Evidence of Strike-Slip Faulting in Brunei Darussalam, NW Borneo

Summary Clear trace of a relatively large sinistral strike-slip fault was mapped on the aerial photographs obtained from the Survey Department, Ministry of Development, Brunei Darussalam, which covers an extent ∼48 meters with the map scale of 1:1000. This exposed portion of the rock outcrop shows the extent of the fault to ∼65 meters and it cuts through Miri Formation (Mid-Miocene) of the shallow marine environment. Field excursions at selected locations revealed the full extent of faulting at Sengkurong. The mapped faults are ∼E-W trending and dip southwards. The lateral displacement varies from >2 m to < 0.1 m, which is suggested by the displacement of marker beds. There was no evidence of reactivation or normal faulting, and the outcrop exposes large scale sinistral faulting. These faults lie towards the west of the regional thrust fault, known as Sengkurong fault, and do not extend further east of the fault, which could suggest that these faults have formed after the regional compression that formed this fault zone or during it. The fault cuts through the left limb of the Jerudong anticline, and we have named the fault as Lion King Fault because it is located close to the famous Lion King outcrop.