High-resolution record of multiple organic carbon-isotope excursions in lacustrine deposits of Upper Sinemurian through Pliensbachian (Early Jurassic) from the Sichuan Basin, China

The Sinemurian-Pliensbachian boundary event (ca. 193 Ma) is recorded as a global perturbation of the carbon cycle, as evi-denced by a large negative carbon-isotope excursion recorded in many marine sedimen-tary successions. Whereas multiple lines of evidence testify that the Sinemurian-Pliens-bachian boundary event was associated with environmental and climatic changes, sea-level oscillations, and biotic turnovers in marine settings, the record and effects of the event on continents are poorly known. In this paper, we report a high-resolution delta 13Corg record and palynological data from the Lower Jurassic lacustrine succession of the Sichuan Basin that allow a prominent 8 parts per thousand negative carbon-isotope excursion to be identified at the Sinemurian-Pliensbachian transition. We therefore interpret this per-turbation as the expression of the Sinemu-rian-Pliensbachian boundary event in the Sichuan Basin, and we propose a correlation with the marine realm. Facies evolution illus-trates that the Sinemurian-Pliensbachian boundary event coincided with a phase of expansion of the lacustrine systems. Palyno-logical analyses indicate a sharp shift from arid to humid climate conditions coincident with the carbon-isotope perturbation that supports a scenario of lake expansion driven by increased rainfall. In contrast to observa-tions in the Sichuan Basin, where deep lake conditions persisted across the Sinemurian-Pliensbachian boundary event, a global drop in the sea level is documented at the onset of the isotope perturbation. This suggests that eustatic oscillations due to increased conti-nental water storage in lakes and aquifers in the context of a wetter climate phase may have been associated with the early stages of the Sinemurian-Pliensbachian boundary event.