Controls on isolated carbonate platform evolution and demise, Central Luconia Province, South China Sea
Numerous isolated carbonate platforms developed in the Central Luconia Province of offshore Sarawak (during Middle to Late Miocene time). Fault-bounded highs produced largely by extensional deformation and later overprinted by strike-slip deformation provided substrates for the platforms and affected their growth histories. Flooding of these structural highs at ~16.5 Ma initiated carbonate sedimentation nearly simultaneously across the area. Later, third-order sea-level fluctuations and extrinsic factors such as differential subsidence, paleowind patterns and siliciclastic influx then controlled the internal architecture of the platforms. 2-D regional seismic lines, publicdomain data and published literature were used to analyze growth patterns and demise of carbonate platforms across the study area. Five Growth Stages were recognized in the carbonate platforms based on seismic facies analysis and stratigraphic relationships between reflectors. Platforms from the southeastern part of Central Luconia are thicker and larger than platforms located toward the central and northwestern areas, which reflect greater long-term tectonic subsidence to the southeast. Additionally, northwestward prograding siliciclastic sediments from mainland Borneo caused additional flexural subsidence in the eastern part of the area and environmental deterioration for platforms located beyond the range of active siliciclastic sedimentation. Both of these factors reduced the growth potential of platforms and thus subdued carbonate development. Platform termination was regionally diachronous and was produced in two steps. The first platforms drowned (~12.5-9.7 Ma) were in the eastern parts of the study area which were affected by incoming siliciclastic sediments and high local subsidence. Platforms drowned later (~6.3-5.5 Ma) were caused by a rapid sea-level rise combined with an intense local subsidence. Carbonate accumulation rates were measured between intraplatform markers, resulting in a trend that indicates a decrease in sedimentation rate with the square root of time. Comparisons between Central Luconia carbonates and age-equivalent carbonate platforms elsewhere in East Natuna Basin showed that Central Luconia carbonate platforms were drowned earlier (latest late Miocene time) than East Natuna carbonate platforms (Early Pliocene time).