Propagation history and passive rotation of mesoscale normal faults: implications for synrift stratigraphic development

Field data from onshore exposures of the Oligo-Miocene Gulf of Suez Rift in the Sinai document the passive rotation of early formed mesoscale syntheti c and antithetic faults and associated half-graben due to long-lived activi ty on large displacement (2-5 km) block-bounding faults. Early formed small -displacement( <350 m) mesoscale antithetic faults and half-graben within r egional-scale fault blocks underwent progressive steepening due to footwall uplift, rotational faulting and footwall flexing on large-displacement, bl ock-bounding faults. In contrast, mesoscale synthetic faults were progressi vely rotated to shallower angles. Analysis of palaeohorizontal surfaces wit hin synrift sediments deposited in half-graben adjacent to the mesoscale fa ults indicate passive rotations of up to 25<degrees> about horizontal axes since deposition. Passive burial and in-filling of early formed mesoscale f aults and half-graben by synrift sediments is consistent with extension bei ng transferred from numerous mesoscale faults to few block-bounding macrosc ale faults as extension preceded. Furthermore, this transfer of extension a ppears to be associated with a marked change in basin configuration, synrif t sediment dispersal patterns and facies development. Identification of ear ly formed, passively rotated normal faults and half-graben is important for correctly reconstructing the early stages of basin palaeogeography and sed iment dispersal, and for addressing models of rift basin evolution.