Chronostratigraphic Constraints on the Lower Cretaceous Volcano-Sedimentary Succession of the Liuhe Basin: Implications for the Jehol Biota Sensu Lato and Paleo-Pacific Plate Rollback

The North China Craton (NCC) is a major tectonic unit in East Asia that experienced significant lithspheric destruction during the Late Mesozoic, driven by processes such as subduction, trench retreat, and rollback of the paleo-Pacific Plate. This decratonization was accompanied by widespread magmatism, rifting, and basin development, profoundly influencing surface environments. The Early Cretaceous Jehol Biota developed during this interval and represents a world-renowned terrestrial fossil assemblage, offering key insights into ecosystem evolution under active tectonic conditions. The Liuhe Basin, located in the northeastern NCC, is a small rift basin that preserves Lower Cretaceous strata bearing fossil assemblages assigned to the Jehol Biota sensu lato. However, the depositional ages of these fossil-bearing successions have long remained poorly constrained, limiting accurate stratigraphic correlation and paleoenvironmental interpretation. To address this issue, this study presents new zircon U–Pb SIMS ages obtained from three tuff layers within the Lamenzi, Dashatan, and Baodaqiao formations, with the aim of establishing a robust chronostratigraphic framework. The new data yield weighted mean 206Pb/238U ages of 127.1 ± 0.9 Ma, 124.6 ± 1.2 Ma, and 122.1 ± 1.4 Ma for the Lamenzi, Dashatan, and Baodaqiao formations, respectively. These results constrain the lower part of the basin succession to the late Hauterivian-early Aptian interval. Combined with previous biostratigraphic evidence, the overlying Xiahuapidianzi and Hengtongshan formations are interpreted as mainly Aptian in age, whereas the Heiwaizi Formation likely extends into the early Albian. This refined temporal framework significantly improves age constraints on fossil-bearing strata and supports regional correlations with other Jehol Biota successions. Sedimentologically, the Liuhe Basin records a transition from volcanically influenced fluvial-lacustrine deposition to dominantly clastic sedimentation. The lower three formations are characterized by abundant volcanic rocks and tuffaceous deposits, indicating active rifting and magmatism between ~127 to 122 Ma. In contrast, the overlying formations consist mainly of clastic sediments, reflecting more stable depositional conditions after ~122 Ma. This transition marks a fundamental shift from syn-rift volcanic activity to post-rift basin infilling. Regional comparison reveals that the timing of this volcanic-to-clastic transition becomes progressively younger eastward along the northern NCC. While similar transitions occurred at ~130-129 Ma in western Jingxi, Luanping and Sichakou basins, and ~124 Ma in the Liaoxi region, the Liuhe Basin records a later transition at ~122 Ma. This diachronous pattern is consistent with geodynamic models involving eastward rollback of the paleo-Pacific Plate, which induced migrating lithospheric thinning and basin development. Overall, this study provides new geochronological constraints on the Liuhe Basin and highlights the close coupling between basin evolution, craton destruction, and terrestrial ecosystem development during the Early Cretaceous. This study was supported by the National Natural Science Foundation of China (Grant Nos. 42372022, 42288201).