The thesis is about heterolithic sequence in Lambir formation at Miri, Sarawak. A range of thinly interbedded (milimeter-decimeter scale) sandstones and mudstones, characterizes the sequence. The study is conducted to further characterize the heterolithic facies and sedimentary structures in the locality in further detail due to lack of information available and can be used to interpret and gain further knowledge of palaeo-environment, diagenesis, and compositional variation of a certain facies. The main objective of this study is to describe the spatial and temporal variability in the tidal flats facies in the Lambir formation since seismic survey cannot detect heterolithic sequences and sedimentary microstructures.