L'accident du Toulourenc : une limite tectonique entre la plate-forme provençale et le Bassin vocontien à l'Aptien–Albien (SE France)

The WNW–ESE trending Toulourenc Fault Zone (TFZ) is the western segment of the major Ventoux–Lure Fault Zone, which separates the Provençal platform from the Baronnies Vocontian Basin. The TFZ was subject to polyphased Mid-Cretaceous movements, during the Early Aptian and Middle–Late Albian times. The latter faulting episode generated conglomerates and olistoliths resulting from dismantled faultscarps cutting Barremian–Bedoulian limestones. The deformation is related to compressional wrench faulting (NE–SW sinistral faults; dextral component for the TFZ). It induced the uplift of the northwestern corner of the platform, as indicated by a mid-Cretaceous hiatus (Early Aptian pro parte to Early Albian) narrowly delimited in space. The opening of submeridian grabens within the platform favoured the northward transit of channelised coarse-grained Albian sands originating from a southern area. To cite this article: C. Montenat et al., C. R. Geoscience 336 (2004).     

Late Quaternary downcutting rates of the Qianyou River from U/Th speleothem dates, Qinling mountains, China

Dating deposits in caves formed by rivers may yield insight into rates and processes of bedrock incision. Three cave passages at different levels have developed in the walls of the Qianyou River valley in the Qinling mountains, south of the city of Xian, China. Twelve speleothem samples near the position of palaeowater tables in three cave passages are dated by the ²³⁰Th dating method. The results show that the river cut down at the rate of 0.23 ± 0.02 mm/yr from 358,000 ± 38,000 to 247,000 ± 28,000 yr ago, 0.19 ± 0.03 mm/yr from 247,000 ± 28,000 to 118,000 ± 19,000 yr ago, and 0.51 ± 0.08 mm/yr from 118,000 ± 19,000 yr ago until today. These fall very close to the glacial-interglacial transition following marine oxygen isotope stages 10, 8, and 6, respectively. The increase in downcutting rates during the interglacial period is consistent with warm, wet weather, increasing rates of erosion. This may lead us toward an underlying mechanism for modulating incision that is not in a direct response to the presence of headwater glaciers.     

Formation and shortening deformation of a back-arc rift basin revealed by deep seismic profiling, central Japan

The northern Fossa Magna (NFM) basin is a Miocene rift system produced in the final stages of the opening of the Sea of Japan. It divides the major structure of Japan into two regions, with north-trending geological structures to the NE of the basin and EW trending structures to the west of the basin. The Itoigawa-Shizuoka Tectonic Line (ISTL) bounds the western part of the northern Fossa Magna and forms an active fault system that displays one of the largest slip rates (4–9 mm/year) in the Japanese islands. Deep seismic reflection and refraction/wide-angle reflection profiling were undertaken in 2002 across the northern part of ISTL in order to delineate structures in the crust, and the deep geometry of the active fault systems. The seismic images are interpreted based on the pattern of reflectors, the surface geology and velocities derived from refraction analysis. The 68-km-long seismic section suggests that the Miocene NFM basin was formed by an east dipping normal fault with a shallow flat segment to 6 km depth and a deeper ramp penetrating to 15 km depth. This low-angle normal fault originated as a comparatively shallow brittle/ductile detachment in a high thermal regime present in the Miocene. The NFM basin was filled by a thick (>6 km) accumulation of sediments. Shortening since the late Neogene is accommodated along NS to NE–SE trending thrust faults that previously accommodated extension and produce fault-related folds on their hanging wall. Based on our balanced geologic cross-section, the total amount of Miocene extension is ca. 42 km and the total amount of late Neogene to Quaternary shortening is ca. 23 km.     

Pliocene and Quaternary regional uplift in western Turkey: the Gediz River terrace staircase and the volcanism at Kula

Along the upper reaches of the Gediz River in western Turkey, in the eastern part of the Aegean extensional province, the land surface has uplifted by 400 m since the Middle Pliocene. This uplift is revealed by progressive gorge incision, and its rate can be established because river terraces are capped by basalt flows that have been K–Ar and Ar–Ar dated. At present, the local uplift rate is 0.2 mm a⁻¹. Uplift at this rate began around the start of the Middle Pleistocene, following a span of time when the uplift was much slower. This was itself preceded by an earlier uplift phase, apparently in the late Late Pliocene and early Early Pleistocene, when the uplift rate was comparable to the present. The resulting regional uplift history resembles what is observed in other regions and is analogously interpreted as the isostatic response to changing rates of surface processes linked to global environmental change. We suggest that this present phase of surface uplift, amounting so far to 150 m, is being caused by the nonsteady-state thermal and isostatic response of the crust to erosion, following an increase in erosion rates in the late Early Pleistocene, most likely as a result of the first large northern-hemisphere glaciation during oxygen isotope stage 22 at 870 ka. We suggest that the earlier uplift phase, responsible for the initial 250 m of uplift, resulted from a similar increase in erosion rates caused by the deterioration in local climate at 3.1 Ma. This uplift thus has no direct relationship to the crustal extension occurring in western Turkey, the rate and sense of which are thought not to have changed significantly on this time scale. Our results thus suggest that the present, often deeply incised, landscape of western Turkey has largely developed from the Middle Pleistocene onwards, for reasons not directly related to the active normal faulting that is also occurring. The local isostatic consequences of this active faulting are instead superimposed onto this “background” of regional surface uplift. Modelling of this surface uplift indicates that the effective viscosity of the lower continental crust beneath this part of Turkey is of the order of 10¹⁹ Pa s, similar to a recent estimate for beneath central Greece. The lower uplift rates observed in western Turkey, compared with central Greece, result from the longer typical distances of fluvial sediment transport, which cause weaker coupling by lower-crustal flow between offshore depocentres and eroding onshore regions that provide the sediment source.     

