Compound-specific carbon isotopes from Earth's largest flood basalt eruptions directly linked to the end-Triassic mass extinction

Abstract

A leading hypothesis explaining Phanerozoic mass extinctions and associated carbon isotopic anomalies is the emission of greenhouse, other gases, and aerosols caused by eruptions of continental flood basalt provinces. However, the necessary serial relationship between these eruptions, isotopic excursions, and extinctions has never been tested in geological sections preserving all three records. The end-Triassic extinction (ETE) at 201.4 Ma is among the largest of these extinctions and is tied to a large negative carbon isotope excursion, reflecting perturbations of the carbon cycle including a transient increase in CO(2). The cause of the ETE has been inferred to be the eruption of the giant Central Atlantic magmatic province (CAMP). Here, we show that carbon isotopes of leaf wax derived lipids (n-alkanes), wood, and total organic carbon from two orbitally paced lacustrine sections interbedded with the CAMP in eastern North America show similar excursions to those seen in the mostly marine St. Audrie's Bay section in England. Based on these results, the ETE began synchronously in marine and terrestrial environments slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, a CO(2) super greenhouse, and marine biocalcification crisis. Because the temporal relationship between CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same place, this is the strongest case for a volcanic cause of a mass extinction to date.

Fig. 1.

Map of Pangea at 201 Ma showing the distribution of the CAMP and the localities discussed in the text: 1, St. Audrie’s Bay; 2, Newark basin; 3, Hartford basin; 4, Kennecott Point; 5, Val Adrara; 6, Moroccan CAMP sections. Base map (orthographic projection) courtesy of C. Scotese based on the latitudinal positions of ref. .

Fig. 2.

Compound-specific, wood, and total organic carbon isotopes from Newark and Hartford basin strata interbedded with the CAMP lava flows (diagonal hachures) compared to marine total organic carbon () records from St. Audrie’s Bay (and East Quantoxhead), United Kingdom (4, 7) and Kennecott Point, British Columbia, Canada (4). Compound-specific carbon isotopes are of the weighted mean odd C₂₅–C₃₁ n-alkanes (). Newark and Hartford sections calibrated in time with NBAGPTS (23). Dates in italics are ²⁰⁶Pb/²³⁸U single crystal chemically abraded-thermal ionization mass spectroscopy ages from the North Mountain Basalt of the Fundy basin (bold red) correlative with the Orange Mountain Basalt and Talcott Formation of the Newark and Hartford basins, and from marine ammonite-bearing strata from Peru (black) (from refs.  and 22) correlated to the St. Audrie’s Bay isotope curve using the bio-and carbon isotope-stratigraphy of ref. . The St. Audrie’s Bay and Kennecott Point data are from refs.  and and are shown in depth with the fiducial levels of correlation (red lines) among all sections being the base of the ETE (extinction level) and the Hettangian–Sinemurian boundary constrained in the Newark and Hartford basins by paleomagnetic stratigraphy (17) (polarity) and cyclostratigraphy (from ref. 7). The blue line indicates the projected Triassic–Jurassic boundary (J/Tr) based on correlation to the first appearance datum (FA) of the ammonite P. spelae chosen for the marker for the base of the Hettangian at the GSSP in Kuhjoch, Austria (38) projected to the Newark and Hartford data from St. Audrie’s Bay, itself correlated to Kuhjoch in ref. . Abbreviations are GSSP, global stratotype section and point for the base of the Sinemurian at St. Audrie’s Bay (East Quantoxhead) (7); ICIE, initial carbon isotopic excursion of ref. ; J/Tr, base of Triassic-Jurassic boundary; P.p., Planorbis Zone. The gray-circles indicate rejected points in the Hartford and Newark sections because of thermal alteration or very low carbon preference index values (SI Text).

Fig. 4.

Detailed comparison and correlation between the Newark and Hartford compound-specific carbon isotopes of the weighted mean odd C25–C31 n-alkanes () from lacustrine rocks interbedded with the CAMP flood basalt flows (from Fig. 2) with environmentally and biological relevant data from other sections. These are new compound-specific carbon isotopes of the weighted mean odd C₂₅–C₃₁ n-alkanes () from St. Audrie’s Bay and total organic carbon () data from refs.  and , Os isotopic data from ref. , and paleomagnetic polarity stratigraphy from ref. , all from St. Audrie’s Bay; carbon isotope data from wood () (9), leaf stomatal density proxy data for CO₂ (9) and floral species extinction rate [Proportional Extinction (%)] from Jamesonland, Greenland (Astartekløft); and the ranges of critical taxa (pollen, Patinasporites and Rhaetipollis, cited in refs.  and 20), invertebrates (Choristoceras) (4, 35), conodonts (20), “Jurassic aspect” ammonites including P. spelae (35) and P. planorbis (20), and tetrapod footprint (16) (noncrocodylomorph crurotarsans) (e.g., Brachychirotherium and Apatopus and the large theropod dinosaur track Eubrontes giganteus). CAMP basalt flows in the Newark and Hartford basins are indicated by the light blue-green bars (flows) and a basaltic ash by a dark blue bar (Pompton Tuff, SI Text), while other CAMP basalt flows are shown in orange for the Central High Atlas from Morocco (24, 25), and yellow for the Culpeper basin (Virginia) (23). Jamesonland data correlated to St. Audrie’s Bay and Newark and Hartford sections by the initiation of the plant extinctions (terrestrial ETE) and wood isotopic records. Abbreviations are as in Fig. 2 with the addition of BA, Blue Anchor Formation; L, Lilstock Formation; and Westb, Westbury Formation.

Fig. 3.

Comparison between power spectra of carbon isotopic data from the Newark and Hartford basins and the St. Audrie’s Bay section using the same time scale (NBAGPTS) based on the correlation to the base of the ETE and the Hettangian–Sinemurian boundary. Note the correspondence between the approximately 100 ky periods in and in both the Newark–Hartford and St. Audrie’s data and the presence of the approximately 20 ky cycle in the St. Audrie’s data. Coherence in the Newark–Hartford data and in the St Audrie’s data is shown between the and with the spectrum for color shown for reference as it is tuned to the NBAGPTS. Nonzero coherence is greater than 0.6.