Page 90 - BE Book PESD 2021 22

1. Professor Subir Bera, Centre for Advanced Study, Department of Botany, Calcutta
University 2. Dr Suchana Taral, Postdoctoral Fellow, Department of Geology and
Geophysics, IIT, Kharagpur
5. Date of Commencement:
01/04/2018

6. Expected date of Completion:
31/03/2023
7. Interim report(max 500 words) including complete list of publications and patents
based on the work from the project:
1. During the field season of last two years, the Siwalik successions along several
rivers and road sections (e.g. Bhalukpong, Itanagar and Likhabali sections) were
studied and mapped in 1:50000 scale introducing a new lithostratigraphic unit,
named as the Siji River Formation following the guidelines provided in the code of
stratigraphic nomenclature and the stratigraphic guide as a replacement for
traditional three-fold classification. This newly defined formation is a 750-1050 m
thick, characterised by grey mudstone-siltstone-sandstone units with minor
conglomeratic beds, and occurs in between the Middle Siwalik Subansiri Formation
and the Upper Siwalik Kimin Formation. Siji River section has been proposed as the
type section for this Formation.

The detailed sedimentology and paleocurrent pattern were measured from three key sections
name the Bhalukpong (~4000 m), Itanagar-Gohpur Road (2500 m) and Siji River (~4700 m)
about 1000 paleocurrent vectors were measured from these sections. The wave- and tide-
generated sedimentary structures, marine trace fossils and bimodal or polymodal
paleocurrent pattern as recorded from the Dafla Formation and the Siji River Formation
indicate that these two units represent deposition in the wave- and tide-affected shallow
marine environments. Hence there were two phases of marine transgression during the
deposition of the Siwalik succession in the eastern Himalaya.

Systematic sampling was done across 3500 m succession of the Lower and Middle Siwalik
rocks exposed in the Siji River section. The samples were collected with an average spacing
of 70-100 m of stratigraphic thickness between them and is being studied to examine the
progressive temporal evolution of the source terrain. During petrography and EPMA of thin
sections of a number of sandstones, Verdine facies mineral is found which is associated with
shallow marine shelf /lagoonal environment.

Papers published or communicated:

• Taral, S., Sarkar, S., and Chakraborty, T., An ichnological model for a deltaic
depositional system: New insights from the Neogene Siwalik Foreland Basin of
Darjeeling-Sikkim Himalaya. Palaeogeography, Palaeoclimatology, Palaeoecology,
doi: 10.1016/j.palaeo.2018.08.004.
• Taral, S., Chakraborty, T., Huyghe, P., van der Beek, P., Vögeli, N., Dupont-Nivet,
G., 2019. Shallow marine to fluvial transition in the Siwalik succession of the

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