Moyra E. J. Wilson
Department of Geological Sciences, Durham University, South Road, Durham, DH1 3LE,
& SE Asia Research Group University of London

        Cenozoic carbonate production was extensive and diverse in the seas surrounding Borneo, and mirrors the variety of modern and ancient carbonate depositional systems developed throughout SE Asia. Sites of Cenozoic carbonate sedimentation in Borneo varied from mixed carbonate clastic shelves, localised and transient shoals and buildups, a variety of platform top settings to deep water slope and basinal settings. The availability of favourable conditions for carbonate sedimentation around Borneo was related to a combination of factors, including tectonic setting, the formation of large basinal areas, differential subsidence providing shallow marine areas, a tropical climate and a range of local factors, such as currents or limited clastic input.

        Paleogene carbonates developed extensively as shoals and large-scale platforms in eastern Borneo around the margins of basins bordering the Makassar Straits. These carbonates were dominated by larger benthic foraminifera and were rarely affected by subaerial exposure. Neogene carbonate sedimentation occurred in eastern and northern Borneo as large-scale platforms and numerous carbonate buildups. Neogene carbonates contain abundant corals and other aragonitic bioclasts and were often affected by subaerial exposure and leaching. Reservoir potential is best developed in Paleogene carbonates with primary intergranular porosity or secondary fracture porosity. In comparison, Neogene carbonate reservoirs are better developed with secondary biomoldic, vuggy or fracture porosity enhancing original primary porosities and permeabilities.

        An understanding of carbonate depositional environments, spatial facies relationships, and diagenesis is essential in order to develop models for these carbonates which can be used as predictive tools in the subsurface. This study also helps to evaluate tropical carbonate development in SE Asia and the evolution of sedimentary environments in Borneo during the Cenozoic.

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