Molecular fossil responses to Toarcian (Early Jurassic) climate warming in the high-latitude lacustrine Junggar Basin, China

Abstract

The Early Jurassic Toarcian Oceanic Anoxic Event (T-OAE), also known as the Jenkyns Event, approximately aligns negative carbon isotope excursions (N-CIE), a stratigraphic marker for Toarcian environmental change. It represents a significant period of greenhouse warming and marine anoxia during the late Early Jurassic, impacting both marine and terrestrial ecosystems. This study explores its effects on terrestrial ecosystems at high latitudes for the first time, specifically focusing on the lacustrine Junggar Basin in northwest China, located at approximately 60°N. By utilizing organic geochemical analyses of fine-grained sedimentary rocks from the Lower Jurassic Sangonghe Formation, we mapped the presence of higher-plant-derived hydrocarbons to reconstruct vegetation shifts before, during, and after the N-CIE interval. Our findings reveal an initial dominance of ferns, with a shift toward gymnosperms such as conifers and cycads during the event, and a subsequent return to fern dominance, as recorded by anomalies in di- and tri-cyclic aromatic hydrocarbon fractions. This suggests significant ecological adaptations and potential recovery or further adaptation following the N-CIE. Our findings underscore the sensitivity of high-latitude terrestrial ecosystems to dramatic climatic events like the T-OAE, emphasizing their importance in understanding past environmental changes and improving predictions of future ecological responses. These results also highlight the suitability of molecular terrestrial plant fingerprints as archives of global environmental changes.