北半球白垩纪-古近纪之交生物灭绝期孢粉地层学     

Antoine BERCOVICI  Vivi VAJDA  Arthur SWEET 《地层学杂志》2012,(2):165-178

长期以来,科学家们对白垩纪-古近纪(K-Pg)之交陆地上生物大灭绝事件的趋势与灭绝速率争论不断。这些争论主要集中在脊椎动物上,尤其是非鸟恐龙。尽管如此,在理解K-Pg之交的生物响应以及相关的生态系统扰动时,植被的演化也是一个重要的组成部分。本文综述北半球内白垩纪晚期至古近纪Aquilapollenites古孢粉地理大区的孢粉地层学:在美国,晚白垩世生物组合以一系列关键门类的出现为标志,其中三冬期—坎潘期过渡期以Aquilapollenites以及相关的三突起型属的出现为标志,而马斯特里赫特阶的底界以睛形型的Wodehouseia属与Kurtzipitessp.的出现为标志;Wodehouseia spinata生物组合带以较大的个体与复杂的壁构造为特征,其中一系列的被子植物孢粉单元在K-Pg之交的记录中消失了,这使得K-Pg灭绝事件容易识别;具孔类花粉和Momipites与Caryapollenites两个属的关键种的出现,标志着古近纪孢粉植物群的复苏。近期的资料涵盖了北美大陆的大部分记录,而中国、欧洲和南半球的更多研究将更有助于理解全球陆地生物圈对K-Pg之交撞击事件的响应。  相似文献   

Blocky regularization schemes for Full‐Waveform Inversion★     

Antoine Guitton 《Geophysical Prospecting》2012,60(5):870-884

With ill‐posed inverse problems such as Full‐Waveform Inversion, regularization schemes are needed to constrain the solution. Whereas many regularization schemes end up smoothing the model, an undesirable effect with FWI where high‐resolution maps are sought, blocky regularization does not: it identifies and preserves strong velocity contrasts leading to step‐like functions. These models might be needed for imaging with wave‐equation based techniques such as Reverse Time Migration or for reservoir characterization. Enforcing blockiness in the model space amounts to enforcing a sparse representation of discontinuities in the model. Sparseness can be obtained using the ?¹ norm or Cauchy function which are related to long‐tailed probability density functions. Detecting these discontinuities with vertical and horizontal gradient operators helps constraining the model in both directions. Blocky regularization can also help recovering higher wavenumbers that the data used for inversion would allow, thus helping controlling the cost of FWI. While the Cauchy function yields blockier models, both ?¹ and Cauchy attenuate illumination and inversion artifacts.  相似文献   

First Imaging of Coronal Mass Ejections in the Heliosphere Viewed from Outside the Sun – Earth Line     

Richard A. Harrison  Christopher J. Davis  Christopher J. Eyles  Danielle Bewsher  Steve R. Crothers  Jackie A. Davies  Russell A. Howard  Daniel J. Moses  Dennis G. Socker  Jeffrey S. Newmark  Jean-Philippe Halain  Jean-Marc Defise  Emmanuel Mazy  Pierre Rochus  David F. Webb  George M. Simnett 《Solar physics》2008,247(1):171-193

We show for the first time images of solar coronal mass ejections (CMEs) viewed using the Heliospheric Imager (HI) instrument aboard the NASA STEREO spacecraft. The HI instruments are wide-angle imaging systems designed to detect CMEs in the heliosphere, in particular, for the first time, observing the propagation of such events along the Sun – Earth line, that is, those directed towards Earth. At the time of writing the STEREO spacecraft are still close to the Earth and the full advantage of the HI dual-imaging has yet to be realised. However, even these early results show that despite severe technical challenges in their design and implementation, the HI instruments can successfully detect CMEs in the heliosphere, and this is an extremely important milestone for CME research. For the principal event being analysed here we demonstrate an ability to track a CME from the corona to over 40 degrees. The time – altitude history shows a constant speed of ascent over at least the first 50 solar radii and some evidence for deceleration at distances of over 20 degrees. Comparisons of associated coronagraph data and the HI images show that the basic structure of the CME remains clearly intact as it propagates from the corona into the heliosphere. Extracting the CME signal requires a consideration of the F-coronal intensity distribution, which can be identified from the HI data. Thus we present the preliminary results on this measured F-coronal intensity and compare these to the modelled F-corona of Koutchmy and Lamy (IAU Colloq. 85, 63, 1985). This analysis demonstrates that CME material some two orders of magnitude weaker than the F-corona can be detected; a specific example at 40 solar radii revealed CME intensities as low as 1.7×10⁻¹⁴ of the solar brightness. These observations herald a new era in CME research as we extend our capability for tracking, in particular, Earth-directed CMEs into the heliosphere.  相似文献   

Mud bank colonization by opportunistic mangroves: A case study from French Guiana using lidar data     

Christophe Proisy  Nicolas Gratiot  Edward J. Anthony  Antoine Gardel  François Fromard  Patrick Heuret 《Continental Shelf Research》2009

