No Cretaceous‐Paleogene Boundary in Exposed Rajahmundry Traps: A Refined Chronology of the Longest Deccan Lava Flows From 40Ar/39Ar Dates, Magnetostratigraphy, and Biostratigraphy. (4th September 2020)

• Record Type: Journal Article
• Authors: Fendley, Isabel M.; Sprain, Courtney J.; Renne, Paul R.; Arenillas, Ignacio; Arz, José A.; Gilabert, Vicente; Self, Stephen; Vanderkluysen, Loÿc; Pande, Kanchan; Smit, Jan; Mittal, Tushar
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 21:Number 9(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-09-04
• Subjects: Deccan Traps -- large igneous province -- mass extinction -- flood basalt -- Rajahmundry Traps -- geochronology; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2020GC009149
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: 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 40 Ar/ 39 Ar 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, ±1 σ 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. Plain Language Summary: Flood basalt eruptions are among the largest volcanic eruptions in Earth's history and are frequently associated with mass extinctions. The Deccan Traps flood basalt erupted close in time to the end‐Cretaceous mass extinction, which marked the demise of the dinosaurs. We determine the timing of the largest known Deccan eruptions, the Rajahmundry Traps, which are potentially the longest lava flows in the world. These eruptions were thought to have played a role in the mass extinction. We estimate when these eruptions happened using techniques including 40 Ar/ 39 Ar radioisotopic dating, paleomagnetism, micropaleontology, and geochemistry. We find that the Rajahmundry Traps erupted after the mass extinction. Additionally, we find that the eruptions happened around the same time interval as climate warming which may have impacted the ecological recovery after the mass extinction. We model the climate effects of the Rajahmundry eruptions and find that their eruptive CO2 emissions were likely not enough to directly cause multi‐degree warming. However, volcanic systems may non‐eruptively emit CO2 or may cause other environmental effects which could indirectly increase the amount of climate warming. Key Points: Exposed Rajahmundry Traps lava flows were all erupted after the Cretaceous‐Paleogene boundary, between 65.92 and 65.27 million years ago Rajahmundry Traps consistent with Deccan Traps chronostratigraphy and chemostratigraphy thus are very long flows from main Deccan eruptive vents Model and climate records show that eruptive CO2 release from large individual Deccan eruptions is insufficient to cause significant warming