Gulpuliyul structure: a possible impact structure of Mesoproterozoic age in western Arnhem Land,Northern Territory     

K. A. Plumb 《Australian Journal of Earth Sciences》2013,60(4-5):665-673

The Gulpuliyul structure is the eroded remains of a possible impact structure of Mesoproterozoic age, in western Arnhem Land, Northern Territory, on the Arnhem Shelf of the northwestern McArthur Basin. Enigmatic, highly deformed and brecciated strata, within the roughly circular or pentagonal feature about 8.5 km across, contrast with mildly deformed rocks of the surrounding Arnhem Shelf. Shock-metamorphic features have yet to be observed. Other features of the Gulpuliyul Structure are: (i) sharp and faulted outer boundaries; (ii) strata within the structure are younger than adjacent country rocks; i.e., the rocks have been emplaced downwards into the structure; (iii) outcrops display an overall concentric or tangential pattern, the stratigraphy is essentially coherent, and there is an overall younging from the centre outwards; and (iv) strata are commonly overturned by southward-directed thrusting and recumbent folding. It is suggested that the projectile impacted at a shallow angle from the north, to produce a southward-deepening crater about 8.5 km across. The depth of the transient crater was probably between ～500?–?700 m (minimum) and ～800 m (maximum). The central uplift probably rebounded only about 300?–?400 m. The present erosion level is thought to lie near the top of the low central uplift, at about or just below the floor of the final crater. The age of the possible impact is Mesoproterozoic (ca 1600?–?1325 Ma); it is most likely to have occurred very early in the Mesoproterozoic (1600?–?1500 Ma).  相似文献   

Coupled asteroid impacts and banded iron-formations,Fortescue and Hamersley Groups,Pilbara, Western Australia     

A.Y. Glikson  A.H. Hickman 《Australian Journal of Earth Sciences》2013,60(5):689-701

Asteroid impact spherule layers and tsunami deposits underlying banded iron-formations in the Fortescue and Hamersley Groups have been further investigated to test their potential stratigraphic relationships. This work has included new observations related to the ca 2.63 Ga Jeerinah Impact Layer (JIL) and impact spherules associated with the 4th Shale-Macroband of the Dales Gorge Iron Member (DGS4) of the Brockman Iron Formation. A unit of impact spherules (microkrystite) correlated with the ca 2.63 Ga JIL is observed within a >100 m-thick fragmental-intraclast breccia pile in drill cores near Roy Hill. The sequence represents significant thickening of the impact/tsunami unit relative to the JIL type section at Hesta, as well as relative to the 20–30 m-thick ca 2.63 Ga Carawine Dolomite spherule-bearing mega-breccia. The ca 2.48 Ga-old Dales Gorge Member of the Brockman Iron Formation is underlain by an ?0.5 m-thick rip-up clast breccia located at the top of the ca 2.50 Ga Mt McRae Shale, and is interpreted as a tsunami deposit. We suggest that the presence of impact ejecta and tsunami units stratigraphically beneath a number of banded iron-formations, and units of ferruginous shale in the Pilbara and South Africa may result from a genetic relationship. For example, it could be that under Archean atmospheric conditions, mafic volcanism triggered by large asteroid impacts enriched the oceans in soluble FeO. If so, seasonal microbial and/or photolytic oxidation to ferric oxide could have caused precipitation of Fe₂O₃ and silica. In view of the possible occurrence of depositional gaps and paraconformities between impact ejecta units and overlying ferruginous sediments, these relationships require further testing by isotopic age studies.  相似文献   

Assessing human impact on alluvial fan development: a multidisciplinary case-study from Lower Khuzestan (SW Iran)     

