Causes of pulsating evolution of fluvial landforms since the marine isotopic stage-2 in the belt of Schuppen, Nagaland, NE India

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 Dzudza 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 Dzudza 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.