The response of a basin‐scale Miocene barrier reef system to long‐term,strong subsidence on a passive continental margin,Barcoo Sub‐basin,Australian North West Shelf          下载免费PDF全文

Beke Rosleff‐Soerensen  Lars Reuning  Stefan Back  Peter A. Kukla 《Basin Research》2016,28(1):103-123

The Miocene sedimentary succession of the southern Browse Basin records the response of a tropical reef system to long‐term, strong subsidence on a passive continental margin. Geological interpretation of a comprehensive two‐dimensional (2D) seismic reflectivity data set documents for the first time the development of a continuous Miocene barrier reef on the Australian North West Shelf. With a length of over 250 km, this barrier reef is among the Earth's largest in the Neogene record. A sequence stratigraphic analysis tied to well data shows that the main controls for the evolution, growth and demise of the reef system were subsidence, third‐order global‐scale eustatic variations and antecedent topography. The generally very high Miocene subsidence rates estimated for the study area cannot be explained by typical passive‐margin subsidence controlled by lithospheric cooling and sedimentary loading alone. Additional dynamic subsidence induced by mantle convection, though documented as unusually large on the northern margin of Australia during the Neogene, can be also regarded as being of only minor importance. Therefore, accelerated tectonic subsidence related to the collision of the Australian and Eurasian Plates 250–500 km north of the study area seems to exert an important influence on reef development and demise, complicated by local tectonic inversion. The Miocene tectonic reactivation and inversion of an older structural grain is interpreted to have controlled the reef development considerably by providing localized topographic highs along transpressional anticlines above basement‐rooted faults that served as preferential sites for reef growth and retreat during times of rapidly rising sea level. This exemplarily shows that the far‐field effects of collision‐induced tectonic subsidence can significantly influence carbonate systems on passive margins.  相似文献   

Sediment Denitrification in Two Contrasting Tropical Shallow Lagoons     

Alex Enrich-Prast  Ana Lúcia Santoro  Rodrigo S. Coutinho  Lars Peter Nielsen  Francisco A. Esteves 《Estuaries and Coasts》2016,39(3):657-663

Sediment denitrification was monthly evaluated in two tropical coastal lagoons with different trophic states using the ¹⁵N isotope pairing technique. Denitrification rates were very low in both environments, always <5.0 μmol N₂ m^?2 h^?1 and were not significantly different between them. Oxygen consumption varied from 426 to 4248 μmol O₂ m^?2 h^?1 and was generally three times higher in the meso-eutrophic than the oligotrophic lagoon. The low denitrification activity was ascribed to both low water NO₃ ^? concentrations (<2.0 μM) and little nitrate supply from nitrification. There was no correlation of denitrification with nitrate or ammonium fluxes. Sediments in temperate environments with similar oxygen consumption rates usually presented a higher proportion of nitrification–denitrification rates. Sediment oxygen consumption was a good predictor of sediment denitrification in both studied lagoons.  相似文献   

NGI‐ADP: Anisotropic shear strength model for clay     

Gustav Grimstad  Lars Andresen  Hans P. Jostad 《国际地质力学数值与分析法杂志》2012,36(4):483-497

Many geotechnical problems involve undrained behavior of clay and the capacity in undrained loading. Most constitutive models used today are effective stress based and only indirectly obtain values for the undrained shear strength. To match the design profiles of undrained shear strengths, in active (A), direct simple shear (D) and passive (P) modes of loading are complicated. This paper presents the elastoplastic constitutive model NGI‐ADP which is based on the undrained shear strength approach with direct input of shear strengths. Consequently, exact match with design undrained shear strengths profiles is obtained and the well‐known anisotropy of undrained shear strength and stiffness is accounted for in the constitutive model. A non‐linear stress path‐dependent hardening relationship is used, defined from direct input of failure strains in the three directions of shearing represented by triaxial compression, direct simple shear and triaxial extension. With its clear input parameters the model has significant advantages for design analysis of undrained problems. The constitutive model is implemented, into finite element codes, with an implicit integration scheme. Its performance is demonstrated by a finite element analysis of a bearing capacity problem. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Atmospheric effects on satellite gravity gradiometry data     

