The tectonic evolution and associated sedimentation history of Sarawak Basin, eastern Malaysia: a guide for future hydrocarbon exploration

Abstract

A seismic-stratigraphic study of the reprocessed regional lines for the offshore Sarawak area was undertaken with the aim of reviewing the present understanding of the tectonics and the palaeo-depositional environments of the Sarawak Basin. The study was integrated with biostratigraphy and wireline-log data from the wells drilled throughout the basin.Seven unconformities were identified within the Tertiary sediments and these were used as the markers for the seismic correlations. Where the unconformities become conformable, well data were used to guide the correlation of the conformities. Palaeoenvironment maps were generated which document the interaction of tectonics and sediments throughout the basin history. The development of the Sarawak Basin commenced in late Oligocene times with deposition along a coastline running in a NW-SE direction, which is almost perpendicular to the present-day coastline. The coastline was oriented to the present-day NE-SW during late Miocene times.Geochemistry of Sarawak Basin oils shows generation of hydrocarbons from land plant dominated source rocks. The distribution of these types of source rocks are favoured in the Coastal Fluvial, Coastal and Lower Coastal Plain environments. The quantity and quality of the source rocks deteriorates with the distance from the coastline. The palaeoenvironment maps illustrate the likely distribution of Sarawak Basin source rocks which will help in effectively planning for future exploration in Sarawak.The study also revealed that the Sarawak Basin was formed as a result of NW-SEtrending right-lateral fault movement during late Oligo-Miocene times. This dextral movement was responsible for creating the NW-SE coastline and divided the offshore Sarawak area into two sub-basins. Deposition and preservation of coastal plain and shallow marine sediments continued in the eastern area while the western area remained as a 'high' until late Miocene times. The dextral strike-slip movement which controlled the evolution of the Sarawak Basin is sub-parallel to a number of lineaments elsewhere in Sarawak. The timing of movement of these suggests progressive younging in an eastward direction. It is also believed the late structuration of the sediments and the formation of structural traps is linked to these tectonic movements.

A review of the Sarawak Cycles: History and modern application

“…The base Cycle III and base Cycle IV transgressions are strongly focussed in the northwest where the Bunguran Trough was opening ( Figure 19). This is the increase in basement subsidence observed on regional seismic at the base of sequence T3S of Ismail & Swarbrick (1997). Associated with this there was also a transgression in the southwest over the eroded high of the Tatau Province.…”

“…As such it is not a good example of a typical reef for the region. Ismail & Swarbrick (1997) and Cycle IV to basal V (TB2.6) maps of Kosa (2015), showing the same effects of the transition at this cycle boundary, a deepening of the central and northern parts of the area, but very soon after, or simultaneous with this a rapid influx of sediment from the east impinges on the northeast side of re-formed basin. Figure 8 of Ho (1978) shows that by the later Middle Miocene a new sedimentary setting had been established with clastic input derived from the southeast, prograding northwestwards.…”

Heat flow and surface hydrocarbons on the Brunei continental margin

“…(0.05 cm/yr; 0.02 in./yr) over the last 3 m.y. (Mat-Zin and Swarbrick, 1997). This implies more than 30 times focusing of the 1.7-cm/yr (0.67-in./yr) (5.5 Â 10 À 10m/s; 1.80 Â 10 À 11 -ft/s) flow required to account for the megaseep heat flow, at least three times the values estimated by Ritter et al (2004).…”

Offshore Carbonate Facies Characterization and Reservoir Quality of Miocene Rocks in the Southern Margin of South China Sea

“…A prominent lineament, the West Baram Line, separates Central Luconia from the Baram Delta. To the south is the compressed Balingian Province (Doust, 1981;Haq et al, 1987;Mat-Zin and Swarbrick, 1997;Hutchison, 2004;Cullen, 2010: Fig. 2).…”