共查询到20条相似文献，搜索用时 625 毫秒
1.
Linking Tarim Basin sea retreat (west China) and Asian aridification in the late Eocene 总被引：1，自引：0，他引：1
R. Bosboom G. Dupont‐Nivet A. Grothe H. Brinkhuis G. Villa O. Mandic M. Stoica W. Huang W. Yang Z. Guo W. Krijgsman 《Basin Research》2014,26(5):621-640
The Tarim Basin in western China formed the easternmost margin of a shallow epicontinental sea that extended across Eurasia and was well connected to the western Tethys during the Paleogene. Climate modelling studies suggest that the westward retreat of this sea from Central Asia may have been as important as the Tibetan Plateau uplift in forcing aridification and monsoon intensification in the Asian continental interior due to the redistribution of the land‐sea thermal contrast. However, testing of this hypothesis is hindered by poor constraints on the timing and precise palaeogeographic dynamics of the retreat. Here, we present an improved integrated bio‐ and magnetostratigraphic chronological framework of the previously studied marine to continental transition in the southwest Tarim Basin along the Pamir and West Kunlun Shan, allowing us to better constrain its timing, cause and palaeoenvironmental impact. The sea retreat is assigned a latest Lutetian–earliest Bartonian age (ca. 41 Ma; correlation of the last marine sediments to calcareous nannofossil Zone CP14 and correlation of the first continental red beds to the base of magnetochron C18r). Higher up in the continental deposits, a major hiatus includes the Eocene–Oligocene transition (ca. 34 Ma). This suggests the Tarim Basin was hydrologically connected to the Tethyan marine Realm until at least the earliest Oligocene and had not yet been closed by uplift of the Pamir–Kunlun orogenic system. The westward sea retreat at ca. 41 Ma and the disconformity at the Eocene–Oligocene transition are both time‐equivalent with reported Asian aridification steps, suggesting that, consistent with climate modelling results, the sea acted as an important moisture source for the Asian continental interior. 相似文献
2.
Occurrence of polar seabirds at sea in relation to prey concentrations and oceanographic factors 总被引：2，自引：0，他引：2
The distribution and abundance of breeding and foraging seabirds is usually a reflection of the availability of prey in the marine ecosystems on which the birds depend. At the scale of hundreds of km, differences in marine communities may be reflected in variation in the species composition of resident seabirds. At small scales, environmental features such as fronts or ice can influence where birds will aggregate to forage. Features at which prey become concentrated near the surface are of particular importance to bird species dependent upon small planktonic organisms. Concentrations of foraging seabirds frequently indicate the presence of such features, or of areas of unusually high prey biomass. The absence of birds does not mean that concentrations of potential prey are absent. "Assembly rules," by which one might predict aspects of the marine environment that birds should use in selecting foraging areas are proposed. 相似文献
3.
This paper documents the importance of three‐dimensional (3D) seismic data for integrated stratigraphic–morphological analysis of slope systems. Furthermore, it contributes to the general understanding of the evolutionary mechanisms of slope‐confined submarine canyons on continental margins and their significance in a sequence stratigraphic framework. Recently acquired 3D seismic data from the Ebro Continental Margin (Western Mediterranean) have been used to study a series of remarkably well‐imaged submarine canyons in the Plio‐Pleistocene succession. Detailed mapping shows that these canyons are restricted to the slope, and thus can be compared with slope‐confined canyons observed on the present day seabed of many continental margins. The slope‐confined canyons are typically 0.5–2 km wide, 10–15 km long, and incise more than 50 m into the slope units. Their most striking characteristic is an upslope branching geometry in the head region involving up to three orders of bifurcation, with downslope development of a single incisional axis. The submarine canyons are characterized by a nested stacking pattern, undergoing alternating phases of cutting and filling. Limited parts of the upper and middle slope remain outside the canyon system, confined in sharp depositional ridges. The canyons are observed on closely spaced surfaces and exhibit a geometry that allowed the construction and discussion of a local sequence stratigraphic model for their evolution. In general, active incision of the canyons is observed at times throughout almost the entire cycle of base‐level change. However, erosional activity is more significant during the later stages of the relative sea level rise and the entire falling stage, with the timing of maximum erosion observed at the end of the cycle. The minimum erosional activity of the canyons is linked instead to the earliest part of the relative sea level rise. 相似文献
4.
