188
younger aggradation phase (Phase-IV) represented by discontinuous terrace deposits (T-1 and T-2) is recorded across MCT. The Late Quaternary sedimentary archives
in the valley across MCT and correlation of aggradation and incision phases correlates well with ISM dynamics (δ
18
O record), and profound control of glacialinterglacial cycles and ISM variation in the area since MIS-5e.
Keywords Late quaternary sedimentary deposits · Fluvial landforms · ISM
dynamics and Palaeoclimate · Chronology of deposits
1 Introduction
The Quaternary period has been recognized by rhythmic climatic variations in the
form of glaciations interspersed with relatively warm, interglacial intervals as established from marine records (Shackleton and Opdyke 1973; Imbrie et al. 1984;
Chappel and Shackleton 1986; Shackleton 1987; Lisiecki and Raymo 2005). In
terrestrial orogenic settings, such glacial-interglacial transitions controls the hydrological regime and sediment load, is thus the governing factor in determining the
river morphology (Vandenberghe 2008; Pan et al. 2003). However, studies have also
suggested that the tectonics of the area may induce uplift and incision (Srivastava
et al. 2008; Kasse et al. 1995; Singh et al. 2001; Törnquist 1995; Berendsen and
Stouthamer 2000; Wallinga et al. 2004; Busschers et al. 2005). Fluvial terraces
along with tectonically active mountain system attracted scientists through decades
to comprehend the geomorphic evolution of river valleys in response to Late
Quaternary climatic fluctuations and tectonic perturbations (Srivastava et al. 2007,
2008; Bridgland 2000; Holdbrook and Schumm 1999; Srivastava and Mishra 2008;
Ray and Srivastava 2010; Sinha et al. 2010; Dutta et al. 2012). It is argued that terrace formation is a result of either climatically triggered valley accretion due to high
sediment/discharge ratio during drier climatic conditions and subsequent incision
during high discharge-wetter climatic periods (Bridgland 2000; Maddy et al. 2000;
Srivastava et al. 2007; Starkel 2003; Antoine et al. 2000). Moreover, it is emphasized that the critical thresholds of sediment/water budget and crustal deformational
forces together regulates the sediment fluxes and sediment aggradation or incision
in the river systems in orogenic settings giving rise to staircases of terraces. Besides,
ample research has focused on the above issues, but definite answer to the relative
role of climate and tectonics remained elusive and results varies on regional scale.
For better assessment, detailed geomorphic and chronological correlation of terrace
sequences across tectonic/structural discontinuities to provide synoptic view of fluvial response to climatic changes and tectonic deformation is cardinal.
The Yamuna is a perennial river that originates near Yamunotri and flows through
Higher Himalayan Crystalline (HHC), Lesser Himalayan siliciclastic rocks separated by major tectonic discontinuities like Main Central Thrust (MCT), Main
Boundary Thrust (MBT) respectively and exits to Indo-Gangetic plains after crossing Himalayan Frontal Thrust (HFT) separating Sub-Himalaya from Indo-Gangetic
S. Dutta et al.
younger aggradation phase (Phase-IV) represented by discontinuous terrace deposits (T-1 and T-2) is recorded across MCT. The Late Quaternary sedimentary archives
in the valley across MCT and correlation of aggradation and incision phases correlates well with ISM dynamics (δ
18
O record), and profound control of glacialinterglacial cycles and ISM variation in the area since MIS-5e.
Keywords Late quaternary sedimentary deposits · Fluvial landforms · ISM
dynamics and Palaeoclimate · Chronology of deposits
1 Introduction
The Quaternary period has been recognized by rhythmic climatic variations in the
form of glaciations interspersed with relatively warm, interglacial intervals as established from marine records (Shackleton and Opdyke 1973; Imbrie et al. 1984;
Chappel and Shackleton 1986; Shackleton 1987; Lisiecki and Raymo 2005). In
terrestrial orogenic settings, such glacial-interglacial transitions controls the hydrological regime and sediment load, is thus the governing factor in determining the
river morphology (Vandenberghe 2008; Pan et al. 2003). However, studies have also
suggested that the tectonics of the area may induce uplift and incision (Srivastava
et al. 2008; Kasse et al. 1995; Singh et al. 2001; Törnquist 1995; Berendsen and
Stouthamer 2000; Wallinga et al. 2004; Busschers et al. 2005). Fluvial terraces
along with tectonically active mountain system attracted scientists through decades
to comprehend the geomorphic evolution of river valleys in response to Late
Quaternary climatic fluctuations and tectonic perturbations (Srivastava et al. 2007,
2008; Bridgland 2000; Holdbrook and Schumm 1999; Srivastava and Mishra 2008;
Ray and Srivastava 2010; Sinha et al. 2010; Dutta et al. 2012). It is argued that terrace formation is a result of either climatically triggered valley accretion due to high
sediment/discharge ratio during drier climatic conditions and subsequent incision
during high discharge-wetter climatic periods (Bridgland 2000; Maddy et al. 2000;
Srivastava et al. 2007; Starkel 2003; Antoine et al. 2000). Moreover, it is emphasized that the critical thresholds of sediment/water budget and crustal deformational
forces together regulates the sediment fluxes and sediment aggradation or incision
in the river systems in orogenic settings giving rise to staircases of terraces. Besides,
ample research has focused on the above issues, but definite answer to the relative
role of climate and tectonics remained elusive and results varies on regional scale.
For better assessment, detailed geomorphic and chronological correlation of terrace
sequences across tectonic/structural discontinuities to provide synoptic view of fluvial response to climatic changes and tectonic deformation is cardinal.
The Yamuna is a perennial river that originates near Yamunotri and flows through
Higher Himalayan Crystalline (HHC), Lesser Himalayan siliciclastic rocks separated by major tectonic discontinuities like Main Central Thrust (MCT), Main
Boundary Thrust (MBT) respectively and exits to Indo-Gangetic plains after crossing Himalayan Frontal Thrust (HFT) separating Sub-Himalaya from Indo-Gangetic
S. Dutta et al.