基于地理本体建模的河流阶地识别方法研究——以汉中盆地为例

目前尚缺乏自动提取河流阶地的有效方法。提供了一种用于自动识别和提取河流阶地的方法。首先借助ASTER GDEM与Landsat5 TM数据,以汉中盆地为例,依托地理本体对河流阶地进行建模;然后在此基础上通过基于对象的影像分类技术对其进行提取。在基于对象分类技术中使用地理本体建模方法,能够有效地自动识别和提取河流阶地。     

Stratigraphy of Beds I through IV, Olduvai Gorge, Tanganyika

Bed I at Olduvai Gorge is a conformable sequence of lava flows and varied sedimentary deposits that extend upward from a welded tuff overlying the Precambrian basement to the top of a widespread marker bed. Bed II is a sequence of lacustrine clays and laterally equivalent fluvial, eolian, and pyroclastic deposits. Bed III is made up of alluvial deposits and a laterally equivalent assemblage of fluvial, lacustrine, and eolian beds. Bed IV can be subdivided into a lower unit of fluvial clays, sandstones, and conglomerates, and an upper unit of eolian tuffs. The climate was relatively dry throughout much of the time that these beds were deposited, and semidesert or desert conditions may have prevailed at least twice. Tectonic movement seems to have taken place between the deposition of Beds III and IV.     

Geologic framework of nonmarine cretaceous-tertiary boundary sites, raton basin, new Mexico and colorado

Iridium concentrations are anomalously high at the palynological Cretaceous-Tertiary boundary in fluvial sedimentary rocks of the lower part of the Raton Formation at several localities in the Raton Basin of New Mexico and Colorado. The iridium anomaly is associated with a thin bed of kaolinitic claystone in a discontinuous carbonaceous shale and coal sequence.     

Rock avalanches caused by earthquakes: source characteristics

Study of a worldwide sample of historical earthquakes showed that slopes most susceptible to catastrophic rock avalanches were higher than 150 meters and steeper than 25 degrees. The slopes were undercut by fluvial or glacial erosion, were composed of intensely fractured rock, and exhibited at least one other indicator of low strength or potential instability.     

喀斯特山区不同母质（岩）发育的土壤主要重金属含量差异性研究

在贵州喀斯特山区采集了白云岩、石灰岩、钙质紫色砂页岩等9种母质(岩)上发育的土壤样品763个,测定了土壤主要重金属元素含量和土壤理化性质.对比分析表明,不同母质(岩)发育的土壤重金属含量具有很大的差异:钙质紫色砂页岩、石灰岩、河流冲积物等发育的土壤中镉、铬、汞的含量较高,而红色粘土、河流冲积物和石灰岩等发育的土壤中铅和砷的含量较高,砂岩发育的土壤中5种重金属元素的含量均为最低,其余母质(岩)发育的土壤中5种重金属元素的含量均介于上述之间.相关性分析结果表明,研究区域内土壤重金属镉、铬、汞、铅、砷的含量差异主要是由于成土母质(岩)的"遗传"差异性所致,土壤理化性质的变化是影响土壤重金属含量的次要因素.     

Altered river morphology in south africa related to the permian-triassic extinction

The Permian-Triassic transition in the Karoo Basin of South Africa was characterized by a rapid and apparently basin-wide change from meandering to braided river systems, as evidenced by preserved sedimentary facies. This radical changeover in river morphology is consistent with geomorphic consequences stemming from a rapid and major die-off of rooted plant life in the basin. Evidence from correlative nonmarine strata elsewhere in the world containing fluvial Permian-Triassic boundary sections suggests that a catastrophic terrestrial die-off of vegetation was a global event, producing a marked increase in sediment yield as well as contributing to the global delta(13)C excursion across the Permian-Triassic boundary.     

