龙门山南段青衣江阶地沉积物的化学风化特征及其意义

本文通过对龙门山南段青衣江阶地的研究, 尝试以常量元素所体现的风化特征, 来解决阶地对比的问题, 并取得了一定的进展。通过主量元素的分析, 发现CIA指标、 A-CN-K三角模型等, 在区分不同年龄的阶地有很好的效果, 而且沉积物砾石之间的基质颜色也一定程度地反映了新老关系。结合流域内更古老洪积扇的研究, 发现河流阶地在距今200ka内化学风化速度较稳定, 但更老的地貌面风化呈现非线性。另外, 在本文研究的600ka时间尺度内, 阶地风化速度与全球气候变化相关, 体现为冰期风化速度慢, 间冰期风化速度快, 并具一定的滞后效应。     

利用河流阶地约束活动逆冲- 褶皱构造变形速率的不确定性：以天山北麓为例

河流地貌，特别是河流阶地是新构造与构造地貌、活动构造研究的一个重要对象，常用来刻画下伏构造变形的速率与时空模式，但利用河流地貌约束构造变形速率存在潜在的不确定性。基于十多年在天山北麓开展的构造地貌研究，认为不确定性主要包括以下4个方面：① 与阶地定年策略有关的不确定性。对于晚更新世末—全新世的年轻阶地，利用阶地沉积顶部年龄和上覆堆积底界年龄分别约束得到的变形速率可能存在比较大的差异，本研究中这种差异为50%；对于更老阶地，用这两个年龄限定的变形速率差异不大。② 与阶地对比有关的不确定性。沿背斜走向，河流过程对构造活动（如背斜基岩抬升）的响应存在时间上的不同步性。因此，对于发育在同一背斜构造上的不同河流，用某条河流已定年阶地的年龄，基于河流间的阶地对比确定另一条河未定年阶地的年龄，可能会导致阶地年龄不可忽视的偏差，进而造成对变形速率及其时空模式的误判。③ 与河流阶地位相相关的不确定性。不同成因的阶地均能呈现特定的阶地位相（向下游收敛或发散），这不利于基于阶地拔河高度的上下游阶地对比，也不利于利用阶地探讨构造活动的空间特征。④ 对于跨背斜或者断层的地貌面，由于背斜翼部或断层下降盘相对构造下沉，早期形成的地貌面将被后期的沉积物埋藏，这增加了利用该地貌面准确刻画下伏构造变形特征的难度，相关工作也要求构造两侧的变形参考面为同级地貌面。以上不确定性在利用河流地貌刻画逆断裂- 褶皱构造变形特征的研究中需要予以注意。     

贵州普定碳酸盐岩上覆松散堆积物的沉积环境初探

通过对贵州省普定县马官地区不同地貌部位的4个剖面进行详细的粒度分析,把粒度参数以及频率曲线与各种沉积环境的特征进行对比,排除了河流沉积、风成沉积的可能性。研究区域各剖面的粒度分布特征表明其沉积环境属于碳酸盐岩溶蚀残余风化,同时还有坡面流水和地下水作用的参与。     

大渡河金川-巴底河段河流地貌特征研究

对大渡河中游金川-巴底河段水系格局、河谷形态、河流阶地及第四纪沉积物进行研究,分析河流地貌的发育特征、影响因素以及发育演化史,为区域稳定性评价提供依据。研究表明,该区域为具有夷平面的深切峡谷地貌区,发育三级夷平面和4~6级阶地,河流地貌发育经历三个阶段,河流地貌的形成与演化受构造、岩性影响明显。     

大渡河中游泸定-石棉段阶地特征及河谷发育史探讨

基于大渡河中游泸定一石棉河段野外观察和阶地沉积物研究,分析河流的发育特征,影响及其发育演化史。研究表明,该区存在多级构造裂点或岩性裂点,发育有三级夷平面和4～6级阶地,并对阶地沉积物的ESR年代测定,结合前人的阶地测年的数据,阐述了大渡河河谷第四纪的形成过程和青藏高原形成的响应。     

