Abstract

The southern edge of the Sengkang Basin, situated in the South Arm of Sulawesi, contains well exposed outcrops of algal reef limestone. Numerous discrete mound-shaped biocherms are recognised, rooted into an Upper Miocene limestone platform and covered by pelagic calcareous mudstones of Upper Miocene to Pliocene age.

The bioherms are composed mainly of filamentous calcareous algae; corals form a significant proportion of the framework only at the base. Internally, no lateral facies trends are apparent. Flanking biostromes are thick and coarsegrained at the base where corals are common, but are thin towards the crest of the bioherms. The flanks generally possess fore-reef characteristics.

During the Upper Miocene, shallow water, moderate to high energy deposition gave way to open pelagic sedimentation. During this period of continual subsidence, the algal bioherms flourished and then died. The deterioration in reef growth is attributed to gradual subsidence below the photic zone.