3D seismic geomorphology of the late quaternary fluvial to deltaic depositional systems within a source-to-sink framework of the central Sarawak, Malaysia

Abstract

Source-to-sink studies determine the source areas, transport and depositional environments of sedimentary systems under evaluation, but are often incomplete. However, this study of the Late Quaternary of Central Sarawak (NW Borneo) provides an opportunity to investigate a relatively complete source-to-sink system, based on extensive 3D seismic data, high-resolution 2D seismic data and borehole data, most notably on seismic facies and lithofacies properties, from shallow (mainly < 200 m below seabed) site surveys. Seismic stratigraphic methods have defined the morphology and stratigraphic architecture of ca. 200 – 350 km-long incised valleys. The valley mouths terminated in two types of deltas: (i) shelf deltas, and (ii) shelf-edge deltas. The resulting LGM paleogeography map comprised a ca. 360 km long source-to-sink system, extending from the continental drainage divide (presently at ca. 1,500 m elevation) to the basin floor of the NW Borneo Trough (presently ca. 2,500 m deep) and was characterised by the following elements: (i) multiple palaeo-drainages and incised valleys in the source area (i.e., hinterland Sarawak, inner shelf), (ii) a shelfal area characterised by a network of mainly northward-flowing rivers within incised valleys, (iii) shelf deltas and shelf-edge deltas immediately downstream of valley mouths, (iv) canyons, channels and gullies along the upper slope, and (v) basin-floor fans in the sink area. The total palaeo-drainage area of the study area was only ca. 60,000 km2, reflecting the narrow shelf width and short river lengths. The sediment budget estimations revealed an inversely proportional relationship between sediment storage on the continental shelf and sediment bypass to the deep-water. This thesis demonstrates that a complete source-to-sink reconstruction allows for observing fluvial to deltaic variations and understanding siliciclastic sediment pathways for the recently uplifted, humid-tropical climate, and tectonically-influenced shelf-edge of NW Borneo.