Numerical experiments on the generation of long ocean waves in coastal waters of the Buenos Aires province,Argentina

A numerical model (two horizontal dimensions, vertically integrated) is used to investigate the generation of long ocean waves, ranging from 20 min to almost 2 h, at Buenos Aires continental shelf. The domain includes the Río de la Plata estuary and the continental shelf together and extends from 33.5° to 40.5°S latitude, and from 51° to 63°W longitude. Sea-level oscillations are modeled by forcing with passage of atmospheric cold fronts and atmospheric gravity waves. Both forcing mechanisms, which have been present during high activity lapses of long ocean waves, are mathematically implemented. After several numerical simulations, it is concluded that the pressure and wind fields associated to cold fronts do not generate long ocean waves in the area, though they do produce disturbances with periods longer than the tidal ones. On the other hand, it is so concluded that atmospheric gravity waves are an effective mechanism to force long ocean waves. Results obtained show that generation of long ocean waves is highly sensitive depending on the propagation direction and the phase speed of the atmospheric gravity waves. The long ocean wave event detected during the large-amplitude gravity-wave event of 13 October 1985 is successfully simulated. Finally, all our results suggest that atmospheric gravity waves are a highly effective mechanism forcing for the generation of long ocean waves in Buenos Aires coastal waters.     

Unstructured,anisotropic mesh generation for the Northwestern European continental shelf,the continental slope and the neighbouring ocean

A new mesh refinement strategy for generating high quality unstructured meshes of the Northwestern European continental shelf, the continental slope and the neighbouring ocean is presented. Our objective is to demonstrate the ability of anisotropic unstructured meshes to adequately address the challenge of simulating the hydrodynamics occurring in these three regions within a unique mesh. The refinement criteria blend several hydrodynamic considerations as the tidal wave propagation on the continental shelf and the hydrostatic consistency condition in steep areas. Several meshes illustrate both the validity and the efficiency of the refinement strategy. The selection of the refinement parameters is discussed. Finally, an attempt is made to take into account tidal ellipses, providing another cause for anisotropy in the mesh.     

基于数码相机立体像对的物体3维信息快速获取方法

研究了数码相机的内方位元素检测和镜头畸变差校正，应用近景摄影测量的原理与方法，提出了一种基于立体像对无物方控制的物体表面3维模型信息快速获取方法，试验表明，该方法获取3维信息速度快、精度较高。同时文中还比较了可变焦数码相机和固定焦距相机在获取3维信息精度方面的差异。     

Modelling the Quaternary evolution of shore platforms and erosional continental shelves

A mathematical model was used to investigate the effect of glacially induced fluctuations in sea level on the evolution of wave‐cut shore platforms and erosional continental shelves during the Quaternary. The model used two deep‐water wave sets, which were used to calculate breaker height and depth, and the force of the waves at the waterline, according to the width and bottom roughness of the surf zone and the gradient of the submarine slope. The model also incorporated an erosional threshold related to the strength of the rocks, the number of hours each year in which the water level is at each intertidal elevation and the amount and persistence of the debris at the cliff foot. Most runs were made using a sea level model that consisted of 26 glacial cycles from 2 million to 0·9 million years ago, and nine, of approximately twice the amplitude and wavelength, in the last 0·9 million years. The model emphasized the dynamic association between the contemporary intertidal platform and the continental shelf. Both surfaces trend towards a state of static equilibrium under oscillating sea level conditions, when attenuated waves are unable to continue eroding the rock. If there has not been enough time to reduce the gradient of the shallower portions of the continental shelf, however, intertidal shore platforms can be in a temporary, though possibly long‐lasting, state of dynamic equilibrium. The model suggests that most platforms are, at least in part, inherited from one, or in many cases more, interglacial stages when sea level was similar to today's. Copyright © 2001 John Wiley & Sons, Ltd.     

Lower Pleistocene deltaic and marine sediments in boreholes from the central North Sea

Lower Pleistocene sediments recovered in boreholes from the Aberdeen Ground Formation in the central North Sea indicate that the unit was deposited in a delta front to prodelta/shallow, open shelf marine setting. Possible estuarine and clastic nearshore marine deposits have been identified on the western margin of the basin. The delta front sediments consist of interbedded, structureless to laminated sands and muds with organic debris, ferruginous nodules and common soft sediment deformation structures. Sporadic rippled and graded beds, basal scours to beds and starved ripples suggest periodic wave–current reworking. Prodelta/shelf marine sediments are predominantly argillaceous with only occasional thin sand beds and rare phosphatic bands. One exceptionally thick sand body or submarine channel-fill although this remains uncertain. The estuarine/clastic nearshore marine sediments include coarse channel-lag deposits and rippled and laminated subtidal sands. A rich microfossil assemblage recovered from the prodelta/shelf marine sequence indicates that deposition occurred under fluctuating climatic conditions.     

