214
variations and tectonic activity, river valleys and concomitant landforms in the form
of river terraces are potential archives. Their sedimentological and geomorphological development in time and space documents the potential linkages of monsoon
driven precipitation, glacial-interglacial transition and related disparity in surficial
processes operated in variable climatic domains. The late Pleistocene geomorphic
and sedimentological records in the Yamuna valley suggest aggradation and incision
that took place in pre-existing (antecedent) valley and controlled by sedimentary
fluxes from trunk and Tributary Rivers. These fluxes are mainly derived by glacial
as well as non-glacial (landslide, avalanche, local creep and weathered mass etc.)
sediment readjustment in the river system resulted in spatial and temporal geomorphic evolution of the Yamuna valley in the form of alluvial fans and fluvial terraces.
We synthesized the sedimentological and geomorphological data along the Yamuna
valley in the transect between Hathiyari (near MBT) and Kharsali (north of MCT)
and attempted OSL based chronology of Late Quaternary sedimentary deposits to
understand the linkages between palaeoclimate variations and tectonics in this monsoon dominated valley. In general, the data illustrates several periods of enhanced
sediment supply in the trunk river from catchment owing to extensive erosional
activities. This led to rise in palaeofloodplain of Yamuna (due to sediment aggradation) to distinct levels with the maximum recorded palaeofloodplain height of
around 2–20 m above present day Yamuna river bed. The sediment aggradation
phases are punctuated by shorter incisional phases to attain its base level of erosion
leaving behind multiple degradational terrace levels. The OSL based chronological
data suggests abandonment of these terraces might have occurred during major climatic fluctuations and related to changes in moisture as well as sediment availability in the catchments which is reflection of glacial-inter glacial oscillations and
related arid to humid or vice versa transitions. Such climatic variations control the
water: sediment budget and also the availability of soil and regolith for erosion as
well as changes in river hydraulics. To understand the impact of such climatic fluctuations in river valley development during late Quaternary in context of sediment
erosion and related aggradation phases, an attempt has been made during the study
to address the variations in palaeomonsoon, glacial-interglacial conditions and its
impact on surficial processes in the valley. The Palaeoclimatic studies show that
adjacent to India and Africa such major climatic variability is related to large fluctuations in the wind and precipitation fields associated with monsoonal circulations
(Prell and Kutzbach 1987; Kathayat et al. 2016).
The timing of Phase-I aggradation (~105 ka to ~80 ka) occurred during Marine
Isotopic Stage-5 (MIS-5). This stage is sub-divided in to five sub-stages with alternate warm and cold periods deduced from oxygen isotope data (δ O
18
) from marine
cores reflecting changes in temperature. The data illustrates that the Yamuna valley
floor was aggraded with fluvial sediments upto around 220 m height above present
river bed during this palaeoclimatic stage (Fig. 19). Also, the MIS-5 has been
recorded as marked variability in Northern Hemisphere summer insolation (NHSI)
which suggest to be the controlling factor responsible for monsoon variability by
precession-induced changes in NHSI (Kathayat et al. 2016). Moreover, it is also
argued that changes in elevation of Himalaya-Tibet have significant effects on the
S. Dutta et al.
variations and tectonic activity, river valleys and concomitant landforms in the form
of river terraces are potential archives. Their sedimentological and geomorphological development in time and space documents the potential linkages of monsoon
driven precipitation, glacial-interglacial transition and related disparity in surficial
processes operated in variable climatic domains. The late Pleistocene geomorphic
and sedimentological records in the Yamuna valley suggest aggradation and incision
that took place in pre-existing (antecedent) valley and controlled by sedimentary
fluxes from trunk and Tributary Rivers. These fluxes are mainly derived by glacial
as well as non-glacial (landslide, avalanche, local creep and weathered mass etc.)
sediment readjustment in the river system resulted in spatial and temporal geomorphic evolution of the Yamuna valley in the form of alluvial fans and fluvial terraces.
We synthesized the sedimentological and geomorphological data along the Yamuna
valley in the transect between Hathiyari (near MBT) and Kharsali (north of MCT)
and attempted OSL based chronology of Late Quaternary sedimentary deposits to
understand the linkages between palaeoclimate variations and tectonics in this monsoon dominated valley. In general, the data illustrates several periods of enhanced
sediment supply in the trunk river from catchment owing to extensive erosional
activities. This led to rise in palaeofloodplain of Yamuna (due to sediment aggradation) to distinct levels with the maximum recorded palaeofloodplain height of
around 2–20 m above present day Yamuna river bed. The sediment aggradation
phases are punctuated by shorter incisional phases to attain its base level of erosion
leaving behind multiple degradational terrace levels. The OSL based chronological
data suggests abandonment of these terraces might have occurred during major climatic fluctuations and related to changes in moisture as well as sediment availability in the catchments which is reflection of glacial-inter glacial oscillations and
related arid to humid or vice versa transitions. Such climatic variations control the
water: sediment budget and also the availability of soil and regolith for erosion as
well as changes in river hydraulics. To understand the impact of such climatic fluctuations in river valley development during late Quaternary in context of sediment
erosion and related aggradation phases, an attempt has been made during the study
to address the variations in palaeomonsoon, glacial-interglacial conditions and its
impact on surficial processes in the valley. The Palaeoclimatic studies show that
adjacent to India and Africa such major climatic variability is related to large fluctuations in the wind and precipitation fields associated with monsoonal circulations
(Prell and Kutzbach 1987; Kathayat et al. 2016).
The timing of Phase-I aggradation (~105 ka to ~80 ka) occurred during Marine
Isotopic Stage-5 (MIS-5). This stage is sub-divided in to five sub-stages with alternate warm and cold periods deduced from oxygen isotope data (δ O
18
) from marine
cores reflecting changes in temperature. The data illustrates that the Yamuna valley
floor was aggraded with fluvial sediments upto around 220 m height above present
river bed during this palaeoclimatic stage (Fig. 19). Also, the MIS-5 has been
recorded as marked variability in Northern Hemisphere summer insolation (NHSI)
which suggest to be the controlling factor responsible for monsoon variability by
precession-induced changes in NHSI (Kathayat et al. 2016). Moreover, it is also
argued that changes in elevation of Himalaya-Tibet have significant effects on the
S. Dutta et al.