Sedimentary Filling Evolution In The Southern South China Sea Since The Miocene And Its Enlightenment To The Process Of Subduction And Collision

The continental margin basins of the South China Sea are rich in natural resources,especially rich in oil and gas resources.The northern part of the South China Sea has been explored and developed by our country for many years,but the degree of exploration and development in the southern margin is extremely low.Although foreign oil and gas companies have carried out a certain degree of exploration in the coast of Borneo and Vietnam,they have proved to have good oil and gas prospects.There is less oil and gas exploration in deep water areas,and the degree of research is also very weak.The southern margin of the South China Sea is located at the junction of the South China block and the Sunda block.Since the Miocene,many micro-blocks have undergone a dynamic process from subduction to collision,leading to the end of the South China Sea spreading and the Scissor closure of the Proto-South China Sea from west to east.The southern margin of the South China Sea has a complete and continuous Cenozoic sedimentary filling record,especially the thicker sedimentary record since the Miocene(16 Ma).This feature provides for the study of the sedimentary response of the multi-episode collision process in the post-South China Sea spreading period as the best place.In addition,the sedimentary layer corresponding to the post-South China Sea spreading period is an important target layer for deep-water oil and gas exploration in the southern South China Sea.It has been proven to have rich oil and gas resource potential and is expected to become a new growth point for my country's "fossil energy".Therefore,strengthening the study of sedimentary filling in the southern South China Sea since the Miocene can not only provide sedimentary evidence for the history of Proto-South China Sea subduction and South China Sea spreading,but also has great economic and strategic significance for the study of my country's long-term energy supply and defense of territorial waters.In this thesis,guided by the theories of tectonics-stratigraphy,sequence stratigraphy,structural geology,etc.,through the analysis of my country's existing seismic profile data and collected overseas drilling and seismic data,combined with the simulation calculation of deposition and subsidence history,depositional features in southern margins of South China Sea have been revealed.This thesis discusses the spatial and temporal characteristics of the depositional system in this margin,and the difference in sedimentary response in different structural zones.The genetic relationship between the evolution of the southern marginal sedimentary filling and the multi-episode collision process in the southern margin of South China Sea has been summarized.1.Based on the multi-episodic tectonics of the southern margin,the framework of the southern marginal tectonic sequence correlation was constructed,and the sequence stratigraphic framework of the southern marginal basin was proposed: the Sarawak movement,the Sabah movement and the Palawan movement are the three most important tectonic events in the Cenozoic occurred in the southern part of the South China Sea.These tectonic events from west to east on the southern margin show different tectonic styles and interface attributes.Based on the identification of the above key structural changes,a tectonic sequence comparison framework for the southern margin is constructed,and comparing with regional plate tectonic movement reorganization events,establish the tectonic-sedimentary framework of the southern marginal basin.2.Quantitatively difference in sedimentation and subsidence rates of the southern margin of South China Sea from west to east,from the shelf to the continental slope and the deep sea has been analyzed: according to the structural background feature,five typical sections are selected for the simulation of the subsidence history,and the key layers are explained finely.The results show that from the Early Miocene-Middle Miocene to Late Miocene,the Zengmu Basin-Brunei Sabah Basin-Palawan Basin successively appeared high subsidence centrals,which collided with the southern continental margin of the Proto-South China Sea.The process is consistent,indicating a large-scale supply of sediments in southern Borneo after the collision.In addition,the different structural sections of the Nansha Trough showed quite continuous subsidence of the inclined blocks of the continental slope,indicating that there were multi-stage rifting in a long period of time.The subsidence variation near the unconformity of the Late Miocene in Palawan was not only affected by the double subducting oceanic crust,but also by global sea level changes.3.The spatial and temporal characteristics of the Cenozoic sedimentary system in the southern margin of the South China Sea were ascertained: Since the Eocene-Early Miocene,the southern basin has been deposited in a deep-semi-deep-sea sedimentary environment as a whole,and has gradually become littoral facies after the Early Miocene.In the deep sea and semi-deep sea environment,mudstone,shale and semi-deep sea limestone deposits are dominated.In the littoral environment,there are mainly sandstone and siltstone deposits,and large-scale carbonate deposits in some structural highlands.In particular,large-scale continental shelf and shelf-margin delta developed between Borneo and Nansha block during the Miocene,deep-water fans and slope fan deposits developed in some steep slope belts close to the provenance.The transition from semi-deep sea deposits to carbonate deposits in the Palawan area.From the Pliocene to the present,most of the southern basins have shallow sea sandy mud deposits.4.The development and evolution characteristics of the large-scale delta system on the southern continental margin and the carbonate platform have been summarized:combined with the analysis of drilling,seismic and field outcrops,the plane distribution of the Rajing River delta and the Baram delta was drawn,and the carbonate platform distribution since the Paleocene was drawn.Three delta models are proposed,namely shelf edge delta and shelf delta under compressional background and shelf edge delta under extensional background.Five carbonate development models are proposed,namely shelf platform and shelf under extensional background.Edge platform,isolated sea rise platform and thrust top platform and front rise platform in the background of squeezed basin.5.Four types of land margin filling patterns in the south margins have been summarized: the "Sarawak-Zengmu" model,the "Sabah-Nansha block" model,the"Liyue-Southwest Palawan-Cagayan" model,and the "Cagayan" model,MindroNorthwest Palawan" model.Because the southern marginal collision process exhibits the characteristics of migration from west to east,the southern marginal foreland into the peripheral foreland stage also presents the same characteristics showing early in the west and late in the east,and they also have an important control effect on their respective continental margin sedimentary systems.6.The difference in sedimentary filling evolution of the southern margin and its relationship with multi-episodic collisions have been revealed: The southern margin of the South China Sea can be divided into 4 zones from west to east,and the collision events migrate from west to east,resulting in the distinct features in different zones.There are obvious differences of sedimentation and filling in different belts.It is quite clear that the difference in sedimentation and filling evolution is related to the collision of the Borneo micro-block(Sarawak area)and the Zengmu micro-block,the Borneo micro-block(Sabah)and the Nansha micro-block,the Sulu micro-block(Cagayan Island Arc)and the Lile-Palawan micro-block,and the Northwest Palawan micro-block and the Mindoro Arc.The collision of these micro-blocks shows obviously the migration eastwards.The characteristics of micro-blocks collision show the temporal variation from the west to the east,and recorded the entire process of the Proto-South China Sea closing in a scissor style.Correspondingly,the sedimentary records also show obvious migration features,such as the migration of delta lobe.