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Asia and Australasia |
Geological Research Division, Scripps Institution of Oceanography, La Jolla, California 92093, U.S.A.
Sedimentation in the Sunda Trench and forearc region is dominated by the transport of terrigenous detritus from orogenic and volcanic terranes around the margins of the north-eastern Indian Ocean. Quartzose Himalayan detritus is transported 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 of these hemipelagic deposits. Higher on the slope, terrigenous and hemipelagic sediments accumulate in large trench-slope basins.
The Sunda forearc basin is a series of smaller individual basins separated from each other by transverse highs, isolating the respective sedimentary sequences. Off north Sumatra, quartzose detritus accumulates, whereas off Java, volcaniclastic sediments predominate.
Long-distance transport of sediment down the trench axis, damming of sediments behind the outer-arc ridge, and the segmented nature of the forearc basin leads to the juxtaposition of sediment bodies with different provenances.