The composition, volume and stratigraphic organisation of submarine fan systems deposited along continental margins are expected to reflect the landscape from which the sediment was derived. During the Late Cretaceous, the Møre‐Trøndelag margin, Norwegian North Sea was dominated by the deposition of deep‐marine fines; the emplacement of 11 sand‐rich submarine fan systems occurred only during a c. 3 Myr period in the Turonian‐Coniacian. The systems were fed by sediment that was routed through submarine canyons incised into the basin margin; the canyons are underlain by angular unconformities and are interpreted to have resulted from tectonically induced changes in slope physiography and erosion by gravity flows. The areal extent of the onshore drainage catchments that supplied sediment to the fans has been estimated based on scaling relationships derived from modern source‐to‐sink systems. The results of our study suggest that the Turonian fans were sourced by drainage catchments that were up to ca.3600 km2, extending more than ca.100 km inland from the palaeo‐shoreline. The estimated inboard catchment extent correlates with the innermost structures of a large, long‐lived, basement‐involved, normal fault complex. On the basis of our analysis, we conclude that increased sediment supply to the Turonian fan systems reflects tectonic rejuvenation of the landscape, rather than eustatic sea‐level or climate fluctuations. The duration of fan deposition is thus interpreted to reflect the ‘relaxation time’ of the landscape following tectonic perturbation, and fan system retrogradation and abandonment is interpreted to reflect the eventual depletion of the onshore sediment source. We demonstrate that a better understanding of the stratigraphic variability in deepwater depositional systems can be gained by taking a complete source‐to‐sink view of ancient sediment dispersal systems. 相似文献
5.
ABSTRACTIn this century Chinese tourists in Australia have rapidly become the most numerous national source. Relatively little is known about their socio-economic status, their geographical origins and expectations of tourism, and their attitudes to and perceptions of Australia, although every Australian state has devised a specific Chinese tourism strategy to tap into this market. Chinese tourism is concentrated in metropolitan areas in the eastern states, has evolved from group tours to individual plans, and is relatively high spending. Unless geographical and tourism research on Chinese tourism aligns with contemporary theoretical developments in tourism studies, the type of knowledge being produced will be limited. Whilst there is value in extending existing knowledge, important social insights into the Chinese tourists’ experience of Australia will not emerge. Although Chinese tourism is similar to earlier waves from East Asia, it constitutes a distinct component of the contemporary Australian market. A deeper understanding of this phenomenon requires the adoption of practice theories that privilege social practices as the entry point for theorising and conducting research. In advocating such an approach, we highlight challenges of linguistic and cultural differences, scale and governmentality in providing a qualitative research agenda for geographical and tourism studies’ engagements with Chinese tourism. 相似文献
6.
1990年以来中国大陆海岸线稳定性研究 总被引：1，自引：1，他引：0
海岸线变迁是一个动态的演变过程,它是自然与人类共同作用的结果。基于1990年、2000年、2007年和2012年4个时期的资源卫星、Landsat系列卫星的遥感影像,采用色差Canny算子计算方法提取岸线数据,计算近22 a来中国大陆海岸线向海推进或向陆后退的空间位置变化量及年均变化速度,研究中国大陆海岸线空间位置与稳定性的演变规律,得出以下结论：① 中国海岸线空间位置变化以向海推进为主;② 中国海岸线多为相对稳定海岸线,其次为强烈岸进岸线,稳定性岸线全国均有分布,而强烈岸进岸线多分布于江苏和辽宁两省;③ 自1990年以来,中国大陆岸线的稳定性指数逐渐降低,22 a下降了1.1,以长江入海口为分界,南方沿海城市岸线稳定性指数高于北方。 相似文献
7.
