Spatial Distribution Pattern of Siwalik Fossils and its Potential Causes

Sikdar, Abhishek (2022) Spatial Distribution Pattern of Siwalik Fossils and its Potential Causes. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Abhishek Sikdar (17MS117)) 17MS117_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (1MB)

Abstract

The Siwalik Subgroup sediments are well known for rich preservation of fossil assemblages belonging to the Miocene to Pleistocene sedimentary rocks exposed in different sub-basins spreading out from Potwar in Pakistan to Arunachal Pradesh of India, through Nepal. Sedimentologically and paleoenvironmentally, all these sub-basins show lateral variations. In this study I used a list of fossils reported in previously published literature to find if there is any spatial distribution pattern of the occurrence of fossil assemblages in these subbasins. Moreover, I ask, if there is any spatial pattern in fossil distribution, what are the sedimentological or paleoenvironmental controls on that pattern. I find that throughout the Siwalik sub-basins, a total of 393 genera under 125 families have been reported. Paleoenvironmentally, these fossils can be classified into eight categories: terrestrial fauna, terrestrial flora, marine vertebrates, freshwater vertebrates, and vertebrate present in both terrestrial marine as well as freshwater environment, marine invertebrates, freshwater invertebrates, freshwater plants, and ichnotaxa. It is revealed through cluster analysis that Potwar has shown the highest abundance of terrestrial fauna and as we move spatially towards the eastern part of the Siwaliks, its abundance decreases. The abundance of terrestrial flora increases from Nepal onwards till Arunachal Pradesh, with Sikkim-Darjeeling showing highest abundance for terrestrial flora. PCA analysis for the same also supports the result obtained through cluster analysis. PCA for sedimentological (host rock lithology) and environmental variable (depositional environment) for the sub-basins reveals that the environmental variables (depositional environment) along with geographical positioning of Jammu and Kangra subbasins may have been responsible for showing a similarity in taxa; whereas sedimentological variables (host rock lithology) may have been responsible for Nepal and Sikkim-Darjeeling. The clustering of Subathu, DehraDun, and Arunachal Pradesh could not be explained via these two variables, as their lithology and depositional environment were different from each other.

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