Versão online: http://www.lneg.pt/iedt/unidades/16/paginas/26/30/185 Comunicações Geológicas (2014) 101, Especial III, 1473-1476 IX CNG/2º CoGePLiP, Porto 2014 ISSN: 0873-948X; e-ISSN: 1647-581X Assessing the causes of the End-Triassic biotic crisis, a review Avaliando as causas da crise biótica fini-triássica, uma revisão N. Youbi1,2*, A. Marzoli3, H. Bertrand4, E. Font5, J. Dal Corso3, L. Martins2, J. Madeira5, J. Mata2, G. Bellieni3, S. Callegaro3, M. Kh. Bensalah1,2, M. Bahir1 Artigo Curto . Short Article © 2014 LNEG – Laboratório Nacional de Geologia e Energia IP Abstract: The end-Triassic biotic crisis marks one of the major mass 4Université Lyon 1 et Ecole Normale Supérieure de Lyon, Laboratoire de extinction events in the history of life. Several explanations for this Géologie de Lyon, UMR CNRS 5276, Lyon Cedex 7, France event have been suggested, but all present unanswered challenges: (i) 5Instituto Dom Luiz (LA), Universidade de Lisboa, Faculdade de Ciências, sea-level fluctuations during the Late Triassic, does not explain the Departamento de Geologia, Lisboa, Portugal. suddenness of the extinctions in the marine realm; (ii) no impact *Corresponding author / Autor correspondente: [email protected] crater has been dated to coincide with the Triassic–Jurassic boundary (the impact responsible for the annular Manicouagan Reservoir occurred about 12 million years before the extinction event and the Rochechouart impact predates the Tr-J boundary by 1-2 Ma); (iii) 1. Introduction massive volcanic eruptions, specifically the flood basalts of the Central Atlantic Magmatic Province (CAMP), would have released The end-Triassic biotic crisis is one of the so called “big carbon dioxide or sulfur dioxide and aerosols, which would cause five” Phanerozoic mass extinctions (e.g., Raup & either intense global warming (from the former) or cooling (from the Sepkoski, 1982), when ca. 50% of marine genera latter). In this work we will discuss the possibility of causal link disappeared and a significant turnover of terrestrial fauna between the CAMP, the bolide impact(s) and the end-Triassic mass and flora occurred. During the last decades, there has been extinction. a vigorous debate about the stratigraphic position of the Keywords: Triassic–Jurassic boundary, Mass extinctions, Central Triassic-Jurassic (Tr-J) boundary and the mechanisms that Atlantic Magmatic Province (CAMP) volcanism, Impact craters, Newark Supergroup. triggered the associated mass extinction. Proponents of the idea that continental flood basalts of the Central Atlantic Resumo: A crise biótica final do Triássico marca um dos principais Magmatic Province (CAMP) are responsible for the end- eventos de extinção em massa na história da vida. Foram propostas Triassic biotic crisis (e.g., Knight et al., 2004; Marzoli et várias explicações para este evento, mas todas têm desafios sem al., 2004; Nomade et al., 2007; Vérati et al., 2007; resposta: (i) flutuações do nível do mar durante o final do Triássico, Schaltegger et al., 2008; Tanner et al., 2008; Martins & que, no entanto, não explicam a rapidez das extinções no reino marinho; (ii) impacto de um asteróide, mas nenhuma cratera de Mata, 2010-11; Schoene et al., 2010; Dal Corso et al., impacto datada coincide com o limite Triássico-Jurássico (o impacto 2014) are opposed by those who favor an extraterrestrial responsável pela estrutura anular de Manicouagan ocorreu cerca de origin linked to meteoritic impact(s) (Olsen et al., 2002). 12 milhões de anos antes do evento de extinção e o impacto de The choice between these hypothesis is not easy given the Rochechouart antecede o limite Tr- J em 1–2 Ma); (iii) volumosas difficulties to date and correlate the onset of the CAMP in erupções vulcânicas, especificamente os traps basálticos da CAMP, continental areas with the marine realm turnover (e.g., que libertaram dióxido de carbono e/ou dióxido de enxofre e aerossóis, o que causaria intenso aquecimento global (no caso do Whiteside et al., 2007, 2008; Marzoli et al., 2008; Deenen primeiro) ou arrefecimento (no segundo caso). Neste trabalho et al., 2010, 2011a, 2011b), and to date impact craters. discute-se a possibilidade de nexo de causalidade entre a CAMP, Indeed, there are 184 confirmed impact structures known impacto(s) meteorítico(s) e a extinção em massa do final do on Earth (Spray & Elliott, 2014) but only a very small Triássico. number of impact structures has yielded well-constrained Palavras-chave: Limite Triássico-Jurássico, Extinções em massa, ages (e.g., Jourdan et al., 2009). Other possible causes of Vulcanismo da província magmática do Atlântico Central (CAMP), the end-Triassic mass extinction are, among others, the Crateras de impacto, Supergrupo de Newark. sea-level change and anoxia (Hallam & Wignall, 1997; Wignall, 2001). However, these mechanisms do not explain extinction in both marine and terrestrial 1 Department of Geology, Faculty of Sciences-Semlalia, Cadi Ayyad ecosystems. In this work, we will discuss the possibility of University, P.O. Box 2390, Marrakech, Morocco. 