Revisiting the diachronous transition of C₃ to C₄ plants in the Himalayan foreland and other parts of the globe: A sedimentological perspective

Abstract

The Himalayan foreland basin and other parts of the world had witnessed a dramatic change in the ecological structure during the Late Miocene, as indicated by the increase in abundance of C 4 plants in a C 3 dominated ecosystem. However, the asynchronous expansion of C 4 plants across the latitudes, as well as within the different sub-basins of the Himalayan foreland basin, tentatively suggests that regional climatic factors and sedimentary architecture vis-à-vis geomorphological settings might have an important influence in controlling the abundance of C 4 plants. This study has carried out sedimentological and palaeohydrological analyses of the Siwalik channels at Naladkhad and Ranital regions of the Kangra sub-basin, north-west Himalaya, and estimated slope and sinuosity of the modern Himalayan fan rivers (n > 100), which provides a hydrological analogue for the Siwalik channels. The results suggest that the Siwalik Group in the Kangra sub-basin was deposited by braided rivers, situated at the proximal part of palaeo-alluvial fan. In addition to climate-driven changes, the comparison between sedimentary architecture and published carbon isotope data from the Kangra sub-basin suggests that channel-fill dominated fan-proximal Naladkhad and Ranital regions favoured the growth of C 3 plants until ca 6 Ma, a time when Pakistan Siwaliks were dominated by C 4 plants. In comparison to the Kangra sub-basin, Pakistan Siwaliks are characterized by a higher abundance of floodplain sediments and possibly represent a distal fan deposit. Data from other parts of the world similarly suggest that, in addition to climate forcing, the dominance of overbank fines favoured the growth of C 4 plants. Therefore, detailed knowledge of the depositional environment and palaeo-geomorphic setting of the sedimentary archives is essential to understand the influence of sedimentary architecture on the spatio-temporal variation in the abundance of C 4 vegetation, especially for foreland basin settings, where lateral facies transition rate is high.

Asian monsoon and vegetation shift: evidence from the Siwalik succession of India

“…Recently, Ghosh et al (2018Ghosh et al ( , 2021 suggested that changes in C 3 /C 4 vegetation may also depend on the substrate (sand/clay). They explained that areas of fine-grained (silt and clay) overbank sediments, far from the active channels, have a pore water deficiency and favour the growth of C 4 plants.…”

“…A comparative study of the sedimentary structures among different Siwalik regions indicates that the abundance of fine-grained (silt and clay) overbank sediments is higher in the western Siwalik than the central and eastern Siwalik. The strong correlation between δ 13 C values and abundance of fine-grained (silt and clay) overbank sediments across different Siwalik regions suggests a significant influence of substrate on the abundance of C 4 plants (Ghosh et al 2018(Ghosh et al , 2021. Therefore, substrate level control in limiting the growth of C 4 vegetation since 13 Ma in NE India cannot be ignored.…”

Biomarker and Carbon Isotopic Evidence of Marine Incursions in the Himalayan Foreland Basin During Its Overfilled Stage

“…The temporal variations observed in δ 13 C org values in conjunction with n-alkane distributions may suggest mixed terrestrial and marine OM sources, with the higher δ 13 C org values possibly arising from increased marine input. However, these temporal variations in δ 13 C org values can also be influenced by different vegetation types (C 3 -C 4 ; C 3 = −27.5 ± 1.9‰; and C 4 = −10.6‰ ± 1.4‰) of the late Miocene-Pliocene, instances of which are commonly observed in the time-equivalent Siwalik deposits of the western and central part of HFB (Ghosh et al, 2017(Ghosh et al, , 2018(Ghosh et al, , 2021Hoorn et al, 2000;Roy et al, 2020aRoy et al, , 2020bSanyal et al, 2004Sanyal et al, , 2005Sanyal et al, , 2010. The δ 13 C org values are also affected by OM degradation and burial of sediments; the post-depositional processes usually lead to the liberation of 12 C-enriched CO 2 , and the residual bulk OM gets enriched in 13 C-components (Meyers, 1994;Meyers & Doose, 1999;Mollenhauer & Eglinton, 2007;Tu et al, 2004).…”

“…Although underfilled and filled deposits are less exposed across the HFB, the overfilled fluvial sedimentary sequences (1,000-5,000 m thick) of middle Miocene-Pleistocene Siwalik Group are reported all along the Himalayan arc. The Siwalik sediments in the western and central part of HFB are acknowledged to be exclusively terrestrial and deposited by meandering and braided rivers in a transversely oriented alluvial fan systems (DeCelles et al, 1998;Ghosh et al, 2021;Kumar et al, 2003aKumar et al, , 2003bKumar et al, , 2011Nakayama & Ulak, 1999;Parkash et al, 1980;Roy et al, 2020aRoy et al, , 2020bSanyal et al, 2005;Thomas et al, 2002). However, based on geological and paleontological evidence, it was suggested that the eastern part of the foreland basin was not connected to its western and central region prior to middle Miocene (Rao, 1983;Sinha et al, 1982).…”