大堡礁海洋公园与澳大利亚海洋保护区建设     

梅宏 《湿地科学与管理》2012,(4):29-31

为保护大堡礁独特的生态系统,澳大利亚制定多部法案,启动"大堡礁滨海湿地保护项目"。健全的多功能分区保护制度、可操作性较强的环境管理费征收制度和独具特色的船舶管理措施,已成为大堡礁海洋公园管理中的亮点。2012年6月,澳大利亚联邦政府宣布计划建成全球最大的海洋保护区,这是进一步加强大堡礁海洋公园管理的机遇。  相似文献   

The hydrodynamic and sedimentary setting of nearshore coral reefs, central Great Barrier Reef shelf, Australia: Paluma Shoals, a case study   总被引：4，自引：0，他引：4  

Piers Larcombe  rew Costen  & Ken J. Woolfe 《Sedimentology》2001,48(4):811-835

The Great Barrier Reef (GBR) shelf contains a range of coral reefs on the highly turbid shallow inner shelf, where interaction occurs with terrigenous sediments. The modern hydrodynamic and sedimentation regimes at Paluma Shoals, a shore‐attached ‘turbid‐zone’ coral reef, and at Phillips Reef, a fringing reef located 20 km offshore, have been studied to document the mechanisms controlling turbidity. At each reef, waves, currents and near‐bed turbidity were measured for a period of ≈1 month. Bed sediments were sampled at 135 sites. On the inner shelf, muddy sands are widespread, with admixed terrigenous and carbonate gravel components close to the reefs and islands, except on their relatively sheltered SW side, where sandy silty clays occur. At Paluma Shoals, the coral assemblage is characteristic of inner‐shelf or sheltered habitats on the GBR shelf (dominated by Galaxea fascicularis, up to >50% coral cover) and is broadly similar to that at Phillips Reef, further offshore and in deeper water. The sediments of the Paluma Shoals reef flats consist of mixed terrigenous and calcareous gravels and sands, with intermixed silts and clays, whereas the reef slope is dominated by gravelly quartz sands. The main turbidity‐generating process is wave‐driven resuspension, and turbidity ranges up to 175 nephelometric turbidity units (NTU). In contrast, at Phillips Reef, turbidity is <15 NTU and varies little. At Paluma Shoals, turbidity of >40 NTU probably occurs for a total of >40 days each year, and relatively little time is spent at intermediate turbidities (15–50 NTU). The extended time spent at either low or high turbidities is consistent with the biological response of some species of corals to adopt two alternative mechanisms of functioning (autotrophy and heterotrophy) in response to different levels of turbidity. Sedimentation rates over periods of hours may reach the equivalent of 10 000 times the mean global background terrigenous flux (BTF) of sediment to the sea floor, i.e. 10 000 BTF, over three orders of magnitude greater than the Holocene average for Halifax Bay of <3 BTF. As elsewhere along the nearshore zone of the central GBR, dry‐season hydrodynamic conditions form a primary control upon turbidity and the distribution of bed sediments. The location of modern nearshore coral reefs is controlled by the presence of suitable substrates, which in Halifax Bay are Pleistocene and early Holocene coarse‐grained (and relatively stable) alluvial deposits.  相似文献   

对1216年雷波马湖地震震中位置的质疑   总被引：2，自引：0，他引：2  

梁小华  李文纲  杨建宏  蒋溥 《中国地震》2002,18(4):382-388

本文从地震地方志史料，马湖堰塞湖现场考察，马湖地区地震地质环境以及已有的研究成果出发，在目前普遍使用的1216年四川雷波马湖地震震中位置提出了质疑。  相似文献   

Shelf-edge deltas and drowned barrier–island complexes on the northwest Florida outer continental shelf     

J.V. Gardner  P. Dartnell  L.A. Mayer  J.E. Hughes Clarke  B.R. Calder  G. Duffy   《Geomorphology》2005,64(3-4):133-166

