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Bedded trona (Na2CO3·NaHCO3·2H2O) in the lacustrine Green River Formation of Eocene age in the Green River Basin, southwest Wyoming, constitutes the largest known resource of natural sodium carbonate in the world. In this study, 116 gigatons (Gt) of trona ore are estimated to be present in 22 beds, ranging from 1.2 to 11 meters (m) in thickness. Of this total, 69 Gt of trona ore are estimated to be in beds containing less than 2 percent halite and 47 Gt in beds containing 2 or more percent halite. These 22 beds underlie areas of about 130 to more than 2,000 km2 at depths ranging from about 200 m to more than 900 m below the surface. The total resource of trona ore in the basin for which drilling information is available is estimated to be about 135 Gt.Underveloped trona beds in the deeper southern part of the basin may be best developed by solution mining. Additional unevaluated sodium carbonate resources are present in disseminated shortite (Na2CO3·2CaCO3) in strata interbedded with the trona and in shallow sodium carbonate brines in the northeast part of the basin. Estimates of the shortite and brine resources were not made. 相似文献
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Kota Katsuki Yasushi Miyamoto Kazuyoshi Yamada Hiroyuki Takata Keiko Yamaguchi Daisuke Nakayama Hugo Coops Hidenobu Kunii Ritsuo Nomura Boo-Keun Khim 《Journal of Paleolimnology》2008,40(4):1115-1125
Lake Nakaumi, southwest Japan, is an enclosed lagoon characterized by polyhaline and halocline conditions. Since the last
century, its ecological state has been altered by eutrophication. We used a paleolimnological approach and studied multiple
proxies, including chemical compounds, diatoms, foraminifera and molluscs, to infer the eutrophication history of the ecosystem.
Eutrophication in Lake Nakaumi was associated with several factors, including increased nutrient loading, input of herbicides,
and dike building since the 1920s. The ecological condition of this lake was divided into several stages that reflect the
eutrophication process after the 1940s. A catastrophic “regime shift” from a clear state with aquatic vegetation to a turbid
one with phytoplankton occurred in the early 1950s. Environmental degradation in the Honjo area, a part of Lake Nakaumi, was
attributed primarily to physical changes caused by the construction of an enclosing dike. Eutrophication occurred almost simultaneously
with the physical changes to the Honjo area in the 1970s. Until recently, no regime shift was observed in this area, though
the core-top sediments show possible symptoms of incipient change. 相似文献
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F. Masson A. W. B. Jacob C. Prodehl P. W. Readman P. M. Shannon A. Schulze & U. Enderle 《Geophysical Journal International》1998,134(3):689-705
A wide-angle seismic profile across the western peninsulas of SW Ireland was performed. This region corresponds to the northernmost Variscan thrust and fold deformation. The dense set of 13 shots and 109 stations along the 120 km long profile provides a detailed velocity model of the crust.
