216
gesting widespread aggradation through local and might be through trunk river sediment progradation under enhanced monsoon precipitation. The third aggradation
phase occur during Last Glacial Maxima (LGM) on account of transition from
humid pre-LGM to cool-arid LGM climate during ~19 to <16 ka. The Sub-Himalaya
equivalent phase is recorded across MBT in the form of valley aggradation during
>15 to 11 ka (Dutta et al. 2012) and also in the south of HFT along Ganga valley
(Sinha et al. 2010). The cold and arid conditions during LGM is witnessed as intra
valley floodplain development and pedogenesis further south in the Ganga plain
(Sinha et al. 2007a), accumulation of aeolian and lacustrine sediments in valley
margin (Gibling et al. 2005). Combining the data with present study supports widespread aggradation phases along Yamuna river valley along the Himalayan as well
as in plains which suggests widespread sediment progradation under humid and
wetter palaeoclimate, punctuated by periods of incision mainly guided by sediment:
water budget in the river system from catchment. However, in Indo Gangetic plain
(IGP), the sedimentary sequences are discontinuity bounded suggesting distinct
phases of aggradation, floodplain abandonment and pedogenesis (Gibling et al.
2005; Sinha et al. 2007b). However, overprinting of higher Himalayan crystalline
sediment by Lesser Himalayan metasediments is notable in the study area during
aggradation phases because of local channel fan progradation. The sediment aggradation in the valley broadly follow the recorded Indian Summer Monsoon (ISM)
precipitation variations (Prell and Kutzbach 1987) and ISM intensity based on stack
of several proxy records from Arabian sea sediment core (Clemens et al. 2003).
Notably, the sediment aggradation in the valley occurred during strong ISM intensity whereas, degradation/incision periods are marked by weak ISM phases.
6 Conclusion
The sedimentological as well as geomorphological data corroborated with OSL
based chronology infers:
(a) Three to Four major periods of sediment dispersal and aggradation in the valley
under warm climatic conditions. These are well correlatable with Warm phases
(Interglacial) in MIS record. Data correlation with other studies reflects widespread sediment aggradation from source to Ganga plain suggesting enhanced
ISM intensity during these phases.
(b) The sediment aggradation and incision rhythms are primarily manifested on
account of river sediment: discharge variability which is guided by sediment
availability and monsoon driven precipitation in the study area.
(c) The continuation of palaeo-floodplain across MCT and MBT further suggests
profound climate control of sediment generation, dispersal and aggradation.
S. Dutta et al.
gesting widespread aggradation through local and might be through trunk river sediment progradation under enhanced monsoon precipitation. The third aggradation
phase occur during Last Glacial Maxima (LGM) on account of transition from
humid pre-LGM to cool-arid LGM climate during ~19 to <16 ka. The Sub-Himalaya
equivalent phase is recorded across MBT in the form of valley aggradation during
>15 to 11 ka (Dutta et al. 2012) and also in the south of HFT along Ganga valley
(Sinha et al. 2010). The cold and arid conditions during LGM is witnessed as intra
valley floodplain development and pedogenesis further south in the Ganga plain
(Sinha et al. 2007a), accumulation of aeolian and lacustrine sediments in valley
margin (Gibling et al. 2005). Combining the data with present study supports widespread aggradation phases along Yamuna river valley along the Himalayan as well
as in plains which suggests widespread sediment progradation under humid and
wetter palaeoclimate, punctuated by periods of incision mainly guided by sediment:
water budget in the river system from catchment. However, in Indo Gangetic plain
(IGP), the sedimentary sequences are discontinuity bounded suggesting distinct
phases of aggradation, floodplain abandonment and pedogenesis (Gibling et al.
2005; Sinha et al. 2007b). However, overprinting of higher Himalayan crystalline
sediment by Lesser Himalayan metasediments is notable in the study area during
aggradation phases because of local channel fan progradation. The sediment aggradation in the valley broadly follow the recorded Indian Summer Monsoon (ISM)
precipitation variations (Prell and Kutzbach 1987) and ISM intensity based on stack
of several proxy records from Arabian sea sediment core (Clemens et al. 2003).
Notably, the sediment aggradation in the valley occurred during strong ISM intensity whereas, degradation/incision periods are marked by weak ISM phases.
6 Conclusion
The sedimentological as well as geomorphological data corroborated with OSL
based chronology infers:
(a) Three to Four major periods of sediment dispersal and aggradation in the valley
under warm climatic conditions. These are well correlatable with Warm phases
(Interglacial) in MIS record. Data correlation with other studies reflects widespread sediment aggradation from source to Ganga plain suggesting enhanced
ISM intensity during these phases.
(b) The sediment aggradation and incision rhythms are primarily manifested on
account of river sediment: discharge variability which is guided by sediment
availability and monsoon driven precipitation in the study area.
(c) The continuation of palaeo-floodplain across MCT and MBT further suggests
profound climate control of sediment generation, dispersal and aggradation.
S. Dutta et al.