大陆架在国家可管辖海域划界问题研究 总被引：3，自引：0，他引：3
大陆架是地质地理学研究的内容,随着人类对海洋的开发,大陆架已成为国家在海洋权益维护方面重要的内容。该文阐述了大陆架制度的形成以及在可管辖海域划界中的作用,并对我国专属经济区和大陆架制度以及大陆架在我国可管辖海域划界中所面临的问题进行了分析。 相似文献
8.
在回顾南海北部海岸和陆架地层证据的基础上,梳理了珠江三角洲晚第四纪演变历史。结果显示：1）本区晚第四纪地层拥有2套海相沉积,上（新）海相层是当前间冰期（或10.5 ka B.P.以来）高海平面期间形成的沉积物,而下（老）海相层最可能是末次间冰期（126―120 ka B.P.）高海平面阶段留下的沉积物;2）老海相层顶面埋深在三角洲盆地内至少比现今海平面低10~15 m,在珠江口一带则低于20 m,这说明珠江三角洲盆地存在构造沉降,因为2次间冰期的海平面高度是相近的;3）在新生代欧亚板块大陆向东南伸展的构造格局下,南海北部陆架和海岸带经历长期连续的沉降,而长期平均沉降率在0.12 mm/a左右,明显低于GPS测出的现代沉降率;4）在这种板块运动基础上,晚第四纪断裂活动增强了三角洲盆地的沉降,为2次海侵提供了可容沉积空间。 相似文献
9.
The application of high‐resolution seismic geomorphology, integrated with lithological data from the continental margin offshore The Gambia, northwest Africa, documents a complex tectono‐stratigraphic history through the Cretaceous. This reveals the spatial‐temporal evolution of submarine canyons by quantifying the related basin depositional elements and providing an estimate of intra‐ versus extra‐basinal sediment budget. The margin developed from the Jurassic to Aptian as a carbonate escarpment. Followed by, an Albian‐aged wave‐dominated delta system that prograded to the palaeo‐shelf edge. This is the first major delivery of siliciclastic sediment into the basin during the evolution of the continental margin, with increased sediment input linked to exhumation events of the hinterland. Subaqueous channel systems (up to 320 m wide) meandered through the pro‐delta region reaching the palaeo‐shelf edge, where it is postulated they initiated early submarine canyonisation of the margin. The canyonisation was long‐lived (ca. 28 Myr) dissecting the inherited seascape topography. Thirteen submarine canyons can be mapped, associated with a Late Cretaceous‐aged regional composite unconformity (RCU), classified as shelf incised or slope confined. Major knickpoints within the canyons and the sharp inflection point along the margin are controlled by the lithological contrast between carbonate and siliciclastic subcrop lithologies. Analysis of the base‐of‐slope deposits at the terminus of the canyons identifies two end‐member lobe styles, debris‐rich and debris‐poor, reflecting the amount of carbonate detritus eroded and redeposited from the escarpment margin (blocks up to ca. 1 km3). The vast majority of canyon‐derived sediment (97%) in the base‐of‐slope is interpreted as locally derived intra‐basinal material. The average volume of sediment bypassed through shelf‐incised canyons is an order of magnitude higher than the slope‐confined systems. These results document a complex mixed‐margin evolution, with seascape evolution, sedimentation style and volume controlled by shelf‐margin collapse, far‐field tectonic activity and the effects of hinterland rejuvenation of the siliciclastic source. 相似文献
10.
