EVOLUTION OF THE MESOZOIC STRATA IN THE MIDDLE RANGE OF THE HUANGHUA DEPRESSION

The Mesozoic structural pattern and evolution of the Bohai Bay basin is debated until now. Especially the Yanshanian deformation pattern is a key problem. We try to select the middle range of the Huanghua Depression of the Bohai Bay basin to study structures of this area, using a large number of seismic profiles. The Mesozoic evolution in the middle range of the depression can be mainly divided into four periods by using the balanced cross-section technique to reconstruct palaeo-structure in conjunction with tec-tonic setting. The first-generation structures are gentle east-west-plunging folds and the following eastwest-striking thrust formed in the late Indosinian. The second-generation strustures are NNE-plunging folds and the following strike-slip faults formed in the early Yanshanian. In the middle Yanshanian, a series of structures were under the ongoing compression, subsequently the dextral normal-slip faults formed under the extension. At last, some normal faults in this area were under regional intensive extension from the late Yanshanian to the early Himalayan.