High-resolution magnetostratigraphy of the Lower Cretaceous Dabeigou Formation in the Luanping Basin, northern China

The Lower Cretaceous Dabeigou Formation and its equivalent strata in northern Hebei Province, China, are of great interest because they contain early representatives of the Jehol Biota, and record significant evolutionary and geological events. Despite recent advances in paleontology, biostratigraphy, radiometric dating and cyclostratigraphy, there is no consensus about the exact age of the Dabeigou Formation. Here, we report new high-resolution magnetostratigraphy coupled with detailed rock magnetic results from the Zhangjiagou section in the Luanping Basin. Rock magnetic results indicate that both magnetite and greigite are the primary carriers of the characteristic remanent magnetizations. Correlation to the geomagnetic polarity timescale was achieved by integrating magnetostratigraphy and previously published SIMS UPb zircon ages for the same section. Magnetostratigraphic results show that the sedimentary succession spans from Subchron M10Nn.3n to Subchron M10Nn.1n, and the age of the section can be constrained to the early Hauterivian stage. Therefore, the basal age of this succession is no later than 132 Ma, providing new constraints on the formation age of the Luanping Basin and a minimum age estimate for the early representatives of the Jehol Biota. Our new magnetostratigraphic findings provide important evidence for integrating marine and terrestrial records and further lay a foundation for studying paleoenvironmental changes and their impact on the evolution of the Jehol Biota.