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The Controlling Effect of Transfer Zones on Stratal Architectural Variability and Depositional Facies Distribution


In sedimentary basins, transfer zones are of great interest because they have good prospects for hydrocarbon exploration. A large number of transfer zones have been reported in the last decades, but most of them mainly focused on their tectonic characteristics and formation mechanisms. Few study based on tectono-sequence stratigraphy has been carried out to determine the controlling effect of transfer zones on stratal architecture and facies distribution, although a better understanding of this effect 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. Systematic analysis 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 transfer zone area and gentle slope in the eastern area) together with a large-scale transfer zone were developed in this depression. It appears that the occurrence of the transfer zone complicated the stratal architecture, and resulted in architectural variability of stratigraphic sequences by dividing the Fushan Depression into two disconnected tectonic systems. In addition, our study suggests that the transfer zone plays a significant role in controlling depositional facies distribution, but the controlling parameters are different between highstand and lowstand stages. During the highstand stage, the distribution of depositional systems was mainly controlled by sediment supply and the NW-trending transfer faults. Sedimentary flow paths were parallel to the transfer zone axis with sedimentary flows constrained to the adjacent areas of the NW-trending transfer faults. By contrast, during the lowstand stage, large-scale sublacustrine fan sediments spilled over delta fronts and were rapidly transported down the slope flexure into the deep lake towards northeast, rather than parallel to the transfer zone axis. It seems that the NW-trending transfer faults had little control over facies distribution during the lowstand stage, and the flow division in the lowstand stage might be greatly influenced by flow type and topography. The transfer zone has many interesting advantages for hydrocarbon accumulation, indicating that the recognition of transfer zones can improve the prediction of hydrocarbon occurrences in similar settings.