Seismic Characteristics and Identification of Negative Flower Structures, Positive Flower Structures, and Positive Structural Inversion

ABSTRACT Negative and positive flower structures and positive inverted structures imply specific modes of formation, and their distinctive characteristics make them important criteria for the identification of certain structural styles. A negative flower structure from the Andaman Sea consists of a shallow synform bounded by upward-spreading strands of a wrench fault that have mostly normal separations. Paralleling monoclines and oblique, en echelon normal faults flank the divergent wrench fault. A positive flower structure from the Ardmore basin, Oklahoma, consists of a shallow antiform displaced by the upward diverging strands of a wrench fault that have mostly reverse separations. En echelon folds are present on either side of this convergent wrench fault. Flower structures may resemble extensional or contractional fault blocks on individual seismic profiles. Flower structures are identified by their unique internal fault and fold architecture, by their association with a straight and throughgoing zone of deformation, and by their lack of a consistent sense of separation or regional upthrown side. Positive structural inversion at the Rambutan oil field, South Sumatra basin, has formed a shallow anticlinorium and has partly uplifted the underlying graben. Deeper fault segments bounding the graben have retained their normal fault profiles, but at shallow levels some of these faults have reverse separations. Similar changes of separation with depth may be produced by strike slip, but sets of faults with listric profiles and nearby blocklike trend patterns identify the inversion as a dip-slip event. Where correlation of reflections is uncertain or deep control is unobtainable, positive inverted structures may also resemble contractional fault blocks, detached normal fault assemblages, and certain negative inverted structures.