Changing of the guards: Detrital zircon provenance tracking sedimentological reorganization of a post-Gondwanan rift margin

Understanding the development of sedimentary systems during continental rifting is important for tracking environmental change and lithospheric processes. Conceptual models have been developed for the sourcing, routing and facies architecture of sediments in rift-settings, driven in part by quantitative sediment tracking. Here, we present laser ablation split-stream detrital zircon U/Pb geochronology and Hf-isotopes for post-rift (Cretaceous-Paleogene) clastic sediments from Ocean Drilling Program (ODP) wells and Plio-Pleistocene palaeoshoreline material, from the southern margin of Australia. Provenance results are contextualized through comparison with well-characterized source regions and regional pre- and syn-rift sediment reservoirs to track changes associated with Australia-Antarctica separation during East Gondwana break-up. The provenance character of the post-rift sediments studied are distinct from pre-existing sediment reservoirs and demonstrate termination of previously stable sediment routing systems and a dominance of local basement of the Proterozoic Madura and Coompana provinces (~1.2 Ga and CHUR-like Hf-signatures; Moodini Supersuite) in offshore ODP wells. A composite post-rift Cretaceous?-Eocene sample in the easternmost well expresses characteristic Phanerozoic zircon age signatures associated with source regions in eastern Australia that are interpreted to reflect inversion in the Ceduna Sub-basin to the east. Detrital zircon signatures in Plio-Pleistocene palaeoshoreline sediment are also relatively distinct, indicating derivation from coastal erosion in the Leeuwin Complex (~0.5 and 0.7 Ga subchondritic grains) and Albany–Fraser Orogen (~1.2 Ga subchondritic grains) several hundred, to over a thousand kilometers to the west. Collectively, results highlight the fundamental geological processes associated with rifting that dramatically change the character of sediment provenance via (a) isolation of pre-existing primary and secondary sources of detritus, (b) development of new source regions in basin compartmentalized highs and localized fault scarps, and (c) establishment of marine and coastal currents that redefine clastic sediment transport.     

基于AHP_熵权法的孟印缅地区洪水灾害风险评估

孟印缅三国地处亚热带与热带季风气候区,因自然条件制约,洪涝灾害频繁发生,对“孟中印缅经济走廊”建设将会带来重大影响。开展孟印缅地区的洪水风险评估可为“孟中印缅经济走廊”的建设安全提供必要的信息和科技支撑。利用1980—2016年的降水数据,结合河网、数字高程和土地利用等数据,选取雨季降雨量、暴雨天数、高程、坡度、河网密度、植被覆盖度、土壤可蚀性、人口密度、地均GDP和土地利用10个指标,采用层次分析法和AHP_熵权法对孟印缅地区的洪水灾害风险分布进行了比较研究。研究表明：孟印缅地区高风险区和较高风险区分别占总面积的1.05%和28.76%,高风险区主要分布在印度北部的恒河平原、印度东北部的阿萨姆邦、孟加拉国大部分地区和缅甸南部。受自然、人口和经济条件的制约,孟加拉国是孟印缅三国中洪水风险最高的国家,高风险区和较高风险区分别占总面积的10.61%和65.87%。层次分析法和AHP_熵权法结果间的比较表明,后者比前者识别出更大范围的洪水高风险区。本研究为中国开展周边国家自然灾害的风险评估提供了有效的方法,有助于推进国家孟中印缅经济走廊的建设。     

Carbon isotopes and lignin phenols for tracing the floods during the past 70 years in the middle reach of the Changjiang River

The Lake Tian E Zhou(TEZ,an oxbow lake)was formed during the rerouting of the Changjiang River in 1972,with strong influences from the main river channel and flood events.Herein,a sediment core was collected from the Lake TEZ for the measurements of carbon isotopes and biomarkers,including stable carbon isotopes(δ13C),radiocarbon composition(?14C),and lignin phenols,as well as lead-210 to reconstruct recent heavy flood events over the past 70 years.At the 24–26 cm interval,the sediment contained the highest OC%,TN%,and lignin phenols content,as well as significantly depleted 13C but enriched 14C,corresponding to the extreme flood event in 1998.In addition,statistics from t-test showed that lignin phenols normalized to OC(Λ8),the concentration of 3,5-dihydroxy benzoic acid(3,5-BD),and the ratio of p-hydroxy benzophenone to total hydroxyl phenols(PHB/HP)were all significantly different between the layers containing flood deposits and the layers deposited under normal non-flood conditions(p<0.05).These results indicate that the later three parameters are highly related to flood events and can be used as compelling proxies,along with sediment chronology,for hydrological changes and storm/flood events in the river basin and coastal marine environments.     

