Late Quaternary History of the Ganga Plain
Late Quaternary History of the Ganga Plain
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恒河平原晚第四纪历史
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发表时间：
2004
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通讯作者：
I. Singh
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作者：
I. Singh
印度岩石圈的挠曲沉降在喜马拉雅造山带前形成了恒河平原前陆盆地，并在晚第四纪形成了现今的构造。气候变化、新构造运动和基准面变化影响了恒河平原现今地貌的演变。区域地貌面为：（1）高地河间面（T2）;（2）边缘平原高地面（MP）;（3）Megafan面（MF）;（4）皮埃蒙特扇面（PF）;（5）河谷阶地面（T1）;（6）活动洪泛平原面（T0）。高地河间面（T 2）是广泛的参考面;其他面被切割或覆盖在此面上。这些地表的形成与晚更新世-全新世（128 kaBP）的气候旋回有关。这些表面是沉积的，有一系列的上覆沉积物，比各自表面的形成时间更年轻。来自喜马拉雅山脉的沉积物在冲积平原中经历了显著的化学风化作用，其中大量的Na、Ca、Sr、K、Mg被去除，而As、Cr、Ni和Th被富集。在适当的条件下，形成蒙皂石和高岭石。这些沉积物部分被侵蚀并被搬运到三角洲地区和更远的地方。恒河平原由大量的河流系统组成;起源于喜马拉雅山的不同部分，半岛的冲积平原和冲积平原形成于晚更新世-全新世的不同时期。地表径流和地下水是水的主要来源。很难制定有意义的渠道分类方案。根据沉积物-水的传输模式，渠道分为三大类。河流系统处于不同的演化阶段。活跃的常年河流切割在冲积层内，出现10 4 - 10 5年规模的撕脱;一些渠道（古代网状网络的一部分）充当洪水渠道，出现10 1 - 10 2年规模的撕脱。高地河间面（T2）显示了一系列微地貌特征，这些微地貌特征有助于恒河平原近20 kaBP以来历史的重建：20-13 kaBP-低密度的新水系，13-8 kaBP-水系的扩展，高降雨量; 8-6 kaBP-基准面上升和构造运动导致的河道中断，形成大规模湖泊，保留了T2表层的大部分水和沉积物：6- 4kaBP-气候干燥，湖泊中陆源碎屑沉积物增多; 4- 2kaBP-湖泊淤积增加，降雨量适中; 2-0 kaBP-湖泊破碎和干涸，人为影响强烈。盆地构造活动活跃，皮埃蒙特带以收缩体系为主，南部以伸展体系为主。恒河平原历史上最重要的事件之一是8-5 ka BP的构造，它产生了向心排水区，并将河流景观变成了池塘和湖泊的景观，几乎没有高地。这得益于大约5 ka BP从潮湿到干燥的气候变化。
Flexural subsidence of the Indian lithosphere created the Ganga Plain foreland basin in front of the Himalayan orogen, which attained its present configuration during the late Quaternary. Climate change, neotectonics and base level changes influenced the evolution of the present landforms of the Ganga Plain. The regional geomorphic surfaces are: (1) Upland Interfluve Surface (T 2 ); (2) Marginal Plain Upland Surface (MP); (3) Megafan Surface (MF); (4) Piedmont Fan Surface (PF); (5) River Valley Terrace Surface (T 1 ) and (6) Active Flood plain Surface (T 0 ). The Upland Interfluve Surface (T 2 ) is widespread reference surface; other surfaces are either incised or overlie this surface. Formation of these surfaces is essentially related to the climate cycles of late Pleistocene-Holocene (128 ka BP). These surfaces are depositional and have a succession of overlying sediments, younger than the time of formation of the respective surfaces. The sediments coming from the Himalaya undergo significant chemical weathering in the alluvial plain where much Na, Ca, Sr, K, Mg, is removed; while As, Cr, Ni and Th are enriched. In suitable conditions smectite and kaolinite are formed. These sediments are partly eroded and transported to the delta region and beyond. The Ganga Plain consists of a large number of river systems; originating in different parts of the Himalaya, Peninsular Craton, and alluvial plain formed at different times during the late Pleistocene-Holocene. Surface runoff and groundwater are the main sources of water. It is difficult to make meaningful scheme of classification of channels. Based on the sediment-water transfer patterns, the channels are classified into three broad categories. The river systems are in different stages of evolution. The active perennial rivers are incised within the alluvium, and show avulsion on a scale of 10 4 -10 5 years; some channels, part of the ancient anastomosing network, act as flood channels and show avulsion on a scale of 10 1 -10 2 years. The Upland Interfluve Surface (T 2 ) exhibits a number of microgeomorphic features which have helped in the reconstruction of the history of the Ganga Plain during the last ∼20 ka BP: 20-13 ka BP - new drainage of low density; 13-8 ka BP - extension of drainage system, high rainfall; 8-6 ka BP - channel disruption due to base-level rise and tectonics and formation of large lakes which retained most water-sediment of T 2 -Surface; 6-4 ka BP - dry climate, increased terrigenous clastic sediments in lakes; 4-2 ka BP - increased siltation of the lakes, moderate rainfall; 2-0 ka BP - fragmentation and drying of lakes, strong anthropogenic influence. The basin exhibits active tectonism, which is mostly in the form of contractional system in the piedmont zone, and prominent extensional system in the southern part of the basin. One of the most significant events in Ganga Plain history is tectonics of 8-5 ka BP, which produced areas of centripetal drainages and changed the fluvial landscape into a landscape of ponds and lakes with few high grounds. It was helped by the climate change from humid to dry around 5 ka BP.