Downloaded from specialpapers.gsapubs.org on August 28, 2014 Geological Society of America Special Papers Online First Atmospheric halogen and acid rains during the main phase of Deccan eruptions: Magnetic and mineral evidence Eric Font, Sébastien Fabre, Anne Nédélec, et al. Geological Society of America Special Papers, published online August 21, 2014; doi:10.1130/2014.2505(18) E-mail alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions to subscribe to Geological Society of America Special Papers Permission request click www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA. Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. 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Notes © Geological Society of America Downloaded from specialpapers.gsapubs.org on August 28, 2014 OLD G The Geological Society of America Special Paper 505 2014 OPEN ACCESS Atmospheric halogen and acid rains during the main phase of Deccan eruptions: Magnetic and mineral evidence Eric Font* Instituto Dom Luís, Faculdade de Ciências, Universidade de Lisboa (IDL-FCUL), Edifício C8-8.3.22, Campo Grande, 1749-016, Portugal Sébastien Fabre Institut de Recherche en Astrophysique et Planétologie (IRAP), Observatoire Midi-Pyrénées (OMP), Université de Toulouse, 31028 Toulouse 24 Cedex 4, France Anne Nédélec Géosciences Environnement Toulouse (GET), UMR 5563, Université de Toulouse, 31400 Toulouse, France Thierry Adatte Earth Sciences Institute (ISTE), Université de Lausanne, Geopolis, CH-1015 Lausanne, Switzerland Gerta Keller Geosciences Department, Princeton University, Princeton, New Jersey 08544, USA Cristina Veiga-Pires Centro de Investigação Marinha e Ambiental (CIMA), Faculdade de Ciencias e Tecnologia, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal Jorge Ponte Instituto Dom Luís, Universidade de Lisboa (IDL-UL), Edifício C8-8.3.22, Campo Grande, 1749-016, Portugal José Mirão HERCULES Laboratory (HERança CULtural Estudos e Salvaguarda/Cultural Heritage Studies and Safeguard), University of Evora, 7000-809 Evora, Portugal Hassan Khozyem Earth Sciences Institute (ISTE), Université de Lausanne, Geopolis, CH-1015 Lausanne, Switzerland and Geology Department, Faculty of Sciences, Aswan University, 81528-Aswan, Egypt Jorge E. Spangenberg Institute of Earth Surface Dynamics (IDYST), University of Lausanne, Building Géopolis, CH-1015 Lausanne, Switzerland *[email protected] Font, E., Fabre, S., Nédélec, A., Adatte, T., Keller, G., Veiga-Pires, C., Ponte, J., Mirão, J., Khozyem, H., and Spangenberg, J., 2014, Atmospheric halogen and acid rains during the main phase of Deccan eruptions: Magnetic and mineral evidence, in Keller, G., and Kerr, A.C., eds., Volcanism, Impacts, and Mass Extinctions: Causes and Effects: Geological Society of America Special Paper 505, p. 353–368, doi:10.1130/2014.2505(18). For permission to copy, contact editing@geosociety. org. © 2014 The Geological Society of America. All rights reserved. Gold Open Access: This chapter is published under the terms of the CC-BY license and is available open access on www.gsapubs.org. 353 Downloaded from specialpapers.gsapubs.org on August 28, 2014 354 Font et al. ABSTRACT Environmental changes linked to Deccan volcanism are still poorly known. A major limitation resides in the paucity of direct Deccan volcanism markers and in the geologically short interval where both impact and volcanism occurred, making it hard to evaluate their contributions to the mass extinction. We investigated the low-magnetic-susceptibility interval just below the iridium-rich layer of the Bidart (France) section, which was recently hypothesized to be the result of paleoenviron- mental perturbations linked to paroxysmal Deccan phase 2. Results show a drastic decrease of detrital magnetite and presence of scarce akaganeite, a hypothesized reaction product formed in the aerosols derived from reaction of a volcanic plume with water and oxygen in the high atmosphere. A weathering model of the conse- quences of acidic rains on a continental regolith reveals nearly complete magnetite dissolution after ~31,000 yr, which is consistent with our magnetic data and falls within the duration of the Deccan phase 2. These results highlight the nature and importance of the Deccan-related environmental changes leading up to the end- Cretaceous