Anomalously low silicate weathering in the North China Craton during the hydroclimatic crisis of the Oceanic Anoxic Event 1a interval

Enhanced chemical weathering is a well-documented consequence of the warming associated with the Early Cretaceous Oceanic Anoxic Event 1a. This process likely contributed to the reduction of greenhouse gas levels and facilitated the termination of the event. While the role of enhanced silicate weathering as a terminator of Oceanic Anoxic Event 1a has been established, the coeval changes in silicate weathering in inland East Asia, which is far from the ocean, are not well-known. This study analysed strontium-isotope, oxygen-carbon isotope, clay mineral, and elemental geochemistry in shales and dolomites from three Early Cretaceous terrestrial sections (Zhifengzhuang, Shuinan and Lingshandao formations) within the North China Craton to decipher silicate weathering patterns during Oceanic Anoxic Event 1a. The results revealed that the dramatic warming associated with Oceanic Anoxic Event 1a led to a severe hydroclimatic crisis in East China, where aridification decreased lake levels and rapidly increased their salinity. However, chemical weathering was extremely weak during this period. These findings aligned with equivalent data obtained from two contemporaneous terrestrial sections (Chaoyang and Fuxin basins) located further north-east on the North China Craton. Anomalously low silicate weathering during the Oceanic Anoxic Event 1a hyperthermal interval resulted in ineffective climate regulation within the North China Craton. Finally, Sr-isotope ratios were compared with equivalent data from two coeval marine sections (Resolution Guyot in the Pacific Ocean and Gucuo in Tibet). During the initial stage of Oceanic Anoxic Event 1a in Tibet, chemical weathering, indicated by weathering indicators, intensified. This finding presented a stark contrast to the results from the study areas. The gradual increase in the measured Sr-isotope ratios at the end of this event contrasted with the decline observed at Resolution Guyot. This contrast was attributed to the stronger influence of humidity, compared with temperature, on continental weathering in inland arid areas under greenhouse regimes. Consequently, as Oceanic Anoxic Event 1a came to an end with increased humidity, chemical weathering gradually intensified. This study provides insights into the closely linked dynamics of climatic, environmental and chemical weathering factors, which ultimately enhances our understanding of Earth's responses to the Oceanic Anoxic Event 1a hyperthermal event.