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1.
Results are presented from a new cellular model of braided river dynamics that simulates flow, sediment transport, morphological change and the effects of braidplain vegetation. This model is used to investigate the effect of changes in upstream sediment supply on braided river systems over simulation periods of 200 years. Modelled changes in channel morphology, associated with both aggradation and degradation, were seen to be consistent with those reported in the literature. In addition, simulation results allowed the identification of diagnostic characteristics of aggrading and degrading reaches, in the form of relationships between the age, extent and relative elevation of fluvial surfaces. Interpretation of spatial patterns of valley floor surface characteristics in the Avoca River, New Zealand, on the basis of these relationships, allowed the identification of channel reaches that appear to be experiencing either aggradation or degradation. These inferences are shown to be consistent with independent evidence of spatial patterns of sediment supply to the main valley floor, derived from aerial photographs and an existing sediment source inventory. These results illustrate the potential for using cellular models to develop an improved understanding of natural river behaviour. 相似文献
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In contrast to the abundant evidence of former shorelines on the sea floor of the Sahul Shelf in northern Australia, little evidence has been reported for late Pleistocene coastal landforms along the modern coast of north Australia. Using radiocarbon, thermoluminescence and uranium/thorium dating techniques, however, it can be shown that the present coastal morphology on the Cobourg Peninsula is partly inherited from features both deposited and eroded during the late Quaternary. Shore platforms, in particular, are veneered with ferricretes, some of which can be U/Th dated. In places bedforms are preserved within the ferricrete, suggesting that the platform existed at, and was modified during, the Last Interglacial, and probably formed during earlier interglacials. TL dating indicates that sands around Cape Don were deposited when sea level was lower, but may have been reworked during a Holocene high stand. A sequence of beach ridges at Smith Point indicates Holocene progradation over an earlier planation surface, and also provides support for slight Holocene emergence. 相似文献
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An integrated model of clastic injectites and basin floor lobe complexes: implications for stratigraphic trap plays 
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下载免费PDF全文 Sarah Louise Cobain David Mark Hodgson Jeff Peakall Michelle Nicole Shiers 《Basin Research》2017,29(6):816-835
Injectites sourced from base‐of‐slope and basin‐floor parent sandbodies are rarely reported in comparison to submarine slope channel systems. This study utilizes the well‐constrained palaeogeographic and stratigraphic context of three outcrop examples exposed in the Karoo Basin, South Africa, to examine the relationship between abrupt stratigraphic pinchouts in basin‐floor lobe complexes, and the presence, controls, and character of injectite architecture. Injectites in this palaeogeographic setting occur where there is: (i) sealing mudstone both above and below the parent sand to create initial overpressure; (ii) an abrupt pinchout of a basin‐floor lobe complex through steep confinement to promote compaction drive; (iii) clean, proximal sand beds aiding fluidization; and (iv) a sharp contact between parent sand and host lithology generating a source point for hydraulic fracture and resultant injection of sand. In all outcrop cases, dykes are orientated perpendicular to palaeoslope, and the injected sand propagated laterally beneath the parent sand, paralleling the base to extend beyond its pinchout. Understanding the mechanisms that determine and drive injection is important in improving the prediction of the location and character of clastic injectites in the subsurface. Here, we highlight the close association of basin‐floor stratigraphic traps and sub‐seismic clastic injectites, and present a model to explain the presence and morphology of injectites in these locations. 相似文献