1947年中国南海断续线精准划定的地形依据 总被引：3，自引：0，他引：3
基于1947年中国政府内政部印制的1:400万《南海诸岛位置图》,采用地理信息系统及数字化仿射变换精准测量出11段断续线的地理坐标,同时利用4.4万多个实测水深点数据建立南海海底三维地形模型,通过叠加分析获得了1947年南海断续线所在位置的海底地形特征。结果显示：断续线东长西短,间距东西大、南北小,其走向、形态与下伏地形特征相符合,主要分布在大陆坡和大陆架上;并基于断续线下伏海底地形分析,推断出当时断续线划定时可能遵循如下依据：① 在浅海盆地、海峡处采用“等距离中间线”原则进行划分;② 在具有明显地形变化处沿海槽坡麓或海槽槽沟中线进行划分;③ 在西南部陆坡陆架区,结合岸线走向及下伏地形特征进行划分。 相似文献
11.
Has the notion of ‘sea change’ and its considerable implications for non-metropolitan coastal Australia been exaggerated? In this article alternative perspectives of ‘sea change’ in Australia are reviewed, and the policy implications of each assessed. One perspective regards migration to coastal areas beyond the capital cities as incidental to continued metropolitan primacy and unlikely to affect or change Australia's overall urban or economic structure. The other considers the movement as a significant and enduring process with major environmental and socio-economic repercussions. With reference to research conducted for the National Sea Change Taskforce, the article finds partial support for both positions, leading to a more revealing understanding of ‘sea change’ in Australia. A set of policy responses, sensitive to the particular qualities of Australian coastal environments and communities, are proposed for consideration by all three tiers of government. 相似文献
12.
Johnstone Strait in coastal British Columbia, Canada, is a core habitat for seasonal concentrations of killer whales (Orcinus orca), which have attracted considerable attention from commercial whale-watching operators and recreational boaters. Within the Strait lies the Robson Bight–Michael Bigg Ecological Reserve, a marine reserve set aside as critical habitat for killer whales and closed to recreational boat traffic. The geography of encounters between killer whales and seven types of whale-watching vessels (including kayaks, charter and pleasure craft) in and near this reserve was analysed with a suite of geostatistics in a geographic information system (GIS) vector environment. Reserve boundary violation was high among most user groups, with kayakers being the most frequent offenders. Motorized vessels had significantly longer contact times with whales compared to kayaks and sailboats. Motorized vessels showed the travel characteristic of deliberate tracking of whales. The movements of killer whales also appear to be affected by boats. These results have important implications for killer whale conservation and management in areas where they are subject to intensive whale-watching activities, and possible chronic disturbance. 相似文献
13.
对1999年春季采集于北极拉普捷夫海东南部的冰藻和冰下浮游植物群落的种类组成进行了分析,并对丰度和生物量进行了统计和对比。藻种以硅藻占绝对优势,其中又以羽纹硅藻为主。优势种集中,主要包括海洋拟脆杆藻(Fragilariopsisoceanica)、圆柱拟脆杆藻(F.cylindrus)、寒冷菱形藻(Nitzschiafrigida)、普罗马勒菱形藻(N. promare)、带纹曲壳藻(Ach nanthestaeniata)、新寒冷菱形藻(Nitzschianeofrigida)、大洋舟形藻(Naviculapelagica)、范氏舟形藻(N. vanhoeffenii)、北极直链藻(Melosiraarctica)、北方舟形藻(N. septentrionalis)、新月细柱藻(Clindrothecaclosterium)和绿藻门的塔形藻(Pyramimonassp. )。微藻主要集中在冰底10cm,丰度为14. 6-1562. 2×104 cells·L-1,平均为639. 0×104 cells·L-1;生物量为7. 89-2093. 5μgC·L-1,平均为886. 9μgC·L-1,总体上比次冰底高1个数量级,比冰下表层水柱高2个数量级。冰底20cm冰柱的累计丰度和生物量平均分别为冰下20m水柱累计量的7. 7和12. 2倍,显示冰藻在春季海冰融化前在近岸生态系统中的重要作用。尽管各站位冰底和冰下表层水柱藻类群落的相似性普遍不高,但整个调查海域冰底和冰下水柱优势种极为相似,春季期间冰藻对冰下浮游植物群落的影响明显。由于 相似文献
14.
