Nanpu sag of the Bohai Bay basin: A transtensional fault-termination basin

Abstract

The Nanpu (南堡) sag has previously been modeled as (1) a pull-apart basin, (2) a rift basin, without significant strike-slip deformation, and (3) a transtensional basin. We present a new model for the Nanpu sag in which the basin is a transtensional fault-termination basin. Although transtensional fault-termination basins is an important basin type, it is not as well studied as other classic basin types. On the base of 3D seismic data interpretation, the faults geometries and kinematics and their controls on depocenters are presented. The Nanpu sag is developed in the context of dextral transtension of the Bohai (渤海) Bay basin and attributed to a transtensional fault-termination basin. During deposition of the Es3-Es2 members, the basin border Xi’nanzhuang (西南庄) fault and Baigezhuang (柏各庄) fault linked to a mixed normal and strike-slip fault system, or a linked fault system controlled the basin by dominant extension and weak strike-slip and created fan-shaped depocenters surrounded by the two faults. From Es1 Member to Dongying (东营) Formation, two major depocenters controlled by two mixed normal and sinistral strike-slip fault systems are located on the Linque (林雀) and Caofeidian (曹妃甸) subsags. During deposition of the Guantao (馆陶)-Minghuazhen (明化镇) Formation, the Nanpu sag successively developed and significantly expanded.