Luminescence chronology of alluvial fan in North Bengal, India: Implications to tectonics and climate

Alluvial fans are important geomorphic archives because of its strategic location at mountain front which can provide clues to the past climate and tectonics. In general, they provide information about optimum climate condition suitable for fan formation. We provide a detailed luminescence chronology of alluvial fan in north West Bengal, India. The regional fan surface (T₄4) has been dissected by E-W trending Himalayan thrusts known as Matiali and Chalsa thrusts and have various terraces named as T₃, T₂ and youngest one as T₁. Luminescence ages suggest that the formation of the alluvial fan (regional surface) started before 171 ka and continued till 72 ka covering a time span of nearly 100 ky; suggesting of weaker monsoon at 72 ka. Matiali fault activated after 171 ky. Chalsa fault is suggested to be active during 48–41 ka. The last aggradational phase was around 6 ka which led to the formation of T_1a terrace. The study suggests that climatic fluctuation during the period were shaping the morphology of the alluvial fan, along with tectonic activities on the two faults.