mass extinction. INTRODUCTION al., 2008a), 1500 km across India near the end of phase 2, with the fi nal megafl ow at the Cretaceous-Paleogene boundary mass The history of Earth is punctuated by fi ve severe global cli- extinction (Keller et al., 2008). matic and environmental catastrophes that led to nearly total mass Current research thus narrows the main phase 2 of Dec- extinctions of calcareous marine and many continental species. can volcanism to the geologically short interval of the Creta- The most famous case is the Cretaceous-Paleogene boundary ceous planktic foraminiferal zone CF1, which spans the last (KPB or Cretaceous-Tertiary boundary [KTB]) mass extinction, ~160,000 yr below to the Cretaceous-Paleogene boundary, which is still the center of acrimonious debates between partisans whereas the Chicxulub impact is commonly placed at the of the bolide impact theory (Schulte et al., 2010) and those who Cretaceous- Paleogene boundary (Schulte et al., 2010) or within favor a terrestrial origin linked to Deccan Traps volcanism (Cour- zone CF1 preceding the mass extinction (Keller et al., 2012). tillot, 2012; Keller et al., 2012). Others argue that each process, This short interval limits our ability to separate the main Dec- individually, is unlikely to have caused a global biological col- can volcanic phase (i.e., phase 2) from the Chicxulub impact lapse, and a scenario of multiple causes is preferred (White and within resolvable radiometric ages and to evaluate their respec- Saunders, 2005; Keller et al., 2009; Renne et al., 2013). tive biotic effects and their contributions to the Cretaceous- In recent years, Deccan volcanism studies have resulted in Paleogene boundary mass extinction. Radiometric (K-Ar and major advances that now facilitate recognition and evaluation of Ar-Ar) methods are subject to intrinsic errors (~1%–2%), linked its global effects, such as attempted in this study. For example, to interlaboratory calibration, imprecise K and Ar isotopic stan- three discrete Deccan volcanism phases with variable intensity dards (Fish Canyon standard), and uncertainty of decay con- have been dated based on magnetostratigraphy and 40K-40Ar ages stants (Kuiper et al., 2008; Channell et al., 2010; Renne et al., (Chenet et al., 2007): Phase 1 in the early late Maastrichtian (base 2010, 2013), preventing any precise radiometric age correlation magnetozone C30n, ca. 67.4 Ma) accounts for ~6% of the total between continental Deccan fl ood basalts and the mass extinc- lava pile, which today forms mountain peaks of 3500 m (Self et tion recorded in marine sections. In addition, because volcanic al., 2006). Most of the lava pile (80%) erupted during phase 2 mineralogical markers (aerosols) are generally restricted to the in the latest Maastrichtian paleomagnetic chron C29r. The fi nal vicinity of the volcanic source, the discrimination between Dec- phase 3 erupted in the early Danian base of C29n and accounts can phase 2 and the Chicxulub impact in distal sections is even for ~14% of total Deccan eruptions (Chenet et al., 2007, 2008; harder within such a short temporal interval. Keller et al., 2011, 2012). The original size prior to erosion is Are volcanic signals present but unrecognized outside estimated to have been 1.5 × 106 km2, and the volume of lava India? A recent study of Cretaceous-Paleogene boundary sec- extruded is estimated at ~1 × 106 km3 (Self et al., 2006; Chenet tions at Bidart, France, and Gubbio, Italy, suggests so (Font et et al., 2007). al., 2011). In these sections, a 50-cm-thick yellow-red interval Most critical for the current study is Deccan volcanism phase of very low magnetic susceptibility (MS) directly underlies the 2, which has been directly linked to the Cretaceous- Paleogene Cretaceous-Paleogene boundary (Fig. 1), as also observed in boundary mass extinction in outcrops and deep wells of the Oman (Ellwood et al., 2003) and other marine sections. Pre- Krishna-Godavari Basin in India (Keller et al., 2011, 2012). liminary data indicate that this low-MS interval contains an These studies revealed Earth’s longest lava megafl ows (Self et enigmatic Cl-rich iron oxyhydroxide that could have formed by Downloaded from specialpapers.gsapubs.org on August 28, 2014 Evidence of atmospheric halogen and acid rains during the main phase of