TY - JOUR
T1 - No Cretaceous-Paleogene Boundary in Exposed Rajahmundry Traps
T2 - A Refined Chronology of the Longest Deccan Lava Flows From 40Ar/39Ar Dates, Magnetostratigraphy, and Biostratigraphy
AU - Fendley, Isabel M.
AU - Sprain, Courtney J.
AU - Renne, Paul R.
AU - Arenillas, Ignacio
AU - Arz, José A.
AU - Gilabert, Vicente
AU - Self, Stephen
AU - Vanderkluysen, Loÿc
AU - Pande, Kanchan
AU - Smit, Jan
AU - Mittal, Tushar
N1 - Funding Information:
We thank the editor, Marie Edmonds, and the two reviewers, Darren Mark and Matthias Sinnesael, for thoughtful and constructive reviews which improved the manuscript. We thank Mark Richards, Abhiram Kondepudi, and Andy Tholt for many fruitful discussions and field assistance. We thank Tim Becker, Abed Jaouni, and Lisa Smeenk for help with geochronologic and paleomagnetic analyses. This work was supported by the Esper S. Larsen Fund of UC Berkeley and National Science Foundation (NSF) (EAR-1615021, EAR-1736737, and EAR-1615003). The micropaleontologic work (I.A., J.A.A., and V.G.) was supported by MCIU/AEI/FEDER, UE (project number PGC2018-093890-B-I00). I.M.F. and C.J.S. were supported by NSF Graduate Research Fellowships and V.G. by an FPI grant BES-2016-077800 of the Spanish Ministry of Economy and Competitiveness.
Funding Information:
We thank the editor, Marie Edmonds, and the two reviewers, Darren Mark and Matthias Sinnesael, for thoughtful and constructive reviews which improved the manuscript. We thank Mark Richards, Abhiram Kondepudi, and Andy Tholt for many fruitful discussions and field assistance. We thank Tim Becker, Abed Jaouni, and Lisa Smeenk for help with geochronologic and paleomagnetic analyses. This work was supported by the Esper S. Larsen Fund of UC Berkeley and National Science Foundation (NSF) (EAR‐1615021, EAR‐1736737, and EAR‐1615003). The micropaleontologic work (I.A., J.A.A., and V.G.) was supported by MCIU/AEI/FEDER, UE (project number PGC2018‐093890‐B‐I00). I.M.F. and C.J.S. were supported by NSF Graduate Research Fellowships and V.G. by an FPI grant BES‐2016‐077800 of the Spanish Ministry of Economy and Competitiveness.
Publisher Copyright:
©2020. American Geophysical Union. All Rights Reserved.
PY - 2020/9/1
Y1 - 2020/9/1
N2 - 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.
AB - 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.
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U2 - 10.1029/2020GC009149
DO - 10.1029/2020GC009149
M3 - Article
AN - SCOPUS:85091629359
SN - 1525-2027
VL - 21
JO - Geochemistry, Geophysics, Geosystems
JF - Geochemistry, Geophysics, Geosystems
IS - 9
M1 - e2020GC009149
ER -