Stratigraphic Framework, Biostratigraphic Sequences and Correlation of Major Stratigraphic Boundaries of the Terrestrial Jurassic in the Northeast Sichuan Basin, Southern China

The Sichuan Basin, situated in southern China, preserves a complete and uninterrupted continental succession spanning the Late Triassic through Jurassic intervals. This stratigraphic archive constitutes a pivotal reference for regional and global correlation, as well as for elucidating the evolutionary trajectories of life and terrestrial ecosystems. The Triassic–Jurassic succession within the basin is internationally acclaimed for its abundant and exceptionally preserved fossil biotas, encompassing the Xujiahe Flora, the endemic East Asian Mamenchisaurus dinosaur fauna, diverse invertebrate assemblages (notably conchostracans and bivalves), and superlative silicified wood occurrences. In response to the prevailing state of research on Jurassic strata in the northeastern Sichuan Basin, we executed systematic field investigations integrated with latest advances in research across relevant disciplinary domains. Our investigation targeted three fundamental and innovative research vectors: (i) stratigraphic boundary delineation and correlation; (ii) systematic palaeontology and assemblage characterization; and (iii) palaeoenvironmental dynamics. Our principal objective entailed comprehensive palaeontological analysis of representative outcrop sections and subsurface core material, thereby establishing a rigorous biostratigraphic architecture for the study domain. Through exhaustive taxonomic interrogation of disparate fossil groups, we quantified biodiversity across seven major categories: megafloras, permineralized wood, sporomorphs, algae, conchostracans, bivalves, and ostracods. Specifically, we documented 94 genera and 132 species across four of these groups as novel occurrences, and established approximately 20 diagnostic biozonation schemes. These findings substantially refine the resolution of regional and transcontinental biostratigraphic correlation for Jurassic strata within the study area. Grounded in integrated correlation of pivotal stratigraphic packages and subsurface drilling archives, we resolved the positions of critical Jurassic sequence boundaries and formulated robust criteria for their discrimination and correlation. Notably, we established definitive recognition criteria for the Triassic–Jurassic System boundary and the Lower–Middle Jurassic Series boundary, integrating multiple independent lines of evidence encompassing fossil biozones, lithofacies associations, and stratigraphic contact relationships. Upon this foundation, we propose a comprehensive stratigraphic subdivision and correlation paradigm that reconciles persistent ambiguities surrounding regional stratigraphic alignment, depositional environment reconstruction, and basin-fill architecture. This contribution elevates the biostratigraphic resolution for the study area and contiguous regions, furnishing a rigorous underpinning for reconstructing the Mesozoic geodynamic setting, chronostratigraphic framework, fossil biofacies, and the evolutionary history of vegetation and terrestrial ecosystems.