Sediment-derived Volatile Release During LIP Emplacements The Key To Explain Environmental/climatic Impacts?
Abstract
Sills of the Central Atlantic Magmatic Province (CAMP) and Karoo Large Igneous Province (LIP) are temporally linked to the end-Triassic (ca. 201 Ma) and Toarcian (ca. 183 Ma) crises, respectively. Both of these events are characterized by major carbon cycle perturbations, including negative carbon isotope excursions (CIEs), attesting to the input of isotopically light carbon. Furthermore, the end-Triassic crisis includes one of the big five Phanerozoic mass extinctions (the end-Triassic extinction; ETE), while the Toarcian crisis represents minor biotic loss. Both the CAMP and Karoo LIPs are characterized by widespread sill emplacements within sedimentary basins hosting volatile-rich rocks, such as shales with a significant component of organic matter. Sill heating and contact metamorphism of these rocks likely led to the generation of thermogenic carbon gases (CO2 and CH4) in the order of several thousand gigatons, which represents a credible carbon source for the negative CIEs. Carbon cycle modeling demonstrates, by testing detailed emission scenarios, that the carbon cycle perturbations associed with both the ETE and Toarcian crisis can be accounted for by the release of sediment-derived thermogenic carbon. The Amazonas and Solimões sedimentary basins (Brazil), which host most of the CAMP sills, comprise significant deposits of limestone and evaporites, in addition to organic-rich shales. Detailed borehole logs and geochemical investigations of sill samples drilled in these basins suggest that interactions between the intruding magma and sedimentary rock likely generated sediment-derived volatiles such as SO2 and Cl-compounds in addition to thermogenic CO2 and CH4. The release of such a mix of volatiles could explain the severity of the biotic loss during the ETE. Our investigations strengthen the case for an active involvement of CAMP and Karoo LIP in the end-Triassic and Toarcian crises, and that the sub-volcanic part of a LIP represents a key driver for environmental and climatic perturbations.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMPP31B..01H