Rapid light carbon releases and increased aridity linked to Karoo–Ferrar magmatism during the early Toarcian oceanic anoxic event

Abstract

Large-scale release of isotopically light carbon is responsible for the carbon isotope excursion (CIE) of the Toarcian Oceanic Anoxic Event during the Lower Jurassic. Proposed sources include methane hydrate dissociation, volcanogenic outgassing of carbon dioxide and/or thermogenic methane release from the Karoo‐Ferrar magmatic province (southern Africa). Distinct small-scale shifts superimposed on the long-term CIE have been interpreted as rapid methane pulses linked to astronomically forced climate changes. In the Peniche reference section (Portugal), these small-scale shifts correspond to distinct brownish marly layers featuring markedly high mercury (Hg) and magnetic mineral concentration. Total organic carbon and Hg increase are uncorrelated, which suggests input of Hg into the atmosphere, possibly released after the intrusion of the Karoo-Ferrar sills into organic-rich sediments. Enhanced magnetic properties are associated with the presence of martite, washed-in oxidized magnetite, inferred to be due to increased aridity on the continental hinterland. This study provides strong evidence for a direct link between the Karoo-Ferrar magmatism, the carbon-isotope shifts and the resulting environmental changes.

Early Jurassic large igneous province carbon emissions constrained by sedimentary mercury

“…The largest peaks in Hg R , and hence largest potential CO 2 emissions, of the entire 20 Myr record occur within the interval of the T-OAE n-CIE (Figs. 2 and 3), consistent with previous studies that documented elevated Hg concentrations at the Pliensbachian/Toarcian boundary and the T-OAE interval 30,32,33,37 . The relative magnitude of these peaks compared with the rest of the Hg R record suggests that KFLIP-associated gas emissions were greatest during this part of the Early Jurassic 30,32 .…”

“…Volcanic systems emit mercury gas during eruptive and non-eruptive degassing, including intrusive magmatic activity 29 . Indeed, large-scale and prolonged subaerial volcanism 30,31 can be traced by sedimentary Hg concentrations in the geological record: increases in Hg have been found to occur coeval with, for example, the main-phase eruptive intervals of the KFLIP 30,[32][33][34] and CAMP 17 .…”

Dinosaur extinctions related to the Jenkyns Event (early Toarcian, Jurassic)

“…The early stages of Karoo-Ferrar LIP volcanism occurred at the Pliensbachian-Toarcian boundary (Them et al, 2018;Xu et al, 2018b) and coincided with the initial shift in land plant communities (Slater et al, 2019) and a temperature fluctuation about 5ºC warming followed by 8ºC cooling in the middle Polymorphum (Tenuicostatum) ammonite Zone. The main impact on land plant communities recorded at the start of the negative CIE contemporaneous with the main activity phase of the Karoo-Ferrar LIP (Sell et al, 2014;Burgess et al, 2015;Moulin et al, 2017;Them et al, 2018;Font et al, 2022;Ruhl et al, 2022;Fig. 1) and Chon Aike LIP volcanism (Pankhurst & Rapela, 1995) was accompanied by about 10ºC warming (Ruebsam et al, 2020b) and enhanced continental weathering (Percival et al, 2016;Them et al, 2017b;Fig.…”

“…In addition to the extinction, the biotic crisis is also expressed in a decrease of diversity, mainly affecting benthic communities, as well reductions in body size of some taxa (Harries & Little, 1999;Piazza et al, 2020). Key triggers of the Jenkyns Event include the emission of volcanic CO 2 and thermogenic CH 4 associated with the emplacement of the Karoo-Ferrar Large Igneous Province (LIP) and probably the Chon Aike LIP volcanism (Pankhurst & Rapela, 1995), that broadly coincide with the negative CIE (Hesselbo et al, 2007;Moulin et al, 2017;Fantasia et al, 2019;Font et al, 2022;Fig. 1).…”

“…We might assume heating and acid rain on land, leading to a loss of forests and soil wash into the sea, together with aridity and sporadic heavy rainfall conditions on land, all features of the standard hyperthermal extinction model (Benton & Newell, 2014;Benton, 2018). Even though the Jenkyns Event has been mainly studied in marine sediments, it also impacted terrestrial settings, and many authors have identified a displacement of climatic belts with the spread of aridity (Rodrigues et al, 2019;Lu et al, 2020;Font et al, 2022) and enhanced weathering (e.g., Brazier et al, 2015;Montero-Serrano et al, 2015;Percival et al, 2016;Them et al, 2017b). During the Jenkyns Event, global warming also affected continental ecosystems.…”