Astronomical age constraints and extinction mechanisms of the Late Triassic Carnian crisis

Abstract

The geological record contains evidence for numerous pronounced perturbations in the global carbon cycle, some of which are associated with mass extinction. In the Carnian (Late Triassic), evidence from sedimentology and fossil pollen points to a significant change in climate, resulting in biotic turnover, during a time termed the ‘Carnian Pluvial Episode’ (CPE). Evidence from the marine realm suggests a causal relationship between the CPE, a global ‘wet’ period, and the injection of light carbon into the atmosphere. Here we provide the first evidence from a terrestrial stratigraphic succession of at least five significant negative C-isotope excursions (CIE)’s through the CPE recorded in both bulk organic carbon and compound specific plant leaf waxes. Furthermore, construction of a floating astronomical timescale for 1.09 Ma of the Late Triassic, based on the recognition of 405 ka eccentricity cycles in elemental abundance and gamma ray (GR) data, allows for the estimation of a duration for the isotope excursion(s). Source mixing calculations reveal that the observed substantial shift(s) in δ13C was most likely caused by a combination of volcanic emissions, subsequent warming and the dissociation of methane clathrates.

Multiple negative carbon-isotope excursions during the Carnian Pluvial Episode (Late Triassic)

“…Distinct large-scale intercalations of coarse siliciclastics that interrupt shallow-water carbonate successions in the northwestern Tethys, as well as repeated shifts in the composition of the microflora, from xerophytic to hygrophytic forms, are recorded in sedimentary successions (Roghi et al, 2010;Mueller et al, 2016a and references therein). This evidence, coupled with recent age models based on cyclostratigraphy of gamma-ray and elemental abundances (Zhang et al, 2015;Miller et al, 2017), which assign to the CPE a duration of approximately 1.2 Myr, show that this event was not characterized by uniform climatic conditions and a more complex series of events occurred over such an extended period of time. Furthermore, Sun et al (2016) reported three NCIE in bulk carbonates of the Carnian sedimentary succession of South China (Guizhou): at the base of the Julian 2, at the Julian Tuvalian boundary, and in the Tuvalian 1.…”

“…Dal Corso et al A C C E P T E D M A N U S C R I P T ! Miller et al, 2017). Such a pattern suggests that for the NCIE-1 the differences could be linked to local changes in the source of the organic carbon, i.e.…”

“…Such shifts are not recorded by organic matter from the same stratigraphic succession, which in turn records a long-term negative shift that starts at the base of the Julian 2 and rebounds to pre-excursion values at the top of the Tuvalian 1. However, Miller et al (2017) detected five NCIE in leaf-wax n-alkanes and bulk organic matter from the WP borehole 1 drilled in the Carnian…”

“…1). The CPE was characterized by major environmental changes in continental to shallow-and deeper water settings, and biological turnovers on land and in the ocean (e.g., Schlager and Schšllnberg, 1974;Benton, 1983;Simms and Ruffell 1989;Benton 1991;Krystyn 1991;Simms et al, 1995;Gianolla et al, 1998;Roghi et al, 2004;Hornung and Brandner, 2005;Furin et al, 2006;Keim et al, 2006;Hornung et al, 2007;Rigo et al, 2007;Breda et al, 2009;Preto et al, 2010;Balini et al, 2010;Roghi et al, 2010;Stefani et --Franz et al, 2014;Chen et al, 2015;Dal Corso et al, 2015Gattolin et al, 2015;Ruffell et al, 2016;Mueller et al, 2016a,b;Sun et al, 2016;Miller et al, 2017;Dunhill et al, 2017;Bernardi et al, 2018). The onset of the CPE coincided with a perturbation of the carbon cycle characterized by a sharp 2 -isotope excursion (NCIE).…”

“…The onset of the CPE coincided with a perturbation of the carbon cycle characterized by a sharp 2 -isotope excursion (NCIE). The NCIE is found in terrestrial and marine organic matter (biomarkers and total organic carbon) and marine carbonates in stratigraphic sections in Europe and China (Dal Corso et al, 2012Muttoni et al, 2014;Mueller et al, 2016aMueller et al, , 2016bSun et al, 2016;Miller et al, 2017). This NCIE suggests an injection of large quantities of 13 C-depleted CO 2 into the ocean atmosphere system that is thought to have induced the climate change and be possibly linked to the eruption of the Wrangellia, also called Nikolai, Large Igneous Province (LIP;Dal Corso et al, 2012Mueller et al, 2016a;Sun et al, 2016).…”