Carbon cycle perturbation and mercury anomalies in terrestrial Oceanic Anoxic Event 1b from Jiuquan Basin, NW China

Oceanic Anoxic Event (OAE) 1b is well documented in western Tethys; however, records in Eurasia are still lacking. Here, we carried out high-resolution organic carbon isotope (δ13Corg), total organic carbon (TOC) content and mercury (Hg) concentration analysis of the lacustrine sediments from the Xiagou and Zhonggou formations in the Hanxiagou section of the Jiuquan Basin, NW China. The lacustrine δ13Corg curve presents three stages of negative excursions above the basalt layer dated at 112.4 ± 0.3 Ma in the lowermost Zhonggou Formation. The three negative δ13Corg excursions correspond well with the three sub-events (Kilian, Paquier and Leenhardt) of the OAE 1b in the Poggio le Guaine (central Italy), Vocontian Basin (SE France) and St Rosa Canyon (NE Mexico) sections, supporting the record of the terrestrial OAE 1b in the Jiuquan Basin. Five mercury enrichment intervals in Hg/TOC ratios were recognized, indicating that the pulsed volcanism from the Southern Kerguelen Plateau likely triggered OAE 1b. However, the decoupling between negative isotopic excursion shifts and mercury enrichments, signifying another carbon reservoir (with no link to mercury), probably contributed to the global carbon cycle perturbation during the OAE 1b period. Our results provide direct evidence to link OAE 1b and the terrestrial ecosystem in Eurasia.