Faisal Alqahtani, Howard D. Johnson, Christopher Aiden-Lee Jackson , Rapi B. Som

Understanding the stratigraphic fill and reconstructing the palaeo-hydrology
of incised valleys can help to constrain those factors that controlled their origin,
evolution and regional significance. This condition is addressed through
the analysis of a large (up to 18 km wide by 80 m deep) and exceptionally
well-imaged Late Pleistocene incised valley from the Sunda Shelf (South
China Sea) based on shallow three-dimensional seismic data from a large
(11 500 km2), ‘merge’ survey, supplemented with site survey data (boreholes
and seismic). This approach has enabled the characterization of the planform
geometry, cross-sectional area and internal stratigraphic architecture, which
together allow reconstruction of the palaeo-hydrology. The valley-fill displays
five notable stratigraphic features: (i) it is considerably larger than
other seismically resolvable channel forms and can be traced for at least
180 km along its length; (ii) it is located in the axial part of the Malay Basin;
(iii) the youngest part of the valley-fill is dominated by a large (600 m wide
and 23 m deep), high-sinuosity channel, with well-developed lateral accretion
surfaces; (iv) the immediately adjacent interfluves contain much smaller,
dendritic channel systems, which resemble tributaries that drained into
the larger incised valley system; and (v) a ca 16 m thick, shell-bearing, Holocene
clay caps the valley-fill. The dimension, basin location and palaeohydrology
of this incised valley leads to the conclusion that it represents the
trunk river, which flowed along the length of the Malay Basin; it connected
the Gulf of Thailand in the north with the South China Sea in the south-east.
The length of the river system (>1200 km long) enables examination of the
upstream to downstream controls on the evolution of the incised valley,
including sea-level, climate and tectonics. The valley size, orientation and
palaeo-hydrology suggest close interaction between the regional tectonic
framework, low-angle shelf physiography and a humid-tropical climatic setting.