DISTRIBUTION AND ORIGIN TYPES OF THE FOLDS IN THE NORTH YELLOW SEA BASIN

North Yellow Sea basin is a Mesozoic/Cenozoic fault basin superposing on North China platform, which has distorted stratum and well-developed fold structures due to the reconstruction of several structure movements. The folds in the North Yellow Sea basin are mainly classified into four origin types, namely extensional folds, compressional folds, gravitational force folds and thermogene folds. The extensional folds related to normal faults are distributed most widely, which can be further divided into drag folds, reverse-drag folds, rolled folds, compensation squeezed anticlines and fault-displacement folds;the compressional folds including non-reverse squeezed folds and reverse folds are caused by territorial extrusion stress and spread both in the eastern sag and the mid-sag apparently. As a kind of gravitational force folds, buried-hill drape anticlines are quite easily observed in the North Yellow Sea basin, while the thermogene folds only appear in the eastern sag owing to inactive magmation.