A rich and diverse palynoassemblage recovered from the Churanthi River section (26°53' 59.3" N, 88°34' 17.2" E), Darjeeling foothills Eastern Himalaya, has yielded 87 species assigned to 69 genera. The palynoassemblage is rich in angiosperm taxa (45.63%) followed by gymnosperms (0.45%), pteridophytes (18.49%) and fungal remains (23.88%). Based on their nearest living relatives, a wet evergreen to semi-evergreen forest under a humid tropical to sub-tropical environment during the Mio-Pliocene age has been suggested. A lot of angiosperms such as Palaeosantalaceaepites, Araliaceoipollenites, Malvacearampollis, Zonocostites, Neocouperipollis, Dicolpopollis, Palmidites, Palmaepollenites, isolated salt glands of mangrove plant leaves (Heliospermopsis) and Mediaverrunites type of fungal spores, along with ichnofossils like Planolites, Palaeophycus, Skolithos, Rosselia, Ophiomorpha and Teichichnus associated with rippled mudstone-siltstone suggest an environment strongly influenced by brackish water. Primary sedimentary structures in the associated strata indicate strong wave agitation common in shallow marine setting. Some high elevation components (5.14%) such as Alnipollenites, cf. Corylus (Betulaceae), Juglanspollenites, Engelhardtioipollenites (Juglandaceae), Quercoides, Cupuliferoidaepollenites, Lithocarpus, Castanopsis (Fagaceae), Abietineaepollenites (Pinaceae) represent hinterland vegetation possibly transported to the prograding deltaic coastline by the rivers. Reworked palynotaxa (Striatopodocarpites sp., Striatites sp., Faunipollenites sp., Circumstriatites sp., Crescentipollenites sp., Cuneatisporites sp., Parasaccites sp., Scheuringipollenites sp., Rhizomaspora sp., Marsupipollenites sp., Lophotriletes sp.) of Permian age have also been recorded in the palynoassemblage (11.55%) indicating the abundance of Permian Gondwana strata in the source area.

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This paper presents the sedimentological analysis of about 1.3 km succession of Neogene Siwalik Group exposed in the Gish River section, Darjeeling foothills. Contrary to the existing alluvial fan-braided stream depositional model, the facies analysis shows that the succession accumulated in a shallow marine deltaic setting. Nine facies identified represent deposition from various processes related to unidirectional and oscillatory current, suspension settlement in quiet water and also to processes related to soil formation. Abundant trace fossils of marine affinity occur throughout the succession and include Cylindrichnus, Rosselia, Teichichnus, Rhizocorallium, Chondrites and Zoophycos. The studied succession has been subdivided into seven facies associations that can be interpreted in terms of the different sub-environments of a river-dominated delta. The lower~550 m of the succession comprises sand-mud alternation of delta front, delta mouth and delta plain deposits (FA3, 4, 5 and 6), organized in stacked, 10-30 m coarsening-upward units, and is inferred to represent progradation of the delta lobes. The overlying 300 m mud-dominated interval is dominated by prodelta to open marine bay-fill succession (FA1 and 2); the pebbly sandstones and conglomerates of the uppermost~500 m represent a braidplain delta environment. A kilometre-scale coarsening-upward trend of the Siwalik deposits of this section is attributable to southward propagation of the thrust front related to the activity of the Main Boundary Thrust (MBT). The sedimentological analysis shows that a marine embayment existed in the Eastern Himalaya during the Siwalik time and the deltaic succession reported here provides the link between the upland transverse drainages recorded from Western Himalaya and the deep marine Bengal Fan succession.

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