基于重磁异常的新生代丽水—椒江凹陷基底分布特征研究

Distribution Characteristics Study of Cenozoic Basement of Lishui-Jiaojiang Sag Based on Gravity and Magnetic Anomalies

丽水—椒江凹陷位于东海陆架盆地西南部,是在中生代残留盆地基础上发育起来的新生代具有典型东断西超特点的断陷,是油气勘探的新区域。区域地质条件复杂、构造叠加、沉积厚度大,地震勘探无法获得较好的反射数据,因此采用面积广、深度大的重磁数据结合地震数据来描述基底构造和火成岩岩性特征,通过重磁数据的阶跃边界识别技术划分区域断裂。丽水—椒江凹陷内断裂呈北东向分布,控制凹陷的形状,且断裂作用使凹陷形成多个小型次凹,断陷特征明显。中—新生代火成岩具有较高的重磁异常,结合质量较好的地震剖面来获得地层、火成岩及岩性分布特征,并建立了多联通域地层的计算公式。区域内中古生界较为发育,但凹陷内中新生代火成岩侵入较少,不会对于油气构造造成大的破坏,因此该凹陷具有良好的油气前景。

Located in the southwestern part of the East China Sea continental shelf basin,the Lishui-Jiaojiang sag is a Cenozoic fault depression with typical east fault and west overpassing characteristics developed on the basis of the Mesozoic residual basins,and it is a new area for oil and gas exploration.Due to the complex geological conditions in this area such as the superimposed structure and the sedimentary thickness,the useful reflection data are not available through seismic exploration.The authors adopted the combination of gravity and magnetic data that are used for a wide area and large depth with seismic data to describe the structure,igneous rock,and lithological characteristics of the basement,and divided the regional faults by using the step boundary recognition technology of gravity and magnetic data.The inner faults in the sag show a north-eastward distribution,which control the shape of the sag.The fault depression is characterized by many small secondary depressions formed by the faults.The Mesozoic and Cenozoic igneous rocks have high gravity and magnetic anomalies.We obtained the strati-graphic,igneous and lithology distribution characteristics from the seismic profile with good quality,and established the formula for the calculation of the mulch-continuous domain strata.The Mesozoic strata are relatively developed in the region,and there are less Mesozoic and cenozoic igneous rocks in the sag,which will not cause the great damages to oil and gas structure.Therefore,this sag has a good oil and prospects.