On the onset of Central Atlantic Magmatic Province (CAMP) volcanism and environmental and carbon-cycle change at the Triassic-Jurassic transition (Neuquen Basin, Argentina)

The Triassic-Jurassic transition is characterized by the end-Triassic mass extinction approximately synchronous with the onset of emplacement of the Central Atlantic Magmatic Province (CAMP), and associated with a major negative carbon-isotope excursion (CIE) affecting the ocean-atmosphere system. Here, we present new data (total organic carbon, pyrolysis analysis, carbon-isotopes from bulk organic matter, elemental mercury, and other elemental contents) from a southern-hemisphere Triassic-Jurassic boundary succession in the Neuquen Basin, Argentina. The end-Triassic mass extinction there coincides with a relatively small (2-3 parts per thousand) negative CIE in bulk organic matter, and we present a model that suggests that extreme aridity across the western Pangaean landmass may have resulted in rather limited terrestrial organic-matter flux to the sedimentary realm in eastern Panthalassic marine basins, hypothetically reducing the magnitude of the observed negative CIE in delta C-13(Toc). Increased deposition of sedimentary Hg (and Hg/TOC and Hg/Zr) in the marine Neuquen Basin began stratigraphically before the negative CIE associated with the end-Triassic mass extinction, and thus before the commencement, in North America and Africa, of CAMP-related basaltic volcanism, but possibly coinciding with the early emplacement of CAMP-associated intrusives (dykes and sills). This relative chronology suggests thermal alteration of intruded country rocks and/or intrusive magmatic degassing of Hg as potential major sources of elevated Hg fluxes to the atmosphere at this time. The Neuquen Basin experienced the development of dysoxic-anoxic marine conditions across the Triassic-Jurassic transition, enabling increased preservation of organic matter. Simple mass-balance calculations show that enhanced carbon burial rates can explain the inferred evolution of the global exogenic carbon cycle across this time-interval.