Orbital forcing of Triassic megamonsoon activity documented in lacustrine sediments from Ordos Basin, China

The “hothouse” Triassic climate provides a key window to study megamonsoon systems. However, high-quality paleoclimate proxy records are rarely reported from the Tethys realm, where the seasonal meridional migration of the intertropical convergence zone (ITCZ) should be the most remarkable. Here, continuous and well-dated proxy records are used to study monsoon activity in the northeastern Tethys from the Middle Triassic lacustrine sediments (Ch7 black shale, Yanchang Formation) in the Ordos Basin (China). The proxies, including natural gamma-ray intensity, magnetic susceptibility, and element concentrations and ratios (U, K, Zr/Al, Zr/Rb and Sr/Rb), document a strong precession signal in the sediments. We propose that the periodic deposition of the Ch7 black shale occurred in response to intensifications in a monsoon-driven climate enhanced by the early Ladinian warming event. Climate variability in the Ordos Basin (~25°N) reflects the harmonics of ~100 kyr, ~20 kyr and ~10 kyr cycles and is highly coherent with solar insolation at 9° latitude, suggesting that this monsoon system might have been modulated by tropical solar insolation. The dominance of tropical climate processes in this mid-latitude monsoon region can be attributed to the dramatic dynamics of the ITCZ and intense monsoon circulation in the Tethys realm. •Deposition of Ch7 black shale was paced by the precession-controlled monsoon activity.•Warming event in the early Ladinian triggered Ch7 black shale deposition.•Semi-precession signal in the Ordos Basin responded to tropical insolation forcing.•Tropical insolation was the dominant driver of the Tethyan monsoon.