晚中新世以来孟加拉-尼科巴扇跷跷板式沉积转换及其源-汇成因机制

利用沉积转换事件再造关键变革期的构造活动和气候演变是源-汇系统研究的新动向和切入点。新生代以来,印度大陆与亚洲大陆的汇聚隆升以及喜马拉雅-青藏高原的剥蚀、向孟加拉湾的物质输入,形成了当今世界上最大的源-汇系统(喜马拉雅-孟加拉湾源-汇系统)。利用3D地震数据和IODP 354与362航次获取的碎屑锆石数据揭示了晚中新世以来孟加拉-尼科巴扇沉积转换事件及其源-汇成因机制。研究认为尼科巴扇和孟加拉扇经历了此消彼长的沉积建造过程:尼科巴扇经历了“晚中新世快速进积→上新世缓慢建造→第四纪相对静止”的建造过程;而孟加拉扇经历了“晚中新世相对静止→上新世缓慢建造→第四纪快速进积”的沉积建造过程。喜马拉雅-孟加拉湾源-汇系统碎屑锆石年龄核密度统计结果显示:晚中新世以来,指示古布拉马普特拉河迁移演化路径的60~0 Ma碎屑锆石在若开-尼科巴扇呈现出逐渐减少的变化趋势,而在孟加拉扇呈现出逐渐增多的变化趋势。这一碎屑锆石年龄核密度变化特征表明:(1)在晚中新世,古布拉马普特拉河主沉积物分散路径靠近孟加拉湾东部一侧发育且大量碎屑颗粒向尼科巴扇搬运分散,形成“快速进积的尼科巴扇和相对静止的孟加拉扇”;(2)在上新世初,青藏高原隆升所诱发的西隆高原抬升使古布拉马普特拉河向西迁移分流,在古西隆高原北缘Mikir山附近分流为东西两支,东支向尼科巴扇搬运分散的碎屑颗粒开始减少,而西支向孟加拉扇搬运分散的碎屑颗粒开始增多,形成“以缓慢建造为演化特征的尼科巴-孟加拉扇”;(3)在第四纪初,印度板块-亚洲板块最强碰撞造成青藏高原最强隆升并达到最大海拔高度,古布拉马普特拉河东支袭夺废弃,向尼科巴扇卸载的沉积物相应显著减少,而古布拉马普特拉河西支与恒河并流后向孟加拉扇卸载的沉积物亦相应显著增加,形成“相对静止的尼科巴扇和快速进积的孟加拉扇”。由此可见,尼科巴-孟加拉扇“此消彼长的跷跷板式沉积转换事件”是古布拉马普特拉河沉积物分散路径迁移演化的源-汇响应;其在上新世-第四纪之交发生了一起最为显著的沉积转换事件,其是上新世晚期印度板块-亚洲板块碰撞的源-汇响应。     

基于RS、GIS的东喜马拉雅南迦巴瓦峰地区断裂构造的定量研究

东喜马拉雅南迦巴瓦峰地区地质构造十分复杂,对该区板块缝合带的空间位置问题,长期以来,一直认为沿雅鲁藏布江呈弧形展布。笔者以ETM+为主要信息源,以遥感与GIS为技术支撑,对南峰地区的断裂构造进行了详细的遥感解译分析,从构造统计分析的角度对断裂构造进行定量研究,从分维值及趋势值的空间分布及变化特征分析,认为缝合带的南东段、北段大致沿雅鲁藏布江展布,而北西段位于雅鲁藏布江的北西侧,沿东久-米林(断裂带)展布,这也与近几年来开展了1∶25万区域地质调查获得的新认识相一致。     

