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Carbon isotope (delta C-13) compositions of total organic carbon (TOC) as well as several extracted higher plant derived lignin biomarkers, along with the recovery of grass phytoliths, provide the first direct evidence of existence of extensive grass land (C4) vegetation over the Ganges deltaic plain during the Last Glacial Maximum (LGM). The earliest Holocene (similar to 9 ka) is marked by pronounced C-13 depletion in the lignin phenols coinciding with rapid sea level rise, intensified monsoon, and replacement of grassland vegetation by mangroves. Another C4 invasion phase is identified during the late Holocene (similar to 6-2 ka). Both the LGM and late Holocene C4 phases coincide with the well known monsoon minima. The study suggests that change in pCO(2) might not be the singular driver of vegetation change as proposed recently and the climate models must take the monsoon like mega-climate processes into account for reconstructing the glacial biomes. (C) 2014 Elsevier Ltd and INQUA. All rights reserved.