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height of 20 m from present day riverbed and forms extensive surface running parallel to Yamuna River. Below this, around 5 m thick terrace section is also observed
which is extensively modified due to anthropological activities. The section of these
two lower level terrace are poorly exposed. At this locality, the active channel is
about 100 m wide and displays braiding with extensive development of longitudinal
bars and multi-channel flow (Fig. 11d). The OSL sample could not be dated from
this section because of poor sensitivity of quartz. However, this surface is equivalent
to prominently preserved T-6 surface in Barkot area and continues downstream. The
sequence indicates deposition as sedimentary fill under humid stream flow environment with extensive sediment supply. Though the terrace deposits were laid down
during humid conditions but reduced sedimentary supply and moderate energy conditions lead to lateral erosion resulting in degradation of the terrace.
Chattanga Section
Further downstream, opposite to Chattanga Village, multiple level of terrace stair
cases (5 terrace levels) are present exposing almost complete sequence of terrace
deposits along road cuttings (Fig. 12). Four terrace sections were measured and
logged. On the right bank, three level of terraces at heights of ~120 m, ~108 m and
~95 m respectively from preset day river bed are exposed. The top most terrace
deposit is characterized by 6 m thick clast supported, moderately sorted, well imbricated, well rounded to rounded clasts (Gm) stacked in two distinct units with
coarsening upward clasts size (Figs. 12 and 14e). The sedimentary sequence shows
cross stratification in gravel which occurs as lensoidal bodies with very less amount
of matrix. However, lenses of medium to fine laminated sand are present in lower
middle and upper part of the section. The top part of terrace section at the height of
around 108 m from the present day Yamuna consist of about six-meter-thick clast
supported, moderately sorted, well imbricated, well rounded to rounded clasts (Gm)
with very less amount of matrix cross stratified at places (Figs. 12 and 14c) is
observed. This unit is overlain by 5 m thick clast supported, moderately sorted, well
imbricated, well rounded to rounded clasts (Gm) in sandy matrix. Along the road
cutting around 75 m thick gravel sequence consisting of vertical stacking of moderately sorted, rounded to surrounded clast supported gravel in sandy matrix (Gm)
(Figs. 12 and 14b) is present. The sequence shows vertical deposition of gravel in
lensoidal and cross stratified fabric. On the left bank, equivalent to third level of
terrace from the top, a terrace deposit is present on road cutting consisting of alternate units of clast supported, moderately sorted, well imbricated, rounded to sub
rounded gravel in sandy matrix (Gm) stacked vertically in lensoidal and cross stratified fashion (Figs. 12 and 14d). Few sand lenses are present in the middle part of the
section. The active channel at this place is very wide and the width is about 45–50 m
(Figs. 12 and 14d). The depositional fabric and sedimentary attributes, indicate
deposition under braided channel with multiple channel bar accumulation under
excessive sediment load in warm-humid climate.
S. Dutta et al.
height of 20 m from present day riverbed and forms extensive surface running parallel to Yamuna River. Below this, around 5 m thick terrace section is also observed
which is extensively modified due to anthropological activities. The section of these
two lower level terrace are poorly exposed. At this locality, the active channel is
about 100 m wide and displays braiding with extensive development of longitudinal
bars and multi-channel flow (Fig. 11d). The OSL sample could not be dated from
this section because of poor sensitivity of quartz. However, this surface is equivalent
to prominently preserved T-6 surface in Barkot area and continues downstream. The
sequence indicates deposition as sedimentary fill under humid stream flow environment with extensive sediment supply. Though the terrace deposits were laid down
during humid conditions but reduced sedimentary supply and moderate energy conditions lead to lateral erosion resulting in degradation of the terrace.
Chattanga Section
Further downstream, opposite to Chattanga Village, multiple level of terrace stair
cases (5 terrace levels) are present exposing almost complete sequence of terrace
deposits along road cuttings (Fig. 12). Four terrace sections were measured and
logged. On the right bank, three level of terraces at heights of ~120 m, ~108 m and
~95 m respectively from preset day river bed are exposed. The top most terrace
deposit is characterized by 6 m thick clast supported, moderately sorted, well imbricated, well rounded to rounded clasts (Gm) stacked in two distinct units with
coarsening upward clasts size (Figs. 12 and 14e). The sedimentary sequence shows
cross stratification in gravel which occurs as lensoidal bodies with very less amount
of matrix. However, lenses of medium to fine laminated sand are present in lower
middle and upper part of the section. The top part of terrace section at the height of
around 108 m from the present day Yamuna consist of about six-meter-thick clast
supported, moderately sorted, well imbricated, well rounded to rounded clasts (Gm)
with very less amount of matrix cross stratified at places (Figs. 12 and 14c) is
observed. This unit is overlain by 5 m thick clast supported, moderately sorted, well
imbricated, well rounded to rounded clasts (Gm) in sandy matrix. Along the road
cutting around 75 m thick gravel sequence consisting of vertical stacking of moderately sorted, rounded to surrounded clast supported gravel in sandy matrix (Gm)
(Figs. 12 and 14b) is present. The sequence shows vertical deposition of gravel in
lensoidal and cross stratified fabric. On the left bank, equivalent to third level of
terrace from the top, a terrace deposit is present on road cutting consisting of alternate units of clast supported, moderately sorted, well imbricated, rounded to sub
rounded gravel in sandy matrix (Gm) stacked vertically in lensoidal and cross stratified fashion (Figs. 12 and 14d). Few sand lenses are present in the middle part of the
section. The active channel at this place is very wide and the width is about 45–50 m
(Figs. 12 and 14d). The depositional fabric and sedimentary attributes, indicate
deposition under braided channel with multiple channel bar accumulation under
excessive sediment load in warm-humid climate.
S. Dutta et al.