Re-Os isotope systematics of sediments of the Brahmaputra River system

Re-Os analyses were performed on suspended loads and coarser grained bank sediments of the Brahmaputra River system. Re and Os concentrations of these sediments vary from 7 to 1154 ppt and from 3 to 173 ppt, respectively. ¹⁸⁷Os/¹⁸⁸Os ratios range from 0.178 to 6.8, and thus vary from nearly mantle to very radiogenic crustal values. Nevertheless, most of the sediments have ¹⁸⁷Os/¹⁸⁸Os ratios less than 1.5, and nearly all of the samples of the Brahmaputra main channel have ratios less than 1.2. Thus, as previously suggested, the Brahmaputra is much less radiogenic than the Ganga. The Siang River, the northern extension of the Brahmaputra, is quite radiogenic in Os despite receiving sediments from the Tsangpo River, which flows along a suture zone with ultramafic outcrops. The Brahmaputra main channel has a fairly constant ¹⁸⁷Os/¹⁸⁸Os ratio even though its tributaries contribute sediments with very heterogeneous Os isotopic compositions. These data, along with the corresponding Nd isotopic compositions, suggest that about 60-90% of the sediment in the Brahmaputra system is derived from Himalayan formations (Higher Himalaya and Lesser Himalaya) whereas 10-40% comes from ophiolite-bearing sequences, perhaps eastern equivalents of those of the Transhimalayan Plutonic Belt. Os data also confirm previously published Sr and Nd results, indicating that about half of the sediments delivered to the Brahmaputra are supplied by the Siang River, while the Himalayan and the eastern tributaries account for 40 and 10%, respectively.The lower ¹⁸⁷Os/¹⁸⁸Os of the Brahmaputra River compared to that of the Ganga is due to two factors. One is the more limited presence of the Lesser Himalaya and hence the lower black shale content of the eastern Himalaya. The other is the non-radiogenic Os supplied by the eastern and southern tributaries, reflecting the presence of mantle-derived lithologies in this region. Despite the lower sediment supply from these tributaries, they contribute greatly to the Os budget of the Brahmaputra River. This study indicates that the Brahmaputra River has little effect on the present-day seawater Os budget. However, reconsideration of this budget suggests that the Ganga, which provides the most radiogenic Os of major rivers studied to date, may have significant impact on the marine Os isotopic composition. The Indo-Asian collision cannot be excluded as an important cause of the increase in the marine ¹⁸⁷Os/¹⁸⁸Os over the past 16 million years until the contributions of all of the rivers draining the Himalayan Tibetan Plateau are known.     

雅鲁藏布江深厚砂砾卵石覆盖层钻探工艺

为了开展雅鲁藏布江流域综合规划及其水资源开发利用与保护专题研究工作,在雅鲁藏布江干流里龙坝址和本宗坝址共布置了4个200~300 m深的钻孔。主要通过在西藏高寒地区4个深厚覆盖层钻孔的成功实施经验,对西藏高寒地区深厚覆盖层勘探成孔工艺与技术进行研究探讨。     

青藏高原南部雅鲁藏布江蛇绿岩带的时空分布特征及地质意义

雅鲁藏布江缝合带是青藏高原上重要的缝合带之一,位于青藏高原南部,蛇绿岩是该带的主体。雅鲁藏布江缝合带按蛇绿岩的出露规模、岩石层序以及侵位时间,大致可以分为东段、中段和西段。在蛇绿岩出露规模上存在显著差异,东段规模较小,中段次之,西段最大,并且在西段分成两支蛇绿岩带;蛇绿岩岩石层序出露比较齐全的是中段日喀则和东段罗布莎,其他地方的蛇绿岩均被肢解,不能组成完整的蛇绿岩岩石剖面;在蛇绿岩的形成和侵位时间上,也有着不同的特点,东段和西段集中形成于晚侏罗世—早白垩世,而中段形成时间较早,时代从中三叠世一直持续到早白垩世,主要集中形成于晚侏罗世—早白垩世。笔者系统研究雅鲁藏布江缝合带蛇绿岩在东西方向上所表现出来的差异性,对更全面深刻地了解新特提斯洋的产生、俯冲及其消亡过程和演化历史具有重要意义。     

On the occurrences of dry and wet sequences in the Brahmaputra valley

Occurrence of dry and wet days in the Brahmaputra Valley has been studied using a first-order Markov Chain model. The model is fitted to the daily rainfall series recorded at ten stations widely distributed in the valley. The adequacy of the model is tested and found suitable. At all the stations, dry and wet spells having different durations follow geometric distribution. For pre-monsoon and monsoon seasons, the expected dry and wet days, the expected length of a weather cycle and the return period of dry spells having different, durations are calculated, and the results for different stations are compared.     