青藏高原北部不同地区河流和湖岸阶地的演化特征

把青藏高原北部空白区已完成的1∶25万区调成果报告中有关河流和湖岸地貌的剖面、实测数据提炼出来,将其位置点绘于同一张水系分布图上,然后根据不同位置、不同的剖面、不同的测试数据进行区域性对比研究,结果表明:①青藏高原北部昆仑山中部和东部地区,河谷、湖岸地貌都具有100kaBP、10kaBP、5～6kaBP的阶地,这3个时期东西部河谷、湖岸地貌的形成具有同步性;②昆仑山中部地区具有70kaBP的阶地,昆仑山东部地区具有50kaBP的阶地,这2个时期昆仑山东西部河流、湖岸地貌的形成不具有同步性。对该地区河流、湖岸地貌成因分析后认为,除气候作用外,河流阶地、湖岸阶地对高原北部的隆升具有一定的指示作用,表现为从西向东抬升速率逐渐减小,总体上同一地方从老到新抬升速率逐渐增加。     

青藏高原北部不同地区河流和湖岸阶地的演化特征

把青藏高原北部空白区已完成的1:25万区调成果报告中有关河流和湖岸地貌的剖面、实测数据提炼出来,将其位置点绘于同一张水系分布图上,然后根据不同位置、不同的剖面、不同的测试数据进行区域性对比研究,结果表明:①青藏高原北部昆仑山中部和东部地区,河谷、湖岸地貌都具有100 kaBP、10 kaBP、5～6 kaBP的阶地,这3个时期东西部河谷、湖岸地貌的形成具有同步性;②昆仑山中部地区具有70 kaBP的阶地,昆仑山东部地区具有50 kaBP的阶地,这2个时期昆仑山东西部河流、湖岸地貌的形成不具有同步性.对该地区河流、湖岸地貌成因分析后认为,除气候作用外,河流阶地、湖岸阶地对高原北部的隆升具有一定的指示作用,表现为从西向东抬升速率逐渐减小,总体上同一地方从老到新抬升速率逐渐增加.     

青藏高原北部不同地区河流和湖岸阶地的演化特征

把青藏高原北部空白区已完成的1:25万区调成果报告中有关河流和湖岸地貌的剖面、实测数据提炼出来,将其位置点绘于同一张水系分布图上,然后根据不同位置、不同的剖面、不同的测试数据进行区域性对比研究,结果表明:①青藏高原北部昆仑山中部和东部地区,河谷、湖岸地貌都具有100 kaBP、10 kaBP、5～6 kaBP的阶地,这3个时期东西部河谷、湖岸地貌的形成具有同步性;②昆仑山中部地区具有70 kaBP的阶地,昆仑山东部地区具有50 kaBP的阶地,这2个时期昆仑山东西部河流、湖岸地貌的形成不具有同步性.对该地区河流、湖岸地貌成因分析后认为,除气候作用外,河流阶地、湖岸阶地对高原北部的隆升具有一定的指示作用,表现为从西向东抬升速率逐渐减小,总体上同一地方从老到新抬升速率逐渐增加.     

四川马尔康日部地区地貌及地质特征对工程选址的影响

工程区周边地貌特征不但是判识新构造运动的重要标志,而且对河谷发育及区域稳定性评价是十分重要的.对拟建的大渡河巴拉水电站的河谷阶地以及水电站的上、中、下坝区域内的现存地貌和第四系进行了详细的调查,从研究当地地貌和河谷地貌特征、河流阶地及第四系河床沉积物入手,分析当地地质作用发育史及其主要影响因素.     

北京西山大石河山峡阶地发育特征

大石河山峡总体上阶地较发育,阶地类型以基座阶地为主。下游陈家台—红煤场一带1~4级阶地发育较全,上游至庄户台一带,阶地数量减少,仅见一级阶地。上游沉积物多为砾石,砂、粘土等含量较少;而至下游,沉积物中砂、粘土组分的含量增加。红煤厂四级阶地棕红色泥质含砾粉砂中获得ESR年龄567±56ka,显示大石河河谷在第四纪中更新世早期初始发育,由于新构造运动产生间歇性隆升,在高位宽谷之下发育4级阶地,形成了如今的地貌特征,对比得出大石河流域辛开口至龙门台一段(山区)平均比降为7.71‰,600ka以来,大石河流域山区隆升速率为0.96mm/a。     

