Seismic interpretations reveal two low angle detachment systems in the Jiaolai basin: one

developed 8～10 km beneath the Zhucheng depression in the southern part of the basin

has a detachment surface gently dipping to the south; the other

developed in the north Gaomi and Laiyang depressions

consists of a series of N-dipping listric normal faults and has a major detachment surface gently dipping to the north or NNE.Based on the sed-imentary records analysis

profile retro-deformation

and estimated stretch properties of the above-mentioned depressions

in combination with the fault slip data analyses at the surface

the southern detachment system is considered to be formed during the early Cretaceous Laiyang stage when the Zhucheng depression had a N-S stretching rate of 36%～41% and a possible NW-SE maximum stretching.This detachment system inherited an early deep decollement zone in the Jiaonan(or Su-Lu) orogenic belt;its late reactivation dominated the asymmetric extension pattern and controlled the development of the narrow

elongate sedimentary depression in the Jiaolai basin in Laiyang stage.The northern detachment system had taken shape during the stretching stage in the late Cretaceous.It is possible that the stretching process continued until the Paleocene and controlled the deposition of the Wangshi Formations.The N-S extension across the Laiyang and Gaomi depressions during the stage is estimated to be at 20%～25%

the maximum stretching direction being nearly N-S.This detachment system accommodated the N-S pull-apart stretching of Jiaolai basin and its formation was related to the right-lateral shear along the NNE-trending boundary fault zones on the eastern and western sides of the basin.The spatial and temporal superimposition of these two detachment systems resulted in the complex extensional structural styles in the Jiaolai basin.The identification of these two deep detachment systems not only provides structural constraints on the mechanisms and dynamic setting of the basin formation

but also is of great significance for petroleum exploration in the basin.