Astronomically tuned chronostratigraphy of an Upper Triassic–Middle Jurassic lacustrine succession in Southwest China

The Triassic–Jurassic transition (i.e., Late Triassic to Early Jurassic, ∼237–174 Ma, TJT) represents a critical interval in Earth's history, characterized by significant environmental perturbations both on land and in the oceans. Marine sediment records from this interval have been extensively studied, while terrestrial environmental records remain limited. In this work, we present a continuous lacustrine succession through the TJT from the Chuxiong Basin in Yunnan Province, Southwest China, based on analysis of an ∼1800-m-long core. By integration of sedimentological, paleontological, geochemical, and astronomical data, we establish a detailed geochronology spanning ∼23.5 million years from the Rhaetian (Upper Triassic) to the Aalenian (Middle Jurassic), calibrated to 405-kyr (long-eccentricity) cycles. We identify three significant negative excursions in organic carbon isotopes (i.e., at the Rhaetian–Hettangian boundary, the Sinemurian–Pliensbachian boundary, and within the lower Toarcian) that correspond to global events recorded in marine and terrestrial sections. Based on an astronomically calibrated carbon-isotope stratigraphy that conforms to other Lower Jurassic sequences, the duration of the Hettangian, Sinemurian and Pliensbachian stages are estimated to be 1.9 ± 0.3 Myr, 6.6 ± 0.3 Myr, and 9.4 ± 0.3 Myr, respectively. Our results provide insight into high-resolution climate and environmental variation during this time interval, enhancing our understanding of Early Jurassic global events and refining the Early Jurassic timescale.