龙门山南段活动构造分布特征

本文在综合解译地质图、遥感影像及数字高程模型的基础上,沿着青衣江河谷对龙门山南段多条断裂进行了详细调查。将前第四纪大规模不整合边界作为断裂的分布范围,同时通过构造地貌标志确定最新的活动断裂位置,如断错山脊、断层槽谷、河道形态变化等。解译过程中也参考了前人研究成果,如开挖探槽位置信息,浅层地震剖面资料。调查结果显示,松潘—甘孜褶皱带与龙门山接触地带发育了中岗断裂、永富断裂,晚第四纪活动特征不明显。龙门山后山、中央、前山3条主干断裂在南段依次对应耿达—陇东断裂、岩井—五龙断裂、与双石—大川断裂,与北段具有相似的断块构造。3条断裂都有断错地貌特征但断裂分支较多,其中盐井—五龙断裂有一条分支为宝兴断裂,双石—大川断裂有小关子断裂一条分支。在前陆地区,基底滑脱带延伸至浅部盖层,断坡处发育了始阳断裂、新开店断裂等浅部分支断裂。通过这些断裂分布样式、断错地貌特征、与实测地质剖面发现,龙门山南段具有纯挤压特征,最新构造活动已经开始改造前陆地区,是扩展的边界。而龙门山北段具有和逆冲相当的走滑分量,表明青藏高原在推挤龙门山的过程中,龙门山北缘向西秦岭方向发生走滑逃逸,龙门山南段由于同时受川滇块体向东推挤作用而呈现纯挤压特征。高原推挤作用集中于松潘—甘孜褶皱带东缘的小金弧形构造,控制了龙门山断裂带南北构造差异。     

龙门山造山带早期断裂活动的古地震制约——来自汶川科钻(WFSD)岩心的证据

强地震是断裂活动的表现形式,可以诱发地表沉积层序顶部未固结的软沉积物发生变形,形成新的变形层(即震积岩***)。因此,在连续沉积剖面中赋存的多层震积岩应是断裂活动的直接证据。川西前陆盆地中的软沉积物变形记载了龙门山断裂带的活动信息,对认识龙门山造山带演化历史具有重要意义。本文通过"汶川地震断裂带科学钻探"一号孔(WFSD-1)和三号孔(WFSD-3)连续岩心剖面的岩性分析和构造研究,识别出11段不同深度的液化角砾岩层,它们是地震触发成因的软沉积物变形岩层。11个液化角砾岩段厚度从~20m至102m不等,分布在晚三叠世须家河组二-五段。这些液化角砾岩层记录了龙门山前陆盆地形成过程中晚三叠世断裂活动特征及趋势。这些厚度不等的震积岩粗略指示约2~20万年的地震活动长周期(地震幕),以及约4至70万年的间震期(地震幕的间隔时间),反映了龙门山断裂早期脉动式(幕式)活动特征。从不同段液化角砾岩层分布间隔规律来看,地震活跃期间隔(即间震期)越来越短,显示龙门山造山带断裂活动越来越强的趋势。结合前人地表软沉积物变形研究,我们认为龙门山造山带在晚三叠世经历了多期次的正断-逆冲活动的造山作用(至少经历14个地震活跃期),形成龙门山雏形及前陆盆地。     

Analysing laser‐scanned digital terrain models of gravel bed surfaces: linking morphology to sediment transport processes and hydraulics

The grain‐scale topography of a sediment surface is a key component of a fluvial system, affecting aspects including sediment transport, flow resistance and ecology. However, its effect is hard to quantify because of the need for grain‐scale elevation data from in situ fluvial gravel surfaces which are difficult to collect. The sediment surface properties are, therefore, commonly estimated as a function of the sediment grain‐size distribution; however, because of additional factors, such as grain packing and shape, there is not necessarily a unique relationship between the two. A new methodology has been developed that uses terrestrial laser scanning to collect grain‐scale topographic data from in situ fluvial gravel surfaces, from which digital terrain models are created. This paper investigates methods of analysing such digital terrain models, and possible sedimentological interpretations that can be drawn from the analysis. Eleven digital terrain models from exposed gravel surfaces in two contrasting rivers (the River Feshie and Bury Green Brook) were analysed by calculating: the distribution of surface elevations, semivariograms, surface inclinations, surface slopes and aspects and grain orientation. The distribution of surface elevations and surface slope and aspect analysis were found to be most informative. In the River Feshie, grain‐size was interpreted as being a dominant control on sediment surface structure and gravel imbrication was identified. In Bury Green Brook, the location of the digital terrain models within the riffle–pool sequence was the dominant control on surface structure and grain orientation. Such digital terrain models therefore provide a new approach to measuring and quantifying the topography of fluvial sediment surfaces.     

