Abstract
The eruption of the Central Atlantic Magmatic Province (CAMP)—the largest igneous province known—has been linked to the end-Triassic mass extinction event, however reconciling the response of the biosphere (at local and nonlocal scales) to potential CAMP-induced geochemical excursions has remained challenging. Here we present a combined sedimentary and biological response to an ecosystem collapse in Triassic-Jurassic strata of the southwest United Kingdom (SW UK) expressed as widely distributed carbonate microbialites and associated biogeochemical facies. The microbialites (1) occur at the same stratigraphic level as the mass extinction extinction, (2) host a negative isotope excursion in δ13Corg found in other successions around the world, and (3) co-occur with an acme of prasinophyte algae ‘disaster taxa’ also dominant in Triassic-Jurassic boundary strata of other European sections. Although the duration of microbialite deposition is uncertain, it is likely that they formed rapidly (perhaps fewer than ten thousand years), thus providing a high-resolution glimpse into the initial carbon isotopic perturbation coincident with the end-Triassic mass extinction. These findings indicate microbialites from the SW UK capture a nonlocal biosedimentary response to the cascading effects of massive volcanism and add to the current understanding of paleoecology in the aftermath of the end-Triassic extinction.
Highlights
The end-Triassic extinction, one of the ‘big five’ mass extinctions of the Phanerozoic[1], has been linked to the eruption of the Central Atlantic Magmatic Province (CAMP)[2]
Several lines of evidence converge to suggest the microbialites of the Upper Cotham Member were coincident with the end-Triassic extinction: (1) The shift in δ 13Corg from about − 25.8‰ to − 29.6‰ within the microbialites (Figs. 1 and 2C) corresponds in absolute value and magnitude to the initial carbon isotope excursion” (I-CIE) from St Audrie’s Bay[8], where the I-CIE co-occurs with the extinction[17] and has been correlated with the I-CIE at other European sites, where it co-occurs with the extinction[10]
The equivalence of the I-CIE and the Cotham Marble microbialites has been demonstrated at Stowey Quarry[21]
Summary
The end-Triassic extinction, one of the ‘big five’ mass extinctions of the Phanerozoic[1], has been linked to the eruption of the Central Atlantic Magmatic Province (CAMP)[2]. We present combined biogeochemical and petrographic evidence that indicates the Cotham Marble microbialites host geochemical (I-CIE) and biological characteristics (abundant fossilized clusters of prasinophyte algae) that directly link them to other UK and European end-Triassic sections. At St Audrie’s Bay, the Upper Cotham Member contains the I-CIE coincident with the extinction horizon www.nature.com/scientificreports/. The microbialites occur about a meter above the fissured horizon at the top of the Upper Cotham Member. The microbialite mounds do not occur in all localities where the Upper Cotham Member is present They are absent from the well-studied sections at St Audrie’s Bay and Lavernock Point, rendering the stratigraphic position of the microbialite mounds with respect to the extinction and carbon isotopic excursion unclear (until now)
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