Relative role of accommodation zones in controlling stratal architectural variability and facies distribution: Insights from the Fushan Depression, South China Sea

In sedimentary basins, a better understanding of the controlling effect of accommodation/transfer zones on stratal architecture and facies distribution can improve the success rate of locating hydrocarbon reservoirs. The Fushan Depression is a half-graben rift sub-basin located in the southeast of the Beibuwan Basin, South China Sea. In this study, comparative analysis of seismic reflection, palaeogeomorphology, fault activity and depositional fades distribution indicates that three different types of inner-basin slopes (i.e. multi-level step-fault slope in the western area, slope flexure zone in the accommodation zone area and gentle slope in the eastern area) were developed along the southern slope of the Fushan Depression, together with a large-scale accommodation zone located at the intersection of the western and eastern fault systems. Further analysis shows that the accommodation zone played an important role in controlling not only stratal architectural variability in the southern slope but also depositional facies distribution in the accommodation zone area. During the high-stand stage, the deposition of depositional systems was mainly controlled by sediment supply and the NW-trending transfer faults. Major drainage systems entered the Fushan Depression through the accommodation zone along the direction of sediment supply, and sedimentary flow paths were parallel to the accommodation zone axis with sedimentary flows constrained to the adjacent areas of the NW-trending transfer faults. By contrast, during the low-stand stage, the transfer faults had little control over depositional facies distribution, and the sublacustrine fan sediments diverted away from the accommodation zone and flew down along the northeast, oblique to the accommodation zone axis. The flow division in the lowstand stage might be greatly influenced by flow type and topography. In addition, the accommodation zone area demonstrated unique hydrocarbon accumulation models different from the western and eastern areas, suggesting that the future exploration should be conducted at different levels in the Fushan Depression. (C) 2015 Elsevier Ltd. All rights reserved.