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Himalayan Geology, Vol. 30 (2), 2009, pp.155-165 Printed in India
Variable period of aggradation and termination history of
two distinct late Quaternaryalluvial fans in the Soan Dun, NW Sub Himalaya:
Impact of tectonic and climate
N. SURESH, ROHTASH KUMAR
Wadia Institute of Himalayan Geology, Dehra Dun-248 001,
India
Abstract: Two alluvial fans, the
Amb and Barera fans, deposited under different tectonic settings in the
northwestern and southeastern part of the Soan Dun respectively, were
studied to understand their evolution through time. The Amb Fan is deposited
in front of Soan Thrust whereas the Barera Fan is abutting anticlinally
folded Siwaliks with unconformable contact. Both the fan deposits have been
entrenched by streams forming 10 to 25m thick vertical scarps having more or
less similar facies association dominated by sand and mud litho-units with
rare gravels. Based on quartz optically stimulated luminescence (OSL)
dating, the Barera Fan is assigned an older age (36-29 ka B.P.) and the Amb
Fan an younger age (23-10 ka B.P.). The abandonment of the Barera Fan and
continuous sedimentation in the Amb Fan reveal that creation of
accommodation space in the northwestern part of the dun in response to Soan
Thrust activity. The Barera and Amb fans were terminated at 29 and 10 ka B.P.
respectively and both the fans subsequently entrenched in the increased
monsoon phase. |