福建第四纪红土上发育土壤的富铝化特征

研究了福建分布在红土台地和不同比高河成阶地上的典型赤红壤和红壤的若干土壤化学特性,认为可按交换性Al~(3+),铝饱和度,ECEC的显著差异,将16个剖面划分成高级富铝化系列和中级富铝化系列2个组合,它们在地域分布上并不受传统水平地带性理论的控制。     

洞庭湖区土壤肥力的综合评价

以洞庭湖区生态地球化学调查数据为基础,采用模糊综合评价法,讨论了区域土壤肥力分布状况及影响因素.结果显示,洞庭湖区土壤肥力处于较高水平,但区域内土壤肥力存在差异,其中平原区河流冲积物区土壤肥力最高,丘岗山地区的红层、花岗岩等区土壤肥力较低;地质背景对土壤肥力有显著影响;土地利用类型对土壤微量养分影响最为显著,认为在合适的区域,以合理的耕种方式和有效地防止水土流失对培肥地力至关重要.     

Cambrian river terraces and ridgetops in central australia: oldest persisting landforms?

Fluvial sediments in paleovaileys cut in the Ashburton surface of the Davenport province of central Australia form terrace remnants that appear to retain their original depositional tops and have probably existed as subaerial landforms since their inception. Marine fossils in sediments conformable with the fluvial sediments near the southeast margin of the province give a Cambrian age for the terraces; the Ashburton surface forming the ridgetops between the paleovalleys is Cambrian or older.     

浑善达克沙地沙粒特征及其沉积环境

对浑善达克沙地进行野外考察和采集表层沙样,通过激光粒度仪测量其沙粒粒径,分析其内部不同区域沉积物粒度特征、空间分异规律和沉积环境,为治理该沙地提供理论依据。结果表明,浑善达克沙地内部不同区域表层沉积物粒度组成上有较大的差异,总体以细沙和中沙为主,平均含量分别为43.9%和34.72%;粉沙、极细沙、粗砂含量较少。中值粒径从西到东逐渐变细;分选系数为0.94Φ,分选性整体较差,沿盛行风向有变好的趋势;偏度和峰度均值分别为0.16和1.23。粒度频率曲线指示该沙地沉积环境多样,沉积过程复杂。中西部沙物质以河流及湖泊沉积为主;东部则主要分布风成沉积,其部分物质可能来源于沙地内部的河流碎屑物或更西部的河湖相沉积。     

Athabasca Valles, Mars: a lava-draped channel system

Athabasca Valles is a young outflow channel system on Mars that may have been carved by catastrophic water floods. However, images acquired by the High-Resolution Imaging Science Experiment camera onboard the Mars Reconnaissance Orbiter spacecraft reveal that Athabasca Valles is now entirely draped by a thin layer of solidified lava-the remnant of a once-swollen river of molten rock. The lava erupted from a fissure, inundated the channels, and drained downstream in geologically recent times. Purported ice features in Athabasca Valles and its distal basin, Cerberus Palus, are actually composed of this lava. Similar volcanic processes may have operated in other ostensibly fluvial channels, which could explain in part why the landers sent to investigate sites of ancient flooding on Mars have predominantly found lava at the surface instead.     

淮山药组培苗假植基质的初步研究

探讨淮山药组培苗假植的适宜基质,结果显示:不同基质对淮山药组培苗生长的影响不同,以处理Ⅰ生长最好,即泥炭土5∶珍珠岩3∶河沙2配比的基质较为适宜.     

Recycling of graphite during Himalayan erosion: a geological stabilization of carbon in the crust

At geological time scales, the role of continental erosion in the organic carbon (OC) cycle is determined by the balance between recent OC burial and petrogenic OC oxidation. Evaluating its net effect on the concentration of carbon dioxide and dioxygen in the atmosphere requires the fate of petrogenic OC to be assessed. Here, we report a multiscale (nanometer to micrometer) structural characterization of petrogenic OC in the Himalayan system. We show that graphitic carbon is preserved and buried in marine sediments, while the less graphitized forms are oxidized during fluvial transport. Radiocarbon dating indicates that 30 to 50% of the carbon initially present in the Himalayan rocks is conserved during the erosion cycle. Graphitization during metamorphism thus stabilizes carbon in the crust over geological time scales.     

Carbon-13 and carbon-14 abundances in alaskan aquatic organisms: delayed production from peat in arctic food webs

Inputs of terrestrial peat carbon to the nearshore Alaskan Beaufort Sea from erosion and fluvial transport are of the same magnitude as in situ primary production within 10 kilometers of shore. Nevertheless, carbon-13/carbon-12 ratios and carbon-14 abundances in marine organisms show that only small amounts of the terrestrial carbon are transferred beyond the microbial level. Freshwater organisms, however, are heavily dependent on peat, as shown by pronounced seasonal radiocarbon depressions in resident fish and ducks. Tundra ponds and lakes are areas where accumulated terrestrial peat carbon is apparently transferred to aquatic insect larvae and passed on to higher organisms. The lack of functionally analogous abundant marine prey organisms may explain why peat carbon is not efficiently transferred to apical food web species in the marine environment.     

