An evaluation of Deccan Traps eruption rates using geochronologic data

Abstract

Abstract. Recent attempts to establish the eruptive history of the Deccan Traps large igneous province have used both U-Pb (Schoene et al., 2019) and 40Ar/39Ar (Sprain et al., 2019) geochronology. Both of these studies report dates with high precision and unprecedented coverage for a large igneous province, and agree that the main phase of eruptions began near the C30n-C29r magnetic reversal and waned shortly after the C29r-C29n reversal, totaling ~700-800 ka duration. Nevertheless, the eruption rates interpreted by the authors of each publication differ significantly. The U-Pb dataset was interpreted to indicate four major eruptive pulses, while the 40Ar/39Ar dataset was used to argue for an increase in eruption rates coincident with the Chicxulub impact (Renne et al., 2015; Richards et al., 2015). Although the overall agreement in duration is an achievement for geochronology, the disparate eruption models may act to undermine this achievement in the eyes of the broader geologic community. Here, we generate chronostratigraphic models for both datasets using the same statistical techniques and conclude that 1) age modeling of the 40Ar/39Ar dataset results in constant eruption rates with relatively large uncertainties through the duration of the Deccan Traps, and cannot verify or disprove the pulses identified by the U-Pb data, 2) the stratigraphic position of the Chicxulub impact within the 40Ar/39Ar dataset is much more uncertain than was presented in Sprain et al. (2019), and 3) neither dataset supports an increase in eruption rate as a result of the Chicxulub impact. While the production of precise and accurate geochronologic data is of course essential to studies of Earth History, our analysis underscores that the accuracy of a final result also is critically dependent on how such data are interpreted and presented to the broader community of geoscientists.

Radiometric Constraints on the Timing, Tempo, and Effects of Large Igneous Province Emplacement

“…U-Pb dates on impact ejecta come from zircon geochronology of ash beds bracketing Chicxulub ejecta in the Denver Basin, Colorado (Clyde et al, 2016); the 40 Ar/ 39 Ar date comes from both sanidine extracted from ash beds bracketing Chicxulub ejecta in Hells Creek, Montana, and on glassy tektites defining the Cretaceous-Paleogene boundary from both Haiti and Columbia 2019); new 40 Ar/ 39 Ar data are from Sprain et al (2019); Re-Os data are from Allègre et al (1999); and old K-Ar and 40 Ar/ 39 Ar are from Baksi (1994), Chenet et al (2007), Courtillot et al (1986Courtillot et al ( , 1988Courtillot et al ( , 2000, Duncan and Pyle (1988), Hofmann et al (2000), Hooper et al (2010), Knight et al (2003), Pande (2002), Venkatesan et al (1993). Ar/ 39 Ar and U-Pb data sets (Sprain et al, 2019;Schoene et al, 2019), compared using the same Bayesian techniques for generating an eruptive age model from each data set (Schoene et al, 2020). Upper plot shows the age of stratigraphic units versus the cumulative volume of basalt, using the volume model of Richards et al (2015).…”

The Anthropocene within the Geological Time Scale: a response to fundamental questions

“…Flood basalt outpourings of the kind that led to Earth System shifts now marked by chronostratigraphic boundaries are also relatively rare. Flood basalt provinces, too, develop over long timescales: ~0.8 myr for the Deccan Traps (Schoene et al, 2020) and ~ 2 myr for the Sibe-rian Traps (Burgess et al, 2017), so much more gradually than the greatly accentuated evolution (within 0.0001 myr) of the Earth System today. In the unlikely event of another flood basalt province emerging on Earth in the near future, its effects (including elevated CO 2 emissions) would undoubtedly interact with, though not efface, those generated by humans.…”

Reply to comment(s) on “Emplacement history and evolution of the Deccan Volcanic Province, India, by Kale et al. (2020)” by Sudha Vaddadi

“…The meticulous work of the GSI has been compiled in the zonal stratigraphy that now takes shape (Kale et al, 2019(Kale et al, , 2020. Some of the most recent publications (e.g., Eddy et al, 2020;Schoene et al, 2020) too prefer the zonal stratigraphy rather than extrapolation of the western chemical stratigraphy across the province. Work on these lines is continuing.…”