GEOLOGICAL SOCIETY OF THE PHILIPPINES
STRUCTURAL STYLE AND STRATIGRAPHY OF NEOGENE SEDIMENTS OF THE SOUTHERN SABAH BASIN, MALAYSIA, NORTHERN BORNEO
Balaguru, A., Nichols, G. and Hall, R.
Royal Holloway, University of London,
Egham, Surrey TW20 0EX
Integrated detailed outcrop studies and SAR image interpretations carried out in the Malibau, Tidung and Meliau areas of southern Sabah have provided new insights into the structural style and stratigraphy of the area. Two coarsening-upward megasequences of Miocene fluvio-deltaic to shallow marine deposits rest unconformably on the Oligocene deep to shallow marine argillaceous sediments. Miocene palaeocurrent direction of sediments were towards NE and SE. A prominent southeasterly plunging fold belt trends SE-NW consists of asymmetric inclined folds that pass into overturned folds with a SW vergence dominate the Tidung area. Towards NW the fold belt curves NNE with a SSW plunge with tight anticlines and broad synclines. The tight anticlines are associated with faults. These broad synclinal structures were enhanced by erosion and were previously known as Meliau and Malibau ‘basins’. In the Tidung area the fold wavelength are shorter with tight plunging anticlines and broad synclines. Within these apparently broad synclinal structures there are a few open to tight folds. The area has been cut by numerous faults mainly trending NE-SW and NW-SE. These are interpreted as strike slip and normal faults. Relatively less tectonised thick continuous sections are preserved within the Malibau and Meliau Synclines. North of these areas, a series of WNW-ESE trending imbricate fold-thrust belts are clearly dissected by NE-SW trending faults.
This study has shown that these sediments were not deposited in a series of isolated sub-circular basins, but were deposited in an extensive basin, with sediment input from the W and N. The ‘sub-basins’ or more strictly structural provinces, are the outliers or remnants of a single large basin, which now have their present shape due to the contraction, uplift and erosion.
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