Mehdi Eshagh  Lars E. Sjöberg 《Journal of Geodynamics》2009,47(1):9-19

Atmospheric masses play an important role in precise downward continuation and validation of satellite gravity gradiometry data. In this paper we present two alternative ways to formulate the atmospheric potential. Two density models for the atmosphere are proposed and used to formulate the external and internal atmospheric potentials in spherical harmonics. Based on the derived harmonic coefficients, the direct atmospheric effects on the satellite gravity gradiometry data are investigated and presented in the orbital frame over Fennoscandia. The formulas of the indirect atmospheric effects on gravity anomaly and geoid (downward continued quantities) are also derived using the proposed density models. The numerical results show that the atmospheric effect can only be significant for precise validation or inversion of the GOCE gradiometric data at the mE level.  相似文献   

Erratum to: EPR investigation of NO2 and CO2 − and other radicals in beryl     

Lars Olov Andersson 《Physics and Chemistry of Minerals》2010,37(7):453-453

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Opening a new window to other worlds with spectropolarimetry     

Maren Mohler  Johannes Bühl  Stephen Doherty  Siegfried Eggl  Vera Theresa Eybl  François Farago  Aleksandar Jaćimović  Lars Hunger  Nynne L. B. Lauritsen  David Ludena  Martina Meisnar  Alexander Reissner  Nicolas Sarda  Benjamin Toullec  Meritxell Viñas Tió 《Experimental Astronomy》2010,28(2-3):101-135

A high level of diversity has already been observed among the planets of our own Solar System. As such, one expects extrasolar planets to present a wide range of distinctive features, therefore the characterisation of Earth- and super Earth-like planets is becoming of key importance in scientific research. The Search (Spectropolarimetric Exoplanet AtmospheRe CHaracerisation) mission proposal of this paper represents one possible approach to realising these objectives. The mission goals of Search include the detailed characterisation of a wide variety of exoplanets, ranging from terrestrial planets to gas giants. More specifically, Search will determine atmospheric properties such as cloud coverage, surface pressure and atmospheric composition, and may also be capable of identifying basic surface features. To resolve a planet with a semi major axis of down to 1.4 AU and 30 pc distant Search will have a mirror system consisting of two segments, with elliptical rim, cut out of a parabolic mirror. This will yield an effective diameter of 9 m along one axis. A phase mask coronagraph along with an integral spectrograph will be used to overcome the contrast ratio of star to planet light. Such a mission would provide invaluable data on the diversity present in extrasolar planetary systems and much more could be learned from the similarities and differences compared to our own Solar System. This would allow our theories of planetary formation, atmospheric accretion and evolution to be tested, and our understanding of regions such as the outer limit of the Habitable Zone to be further improved.  相似文献   

A method for estimating sediment budgets of washover deposits using digital terrain models     

Lars Ø. Hansen  Verner B. Ernstsen  Lars B. Clemmensen  Zyad Al-Hamdani  Aart Kroon 《地球表面变化过程与地形》2021,46(4):804-821

Washover fans are located on small barriers in fetch-limited micro-tidal coastal environments in Denmark. These washover fans are formed during high-energy storm events and we present a method to quantify their volumes and to estimate sediment exchanges between washover fans and their adjacent morphologies. We use high resolution digital terrain models (DTMs) based on light detection and ranging (LiDAR) data. We have delineated landforms using known methods of scale analysis and geomorphometric classification. We quantified volumes of the delineated landforms and estimated the related sediment budgets. These computed volumes were compared using different pre-depositional surfaces. Finally, we assessed the sediment exchange and associated sources of sediments of the washover fans. We applied a scale analysis to determine suitable DTM resolution and focal statistics window size as input to a geomorphometric classification analysis. Landform areas and landforms were delineated using morphometric threshold values, and volumes and sediment budgets of the delineated landforms were computed using different assumptions to define the pre-depositional surface. Resulting washover fan volumes were validated against digital elevation model (DEM) of difference (DoD) derived volumes. Sediment budgets were derived from representative volumes of the washover fans and adjacent berms. We show that quantification of washover features derived from DTMs, using geomorphometric analysis is feasible and that the presented approach provides estimates of washover deposit volumes with an accuracy between 1% and 28% compared to control volumes. © 2021 John Wiley & Sons, Ltd.  相似文献   

Reconstruction of propagating Kelvin–Helmholtz vortices at Mercury's magnetopause     

Torbjörn Sundberg  Scott A. Boardsen  James A. Slavin  Lars G. Blomberg  Judy A. Cumnock  Sean C. Solomon  Brian J. Anderson  Haje Korth 《Planetary and Space Science》2011,59(15):2051-2057

A series of quasi-periodic magnetopause crossings were recorded by the MESSENGER spacecraft during its third flyby of Mercury on 29 September 2009, likely caused by a train of propagating Kelvin–Helmholtz (KH) vortices. We here revisit the observations to study the internal structure of the waves. Exploiting MESSENGER's rapid traversal of the magnetopause, we show that the observations permit a reconstruction of the structure of a rolled-up KH vortex directly from the spacecraft's magnetic field measurements. The derived geometry is consistent with all large-scale fluctuations in the magnetic field data, establishes the non-linear nature of the waves, and shows their vortex-like structure. In several of the wave passages, a reduction in magnetic field strength is observed in the middle of the wave, which is characteristic of rolled-up vortices and is related to the increase in magnetic pressure required to balance the centrifugal force on the plasma in the outer regions of a vortex, previously reported in computer simulations. As the KH wave starts to roll up, the reconstructed geometry suggests that the vortices develop two gradual transition regions in the magnetic field, possibly related to the mixing of magnetosheath and magnetospheric plasma, situated at the leading edges from the perspectives of both the magnetosphere and the magnetosheath.  相似文献   

Disturbance of isotope systematics during experimental shock and thermal metamorphism of a lunar basalt with implications for Martian meteorite chronology     

Amy M. GAFFNEY  Lars E. BORG  Yemane ASMEROM  Charles K. SHEARER  Paul V. BURGER 《Meteoritics & planetary science》2011,46(1):35-52

Abstract– To better determine the effects of impact‐related processes on radiometric chronometers in meteorites, we undertook an isotopic study of experimentally shocked and heated samples of lunar basalt 10017. Shock experiments at 55 GPa were completed on one subsample, and a second subsample was heated in an evacuated quartz tube at 1000 °C for 170 h. A third subsample was maintained as a control. Samarium‐neodymium, Rb‐Sr, ²³⁸U‐²⁰⁶Pb, and ²⁰⁶Pb‐²⁰⁷Pb isotopic analyses were completed on mineral fractions (leached and unleached), leached whole rocks, and complementary acid leachates. Disturbance in the shocked and heated samples was evaluated through comparison of their isochron diagrams with those of the control sample. The Sm‐Nd isotope system was the least disturbed, the Rb‐Sr isotope system was more disturbed, and the ²³⁸U‐²⁰⁶Pb and ²⁰⁶Pb‐²⁰⁷Pb isotope systems were the most disturbed by shock and annealing. Samples that experienced extended heating demonstrated greater isotopic disturbances than shocked samples. In some cases, the true crystallization age was preserved, and in others, age information was degraded or destroyed. In no case did the experiments generate isochrons that maintained linearity while being rotated or completely reset. Although our results show that neither experimental shock nor thermal metamorphism alone can account for the discordant ages represented by different isotope systems in some Martian meteorites, we postulate that shock metamorphism may render a meteorite more susceptible than its unshocked counterpart to subsequent disturbance during extended impact‐related heating or aqueous alteration. The combination of these processes may result in the disparate chronometric information preserved in some meteorites.  相似文献   

Are there social limits to adaptation to climate change?   总被引：1，自引：0，他引：1  

W. Neil Adger  Suraje Dessai  Marisa Goulden  Mike Hulme  Irene Lorenzoni  Donald R. Nelson  Lars Otto Naess  Johanna Wolf  Anita Wreford 《Climatic change》2009,93(3-4):335-354

While there is a recognised need to adapt to changing climatic conditions, there is an emerging discourse of limits to such adaptation. Limits are traditionally analysed as a set of immutable thresholds in biological, economic or technological parameters. This paper contends that limits to adaptation are endogenous to society and hence contingent on ethics, knowledge, attitudes to risk and culture. We review insights from history, sociology and psychology of risk, economics and political science to develop four propositions concerning limits to adaptation. First, any limits to adaptation depend on the ultimate goals of adaptation underpinned by diverse values. Second, adaptation need not be limited by uncertainty around future foresight of risk. Third, social and individual factors limit adaptation action. Fourth, systematic undervaluation of loss of places and culture disguises real, experienced but subjective limits to adaptation. We conclude that these issues of values and ethics, risk, knowledge and culture construct societal limits to adaptation, but that these limits are mutable.  相似文献