Orbital controls and threshold effects on carbon isotope excursions during the Toarcian Oceanic Anoxic Event

During the Toarcian, Early Jurassic, the Earth experienced a global carbon cycle perturbation associated with global warming and widespread oceanic anoxia, known as the Toarcian Oceanic Anoxic Event (T-OAE). Carbon isotope data from oceans and land around the world record a clear negative excursion (ranging from ~2 ‰ to 8.5 ‰). However, the factors controlling the differences in the magnitude of this negative carbon isotope excursion (CIE) are still unclear, and there are many different explanations for the different durations of the Toarcian negative CIE. This study compiled nine high-resolution marine boreholes and sections data from Western Tethys Ocean and two continental drill hole data from the Eastern Tethys region. Through cyclostratigraphic analysis, it was found that the duration of the negative CIE was ~350–1800 kyr. In addition, by combining power decomposition analysis (PDA) with machine learning methods, it is believed that long eccentricity and precession affect the changes in carbon isotope characteristics during T-OAE, but there may be a threshold effect in the driving process. When the long eccentricity/precession is below the threshold, or even within a certain range, the stronger the effect of the orbital cycle, the longer duration of the negative CIE, and the greater the magnitude of the excursion. This study enriches the terrestrial records in T-OAE research and deeply explores the impact of different factors on the Early Jurassic oceanic anoxic event, which is of great significance for understanding the impact mechanism of oceanic anoxic events.