Sequence Stratigraphic Model From The Background Of Wide-Sustained Shelf

Northen margin of the south China sea have been detached to east and west part with the boundary of faults:The east part involves beibu gulf、southeast hainan、pearl river estuary、taixi basin and the like; The west part has yinggehai basin. Though the problem of technology attributes perplex many searchers,east of Northen margin of the south China sea is nonvolcanic types of passive continental margin while the west is volcanic type. Since1996, east of pearl river estuary basin in Northen of the south China sea has producted1billion t oil, which is the largest meso-cenozoic sedimentary basin in Northen of the south China sea and one of the main petroleum resources bases in China Among many gas discovery formations in the basin,Zhujiang formation is the research objects of this basin.This study bases on the theory of sequence stratigraphy with core、drilling logging and paleontology data and research results of privators to analyse space-time evolution regularities in sequence stratigraphy and sedimentary geology, which is to acknowledge depositional filling model and main controlling factors with planar distribution of faces in Zhujiang formation of pearl river estuary basin, and then to know the sequence mode.It is can be concluded that there are four sedimentary faces in Zhu Jiang formation of Pearl River Mouth basin, and they are delta、shore、shallow sea-half deep sea and carbonate platform face.This study focus on chronotaxy of ODP1148and pearl river estuary basin with the help of continuous coring, which can truly reflect the change of sea-level in oligocene to miocene and have better guidance to the sequence research of pearl river estuary basin. By using regional paleontology data, this study makes foraminiferal abundance another tool to divide boundary of sequence and maximum flooding surface. The study finds uplap、downlap、toplap、truncation and the like unconformity characters combine with sequence and tract system divided by single well, with the help of seismic data over170thousand square kilometers in pearl river estuary basin which can conclude that there are six three-grade sequence interfaces:NSB1(23.8Ma)、NSB2(21Ma)、 NSB3(18Ma)、NSB4(17.5Ma)、NSB5(17Ma)、NSB6(16.5Ma)Sea level changes、sediment supply and topography and geomorphology are important controlling factors to demand development and distribution characters of different third-order sequences and sequence mode. The controlling effect of sea level changes to sequence involve rate of sea level changes、change range have an important roles in demanding development and distribution characters of different third-order sequences. Sea level changes affect development and distribution characters of different third-order sequences and sequence mode by controlling accommodation changes. Different rate of sediment supply is the parameter of sediment supply and sediment topography to affect extendible extent and limit of progradation toward sea; In another aspect, it can demand the type of sediment (clastic or carbonate). Palegeographuy geomorphology background(sedimentary palebase slope、salient on terrain and the water paledepth) affect slope of delta front by demanding unloading and accumulation rate through affecting speed of water.; Moreover, steep and sustained terrain influence reformation of previous deposition.Zhujiang formation’s development of faces type is the most complex layer unit in pearl river estuary basin of neogene.There are five face types developed in Zhujiang sedimentary time which are delta、onshore、neritic shelf and carbonate platform, three provenances are paleopearl river、paleoHan river and Dong sha uplift. And provenance of paleopearl river is major, while delta of paleoHan jiang is minor. To analyse character of Zhujiang face systematically,this character analyse expension feature of faces divided into five sequences based on the isochronous stratigraphic framework.Neogene Zhujiang formation in Huizhou depression has developed four faces with comprehensive analyses of core and logging data, types of which are delta、shoreline、 neritic to bathyal and carbonate platform facies.The study concludes development mode in different sequence of research area with analyses of development mode and sequence distribution in different interface and location of area.With control factors of sequence and characters of system tract, there are two sequence modes in Zhu Jiang formation of northen shelf of South sea:When the sea level lower than slope break fast, the sequence mode include low and high stand system tracts、transgressive system tract,in this sequence, low stand system tract often developed in low position which canbe controled by sedimentary slope break that make slope fan and progradation complex sediment seen at the slope or under the slope; transgressive system tract is charactered by costal onlap moving shoreward, and develop transgressive delta while restricted on north, the flooding surface often onlap the slope break; High stand system tract is often conformed by regression delta; Far away to shallow shelf, high stand system tract and transgressive system tract can develop shelf sand body for high geomorphologic background.When the sea level haven’t been lower than slope break, the sequence mode include high stand system tract and transgressive system tract,which shown ascent-descent slowly and enough sediment source. Transgressive system tract often has transgressive delta or shore system tract while high stand system tract develop high stand delta, it is easy to conform shelf sand on the high position near the seawhich affected by ancient landform or previous sediment.In the time of23.8to18.5Ma, sediment layers include low stand system tract and transgrassive system tract of NSQ1and NSQ2.In this part, sea level is relative low while sedimentary hydrodynamic is strong, so the granularity is comparatively rough and sandbody is major;In the end of the shelf, with middle sedimentary hydrodynamic the granularity changed periodly, and also the sand and mud;In the center of basin, mud is major for weak sedimentary hydrodynamic;In18.5to16.5Ma, sea level of Pearl River Mouth basin is coming down but amplitude is lower than the time of23.8to18.5Ma.Under this background, percentage content of sanf is growing.