62 / 2025-03-30 18:40:07

Fossil Plant and Palynological Evidence from the Upper Triassic Huangshanjie Formation, Junggar Basin, Northwest China: Implications for Hydrocarbon Generation Potential and Environmental Response to the Carnian Pluvial Episode

palynofacies,lacustrine source rocks,hydrocarbon potential,Triassic,Xinjiang

Theme 3: Earth-Life Co-evolution Through Time > Session 3g: Impact of Volcanism on the Habitability of the Earth

The Carnian Pluvial Episode (CPE) was a significant climate event during the Late Triassic, characterized by a dramatic shift from relatively dry, arid conditions to a much wetter and more humid climate, leading to widespread environmental changes. In this study, we investigate the hydrocarbon generation potential and paleoenvironmental changes of the Upper Triassic Huangshanjie Formation in the Junggar Basin, China, through integrated fossil plant (primarily fossil wood), palynological, and palynofacies analyses. A total of 63 fossil wood specimens and 59 sporopollen samples from the Dalongkou section were analyzed. All the fossil woods belong to the genus Junggaropitys. The stratigraphic age of the Huangshanjie Formation is constrained to the Carnian–early Norian, based on key sporomorphs (e.g., Aulisporites astigmosus). The fossil woods, spores and pollen indicate a humid climate in the Carnian Junggar Basin. Three palynofacies assemblages were identified (PF 1–3). Palynofacies trends indicate a depositional shift from proximal fluvial-deltaic (PF 1) to anoxic lacustrine (PF 2), and distal dysoxic-anoxic deep lake environments (PF 3), reflecting lake-level fluctuations during the Late Triassic. Thermal Alteration Index (TAI) values (2–3+) and kerogen types (II and III) suggest early-mature organic matter with moderate hydrocarbon potential, dominated by type III kerogen, though localized oil-prone layers rich in amorphous organic matter were also present. Additionally, by comparing the Late Triassic source rocks from key continental basins worldwide, the impact and patterns of the CPE on source rock characteristics were further discussed.