Expression of the early Aptian Oceanic Anoxic Event (OAE) 1a in lacustrine depositional systems of East China

The early Aptian (~120 Ma) Oceanic Anoxic Event 1a (OAE 1a) was associated with marked changes in palaeoclimate linked to a perturbation of the global carbon cycle. While it is well-studied in the marine realm, OAE 1a is poorly known from continental records. Here, we fill that knowledge-gap by describing OAE 1a from lacustrine facies in the East Asia continental margin (Jiaolai Basin and Lingshan Island in eastern China). Specifically, we integrate data from bulk organic carbon-isotopes (δ13Corg), total organic carbon (TOC), and redox-and productivity-sensitive trace elements, as well as existing records on depositional environments, clay mineral compositions, elemental geochemistry and the latest detrital zircon UPb ages. We propose a conceptual model of the response of the lake system to OAE 1a through analysis of the palaeoenvironmental and palaeoclimatic context. During the initial stage, an extreme greenhouse climatic event resulted in an abrupt increase in palaeosalinity in the lake system. This led to anoxic conditions, resulting in a high preservation rate of TOC and the development of organic-rich black shale. Organic carbon isotopes documented in the organic-rich black shale show negative and then positive excursions, consistent with the carbon cycle disturbance found in marine OAE 1a records. In addition, the data show that this event may have been associated with a transition from an extreme greenhouse climate to a cooling phase. The framework presented here facilitates further research on the expression of OAE 1a in continental ecosystems and its fingerprint in lacustrine depositional systems. [Display omitted] •Evidence of OAE1a was identified in lacustrine depositional systems.•Lacustrine black shale in East China preserves information on early Aptian C-cycle perturbation during OAE 1a.•Palaeosalinity and RSTE data indicate environmental instability of inland lakes in East China during OAE 1a.•Terrestrial records suggest an extreme greenhouse climate led to OAE 1a.•The OAE 1a itself may represent a period of transition from an extreme greenhouse climate to a cooling phase.