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Comparing and Contrasting Controls on Sediment Patterns in Contemporary Isolated Carbonate Platforms as Analogs for Ancient Examples – Case Studies From South East Asia


South East Asia contains a wide range of carbonate settings ranging from coastal barrier reefs to isolated carbonate platforms; nurtured by clear tropical waters conducive to extensive coral growth and associated production of carbonate sediments. Unique to the region is the occurrence of the East Asian Monsoon, which seasonally reverses atmospheric and ocean surface circulation in the region. This study focused on the responses of sedimentation patterns in carbonate platforms to dominant wave and current directions and to seasonal shifts in ocean surface circulation, using examples within the Spratly Islands and comparing those with the Semporna Archipelago. Using Google Earth imagery supplemented with bathymetry and historical climate data, two ocean surface circulation indicators (wave shadows and wave breakers) and two reef facies classes (dominant reef crests and reef sand aprons), were mapped and quantitatively evaluated. Trends in the orientation of marine facies classes were analyzed in relation to the orientation of surface-water movement indicators. The marine facies classes were found to preferentially align with the surface circulation indicators: thicker reef crests develop where more breaking waves are observed, whereas sand aprons tended to align with the direction of wave shadows. A bimodal and a unimodal distribution of marine facies class orientations were found for the Spratly Islands and Semporna Archipelago respectively. Within the bimodal distribution of the Spratly islands, a moderate asymmetry which correlates with the stronger northeasterly winds associated with the winter East Asian Monsoon season was observed. The uni-modal sediment pattern trend in the Semporna archipelago suggests a strong surface-circulation control relative to other factors in this region; sheltered by the island of Borneo, the archipelago experiences a mostly unidirectional surface-water movement throughout the year despite the East Asian Monsoon. These findings from the contemporary South China and Celebes Sea were then applied to the subsurface carbonate platforms of Central Luconia in order to improve reservoir architecture and facies pattern prediction.