Mio–Pliocene monsoonal record from Himalayan foreland basin (Indian Siwalik) and its relation to vegetational change

Cenozoic Climatic Record for Monsoonal Rainfall over the Indian Region

“…4), due to the intensification of monsoon in this region at 8.5-6.5 Ma (Quade et al, , 1995. Sanyal et al (2004) documented δ 13 C values of soil carbonates show that, from 10.5 to 6 Ma, the vegetation was C 3 type and around ~6 Ma C 4 grasses dominated. The δ 18 O variations of soil carbonates suggest that the monsoon system intensified, with one probable peak at around 10.5 Ma and a clear intensification at 6 Ma, with peak at 5.5 Ma.…”

“…There are several proxies which were introduced over the past two decades (Royer et al, www.intechopen.com 2001,2006); the δ 13 C of pedogenic minerals (Cerling, 1991;Yapp & Poths, 1992); the stomatal densities and indices in plants (van der Burgh et al, 1993;McElwain & Chaloner, 1995); the δ 13 C of long-chained alkenones in haptophytic algae (Pagani et al, 1999); the δ 11 B of marine carbonate (Pearson & Palmer, 1999;Pagani et al, 2005b); and the δ 13 C of liverworts (Fletcher et al, 2005). Some of the proxy records including soil carbonates Sanyal et al, 2004), palaeosols (Rettallack, 1995;Thomas et al, 2002, microfossils (Phadtare et al, 1994), pollens (Hoorn et al, 2000), palaeomagnetic record (Sangode & Bloemendal, 2004) and general sedimentation parameter where precipitation pattern have been used to decipher the changes in the Indian monsoon strength. In the following sections we have provided overviews of monsoon variability.…”

“…Reverse circulation of wind occurs during the winter; the radiative cooling of Tibetan Plateau causes flow of cold dry continental air towards the Indian Ocean. It has been argued that uplift of the Himalayas and Tibetan Plateau strengthen the land-sea thermal contrast (Hahn & Manabe, 1975) that led to the onset or major intensification of the Indian Age (Ma) (Sanyal et al, 2004); (e) δ 18 O and δ 13 C of the soil carbonate from Upper Siwalik . Grey zone shows a major excursion of monsoon intensification.…”

Spatial and temporal variations of C3/C4 relative abundance in global terrestrial ecosystem since the Last Glacial and its possible driving mechanisms

“…Obviously, there are not contemporaneous C 4 expansions recorded by paleoecological proxies since the late Miocene. Such as,   13 C data of pedogenic carbonate [6,73], total organic matter [73,82], fossil animals [7,8,81], long-chain n-alkanes [83] of higher plant origins from Siwalik sediments in Indian subcontinent and marine sediments in the Bay of Bengal (Figure 1) indicate the remarkable C 4 expansion during the late Miocene in this area, and the main expansion happened among 7-5 Ma. However, in the north of the Tibet Plateau, carbon isotopic data of fossil animals from the Linxia Basin (Figure 1) indicate that only during the Quaternary, C 4 plants become a significant fraction of the local vegetation [85].…”

“…The proposition of Cerling et al [7,8] has been challenged on the scale of the C 4 expansion [74,75], on the process of the transition from the Miocene to the Pliocene [76], and on the relationship between environmental factors and vegetation evolution [77][78][79][80]. We summarize the C 3 /C 4 records [6][7][8][73][74][75][81][82][83][84][85][86][87][88][89][90][91][92] since the late Miocene, the results are shown in Table 1. Obviously, there are not contemporaneous C 4 expansions recorded by paleoecological proxies since the late Miocene.…”