Terrestrial Biotic Turnover Linked with Cretaceous Oceanic Anoxic Event 1a

The Early Cretaceous Oceanic Anoxic Event 1a (OAE 1a, ~120 Ma) was a major episode of global warming. However, terrestrial environmental and biological responses to this hyperthermal event are still poorly understood. Here, we present high-resolution mercury (Hg) concentrations and isotopes, chemical index of alteration (CIA) values and clay-mineral assemblages from two lacustrine sequences spanning OAE 1a of East Asia. Our terrestrial Hg anomalies and Δ199Hg signatures indicate elevated volcanism, likely subaerial activity on the Greater Ontong Java Plateau that dispersed Hg into continental environments. Our weathering proxies and Earth System modeling simulations indicate that both the volcanism-induced global warming and the existence of an eastern plateau in North China amplified hydroclimatic contrasts in East Asia during OAE 1a. Our integrated biostratigraphic, chemostratigraphic and sedimentological data demonstrate that this climatic upheaval coincided with the sudden, widespread demise of key components of the famous Jehol Biota, including insects, clam shrimps, ostracods, fishes and birds. The turnover from Jehol Biota to the newly evolved assemblage represents a significant terrestrial ecosystem reorganization driven by the hyperthermal event. This result resolves the long-standing mystery of the Jehol Biota's disappearance and highlights the role of the hyperthermal event in shaping terrestrial ecosystems.