TIMING OF THE END-TRIASSIC MASS EXTINCTION AND CARBON CYCLE PERTURBATIONS, AND EARLY JURASSIC (HETTANGIAN) RECOVERY

Timing of events at the Triassic–Jurassic transition, such as mass extinction and biotic recovery, changes in global (bio)geochemical cycling, and climatic and environmental disturbance, are poorly constrained and contested because of the limited availability of biostratigraphically well-constrained, complete and expanded sedimentary successions spanning this time interval that also allow for astrochronological or radiometric age constraints. Such understanding is however essential to identify the causes of these events and the fundamental Earth system processes at play at this time.

Here, we present new sedimentary geochemical data from the CRN-2 core in the Larne Basin, Northern Ireland. The stratigraphically well constrained sedimentary succession in this core spans the upper Rhaetian (Upper Triassic) to lower Sinemurian (Lower Jurassic) and presents one of the most expanded and complete sedimentary successions spanning the Triassic–Jurassic transition.

Utilising the obtained data we show astronomical forcing of the depositional environment within the Larne Basin, and of possibly the global carbon cycle at this time. We show that the negative carbon isotope excursion (CIE) coinciding with the end-Triassic mass extinction, and inferred to represent a major global carbon cycle disturbance at the onset of Central Atlantic Magmatic Province (CAMP) magmatism, is characterised by an astronomically paced, step-wise shift to more negative values, thus questioning the main source of isotopically light carbon released into the global ocean-atmosphere.

Furthermore, the rate of biotic and global biogeochemical recovery following the end-Triassic mass extinction is contested because of varying duration estimates for the Early Jurassic Hettangian Stage, of between 1.8–4.5 myr. We show that the Hettangian likely had a fairly short duration of ~2.3 myr and that initial biotic recovery occurred within a few 100 kyr after the onset of the end-Triassic mass extinction, and coinciding with the emplacement of CAMP.