Evidence of Hg enrichment at the SPBE from Lower Jurassic continental succession of the Sichuan Basin, China

In the Early Jurassic, there is a globally recognized perturbation of the carbon cycle occurred at the Sinemurian-Pliensbachian transition, named“Sinemurian-Pliensbachian Boundary Event” (SPBE, ~ 192.5 Ma). The SPBE is associated with environmental and climate perturbations such as increased runoff, changes in marine shallow water carbonate production, enhanced preservation of organic matter and dysoxic conditions in the oceans. Evidence mainly comes from the marine realm, while other sedimentary settings around the world has been less investigated. Recent works have highlighted the presence of a prominent negative perturbation of the δ13Corg in Lower Jurassic lacustrine succession of the Sichuan Basin, which has been correlated to the SPBE (Franceschi et al., 2022). The causes of the SPBE are still unclear, but a potential link to late phases of volcanism of the Central Atlantic Magmatic Province has been hypothesized based on mercury (Hg) enrichments observed in Sinemurian – Pliensbachian marine successions of the Western Tethys (Shöllhorn et al., 2020). Studies have put forward the hypothesis of a warming trend in the lower Pliensbachian that may have culminated in short-lived hyperthermals (e.g. Silva et al., 2015). In this contribution, we present Hg and TOC content data from the Lower Jurassic lacustrine succession of the Sichuan Basin (Eastern Tethys) in the Dacao section where a high resolution δ13Corg record is already available (Franceschi et al., 2022). Results highlight Hg enrichments coincident with the negative δ13Corg shift that is interpreted as the SPBE. The relative low correlation with TOC data, suggests that Hg could be volcanogenic. This, together with the fact that the Hg enrichment at the Sinemurian‑Pliensbachian transition is documented in the continental realm, strengthen the hypothesis of a global‑scale link between the SPBE and volcanic activity. Preliminary results of elemental analysis carried out with pXRF further reveals enrichment trends in elements such those of the group of clay minerals that may be compatible with variations in runoff intensity caused by climate change to more humid conditions at the SPBE. Our results provide clues as to how climate changes associated with the SPBE may have been linked to volcanic activity and have had global extent. Reference Franceschi, M. et al.,2022. GSA Bulletin. High-resolution record of multiple organic carbon-isotope excursions in lacustrine deposits of Upper Sinemurian through Pliensbachian (Early Jurassic) from the Sichuan Basin, China. 2022; doi: https://doi.org/10.1130/B36235.1 Schöllhorn, I. et al., 2020. Sedimentary Geology 406, 105665. Pliensbachian environmental erturbations and their potential link with volcanic activity: Swiss and British geochemical records; doi:10.1016/j.sedgeo.2020.105665 Silva, R, L., Luís V. Duarte. Global and Planetary Change, Volume 131,2015,Pages 24-34,ISSN 0921-8181. Organic matter production and preservation in the Lusitanian Basin (Portugal) and Pliensbachian climatic hot snaps; https://doi.org/10.1016/j.gloplacha.2015.05.002