The Chicxulub bolide impact has for several decades been implicated as the sole cause for the end-Cretaceous mass extinction. However, over that same time period nearly all mass extinction events have been shown with increasing precision to correlate with large igneous province eruptions.  As a result, there has been a renewed interest in understanding the role that the Deccan Traps large igneous province may have played in the end-Cretaceous extinction.  To understand the drivers of, and feedbacks from, mass extinction events, a more precise timeline needs to be established for flood basalt volcanism, biotic extinction and recovery, and climate and carbon cycle proxy records.

            The goals of this project were to build a timeline for the eruption of the Deccan Traps using U-Pb geochronology to quantify eruption rates over the ~700 kyr of volcanic activity.  The goal was to see whether or not the Deccan Traps played a quantifiable role in environmental degradation and biologic extinction and recovery before and after the height of the extinction at the K-Pg boundary.

            The initial work that motivated the proposal for this project included a proof-of-concept field campaign in which we found and dated zircon-bearing ashbeds between major basalt flows in the Deccan Traps. We demonstrated that we could date horizons with tens of kyr precision by targeting paleosol material that contained minor amounts of distal volcaniclastic material. Major activities carried out during this grant period included two additional 3-week field campaigns to India to collect samples for geochronology and geochemistry and paleosol horizon analysis.  This resulted in 15010-kg paleosol/volcaniclastic samples collected for U-Pb geochronology. The PIs group was responsible for processing these samples, picking zircons (with an ~20-30% success rate), and carrying out high-precision U-Pb ID-TIMS geochronology on single zircon crystals.  We have over 400 high-precision U-Pb zircon dates, with enough zircon-bearing samples to carry on geochronology for a year or more from more distal parts of the volcanic province.

We are currently preparing two manuscripts for publication that will document:

a) U-Pb geochronology is a viable way to date mafic large igneous provinces. This proof-of-concept was a result of the methodological leap of targeting zircon-bearing volcanic ashes between basalt flows rather than the flows themselves, resulting in the ability to place better than 0.1% precision on eruptive histories.  This approach has already been influential in guiding work on other large igneous provinces.

b) The Deccan traps erupted in 3 or more pulses over a 700 kyr period spanning the end-Cretaceous mass extinction. The timing of these pulses, given more accurate models for volumes of eruptions (see below), will be correlated with carbon cycle proxy records.

c) Our high-resolution time constraints show that the existing stratigraphy of the Deccan traps needs to be revised using geochronological, in addition to existing geochemical, correlations. Without this, attaining eruptive and gas fluxes will not be possible.

            This low budget project has made significant progress towards understanding the eruptive history of the Deccan Traps, assessing the areal extent and continuity of defined formations, and gauging their affect on K-Pg climate change, biotic evolution, and carbon cycling. The Deccan Traps are now the best-calibrated large igneous province in Earth history, and will therefore inform our understanding of the generation, storage, transport, and eruption of flood basalts.

            This project has trained two lab technicians at Princeton in the art of separating zircons from paleosol/ashbed deposits, one Princeton PhD student and one postdoc in high-precision U-Pb ID-TIMS geochronology and how to generate and interpret high-precision zircon datasets, and given field and lab research opportunities to 3 Princeton undergraduates. Several Master's students from Switzerland have also been involved in the field and laboratory work in collaboration with our Swiss colleagues at the University of Lausanne. This project has also solidified an nurtured collaboration with Indian colleagues at the University of Amravati, who were involved in, and essential to, the field work carried out as part of this grant.

            The public and media are fascinated by mass extinction events in Earth history, in particular the extinction of the dinosaurs, which occurred at the Cretaceous-Paleogene boundary.  Through our work, the Deccan Traps is now the best temporally resolved large igneous province in Earth history, which will help constrain the contributions of both the Chicxulub impact and the Deccan Traps on the end-Cretaceous catastrophe. Our work serves as a template for connecting massive volcanism with other mass extinctions as well, which also continues to garner public interest.  Of societal importance, understanding the impact of anthropogenic greenhouse gases on modern climate may require a paleoclimate perspective as well to better know the limits of the Earth system. Flood basalt volcanism clearly has had an important impact on the ocean-atmosphere-biologic system through the Phanerozoic, and our results from the Deccan Traps will therefore contribute directly to our understanding of current and future climate change.   

Last Modified: 07/05/2017
Modified by: Blair Schoene