Distribution and fractionation of heavy metals in the surface sediments of the Ganges- Brahmaputra-Meghna river system in the Bengal basin

 The lower Ganges-Brahmaputra-Meghna (G-B-M) drainage basin occupies the total Bengal Basin, which is one of the unique basins of the world because of its location and size, density of population, and catastrophic deposition of sediments. The increased heavy metal concentration in the 63 m fraction of surface sediments shows similarity among major segments of the G-B-M system in the basin, which reflects the homogenization of lithologic and chemical diversity of the greater denudation regime by the river processes. The differences in heavy metal concentation in the lower G-B-M system with that of its upper and middle counterpart is mainly related to the contrast between Himalayan rivers and the other major South Asian rivers, and may be due to the geological differences of their denudation regime. Heavy metals in the Lower G-B-M system have an affinity towards the clay fraction of the sediments. The correlation matix of heavy metals in the lower Brahmaputra and Meghna suggests the importance of Fe-Mn oxyhydroxides in their accumulations. Iron, Ti and Mn are higher in the Meghna main channel, Zn is higher in the Meghna tributaries, and Cr is higher in both the Brahmaputra and Meghna compared to the value for standard shale. The enrichment factor is ≤1 for most of the metals except Mn which is relatively higher in the Meghna and lower Ganges main channels. The geoaccumulation index (I_geo) for most of the heavy metals lies below grade zero, suggesting unpolluted sediment quality. The lower Ganges system shows relatively higher concentration in the nondetrital fraction of heavy metals, probably due to the presence of petroleum refinery, industrial and mining effluents, and agricultural runoff in the drainage basin. The relative uniformity in concentration of heavy metals in vertical profiles may be due to the uniformity in sediment grain size and catastrophic deposition of sediments, where the time period represented by the vertical sediment column is not enough to reflect the cultural accumulation of heavy metals. The Bengal basin thus represents a relatively unperturbed alluvial basin with regards to heavy metal pollution. Received: 21 July 1997 · Accepted: 13 October 1997     

Chemical erosion in the eastern Himalaya: Major ion composition of the Brahmaputra and δC of dissolved inorganic carbon

Major ion composition of waters, δ¹³C of its DIC (dissolved inorganic carbon), and the clay mineral composition of bank sediments in the Brahmaputra River System (draining India and Bangladesh) have been measured to understand chemical weathering and erosion and the factors controlling these processes in the eastern Himalaya. The time-series samples, collected biweekly at Guwahati, from the Brahmaputra mainstream, were also analyzed for the major ion composition. Clay mineralogy and chemical index of alteration (CIA) of sediments suggest that weathering intensity is relatively poor in comparison to that in the Ganga basin. This is attributed to higher runoff and associated physical erosion occurring in the Brahmaputra basin. The results of this study show, for the first time, spatial and temporal variations in chemical and silicate erosion rates in the Brahmaputra basin. The subbasins of the Brahmaputra watershed exhibit chemical erosion rates varying by about an order of magnitude. The Eastern Syntaxis basin dominates the erosion with a rate of ∼300 t km⁻² y⁻¹, one of the highest among the world river basins and comparable to those reported for some of the basaltic terrains. In contrast, the flat, cold, and relatively more arid Tibetan basin undergoes much slower chemical erosion (∼40 t km⁻² y⁻¹). The abundance of total dissolved solids (TDS, 102-203 mg/L) in the time-series samples collected over a period of one year shows variations in accordance with the annual discharge, except one of them, cause for which is attributable to flash floods. Na* (Na corrected for cyclic component) shows a strong positive correlation with Si, indicating their common source: silicate weathering. Estimates of silicate cations (Na_sil+K_sil+Ca_sil+Mg_sil) suggest that about half of the dissolved cations in the Brahmaputra are derived from silicates, a proportion higher than that for the Ganga system. The CO₂ consumption rate due to silicate weathering in the Brahmaputra watershed is ∼6 × 10⁵ moles km⁻² y⁻¹; whereas that in the Eastern Syntaxis subbasin is ∼19 × 10⁵ moles km⁻² y⁻¹, similar to the estimates for some of the basaltic terrains. This study suggests that the Eastern Syntaxis basin of the Brahmaputra is one of most intensely chemically eroding regions of the globe; and that runoff and physical erosion are the controlling factors of chemical erosion in the eastern Himalaya.     

