New Insights into the Genetic Mechanism of the Miocene Mounded Stratigraphy in the Qiongdongnan Basin, Northern South China Sea

The origin of deep-water mounds has been a topic of debate in recent years. In this study, newly collected seismic data were employed to characterize the mounds within the Meishan Formation in the Qiongdongnan Basin and a novel model was proposed. The result showed that pervasive mounds and ‘V’-shaped troughs were alternately distributed at the top of the Meishan Formation. They appeared as elongated ridges flanked by similarly elongated gullies, with the trending parallel with the strike of the basinward slope. The mounded features were considered to be formed in response to the tectonically induced seabed deformation. The differential subsidence steepened the slope that was equivalent to the top of the Meishan Formation (ca. 10.5 Ma), which offered sufficient driving forces triggering the slope’s instability. Correspondingly, the uppermost deposits glided along a bedding-parallel detachment surface, creating a number of listric detachment faults that ceased downward to this surface. The uppermost layer was cut into a range of tilted fault blocks with tops constituting a seemingly mounded topography. Some of the downfaulted troughs between mounds steered the gravity flows and were filled by sand-rich lithologies. The differential subsidence played a decisive role in the formation of a mounded stratigraphy, which in turn acted as clues to the important tectonic phase since the late Miocene.