Longdistance transport pathways of Yanshan sources in the northern Huanghua Depression and their control on the development of largescale fan bodies in the deep sag area

【Purpose】The deep sag area of faulted basins is a key target for current hydrocarbon exploration. Identifying sediment sourcetosink processes and transport pathways is crucial for the exploration of subtle reservoirs. In recent years, several subaqueous fans have been discovered in the Oligocene Dongying Formation in the deep sag area of the Qikou Sag, and commercial oil flows have been obtained. However, the provenance direction of these fans remains controversial. Although some scholars have proposed that the sources came from the northern Yanshan fold belt, the source area is about 60 km away from the deep sag area, with several uplift units developed in between. The sediment supply capacity, transport pathways, and sourcetosink processes lack systematic research.【Methods】Based on highresolution seismic, welllogging, and core data, this study employed methods including core observation, heavy mineral analysis, detrital zircon UPb dating, paleogeomorphic restoration, and seismic attribute analysis to determine the provenance direction of the fans, identify the transport pathways of the Yanshan sources, and further reveal the sourcetosink processes and development mechanisms.【Results】The results show that the detrital zircon age spectra of the fans are consistent with the ages of igneous rocks in the Yanshan orogenic belt, and the heavy mineral assemblages are also similar to those of the Yanshan source area, indicating that the sources are mainly from the Yanshan orogenic belt in the northern basin. Previous apatite fissiontrack analysis reveals that during the deposition of the Dongying Formation (28.5–23.8 Ma), the Yanshan orogenic belt experienced rapid uplift, providing strong source supply. Paleogeomorphic analysis indicates that during this period, the Qikou Sag entered a depression stage, with intrabasinal low uplifts submerged underwater. Clastic materials from the Yanshan fold belt formed braided river deltas, converged in the Beitang subsag, were constrained by fault troughs formed by faults such as the Dashentang and Jiannan faults, and were transported southward in a “relay” manner along multilevel fault terraces. Finally, under the large topographic relief created by the XingangHaihe fault, they transformed into gravity flows and deposited in the deep sag area to form multistage superimposed distal subaqueous fans.【Conclusion】Accordingly, this paper establishes a sourcetosink model characterized by “strong Yanshan supply, multilevel faultterrace sand transport, topographic slope controlling facies, and deepsag topography accumulating sand, ” revealing the dynamic response between the uplift and erosion of extrabasinal sources and intrabasinal sedimentation. This model indicates that under the coupling of strong source supply and an efficient tectonicgeomorphic transport system, continental faulted lacustrine basins can achieve longdistance transport across multiple geomorphic units, forming largescale gravityflow fans in the deep sag area. This study provides a theoretical basis for hydrocarbon exploration in the deep sag area of the Qikou Sag, and also demonstrates that similar deep sag areas in other basins have the potential to develop largescale highquality reservoir sand bodies, providing an important reference for sourcetosink research in deep sag areas.