Literature Review Highlights: What was the role of Deccan Trap volcanism in K/Pg mass extinction?
For the last decade, it has been hotly contested within the scientific community whether the collision of a ~10 km wide asteroid (the Chicxulub impact) e.g. Alvarez et al., (1980) or widespread volcanic eruptions covering most of western India (Deccan Trap volcanism) e.g. Keller et al., (2020) acted as the main driver of the dinosaur extinction (also known as the Cretaceous-Paleogene (K/Pg) mass extinction event). Many landmark studies have since become the subject of intense debate and controversy.
In undertaking my current Masters by Research (MScR) research project, it is important to first conduct what is known as a Literature Review. A Literature Review as it you may have guessed is a review of the literature in any one given topic. However, it is not to be just to be a summary of other people's work. Amongst many things, a Literature Review serves as the synthesis of all the major arguments within a given topic, with the writer (in this case myself) acting as a critic when it comes to discerning which arguments are stronger or weaker than others. This was particularly interesting for me, as I began to work my way through one of the most contentious debates within the world of geoscience - What caused the dinosaur extinction and did Deccan volcanism play a role?
Before I begin you might be asking why there is still debate on this topic? Is it not a well known fact that the cause of the mass extinction 66 million years ago, was the asteroid impact which killed off the non-avian dinosaurs?? Well. Such is the world of Science that not everyone agrees on this, with some authors advocating the Deccan Traps as an alternative cause. Despite this, a majority of the scientific community still implicate the Chicxulub impact as the cause of the K/Pg mass extinction. However, although I do agree with the latter it is important to show that some landmark studies fail to consider all the facts. Such is seen within the last decade of K/Pg boundary research with the publication of the the Schutte et al., (2010a) review.
This review paper made a simple argument. The cause of the K/Pg mass extinction was the asteroid impact. All the evidence they cited pointed to an abrupt extinction of three quarters of all life at the time. And this coincided with the occurrence of the Chicxulub ejecta layer (a layer of material expelled from the crater which is found globally). So, case closed? Not by a long shot. This particular study was met by a number of responses (i.e. Archibald et al., 2010; Courtillot & Fluteau 2010; Keller et al., 2010) who all highlighted one thing - What about Deccan volcanism? This, I find was a major limit of the Schutte et al., (2010a) review, it neglected to discuss what role Deccan volcanism played (if any) in the extinction by focusing on the K/Pg boundary alone. One response (Courtillot & Fluteau, 2010) went further by stating the review had misinterpreted their earlier work (i.e. Chenet et al., 2009) leading to what they argue to be misleading comments concerning the rate of climate cooling sulfur released by the Deccan Traps.
The debate continued to rage on with more recent studies placing a greater focus on trying to constrain the timing of Deccan volcanism relative to the K/Pg boundary. This was best seen when two opposing studies, published last year
(Schoene et al., 2019 and Sprain et al., 2019) placed the largest pulse of lava erupted by the Deccan Traps either just before or just after the K/Pg boundary. These studies failed to resolve if Deccan volcanism played a role in the K/Pg mass extinction, as both studies used different, incomparable dating techniques (Renne et al., 2013; 2015) and produced dates which lay within the margin of error. A new dating study published earlier this year by Eddy et al., (2020) further adds to this debate by arguing that both Schoene et al. (2019) and Sprain et al., (2019) miscalculate the duration of the earliest pulses of Deccan volcanism. They recommend the analysis of rock layers leading up to the K/Pg boundary (known as stratigraphy) alongside existing dating techniques in resolving the magnitude of Deccan volcanic pulses.
Many studies published in the last year alone have tried to deduce what environmental changes occurred at the end of the Cretaceous, and if these can be correlated to either the Chicxulub impact or Deccan Trap volcanism. Abrupt climatic warming occurring within ~25 thousand years of the K/Pg boundary at Elles, as been argued by Keller et al., (2020) to responsible for causing the mass extinction. These authors correlate this warming event to Deccan volcanism by the presence of a large spike in Mercury (Hg) found in the rock strata just below the K/Pg boundary. The use of Hg stratigraphy has become a novel technique in many studies associating Large Igneous Provinces (LIPs) like the Deccan Traps to other extinction boundaries.
However, a new study by Chiarenza et al. (2020) challenges this view. They alternatively interpret that a Deccan-induced temperature increase at this time would have acted as a buffer against cooling brought on by the asteroid impact. A real strength of the Chiarenza et al. (2020) study over Keller et al., (2020) is that it compares and contrasts the varying effects of both the Chicxulub impact and Deccan volcanism on the biosphere using computer modelling. They conclude that only the Chicxulub induced impact winter could decimate non-avian dinosaur habitats. This further advocates previous studies which propose the Chicxulub impact as the major cause of the K/Pg mass extinction (e.g. Alvarez et al., 1980; Schutte et al. 2010a).
