No Cretaceous-Paleogene Boundary in Exposed Rajahmundry Traps: A Refined Chronology of the Longest Deccan Lava Flows From 40Ar/39Ar Dates, Magnetostratigraphy, and Biostratigraphy

Isabel M. Fendley*, Courtney J. Sprain, Paul R. Renne, Ignacio Arenillas, José A. Arz, Vicente Gilabert, Stephen Self, Loÿc Vanderkluysen, Kanchan Pande, Jan Smit, Tushar Mittal

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review


Deccan Traps flood basalt volcanism affected ecosystems spanning the end-Cretaceous mass extinction, with the most significant environmental effects hypothesized to be a consequence of the largest eruptions. The Rajahmundry Traps are the farthest exposures (~1,000 km) of Deccan basalt from the putative eruptive centers in the Western Ghats and hence represent some of the largest volume Deccan eruptions. Although the three subaerial Rajahmundry lava flows have been geochemically correlated to the Wai Subgroup of the Deccan Traps, poor precision associated with previous radioisotopic age constraints has prevented detailed comparison with potential climate effects. In this study, we use new 40Ar/39Ar dates, paleomagnetic and volcanological analyses, and biostratigraphic constraints for the Rajahmundry lava flows to ascertain the timing and style of their emplacement. We find that the lower and middle flows (65.92 ± 0.25 and 65.67 ± 0.08 Ma, ±1σ systematic uncertainty) were erupted within magnetochron C29r and were a part of the Ambenali Formation of the Deccan Traps. By contrast, the uppermost flow (65.27 ± 0.08 Ma) was erupted in C29n as part of the Mahabaleshwar Formation. Given these age constraints, the Rajahmundry flows were not involved in the end-Cretaceous extinction as previously hypothesized. To determine whether the emplacement of the Rajahmundry flows could have affected global climate, we estimated their eruptive CO2 release and corresponding climate change using scalings from the LOSCAR carbon cycle model. We find that the eruptive gas emissions of these flows were insufficient to directly cause multi-degree warming; hence, a causal relationship with significant climate warming requires additional Earth system feedbacks.

Original languageEnglish
Article numbere2020GC009149
JournalGeochemistry, Geophysics, Geosystems
Issue number9
Early online date6 Aug 2020
Publication statusPublished - Sep 2020


  • Deccan Traps
  • flood basalt
  • geochronology
  • large igneous province
  • mass extinction
  • Rajahmundry Traps


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