Gravity And Magnetic Field Characteristic And Structural Analysis In The Wanan Basin

The Wanan basin is a tectonic sedimentary basin located in the southeastern margin of the Kun-chung block and the west side of the Nansha block,which has a complex base and strike-slip type.In the eighties of last century,there was no degree of exploration in the Wanan basin at home and abroad.The strata,fault system and tectonic unit of the basin are divided based on seismic data by different scholars.The Wanan basin was experienced several tectonic movements and six stages of tectonic evolution during the Cenozoic,which caused fracture extremely developed.The fault system played an important role in the division of the tectonic units.In this paper,we obtain a comprehensive understanding of the structure and stratigraphy of the Wanan basin by using collected the gravity and magnetic data of the Wanan basin with combining the predecessors' research results.This research results can provide geophysical foundation oil and gas exploration in Wanan basin.In this paper,we collected the gravity and magnetic data of the Wanan basin,which has accuracy of about 1: 1,000,000 gravity and magnetic data,processed the data through analytical continuation,moving average,regulariseringen filter,the total horizontal gradient and vertical derivative method,obtained different parameters of gravity conversion parameters.We systematically analyzed the characteristics of gravity and magnetic field of the Wanan basin based on the regional geological data and explained the causes of local gravity and magnetic anomalies.We reconstructed and explained fracture system of the Wanan basin by different parameters of magnetic and magnetic conversion parameters with explaining some new faults,which is different with the predecessors' research results,and divided the tectonic units.We discussed the stratigraphic distribution of different tectonic units based on the results of gravity fitting of four main sections.The main achievements and conclusions are as follow:1)The anomalies of Bouguer gravity in the Wanan basin can be divided into western low-value area,high-value area,high-value area and high-value area.The residual gravity anomaly is more complicated.The Cenozoic pattern of the basement uplift and depression is basically reflected by high gravity and low gravity,which displays as interphase distribution.The characteristic of the residual gravity anomaly is related to the thickness of the Cenozoic sedimentary.The local magnetic anomaly is more developed in the basin,which Mainly distributes in the south and east of the basin,suggesting that the main events are caused by the Miocene volcanic activity and the basal magma tic rock intrusion.2)The Wanan basin has complicated well-developed faults,which are mainly NNE trending and NE trending,followed by NW trending.Compared with the previous results,fault named wanan does not extends to the southeast margin of basin with terminating in the central basin.Fault F2 and Fault F4 is divided new in this paper.Fault F2 controls the boundary of the southern depression and eastern depression in basin.West marginal fault zone of the South China Sea(Wan'an Basin)is the southern boundary of the Indochina block and Nansha block.3)The basement of the Wanan basin is a wavy terrain from northwest to south east.The Cenozoic strata of the basin are well developed.The Wanan basin tectonic unit can be divided into six tectonic units,which included northwest depression,northern uplift,central depression,the central uplift,southern depression and eastern depression.