Constraints From Detrital Zircon Geochronology and Morphology on Sediment Routing and Drainage Evolution of the Paleogene Raoyang Sag, Bohai Bay Basin, China

ABSTRACT Although detrital zircon geochronology is widely used to link sediment sources with sedimentary deposits, this method is not always effective in reconstructing specific sediment transport pathways and differentiating sedimentary recycling from first‐cycle deposition. The morphology of detrital zircon grains, including roundness, can change during transport in sedimentary systems as a result of mechanical abrasion, potentially enabling additional constraints in reconstructing ancient patterns of sediment routing. Integration of detrital zircon morphology with U–Pb geochronology suggests the Paleogene Raoyang Sag, Bohai Bay Basin, primarily received sediments from four sources: the northern margin of the North China Craton (NCC), Fuping Region, Taihang Mountain and Wutai Mountain. Kernel density estimation reveals potential bimodal roundness distributions within the 100–200 Ma, 200–500 Ma and 1700–2000 Ma age fractions, indicating multiple sources with distinct sediment transport histories. Relatively less rounded detrital zircons in these three U–Pb age fractions were interpreted to have been transported directly (first cycle) from respective crystalline sources to the Raoyang Sag. In contrast, anomalously rounded detrital zircons in these three age fractions are interpreted to have been originally sourced from more distant Mesozoic intrusive rocks, Palaeozoic igneous rocks and Paleoproterozoic metamorphic rocks that crop out in the northern margin of the NCC. Sediments from these more distant sources were eroded during the collision of the NCC and Siberia Plate, transported via aeolian and/or fluvial processes, and deposited in the Taihang Mountain area before being re‐exhumed during the Paleogene uplift of Taihang Mountain. This sedimentary recycling of older aeolian/fluvial sediment contributed to a higher degree of roundness relative to first‐cycled sediment sources. This study suggests that morphological analysis of detrital zircon grains, including roundness, sphericity, aspect ratio and equivalent spherical diameter, when integrated with U–Pb geochronology, can provide additional constraints in reconstructing ancient sediment routing systems.