Depositional Modeling Of The Pearl River Delta-deepwater Fan System In Themiddle Of Early Miocene

Taking the Pearl River delta-submarine fan system as the major research object,this study utilizes DionisosFlow-a forward modeling software,to quantitatively simulate the sedimentary processes of this delta-fan system during the middle of the Early Miocene.According to the analysis of the paleogeomorphology and depositional facies,combined with the modern Pearl River Delta and shelf-slope geomorphology of the northern South China Sea,we first set up the geological background parameters such as paleotopography and tectonic subsidence,as well as the possible range of waves,tides,and sediment texture.On this basis,two key factors including sea level change and the sediment supply are selected as the major controlling factor and three sets of experiments are herein conducted.By comparison between simulation results and drilling information from tens of exploration wells within the study area,we managed to reach the following conclusions on sequence stratigraphy and sedimentary facies:(1)In terms of sequence stratigraphy,two third-order sequences were recognized during 21 Ma-18 Ma,e.g.SQ21 and SQ19.4,which contrasts the previous subdivision scheme involving only one single sequence.Each sequence can be further divided into four system tracts,including the lowstand(LST),transgressive(TST),highstand(HST)and falling-stage(FSST)systems tracts.A detailed analysis of the internal architecture of systems tracts reveals significant lateral variability between the east and west within the study area.This difference is attributed to the variations on the submarine topography along the depositional-strike.(2)In terms of sedimentary facies,it is found that shelf edge deltas and the deep-water fans are mainly developed in the falling-stage and lowstand systems tracts.The deep-water fans within the LST of SQ21 mainly lie in the west of the Baiyun Sag.In contrast,the shelf-edge delta of the FSST of SQ21 tended to extend to the north of the Dongsha Rise,forming thick sand bodies in the east region.Contemporaneous deep-water fans are distributed in the central and eastern area of the Baiyun Sag.(3)Finally,3D sedimentary model of the Pearl River delta-submarine fan system is constructed according to the sequence stratigraphic architecture,along-strike variability,and sedimentary facies.We also predict that there might be four favorable reservoir systems in the study area,with various characteristics from different stratigraphic levels.Therefore,various trap types may be present within the study area,which should be treated with cautions.