A high-resolution multibeam survey of the northwest Florida shelf mapped six relict shelf-edge deltas, each with a drowned barrier–island system developed on its south and southwestern rims. The deltas appear to have formed during periods of sea-level stasis that occurred between 58,000 and 28,000 years ago. The barrier islands formed on the deltas during periods of slow regression during this same time interval. Large fields of asymmetric dunes are found on the delta surfaces as well as on the south and southwestern flanks of the deltas. The asymmetry and orientation of the dunes suggest that a northward-flowing current was sheared by the presence of the delta topography, and as a result, the upper layer of the flow continued to the north, whereas the lower layer was steered by the topography. The topographic steering accelerated the northward flow around the south and southwestern flanks with speeds adequate to form large dunes. The flow slowed after rounding southwestern flank but accelerated again as it encountered the next delta flank to the north. The age of the dune formation is unknown, and no northward-flowing geostrophic flow has been reported in the literature from this area.  相似文献   

Shallow bias in Mediterranean paleomagnetic directions caused by inclination error     

Wout Krijgsman  Lisa Tauxe 《Earth and Planetary Science Letters》2004,222(2):685-695

A variety of paleomagnetic data from the Mediterranean region show a strong bias toward shallow inclinations. This pattern of shallow inclinations has been interpreted to be the result of (1) major northward terrane displacement, (2) large nondipole components in the Earth's magnetic field, and (3) systematic inclination flattening of the paleomagnetic directions. Here, we use the observation that, in addition to the well-known variation of magnetic inclination with latitude, the N-S elongation of directional dispersion also varies, being most elongate at the equator and nearly symmetric at the poles. Assuming that inclination shallowing follows the relationship long known from experiment, we invert the inclinations using a range of “flattening factors” to find the elongation/inclination pair consistent with a statistical model for the paleosecular variation. We apply the so-called “elongation/inclination” method to the extensive paleomagnetic data sets from the Miocene sediments of the Calatayud basin (Spain) and the island of Crete (Greece). After correction, the Spanish data are in good agreement with the expected middle Miocene latitude of the region. The data from Crete suggest that it occupied a position in the late Miocene about 275 km north of the predicted location. This is in agreement with the geological and geodynamical models for the east Mediterranean region, which indicate that slab rollback processes in combination with Anatolian push generated southward migration of Crete. The 7.5 million year average displacement rate of Crete estimated by the E/I method is 37 mm/yr to the south, which closely coincides with present-day rates based on global positioning system (GPS) and model measurements. We also show that inappropriate tilt corrections lead to a shallow inclination bias as well, explaining that observed in studies of lava flows of the region. We conclude that the east Mediterranean inclination anomaly is caused by sedimentary inclination error and not by a persistent octupolar contribution to the geomagnetic field, or northward transport.  相似文献   

川藏公路通麦天险段山地灾害及其防治     

杨逸畴 《山地学报》1997,(4)

本段是川藏公路有名的严重山地灾害段。近半个世纪来,十几年一遇的特大崩塌、泥石流、雪崩造成的生命、财产损失惨重,该段在雅鲁藏布江大拐弯峡谷顶端范围内,以上升为主的强烈构造活动,以大峡谷水汽通道进入水分、热量,是发生高频率高强度特大山地灾害的基础。结合当地实情,加强调查研究,划分各类灾害危险区段,提出防治措施。  相似文献   

四川地区强震与发震构造几何结构特征关系的探讨   总被引：1，自引：1，他引：1  

黄祖智  唐荣昌 《中国地震》1995,11(2):133-139

本文通过近些年来对四川活动断裂与强震关系的研究，初步总结了四川地区强震与发震构造几何结构特征的关系。作者认为：走滑断层的斜列状结构，断层的交叉，大断裂带的末端，断裂上的枢纽、弯曲、转折部位以及断裂带上的横向隆起、拗主其交替部位都可能是发震构造的结构特征，亦是强震易于发生的部位，这对地震危险区域潜在震源区的划分及其地基预报、地震区划和工程区地震安全性评价具有重要的意义。  相似文献   