2Centro de Geologia da Universidade de Lisboa (CeGUL), Faculdade de a causal link between the CAMP volcanism, bolide Ciências (FCUL), Departamento de Geologia (GeoFCUL), Lisboa, Portugal impact(s) and the end-Triassic mass extinction. 3Dipartimento di Geoscienze e CNR-IGG, Università di Padova, Padova, Italy In some of the exposed Mesozoic rift basins of the Atlantic passive margin of North America (Newark 1474 N. Youbi et al. / Comunicações Geológicas (2014) 101, Especial III, 1473-1476 Supergroup), and North Africa (Argana and Khemissat cycle, specifically with an increase in CO2. The release of basins, Morocco), it has been shown that a palynological more than 8,000 Gt of CO2 (Beerling & Berner, 2002; turnover exists, possibly correlated with the Tr-J boundary Schaller et al., 2011) is thought to have triggered global (Olsen, 1997; Deenen et al., 2010, 2011a, 2011b). The warming, shallow marine anoxia leading to blooms of palynological turnover is located a few meters below the prasinophyte green algae (van de Schootbrugge et al., CAMP basaltic lavas flows, which yielded precise U/Pb 2007; Quan et al., 2008) and the carbon cycle ages ranging from of 201.566 ± 0.031 Ma to 201.274 ± perturbations recorded in the carbon stable isotope 0.032 Ma (e.g., Blackburn et al., 2013). Therefore, it has composition of carbonates and organic matter (Hesselbo been suggested that the entire CAMP LIP postdates the et al., 2002; Galli et al., 2005; van de Schootbrugge et extinction event (by about 20-40 k.y, on the basis of al., 2007). Carbon isotope curves from higher plant n- cyclostratigraphic evidence), thus apparently denying a alkanes and total organic carbon from a marine possible causal link between the magmatic event and the sedimentary succession in Austria (Ruhl et al., 2011) can biotic turnover. be correlated to the carbonate and organic carbon isotope excursions recorded in other marine (e.g., England; 2. Did the CAMP volcanism trigger the end- Triassic Hesselbo et al., 2002) and continental (Morocco, Canada; mass extinction? Deenen et al., 2010, 2011a, 2011b; Dal Corso et al., 2014) geological settings. These stratigraphic The CAMP was emplaced at ca. 201 Ma, close to the correlations suggest that the end-Triassic extinction event Triassic–Jurassic boundary (Marzoli et al., 1999, 2004, occurred slightly before the oldest basalts in eastern 2011; Schoene et al., 2010; Blackburn et al., 2013) during North America, but simultaneously with the eruption of the early stages of the break-up of the supercontinent the oldest flows in Morocco (as also suggested by Pangaea that led to the opening of the Central Atlantic Deenen et al., 2010, 2011a, 2011b). CAMP eruptions, Ocean. CAMP magmatism is nowadays represented by mass extinction, and carbon isotope excursions seem to remnants of intrusive (layered intrusions, sills, dykes) and be coincident, thus making the case for a volcanic cause extrusive (pyroclastic sequences and lava flows) rocks that for the mass extinction. The catastrophic dissociation of occur in once-contiguous parts of northwestern Africa, gas hydrates (suggested as one possible cause of the southwestern Europe, and North and South America (e.g., largest mass extinction of all time, the so-called "Great Youbi et al., 2003; Martins et al., 2008; Callegaro et al., Dying" at the end of the Permian Period) may have 2013, 2014). exacerbated greenhouse conditions (Ruhl et al., 2011). The end-Triassic mass extinction event has been linked to the eruption of the CAMP basalts. The 3. The bolide impact(s) alternative theory estimated volume of erupted basalts (2-4×106 km3) and the brevity of emplacement (probably much less than 1 A viable alternative for a CAMP-induced extinction at the My for the peak activity), centred around the Tr-J end of the Triassic is bolide impact(s). The overall boundary, make the eruption of CAMP basalts the key extinction pattern and associated floral effects at the end of event of the Tr-J boundary interval (e.g., Marzoli et al., the Triassic do parallel those associated with the 2004; Dal Corso et al., 2014). One argument widely used Cretaceous-Tertiary Chicxulub impact (Hildebrand et al., to suggest that CAMP lavas pre-dated the Tr-J boundary 1991). Evidence includes the presence of a massive in Morocco is based on the presence of two brief increase of spores at the Tr-J boundary locally found in the magnetic reversals in the intermediate units of the Newark basin (Fowell et al., 1994). The iridium anomalies Tiourjdal and Oued Lhar sections (Morocco) that were recorded close to the Tr-J boundary in the Newark and correlated to the E23r chron from the Newark basin and Fundy basins are very weak compared to those of the to the SA5n.2r/3r and SA5r chrons of the St Audries Bay Cretaceous-Tertiary boundary and, rather than being a (Knight et al., 2004).