Neogene structures and sedimentation history along the Sunda forearc basins off southwest Sumatra and southwest Java

Twenty multi-channel seismic lines in the southwest Sunda arc margin between Manna and west Java have been studied. This study depicts the structures and stratigraphy of the fore-arc basin since Late Paleogene in relation to the regional tectonic events. The paleomorphology of the Cretaceous continental margin persisted until the Oligocene and the paleoshelf margin of the continent extended north-westward off Sumatra. A residual basin filled with turbidite deposits developed just offshore of this margin. Subsequent fore-arc basin evolution was related to the slow down of subduction rate due to the collision of the Indian and Eurasian Plates in the Eocene. The rising Himalayan orogenic zone shed large amounts of sediment to the Indian Ocean and Sunda Trench beginning in the Late Paleogene which led to the growth of the accretionary prisms and the development of the Neogene fore-arc basin. At least two major structural events can be recognized in the fore-arc basin between Late Oligocene and Pliocene. Back thrust-faulting along the southern border of the fore-arc basin and initiation of the Cimandiri Fault Zone occurred in Late Oligocene, whereas the development of the Sumatra and Mentawai Fault Zones was initiated in Pliocene. eogene sedimentary units can be recognized representing three main transgressive–regressive cycles and basin-fill deposits. The cycles resulted from a complex interplay of tectonically induced basin subsidence, eustatic sea level change and sediment supply related to volcanic activity that became abundant since late Middle Miocene. Turbidite deposition was common along and seaward of the basin slope during sea level lows in late Middle Miocene and Late Miocene. Sediment aggradation and progradation occurred during high sea level still stand and fall, respectively. Basin fills occurred mainly during the Pleistocene.