阿尔金山中段清水泉-茫崖蛇绿构造混杂岩带地质特征

清水泉—茫崖蛇绿构造混杂岩带沿阿尔金山南坡分布,呈醒目的“绿色岩带”,其主要由蛇绿岩、蛇绿岩上覆岩系和元古代外来岩片或岩块组成,现多为构造透镜体,蛇绿岩上覆岩系具远洋深海沉积特征;岩石地球化学资料研究证明,蛇绿岩中的玄武岩与洋内岛弧拉斑玄武岩相似;同位素测年结果显示蛇绿岩形成于早古生代,蛇绿岩源自亏损的软流圈地幔,同时有富集地幔物质加入,暗示早古生代研究区曾出现过小洋盆构造环境。     

Surface Ice Flow Velocity and Tide Retrieval of the Amery Ice Shelf using Precise Point Positioning

Five days of continuous GPS observation data were collected in the frontal zone of the Amery ice shelf and subsequently post-processed using precise point position (PPP) technology based on precise orbit and clock products from the International GNSS service. The surface ice flow velocity of the observed point was derived from PPP to be 2.25 m/day toward the northeast with an azimuth of 41°. Major semi-diurnal and diurnal oceanic tide constituents could be recovered from the 5 days of PPP-derived height variations and compared well with a hydrodynamic ocean tide model. The PPP technique can replace double-difference GPS positioning in remote or hostile environments, and be used to retrieve the surface ice flow velocity without any reference station. Furthermore, the solution can be derived epoch-by-epoch with accuracy in the centimeters to decimeter range.     

Paleoceanographic evolution of the SW Svalbard margin (76°N) since 20,000 C yr BP

Two cores from the southwestern shelf and slope of Storfjorden, Svalbard, taken at 389 m and 1485 m water depth have been analyzed for benthic and planktic foraminifera, oxygen isotopes, and ice-rafted debris. The results show that over the last 20,000 yr, Atlantic water has been continuously present on the southwestern Svalbard shelf. However, from 15,000 to 10,000 ¹⁴C yr BP, comprising the Heinrich event H1 interval, the Bølling-Allerød interstades and the Younger Dryas stade, it flowed as a subsurface water mass below a layer of polar surface water. In the benthic environment, the shift to interglacial conditions occurred at 10,000 ¹⁴C yr BP. Due to the presence of a thin upper layer of polar water, surface conditions remained cold until ca. 9000 ¹⁴C yr BP, when the warm Atlantic water finally appeared at the surface. Neither extensive sea ice cover nor large inputs of meltwater stopped the inflow of Atlantic water. Its warm core was merely submerged below the cold polar surface water.     

广西桂林庙头上泥盆统融县组中的灰岩脉和角砾灰岩体及其成因

广西桂林庙头上泥盆统融县组台地边缘相具鸟眼或溶孔砂屑生屑藻粘结灰岩中发育了大量灰岩脉，灰岩脉呈岩墙状近直立地切过围岩，露头上可见连续垂直延伸长度达十余米，脉内仍是上泥盆统融县组灰岩组分，仅比围岩稍晚或同时代的：角砾状退白云石化藻粘结灰岩、角砾状藻粘结灰岩（快速堆积，角砾多数来自围岩）、细鲕粒颗粒灰岩、含钙球砂屑粒泥灰岩、藻砂屑腹足泥粒灰岩（正常沉积或液化变形软沉积流，均高于围岩层位）及大量栉壳状方解石脉（张性环境）等，灰岩脉内可见软沉积物变形痕迹及液化脉（地震液化），晚期灰岩脉可穿插早期灰岩脉；在其西侧同层位共生有一套楔状（地裂缝）、不规则状角砾灰岩体，角砾棱角状，大小不等，成分是灰色中厚层角砾状藻粘结灰岩、含钙球砂屑粒泥灰岩等。笔者等注意到灰岩脉均出露在北东向正断层的下盘（东侧），而角砾灰岩体则均出露在该断层的上盘（西侧），事实上，灰岩脉及角砾灰岩体分布走向与北东向断层走向一致，角砾灰岩体中的角砾成分显示其来自较灰岩脉围岩稍高层位，与灰岩脉内充填岩性相近，因此，是该断层控制了当时的沉积，此断层是晚泥盆世台地边缘同沉积正断层；灰岩脉是与断层伴生的张性裂隙被围岩角砾或稍晚时段的沉积物充填；角砾灰岩体是同沉积正断层形成的断层崖崩落角砾岩，指示一个消失殆尽的晚泥盆世碳酸盐岩同沉积正断层陡崖，因而，桂林台地，至少西段台地边缘，是与右江各孤立台地边缘一样——在地质图上应标示为同沉积正断层边界。其构造意义是：庙头地区的灰岩脉、角砾灰岩体及同沉积断层是桂林台地对晚泥盆世构造伸展作用的响应，从而说明广西晚古生代的板块拉张，不是从二叠纪才开始的，而是至少从晚泥盆世就开始了；晚古生代至早三叠世持续的孤立台地与深水盆地相间的古地理格局，是在晚泥盆世就奠定了基础。     

Tidally dominated, rimmed-shelf facies of the Picún Leufú Formation (Jurassic/Cretaceous boundary) in southwest Gondwana, Neuquén Basin, Argentina

A palaeoenvironmental model for the Picún Leufú Formation (Jurassic/Cretaceous boundary), which crops out in the Neuquén Basin, Argentina, on the southwestern margin of Gondwana, is presented in this paper for the first time. Detailed stratigraphic sections exposed along National Road 40 where it crosses the Picún Leufú Creek (type locality) and in the Cerrito Caracoles area, were examined and sampled. Based on a combination of the sedimentological data obtained (facies/microfacies analysis) and the relationship between benthic macrofaunas and their taphonomic attributes, it is concluded that the formation reflects a tidally dominated, rimmed-shelf setting characterized by prograding bars dissected by channels and thick lagoonal facies with shoal developments. In the Cerrito Caracoles area, where only the basal part of the formation is exposed, it is interpreted to have been deposited in a shallow subtidal marine environment in which shelf margin facies with patch reefs have been recognized.