Suitability analysis for sand and gravel extraction site location in the context of a sustainable development in the surroundings of Zaragoza (Spain)

Zaragoza city is located in the central Ebro Basin, in the Iberian Peninsula. The fluvial terraces formed by the Ebro River present a valuable resource of sand and gravel deposits. However, taking advantage of these available resources implies conflicts with other land use interests like urban and industrial development as well as agricultural use, which has also traditionally occupied the alluvial terraces. These deposits represent a substantial groundwater resource that should be preserved for future generations. The development of spatial decision support systems (SDSS) has greatly assisted efforts for solving land-use conflicts. These systems combine the benefits of geographic information systems (GIS) and decision support methodologies and are therefore suitable to manage sustainable development of urban areas. In this contribution, an extraction suitability map taking into consideration a variety of environmental criteria is created with the help of a SDSS. The method used is the analytical hierarchy process which is integrated in ArcGIS. Areas most suitable to sand and gravel extraction are located in the high terraces, and in those terraces covered by pediments where the thickness of resource is relatively high. These areas are far from valuable natural areas, outside areas most vulnerable to groundwater contamination, and beneath soils with poor irrigation characteristics.     

岷江演化讨论: 来自四川宜宾地区第四纪河流沉积物的重矿物证据*

河流沉积的重矿物可以较为准确反映源区的母岩性质,进而揭示河流的演化过程。本研究以岷江下游河流阶地沉积与现代沉积的重矿物为主要研究对象,开展了古流向、重矿物组合特征、特征重矿物类型及重矿物特征指数分析。研究结果表明: 岷江下游Ⅴ级阶地至Ⅲ级阶地沉积中的重矿物以岩浆岩型重矿物为主,其物源来自龙门山构造带;现代沉积中的重矿物以变质岩型重矿物为主,其物源来自松潘—甘孜褶皱带。结合重矿物特征指数对比分析,认为造成这种重矿物类型差异的原因是青藏高原东缘阶段性隆升引起的岷江溯源侵蚀。受昆黄运动B幕影响,岷江于0.73—0.7 Ma下切至汶川附近,Ⅴ级阶地形成;受昆黄运动C幕影响,岷江于0.5—0.3 Ma强烈下切,Ⅳ级阶地形成;受共和运动影响,岷江在0.11—0.09 Ma下切至石大关,同时形成Ⅲ级阶地;此后岷江继续溯源侵蚀,在距今27 ka左右形成现代岷江。     

A comparison of grain‐size analysis methods for sand‐dominated fluvial sediments

Grain‐size distribution is a fundamental tool for interpreting sedimentary units within depositional systems. The techniques assessed in this study are commonly used to determine grain‐size distributions for sand‐dominated sediments. However, the degree of consistency and differences in interpretation when using a combination of grain‐size methods have not yet been assessed systematically for sand‐dominated fluvial sediments. Results obtained from laser diffraction, X‐ray attenuation and scanning electron microscopy grain‐size analysis techniques were compared with those obtained from the traditional sieve/hydrometer method. Scanning electron microscopy was shown to provide an inaccurate quantitative analysis of grain‐size distributions because of difficulties in obtaining representative samples for examination. The X‐ray attenuation method is unsuitable for sand‐dominated sediments because of its upper size range of only 300 μm. The consistently strong correlation between the laser diffraction results and the sieve/hydrometer results shows that these methods are comparable for sand‐dominated fluvial sediments. Provided that sample preparation is consistent, the latter two methods can be used together within a study of such sediments while maintaining a high degree of accuracy. These results indicate that data for sand‐dominated fluvial sediments gained from the long‐established sieve/hydrometer method can be compared with confidence to those obtained by modern studies using laser diffraction techniques.     

