Effect of elevated water temperature and stress in chocolate mahseer (Neolissochilus hexagonolepsis): implication for habitat restoration and conservation.

Abstract

Conventionally, epigenetic gorges in tectonically active orogen are attributed to the bedrock geometry and original valley configuration. Because they are invariably associated with fossil valleys containing appreciable sediment succession, it is argued that the older river course was abandoned due to accelerated sedimentation (landslides or widespread fluvial aggradations) as a result of which rivers were forced to occupy the new course (epigenetic gorge). Thus it can be suggested that fossil valleys and gorges are the outcome of the climate–tectonic interaction. The present study is therefore undertaken in the monsoondominated and tectonically active inner Lesser Central Himalaya to understand the role of climate and tectonics in their evolution. Preliminary observations in three river valleys indicate that their locations (epigenetic gorges) are structurally controlled (independent of lithology). However, the abandonment of old river course (fossil valleys) was caused due to the accelerated sedimentation (climatically induced). Chronology of the fill sediment indicates that old river course abandonment occurred during the early Holocene climatic optimum (15–9 ka), whereas the incision leading to the epigenetic gorge formation began after 9 ka.