Characterisation and interpretation of stromatolites and thrombolites Paleo-environment in Setul Limestone succession, Langkawi and Perlis

Microbial deposits in Setul Limestone succession are represented by stromatolites, thrombolites and oncolites layers. Each microorganism exhibits physical geometries that change either from straight, wavy, parallel or network-like complex structure. The results of sedimentary logging on the limestone sequences (Lower Setul Member and Upper Setul Member) in Langgun Island and Perlis area have identified a several microbial facies such as network-like complex thrombolitic facies, parallel stromatolitic facies, compound stromatolitic facies, oncolites facies, columnar stromatolitic facies, wavy stromatolitic facies and straight stromatolitic facies. Thrombolites and parallel stromatolites, dominating in Langgun Island area prove that the growth of microbial is controlled by the strong current flow which causes active scour process in the topography of the microbial structure. On the other hand, the formation of oncolites and columnar, wavy and straight stromatolites are dominant in Perlis area. The gradual changes of microbial facies indicate that the growth of structures is controlled by the environmental depth, in which the influx of organosedimentary materials that interact with micro-organisms relies on the availability of accomodation space. In the context of the paleo-environment interpretation, it is shown that the microbial facies are deposited in shallow marine carbonate environments from subtidal to supratidal zone. The gradual changes of microbial facies distribution indicate that the limestone succession is characterised by the shallow upward sequences that is influenced by the depth of the environment, the hydrodynamic, biological and chemical processes.