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城镇化的快速发展带来城市各类土地用地规模、空间格局与利用强度的改变。论文基于互联网爬虫技术获取郑州市城市住宅小区时空数据,以住宅小区面积与容积率为指标,通过标准差椭圆、核密度分析以及局部空间自相关等方法,分析郑州市城市住宅用地扩展的时空特征与集聚变化情况。结果表明：① 随着主导因素的转变,1985—2019年郑州市住宅用地面积增加趋势明显,但2017年之后呈现下降趋势;住宅用地容积率由缓慢增长趋势逐渐转变为快速增长趋势。② 受常住人口总量迁移规律影响,在研究期内郑州市住宅用地重心由西南向东北移动,但仍主要分布在市内五区交界处;受经济重心的斜“N”变化趋势影响,其东西向迁移速度大于南北向迁移速度。③ 随着住宅用地数量的快速增加,城市住宅用地空间溢出效应更加显著,由分散向集聚演变,空间分异程度由局部突出转变为区域平衡为主。④ 街道尺度下住宅用地容积率出现明显的空间自相关性,经济发展区、城市规划商业中心区成为容积率高—高集聚区,而生态涵养区成为容积率低—低集聚区。 相似文献
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The geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall, globally higher heat flow, and localized hydrothermal systems. Comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin, nor are they indicative of formation by an early global uniformly higher heat flow. In general, valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys. Valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion. With the exception of fluvial valleys on some volcanoes, most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology. In contrast, terrestrial sapping valleys form from and along with runoff valleys. The isolated or clustered distribution of valleys suggests localized water sources were important in drainage development. Persistent groundwater outflow driven by localized, but vigorous hydrothermal circulation associated with magmatism, volcanism, impacts, or tectonism is, however, consistent with valley morphology and distribution. Snowfall from sublimating ice-covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal/hydrothermal activity is sufficient to melt accumulated snowpacks. 相似文献
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Thermokarst landforms and processes in Ares Vallis, Mars 总被引：1，自引：0，他引：1
With a length of 1500 km, Ares Vallis is one of the largest martian outflow channels, and is inferred to have been formed by cataclysmic floods of water conveyed from source areas, which are marked by chaotic terrain, to Chryse Planitia. Near its downstream outlet (14°N, 28°W), the floor of Ares widens to 100 km from its average 25 km width. This area of widened channel floor is marked by a complex of irregular terraces, elongated depressions, linear ridges, sinuous ridges, and other indicators of highly irregular dissection of a formerly continuous surface. Thermokarst processes, following either glacial or alluvial histories, seem best to explain these relationships. Various indicators of fluctuating discharge for water and sediment, ponding of debris, and prolonged flow suggest the emplacement of ice-rich debris in the anomalous reach of Ares Vallis. Post-flood or post-glacial thawing of the ice-rich sediments would then generate the thermokarst landscape. These processes, which are consistent with other indicators of anomalously warm climatic conditions, imply a profound change from the modern martian environment. 相似文献
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半城市化地区住区形态及空间分布特征——以厦门市集美区为例 总被引：7，自引：2，他引：5
半城市化地区在快速的城市化进程中,其人居环境出现了剧烈的变迁,形成了独特的住区形态。本文以厦门市集美区为研究区,采用定性和定量相结合的方法,首先综合考虑不同住区在物质形态和非物质形态方面的特征,对研究区内的住区进行了分类判别和比较。然后结合SPOT-5全色波段影像,利用景观生态学的研究方法,选取不同的景观指数,在城区和样区两个尺度分析了住区的空间分布特征。结果表明:在城区尺度上,农村居民点在所有形态的住区中所占比重达到43%,并在城区内呈分散分布;城市建成区中城中村所占的比例大于城市型住区,前者呈分散分布,后者更趋于集中分布。在样区尺度上,受城市化影响程度不同,不同形态的住区周边的景观格局呈现出城市化梯度特征,而且城市化程度越高的样区,其景观破碎化程度越高。 相似文献
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鲁北平原黄河古河道初步研究 总被引：10，自引：0，他引：10
鲁北平原黄河古河道可分为地面古河道(埋藏深度0—8m)和浅埋古河道(埋藏深度8—40m)。两类古河道部大致可分为三条古河道带,呈SW-NE向近平行展布,每带一般宽5—15km,最宽处可达20km。 古河道沉积层主要由细砂或粉砂组成,为古河床之曲流砂堤或天然堤沉积。各期古河道沉积层之顶、底板主要为粘土或亚粘土和淤泥层所构成,为古黄河泛滥相沉积物。 本区古河道按形成时间顺序可分为三期,下部第一期古河道大约形成于晚更新世晚期—全新世早期,中部第二期古河道形成于全新世早—中期,上部第三期古河道形成于全新世中—晚期。 相似文献
10.
