Are catch-up reefs an artefact of coring?     

Paul Blanchon  David Blakeway† 《Sedimentology》2003,50(6):1271-1282

Drill cores through modern coral reefs commonly show a time lag in reef initiation followed by a phase of rapid accretion to sea level from submerged foundations – the so-called ‘catch-up response’. But because of the difficulty of drilling in these environments, core distribution is usually restricted to accessible areas that may not fully represent reef history, especially if the reef initiated in patches or developed with a prograde or retrograde geometry. As a consequence, core data have the potential to give a misleading impression of reef development, particularly with respect to the timing of initiation and response to sea-level rise. Here, we use computer models to simulate keep-up reef development and, from them, quantify variations in the timing of reef initiation and accretion rate using mock cores taken through the completed simulations. The results demonstrate that cores consistently underestimate the timing of reef initiation and overestimate the reef accretion rate so that, statistically, a core through a keep-up reef will most likely produce a catch-up pattern – an initiation lag followed by a phase of rapid accretion to sea level. This implies that catch-up signatures may be an artefact of coring and that keep-up reefs are significantly more common than previous core studies claim.  相似文献   

Famennian microbial reef facies, Napier and Oscar Ranges, Canning Basin, western Australia   总被引：5，自引：0，他引：5  

Nat P. Stephens  Dawn Y. Sumner 《Sedimentology》2003,50(6):1283-1302

Following the Frasnian–Famennian mass extinction, which eliminated most skeletal reef-building fauna, the early Famennian reefs of the Canning Basin were constructed primarily by reef-framework microbial communities. In the Napier and Oscar Ranges, the Famennian reef complexes had high-energy, reef-flat depositional environments on a reef-rimmed platform that transitioned into low-energy, deep-water reefs growing in excess of 50 m below sea level. High-energy, reef-flat depositional environments contain doming fenestral stromatolites that grade into porous thrombolites and are associated with coarse-grained sandstones and grainstones. The reef-margin subfacies contains mounds of microdigitate thrombolites, which are more delicate than the reef-flat thrombolites and locally contain abundant red algae, Girvanella, renalcids and sediment-filled tubes. Within the thrombolites, the red algae are in upright growth positions, suggesting that the thrombolites are largely composed of carbonate that precipitated in situ. Reefal-slope environments are dominated by Wetheredella and Rothpletzella with locally abundant Girvanella, renalcids and Uralinella. In reefal-slope strata, delicate fans and microdigitate stromatolites of Wetheredella and Rothpletzella are often oriented horizontal or diagonal to bedding and are interpreted as syndepositionally toppled over. Most mesoscale microbial community structures contain several species of microbial fossils, and no single microbial species appears to have controlled the morphology of the community structure. Therefore, the depositional environment must have determined the distribution and morphology of the stromatolites, thrombolites and other microbial community structures. The adaptability of microbial communities to various reef environments allowed them to fill ecological niches opportunistically after the Frasnian–Famennian mass extinction.  相似文献   

土钉支护结构的优化设计   总被引：1，自引：1，他引：1  

邓建刚  傅旭东 《岩土力学》2003,(Z2)

根据复形优化原理,提出了基于Bishop法的土钉支护结构的优化分析方法,编写了优化分析程序。工程实例计算表明,该方法是进行土钉优化设计的有效方法。  相似文献   

A comparison of three image-object methods for the multiscale analysis of landscape structure   总被引：4，自引：0，他引：4  

Geoffrey J. Hay  Thomas Blaschke  Danielle J. Marceau  Andr Bouchard 《ISPRS Journal of Photogrammetry and Remote Sensing》2003,57(5-6):327

Within the conceptual framework of Complex Systems, we discuss the importance and challenges in extracting and linking multiscale objects from high-resolution remote sensing imagery to improve the monitoring, modeling and management of complex landscapes. In particular, we emphasize that remote sensing data are a particular case of the modifiable areal unit problem (MAUP) and describe how image-objects provide a way to reduce this problem. We then hypothesize that multiscale analysis should be guided by the intrinsic scale of the dominant landscape objects composing a scene and describe three different multiscale image-processing techniques with the potential to achieve this. Each of these techniques, i.e., Fractal Net Evolution Approach (FNEA), Linear Scale-Space and Blob-Feature Detection (SS), and Multiscale Object-Specific Analysis (MOSA), facilitates the multiscale pattern analysis, exploration and hierarchical linking of image-objects based on methods that derive spatially explicit multiscale contextual information from a single resolution of remote sensing imagery. We then outline the weaknesses and strengths of each technique and provide strategies for their improvement.  相似文献   

