The Tista River is flowing through Higher Himalaya and Lesser Himalaya lithology and all major lithotectonic boundaries and thrust system of Himalaya. Therefore one important approach to study is sedimentological characteristics of these river sediments reveals source area information.
"Sedimentological studies of Pond deposits from Tista river floodplain, Rangpo, Sikkim"
1. “SEDIMENTOLOGICAL STUDIES OF POND
DEPOSITS FROM TISTA RIVER FLOODPLAIN,
NEAR RANGPO, SIKKIM”
Under the Supervision of
Dr. Anand G. Badekar
Presented by
Pinaki Bhusan Sahoo
Roll No- 16MSGL08
Department of Geology
2. INTRODUCTION
• Any depression in the ground which collects and retains a
sufficient amount of precipitation can be considered as a pond.
They may arise naturally in floodplains as part of a river system,
or they may be somewhat isolated depressions.
• Ponds are the source of information about changes that occurred
in the past in the areas of river drainage basins. Structural and
textural characteristics of these deposits may reflect not only
climate changes, but also allow for an evaluation of the
landform.
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3. LITERATURE REVIEW
• Pond deposits occur associated with alluvial sediments in Miocene sequence of
Madrid basin, Spain. The floodplain facies are typically red mudstone with
interbedded sandstones and siltstones. Palaeosols associated with the ponds show a
pedofacies relationship and the maturity, the maturity of soils increasing with distance
from the main channel. (Sanz et al., 1995)
• Tista River sand in Sikkim is characterized by quartz, plagioclase and K-feldspar.
Rock fragments include mainly high-rank metamorphic grains from the Higher
Himalayan Crystallines (MI* = Metamorphic Indices) reflecting average metamorphic
grade of source rock. (Vezzoli et al., 2017)
• Provenance analysis of sediments is aimed at reconstructing the parent-rock
assemblages of sediments and the climatic physiographic conditions under which
sediments formed. The contributions to the special issue "Quantitative Provenance
Analysis of Sediments" illustrate the intrinsic multidisciplinary and rapid expansion of
QPA. (Garzanti et. al., 2007)
4. IMPORTANCE OF PRESENT STUDY
• Tista river floodplains are important from sedimentological processes as
well as climatic influence, in Tista valley. Pond fill deposits also preserve
the record of sedimentological processes of the area.
• The Tista River is flowing through Higher Himalaya and Lesser Himalaya
lithology and all major lithotectonic boundaries and thrust system of
Himalaya. Therefore one important approach to study is sedimentological
characteristics of these river sediments reveals source area information.
5. AIM OF STUDY
• To understand floodplain development of Tista river system and
identification of different types of lithofacies, structures, mineralogical
assemblages and their interpretation to determine the depositional
characteristics.
• To find out facies variation of floodplain deposits.
• To find out grain size variation throughout lithosection for understanding
energy condition during deposition of sediments.
• To find out Mineralogical assemblage by Petrography analysis and XRD.
• Combining all above aspects for understanding landform evolution of Tista
river.
OBJECTIVES
11. 1. FIELD SEDIMENTOLOGY
• The field sedimentology of Tista river deposits near Rangpo area
includes documentation of grain size, colour variation, lithofacies
variation, measurement of individual lithologies, and observation of
sedimentary structures.
• Sedimentological studies mainly focused on four pond deposits.
Where these pond deposits are located from the southernmost tip of
the deposits and show various sizes. It includes lithosection from S1-
C4.
18. FIELD SEDIMENTOLOGY RESULTS
• These pond deposits are of variable thickness indicate variable size of
depression in floodplain area.
• The characteristics of colour variation changing from base to top as
greenish, dark grey, purple, yellow and orange. This infers depositional
conditions are changing from reducing to oxidative environment.
• Sedimentary structures and bedding shows variation from base to top as
thick mud, parallel lamination, convolute bedding ,climbing ripples, wavy
bedding, lenticular bedding and sand-shale alternation.
• Therefore these pond fill deposits infers depositional condition
changing from calm environment to comparatively high energy
environment.
19. 2. GRAIN SIZE ANALYSIS
For textural studies of river sediment can be revealed by grain size
analysis. Therefore, total 26 sediment samples are collected from Tista
River. The grain size distribution of sediments is carried out by using Sieve
shaker and the produced data are analysed using GRADISTAT software.
Then different statistical parameters are interpreted as follows.
1) Mean
2) Sorting
3) Skewness
4) Kurtosis
24. GRAIN SIZE RESULTS
• Samples are mainly sandy group comprises of mainly very fine to coarse grained size fractions. (18)
samples are very fine , (5) samples are fine, (1) sample is medium and (1) sample is coarse grained out of
25 samples.
• The modality of these samples show unimodality dominating over Bimodal nature of samples.
• The skewness values of samples show variation from Very finely skewed, Finely skewed, Symmetrical
skewed, Coarse skewed to Very coarse skewed. Total (14) samples are symmetrically skewed, (8) samples
are coarsely skewed, (1) sample is very fine skewed, (1) sample is very fine skewed, (1) sample is very
coarse skewed.
• The Kurtosis curves of these samples show variation from Platykurtic, Very platykurtic, Mesokurtic,
Leptokurtic to Very leptokurtic. Total (14) samples are Platykurtic, (5) samples are Very platykurtic, (3)
samples are Mesokurtic, (2) samples are Leptokurtic and (1) sample is Very leptokurtic.
• Therefore energy condition of depositing agent changing from calm
energy condition to high energy condition.
25. 3. PETROGRAPHIC ANALYSIS
• The total Twenty eight samples were collected from fluvial channels, bars
and flood plain characterising pond deposits from Tista river.
• The total points are counted more than 300 grains per thin section (Gazzi-
Dickinson method and Ingersoll et al., 1984).
30. PETROGRAPHIC RESULTS
• The point count of the samples reveals the dominance of lithic metamorphic
fragments than the lithic sedimentary fragments.
• Fluvial detritus from Tista in Sikkim is characterised by quartz, plagioclase and
K-feldspar. This indicates the sediments are immature and they are less
transported from source area.
• Quartz-monocrystalline, Quartz-polycrystalline, Lithic metamorphic, chlorite,
sillimanite, and Kyanite contribute in higher amount indicate metamorphic
source for sediments source is from higher Himalayan crystalline rocks.
• The contribution of lithic sedimentary fragment indicates recycled sedimentary
nature.
• Therefore Petrographic studies of pond deposits show compositional
immaturity of sediments.
33. P-XRD RESULTS
• Mineral assemblages are quartz, orthoclase, mica, garnet, chlorite, illite,
smectite, hematite, goethite
• This infers contribution of Higher Himalayan as well as Lesser Himalayan
source for finer fractions.
• Therefore these assemblages also infer physical weathering is dominating over
chemical weathering.
34. CONCLUSIONS
• From field sedimentology these pond fill deposits infers depositional condition
changing from calm environment to comparatively high energy environment.
• From grain size analysis it is infer that energy condition of depositing agent
changing from calm energy condition to high energy condition.
• Petrographic studies of pond deposits show compositional immaturity of
sediments.
• From P-XRD the mineral assemblages also infers physical weathering is
dominating over chemical weathering.
