Miocene C4 Grassland Expansion as Recorded by the Indus Fan

Sarah J. Feakins, Hannah M. Liddy, Lisa Tauxe, Valier Galy, Xiaojuan Feng, Jessica E. Tierney, Yunfa Miao, Sophie Warny

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

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.

Original languageEnglish (US)
Article numbere2020PA003856
JournalPaleoceanography and Paleoclimatology
Volume35
Issue number6
DOIs
StatePublished - Jun 1 2020
Externally publishedYes

Keywords

  • Expedition 355
  • Indus Fan
  • International Ocean Discovery Program
  • Site U1457
  • biomarker

ASJC Scopus subject areas

  • Oceanography
  • Atmospheric Science
  • Palaeontology

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