Middle Jurassic paleophytoecology of the northeastern Ordos Basin, China

The Middle Jurassic Yan’an Formation in the northeastern Ordos Basin, China, contains diverse and well‑preserved plant fossils, but its paleoecology remains poorly understood. This study systematically analyses the paleoecology of the Middle Jurassic flora in the northeastern Ordos Basin, based on a comprehensive investigation of its composition and characteristics. We reconstructed the paleoecological framework of this flora based on the composition, taphonomy, and ecological characteristics of the plant fossil assemblage. The fossil assemblage comprises bryophytes, sphenophytes, ferns, cycads, ginkgophytes, czekanowskialeans and conifers. Taphonomic analysis indicates that the fossil plants are predominantly autochthonous or parautochthonous, with only a few taxa being allochthonous. Ecologically, these plants can be categorised into four groups: hygrophytes, warm‑temperate plants, mesophytic deciduous trees/shrubs, and mesophytic evergreen trees. Five distinct plant communities can be recognised: upland coniferous, slope mixed broadleaf–conifer, lowland cycad–fern, riparian–wetland sphenophyte and understory bryophyte communities. These communities, which inhabited the marginal slopes and plains of the Ordos Basin, collectively indicate a warm‑temperate forest ecosystem with clear vertical stratification and seasonal variations in temperature and precipitation during the Middle Jurassic.