Impact of Ganges–Brahmaputra interannual discharge variations on Bay of Bengal salinity and temperature during 1992–1999 period

This study investigates the impact of monthly Ganges–Brahmaputra river discharge variations on Bay of Bengal salinity and temperature during the period 1992–1999. The Ganges–Brahmaputra river discharge is characterized by a well-defined seasonal cycle with strong interannual variations. The highest/lowest yearly peak discharge occurs in summer 1998/summer 1992, with 1998 value amounting to twice that of 1992. This river discharge is then used to force an ocean general circulation model. Our main result is that the impact of these rivers on the variability of Bay of Bengal sea surface salinity is strong in the northern part, with excess run-off forcing fresh anomalies, and vice versa. Most of the years, the influence of the interannual variability of river discharge on the Bay salinity does not extend south of ~10°N. This stands in contrast with the available observations and is probably linked to the relatively coarse resolution of our model. However, the extreme discharge anomaly of 1998 is exported through the southern boundary of the Bay and penetrates the south-eastern Arabian Sea a few months after the discharge peak. In response to the discharge anomalies, the model simulates significant mixed-layer temperature anomalies in the northern Bay of Bengal. This has the potential to influence the climate of the area. From our conclusions, it appears necessary to use a numerical model with higher resolution (both on the horizontal and vertical) to quantitatively investigate the upper Bay of Bengal salinity structure.     

孟加拉国布河河道泥沙数学模型计算中几个问题的探讨

针对布河游荡性河道上支汊众多、主流摆动不定、河道防洪能力较差等特性,基于断面输水和输沙相等的概念,将布河宽浅多汊的河道断面合并为等量的单一河道;在分析比较的基础上,确定了部分年份所缺的水沙资料,利用一维非均匀悬移质不平衡输沙数学模型进行验证计算,结果表明计算值与实测值相符较好.在此基础上,作了布河整治方案计算.对一些影响计算结果的因素进行了敏感性分析,指出了其中一些较为敏感的影响因素.     

Understanding the Cyclicity of Chemical Weathering and Associated CO<Subscript>2</Subscript> Consumption in the Brahmaputra River Basin (India): The Role of Major Rivers in Climate Change Mitigation Perspective

Weathering of rocks that regulate the water chemistry of the river has been used to evaluate the CO₂ consumption rate which exerts a strong influence on the global climate. The foremost objective of the present research is to estimate the chemical weathering rate (CWR) of the continental water in the entire stretch of Brahmaputra River from upstream to downstream and their associated CO₂ consumption rate. To establish the link between the rapid chemical weathering and thereby enhance CO₂ drawdown from the atmosphere, the major ion composition of the Brahmaputra River that drains the Himalaya has been obtained. Major ion chemistry of the Brahmaputra River was resolved on samples collected from nine locations in pre-monsoon, monsoon and post-monsoon seasons for two cycles: cycle I (2011–2012) and cycle II (2013–2014). The physico-chemical parameters of water samples were analysed by employing standard methods. The Brahmaputra River was characterized by alkalinity, high concentration of Ca²⁺ and HCO₃ ^? along with significant temporal variation in major ion composition. In general, it was found that water chemistry of the river was mainly controlled by rock weathering with minor contributions from atmospheric and anthropogenic sources. The effective CO₂ pressure (log\({{\text{P}}_{{\text{C}}{{\text{O}}_{\text{2}}}}}\)) for pre-monsoon, monsoon and post-monsoon has been estimated. The question of rates of chemical weathering (carbonate and silicate) was addressed by using TDS and run-off (mm year^?1). It has been found that the extent of CWR is directly dependent on the CO₂ consumption rate which may be further evaluated from the perspective of climate change mitigation The average annual CO₂ consumption rate of the Brahmaputra River due to silicate and carbonate weathering was found to be 0.52 (×10⁶ mol Km^?2 year^?1) and 0.55 (×10⁶ mol Km^?2 year^?1) for cycle I and 0.49 (×10⁶ mol Km^?2 year^?1) and 0.52 (×10⁶ mol Km^?2 year^?1) for cycle II, respectively, which were significantly higher than that of other Himalayan rivers. Estimation of CWR of the Brahmaputra River indicates that carbonate weathering largely dominates the water chemistry of the Brahmaputra River.     

Hydrologic characteristics of floods in Ganges–Brahmaputra–Meghna (GBM) delta

In the middle of 2007, a severe flood affected the People’s Republic of Bangladesh. This is a natural disaster that takes people’s lives, destroys livestock, infrastructures and communication systems and, damages crops and fish ponds. Despite many adverse impacts, the flood situation is an accepted phenomenon to the citizens of Bangladesh, due to the immense increase of soil fertility due to the flood, plus, the recharge of aquifer, ecosystem and fish. The flood of 2007 was the 5th major flood of the last 20 years when more than thirty-five percent of the area of the country was inundated with flood water. As in the past, the flood of 2007 had its own significance. The geography of the country contains a floodplain delta of three major river basins: the Ganges, the Brahmaputra and the Meghna (GBM). The mean monthly rainfall plot from the TRMM satellite data has shown that for both the Meghna and Brahmaputra basins, the rainfall was higher during July 2007 than any other months of the last 2 years. This excess rainfall had accumulated in the Brahmaputra and Meghna rivers and carried downstream to Bangladesh. This was the main cause of the flooding in 2007. The first crossing above the danger level of the river waters was observed at Durgapur station of the Someswari and at Sunamganj station of the Surma on the nineteenth of July, 2007 inside Bangladesh. In terms of magnitude of the peak and duration of the flood, the Brahmaputra was higher in 2007 than during 2004. However, the Ganges river water level never crossed the danger level during flood of 2007. The Meghna was lower during the flood peak for the duration of the flood in 2007. The year–to-year variability in both the magnitude and duration of the flood suggests changes in rainfall and landuse pattern of the catchment.     

在构造和气候因素制约下雅鲁藏布江的演化

雅鲁藏布江位于印度和欧亚大陆汇聚带内，其形成受到冈底期山和喜马拉雅山差异性抬升的控制。冈底期山抬升在先，发生在中生代晚期至新生代早期。一系列起源于冈底期山和青藏高原的水系向南先是流主特提斯海。在特提斯海关闭后流入印度次大陆。喜马拉雅山构造抬升要晚于冈底斯山，大规模抬升发生在中新世早期，其抬升阻断了这些河流的通道，水流开始汇聚在这两个造山带之间，牙鲁藏布江由此形成。在雅鲁藏布江大拐弯地区，在海拔4500m处存在一个平坦的侵蚀面，并构成雅鲁藏布江大峡谷最高的一级谷肩，这表明雅鲁藏布江在下切前就在该面上流动，而且流速不大。在大拐弯以南，雅鲁藏布江的下游－布拉马普特拉河位于印度洋热带季风带内，其下切和源侵蚀速率很大。印度洋热带季风形成于6－9MaB.P.。因此，该河流很可能形成于该时期，要比雅鲁藏布江年轻，它在向北的溯源侵蚀的过程中袭夺了雅鲁藏布江，袭夺处可能就大拐弯的北端，因此大拐弯是袭夺成因。     

松辽盆地情南-黑帝庙次凹青山口组储层成岩作用研究

利用薄片鉴定、扫描电镜、包裹体测温及压汞分析等手段, 进行了储层岩石学特征、成岩作用类型、成岩阶段和成岩演化模式研究。研究区储层岩石类型为细粒2粗粒长石岩屑砂岩和岩屑长石砂岩, 砂岩经历了机械压实压溶、化学胶结、交代、溶蚀和黏土矿物转化等成岩作用。依据成岩标志, 研究区青山口组处于晚成岩期A2-A3亚期。成岩演化模式表明: 嫩二、三段沉积时, 青一段处于晚成岩A1期, 青二、三段处于早成岩B亚期-晚成岩A1亚期; 明水期, 青山口组整体处于晚成岩A2 亚期; 古近纪, 青一段进入晚成岩A3亚期, 青二、三段中上部处于晚成岩A2亚期。     

Stepwise,earthquake-driven coastal subsidence in the Ganges–Brahmaputra Delta (Sundarbans) since the eighth century deduced from submerged in situ kiln and mangrove remnants

Natural Hazards - This study reconstructs the coastal subsidence over the past 1300&nbsp;years in a mangrove region along the coast of the Ganges–Brahmaputra Delta, an area not affected...     

特大桥钻孔灌注柱钻芯取样施工技术

结合贡嘎雅鲁藏布江特大桥钻孔灌注桩钻芯取样工程实例,阐述了在无法清理桩头、回填土层较厚的特殊条件下,成功钻取混凝土芯样的施工工艺.     

