INTERMITTENT OBLIQUITY-FORCED CLIMATE DURING THE EARLY TRIASSIC

The aftermath of the end-Permian mass extinction is marked by 5 million-year (myr) of Earth system upheavals, i.e., unstable biotic recovery, repeated intense warming, ocean anoxia, cyanobacterial blooms, and dramatic perturbations in the global carbon cycle. Intervals between crises were comparably hospitable to life. The causes of these upheavals are linked with recurrent devastating Siberian volcanic eruptions. Other factors, such as the astronomical forcing of Early Triassic climate, have not yet been considered. In younger geologic worlds, million-year-scale climate oscillations have been linked to long-term variations in Earth’s astronomical parameters. For example, the Cenozoic icehouse is paced by 1.2 myr obliquity modulation cycles, and climate changes in the Mesozoic greenhouse are linked to ~2.4 myr orbital eccentricity modulation cycles.

In this study, two equatorial cyclostratigraphic successions, i.e. Chaohu and Daxiakou marine sections from South China are evaluated for astronomical forcing of Early Triassic climate. Astronomical tuning of the gamma-ray series provides a high-resolution timescale for the Early Triassic. A measure for obliquity power/total power is developed for the tuned time series and applied to highlight long-term amplitude modulations of the obliquity variation. In both Chinese records, unexpectedly, enhanced obliquity cycling occurs over multiple prolonged intervals, characterized by a periodicity of 32.8-kyr and strong 1.2-myr period modulations, suggesting a 22-hour length-of-day and representing evidence for 1.2-myr interaction between the orbits of Earth and Mars. These enhanced obliquity intervals coincide with global sea level falls and other evidence for cooling linked to recurrent ocean oxidation/dysoxia and biotic recovery. This evidence suggests that long-term astronomical forcing was involved in the repeated environmental and biotic upheavals that took place during the Early Triassic.