Fossils explained 18: Starfishes     

DANIEL B. BLAKE 《Geology Today》1996,12(6):230-240

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Kinetics of the Coesite-Quartz Transition: Application to the Exhumation of Ultrahigh-Pressure Rocks   总被引：3，自引：0，他引：3  

PERRILLAT  J. P.; DANIEL  I.; LARDEAUX  J. M.; CARDON  H. 《Journal of Petrology》2003,44(4):773-788

The kinetics of the quartz–coesite phase transition hasbeen studied in situ by X-ray diffraction in the 2·1–3·2GPa, 500–1010°C pressure–temperature range.Analysis of the data within Cahn's model of nucleation and growthat grain boundaries reveals that the prograde and retrogradereactions have different kinetics. The quartz  相似文献   

赞比亚班韦乌卢变质克拉通东北部姆巴拉组碎屑锆石U-Pb年龄和Hf同位素特征          下载免费PDF全文

任军平  古阿雷  王杰  孙宏伟  左立波  孙凯  许康康  CHIPILAUKA Mukofu  EVARISTO Kasumb  DANIEL Malung  杜明龙  邢仕  刘子江  张津瑞  董津蒙 《沉积与特提斯地质》2022,42(4):585-597

班韦乌卢变质克拉通活动时间和地壳增长问题一直是地质学家关注的焦点。本文通过对班韦乌卢地块中卡帕图地区姆波罗科索群姆巴拉组石英砂岩进行了碎屑锆石U-Pb年代学和Hf同位素研究,结合变质克拉通已有成果获得认识如下：(1)姆巴拉组的形成时间可能介于(1833±22 Ma)～(1712±22 Ma)之间,属于古元古代。(2)姆巴拉组具有丰富的物质来源,其中2728～2602 Ma(峰值为2650 Ma)的物质可能来源于坦桑尼亚克拉通中的花岗岩类、粗面安山岩及流纹岩等岩石。2246～1833 Ma(峰值为1880 Ma)的物质主要来源于班韦乌卢地块中花岗岩类、石英闪长岩及火山岩类等岩石。(3)班韦乌卢变质克拉通的活动时间包括中太古代、新太古代、古元古代和中元古代四个时期,其中古元古代(1870 Ma)为活动的高峰期,涉及范围广泛,可能与哥伦比亚超大陆的演化密切相关。(4)班韦乌卢变质克拉通沉积岩的源区地壳增生除来自古老地壳的再循环物质外,还存在新生地壳的物质。同时,地壳在古太古代-古元古代均实现了增长,其中凯诺兰超大陆聚合时期(2550 Ma)增长最快。在古元古代之前的地壳主增长期与坦桑尼亚克拉通及全球大陆地壳主增长期基本一致。  相似文献   

The relationship between ¹⁸O/¹⁶O and ¹³C/¹²C ratios of ambient CO₂ in two Amazonian tropical forests     

LEONEL DA S. L. STERNBERG  MARCELO Z. MOREIRA  LUIZ A. MARTINELLI  REYNALDO L. VICTORIA  EDELCILIO M. BARBOSA  LUIZ C. M. BONATES  DANIEL NEPSTAD 《Tellus. Series B, Chemical and physical meteorology》1998,50(4):366-376

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The lithostratigraphy of the Les Echets basin, France: tentative correlation between cores     

DANIEL VERES  BARBARA WOHLFARTH  VALÉRIE ANDRIEU-PONEL  SVANTE BJÖRCK  JACQUES-LOUIS DE  BEAULIEU  GUNNAR DIGERFELDT  PHILIPPE PONEL  LINDA AMPEL  SIWAN DAVIES  EMMANUEL GANDOUIN  SOUMAYA BELMECHERI 《Boreas: An International Journal of Quaternary Research》2007,36(3):326-340

Two new long sediment cores (EC1 and EC3), recovered from different locations within the infilled basin at Les Echets, France, provide a new high-resolution record of terrestrial and lacustrine responses to climatic changes during Marine Isotope Stages (MIS) 3 and 2. The lithologies of the cores are described in detail and correlated with each other by stratigraphic marker horizons, fluctuations in organic matter and AMS radiocarbon ages. The tentative correlation of the new cores to those described and analysed by de Beaulieu et al. (1980) and de Beaulieu & Reille (1984a) provides a preliminary chronostratigraphic framework. Sedimentation during MIS3 started with accumulation of sands and silts and was followed by alternating gyttja and clayey gyttja silts. Exceptionally high sedimentation rates during MIS2 led to the infilling of the basin. Alternating organic-rich and minerogenic-rich sediments appear to coincide with changes in pollen assemblages (de Beaulieu & Reille 1984a) and suggest that millennial-scale climatic changes controlled lake productivity and catchment stability during most of MIS3.  相似文献   

Sensitivity analysis of the climate of a chaotic system     

DANIEL J. LEA  MYLES R. ALLEN  THOMAS W. N. HAINE 《地球，A辑:动力气象学与海洋学》2000,52(5):523-532

