Himalayan Geology, Vol. 42 (2), 2021, pp. 321-328, Printed in India
Sediment Grain size characterization of the sand bars from Upper Reaches of Ganga River System, Garhwal Himalaya: A statistical approach
SUBHAJIT SINHA1*, YOGESH RAY2, SUMIT K GHOSH3, SUBHRONIL MONDAL4
1Department of Geology, University of Calcutta, Kolkata, 700019, India
2National Centre for Polar and Ocean Research (Ministry of Earth Sciences) Headland Sada, Vasco-da-Gama-403804, Goa, India
3Formerly Sc-G, Sedimentology Group, Wadia Institute of Himalayan Geology, Dehradun, 248001, India
4Department of Earth Sciences, IISER, Kolkata, Mohanpur, Nadia, 741246, India
*Email (Corresponding author): subho.ecstasy@gmail.com
Abstract: Fluvial systems responsive to changes in flow conditions, is reflected through the grain size distribution of the sediments. This leads to deviate from the assumption that grain sizes follow log normality. Particle-size data have been obtained from sieved fractions of sand samples from the Alaknanda and Bhagirathi River systems in the Himalaya. The patterns of observed grain-size distributions data were subjected to statistical analysis using three probability density functions (pdf), such as, log-normal, log-hyperbolic and log-skew-Laplace. The statistical models indicated that a log-hyperbolic distribution fitted best for 53%, log-skew-Laplace for 47%, and none for log-normal. Factor analysis suggests F1, F2, and F3 explains the variability of the overall grain size data supported by root mean square of the residuals, which is 0. Factor 1 explains 35% of the entire variation, F2 explains 27% and F3 explains 15%; together explaining 77% of the total variation. A cut off of 0.30 was selected and factor loadings revealed that Factor 1 is mostly explained by γ (loading = 0.94) and δ (loading = 0.75), whereas, F2 is mostly explained by α (loading = 0.93) and Φ (loading = 0.77). F3 is explained by mostly β (loading = 0.77). Individual factors are also correlated with each other with exploratory factor net diagram. The deviation from the log normality may be attributed to changes in flow conditions and input of sediments of varying grain sizes throughout the river course. The accurate characterization of these textural parameters will elucidate the depositional environment, erosional and depositional processes and can be applied to study the sedimentary environments in subsurface geological studies.
Keywords: Himalaya, Alaknanda, Grain size, Hyperbolic, Factor analysis
