Bulletin of the Geological Society of Malaysia, Volume 27, November 1990, pp. 261 – 292
1Department of Geology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor
2Geological Survey of Malaysia, 88320 Kota Kinabalu, Sabah
Abstract: A field survey of the eastern half of the Maliau Basin established the presence of several good quality coal seams in the dominant mudstone sequence of the Early to Middle Miocene Tanjung Formation. Although volumetrically minor, the several metres thick sublitharenite beds dominate the landscape forming high waterfalls, concentric cuesta and other ridges with dipslopes inclined into the basin. Sandstone channel fills are common. Sedimentary current indicators including current ripple marks, tabular and trough cross beds, and lineation of carbonised plant fragments indicate that the majority of currents was towards northeast. The presence of coal, dominant mudstone, marine body and trace fossils suggest that the Tanjung Formation developed in low-energy environment, probably in wide tidal flats. Except for one locality exposing open folds, the beds dip uniformly and gently inward forming an eccentric basinal structure associated with normal faulting. These phenomena could have only been caused by gravitational subsidence without tectonic compression.
The northern boundary strike ridge intercepts internal strike ridges at oblique angles. This pattern and the off-centre position of the youngest beds suggest that the Maliau Basin during the deposition of the Tanjung Formation became progressively narrower while its depocentre migrated towards the south rim.
The structural basins containing the Tanjung Formation and time-equivalent Kapilit Formation are arranged in northeast and southeast rows; the Maliau basin occupying the junction of these two directions. Geologically the Maliau Basin is the landward extension of the Tarakan Trough and is at least partially floored by mélange rocks of the Kinabalu Suture Zone. Subsidence of this basin and other early-middle Miocene basins of east Sabah began when the East Sabah Terrane stopped drifting south and isostatic readjustment sank the denser ophiolitic basement of the suture zone.