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 kyr duration. These datasets can be analyzed in finer detail to determine eruption rates, which are critical for connecting volcanism, associated volatile emissions, and any potential effects on the Earth's climate before and after the Cretaceous–Paleogene boundary (KPB). It is our observation that the community has frequently misinterpreted how the eruption rates derived from these two datasets vary across the KPB. The U−Pb dataset of Schoene et al. (2019) was interpreted by those authors to indicate four major eruptive pulses before and after the KPB. The 40Ar/39Ar dataset did not identify such pulses and has been largely interpreted by the community to indicate an increase in eruption rates coincident with the Chicxulub impact (Renne et al., 2015; Richards et al., 2015). Although the overall agreement in eruption duration is an achievement for geochronology, it is important to clarify the limitations in comparing the two datasets and to highlight paths toward achieving higher-resolution eruption models for the Deccan Traps and for other large igneous provinces. Here, we generate chronostratigraphic models for both datasets using the same statistical techniques and show that the two datasets agree very well. More specifically, we infer 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 eruptions and provides no support for (or evidence against) the pulses identified by the U−Pb data, (2) the stratigraphic positions of the Chicxulub impact using the 40Ar/39Ar and U−Pb datasets do not agree within their uncertainties, and (3) neither dataset supports the notion of an increase in eruption rate as a result of the Chicxulub impact. We then discuss the importance of systematic uncertainties between the dating methods that challenge direct comparisons between them, and we highlight the geologic uncertainties, such as regional stratigraphic correlations, that need to be tested to ensure the accuracy of eruption models. 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 is also critically dependent on how such data are interpreted and presented to the broader community of geoscientists.

Moderate to Elevated Atmospheric CO2 During the Early Paleocene Recorded by Platanites Leaves of the San Juan Basin, New Mexico

“…Instead, our estimates are more in line with recent work based on leaf gas-exchange (Kowalczyk et al, 2018;Milligan et al, 2019), liverworts (Kowalczyk et al, 2018), boron (Henehan et al, 2019) and paleosols (Zhang et al, 2018; Figure 1). Specifically, our estimate of 1,143 at 65.66 Ma is comparable to estimates from Henehan et al Our earliest CO 2 estimate of 1,143 at 65.66 Ma (site AF1405), is roughly coincident with an early Paleocene pulse in Deccan volcanism (e.g., Fendley et al, 2020;Schoene et al, 2019;Schoene et al, 2021) and at the tail end, or just after, the carbon isotope excursion of the Dan-C2 event (Barnet et al, 2019;Lyson et al, 2019). Thus, it may reflect a brief episode of relatively high CO 2 conditions in the early Paleocene.…”

“…After 65.66 Ma, our record documents a ∼40% swing in CO 2 with a drop from 1,143 ppm at 65.66 a.m. to 665 at 65.29 Ma before returning to ∼1,000 ppm by 64.79 Ma. A drop in CO 2 over 300 kyrs is plausible, because the removal of a rapid release of CO 2 into the atmosphere typically requires up to 100–200 kyrs (Archer, 2005; Colbourn et al., 2015; Schaller et al., 2011; Zeebe & Zachos, 2013), and could reflect intensified weathering of Deccan Traps that were erupting during the Late Cretaceous and early Paleocene (Fendley et al., 2020; Schoene et al., 2019; Schoene et al., 2021; Sprain et al., 2019). Assuming an early Paleocene Earth system sensitivity of ∼3–4.5°C (e.g., Farnsworth et al., 2019; Kowalczyk et al., 2018; Royer, 2016), we would expect to observe a 3–4.5°C cooling in response to this halving in CO 2 .…”

The Magmatic Architecture of Continental Flood Basalts I: Observations From the Deccan Traps

“…We refer the reader to the following references for a detailed discussion ‐ Schoene et al. (2021); Sprain (2020); Renne (2020).…”

Supplemental Material: Contribution of orbital forcing and Deccan volcanism to global climatic and biotic changes across the Cretaceous-Paleogene boundary at Zumaia, Spain

“…Our astronomically calibrated age model does not reveal a direct temporal link between the Dan-C2 event and the Ambenali Formation (Fig. 3B) using either the model of isolated megapulses of Schoene et al (2019) or the quasi-continuous model of Sprain et al (2019), the latter recalculated in terms of eruptive rate by Schoene et al (2021) (Fig. 3B).…”