Abstract: Evolution of the Eocene-Miocene Carbonates of the North Sarawak Basin
Azhar Hussin, Tee Abdullah Nuraiteng
During the late Eocene, the northern margin of the Rajang hinterland subsided to form the North Sarawak basin. A broad dissected shelf with clastic sediments, carbonate shoals, reefal bodies, and deltaic sediments to the south was developed.
Upper Eocene bioclastic shoals and bank were formed on folded turbidite sequences in the Batu Gading and Melinau areas, while smaller carbonate shoals accumulated on paleohighs of conglomerate and volcanics in the Arip area. Carbonate sedimentation on the Melinau bank was essentially continuous from the late Eocene to the Oligocene. A localized disconformity separating the upper Eocene and the lower Miocene successions in Batu Gading shoals indicates probable reactivation of vertical movements in the underlying basement. To the northeast of the carbonate bank, pelagic lime-mud and calciturbidites were accumulated in the deeper part of the basin.
During the Miocene, carbonate facies were more extensive and were distributed along two tracts trending north-northwest and northeast. These mark the northernmost extent of the shelfal area of the basin. Reefal facies succeeded earlier carbonates and were also formed on shelfal clastics. In the middle Miocene, reefal facies along the southern part of the basin were drowned and overlain by shelfal muds. To the north (offshore Luconia), sedimentation of middle Miocene reefal facies continued.
By late Miocene, tectonic inversion of the southern part of the North Sarawak basin exposed the Eocene-Miocene succession on land. In contrast, continued subsidence in the north part of the basin caused the existing reefal bodies to be drowned and buried.
AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994