Study of the Pattern of Neogene Sedimentation in the Western Part of Siwalik Foredeep of Arunachal Pradesh (India)

International Journal of Geoinformatics and Geological Science

© 2015 by SSRG - IJGGS Journal

Volume 2 Issue 3

Year of Publication : 2015

Authors : Ashfia Sultana

10.14445/23939206/IJGGS-V2I4P102

How to Cite?

Ashfia Sultana, "Study of the Pattern of Neogene Sedimentation in the Western Part of Siwalik Foredeep of Arunachal Pradesh (India)," SSRG International Journal of Geoinformatics and Geological Science, vol. 2,  no. 3, pp. 11-18, 2015. Crossref, https://doi.org/10.14445/23939206/IJGGS-V2I4P102

Abstract:

The Upper Tertiary rocks of Arunachal Pradesh are represented by Dafla, Subansiri and Kimin Formations. The Dafla Formation is characterized by bedding. The distinctness and the degree of preservation of bedding indicate quietness of water during sediment accumulation. The middle and upper part of this Formation consist of silty sandston containing coal streaks whereas the overlying Subansiri Formation shows poor development of the bedding character. Poor stratification is due to relatively higher velocity of transport and lack of opportunity for local sorting. This Formation mainly consists of medium to fine grained sediment with salt and pepper texture. The Kimin Formation is conglomeratic in nature and consists of sand and gravel deposits. This reflects increase in intensity of turbulance and velocity of current during its deposition. The study of size and shape parameters of Dafla and Subansiri sediments suggests that these sediments are medium to fine grained and deposited in fluviatile environment. The Mean size (Mz) of Dafla and Subansiri sandstones indicates a fine sand type deposited by moderate to low velocity current. Moreover the standard deviation () values of both the sandstone suggest moderately sorted character of the sediments indicating same level of fluctuation in kinetic energy condition for the depositing agent. Positive skewness character is dominant in both Dafla and Subansiri Sandstones shows the presence of more material in the fine tail. Higher values of the average kurtosis (Kg) in Dafla and Subansiri sediments suggest that the major part of the sediments achieved good sorting elsewhere and deposited finally in an environment of low sorting efficiency. Sphericity and roundness study of the grains of both the sandstones have shown high sphericity and moderate roundness suggesting a texturally submature character for these sediments. Further it reveals that the velocity of the current and the degree of turbulance in the depositing medium was moderate and the transportation of the sediment took place for a short distance from the source area before deposition. From the sedimentological evidences deduced from field and laboratory investigations it could be inferred that sediment of both Dafla and Subansiri Formations were deposited under fluviatile condition by river during the Upper Tertiary period. The conglomeratic character of the Kimin Formation and gradual coarsening of the sediments upward, indicate shallowing up of the basin of deposition towards the later part of Upper Tertiary period.

Keywords:

Upper Tertiary, Kurtosis, Texturally submature, source area, Fluviatile.

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