The seismic velocity model, obtained by forward and inverse modelling, defines a five-layer crust. A sedimentary layer, 5–8 km thick, is underlain by an upper-crustal layer of variable thickness, with a base generally at a depth of 10–12 km. Two mid-crustal layers are defined, and a lower-crustal layer below 22 km. The Moho lies at a depth of 30–32 km. A low-velocity zone, which coincides with a well-defined gravity low, is observed in the central part of the region and is modelled as a Caledonian granite which intruded upper-crustal basement. The granite may have acted as a buffer to northward-directed Variscan thrusting. The Dingle–Dungarvan Line (DDL) marks a major change in sedimentary and crustal velocity and structure. It lies immediately to the north of the velocity and gravity low, and shows thickness and velocity differences in many of the underlying crustal layers and even in the Moho. This suggests a deep, pre-Variscan control of the structural development of this area. The model is compatible with thin-skinned tectonics, which terminated at the DDL and which incorporated thrusts involving the sedimentary and upper-crustal layers. 相似文献
The seismic velocity model, obtained by forward and inverse modelling, defines a five-layer crust. A sedimentary layer, 5–8 km thick, is underlain by an upper-crustal layer of variable thickness, with a base generally at a depth of 10–12 km. Two mid-crustal layers are defined, and a lower-crustal layer below 22 km. The Moho lies at a depth of 30–32 km. A low-velocity zone, which coincides with a well-defined gravity low, is observed in the central part of the region and is modelled as a Caledonian granite which intruded upper-crustal basement. The granite may have acted as a buffer to northward-directed Variscan thrusting. The Dingle–Dungarvan Line (DDL) marks a major change in sedimentary and crustal velocity and structure. It lies immediately to the north of the velocity and gravity low, and shows thickness and velocity differences in many of the underlying crustal layers and even in the Moho. This suggests a deep, pre-Variscan control of the structural development of this area. The model is compatible with thin-skinned tectonics, which terminated at the DDL and which incorporated thrusts involving the sedimentary and upper-crustal layers. 相似文献
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日本国际旅游业的特点及新动向 总被引：3，自引：0，他引：3
日本的国际旅游业在世界旅游业发达国家中独具特色,20世纪60年代为界,日本旅游业经历了以入境游为主到以出境游为主的变化,出境游大大超过入境游。本文在介绍和分析日本国际旅游业的发展变化过程及其主要特征的基础上,对新世纪前后日本国际旅游业发展的新动向作了简要介绍分析。 相似文献
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黔西南脆弱喀斯特生态环境空间格局分析 总被引：57，自引：3，他引：54
西南喀斯特地区是我国四大生态脆弱带之一。黔西南具有典型的喀斯特生态环境,是西部大开发中生态环境的重点治理区。长期以来,由于人类不合理的开发利用使得喀斯特地区出现了严重的土地石漠化、土壤侵蚀以及森林生态系统退化等生态问题,制约着地区生态-经济的持续发展。本文根据已有的研究成果,在GIS技术的支持下,分析了研究区内主要生态退化问题的现状和空间格局及其影响因素,运用空间叠加分析功能,构建了生态脆弱度指标,并将研究区分为四个亚区,为生态环境治理提供科学依据。 相似文献
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This paper describes the morphology of near-horizontal basalt and calcarenite shore platforms around Lord Howe Island as well as the lithological and process environment in which they occur. The morphology of platforms around the island is highly varied. For instance, they occur at a wide range of elevations between low-tide level and several metres above the highest tides, and their width ranges between just a few metres to over 100 m. However, common to most platforms is that they have near-horizontal surfaces that terminate abruptly