长江三峡阶地的成因机制 总被引：15，自引：0，他引：15
根据对长江三峡阶地堆积物进行的野外调查与室内分析发现三峡阶地的成因具有以下特点:构成阶地上部的河漫滩相堆积、中部的冲积砾石层与作为阶地基座的基岩平台是在不同时期形成的;阶地上部河漫滩相堆积是在中全新世气候温暖、长江三峡高水位条件下形成的.因此,长江三峡阶地是在构造上升的基础上由于气候及长江三峡流量及水位变化而形成的,并非一定是间歇性构造上升的标志. 相似文献
11.
Morphotectonics and incision of the Kaoping submarine canyon, SW Taiwan orogenic wedge 总被引：1，自引：0，他引：1
The Kaoping submarine canyon developed on the frontal orogenic wedge off SW Taiwan and is the largest one among others. The canyon begins at the mouth of the Kaoping River, crosses the narrow shelf and broad slope region, and finally merges into the northern Manila Trench for a distance of about 260 km. Using reflection seismic sections and bathymetric mapping this paper reveals the geomorphic characteristics of the Kaoping Canyon strongly related to structural and sedimentary processes. The combined morphometry statistics analysis, seismic interpretations of structures and examinations of detailed bathymetric charts indicate that regional canyon morphology is strongly linked to intrusions of mud diapirs in the upper reach of the canyon and thrust faulting in the middle and lower reaches which produce two prominent morphological breaks of the course of the Kaoping Canyon with two sharp bends. Although excavation of floor and enlargement of the Kaoping Canyon are mainly attributed to downslope erosion of seabed, incision of this canyon is also strongly complicated by mud diapiric intrusions (upper reach), westward thrust faults (middle reach), and regional base level tilting (lower reach). The resultant cross-sectional morphology along the Kaoping Canyon changes considerably, ranging from U-shaped, broad V-shaped, to irregular troughs. The Kaoping Canyon may be served as a variant of canyon model of active margins with a distinct morphology of two sharp bends along the canyon course associated with structure deformation. 相似文献
12.
A pockmark field has been encountered in the northwestern Barents Sea, SO km southeast of Hopen island. High resolution seismic records and side scan sonographs show that the features are small (10–20 m diameter), shallow (<1 m deep) structures that may cover up to 25% of the sea floor in local areas. Pockmark existence seem to be dependent on the presence of soft, Holocene mud. In more firm sea-floor they seem to concentrate in the partly infilled troughs of iceberg plough marks. The pockmark distribution, characteristics of the underlying sedimentary bedrock and thin cover of glacigenic sediments in the area, indicate they are formed by ascending gas from a deeper, probably petrogenic source. It is inferred that pockmarks may be found in larger parts of the Barents Sea. 相似文献
13.
The widely used linear diffusion model for hillslope evolution does not accurately predict the degradation of terrace scarps produced by the Late Pinedale West Spalding Bay Channelway (WSBC) near Jenny Lake in Grand Teton National Park, Wyoming USA. These scarps, cut into identical cohesionless quartzite gravel, were formed nearly simultaneously, during the brief period of time the WSBC was active. They are assumed to have had the same initial morphology as scarps currently forming along Snake River that are cut in the same material: a straight midsection sloping at 30° and a horizontal base and crest. The model best able to fit the observed morphology and the change in morphology with scarp height specifies the downslope debris flux is proportional to slope gradient raised to a power of 3.4. 相似文献
14.
