--> ABSTRACT: Seismic Expression and Channel Morphology of a Recent Incised Valley Complex, Offshore Northwest Java, Indonesia, by Mark J. Gresko and Philip Lowry; #91019 (1996)

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Seismic Expression and Channel Morphology of a Recent Incised Valley Complex, Offshore Northwest Java, Indonesia

Mark J. Gresko and Philip Lowry

Interpretation of high-resolution (> 150 Hz) 2-D seismic data over a 6300 km2 area of the modern Java Shelf, has led to the identification and delineation of a recent (Pleistocene-Holocene?) incised valley complex. The youngest in a series of erosional features in this area, this complex was likely formed by incision during the latest eustatic sea-level fall and filled during the subsequent transgression.

Seismic mapping within the first 150 msec of seismic data show that the incised valley complex is comprised of two types of channels: several shallow (10-30 m), low-sinuosity channels, and a single deep (40-50 m), meandering, long (greater than 150 km) channel. Channel fill is characterized on seismic by horizontal, low to moderate strength reflections that onlap the channel walls. No lithological information is available from within the channels, but based on seismic character, the sediment is assumed to be shale-prone.

The location of the incised valley system is within a large present-day bathymetric trough. The trough is presently 20-30 km wide, greater than 300 km long and has over 100 meters of relief. The trough was the primary drainage path for rivers from northwest Java and southeastern Sumatra into the Indian Ocean during sea-level lowstands. During subsequent rises in sea level, the trough filled with sediment except in localized areas where strong currents kept the channel relatively free of sediment. The bathymetric trough had a first-order effect on the location of the incised valley complex, however, comparing the incised valley pattern with subsuface maps it is apparent that structural features, such as regional fault trends and structural highs, also played a significant role in channel morphology.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California