Morphology and facies of the alluvial-fan sedimentation in the Kangra Valley, Himachal Himalaya

Abstract

A number of alluvial fans, having an average width (E-W) of 10–15 km and length (N-S) of 8–15 km, have been mapped using the LANDSAT TM imageries on 1:250,000 scale in the Kangra Valley of Himachal Himalaya. This important geomorphic zone of alluvial fans is confined between the foot of the Dhauladhar Range and the Siwalik ridges. These fans are gently sloping from north to south and are slightly dissected having distinct horizons of glacial, glacio-fluvial, fluvial, lacustrine and loessic sediments derived from the Dhauladhar granitic complex, Dharamsala and Siwalik Formations during the glacial and interglacial climatic stages of the Quaternary period. The vertical lithological profiles of these fans show a dominance of gravelly (nearly 60%) facies along with other lithofacies associations representing a braided-river depositional environment. In general, the thickness of fan sediments ranges between 90 and 120 m. The vertical facies are subdivided into three main facies, i.e. lower-, middle- and upper-fan facies, showing distinct sediment characteristics. The presence of glacial moraines and clay-rich debris-flow deposits is significant in the upper-fan facies. The middle-fan facies is gravel-dominated along with some interbedded sandy channel-fill deposits, whereas the lower-fan facies is composed of sand, silt and mud. The genesis of these three fan facies is closely related with the uplift of the source area and climatic changes during the Pleistocene period.