anisotropy of two Miocene volcanic horizons south of the Bükk Mountains, northeast Hungary, was investigated (28 geographically distributed sites, over 400 samples). The horizons contain rocks from ignimbrites to porous tuffs. Microscopic and rock magnetic investigations showed that the main carrier of anisotropy is multidomain maghemite with varying composition. The complex magnetic fabric was separated into deformational and flow fabric in the upper horizon. This was carried out by monitoring the distribution of minimum susceptibility directions supposed to be elongated towards intermediates as a response to compressional strain. Jelínek's tensor statistics were used in the computations. Filtering out the effects of volcanic flow and compaction, north-south striking horizontal compressional strain was determined for the upper horizon in the geographic system. Owing to the lack of elongated distribution of minima, the characteristic intermediate susceptibility directions were taken as markers of strain directions in the lower horizon (WNW-ESE and NNE-SSW in the geographic system). The strain directions showed correlation with compressional stress orientations observed by microtectonics, thus a homogeneous stress-strain field was supposed within the area investigated. The tectonic component of the strain can be determined by taking the respective paleomagnetic declination rotations as the rotational components of the deformation.  相似文献   

Preface     

E. Gómez-Treviño  George R. Jiracek 《Surveys in Geophysics》1992,13(4-5):305-308

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Statistical properties of 49 years of rainfall rate events     

E. Vilar  A. Burgueño 《Theoretical and Applied Climatology》1995,50(3-4):213-225

Summary The paper presents a detailed investigation of magnitudes and properties pertaining to the large population of rainfall events recorded during 49 years at the Fabra Observatory in Barcelona. The study includes a statistical analysis of event durationT and rainfall quantityQ together with the statistical rainfall rate parameters: , ²(R) and maximum Rm within an event. The decorrelation time is also analysed. It is found thatQ, T, and can be well modelled by a lognormal distribution, but , ² and Rm are only so for a limited range of precipitation ratesR. The regression analysis between pairs of logarithms of the magnitudes investigated is generally good and a regression coefficient is often better than 0.9. Comparison with published work is also carried out. An attempt is made to discriminate between heavy and non-heavy rainfall rates, and the 50 mm/h threshold is used for the study. The twelve-monthly running average indicates that the rainfall amount has a small increasing trend over the fifty year period. However, this trend is reversed when considering heavy rains. Finally, the return period in years to exceeding a thresholdR within an event is also investigated and the distribution of the population of annual extremes is found to be Gumbel II.With 6 Figures  相似文献   

On the problem of selective enhancement of barium in the atmospheres of BaII stars     

L. I. Mashonkina  L. Začs 《Astrophysics and Space Science》1996,236(2):185-199

High-resolution spectroscopy and standard LTE analysis of 31 barium and normal red giants (Astron. Astrophys. 283, 1994, p. 937) shows a selective enhancement of Ba (+0.5 dex) in two stars. HR 3845 and HD 130386, relative to the standard star Vir. We do not overinterpret these enhancements due to possible errors in the equivalent widths or in the atmospheric parameters. The non-LTE analysis of BaII in the atmospheres of red (barium) giants shows that the corrections for the non-LTE effects is relatively small, reaching a maximum of –0.16 dex, therefore, the enhancement of barium had apparently another nature.  相似文献   

An extensive study of planetary nebulae with emission-line nuclei     

Agnès Acker  Sławomir K. Górny  Björn Stenholm 《Astrophysics and Space Science》1996,238(1):63-66

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Limnogeology of Laguna Miscanti: evidence for mid to late Holocene moisture changes in the Atacama Altiplano (Northern Chile)   总被引：1，自引：0，他引：1  

Blas L. Valero-Garcés  Martin Grosjean  Antje Schwalb  Mebus Geyh  Bruno Messerli  Kerry Kelts 《Journal of Paleolimnology》1996,16(1):1-21

Sedimentological, mineralogical and geochemical analyses of sediment cores from 9 m-deep, saline Laguna Miscanti, Chile (23 ° 44S, 67 °46W, 4140 m a.s.l.) together with high-resolution seismic profiles provide a mid to late Holocene time series of regional environmental change in the Atacama Altiplano constrained by ²¹⁰Pb and conventional ¹⁴C dating. The mid Holocene was the most arid interval since the last glacial maximum, as documented by subaerial exposure and formation of hardgrounds on a playa surface. Extremely low lake levels during the mid Holocene appear consistent with lower effective moisture recorded at other sites along the Altiplano and in the Amazon Basin. Termination of this arid period represented a major shift in the regional environmental dynamics and inaugurated modern atmospheric conditions. The cores show a progressive upward increase in effective moisture interrupted by numerous century-scale drier periods of various intensities and durations that characterize a fluctuating late Holocene climate. In spite of chronological uncertainties, the major environmental changes seem to correlate with the available paleorecords from the region providing a coherent account of effective moisture variability in the tropical highlands of South America.This is the 16th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest for these papers.  相似文献   

Low velocity shock-cloud encounters II.     

