Nature, origin and evolution of a Late Pleistocene incised valley‐fill, Sunda Shelf, Southeast Asia

Abstract

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 km 2 ), '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.

Sequence architecture and sedimentary characteristics of a Middle Jurassic incised valley, western Sichuan depression, China

“…Tectonic uplift and climatic changes can drive the base level; however, their influence varies from upstream to downstream. The mid-to downstream segments of rivers are primarily controlled by lake-or sea-level (analogous to the base level) changes (Hampson et al 2012;Alqahtani et al 2015), whereas the upstream segments of rivers may be more directly controlled by tectonism (Shanley and McCabe 1994;Mattheus et al 2007;González-Bonorino et al 2010;Alqahtani et al 2015). show boulder clays; and e shows a basal bounding surface, interpreted as sandy channel facies.…”

“…Periodic base-level (lake-level) fluctuations controlled the progradation and retrogradation of the valleys (Shanley and McCabe 1994;Olsen 1995). The widths and depths of the incised valleys were controlled mainly by the rate and magnitude of local base-level fall and delayed accommodation (Alqahtani et al 2015).…”

Grain‐size variability within a mega‐scale point‐bar system, False River, Louisiana

“…Although numerical models have been developed that can help predict such characteristics based on the geometries observed in three‐dimensional seismic surveys (Yan et al ., ; Colombera et al ., ), such models are best used when the lateral extent of facies and grain‐size variability is well‐constrained. Seismic methods can provide the geometry of the meander externally and sometimes internally (Hubbard et al ., ; Alqahtani et al ., ) but are weak at constraining lithology.…”

Form, evolution and controls of a Jurassic incised valley‐fill: middle part of the Western Sichuan Depression, China

“…in the late lowstand systems tract (LST) and early transgressive systems tract (TST) (Vail et al ., ; Posamentier and Vail, ; Van Wagoner et al ., ; Zaitlin et al ., ; Willis, ; Veiga et al ., ; Catuneanu, ; Catuneanu et al ., ). New models (Rajchl and Ulicny, ; Gouw and Autin, ; González‐Bonorino et al ., ; Hampson et al ., ; Alqahtani et al ., ) focus on the planform geometric variation in incised valleys and analyse their controlling factors from upstream to downstream.…”

“…It is commonly believed that valley forms change from narrower and higher‐sinuosity in their proximal parts to wider and lower‐sinuosity in their distal parts (Schumm et al ., ; Rajchl and Ulicny, ; Alqahtani et al ., ); the valley width changing is mainly attributed to fluvial incision and/or slope failure (Zaitlin et al ., ) at the downstream segment. However, several authors argued for the opposite trend (e.g.…”