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The Siwalik foreland deposit was earlier considered as freshwater continental megafan deposit, formed by southward flowing transverse drainages, analogous to modern Kosi-like megafans. However, this analogy remained incomplete due to lack of evidence of a regionally persistent axial stream system or marginal marine depositional system, like the Ganga-Brahmaputra River and Ganga Delta, as in the present-day foreland basin. In this paper, we report the abundant wave-generated structures and marine trace fossils from the Siwalik succession of the Tista valley and infer that they represent the deltaic part of the Neogene foreland basin. This interpretation provides the link between upland fluvial deposits of the western Himalaya and deep marine sediments of the Bengal Fan and is more consistent with available data from the Siwaliks of the eastern Himalaya. It also implies that a marine embayment existed in the eastern part of the Siwalik foreland basin. [ABSTRACT FROM AUTHOR]