This paper addresses some fundamental methodological issues concerning the sensitivity analysis of chaotic geophysical systems. We show, using the Lorenz system as an example, that a naïve approach to variational ("adjoint") sensitivity analysis is of limited utility. Applied to trajectories which are long relative to the predictability time scales of the system, cumulative error growth means that adjoint results diverge exponentially from the "macroscopic climate sensitivity"(that is, the sensitivity of time‐averaged properties of the system to finite‐amplitude perturbations). This problem occurs even for time‐averaged quantities and given infinite computing resources. Alternatively, applied to very short trajectories, the adjoint provides an incorrect estimate of the sensitivity, even if averaged over large numbers of initial conditions, because a finite time scale is required for the model climate to respond fully to certain perturbations. In the Lorenz (1963) system, an intermediate time scale is found on which an ensemble of adjoint gradients can give a reasonably accurate (O(10%)) estimate of the macroscopic climate sensitivity. While this ensemble‐adjoint approach is unlikely to be reliable for more complex systems, it may provide useful guidance in identifying important parameter‐combinations to be explored further through direct finite‐amplitude perturbations.  相似文献   

Origin of stratified basal ice in outlet glaciers of Vatnajökull and Öræfajökull,Iceland     

GRAHAME J. LARSON  DANIEL E. LAWSON  EDWARD B. EVENSON  ÓSKAR KNUDSEN  RICHARD B. ALLEY  MANTHA S. PHANIKUMAR 《Boreas: An International Journal of Quaternary Research》2010,39(3):457-470

Larson, G.J., Lawson, D.E., Evenson, E.B., Knudsen, Ó., Alley, R.B. & Phanikumar, M.S. 2010: Origin of stratified basal ice in outlet glaciers of Vatnajökull and Öræfajökull, Iceland. Boreas, Vol. 39, pp. 457–470. 10.1111/j.1502‐3885.2009.00134.x. ISSN 0300‐9483. During the period 2000–2005, we collected samples of englacial ice, vent water, frazil/anchor ice and stratified basal ice from warm‐based outlet glaciers of Vatnajökull and Öræfajökull, Iceland, and analysed them for ³H, ¹⁸O and D. Results of ³H analyses show that the stratified basal ice contains ³H from atmospheric thermonuclear testing and is younger than the englacial ice. Results of the ¹⁸O and D analyses show that frazil/anchor and stratified basal ice are both enriched by an average of 2.4‰ in ¹⁸O and 11‰ in D relative to vent water. These values are consistent with fractionation during partial freezing of supercooled subglacial water in an open system, one in which the remaining water is continuously removed and replenished by water of similar composition. The isotopic data and field observations do not support either a regelation or a thermal ad‐freeze‐on origin for the stratified basal ice.  相似文献   

Ensemble covariances adaptively localized with ECO-RAP. Part 2: a strategy for the atmosphere     

CRAIG H. BISHOP  DANIEL HODYSS 《地球，A辑:动力气象学与海洋学》2009,61(1):97-111

Part 1's localization method, Ensemble COrrelations Raised to A Power (ECO-RAP), is incorporated into a Local Ensemble Transform Kalman Filter (LETKF). Because brute force incorporation would be too expensive, we demonstrate a factorization property for Part 1's Covariances Adaptively Localized with ECO-rap (CALECO) forecast error covariance matrix that, together with other simplifications, reduces the cost. The property inexpensively provides a large CALECO ensemble whose covariance is the CALECO matrix. Each member of the CALECO ensemble is an element-wise product between one raw ensemble member and one column of the square root of the ECO-RAP matrix. The LETKF is applied to the CALECO ensemble rather than the raw ensemble. The approach enables the update of large numbers of variables within each observation volume at little additional computational cost. Under plausible assumptions, this makes the CALECO and standard LETKF costs similar. The CALECO LETKF does not require artificial observation error inflation or vertically confined observation volumes both of which confound the assimilation of non-local observations such as satellite observations. Using a 27 member ensemble from a global Numerical Weather Prediction (NWP) system, we depict four-dimensional (4-D) flow-adaptive error covariance localization and test the ability of the CALECO LETKF to reduce analysis error.  相似文献   

Constructing knowledge from multivariate spatiotemporal data: integrating geographical visualization with knowledge discovery in database methods     

ALAN M. MACEACHREN  MONICA WACHOWICZ  ROBERT EDSALL  DANIEL HAUG  RAYMON MASTERS 《International journal of geographical information science》2013,27(4):311-334

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强对流过程对大尺度模式洋面通量加强的参数化研究与进展   总被引：1，自引：0，他引：1  

张强  ZENG Xu-bin  ROBERT E. Dickinson  DANIEL E. Johnson  TAO Wei-kuo 《海洋学报》2001,23(3):133-141

由于地球表面热通量直接决定着大气环流运动,在大气数值模式中如何准确描述地球表面热通量就变处得十分重要.洋面是地球表面最广泛分布的下垫面,它的表面热通量描述尤为被重视.尤其是西赤道太平洋暖池、东赤道太平洋冷舌、ITCZ及信风带等关键区域的洋面热通量的准确估计更是非常重要,这些区域的地表通量变化通常被认为是全球气候变化即ENSO现象的最重要的信号[1].众所周知,中尺度降水对流在以上关键海域频繁发生.中尺度降水对流系统往往有较强的下沉气流(downdraft)[2],这种下沉气流在中尺度降水对流系统与大尺度过程的相互作用中伴演着重要角色.  相似文献