Mud bank colonization by mangroves on the Amazon-influenced coast of French Guiana was studied using light detection and ranging (lidar) data which provide unique information on canopy geometry an sub-canopy topography. The role of topography was assessed through analysis of vegetation characteristics derived from these data. Measurements and analyses of mangrove expansion rates over space and time led to the identification of two distinct colonization processes. The first involves regular step-by-step mangrove expansion to the northwest of the experimental site. The second is qualified as ‘opportunistic’ since it involves a clear relationship between specific ecological characteristics of pioneer Avicennia and mud cracks affecting the mud bank surface and for which probabilities of occurrence were computed from terrain elevations. It is argued from an original analysis of the latter relationship that mud cracks cannot be solely viewed as water stress features that reflect desiccation potentially harmful to plant growth. Indeed, our results tend to demonstrate that they significantly enhance the propensity for mangroves to anchor and take root, thus leading to the colonization of tens of hectares in a few days. The limits and potential of lidar data are discussed with reference to the study of muddy coasts. Finally, the findings of the study are reconsidered within the context of a better understanding of both topography and vegetation characteristics on mangrove-fringed muddy coasts.  相似文献   

Late Permian to Middle Triassic correlations and palaeogeographical reconstructions in south-western European basins: New sedimentological data from Minorca (Balearic Islands, Spain)     

Bastien Linol  Antoine Bercovici  Sylvie Bourquin  Jos Bienvenido Diez  Jos Lpez-Gmez  Jean Broutin  Marc Durand  Uxue Villanueva-Amadoz 《Sedimentary Geology》2009,220(1-2):77-94

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Clinker formation in basaltic and trachybasaltic lava flows     

Sébastien Loock  Benjamin van Wyk de Vries  Jean-Marc Hénot 《Bulletin of Volcanology》2010,72(7):859-870

Clinker is a term used to describe massive or scoriaceous fragments commonly associated with ‘a‘ā lava flows. Clinker is generally considered to form by fragmentation of an upper vesiculated crust, due to an increase in apparent viscosity and/or to an increase in shear strain rate. Surface clinker is considered to be transported to the flow front and incorporated at the base by caterpillar motion. Clinker that we have observed on a variety of lava flows has very variable textures, which suggests several different mechanisms of formation. In order to study clinker formation, we examined several lava flows from the Chaîne des Puys Central France, where good sections, surface morphology and surface textures are widespread and clearly visible. We observed basal and surface ‘a‘ā clinker that has fragmentation textures similar to those observed in ash formed in eruptions under dry conditions. In two pāhoehoe flows we have observed basal clinker that formed in-situ. Two other flows display clinker features identical to those commonly observed in phreatomagmatic ash, such as adhering particles, blocky shapes, spherical glass and attached microphenocrysts. Another pāhoehoe flow has a flakey, angular basal breccia, with microfaulted and abraded clasts. These were probably formed at a cooled lava base by large amounts of simple shear and consequent intra-lava brittle faulting. Using these observations we propose three different ways of fragmentation. (1) Clinker can form at the surface and eventually produce roll-over basal breccia. (2) Water/lava interactions can form basal clinker by phreatomagmatic fragmentation. Water/lava ratio variations may produce different clinker structures, in a manner similar to observed textural changes in phreatomagmatic eruptions. (3) Clinker can be formed by brittle brecciation during basal simple shear. The different clinker can provide information about the mechanisms and environmental conditions during lava flow emplacement.  相似文献   

Ricker‐compliant deconvolution          下载免费PDF全文

Jon Claerbout  Antoine Guitton 《Geophysical Prospecting》2015,63(3):615-625

Ricker‐compliant deconvolution spikes at the center lobe of the Ricker wavelet. It enables deconvolution to preserve and enhance seismogram polarities. Expressing the phase spectrum as a function of lag, it works by suppressing the phase at small lags. A by‐product of this decon is a pseudo‐unitary (very clean) debubble filter where bubbles are lifted off the data while onset waveforms (usually Ricker) are untouched.  相似文献   

Multiple-point geostatistical simulation using enriched pattern databases     

Rezaee  Hassan  Marcotte  Denis  Tahmasebi  Pejman  Saucier  Antoine 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(3):893-913

Stochastic Environmental Research and Risk Assessment - This study presents a new approach of generating a set of alternative training images (ATI) to use in patch-based multiple-point simulation....  相似文献   

Experimental determination of synthetic NdPO₄ monazite end-member solubility in water from 21°C to 300°C: implications for rare earth element mobility in crustal fluids     

Franck Poitrasson  Eric Oelkers  Jean-Marc Montel 《Geochimica et cosmochimica acta》2004,68(10):2207-2221

The solubility of synthetic NdPO₄ monazite end-member has been determined experimentally from 21 to 300°C in aqueous solutions at pH = 2, and at 21°C and pH = 2 for GdPO₄. Measurements were performed in batch reactors, with regular solution sampling for pH measurement, rare earths and phosphorous analysis by inductively coupled plasma mass spectrometry (ICP-MS) coupled with a desolvation system. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to check that no reprecipitation of secondary phases occurred and that the mineral surfaces remained those of a monazite. Coupled with speciation calculations, measured solution compositions permitted the determination of NdPO₄ and GdPO₄ solubility products which are in general agreement with previous experimental determination on rhabdophane at 25°C, but showing that monazite is more than two orders of magnitude less soluble than inferred on the basis of previous thermodynamic estimates. The temperature evolution from 21 to 300°C of the equilibrium constant (K) of the NdPO₄ monazite end-member dissolution reaction given by: