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Pradeep Srivastava Surendra S. Bhakuni Khayingshing Luirei Dileep K. Misra 《第四纪科学杂志》2009,24(2):175-188
Morphological and sedimentary records at the exit of Brahmaputra River at Pasighat in the NE Himalaya inform about the climate–tectonic interplay during the past ca. 15 ka. The geomorphology of the area comprises (1) fan terrace T3, (2) a high‐angle fan (3) terrace T2, (4) terrace T1 and (5) a low‐angle fan. Geomorphic consideration suggests that the fan terrace T3 and high‐angle fans are the oldest units and were coeval. The low‐angle fan is the youngest geomorphic unit. Sedimentological studies and optically stimulated luminescence chronology suggest that (i) fan terrace T3 formed between 13 and 10.5 ka and comprised multiple events of debris flows separated by the aggradation as channel bars in a braided river environment; (ii) the high‐angle fan formed during 15–10 ka and comprises channel bar aggradation in braided river conditions; (iii) terrace T2 formed during 10–8 ka due to aggradation in a braided channel environment with lesser events of debris flows; (iv) terrace T1 formed during <7 and 3 ka took place as bars of the braided river. Sudden coarsening of the sediment indicated a tectonic rejuvenation in the provenance region between 7 and 3 ka; and (v) the low‐angle fans dated to <3 ka formed due to aggradation in a small tributary joining the Brahmaputra River. This implies a phase when the main channel of the Brahmaputra did not flood regularly and the tributaries were actively aggrading. The sedimentation style and incision of these geomorphic units responded to contemporary climatic changes and uplift in the Siwalik range along the Himalayan Frontal Fault. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Girish Ch. Kothyari P. D. Pant Khayingshing Luirei 《Journal of the Geological Society of India》2012,80(1):101-110
Main Boundary Thrust (MBT) zone is constituted of some of the landslide prone areas in southeastern part of Kumaun Sub-Himalaya. Role of landslides as natural hazard and hill slope modifying agent is well documented from various part of Himalayan region and southern hills of Kumaun particularly in the MBT zone, which are susceptible to various type of mass movement. The rocks making up the slopes has been put to a number of brittle deformation phases during the movement along the MBT, and are traversed by number of joint sets. In the open slope these intersecting joint sets forms wedges and are the most favorable site for initiation of rockfalls and other types of landslides. Landslides are taking place primarily due to high angle slopes, formation of structural wedges along the free steep slopes, sheared nature of the rocks due to proximity to the MBT and neotectonic activities along the MBT and other transverse faults. Wedge failure is a common type of landslides in rock slopes characterized by multiple joints and acts as sliding planes for the failed blocks. Field observations and wedge failure analysis indicates most of the landslides taking place in MBT zone of Kumaun Sub-Himalaya are joint controlled. Safety Factor analysis suggests MBT zone of Kumaun Sub-Himalayan region is prone to landslides and related mass movements. This zone is also neotectonically active as indicated by various geomorphic signatures such as structurally controlled drainage pattern, offsetting of fan by MBT and formation of number of small lakes. 相似文献
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The shape of the frontal part of the Himalaya around the north-eastern corner of the Kumaun Sub-Himalaya, along the Kali River valley, is defined by folded hanging wall rocks of the Himalayan Frontal Thrust (HFT). Two parallel faults (Kalaunia and Tanakpur faults) trace along the axial zone of the folded HFT. Between these faults, the hinge zone of this transverse fold is relatively straight and along these faults, the beds abruptly change their attitudes and their widths are tectonically attenuated across two hinge lines of fold. The area is constituted of various surfaces of coalescing fans and terraces. Fans comprise predominantly of sandstone clasts laid down by the steep-gradient streams originating from the Siwalik range. The alluvial fans are characterised by compound and superimposed fans with high relief, which are generated by the tectonic activities associated with the thrusting along the HFT. The truncated fan along the HFT has formed a 100 m high-escarpment running E–W for ～5 km. Quaternary terrace deposits suggest two phases of tectonic uplift in the basal part of the hanging wall block of the HFT dipping towards the north. The first phase is represented by tilting of the terrace sediments by ～30 ° towards the NW; while the second phase is evident from deformed structures in the terrace deposit comprising mainly of reverse faults, fault propagation folds, convolute laminations, flower structures and back thrust faults. The second phase produced ～1.0 m offset of stratification of the terrace along a thrust fault. Tectonic escarpments are recognised across the splay thrust near south of the HFT trace. The south facing hill slopes exhibit numerous landslides along active channels incising the hanging wall rocks of the HFT. The study area shows weak seismicity. The major Moradabad Fault crosses near the study area. This transverse fault may have suppressed the seismicity in the Tanakpur area, and the movement along the Moradabad and Kasganj–Tanakpur faults cause the neotectonic activities as observed. The role of transverse fault tectonics in the formation of the curvature cannot be ruled out. 相似文献
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