in a steep scarp at their seaward edge. Correlations indicate that the variability in platform elevation and width is attributable to variability in key parameters of erosion, such as rock resistance and shoreline water depth. Whereas wider platforms occur in rocks of lesser resistance, platform elevation is shown to increase both as rock resistance and the depth of water at the shoreline increases. Wave exposure has a significant control on platform width in some instances, but an over-arching relationship was not detected. Most platforms around the island appear to have developed over the Holocene and a conceptual model is proposed to account for the varied morphology of platforms that have developed over this period. Resistant plunging cliffs occur along about 18% of the rocky coastline of Lord Howe Island and represent the starting point for the model. Where cliffs have yielded to wave erosion platforms have been initiated at an elevation controlled predominantly by rock resistance and shoreline water depth. At Lord Howe Island narrow platforms up to about 20 m wide in exposed locations generally occur about 4 to 6 m above high tide level, and have apparently been subject to very infrequent erosion. Shore platforms about 20 to 40 m wide have generally formed in less resistant rocks, are somewhat lower at about 2 to 3 m above high tide level, and have been subject to more frequent erosion over the Holocene. Most basalt platforms around the island fall within these first two categories, but there are some instances of platforms about 50 m wide. These platforms have formed in rocks of comparatively low resistance and are relatively low in elevation occurring close to the level of high tide. An interesting feature of some of these wide platforms is that, unlike the morphology of narrower platforms, raised ramparts sometimes occur on their outer edge. 相似文献
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沙丘内部沉积构造保存了沙丘动力演变过程的重要信息。以古尔班通古特沙漠西南缘固定、半固定新月形沙丘区为研究区域,利用探地雷达在春、秋两季对固定、半固定新月形沙丘内部构造进行探测,获取了不同规模形态的固定、半固定新月形沙丘深约8 m的内部构造图像信息。通过图像增益处理、解译和对比分析表明：（1） 古尔班通古特沙漠固定、半固定新月形沙丘共有5种沙丘内部构造雷达相,即高倾角斜层理、楔状交错层理、上凸形交错层理、低倾角-近水平层理和块状层理,其中前4种主要分布在3~5 m的浅层,而块状层理主要分布在4~5 m以下的深度。（2） 高倾角斜层理、楔状交错层理主要分布在高大新月形沙丘（链）的迎风坡上部和丘顶地带,前者为背风坡前积层埋藏而成,反映高大新月形沙丘迎风坡上部和丘顶风沙活动较频繁,沙丘“固身缩顶”后埋藏的前积纹层因风蚀而出露,后者为迎风坡风蚀坑和风蚀槽中由风沙流充填而成的构造或在丘顶风向的季节性变化形成的构造。（3） 与灌丛沙丘相关的上凸形交错层理广泛分布在新月形沙丘的迎风坡中下部,在背风坡也有局部出现,表明灌丛沙丘在沙丘表层的风沙过程中占有重要地位;而深部的块状层理可能是早期风积层受到强烈的生物扰动,原生层理消失而产生。（4） 以上沙丘内部构造的类型与组合分布特点,反映了研究区新月形沙丘总体上趋于稳定或衰退状态,这与现代沙丘“固身缩顶”的地貌变化特征相一致。例如,迎风坡中上部和丘顶常见风蚀槽,背风坡因坡度变缓、前积层发育趋缓,现代风沙活动主要集中于新月形沙丘的上部和丘顶等。由此可见,研究区固定、半固定新月形沙丘内部构造及其组合分布特征异于流动新月形沙丘,也与半个多世纪以来北疆沙漠气候变暖变湿、平均风速减弱、植被盖度增加的区域自然地理环境变化趋势有一定的吻合性。 相似文献
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《Geomorphology》2005,64(1-2):117-132
Aeolian activity on the crests of linear dunes in the arid southwest Kalahari Desert is primarily controlled by vegetation cover. Cover is temporally variable in response to rainfall, with mobility index (MI) values and field based studies demonstrating the dynamic nature of aeolian processes in this dunefield. Landsat TM data for a drought (1984) and wetter (1993) year were analysed for two subscenes in the dune field, one for a pastoral landscape and one for a conservation area, to investigate the spatial dynamics of dune activity, using the empirically determined 14% cover threshold as the limit to crestal aeolian activity. TM band 3 data were found to best represent vegetation