Shelf-margin clinoforms and prediction of deepwater sands 总被引：1，自引：1，他引：1
Early Eocene successions from Spitsbergen and offshore Ireland, showing well‐developed shelf‐margin clinoforms and a variety of deepwater sands, are used to develop models to predict the presence or absence of turbidite sands in clinoform strata without significant slope disturbance/ponding by salt or mud diapers. The studied clinoforms formed in front of narrow to moderate width (10–60 km) shelves and have slopes, 2–4°, that are typical of accreting shelf margins. The clinoforms are evaluated in terms of both shelf‐transiting sediment‐delivery systems and the resultant partitioning of the sand and mud budget along their different segments. Although this sediment‐budget partitioning is controlled by sediment type and flux, shelf width and gradient, process regime on the shelf and relative sea‐level behaviour, the most tell‐tale or predictive signs in the stratigraphic record appear to be (1) sediment‐delivery system type, (2) degree of shelf‐edge channelling and (3) character of shelf‐edge trajectory through time. The clinoform data sets from the Porcupine Basin (wells and 3‐D seismic) and from the Central Basin on Spitsbergen (outcrops) suggest that river‐dominated deltas are the most efficient delivery systems for dispersing sand into deep water beyond the shelf‐slope break. In addition, low‐angle or flat, channelled shelf‐edge trajectories associate with co‐eval deepwater slope and basin‐floor sands, whereas rising trajectories tend to associate with muddy slopes and basin floors. Characteristic features of the shelf‐edge, slope and basin‐floor segments of clinoforms for these trajectory types are documented. Seismic lines along the slope to basin‐floor transects tend to show apparent up‐dip sandstone pinchouts, but most of these are likely to be simply sidelap features. Dip lines aligned along the axes of sandy fairways show that stratigraphic traps are unlikely, unless slope channels become mud‐filled or are structurally partitioned. Another feature that is prominent in the data sets examined is the lack of slope onlap. During the relative rise of sea level back up to the shelf, the clinoform slopes are generally mud‐prone and they are characteristically aggradational. 相似文献
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北京市住宅价格的影响因素及适宜居住面积标准 总被引：2，自引：0，他引：2
针对我国城市住宅市场中的问题,如何通过适宜的住宅面积标准来引导住房建设与消费是当前极为重要和紧迫的课题。然而已有的建筑学和比较研究等方法却存在较大的局限性,难以为政策提供有效的支撑。本文运用微观经济学的理论和方法对适宜居住面积标准的理论框架和方法进行探索,以北京市为例进行实证分析。从住房市场的经济分析出发,将住宅面积标准的优化界定为使消费者的边际效应最大化的问题。通过定量分析,提出适合于不同家庭的居住面积的建议值,并就如何合理地引导住宅建设与消费提出政策建议。根据分析结果,建议以50m2和80m2作为北京地区的适宜建筑面积标准。同时,从鼓励阶段性消费的政策视角出发,提出宜针对特定的目标层,通过减税、补贴等手段降低换购费用,从而创造引导居民理性消费的经济动机。 相似文献
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腾格里沙漠东南缘格状沙丘表面气流及其地貌学意义 总被引：21，自引：9，他引：12
对腾格里沙漠东南缘沙丘形态与区域气流的分析表明,格状沙丘发育在双向低风能环境。沙丘表面气流及沉积过程的观测结果,主梁长期处在横向气流环境,其形态主要受背风坡分离气流控制,并以迎风坡侵蚀、背风坡净堆积形式顺主风向迁移。副梁处在双向-斜向气流环境,背风坡的附体偏向气流控制其形态和动力学过程,而且其强度是原始风入射角余弦的对数函数。在斜向风作用下,副梁迎风坡侵蚀的同时,背风坡中下部也发生沙粒的纵向输移且堆积于主梁背风坡,从而导致副梁沿年合成输沙方向延伸。由此认为,格状沙丘的主梁形成于主风-西北风的作用,而副梁是在主梁基础上并在主风和次风-东北风的交替作用下形成的;其形态动力学类型应属纵向沙丘置于横向沙丘之上一种复杂型沙丘。 相似文献
17.
以大连市内四区为例,将城镇地籍调查数据与互联网房产数据相结合作为基础数据,通过ArcGIS软件生成住宅小区点数据的空间分布图,对大连市住宅小区容积率的时间演变和空间分布进行研究,并利用锡尔指数计算住宅小区容积率的空间差异量化测度指数,最后阐述住宅小区容积率空间差异的机制。结果表明：① 1992~2016年大连市住宅小区的数量在持续发展时期最多,平均容积率展现出波动上涨的趋势。② 区：大尺度包括冷炳荣住宅小区容积率整体上呈现出不均匀性和破碎性,局部又呈现出混乱性和复杂性,东部地区小区容积率分异比西部大。③ 中山区空间差异量化测度指数最高为0.831,甘井子区最低为0.125,西岗区与四区整体格局最为相近。极低等级容积率空间分异指数最高,容积率分异指数由两极向中间递减。大连市住宅小区容积率空间差异主要体现在区域内,其对研究区容积率空间分异影响较大。④ 住宅小区容积率空间差异的主要原因为下垫面性质对住宅小区建设的限制、区位的优良性对住宅类型的指向、城市规划对土地利用的导向、极差地租与容积率的相关性、小区建设成本对容积率的影响。 相似文献
18.
