Sedimentary Stratigraphic Characteristics And Evolution Since The Pliocene In The Offshore Area Of Northern Fujian

The paper is based on the latest full coring geological drilling ECS1601（90.2 m,located at the intersection of the seismic profile line Z3（main line）and L9（liaison line））obtained in the offshore area of Fujian Province,with a resolution of 3,500 km.Shallow stratum seismic section and a 3,500 km single-track seismic section laid in the same network.combined with previous research results,have detailed divided and deeply discussed the sedimentary stratigraphy and sequence of the Pliocene since the study area.On this basis,we established the sedimentary model of the study area and the explored sedimentary tectonic evolution process since the Pliocene in the study area.The main conclusions are as follows:1.The ECS1601 drilling is divided into 4 sedimentation units by measuring the granularity and micro-fabrication,combined with the AMS¹⁴C and OSL dating data,and named DU1,DU3,DU4,and DU5,in order from top to bottom.Represents the Holocene,the middle section of the late Upper Pleistocene group,the lower segment of the Late Pleistocene Upper group,and the Late Pleistocene Lower group.2.Based on the principle of sequence division and identification of reflective interfaces（Overlap up,overlap down,Cutting and covering,overlap at the top,etc.）,the 3500 km high-resolution shallow stratigraphic profile was finely interpreted.The results show that the shallow strata seismic section is divided into four The seismic units are named from the top to the bottom:SU1,SU2,SU3,SU4,and SU5,which represent the Holocene,the upper section of the Upper Pleistocene Upper Unit,and the middle section of the Upper Pleistocene upper group,the lower part of the Upper Pleistocene Upper Group,and the Late Pleistocene Lower Group.According to the interpretation of the 3500km single-track earthquake on the grid,the single-channel seismic profile was divided into four earthquakes.The units,from top to bottom,are named Qh+Qp3,Qp2,Qp1,and N2,which represent the Holocene+Late Pleistocene,Middle Pleistocene,Early Pleistocene,and Pliocene,respectively.3.Through the precise comparison of shallow drills（ECS1601）and seismic profiles,combined with past research results,for the first time,a sediment accumulation model has been established since the Pliocene in the offshore areas of northern Fujian,and the sea level changes since the Pliocene have been analyzed.The influence of tectonic movement and other factors on the depositional environment and sedimentary process control,and explored the sedimentary tectonic evolution process since the Pliocene in the study area,and focused on the sedimentary evolution model since the late Pleistocene.The results indicate that the area has been experienced seawater intrusion three times and seawater retreat twice since the late Pleistocene.4.A large number of seismic profiles show that the special geologic bodies in the study area are relatively developed,especially the paleochannel,and there is an ancient river system.According to the comprehensive analysis of the ancient terrain and geographical location at that time,the paleochannel distribution roughly corresponds to the topography of the seabed at that time.One of the ancient rivers,which is roughly oriented east-west,may originate from the Minjiang River,and the other one that is oriented north-south may originate from the tributaries of the Yangtze River.Through analysis,we have further verified that since the last glacial period,the historical changes of the study area from the occurrence of retreating exposed surface to ancient rivers and the re-invasion of the shallow sea environment.Based on a large number of measured data,the data processing quality of the field survey data satisfies relevant regulatory requirements,and the in-depth analysis of the sedimentary characteristics of the area since the Pliocene has enriched the sequence stratigraphic theory of the East China Sea near the coast.At the same time,due to changes in sea level and structural influences,a large number of active geological faults,paleochannels,shallow gas,and other special geological bodies were discovered in the study area,which provided a scientific basis for major project construction and resource exploration in the area.