Timing and cause of oceanic anoxic event 1a revealed in the terrestrial record

Abstract

The Cretaceous early Aptian oceanic anoxic event (OAE1a) is a globally documented climatic perturbation marked by voluminous deposition of black shales. Volcanism associated with the Greater Ontong Java large igneous province (GOJLIP) or other mechanisms may have caused this event but the exact timing of OAE1a remains uncertain. Evidence of OAE1a derives primarily from marine sedimentary records. Terrestrial records are scarce. Here, we describe a lacustrine sedimentary succession in east Shandong, China that represents a pristine and intact terrestrial record of OAE1a. Carbon and oxygen isotope chemostratigraphic and magnetic susceptibility data document the advent OAE1a within the section. This succession also included a tuffaceous layer containing zircons which were dated using U–Pb geochronologic methods. Coupled with isotopic records, the U–Pb analyses indicate that the onset of OAE1a occurred at 120.39 ± 0.46 Ma. East Asian magmatism that generated the tuffaceous layer may represent an additional significant source of volcanogenic CO2 that contributed to perturbation of the early Aptian carbon cycle.