海洋表层沉积物的磁学性质逐渐被证明是分析海洋沉积物物源的有效手段之一。选取海南岛周边海域39个站位的表层沉积物进行了磁学特征研究。结果表明：海南岛周边海域表层沉积物的低频磁化率和频率磁化率具有明显的空间分异特征,表现为高值区主要出现在海南岛以南海域,而海南岛以东和以西海域则呈现从岸向海逐渐降低的趋势。磁化率的影响因素分析表明：研究区海洋表层沉积物的磁化率主要由陆源碎屑物质贡献,因此可以认为沉积物低频磁化率和频率磁化率的空间分布特征能指示陆源输入的变化。利用多个环境磁学参数对采样点进行Q型聚类,并结合低频磁化率和频率磁化率的空间分布特征及采样点的地理位置将研究区划分为4个区域：海南岛以东水深超过100 m的海域（Ⅰ区）沉积物主要来源于其东北面的珠江水系,同时粤西沿岸河流携带来的物质也有一定程度的影响;海南岛以东水深小于100 m和海南岛以南海域（Ⅱ区）沉积物可能主要来自于海南岛沿岸侵蚀搬运以及入海河流输入;北部湾北部海域（Ⅲ区）沉积物受琼州海峡和北部湾沿岸河流输入物质的共同影响;海南岛以西海域（Ⅳ区）沉积物受来自海南岛西南侧河流输入、沿岸侵蚀物和由南向北的洋流所携带的沉积物的共同影响。研究表明：低频磁化率和频率磁化率组合可有效指示近岸表层沉积物的物源变化。 相似文献
15.
Ilaria Vanni Accarigi 《The Australian geographer》2019,50(4):511-530
ABSTRACTGardens in Australia are considered an important site of heritage maintenance and negotiation for their capacity to materialise transformations in everyday life, design, lifestyles, demographics, environment, as well as social and cultural practices. In the case of conservation areas, gardens tend to be valued in terms of their closeness and potential to preserve specific historical elements. Plants in these gardens are cultivated to evoke period designs, such as Federation (c.1890–1915) and cottage gardens. In this article we turn to gardens and gardening to make sense of entanglements between cultural, historical and environmental elements, and we ask: what role do plants play in shaping our understanding of suburban heritage? To answer this question, we draw on oral histories, archival research and ethnography in Haberfield, the first model garden suburb in Australia. We show how plants channel and mediate multiple concerns that contest and extend ideas of heritage circulating in public discourse. Foregrounding the centrality of plants, this article contributes a dynamic definition of heritage that includes the entanglement of environmental stewardship and individual and collective heritage. 相似文献
16.
F. Ouellet A. Langlois E. A. Blukacz-Richards C. A. Johnson A. Royer E. Neave 《自然地理学》2017,38(2):143-158
AbstractPeary caribou is the northernmost designatable unit for caribou species, and its population has declined by about 70% over the last three generations. The Committee on the Status of Endangered Wildlife in Canada identified difficult grazing conditions through the snow cover as being the most significant factor contributing to this decline. This study focuses on a spatially explicit assessment tool using snow model simulations (Swiss SNOWPACK model driven in an off-line mode by spatialized meteorological forcing data generated by the Canadian Regional Climate Model) to characterize snow conditions for Peary caribou grazing in the Canadian Arctic. The life cycle of Peary caribou has been subdivided into three critical periods: summer foraging and fall breeding (July–October), winter foraging (November–March), and spring calving (April–June). Winter snow conditions are analyzed and snow simulations compared to Peary caribou island counts to identify a snow parameter that could potentially act as a proxy for grazing conditions and explain fluctuations in Peary caribou numbers. This analysis concludes that caribou counts are affected by simulated snow density values >300 kg m?3. A software tool mapping possibly favorable and unfavorable grazing conditions based on snow is proposed at a regional scale across the Canadian Arctic Archipelago. Specific output examples are given to show the utility of the tool, mapping pixels with cumulative snow thickness above densities of 300 kg m?3, where cumulative seasonal thicknesses >7000 cm are considered unfavorable. 相似文献
17.
