Syn-rift basin inversion: An alternative basin inversion model and significant role in oblique rift basins

Abstract:

In rift basins with superposed strike-slip deformation, the structural style of wrench elements and the role they play in syn-rift architecture and evolution are important, poorly understood issues for basin analysis and hydrocarbon exploration. The NE-SW-striking Tan-Lu Fault Zone (TLFZ), located in eastern China, runs through the Liaodong Bay sub-basin within the Cenozoic Bohai Bay Basin and has experienced dextral strike-slip motion during the later syn-rift stage of the basin (ca. 40 Ma to 23 Ma). Investigations of the Liaodong Bay sub-basin indicate that: rift-fault reactivation and wrench-fault development during strike-slip reactivation were strongly controlled by the distribution and geometry of pre-existing rift faults; and that local syn-rift basin inversion, induced by strike-slip reactivation of pre-existing graben during a later syn-rift stage, was a significant manifestation of synchronous strike-slip motion in modification of syn-rift architecture and evolution. Although inversion was limited to a very local area along a narrow fault zone, it substantially modified the basin’s physiography. In this rift system, coincident with local inversion-induced uplift, large-scale, rift-related subsidence occurred beyond the inversion belt within flanking graben, leading to complexity and variety in intra-basinal structural deformation and filling, and exerting a complex influence on hydrocarbon prospects.

Contrasting to the most previous basin inversion models which are characterized by a pulsed extension-compression (or transpression)-extension process, in the syn-rift basin inversion model, the horizontal shortening component of deformation was developed during partitioned transtension, leading to the concurrence of extension and shortening within a rift basin, with no need of changes in regional dynamics. Hence, this new model may lead to different explanations for complex structures, basins and regional dynamics. This model of syn-rift basin inversion has profound implications for the interpretation of inversion structures and basin dynamics in any rift basin with superposed strike-slip deformation.