The late Neogene distribution of C 3 –C 4 plants in the Himalayan Foreland Basin: insight from the δ 13 C values and sedimentological architecture of the Siwaliks

Abstract

Recent studies emphasize that, in addition to climate-driven forces, sediment grain size and depositional setting with respect to the mountain front significantly influenced the abundance of late Neogene C 3 –C 4 plants in the Himalayan Foreland Basin (HFB). The contrasting depositional settings of the Siwalik Group exposed across the western, central and eastern HFB therefore provide an ideal opportunity to understand the influence of sedimentary architecture on the distribution of C 3 –C 4 plants in palaeolandscapes. To this end, we generate new δ 13 C soil carbonate data from the Siwaliks of the Katilukhad region (12 Ma to 6 Ma) of the Kangra sub-basin and synthesize these data with compiled sedimentological data and δ 13 C values of organic matter, soil carbonate and n -alkane data from the western to eastern HFB Siwalik Group. Our comparison suggests that the rate and magnitude of the positive shift in the 13 C/ 12 C ratios were higher in the floodplain-dominated Siwaliks. Despite an existing conducive climate for the growth of C 4 plants in the late Neogene, the channel-fill-dominated Siwaliks favoured C 3 plants over C 4 plants in the eastern HFB.