《Geodinamica Acta》2013,26(5-6):267-285

This paper presents a multidisciplinary approach for studying the evolution of an alluvial fan system in Lower Khuzestan (SW Iran). The study draws on previously collected data from geological and archaeological field campaigns and new data derived from the interpretation of satellite imagery and historical textual sources. Three alluvial fans were identified, successively deposited by the Jarrahi river in progressively downstream/westward direction. Judging from archaeological and historical evidence, the successive phases appear to coincide with a relocation of settlement and irrigation activities. The distributary system of the present-day fan developed over a period of less than four centuries. It is suggested that management of levee breaks by man played a key role in such rapid fan development and in maintaining extremely low gradients. Judging from the extensive patterns of ancient irrigation canals, human activity also played an important role in the formation of the earlier fans.  相似文献   

SWBM模型在锡林河流域气候变化影响评价中的应用          下载免费PDF全文

李杨  朱仲元  贾德斌  姚苏红  刘翠善  李皓冰 《水文》2013,33(2):39-42

以内蒙古地区的锡林河流域为研究对象,采用考虑融雪的水量平衡模型(SWBM模型),在对锡林河流域水文模拟的基础上,评估了流域水资源对气候变化的响应。结果表明:SWBM模型锡林河流域月径流过程具有较好的模拟效果,率定期和检验期的模型效率系数均超过60%,相对误差也均小于8%,在未来全球气候变化背景下,流域水资源以减少趋势为主,2030年之后,减少幅度将可能超过10%。  相似文献   

贵州某煤矿环境综合治理方案研究     

张恒利  唐朝苗  曹正啟 《中国煤炭地质》2013,(11):36-40,50

在研究矿区地质、水文地质及工程地质条件的基础上,结合矿井的开采情况,分析认为矿区存在的环境地质问题主要是土地占用和破坏,地裂缝,固体废弃物的排放等,并对其危害程度进行了预测。结果表明,评估区植被破坏较少,无明显土地荒漠化（石漠化）现象,占用土地大多为旱地,有轻微水土流失,易于治理和恢复;区内地质灾害危害的可能性大;固体弃土、弃渣（矸石）在暴雨或流水作用下,可能发生泥石流等地质灾害。对矿山环境进行了综合评估,将研究区分为三个大区：影响严重区、影响较严重区、影响较轻区,并分别对各大区的地质灾害特征进行了分析说明。根据地质环境现状提出了生态环境恢复、修建截排水沟、废渣（矸石）的处理等一系列切实综合治理方案。此研究对矿山环境综合治理具有指导性,并对类似矿山环境综合治理能起到一定的借鉴作用。  相似文献   

Dynamics of steel offshore platforms under ship impact     

《Applied Ocean Research》2014

This paper deals with the prediction of the dynamic response of steel offshore platforms to high energy impacts from typical supply vessels. The contribution of the high modes of a cantilever beam type structure with a concentrated top mass subjected to transverse impact from rigid and deformable strikers is analysed. A procedure to develop simplified equivalent systems for efficient structural response analysis is presented and its reliability tested by comparing the results from the explicit non-linear FE simulations. Effects such as the overall rotation of the installation, plastic deformations in the contact area, different impact locations and different hinge mechanisms are taken into account. It is shown that the use of the proposed equivalent systems with a reduced number of DOF's can provide accurate results at significantly less computational efforts as compared to the FE simulations. The derivation of some parameters of the equivalent dynamic elastic–plastic SDOF/2SDOF systems, however, needs to consider the complexity of the analysed steel frames and perform preliminary non-linear static analyses. Therefore, further studies of different impact scenarios on platforms with different configurations are recommended to augment the results presented here.  相似文献   

The economic impacts of marine energy developments: A case study from Scotland     

《Marine Policy》2014

Delivering the ambitious renewable energy targets set by the Scottish Government will require significant expenditures. Plans have been set out to develop 1.6 GW of marine (wave and tidal) energy capacity between 2010 and 2020 in the Pentland Firth and Orkney Waters area (off the north coast of Scotland) with construction costs estimated at £6 billion. This paper uses multi-sectoral economic models to explore the impact that these (temporary) expenditures could have on the Scottish economy. It is shown that the standard Input–Output (IO) modelling approach significantly overstates the employment and value added impacts compared to Computable General Equilibrium (CGE) methods—in which short-run scarcity of factors of production are explicitly modelled. CGE results (under myopic and forward-looking model specifications) produce smaller impacts during the timespan of expenditures but, unlike IO methods, identify non-trivial “legacy effects” after the expenditures cease.  相似文献   