Response of a hypersaline salt marsh to a large flood and rainfall event along the west coast of southern Africa

The Orange Estuary lost 27% (276 ha) of its wetland area near the mouth as a result of bad management practices during the 1980s. The salt marsh has been unable to recover over the last 20 years because of the persistently high soil and groundwater salinity. In 2006, a 1 in 5 year flood occurred that completely covered the desertified salt marsh and floodplain with freshwater. The flood was followed by an above average (>45 mm) winter rainfall. Soil and groundwater sampled in April and August 2004 were compared with 2006 data to quantify the impact of the flood and rainfall event. It was hypothesised that the two freshwater events would significantly reduce the soil and groundwater salinity. However, the results showed no significant difference in sediment electrical conductivity throughout the soil profile over the four sampling periods. Soil moisture and organic content however increased significantly after these events in the surface soil layer. The flood deposited silt and scoured sand from the surface layers in significant quantities. The depth to groundwater in the desertified marsh retained a similar pattern after the flood despite 15 cm changes in depth in places. In 2004 a clear groundwater electrical conductivity gradient was present extending from the less saline north part of the marsh (0–15 mS cm⁻¹) to the central part (120–135 mS cm⁻¹) and decreasing again towards the south (60–75 mS cm⁻¹). The flood served to even out the groundwater salinity across the desertified marsh (60–90 mS cm⁻¹). The flood and high rainfall had a limited impact on the soil and groundwater characteristics. The few significant changes that were recorded were mostly restricted to the surface soil layers and on a small spatial scale. The rainfall did however create numerous pools of low salinity (<60 mS cm⁻¹) water on the marsh surface that provided a brief opportunity for salt marsh seeds to germinate. A further benefit of the flood was the increased tidal reach into the desertified marsh importing freshwater from the river mouth and exporting salt. Despite these responses it is unlikely that the hypersaline salt marsh will revegetate naturally. Human intervention is needed to ensure the rehabilitation of this important Ramsar site.     

城市暴雨积水模拟方法分析及研究

在总结目前常用城市暴雨积水模拟方法的基础上,从水体由高到低的运动机理着手,将基于数字地形分析技术的路径算法引入城市暴雨积水模拟,并考虑到管网汇流及城市地形因素,给出数据修正与算法改进的具体方法。     

GIS技术在长江防洪调度系统中的应用

简要介绍GIS的概念和基本功能,结合长江防洪调度系统的开发,探讨GIS及其组件在洪水预报调度领域中的应用。     

三峡与葛洲坝水库泄洪冲沙对宜昌台形变观测的干扰

分析三峡水库与葛洲坝水库蓄水、泄洪、冲沙的非固体潮时、空、强、频特征,研究其对宜昌台地形变观测的影响。     

漫灌条件下内蒙孪井灌区土壤水分动态变化特征

根据内蒙孪井灌区土壤水分观测资料,本文讨论了漫灌条件下该区土壤水分的动态变化规律.由于观测期间降雨对该区影响很小,主要分析了春灌期、灌溉间隔期和作物生长期土壤水分的变化特点.春灌期,灌溉水主要补给上层砂壤土,对下层土壤的补给相对较小;经过2次灌溉过后,土壤含水率不断升高.就蓄水能力而言,粘砂土的蓄水能力最强,砂壤土次之,灌水后水分主要滞留在这2层.结合灌溉渗漏量分析,研究认为,该区灌溉模式使得灌溉渗漏量较大,造成水资源浪费的同时还会引起地下水位上升,致使灌区下游土壤次生盐渍化加重.因此,采用灌溉量较小的喷灌、滴灌等方式,可以避免产生深层渗漏,节约水资源.     

BGP协议在CERNET用户接入中的应用

通过对静态路由和动态路由的考察分析,并结合CERNET用户接入现状,提出将BGP协议应用到CERNET用户接入中,采用BGP协议和静态路由相结合的混合路由方式,是1种全新的CERNET用户接入路由模式。     

一种具有多维收敛能力的内容寻址网络

CAN（Content-Addressable Network）在d维的虚拟空间中利用分布式哈希表（Distributed Hash Table,DHT）来定位资源。CAN提供了一套比较有效的路由算法,但是节点能力的异构性并没有被考虑到算法中。这里提出了一种CAN路由的改进算法,通过扩展CAN邻居的定义和重构路由表等方式,使节点的异构性被考虑在路由算法中。同时该算法使得定位消息能从多维方向向着目标区域收敛,有效地提高了CAN路由消息的效率。