Sedimentation patterns in a gulf coast backbarrier marsh: Response to increasing submergence     

R. D. Delaune  C. J. Smith  W. H. Patrick 《地球表面变化过程与地形》1986,11(5):485-490

The rate of vertical accretion was determined on two backbarrier marshes in the Mississippi River Plain, using ¹³⁷Cs dating techniques. An average accretion rate of 0-55 cm yr^?1 was found on Grande Terre, and 0.78 cm yr^?1 on Grand Isle. Analysis of mineral organic content of the marsh profile shows that the backbarrier marshes accrete through (1) accumulation of low density organic matter, and (2) episodic deposition of high density mineral sediment probably associated with major hurricanes or storm events. The rates of vertical accretion were two to three times less than the rate of submergence due primarily to rapid subsidence in the deltaic plain, and imply that these backbarrier marshes will progressively deteriorate.  相似文献   

Numerical investigation of the gel barrier formation with vertical injection pipe     

Meejeong Kim  M. Yavuz Corapcioglu  Jae-Woo Park 《Environmental Geology》2007,53(3):635-642

Permeation grouting is the injection of a fluid grout into ground and production of a solidified mass to carry increased load and/or fill voids to control water flow. This study examined a technology of constructing horizontal gel barrier by the permeation grouting through multiple vertical injection pipes. Colloidal Silica (CS) solution was used as a gelling liquid to be injected and solidified in the unsaturated soil. Formation of a gel bulb was simulated and the results were compared with those obtained from the sleeve pipe injection with horizontal pipes. The gel bulb generated from the injection method employing vertical pipe showed greater sensitivity of the bulb’s lateral extent to variations in operating conditions compared to the sleeve pipe injection. Although in the limited numbers, in all examined cases, the vertical-pipe system appeared to consume a larger volume of CS solution than the horizontal-pipe system to form an equivalent horizontal gel barrier. This result supports our intuition that the injection with the horizontal pipes may be more effective than the one with vertical pipes in constructing horizontal gel barrier.  相似文献   

Circulation in the Great Barrier Reef Lagoon using numerical tracers and in situ data     

John L. Luick  Luciano Mason  Thomas Hardy  Miles J. Furnas 《Continental Shelf Research》2007

Numerical hydrodynamic models of the northeastern Queensland shelf, forced by regional winds and modelled boundary currents in the northern Coral Sea, are used to provide improved estimates of general flow trajectories and water residence times within the Great Barrier Reef (GBR) shelf system. Model performance was checked against a limited set of current metre records obtained at Lark Reef (16°S) and the Ribbon Reefs (15.5°S). Estimates of water parcel trajectories are derived from a series of numerical tracer experiments, with daily releases of neutrally buoyant, un-reactive particles at 320 sites along the coast between Cape York (10.7°S) and Hervey Bay (25°S). Flow trajectories and residence times for tracer particles introduced to the GBR lagoon in the southern—ca. 22°S, central—19°S, and northern reef—14°S are emphasised. For purposes of the analysis, the year was divided into two seasons based on mean alongshore current direction. Most coastal sourced tracers entering the central GBR lagoon between 16° and 20°S during the northward-current season (January–August) primarily encounter the outer-shelf reef matrix after exiting the lagoon at its northern “head” (nominally 16°S), after 50–150 days. Up to 70% of tracer particles entering in the southward-current season (August–December) eventually crossed the lagoon to the outer-shelf reef matrix, with median crossing times between 20 and 330 days. During favourable wind conditions, tracers introduced at the coast may move rapidly across the lagoon into the reef matrix. The tracer experiments indicate that most coastal-sourced tracers entering the GBR lagoon remain near the coast for extended periods of time, moving north and south in a coastal band. Residence times for conservative tracer particles (and implied residence times for water-borne materials) within the GBR shelf system ranged from ca. 1 month to 1 year—time frames that are very long relative to development times of planktonic larvae and cycling times for nutrient materials in the water column, implying they are transformed long before reaching the outer reef matrix.  相似文献