长江干流主要营养盐含量的变化特征——1998~1999年日中合作调查结果分析

根据1998年和1999年秋季在长江干流从重庆至长江口进行的纵向采样和分析,对长江干流的各态氮、磷含量的沿江变化进行研究。从整体上了解长江干流的水质变化特性,特别是营养盐含量的分布状况。研究结果表明,长江干流的SS浓度很高,介于50~400 mg/l。TN、TP浓度分别在70~110 滋mol/L、2~25 滋mol/L之间,前者以NO3-N为主,后者以PTP为主,PO4-P含量仅占TP的10%~20%。DIN/PO4-P的比值在70~160之间,远高于浮游植物生长P限制值,表明长江口及临近海域中P可能是生物生命活动的主要限制因素。葛洲坝水库对SS、TP、TN、NH4-N、BOD、COD等水质有一定的净化作用。长江水体在通过各大城市以及两大湖泊时,BOD、NH4-N负荷的增加迅速,特别是通过重庆、武汉、南京、上海及洞庭湖和鄱阳湖之后尤为明显。N、P含量的上升与人口增长、生活污水排放量及流域内化肥施用量增加有关。洞庭湖和鄱阳湖水系以及周围的面源负荷,对长江流域的营养盐变动有很大的影响。     

黄河流域天然径流量突变性与周期性特征

突变性和周期性是水文时间序列的两个重要特征。黄河流域面积广阔，各区域水文水资源系统演变规律各不相同，它们的突变和周期变化及其形成的物理机制遍异，因此系统分析各区域水资源突变性和周期性特征及其影响机制具有重要意义。把黄河流域划分为15个区域，计算出各区域1951—1998年的年天然径流量系列。利用Mann-Kendall非参数检验方法检测黄河流域各区域年天然径流量的突变年份，结果表明各区域的突变年份不完全一致，主要在1953—1955年、1979—1983年、1991—1993年等发生了突变，这些突变与北半球气候突变具有一致性，且由于下垫面改变、人类活动等影响而复杂化。利用Morlet小波分析各区域年天然径流量的变化周期，发现主要存在3～4a、7～9a、11a的周期，形成这些周期的物理因子有太阳黑子、海—气相互作用和下垫面因素等。通过分析黄河流域主要产流区不同时段小波系数变化，发现20世纪80年代之后年径流量主要以短周期变化。     

描述黄河中下游河道横断面形态的新指标

描述河流横断面的窄深程度,无非是用来衡量它对过流能力和输沙能力的影响大小,及其在河流地貌方面的时空上的调整变化。回顾总结了以往描述横断面形态的常用指标,包括河相系数、宽深比,或湿周与平均水深的比值,指出这几种指标在描述黄河中下游河道时所存在的共同缺点:(1)缺乏物理意义;(2)不能真正代表断面的窄深程度;(3)明显的夸大了宽浅和窄深断面的差别。从表称流量的概念出发,作者认为,应该使用具有明确物理意义的等面积的表称流速来描述断面形态。如果用表称流速来衡量黄河下游河南和山东河道的断面形态的差别,就会发现,断面形态的不同,其对过流能力的影响不过1:2,远不象河相系数和宽深比所描述的达到1:6甚至1:11那样的悬殊程度;黄河下游河道主槽“多来多排”的主要影响因素是表称流速。     

金沙江流域(云南境内)山地灾害危险性评价

云南境内的金沙江流域是斜坡不稳定的敏感区,根据1988-2000年的区域调查和统计,区内发育山地灾害点1697处,其中流域面积大于1km2的泥石流沟808条,体积大于1×104m3的滑坡580处,体积大于1000m3的崩塌309处。用于山地灾害危险性评价的主要敏感因子包括岩土体类型、山坡坡度、降雨、土地利用、地震烈度和人类活动。在对这些因子进行了敏感性评价的基础上,应用GIS对敏感因子集成评价而产生了云南金沙江流域山地灾害危险性评价图。评价结果表明:高危险区面积占全区面积6464km2的8 77%,中危险区占全区总面积的41 51%,低危险区占41 12%,无危险区占8 60%。山地灾害危险性评价图可以帮助规划者或工程师在土地发展规划中选择最佳建设场所,以减轻灾害的影响。     

嘉陵江流域旅游开发

在研究嘉陵江流域旅游资源优势和开发现状的基础上，针对目前该流域旅游发展现状和存在的问题，提出了具体的应对措施，以期能为该流域的旅游开发提供参考。     

塔里木盆地南缘历史时期气候环境变化的过程与特征

根据塔里木盆地南缘具较高分辨率的湖沼相沉积物碳酸盐δ^13C和粒度等记录，恢复出2162-850BC期间为一相对稳定的温暖干旱时期，之后迅速转冷湿，湿润程度呈持续、阶段式增加，50 BC至500 AD期间呈现的显著冷湿特征于550 AD之后突变转暖干而结束。550 AD和1000 AD前后的具突变性质的气候事件在南疆地区近2．0ka的气候变化中具有重要意义，反映气候状况有过重大调整。850—1300AD期间(相当于中世纪温暖期)冷暖、干湿多变，但温暖特征并不明显。特别是1100—1200AD期间气候快速、频繁变化之后，奠定了本地区现代稳定干旱环境特征。区域对比表明，尼雅剖面记录的气候变化具有广泛的区域一致性。