Bulletin of the Geological Society of Malaysia, Volume 43, Dec. 1999, pp. 611 - 620
Jabatan Geologi, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
Abstract: Radiolaria were found in radiolarite and tuff in the lowermost part of the Pedawan Formation in the Bau and Tubeh areas, Sarawak. Fifty-three taxa of Radiolaria were identified. These radiolarian assemblages represent latest Jurassic and earliest Cretaceous age. The occurrence of index species such as Loopus primitivus in sample B2 indicates that the age of the lower part of the chert belongs to Unitary Association Zone 12 of Baumgartner et al. (1995) early late Tithonian. The occurrence of Artocapsa (?) amphorella and Hsuum raricostatum in sample B5 suggests the age of the top part belongs to Unitary Association Zone 13 to 15, late Tithonian to Berriasian. The whole chert sequence was deposited during early late Tithonian to Berriasian. It seems there was no break in sedimentation at the Jurassic-Cretaceous boundary. The mudstone and radiolarian chert sequence was deposited in a deep marine environment. The vertical succession, from shallow marine Bau Limestone to deep water radiolarian chert suggests a transgression episode during the latest Jurassic-earliest Cretaceous time.