ASTRONOMICAL CALIBRATION OF THE JURASSIC HETTANGIAN STAGE

The first stage of the Early Jurassic, the Hettangian, records the aftermath and recovery immediately following the end-Triassic mass extinction. To fully understand the post-extinction Earth processes, an accurate timescale is required. Although several studies have attempted an astronomical calibration, results are controversial, and differ by a factor of more than two. Here we propose a new age model based on multiple time series datasets (X-ray fluorescence, core gamma-ray, magnetic susceptibility, δ¹³C_org) from the recently drilled (2020–2021) Prees 2C scientific borehole, Cheshire Basin, UK. The results show that the duration of the Hettangian is at least 2.24 Myr, but we find no compelling evidence for the much longer duration of up to 4 Myr recently proposed, indicating a relatively brief post-extinction recovery time. We reanalyse the Somerset coast data from Weedon et al. (2019) using the correlation coefficient method and MTM spectrum and find a different duration in the Tilmanni and Planorbis zones. The total Hettangian duration of Somerset coast site basing on the reanalysed result is 2.27 Myr considering the possible hiatuses, which is highly similar to the duration from Prees. By anchoring through existing U-Pb dates for the Triassic-Jurassic boundary, the Hettangian is suggested to range from 201.36 to 199.12 Ma. Besides the usually reported astronomical cycles, we also detect a weak ~200 kyr eccentricity cycle modulating precession as expressed in grain-size proxies, and affecting provenance and hydrodynamic conditions at this site.