L. Viktor Tóth  András Horváth Jr.  Lauri K. Haikala 《Astrophysics and Space Science》1995,233(1-2):175-179

We report on a comparative study of nearby shocked clouds with and without star formation, based on IRAS, HI(21cm), CO(1-0) NH₃ (and other molecular line) observations. The dark clouds L1780 (no star formation) and L1251 (high SFE) are discussed here. Their density and velocity structure are compared with the predictions of the HD model of Horváth & Tóth (1995), Paper I.  相似文献   

Room Design for Underground Slate Workings: Analysis of Safety Factors for Keyblocks     

Agustín Menéndez-Díaz  Ramón Argüelles-Fraga  Celestino Ordóñez-Galán  Jose Benito Bouza-Rodríguez 《Rock Mechanics and Rock Engineering》2016,49(3):1107-1113

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Complex coastal change in response to autogenic basin infilling: An example from a sub‐tropical Holocene strandplain          下载免费PDF全文

Christopher J. Hein  Duncan M. FitzGerald  Luis H. P. de Souza  Ioannis Y. Georgiou  Ilya V. Buynevich  Antonio H. da F. Klein  João Thadeu de Menezes  William J. Cleary  Thelma L. Scolaro 《Sedimentology》2016,63(6):1362-1395

Thick bay‐fill sequences that often culminate in strandplain development serve as important sedimentary archives of land–ocean interaction, although distinguishing between internal and external forcings is an ongoing challenge. This study employs sediment cores, ground‐penetrating radar surveys, radiocarbon dates, palaeogeographic reconstructions and hydrodynamic modelling to explore the role of autogenic processes – notably a reduction in wave energy in response to coastal embayment infilling – in coastal evolution and shoreline morphodynamics. Following a regional 2 to 4 m highstand at ca 5·8 ka, the 75 km² Tijucas Strandplain in southern Brazil built from fluvial sediments deposited into a semi‐enclosed bay. Holocene regressive deposits are underlain by fluvial sands and a Pleistocene transgressive–regressive sequence, and backed by a highstand barrier‐island. The strandplain is immediately underlain by 5 to 16 m of seaward‐thickening, fluvially derived, Holocene‐age, basin‐fill mud. Several trends are observed from the landward (oldest) to the seaward (youngest) sections of the strandplain: (i) the upper shoreface and foreshore become finer and thinner and shift from sand‐dominated to mud‐dominated; (ii) beachface slopes decrease from >11° to ca 7°; and (iii) progradation rates increase from 0·4 to 1·8 m yr^?1. Hydrodynamic modelling demonstrates a correlation between progressive shoaling of Tijucas Bay driven by sea‐level fall and sediment infilling and a decrease in onshore wave‐energy transport from 18 to 4 kW m^?1. The combination of allogenic (sediment supply, falling relative sea‐level and geology) and autogenic (decrease in wave energy due to bay shoaling) processes drove the development of a regressive system with characteristics that are rare, if not unique, in the Holocene and rock records. These findings demonstrate the complexities in architecture styles of highstand and regressive systems tracts. Furthermore, this article highlights the diverse internal and external processes and feedbacks responsible for the development of these intricate marginal marine sedimentary systems.  相似文献   

Porosity and size gradation of saturated gravel with percolated fines          下载免费PDF全文

Francisco Núñez‐González  Juan Pedro Martín‐Vide  Maarten G. Kleinhans 《Sedimentology》2016,63(5):1209-1232

Fine particles may infiltrate through coarse alluvial beds and eventually saturate the subsurface pore space. It is essential to understand the conditions that lead to bed saturation, and to forecast the packing characteristics of saturated beds to assess the effect of excess fine sediment supply on a number of processes that occur in the stream–sediment boundary. To address this problem, in this study, a new method is introduced to predict the grain‐size distribution for the saturated condition, and the resulting porosity decrease, given the characteristics of the bed and the supplied sediments. The new method consists of the numerical aggregation of infilling fines in a finite bed volume, during which the bed properties change to affect further infilling. An existing semi‐empirical, particle packing model is implemented to identify these properties. It is shown that these types of models are adequate to describe regimes of natural sediment fabric quantitatively, and are thus useful tools in the analysis of sediment infiltration processes. Unlike previous developments to quantify saturated bed conditions, which assume that the supplied material is uniform and finer than the bed pore openings, the method developed herein considers poorly sorted fines, and can identify size fractions that are able to ingress into the bed due to being smaller than the particles that form the bed structure. Application of the new method to published experimental data showed that the final content of infiltrated fines is strongly sensitive to the initial bed packing density, highlighting the need to measure and understand open‐work gravel deposits. In addition, the new method was shown to be suitable for assessing the degree of bed saturation, when it was applied to a published data set of field samples.  相似文献