Mud volcanism phenomenon and giant gas field formation in the Eastern frontier boundary area between Indonesia and Australia

Mud volcanism is widespread along the Sunda–Banda Arc in eastern Indonesia extending from Rote, Timor, Babar, Tanimbar islands and the Kai Archipelago to Ceram Island. Extensive mud volcanic ejecta distributed on the western side of Tanimbar Island and nearby areas provides evidence of the frequent occurrences of mud volcanism. A magnitude 7.5 earthquake that struck Tanimbar on 10 January 2023 was responsible for the formation of two new islands including Batu Arang Besar Island. Fieldwork by a small team from the Marine Geological Institute on the newly created Batu Arang Besar Island, 10 km west of northern Tanimbar Island, found expelled ejecta consisting of boulders and gravels from subsurface Mesozoic strata in a matrix of mud showing lamination, oxidation, red clay, chert and bioturbation. Mud volcanism occurs in the tectonically most active part of non-volcanic Banda Outer Arc and is always accompanied by methane emissions, which indicate that there is a relationship between mud volcano characteristics and the hydrocarbon potential. The event itself is commonly associated with seismic activity that influences mud volcano systems through static and dynamic stress changes that activate liquefaction and open conduits. No hydrocarbon deposits have been found in this most deformed non-volcanic arc region, while on the less deformed Australian continental plate passive margin toward the south and southeast, giant natural gas fields of Babar Selaru and Masela occur on the Indonesian side of the border, and numerous fields are present in the Australian part. Ongoing orogeny is responsible for mud volcanism as well as the formation of these giant gas fields. The field structures were formed during the Pliocene to Pleistocene by plate bending and faulting associated with the Banda Arc and Australian continent collision. Migration and accumulation of oil and gas into these fields mainly occurred during the Pleistocene to Recent. This very young migration provides evidence of the influence of neo-tectonics on the accumulation of hydrocarbons and is manifested by the common occurrence of big earthquakes and mud volcanism.