Terrestrial evidence of the Callovian cooling event from the Middle Jurassic Wanbao Formation, Inner Mongolia, NE China: A Ginkgoites-based perspective

The Middle Jurassic represents a critical transition from greenhouse to coolhouse conditions, with a cooling episode recorded in the Callovian Stage linked to declining atmospheric CO 2 concentrations ( p CO 2 ) and notable geological activity. However, the relationship between p CO 2 fluctuations and terrestrial evidence remains unclear. Here, we report the first in situ zircon U−Pb ages from volcanic interbeds at the coal-bearing Wanbao Formation of the Mangniuhai Coal Mine, Tuquan County, Inner Mongolia, NE China. A weighted-mean age of 163.6 ± 1.2 Ma firmly placed these deposits in the Callovian. Moreover, we present the first quantitative epidermal study of Ginkgoites longifolius in this region, focusing on its abaxial stomatal parameters. Stomatal-based paleo- p CO 2 reconstruction yielded a value of 688.5 ± 140.3 ppmv, indicating relatively low p CO 2 value and a cooler climate consistent with previously recognized Callovian cooling phases. Considering the paleogeographic distribution of its habitats, these results suggest that Ginkgoites longifolius was adapted to and confined within strongly seasonal temperate−subtropical regimes. These findings are crucial for elucidating the paleoenvironmental context underlying feathered dinosaur diversification and early mammalian evolution during the Callovian. • The first in situ zircon U–Pb geochronological data 163.6 ± 1.2 Ma was reported. • Stomatal-based palaeo- p CO 2 reconstruction yields 688.5 ± 140.3 ppmv, consistent with the Callovian cooling events. • The paleogeographic distribution of Ginkgoites longifolius suggests that it was confined within seasonal temperate−subtropical regimes.