Sundarban mangroves stands on a still young and developing Bengal basin delta. Subsidence of the delta is not uniform. Tectonic activity and uneven rate of sediment deposition have caused eastern side of the delta subside more rapidly then the western portion. The only perennial source of freshwater to the forest has significantly experienced shifts in drainage pattern. The west-to-east tilt in the forest caused more freshwater flow through the lower eastern portion; eventually a natural west-to-east salinity gradient across the delta is observed.
Deb, S.C. (1956) Palaeoclimatology and geophysics of the Gangetic Delta. Geological Reviews of India 18: 11-18.