cover, including senesced material, at the end of the dry season, the period when the potential for aeolian activity is normally high due to the wind strength at this time. The extent of 0–14% cover areas ranged from 10% (1984) to 3% (1993) for the pastoral area and 16% (1984) to 6% (1993) for the conservation landscape. The wetter (1993) image residuals have different spatial characteristics in the two subscenes, with bare active dunes in the pastoral lands associated with locations of livestock pressure and those in the conservation area related to natural fire events. The study demonstrates the spatial dynamics of temporally variable linear dune activity in the southwest Kalahari, and also shows that areas devegetated by drought can recover sufficient vegetation in wet years to limit the spatial extent of aeolian transport on dune crests. 相似文献
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Antecedent rainfall and short-term intense rainfall both contribute to the temporal occurrence of landslides in British Columbia. These two quantities can be extracted from the precipitation regimes simulated by climate models. This makes such models an attractive tool for use in the investigation of the effect of global warming on landslide frequencies.In order to provide some measure of the reliability of models used to address the landslide question, the present-day simulation of the antecedent precipitation and short-term rainfall using the daily data from the Canadian Centre for Climate Modelling and Analysis model (CGCM) is compared to observations along the south coast of British Columbia. This evaluation showed that the model was reasonably successful in simulating statistics of the antecedent rainfall but was less successful in simulating the short-term rainfall.The monthly mean precipitation data from an ensemble of 19 of the world's global climate models were available to study potential changes in landslide frequencies with global warming. Most of the models were used to produce simulations with three scenarios with different levels of prescribed greenhouse gas concentrations during the twenty-first century. The changes in the antecedent precipitation were computed from the resulting monthly and seasonal means. In order to deal with models' suspected difficulties in simulating the short-term precipitation and lack of daily data, a statistical procedure was used to relate the short-term precipitation to the monthly means.The qualitative model results agree reasonably well, and when averaged over all models and the three scenarios, the change in the antecedent precipitation is predicted to be about 10% and the change in the short-term precipitation about 6%. Because the antecedent precipitation and the short-term precipitation contribute to the occurrence of landslides, the results of this study support the prediction of increased landslide frequency along the British Columbia south coast during the twenty-first century. 相似文献
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在鄱阳湖西南缘,风成砂质堆积的下风向,有厚层黄棕壤发育,OSL年代显示,为末次冰期风沙和风尘堆积。在厚田—打鼓岭断面,对沙山到黄棕壤的沉积物粒度并结合地貌学进行分析,发现：沿现代冬季风方向（NE 30°）自东北向西南,地表沉积相为沙—沙黄土—粘黄土逐渐过渡,粒度组成和粒度参数表现出从北而南的系统性变化,显示搬运动力和物源均单一且稳定;粒度参数与物源地的距离,服从对数函数分异模式,在约20km范围之内,变化最剧烈,之后渐趋平稳,20 km是碎屑分选的特征距离。研究结果给出了鄱阳湖西南存在风沙—风尘堆积体系的证据,并揭示了近源风成堆积沉积指标的变化规律,可为粉尘堆积的物源示踪提供相关理论参考。 相似文献
