Contourite sedimentation in an intraoceanic forearc system: Eastern Sunda Arc, Indonesia

Abstract

Combined analyses of bathymetry, piston cores, 3.5-kHz echograms, and seismic reflection data reveal that sedimentation patterns in the eastern Sunda forearc are strongly influenced by vigorous deep- and bottom-water circulation. The affected region is located at the intersection of the Sumba Ridge and the Sawu-Timor Ridge, which together form a barrier to the outflow of Pacific Ocean Deep Water from the Sawu Sea to the eastern Indian Ocean. Bottom currents associated with the outflow have eroded a gap in the sill at a water depth of 1150 m, between the islands of Sumba and Sawu. Southwest of the gap, the widespread exposure of well-consolidated, middle Miocene to Pliocene foraminiferal chalks and oozes along the Sumba Ridge suggests that up to 1 km of overburden has been removed by the deep (1–1.5 km) currents. The eroded sediments have been subsequently deposited as muddy contourites in a thick ( > 1 km ) sediment drift in the adjacent Sumba Basin. The drift consists of an elongated mound composed of reworked calcareous ooze and is bounded by moat-like channels. The influence of contour currents on trench-slope sedimentation can be significant and should be considered during studies of modern forearc systems and ancient subduction complexes on land.