对福建省三明市格氏栲天然林及在其采伐迹地上营造的33年生格氏栲人工林和杉木人工林这3种林分的枯枝落叶层及粗木质残体物质化学组成进行研究．结果表明：在分解过程中3种林分枯叶和枯枝水溶性物质和纤维素含量不断下降,而枯枝中苯醇溶性物质和粗蛋白质含量有所上升．除半纤维素和纤维素外,3种林分粗木质残体水溶性物质、木质素和粗蛋白质含量均为L层〉F层,而苯醇溶性物质含量为L层〈F层．格氏栲天然林枯叶和枯枝水溶性物质、木质素、粗蛋白质、半纤维素和纤维素总贮量最高,而苯醇溶性物质总贮量以格氏栲人工林的最高．3种林分F层枯叶和枯枝有机物质的总贮量高于L层．与2种人工林相比,格氏栲天然林粗木质残体中各种有机物质贮量均最高． 相似文献
19.
David J. Milan 《Geomorphology》2012,138(1):319-328
Quantitative assessments of the impacts of extreme floods on channel morphology are rare. Real Time Kinematic (RTK) GPS surveys of a 500-m reach of the Thinhope Burn, an upland gravel-bed stream in the UK, taken in 2003 and 2004 permitted an assessment of geomorphic work whilst the channel was at steady-state. A large flood that occurred on 17 July 2007 resulted in a catastrophic impact to the Thinhope Burn valley floor. The reach was re-surveyed after the event in 2007, and again in 2008 and in 2011. Digital elevation models were produced from the survey data, which allowed the spatial patterns of erosion and deposition and volumetric changes between surveys to be established. A total of 5202 m3 of deposition and 2125 m3 of erosion was recorded in the reach following the flood event. Field walking of the catchment and comparison of aerial photographs for 2003 and 2007 suggested that most of the material mobilised had originated from existing sediment held in terraces and paleoberms on the valley floor. Although slope failures were evident, including peat slides in the headwaters, delivery of sediment from coupling zones to the channel was thought to play a secondary role in the geomorphic response shown by the channel. Similarly, large volumes of erosion and deposition were found after resurveys in 2008 and 2011, suggesting that the system was still in its relaxation phase. The results obtained in this investigation coupled with historical information on the flood history of Thinhope Burn dating back to 1766 suggested that rare large floods are the geomorphically effective flows in the catchment. 相似文献
20.
Mike Hilton Nick Harvey Andrew Hart Kris James Chris Arbuckle 《The Australian geographer》2006,37(3):313-334
Marram grass (Ammophila arenaria) and sea-wheat grass (Thinopyrum junceiforme) have been introduced to Australia and New Zealand. This study examines the morphology of incipient foredunes and established foredunes associated with these species at two sites, Mason Bay in southern New Zealand, and the Younghusband Peninsula in South Australia. Both species invaded the existing foredunes very rapidly. In both cases the antecedent topography comprised relatively sparsely vegetated, irregular foredunes. Invasion resulted in continuous, regular, evenly vegetated foredunes. At Mason Bay a massive foredune has formed since 1958, in conjunction with Ammophila. Thinopyrum has formed an incipient foredune, with a ramp or terrace morphology, along the Younghusband Peninsula, South Australia. In both cases gaps in the former foredune have been closed and the indigenous foredune vegetation has been displaced. Both species may decrease the frequency and severity of blowout development. They are likely to be resilient to aeolian processes of sedimentation compared with dunes formed by indigenous species. Ammophila survives burial, is tolerant of drought and is resistant to erosion associated with storm surge and high waves. Thinopyrum is very tolerant of salinity. These species may adversely affect the long-term development of coastal barriers by inhibiting transgressive dune development. 相似文献