Structures and sedimentary deposition in the Sunda Strait, Indonesia

The Sunda Strait lies between the islands of Java and Sumatra and separates the nearly orthogonal subduction along the south of Java and oblique subduction beneath Sumatra. The Sumatra fault accommodating most of the trench parallel shear of the oblique subduction initiates in the Sunda Strait. This setting implies that the Sunda Strait is an attractive area to study the geodynamic evolution of the western Indonesian region. Thirteen multichannel seismic lines acquired in the Sunda Strait have allowed a detailed study of the structure, sedimentation patterns and volcanic activities that occurred in the Sunda Strait.The Sunda Strait evolution has been strongly tied with the development of the Sumatra fault in this area. The opening of the Sunda Strait initiated in the early Late Miocene following the commencement of the Sumatra fault system in the Middle Miocene. Since then, three major graben systems have been evolved, which are referred to as the West and East Semangko Grabens, and the Krakatau Graben. These graben systems can be regarded as pull-apart basins developed within the releasing fault overstep area in between the main strand of the Sumatra fault and its relay faults south off Ujung Kulon.Prior to the Late Miocene most of the Sunda Strait and the surroundings probably developed in a non-marine environment. In Late Miocene the Sunda Strait started to open and volcanism began and has been the main source of clastics. Three major sedimentary units can be identified which represent Late Miocene, Pliocene and Pleistocene sediments respectively. The Late Miocene unit has been developed in the shelfal area on top of the Middle Miocene unconformity following a relative rapid sea level rise, and a subsequent highstand prior to the sea level fall at the end of Miocene. Its lower part has syn-structurally been deposited into the Late Miocene basement block faulting. The early deposition of the Pliocene unit was in response to the Pliocene sea level rise and abundant clastic supply. The deposition became very rapid due to graben formation combined with stronger volcanism. However, its lateral distribution was confined by uplift of ridges within the grabens.