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In the late Miocene, grasslands spread across the forested floodplains of the Himalayan foreland, but the causes of the ecological transition are still debated. Recent seafloor drilling by the International Ocean Discovery Program (IODP) provides an opportunity to study the transition across a larger region as archived in the Indus submarine fan. We present a multiproxy study of past vegetation change based on analyses of the carbon isotopic composition (δ13C) of bulk organic carbon, plant wax n‐alkanes and n‐alkanoic acids, and quantification of lignin phenols, charcoal, and pollen. We analyze the hydrogen isotopic composition (δD) of plant wax to reconstruct precipitation δD. We use the Branched and Isoprenoid Tetraether (BIT) index to diagnose shifts between terrestrial versus marine lipid inputs between turbidite and hemipelagic sediments. We reconstruct ocean temperatures using the TEX86 index only where marine lipids dominate. We find evidence for the late Miocene grassland expansion in both facies, confirming this was a regional ecosystem transformation. Turbidites contain dominantly terrestrial matter from the Indus catchment (D‐depleted plant wax), delivered via fluvial transport as shown by the presence of lignin. In contrast, hemipelagic sediments lack lignin and bear D‐enriched plant wax consistent with wind‐blown inputs from the Indian peninsula; these show a 7.4–7.2 Ma expansion of C4 grasslands on the Indian subcontinent. Within each facies, we find no clear change in δD values across the late Miocene C4 expansion, implying consistent distillation of rainfall by monsoon dynamics. Yet, a cooling in the Arabian Sea is coincident with the C4 expansion. Plain Language Summary: This project studied the mud and sand on the seafloor in the Indian Ocean, west of India and south of Pakistan. We drilled a core through the mud and focused on a section corresponding to 5.5 to 10 Ma. Much of the sand came from the Indus River, but when the river sediments went elsewhere, layers of chalky sediments formed from the shells of marine organisms. Those chalks contain the history of longer spans of time. In the sediments, we found molecular fossils from the waxy coating on plant leaves and the woody parts of plants as well as pollen and charcoal; these point to the types of plants that were growing on land whose remains were washed or blown out to sea. We also found molecular fossils of microbes that lived in the oceans, whose structures indicate ocean temperatures—although when soils washed out in large amounts, ocean temperature estimates are not available. The main finding is that grasses replaced forests across much of the Indian subcontinent and Indus catchment, accompanied by more grass fire and cooler ocean temperatures. Key Points: Multiproxy study of the Indus Fan organic matter reveals that terrestrial sources differ between turbidite and hemipelagic faciesCarbon isotopes, grass pollen, and charcoal indicate that C4 grasslands expanded between 7.4–7.2 Ma in hemipelagic faciesHydrogen isotopes in plant waxes differ between source regions but do not detect monsoon rainfall changes across the C4 grassland expansion [ABSTRACT FROM AUTHOR]

Detailed interpretation of seismic stratigraphic sequences in the Laxmi Basin of the eastern Arabian Sea are presented in this study using closely spaced high resolution multi-channel seismic (MCS) data. Our stratigraphic interpretation is further corroborated using recent drilling results in the Laxmi Basin, derived from the long sediment cores collected during International Ocean Discovery Program (IODP) Expedition 355. Integrated core-log interpretation discussed in the present study, offer important insights about the lithostratigraphic variations in this region. Analyses of multi-channel seismic reflection data reveal five depositional sequences (ranging from Paleocene to Recent) that led to the development of this marginal basin since the Cenozoic period. Regional igneous basement is successfully imaged, which was also validated by deep sea coring during the IODP Expedition 355. In the present study, we primarily focus on the post-rift sedimentation in the Laxmi Basin and its possible mechanisms. Our detailed interpretation in the prevailing tectonic framework of the basin suggests that near-shelf oldest volcaniclastic sedimentation immediately overlying the acoustic basement is linked to the onset of India–Madagascar and India–Seychelles rifting activities during the Late Cretaceous period. Eventually, during the Early-Mid to Late Miocene, the basin received maximum sedimentation dominantly through an extensive mass transport mechanism implying possible large-scale deformation on the Indian shelf. Subsequent sediment input to the basin appears to have been fed variably via the Indus Fan as well as coastal discharge from the Indian mainland. The total sediment thickness in the Laxmi Basin ranges from 1.1 to 3.5 km. New stratigraphic information and sediment isopach maps presented here provide vital information about syn- and post-rift sedimentation pattern in the region and their long term tectonic implications. [Display omitted] • Seismic stratigraphy unveils the source and time of sediment deposition. • Sediments overlying the acoustic basement host detritus of syn/post rift events. • Each depositional phase correspond to prevailing tectono-climatic changes. • Estimation of sediment budget revealed regional sediment distribution through time. [ABSTRACT FROM AUTHOR]