Sequence Stratigraphy And Depositional Systems Of Zhujiang Formation In The Southern Huizhou Area,Pearl River Mouth Basin

Under the guidance of sequence stratigraphy and sedimentology,the sequence classification scheme of Zhujiang Formation in the Huizhou depression,Pearl river mouth basin,the type of the sedimentary facies,the distribution features and the evolution regularity of the sedimentary system were clarified based on the comprehensive analyses of core,logging,3D seismic data and thin section data.And the probable lithologic trap development zone has been predicted.Six sequence boundaries were founded on the seismic profile and the well logging curves by recognising the features of seismic reflection termination and the surface of discontinuity in well logging curves,the sequence boundaries in the well loggging curves were calibrated to the seismic profile by using the seismic well tie,then tracking the seismic event,so the sequence stratigraphic framework was established.The Zhujiang Formation was divided into five third-order sequence,from bottom to top is SQ1 to SQ5 successively.The depositional facies study were conducted under the sequence stratigraphic framework,and the meandering river delta,the continental shelf,the carbonate platform were recognised.During the Zhujiang Formation depositional period,the sea level rised as a whole,large scale transgression occurred during the deposition from SQ1 to SQ3,the transgression reached to its maximum during the deposition of SQ3,small scale regression occurred during the deposition of SQ4 and SQ5.There exist three direction provenances during the deposition of SQ1 and SQ2,they are from the northwest,northeast and south respectively.The deltas from three directions all prograding to the center of depression,the sands are mainly from delta front,mouth bar and distal bar,the area of shallow sea shelf facies was limited.During the deposition of SQ3,the transgression led the deltas from south and northeast retreat to the outside of the study area,and the delta from the northwest retreated 15 kilometres approximately,the sand in the delta front was restructured by the wave and the tide,and formed beach bar and shelf sand ridge,the sand bodies had a banding distribution and distributed perpendicular to the direction of provenance,theDongsha uplift was barely disturbed by the clastic deposits,the carbonate platform was developed.During the deposition of SQ4 and SQ5,the regression led the delta from northwest prograding towards to the center of the depression about 10 kilometers,the carbonate platform stopped growing,the area of the shallow sea shelf reduced,the sands are mainly from the delta front,the beach bar,and the shelf sand ridge.By analysising the sand content of each sequence,SQ3,SQ4,SQ5 were considered suitable for the development of lithologic trap.By congruenting the sedimentary facies map and the corresponding top surface structure map,we can infer that the sand from the delta front,the beach and bar which were overlapped to the slope between the Dongsha uplift and the Huizhou depression,and were parcelled by the mudstone,so the slope are beneficial to the Formation of lithologic trap.