Antiformal Negative Flower Structure in Nanpu Sag, Bohai Bay Basin

Flower structures are specific modes of formation, and their distinctive characteristics make them important criteria for the identification of a strike-slip zone in vertical cross-sections and on seismic profiles. Two element types of the classical flower structures were respectively negative and positive flower structures. There is a new kind of flower structure termed antiformal negative flower structures in Nanpu sag, Bohai Bay basin. A antiformal negative flower structure in 3D seismic profiles from the Nanpu sag consists of a shallow antiform and a deep synform bounded by upward and outward spreading strands of a strike-slip fault that have mostly normal separations. In map-view, the folds and associated normal faults present an en echelon arrangement. Antiformal negative flower structure formed in the transtensional setting of Nanpu sag. The shallow antiform is forced folds caused by the transtensional faults dragging cover into folds. Antiformal negative flower structure undergone two phases of deformation including: (1) forming of drag fold and (2) fualting and collapsing of the fold crest. The antiformal negative flower structures are a widespread structural styles in the Neogene of the Bohai Bay basin.