MOLECULAR EVIDENCE FOR FIRE AND FOREST CLEARING ASSOCIATED WITH C4 GRASSLAND EXPANSION IN THE LATE MIOCENE

The Miocene C4 grassland expansion was one of the largest ecological shifts of the Cenozoic. This event was not globally synchronous (5-8 Ma), which implies regional causal mechanisms that may or may not have been linked to global climate drivers. However, underlying causes remain obscured by limited high fidelity records of CO₂, drought and other specific environmental drivers. On the Indian Subcontinent, the expansion event is well documented with both stratigraphic and paleontological evidence associated with signatures of increased seasonality caused by the uplift of the Himalayas. A current hypothesis is that this increase in seasonality increased the occurrence of fire, which disturbed forest ecosystems and created new niche space for grasses to exploit. Here, we test this proposed mechanism by using new paleosol data of the abundance and distribution patterns for polycyclic aromatic hydrocarbons (PAHs), n-alkanes, and compound specific carbon isotopes to reconstruct an integrated terrestrial record of fire and vegetation change. Our PAH results indicate both increased pyrogenic input and conifer deforestation were coincident with the carbon isotopic enrichment associated with C4 grassland expansion. This study provides the first evidence directly linking fire disturbance to vegetation community change in the Late-Miocene section of the Pakistan Siwaliks.