对海水和沉积物中239+240Pu活度、240Pu/239Pu比值和239+240Pu存量的分析,可以为海洋环境中水团输运、黑潮海水入侵、颗粒物通量、颗粒清除过程、污染物堆积、沉积年代等问题的研究提供有效途径。针对中国边缘海沉积物中239+240Pu活度分布、240Pu/239Pu比值特征和239+240Pu存量进行比较讨论,发现虽然全球大气沉降和太平洋核试验场的输入是中国边缘海沉积物中239+240Pu的2个主要来源,但是中国边缘海海洋环境中不同区域Pu的来源的比例有差异。同时,文中系统探讨了利用Pu端元法研究中国边缘海海洋沉积物中239+240Pu存量的质量平衡模型,这对认识海洋中沉积物的源与汇以及海洋放射性环境状况具有一定意义。 相似文献
18.
The diets of euros or hill kangaroos (Macropus robustus), domestic sheep (Ovis aries) and feral goats (Capra hircus) in hilly, shrub rangeland in southern Australia were examined in a 12-year study. Levels of dietary overlap between these herbivores, their foraging in relation to resource availability, and the potential for competition in different conditions were also examined. The diet of euros was based around grasses. In dry seasons some shrubs were also eaten but in severe drought grass formed more than 80% of their diet. While grass was important to sheep in wetter conditions, they ate much shrub in dry conditions. Feral goats had broad diets but their preference for browse was high. In drought, euros had only a modest dietary overlap with sheep and goats. Data for dietary niche breadths and electivities pointed to only limited competition between the herbivores. 相似文献
19.
极地海洋环境评价对于极地海洋生态系统保护尤为重要。由于对极地极端恶劣环境的监测能力不足,缺乏长期连续监测数据,极地海洋环境评价变得异常困难。针对目前极地海洋环境评价目标和评价因子均缺乏的情况,在已有文献基础上,本文提出了海水表层叶绿素浓度、海冰覆盖范围、海水表层温度和盐度四个极地海洋环境决定因子,分析了海冰覆盖范围与月份之间高度拟合的三次多项式分布关系,并在此基础上构建了极地海洋环境评价模型,最后提出了一种验证该模型的方法。基于第30、31、32次南极科考获取的海水表层叶绿素浓度、温度、盐度数据以及美国国家冰雪数据中心提供的对应时间内的海冰覆盖范围数据对提出的评价模型和方法进行了验证,实验结果表明:该评价模型及其验证方法具有有效性,根据评价结果能判定某个时间段内极地海洋环境相对于基准时间的变化趋势。 相似文献
20.
近20年来中国古河道研究进展 总被引：2，自引：1，他引：1
近20年来,我国在嫩江大安古河道、莱州湾南岸平原古河道、长江南京以下段古河道及古深槽、海底古河道等区域的研究,获得了大量研究成果,深化了理论认识,拓展了应用领域。这些新成果与新认识进一步表明,中国各外流大河均有末次盛冰期埋藏古河道,该期古河流深切于末次冰期间冰阶的陆地及浅海大陆架,形成切割谷和谷底部的深槽,谷内堆积了末次盛冰期和早全新世的河流相滞留物质和粗颗粒物质,上部被中全新世海相、海陆交互相或陆相细粒物质覆盖,构成了埋深约20~50 m的浅埋古河道带。古河道中蕴藏着比较丰富的地下淡水,是洪冲积平原及浅海陆架地区的重要水源。 相似文献