The response of Middle Jurassic depositional environments to climate change in the Wucaiwan mining area, Junggar Basin, China

The Middle Jurassic represents a typical greenhouse climate period in Earth’s history, during which global carbon cycle perturbations and climatic events left significant records in continental strata. This study investigates the extremely thick coal seam of the Middle Jurassic Xishanyao Formation in the Wucaiwan mining area, Zhundong coalfield, Xinjiang, China. Through integrated coal petrological, geochemical, palynological, and organic geochemical analyses, combined with paleowildfire indicators, it aims to reconstruct the paleoenvironmental and paleoclimatic evolution sequence and explore its response to global changes. The results demonstrate that geochemical indicators and palynological assemblages collectively indicate an aridification trend in the paleoclimate. The high inertinite content and enrichment of combustion-derived polycyclic aromatic hydrocarbons in the coal attest to frequent medium-to low-temperature surface paleowildfire events during peat accumulation. On geological timescales, wildfires acted as a significant short-term carbon source, releasing vast amounts of greenhouse gases; however, over the long term, they ultimately functioned as a net carbon sink through the production of inert black carbon, facilitation of vegetation succession, and enhancement of organic matter burial. The Middle Jurassic paleoenvironmental evolution in the Junggar Basin exhibits synchronicity with global climate events, underscoring the key driving role of wildfire activity in the greenhouse Earth’s carbon cycle.