Publications

Buton Island is a rifted fragment of the northern Australian continent. The ”micro-continent” started colliding with the Southeast Sulawesi arm in the Oligocene to Early Miocene. As a result, a basin formed and accumulated sediment with potential for oil and gas resources. The tectonostratigraphy of Buton Island is divided into 4 events (Davidson, 1991): (1) pre-rift sedimentation consisting of the Doole Formation, Winto Formation, Ogena Formation, (2) rift-drift sedimentation consisting of the Rumu Formation, Tobelo Formation, (3) Syn-Post orogenic sedimentation consisting of the Tondo and Sampolakosa Formations, (4) Recent orogenic sedimentation consisting of younger rocks of the Wapulaka Formation. Magnetotellurics (MT) is a passive geophysical method used to identify the geological state of the subsurface. The MT method utilizes the variation of electric and magnetic properties in the frequency range <10-2 Hz to 10 KHz in order to interpret the subsurface conditions at depths ranging from a few tens of meters to several hundreds of kilometers. It can be used to determine the distribution of the subsurface rocks enabling subsurface structures to be modeled in one or two dimensions. Based on a 2D MT profile of the data trending west-east from Bau-bau to Pasarwajo, it is interpreted that the resistivity of the subsurface structure is divided into four primary layers each of which was used for reconstruction of boundaries of rock formations in the area: (1) igneous and metamorphic rocks of the Mukito Formation (256-2048 m), (2) limestones of the Ogena, Rumu, Tobelo and Tondo formations (16-2048 m), (3) clastic rocks of the Tondo formation (4-256 m), and (4) the Sampolakosa and Wapulaka formations (4-32 m). It is interpreted that the northwest-southeast trending geological structures of Buton Island are affected by tectonic activity that occurred from the Permian to the present. This commenced with normal faulting associated with late Triassic half-grabens decreasing in abundance from east to west. Subsequently folded layers with reverse faulting are associated Miocene micro-continet collisions and obduction. Keywords: Buton, Magnetotelluric, Resistivity