So, in conclusion it appears authors who postulate the asteroid impact driver for the extinction currently have an edge over advocates of Deccan Trap volcanism. However as you can see, current opinion regarding the relationship between Deccan Trap volcanism and the K/Pg mass extinction still remains divided and continues to be a highly active area of research, something which I hope my research project will contribute too.
Over the course of writing my Literature Review, I have identified significant gaps in research remain, which my research project will address. Particularly the exact environmental and biotic impacts of the Deccan trap volcanism remain poorly understood. Deducing what these environmental and biotic impacts were and their magnitude will be the focus of my research project going forward.
Stay tuned and watch this space for further developments on this research project.
References (can be accessed via Google Scholar)
Alvarez, L.W., Alvarez, W., Asaro, F. and Michel, H.V., 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science, 208(4448), pp.1095-1108.
Archibald, J.D., Clemens, W.A., Padian, K., Rowe, T., Macleod, N., Barrett, P.M., Gale, A., Holroyd, P., Sues, H.D., Arens, N.C. and Horner, J.R., 2010. Cretaceous extinctions: multiple causes. Science, 328(5981), pp.973-973.
Chenet, A.L., Courtillot, V., Fluteau, F., Gérard, M., Quidelleur, X., Khadri, S.F.R., Subbarao, K.V. and Thordarson, T., 2009. Determination of rapid Deccan eruptions across the Cretaceous‐Tertiary boundary using paleomagnetic secular variation: 2. Constraints from analysis of eight new sections and synthesis for a 3500‐m‐thick composite section. Journal of Geophysical Research: Solid Earth, 114(B6).
Chiarenzaa, A. A., Farnsworth, A., Mannion, P. D., Lunt, D. J., Valdes, P. J., Morgana, J. V., and Allison, P. A., 2020. Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction. PNAS Latest Articles, p. 1-10.
Courtillot, V. and Fluteau, F., 2010. Cretaceous extinctions: the volcanic hypothesis. Science, 328(5981), pp.973-974.
Eddy, M.P., Schoene, B., Samperton, K.M., Keller, G., Adatte, T. and Khadri, S.F., 2020. U-Pb zircon age constraints on the earliest eruptions of the Deccan Large Igneous Province, Malwa Plateau, India. Earth and Planetary Science Letters, 540, p.116249.
Keller, G., Adatte, T., Pardo, A., Bajpai, S., Khosla, A., Samant, B., SCHULTE, P., ALEGRET, L., ARENILLAS, I., ARZ, J.A. and BARTON, P.J., 2010. Cretaceous extinctions: evidence overlooked [with response]. Science, 328(5981), pp.974-976.
Keller, G., Mateo, P., Monkenbusch, J., Thibault, N., Punekar, J., Spangenberg, J.E., Abramovich, S., Ashckenazi-Polivoda, S., Schoene, B., Eddy, M.P. and Samperton, K.M., 2020. Mercury linked to Deccan traps volcanism, climate change and the end-Cretaceous mass extinction. Global and Planetary Change, 194, p.103312.
Renne, P.R., Deino, A.L., Hilgen, F.J., Kuiper, K.F., Mark, D.F., Mitchell, W.S., Morgan, L.E., Mundil, R. and Smit, J., 2013. Time scales of critical events around the Cretaceous-Paleogene boundary. Science, 339(6120), pp.684-687.
Renne, P.R., Sprain, C.J., Richards, M.A., Self, S., Vanderkluysen, L. and Pande, K., 2015. State shift in Deccan volcanism at the Cretaceous-Paleogene boundary, possibly induced by impact. Science, 350(6256), pp.76-78.
Schoene, B., Eddy, M.P., Samperton, K.M., Keller, C.B., Keller, G., Adatte, T. and Khadri, S.F., 2019. U-Pb constraints on pulsed eruption of the Deccan Traps across the end-Cretaceous mass extinction. Science, 363(6429), pp.862-866.
Schulte, P., Alegret, L., Arenillas, I., Arz, J.A., Barton, P.J., Bown, P.R., Bralower, T.J., Christeson, G.L., Claeys, P., Cockell, C.S. and Collins, G.S., 2010a. The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary. Science, 327(5970), pp.1214-1218.
Sprain, C.J., Renne, P.R., Vanderkluysen, L., Pande, K., Self, S. and Mittal, T., 2019. The eruptive tempo of Deccan volcanism in relation to the Cretaceous-Paleogene boundary. Science, 363(6429), pp.866-870.