Late Miocene environmental change in Nepal and the northern Indian subcontinent: stable isotopic evidence from paleosols

Carbon and oxygen isotopic analyses of Siwalik paleosols from four long Siwalik sections record major ecological changes over the past ~11 m.y. The carbon isotopic composition of both soil carbonate and organic matter shifts dramatically starting ca. 7.0 Ma, marking the displacement of largely C ₃ vegetation by C ₄ grasslands. By the beginning of the Pliocene, all the flood plains of major rivers in this region were dominated by monsoonal grasslands. A similar carbon isotopic shift has been documented in the paleosol and fossil tooth record of Pakistan, and in terrigenous organic matter from the Bengal Fan, showing that the floral shift was probably continent wide. Himalayan uplift, driving both monsoonal intensification and consumption of CO ₂ through weathering, may be the common cause behind major late Miocene environmental change globally. -from Authors