Sedimentation in the Sunda Trench and forearc region

SUMMARY: Sedimentation in the Sunda Trench and forearc region is dominated bythe transport of terrigenous detritus from orogenic and volcanic terranes around the margins of the north-eastern Indian Ocean. Ouartzose Himalayan detritus is an ported into the Bay of Bengal and down the trench axis as far south as the Sunda Strait. Prior to development of the outer-arc ridge, the majority of arc-derived sediment bypassed the forearc basin and was deposited in the trench. Nearly all sediment derived from the arc terranes of Java and Sumatra during the Neogene has been trapped in the forearc basin and has not reached the trench. Hemipelagic sedimentation dominates on the lower part of the inner trench slope. Calcareous microfossils and volcanic ash are the dominant constituents ofthese hemipela-gic deposits. Higher on the slope, terrigenous and hemipelagic sediments accumulate in large trench-slope basins. The Sunda forearc basin i a series of smaller individual basins eparated from each other by transverse highs, isolating the respective sedimentary sequences. Off north Sumatra, quartzose detritus accumulates, whereas off Java, volcaniclastic sediment