Sprain, Courtney J.1, Renne, Paul R.2,3, Clemens, William A.3, Wilson, Gregory P.4, Self, Steve3, Vanderkluysen, Loyc5, Pande, Kanchan6, Fendley, Isabel7, and Mittal, Tushar8.
1University of Florida, Gainesville, United States, 2Berkeley Geochronology Center, Berkeley, USA, 3University of California-Berkeley, Berkeley, USA, 4University of Washington, Seattle, USA, 5Drexel University, Philadelphia, USA, 6Indian Institute of Technology, Mumbai, India, 7University of Oxford, Oxford, United Kingdom, 8Massachusetts Institute of Technology, Cambridge, USA
The Cretaceous-Paleogene boundary (KPB) mass extinction is one of the most important biotic turnover events in Earth history. This event is important to study for several reasons, the most relevant being its implications on our understanding of the effects of abrupt climate change. Although the temporal coincidence between the Chicxulub crater and the KPB has strongly implicated the impact as the main player in the mass extinction, the eruption of the Deccan Traps (DT) cannot be dismissed as a possible contributor. The timing of DT eruptions spans the KPB and, furthermore, the onset of DT volcanism roughly coincides with Late Cretaceous records of environmental change. Both the Chicxulub impact and DT volcanism have similar environmental forcing mechanisms, albeit acting on different timescales. Until recently, insufficient geochronology has made it difficult to tease apart effects from either agent.
To better understand the effects of both the Chicxulub impact and the DT in the KPB crises, we developed a high-precision chronologic framework that outlines the temporal sequence of biotic and climatic changes, and proposed perturbations, around the KPB using 40Ar/39Ar geochronology and paleomagnetism. This work was primarily conducted in two areas: the Hell Creek region of NE Montana, USA and the Deccan Traps, India. The Hell Creek region is one of the best-studied terrestrial KPB sites in the world. We developed a high-precision chronostratigraphic framework for fluvial sediments within the Hell Creek, using 40Ar/39Ar dating, magnetostratigraphy, and chemical fingerprinting. This work constrained the timing of terrestrial faunal decline and recovery while calibrating North American Land Mammal Ages biostratigraphy. The coupling of our magnetostratigraphic sections and high-precision 40Ar/39Ar ages further allowed for calibration of the circum-KPB polarity chron (C29r) at unprecedented precision, enabling correlation of our record to other KPB records around the globe. To better understand the role of the DT in the KPB extinction, we developed high precision 40Ar/39Ar ages for >20 lavas ranging the entire DT stratigraphy.
Tying all of this work together, we are able to determine: 1) the decline in terrestrial faunas began between 400 ka and 150 ka pre-KPB, 2) terrestrial disaster faunas are constrained to the first ~25 ka of the Paleogene, and recovery occurred gradually over the next 850 ka, 3) over 90% of the DT volume was erupted in < 1 Ma, with 50-75% emplaced post-KPB, 4) the onset of volcanism is approximately coincident with the onset of pre-KPB warming, but despite this 5) pre-KPB records of climate change coincide temporally with the eruption of the smallest DT phases, suggesting that if the DT are the source of pre-KPB climate change, the release of climate-modifying gases cannot be directly related to eruptive volume as previously assumed. Overall, our new work highlights the close temporal relationship between the Chicxulub impact, Deccan volcanism, and the KPB. But more work is needed, specifically addressing Deccan volatile release and eruption tempo, in order to fully understand the impact of the DT on the Earth system and its role in the mass extinction.
Courtney Sprain is an Assistant Professor at the University of Florida. She received her Ph.D. in Earth and Planetary Science in 2017 from the University of California, Berkeley and her B.S. degrees in Geology and Geophysics from the University of Minnesota in 2012. She specializes in 40Ar/39Ar Geochronology and Paleomagnetism