THE FOURTH IN AN OCCASIONAL SERIES OF EARTH PHENOMENA

This, the Iargest continental earthquake of the 20th Century, occurred on a low-angle detachment at the eastern end of the Himalayan mountain arc. Great earthquakes in this region are fundamental forces of erosion: above the c.300X150 km-long fault rupture, in the steep-sided valley-tributaries of the upper Brahmaputra, landslides covered about one third (15, 000 km²) of the surface comprising an estimated 5X10¹⁰ m³ of debris, 30 times the volume carried annually by the whole Brahmaputra River. Two English plant-hunters, Jean and Frank Kingdon-Ward, with their Assam guides were based in the upper Lohit Valley, just over the Tibetan border with Assam, waiting for an opportunity to ascend to the Alpine pastures.     

Groundwater arsenic contamination in Ganga–Meghna–Brahmaputra plain, its health effects and an approach for mitigation

The authors’ survey of the Ganga–Meghna–Brahmaputra (GMB) plain (area 569,749 km²; population >500 million) over the past 20 years and analysis of more than 220,000 hand tube-well water samples revealed groundwater arsenic contamination in the floodplains of the Ganga–Brahmaputra river (Uttar Pradesh, Bihar, Jharkhand, West Bengal, and Assam) in India and the Padma–Meghna–Brahmaputra river in Bangladesh. On average, 50 % of the water samples contain arsenic above the World Health Organization guideline value of 10 μg/L in India and Bangladesh. More than 100 million people in the GMB plain are potentially at risk. The authors’ medical team screened around 155,000 people from the affected villages and registered 16,000 patients with different types of arsenical skin lesions. Arsenic neuropathy and adverse pregnancy outcomes have been recorded. Infants and children drinking arsenic-contaminated water are believed to be at high risk. About 45,000 biological samples analyzed from arsenic-affected villages of the GMB plain revealed an elevated level of arsenic present in patients as well as non-patients, indicating that many are sub-clinically affected. In West Bengal and Bangladesh, there are huge surface water in rivers, wetlands, and flooded river basins. In the arsenic-affected GMB plain, the crisis is not over water scarcity but about managing the available water resources.     

青藏高原隆升的地质灾害效应

根据青藏高原隆升具有持续性和阶段性加速的特征,将其整个隆升过程分为 4个隆升阶段 15个隆升幕,即喜马拉雅运动（6个加速隆升幕）---递进式压缩隆升阶段;青藏运动（3个加速隆升幕）---构造变形、断裂运动性质调整阶段;昆黄运动（3个加速隆升幕）---高原造貌主阶段;共和运动阶段（3个加速隆升幕）---地质灾害高发期。由于青藏高原的强烈隆升,最终使其成为我国地质灾害最为严重的地区之一。尤其是青藏高原周缘西北部的黄河上游 流域、东南部的长江上游流域、西藏南部的雅鲁藏布江下游区及其东南部的"三江地区",成为地质灾害事件集中发生的区域,其中的地震、崩滑流、断裂活动等地质灾害效应最为强烈,成为影响现代人类工程活动和生存环境的主要灾害。     

Neotectonic activity of the Bomdila Fault in northeastern India from geomorphological evidences using remote sensing and GIS

One of the major geological structures across the Brahmaputra valley, which stretches from the Eastern Himalayas up to the Naga Hills, is the Bomdila Fault. Parts of the courses of the rivers – the Brahmaputra, Dhansiri (south-S), Bargang and many others – are aligned along this structure. The influence of this structure on the courses of these rivers has been studied in detail using topographic maps, satellite data and field evidences. The signatures obtained such as: (a) an unusually linear course of the lower part of the Dhansiri (S) river from Golaghat up to Dhansirimukh, (b) the abandonment of the westerly course of the earlier Dhansiri (S) river (flowing through Kaziranga) towards the present NW direction by avulsion, (c) knick bends in the MBT–MCT and Naga Thrust of Belt of Schuppen, (d) a linear 15 m high topographic scarp on the left bank of the Dhansiri (S) near Numaligarh and (e) an anomalous SE–NW trending course of the Brahmaputra from Dhansirimukh up to Hartamuli along with the parts of the rivers Buroi and Bargang on the north in the same trend infers the influence of a fault-type structure. Since all these linear segments of the rivers align along the NW–SE trending Bomdila Fault, it infers the influence of the later on the courses of these rivers. The neotectonic activity along this fault might have caused the linear high scarp and abandonment of earlier river courses.