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

The early Aptian (similar to 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 (delta C-13(org)), 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 U-Pb 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.

Automated summary

This study fills the gap in continental records of the early Aptian Oceanic Anoxic Event 1a(OAE 1a) by analyzing lacustrine facies in the East Asia continental margin. The proposed conceptual model illustrates the response of lake systems to OAE 1a, confirming the occurrence of ancient climate changes and carbon cycle disturbances in lacustrine systems.