End-Triassic mass extinction started by intrusive CAMP activity

Abstract

The end-Triassic extinction is one of the Phanerozoic's largest mass extinctions. This extinction is typically attributed to climate change associated with degassing of basalt flows from the central Atlantic magmatic province (CAMP). However, recent work suggests that the earliest known CAMP basalts occur above the extinction horizon and that climatic and biotic changes began before the earliest known CAMP eruptions. Here we present new high-precision U-Pb ages from CAMP mafic intrusive units, showing that magmatic activity was occurring ∼100 Kyr ago before the earliest known eruptions. We correlate the early magmatic activity with the onset of changes to the climatic and biotic records. We also report ages from sills in an organic rich sedimentary basin in Brazil that intrude synchronously with the extinction suggesting that degassing of these organics contributed to the climate change which drove the extinction. Our results indicate that the intrusive record from large igneous provinces may be more important for linking to mass extinctions than the eruptive record.

Figure 1. Map of the circum-Atlantic region during the Latest Triassic.

The positions of CAMP dykes, sills and flows are shown, along with locations of the dated samples, ages in Myr with associated 2 sigma uncertainties and ɛHf isotope values. Approximate locations of the present day continents and country borders are also shown. Previously dated samples are from ref. and ref. . Map is modified after ref. .

Figure 2. U-Pb geochronology and ɛHf isotope compilation for the CAMP showing spatial and temporal variations.

(a) Vertical coloured bars represent ²³⁸U-²⁰⁶Pb Th-corrected ages for single zircon (filled bar) and baddeleyite (dashed bar) crystals. The length of the bar reflects the 2σ analytical uncertainties, and the grey horizontal bar reflects the weighted mean age calculated for the sample, with the thickness of the bar reflecting the 2σ uncertainty on the weighted mean age. The red line represents the ETE from ref. , and the ages from that study, and ref. are also shown. Note that our NMB sample overlaps in age, within uncertainty with both the ref. and ref. ages, although these do not overlap with each other, the age of the NMB should be 201.498±0.028 Myr, which is an average of the ages from refs , and reported here (Supplementary Fig. 2). All ages shown are without the tracer calibration and decay constant uncertainties, these need to be included when comparing the U-Pb ages to ages from other isotope systems. (b) Weighted mean age and average ɛHf data from the dated intrusive rocks. ɛHf data uncertainties are all±1.6ɛ units which represents the external reproducibility of the standard (see Methods section).

Figure 3. Detailed comparison and correlation between various proxy records around the ETE and the timing of CAMP intrusions.

A kernel density estimate of all high precision U-Pb CAMP ages from this study as well as those from ref. and ref. over a 1 Myr time period around the ETE are shown relative to various proxy records, whose age is calculated through astrochronology. δ¹³C_toc and δ¹³C_alk records from the Newark and Hartford basins, δ¹³C_toc and spore abundance (%) from St Audrie's bay, δ¹³C_toc from the Stenlille basin, δ¹³C_toc from New York Canyon, δ¹³C_wood from Jamesonland combined with leaf stomatal density data from CO₂ p.p.m. reconstructions and proportional extinction % (ref. 10) and the δ¹³C_toc and ocean redux indicators from ref. from Kennecott point. The ETE in the continental record from ref. is shown as a horizontal thin red line, the ETE period from the marine record from ref. is shown by the box at the right of the diagram along with the Triassic–Jurassic boundary (T–J) from the same reference recalculated by ref. , both with associated 2σ uncertainty. The Kakoulima intrusion age and associated uncertainty is shown as a grey bar. Red stars indicate the position of seismites from ref. . Small arrows indicate the early carbon isotope excursions from ref. . LO is last occurrence, FO is first occurrence, Cc, Choristoceras crickmayi, Neo, Neophylites, Ps, Psiloceras planorbis. Broadleaf symbol marks the decline of complex terrestrial vegetation species in western Greenland, bivalve symbol represents start of bivalve taxenomic diversity decrease. Benzoanthracene symbol and arrow indicate the identification of polycyclic aromatic hydrocarbons at the ETE horizon in the northern European basin. Correlations are following ref. .