199
(Table 1) were recognized from the exposed outcrops of Quaternary deposits in
Yamuna valley area.
These are present as patches of fluvial terrace, landslide, and alluvial fan surfaces
that indicate variable depositional processes and environment and broadly consisting of gravel, sand and mud facies. The sectorwise account of the individual and
representative composite sections in Sector-I and II is stated forward:
3.2.1 Sector-I
Kharsali Village Section
Around 5.5 Km downstream of Yamunotri temple, at Kharsali, about 50 m high terrace surface running parallel to Yamuna River is observed (Fig. 8). The surface
represents paleo-flood plain of Yamuna River and dominantly consists of very
poorly sorted, clast supported disorganized Gdm facies with sub angular to subrounded clasts in sandy-muddy matrix in exposed middle 5 m part of section
(Fig. 8b). The unit is overlain by around 7 m thick clast supported, imbricated, moderate to poorly sorted fluvial gravel in sandy matrix (Gm) facies (Fig. 8c). The depositional sequence is exposed along road cutting at places. Most of the sections are
concealed due to erection of retaining wall along roadside. The characteristic stacking of sedimentary facies, their arrangement and fabric of deposits suggests pulses
of debris fan progradation (from tributary channel) followed by persistent Yamuna
channel deposition under humid environment.
Phoolchatti Sections
At Phoolchatti (around 5–6 Km downstream from Kharsali) remnants of terrace
surface at the height of ~100 m above present day Yamuna River bed on the right
bank (Fig. 9) were observed. Two sections were measured and composite log is
prepared. The exposed sedimentary sequence on right bank dominantly consists of
stratified Gm facies characterized by poorly sorted, clast supported, and moderately
imbricated, stratified sub-rounded to sub-angular gravel in sandy-gritty matrix
(Fig. 9d). The terrace surface is flat and represents sloping paleo-flood plain of
Yamuna River on right bank (Fig. 5). Overall the facies characters and its vertical
disposition indicates deposition by Yamuna River in pulses during warm humid
condition and pulsatory influx of sediments.
The active channel in this segment occupies a narrow ‘V’-shaped valley having
a width of around 10–15 m only. However, the section on the left bank exposes
equivalent terrace deposit comprising dominantly of 2 m thick moderately sorted
and imbricated clast supported gravel in sandy matrix at the base, (Fig. 9b, c). The
unit is overlain by 4 m thick clast supported, poorly sorted, disorganized gravel in
sandy matrix with imbrication at places. The size of the clast is more than the lower
unit. This unit is overlain by 12 m thick gravel (poorly exposed as on sloping surResponses of Indian Summer Monsoon Dynamics and Late Quaternary Fluvial…
(Table 1) were recognized from the exposed outcrops of Quaternary deposits in
Yamuna valley area.
These are present as patches of fluvial terrace, landslide, and alluvial fan surfaces
that indicate variable depositional processes and environment and broadly consisting of gravel, sand and mud facies. The sectorwise account of the individual and
representative composite sections in Sector-I and II is stated forward:
3.2.1 Sector-I
Kharsali Village Section
Around 5.5 Km downstream of Yamunotri temple, at Kharsali, about 50 m high terrace surface running parallel to Yamuna River is observed (Fig. 8). The surface
represents paleo-flood plain of Yamuna River and dominantly consists of very
poorly sorted, clast supported disorganized Gdm facies with sub angular to subrounded clasts in sandy-muddy matrix in exposed middle 5 m part of section
(Fig. 8b). The unit is overlain by around 7 m thick clast supported, imbricated, moderate to poorly sorted fluvial gravel in sandy matrix (Gm) facies (Fig. 8c). The depositional sequence is exposed along road cutting at places. Most of the sections are
concealed due to erection of retaining wall along roadside. The characteristic stacking of sedimentary facies, their arrangement and fabric of deposits suggests pulses
of debris fan progradation (from tributary channel) followed by persistent Yamuna
channel deposition under humid environment.
Phoolchatti Sections
At Phoolchatti (around 5–6 Km downstream from Kharsali) remnants of terrace
surface at the height of ~100 m above present day Yamuna River bed on the right
bank (Fig. 9) were observed. Two sections were measured and composite log is
prepared. The exposed sedimentary sequence on right bank dominantly consists of
stratified Gm facies characterized by poorly sorted, clast supported, and moderately
imbricated, stratified sub-rounded to sub-angular gravel in sandy-gritty matrix
(Fig. 9d). The terrace surface is flat and represents sloping paleo-flood plain of
Yamuna River on right bank (Fig. 5). Overall the facies characters and its vertical
disposition indicates deposition by Yamuna River in pulses during warm humid
condition and pulsatory influx of sediments.
The active channel in this segment occupies a narrow ‘V’-shaped valley having
a width of around 10–15 m only. However, the section on the left bank exposes
equivalent terrace deposit comprising dominantly of 2 m thick moderately sorted
and imbricated clast supported gravel in sandy matrix at the base, (Fig. 9b, c). The
unit is overlain by 4 m thick clast supported, poorly sorted, disorganized gravel in
sandy matrix with imbrication at places. The size of the clast is more than the lower
unit. This unit is overlain by 12 m thick gravel (poorly exposed as on sloping surResponses of Indian Summer Monsoon Dynamics and Late Quaternary Fluvial…