ABSTRACT

The Belt of Schuppen (BoS) of Nagaland is a NE-SW trending linear zone lying adjacent to the Brahmaputra Valley of Assam in Northeast India. Geomorphic, stratigraphic and chronologic data from the Dzüdza and Chathe river valleys that cut across the BoS have been studied to understand the influence of climate on landform evolution in parts of the BoS. Fluvial landforms in the Dzüdza and Chathe river valleys evolved in four major phases bracketed between 22–17 ka (Phase IV), 13–9.0 ka (Phase III), 7–5 ka (Phase II) and 3.5–1.5 ka (Phase I), indicating multi-centennial to millennial changes in monsoon intensity. Climatically, Phase-III was dominated by valley aggradation initiated by onset of the Indian Summer Monsoon (ISM) and persisted intermittently till the early Holocene-strengthened ISM. The other phases of aggradation are attributed to transient or weak ISM. The present study suggests that fluvial aggradation was associated with enhanced precipitation and sediment supply in the BoS valley, whereas the transient and weak ISM is manifested in episodic pulses of alluvial ingression from the tributaries to the trunk valleys; along with post depositional tectonic modifications of the landforms.

摘要

那加兰邦舒彭带（BoS）是一个东北-西南走向的线性地带，毗邻印度东北部阿萨姆邦的雅鲁藏布江谷。研究人员对穿过BoS的Dzüdza河谷和Chathe河谷的地貌、地层和年代数据进行了研究，以了解气候对BoS部分地区地貌演化的影响。Dzüdza 和 Chathe 河谷的河流地貌经历了四个主要阶段的演变，分别为 22-17 ka（第四阶段）、13-9.0 ka（第三阶段）、7-5 ka（第二阶段）和 3.5-1.5 ka（第一阶段） ），表明季风强度从数百年到千年的变化。气候上，第三阶段以印度夏季季风（ISM）爆发引发的山谷加积为主，并间歇性地持续到全新世早期加强的ISM。其他阶段的恶化归因于短暂的或弱的 ISM。本研究表明，河流淤积与BoS河谷降水和沉积物供应的增加有关，而短暂而弱的ISM则表现为从支流到干河谷的冲积物侵入的间歇性脉冲；以及地貌的沉积后构造变化。