Mediterranean moisture source for an early-Holocene humid period in the northern Red Sea

Paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the northernmost Red Sea were used to infer hydrological changes at the southern margin of the Mediterranean climate zone during the Holocene. Between approximately 9.25 and 7.25 thousand years ago, about 3 per thousand reduced surface water salinities and enhanced fluvial sediment input suggest substantially higher rainfall and freshwater runoff, which thereafter decreased to modern values. The northern Red Sea humid interval is best explained by enhancement and southward extension of rainfall from Mediterranean sources, possibly involving strengthened early-Holocene Arctic Oscillation patterns and a regional monsoon-type circulation induced by increased land-sea temperature contrasts. We conclude that Afro-Asian monsoonal rains did not cross the subtropical desert zone during the early to mid-Holocene.     

Evidence for precipitation on Mars from dendritic valleys in the Valles Marineris area

Dendritic valleys on the plateau and canyons of the Valles Marineris region were identified from Thermal Emission Imaging System (THEMIS) images taken by Mars Odyssey. The geomorphic characteristics of these valleys, especially their high degree of branching, favor formation by atmospheric precipitation. The presence of inner channels and the maturity of the branched networks indicate sustained fluid flows over geologically long periods of time. These fluvial landforms occur within the Late Hesperian units (about 2.9 to 3.4 billion years old), when Mars was thought to have been cold. Our results suggest a period of warmer conditions conducive to hydrological activity.     

Rapid late Pleistocene incision of Atlantic passive-margin river gorges

The direct and secondary effects of rapidly changing climate caused large rivers draining the Atlantic passive margin to incise quickly into bedrock beginning about 35,000 years ago. Measured in samples from bedrock fluvial terraces, 10-beryllium shows that both the Susquehanna and Potomac Rivers incised 10- to 20-meter-deep gorges along steep, convex lower reaches during the last glacial cycle. This short-lived pulse of unusually rapid down-cutting ended by 13,000 to 14,000 years ago. The timing and rate of downcutting are similar on the glaciated Susquehanna and unglaciated Potomac Rivers, indicating that regional changes, not simply glacial meltwater, initiated incision.     

Pollen and lignin records of late quaternary vegetation, lake washington

Analyses of lignin oxidation products and pollen for an 11-meter core from Lake Washington provide independent but similar reconstructions of the late Quaternary vegetation in the Puget Lowland. An exception is in sediments of the late Pleistocene where pollen percentages and influx values suggest conifer forest whereas lignin compositions suggest a treeless source region. This dissimilarity appears to result from different major provenances: eolian transport of pollen to the lake from adjacent or downstream drainage basins as opposed to fluvial transport of lignified plant debris only from the Lake Washington drainage basin.     

Evidence for persistent flow and aqueous sedimentation on early Mars

Landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in Mars Global Surveyor Mars Orbiter Camera and Mars Odyssey Thermal Emission Imaging System images. Evidence of distributary, channelized flow (in particular, flow that lasted long enough to foster meandering) and the resulting deposition of a fan-shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial, and potentially lacustrine, environments.     

The great tumaco, Colombia earthquake of 12 december 1979

Southwestern Colombia and northern Ecuador were shaken by a shal-low-focus earthquake on 12 December 1979. The magnitude 8 shock, located near Tumaco, Colombia, was the largest in northwestern South America since 1942 and had been forecast to fill a seismic gap. Thrust faulting occurred on a 280- by 130-kilometer rectangular patch of a subduction zone that dips east beneath the Pacific coast of Colombia. A 200-kilometer stretch of the coast tectonically subsided as much as 1.6 meters; uplift occurred offshore on the continental slope. A tsunami swept inland immediately after the earthquake. Ground shaking (intensity VI to IX) caused many buildings to collapse and generated liquefaction in sand fills and in Holocene beach, lagoonal, and fluvial deposits.