Discussion on evolution of Min Jiang River: Heavy mineral evidence from the Quaternary fluvial sediments in Yibin area,Sichuan Province

Heavy minerals deposited on river terraces can be used to reflect source rock properties and reveal river evolutionary processes. This study focused on the heavy minerals deposited in the lower Min Jiang River terraces and in the modern deposits. We studied paleo-current direction, characteristics of the heavy mineral assemblages, characteristic metamorphic minerals and heavy mineral characteristic indices. The results show that the lower reaches of the Min Jiang River Ⅴ- to Ⅲ-level terrace deposits consist dominantly of magmatic rock type, which mainly comes from the Longmen Shan mountain tectonic belt. The heavy minerals deposited in modern sediment come from the Songpan-Ganzi fold belt. The heavy mineral characteristic indices suggest that this change is due to headward erosion of the Min Jiang River. Affected by the phase B of the Kunhuang movement, the Min Jiang River was incised to the Wenchuan area at 0.73-0.7 Ma and the Ⅴ-level terrace formed. The Min Jiang River was strongly cut down at 0.5-0.3 Ma due to the phase C of the Kunhuang movement, and as a result the Ⅳ-level terrace formed. Influenced by Gonghe movement, the Min Jiang River was incised to the stone mark and Ⅲ-level terrace formed in 0.11-0.09 Ma. After that, the modern Min Jiang River was formed at around 27 ka.     

Morphologic expression of Quaternary deformation in the northwestern foothills of the Ysyk-Köl basin,Tien Shan

The Tien Shan is one of the most active intracontinental mountain belts exhibiting numerous examples of Quaternary fault-related folding. To provide insight into the deformation of the Quaternary intermontane basins, the territory of the northwestern Ysyk-Köl region, where the growing Ak-Teke Anticline divided the piedmont apron of alluvial fans, is studied. It is shown that the Ak-Teke Hills are a sharply asymmetric anticline, which formed as a result of tectonic uplift and erosion related to motions along the South Ak-Teke Thrust Fault. The tectonic uplift gave rise to the local deviation of the drainage network in front of the northern limb of the fold. Optical (luminescent) dating suggests that the tectonic uplifting of the young anticline and the antecedent downcutting started 157 ka ago. The last upthrow of the high floodplain of the Toru-Aygyr River took place 1300 years ago. The structure of the South Ak-Teke Fault is examined by means of seismologic trenching and shallow seismic profiling across the fault. A laser tachymeter is applied to determine the vertical deformation of alluvial terraces in the Toru-Aygyr River valley at its intersection with the South Ak-Teke Fault. The rates of vertical deformation and an inferred number of strong earthquakes, which resulted in the upthrow of Quaternary river terraces of different ages, are calculated. The study territory is an example of changes in fluvial systems on growing folds in piedmont regions. As a result of shortening of the Earth’s crust in the mountainous belt owing to thrusting, new territories of previous sedimentation are involved in emergence. The tectonic activity migrates with time from the framing ridges toward the axial parts of intramontane basins.     

滇西道街盆地上新世怒江埋藏砾石层、堰塞湖沉积的发现及其磁性地层学

在对怒江道街—惠通桥段的考察研究中,不仅重新厘定了河谷中拔河150m以下的多级低阶地,而且在拔河180～380m的高度上发现了多级由磨圆良好、成分复杂的厚层冲积砾石层所组成的高阶地,厚近100m的堰塞湖成因的砂层及其下伏厚约100m的砾石层。冲积层的同位素年龄测定结果表明,6级低阶地形成于中更新世以来。望江楼剖面的磁性地层研究结果显示,组成相当于第九级阶地上部的湖相砂层,上部以正向极性为主,含2次短期的负极性,下部则为负极性。与标准磁性地层柱对比表明,该湖相地层形成于4.2～2.6MaBP的中—晚上新世,湖相地层之下的埋藏阶地与高阶地则应形成于上新世早期至中新世晚期。据此在进一步的区域地层对比后认为：怒江至少在中新世的中晚期已开始形成并下切,至上新世早期已下切至现今河床附近。上述研究结果为更科学地认识青藏高原东缘的强烈隆升过程提供了非常有价值的新线索。