地震波研究://car          下载免费PDF全文

张海明  陈晓非 《地震学报》2003,25(5):465-474

回顾了近4年来中国地球物理学家在地震波研究方面取得的主要进展. 分别简要地讨论了层状均匀介质、横向不均匀介质和多孔介质中的地震波传播，地震面波及波形反演，以及地震勘探、测井问题中的地震波研究方面取得的新成果. 指出当前地震波研究的重要课题是发展高效的数值方法，并利用该方法开展复杂介质中的地震波激发和传播，以及强地面运动的研究，为精细的地震危险分析与预测奠定基础.   相似文献   

MTMD对建筑结构多模态控制的减震分析   总被引：5，自引：1，他引：5  

涂文戈  邹银生 《地震工程与工程振动》2003,23(5):174-179

本文研究了MTMD对建筑结构多模态减震控制。将主结构简化为多自由度模型，MTMD对结构的反力与地震荷载共同作为结构的荷载输入进行分析；基于主结构多模态耦合进行推导分析，阐述了MTMD与结构之间的相互作用关系，提出MTMD的复惯性质量。提出MTMD的控制类型是加速度相关型的无源被动控制。从频域传递函数，白噪声、宽带和窄带地震激励下的结构相对位移和绝对加速度谱密度，以及El-centro地震波作用下结构的地震响应三个方面，分析了MTMD对顶部带有结构附属物的结构的控制效果。并且给出TMD的控制效果加以比较验证。算例说明MTMD多模态控制对结构的相对位移和绝对加速度均有较好的控制效果，并且优于TMD控制效果。  相似文献   

In-situ Formation of Light-Absorbing Organic Matter in Cloud Water   总被引：1，自引：0，他引：1  

A. Gelencsér  A. Hoffer  G. Kiss  E. Tombácz  R. Kurdi  L. Bencze 《Journal of Atmospheric Chemistry》2003,45(1):25-33

Current climate models seem to underestimate the flux of solar energy absorbed by the global troposphere. All of these models are constrained with the assumption that cloud droplets consist of pure water. Here we demonstrate in a simple laboratory experiment that aromatic hydroxy-acids which are found in continental fine aerosol can react with hydroxyl radicals under typical conditions prevalent in cloud water influenced by biomass burning. The reactions yield colored organic species which do absorb solar radiation. We also suggest that the products of such reactions may be humic-like substances whose presence in continental aerosol has been confirmed but their source mechanisms are still much sought after. We also attempt to give a first order estimate of the enhancement of water absorption at a visible wavelength under atmospheric conditions.  相似文献   

深圳海岸复杂地形气流与湍流特征的数值模拟     

王卫国  蒋维楣 《气象科学》1997,17(3):274-279

利用三维非静力能量闭合（Ｅ－ε）的边界层模式，以深圳海岸复杂地形进行了实际模拟。结果给出了该地区海陆风情形下气流和湍流孤变化特征。在海风发展盛期，气流方向由大面积的水域和内陆的位置决定，不规则海岸线对局地气流影响不大，夜间陆风时，不规则海岸线对局地气流影响较大，湍流能量高值颁在陆地上空的不稳定层内，水面上湍能很小。模拟结果与实测结果上比较吻合。  相似文献   

四川林农复合经营持续发展对策探讨     

向成华  潘攀 《山地学报》1997,(1)

分析了四川林农复合经营的主要类型、效益与障碍，并探讨了其持续发展的原则、有利条件与对策．  相似文献   

台湾恒春半岛的隆起珊瑚礁台地          下载免费PDF全文

王鑫 《第四纪研究》1997,17(4):327-332

台湾本岛南端的恒春半岛,出露隆起珊瑚礁石灰岩和现代珊瑚礁海岸。隆起珊瑚礁石灰岩在地貌上的表现是多阶的台地。最高的公园面可达海拔300m,依次向下,是海拔约100～160m的笼仔埔面,海拔70～80m的埔顶面以及海拔10～20m的垦丁面。在恒春半岛的西侧,珊瑚礁台地面已经倾斜,因此高度的表现不同。ESR及¹⁴C定年表明,抬升的更新世珊瑚礁台地形成于0.5Ma B.P.前后及0.13Ma B.P.两时期;海拔10～20m的全新世珊瑚礁台地约形成于6 000a B.P.的时期。这些证据显示了地质时期里全球变迁的蛛丝马迹。  相似文献