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选用1962—2017年（10月~次年5月）西南地区（四川、贵州、云南和重庆市）90 个地面气象观测台站的逐日降水和日平均气温实测气象要素资料,运用综合气象干旱指数[WTBX](CI)[WTBZ]统计出西南地区累计干旱日数和频次,并分析两者近56 a来的时空变化特征,再挑选其高、低值年进行大气环流形势讨论,最后制作差值图（均为高值年减低值年）与相关场构造的图进行比较。研究结果表明：累计干旱日数和频次均呈逐渐降低的趋势;两者的年代距平在20世纪60年代~80年代同为正,而在20世纪90年代同为负,其后21世纪初两者距平则相反;累计干旱日数具有5 a和9 a的年际周期变化,12 a的年代际周期,干旱频次具有8
a左右的年际周期和20 a的年代际周期;两者均在四川西部地区和云南中北部为大值中心,云南西部、重庆和贵州中东部为小值中心;高、中和低层的环流形势也缺少水汽和系统抬升等配置关系。 相似文献
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PDSI及sc_PDSI干旱指数在中国西南地区适用性分析 总被引：2，自引：1，他引：1
西南地区是中国干旱灾害频发地区,且在全球变暖背景下,干旱发生的频率和程度都有所增加,对农业生产和水资源安全造成威胁。帕默尔干旱强度指数（PDSI,Palmer Drought Severity Index）及在其基础上发展而来的自适应帕默尔干旱强度指数（sc_PDSI,self-calibrating Palmer Drought Severity Index）作为较成熟的干旱监测指标已得到广泛应用。本文利用土壤可含水量（AWC,Available Water Holding Capacity）地理空间模型中土种与AWC的对应关系,反演出西南地区更高分辨率的AWC分布,并采用中国西南70站温度月均值、月累积降水数据,分别计算了PDSI指数及sc_PDSI指数,进而比较分析两种指数的时间变化特征及统计分布性质,探讨二者在西南地区对干旱监测的适用性。结果表明：（1）PDSI与sc_PDSI均反映了西南地区在1965—2010年变干的趋势,但PDSI时间序列振动幅度更大;（2）PDSI的频率分布出现“翘尾”现象,监测到的极端干旱/湿润事件的发生频率高于严重干旱/湿润事件,而sc_PDSI的频率分布则更接近于正态分布;（3）两种指数对2009/2010年西南地区干旱事件的监测结果表明,sc_PDSI对干旱落区和干旱级别的监测均一定程度上优于PDSI,与土壤湿度结果更为接近,而PDSI更易对旱情估计过重;（4）虽然整体上sc_PDSI对PDSI具有一定的调整作用及一定的优越性,但在个别区域（如热带季风气候）并没有体现出调整效果,应用时应当考虑区域因素。 相似文献
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西南地区山洪灾害时空分布特征及其影响因素 总被引：8，自引：1，他引：7
山洪灾害时空特征和影响因素是山洪评估与管理的重要内容。根据1960-2015年中国西南地区历史山洪资料,采用线性回归、标准差椭圆、空间自相关和Logistic回归模型,深入分析了西南地区山洪灾害时空分布特征及其影响因素。结果表明：① 西南地区年度山洪灾害频次呈指数增长,年际变化呈现出稳定（1960-1980年）、缓慢波动增加（1981-1998年）、快速增加（1999-2015年）3个阶段;月际特征明显,山洪主要发生在每年6-8月,尤以7月频次最高;② 西南地区山洪灾害空间差异性显著,灾害高密度区主要集中于滇中高原地区、四川盆地和周边山地单元,山洪灾害数量分布呈显著的空间正相关,空间集聚特征明显（Moran's I指数为0.127、Z = 5.784、P = 0.007）;③ 西南地区历史灾害点的重心在年内存在明显的向正西方向移动的趋势,年内标准差椭圆转角均逐渐弱化,长轴逐渐变长,短轴逐渐变短;④ 降雨因子对山洪的影响度最高,人类活动因子次之,地表环境因子最低,降雨因子中1 h降雨量对山洪的影响最强,优势比值达到3.654。研究结果可为西南地区山洪灾害形成机理、监测预警研究,实施防灾减灾措施等提供科技支撑。 相似文献
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Mima-type mounds in southwest Missouri: Expressions of point-centered and locally thickened biomantles 总被引：1，自引：0，他引：1
Mima-type mounds, formed in gravelly soils of the Diamond Grove Prairie Natural Area near Joplin, Missouri, are the focus of this study. Emphasis is on the spatial and morphological aspects of the mounds, and more particularly on the analysis of mound soils and gravel distributions as a means for shedding light on mound origins in this region. The results strongly suggest that hierarchically dominant point-centered bioturbation by small vertebrates is the mode of mound genesis. Pocket gophers (Geomys bursarius), aided by other biota, create mounds as they burrow in residual gravelly soils that have evolved dense, relatively impermeable claypans that perch water during wet periods. Although pocket gophers do not presently inhabit the Diamond Grove area, evidence of past occupation, along with laboratory and field data, support them as the dominant role in forming the mounds. We conclude that these mounds are expressions of point-centered and locally thickened biomantles. Various subsidiary processes such as aeolian inputs, water erosion, and physical and chemical weathering also have genetically impacted Diamond Grove mounds. 相似文献
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腾格里沙漠西南缘地下水水化学形成特征及演化 总被引：6，自引：2，他引：4
以邓马营湖区为核心,对腾格里沙漠西南缘地下水数据进行水文地球化学特征分析,并运用PHREEQC2.0软件反向模拟沿运移路径地下水的补给机理及演化过程。结果显示:受水文地质条件制约,从山前洪积扇地下水的补给区深入腾格里沙漠过渡带再到邓马营湖区中深层地下水,水化学类型从HCO3-—Ca2+—Mg2+型过渡为Cl-—SO24-—Na+—Mg2+型再过渡到HCO3-—SO42-—Na+型。其影响因素基本包括:溶滤与蒸发浓缩作用、阳离子交换吸附作用、以及微弱的混合作用和地下水补给水源水化学成分控制。矿物饱和指数以及反向水文化学地球化学模拟的结果显示,由西南向东北沿水流方向各物质溶解沉淀情况复杂,除斜长石与方解石外,岩盐、石膏、白云石等浓缩沉淀显著,表明蒸发浓缩作用控制强烈。 相似文献