Social impacts of a temperate fisheries closure: understanding stakeholders' views     

《Marine Policy》2014

The social dimensions of marine protected areas (MPAs) play an important role in MPA success, yet these social dimensions are little understood. We explore the social impacts arising from the establishment of an MPA using Lyme Bay (south west England) as a case study. Through a series of small group semi-structured interviews the social impacts experienced by fishermen (mobile and static gear), recreational users (divers and sea anglers) and recreation service providers (charter boat and dive businesses) were explored. The social impacts expressed varied according to activity in which the stakeholder group engaged. Negative themes included lengthening fishing trips, tension and conflict, fishermen identity, equity and uncertainty in the long-term. Positive themes included improved experiences for both commercial fishermen and recreational users, and expectations for long-term benefits. These impacts need to be understood because they influence stakeholder behaviour. Failure to interpret stakeholder responses may lead to poor decision-making and worsening stakeholder relations. These findings have implications for the success of the MPA in Lyme Bay, but also for the future network of marine conservation zones around the UK. Any assessment of MPA impacts must therefore identify social as well as economic and environmental change.  相似文献   

温州鳌江近海建设工程环境影响潮汐潮流数值模拟(英文)     

吕和娜  汪一航  张钊  单慧洁  岳云飞 《海洋通报(英文版)》2014,(2)

收集了近年来鳌江口附近海域多个工程不同阶段5个潮位站的3~5年潮位实测数据和部分海流实测资料,通过对鳌江口附近海域的不同年份的水位资料进行潮汐调和常数分析,鳌江近海海域主要为半日潮区,其中M2分潮的振幅在170 cm~193 cm;迟角在260°~280°之间,这些站的2007年、2010年、2011年调和常数分析结果相比,主要的半日分潮M2、S2、N2,全日分潮K1、O1及浅水分潮M4、MS4、及M6等分潮振幅、迟角的最大变化分别在1.8 cm~4.4 cm和3°~7°之间。在初步掌握了鳌江口潮汐潮流特征的基础上,采用无结构的三角形网格和有限体积法的FVCOM海洋数值模型,进行模拟结果验证,计算结果与实测数据符合良好。构建重点年份建设工程合拢产生新的岸线水深的潮汐潮流场,刻画鳌江口建设工程的叠加影响。  相似文献   

Tests to evaluate the ecological impact of treated ballast water on three Chinese marine species     

张亚楠  王子羲  蔡磊明  蔡翔  孙文俊  马立青 《中国海洋湖沼学报》2014,32(5):1105-1117

Ballast water has been a topic of concern for some time because of its potential to introduce invasive species to new habitats. To comply with the International Convention for the Control and Management of Ships＇ Ballast Water and Sediments, members of the International Maritime Organization （IMO） must equip their ships with on-board treatment systems to eliminate organism release with ballast water. There are many challenges associated with the implementation of this IMO guideline, one of which is the selection of species for testing the ecological impacts of the treated ballast water. In the United States, ballast water toxicity test methods have been defined by the United States Environmental Protection Agency. However, the test methods had not been finalized in China until the toxicity test methods for ballast water were established in 2008. The Chinese methods have been based on species from three trophic levels： Skeletonema costatum, Neomysis awatschensis, and Ctenogobius gymnauchen. All three species live in broad estuarine and open sea areas of China; they are sensitive to reference toxicants and acclimatize easily to different conditions. In this paper, the biological characteristics, test processes and statistical analysis methods are presented for the three species. Results indicate that the methods for evaluating these three organisms can be included in the ecological toxicity tests for treated ballast water in China.  相似文献