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The Ombilin basin is a Tertiary sedimentary and structural basin located on the crest of the Bukit Barisan Range in Central Sumatra (West Sumatra Province). The basin is well know for its Tertiary coal resources. The southern part of the basin is well exposed, while the northern part is covered by Quaternary tuffs. The exposed part of the basin is 27 km wide and 60 km long, trending in the direction of the Sumatra Trend.Present tectonics show the basin to be asymmetric, being rather gentle on its western side, presumably bounded by normal basement faults, and fairly steeply folded in the eastern part, with pre-Tertiary rocks overriding the Tertiary strata along a reverse fault, the Takung Fault. Sets of normal and strike-slip faults also dominate the basin. The Pre-Tertiary consisb of Carboniferous Limestones (Kuantan Formation), Permian volcanics (Sihngkang Formation), and Triassic sedimentary strata (Tuhur Formation) which were intruded by granites and granodiorites.Detailed geologic mapping of the Tertiary strata based strictly on lithofacies reveals interesting lateral facies relationships. A revised stratigraphic nomenclature is proposed, based on detailed measured sections to serve as stato-types. The lateral lithofacies relationships shed an interesting light on the sedimentary processes within the basin.The oldest Tertiary unit, the Sangkarewang Formation, presumably Paleocene in age (based on palynology), consists of lacustrine shales, where fish fossils have been found. Interfingering with these lacustrine shales are the conglomerates of the Brani Formation, which are shown to be alluvial fan deposits. In the northwestern part of the basin these units are overlain by the Sawahlunto Formation, which is the coal bearing measure. It consists of a sequence of shales, coals and sandstones. The sandstones show indication of lacustrine deltaic deposits. In certain areas the sandstone shows a typical pointbar sedimentary structures sequence. Palynological data suggest an Eocene age for this sequences. The Sawahlunto Formation is overlain by and presumably interfingers with the Sawahlunto Formation, which is Oligocene in age. This formation is composed of cross-bedded quartz sandstones and conglomerates, and is interpreted as having been deposited by braided river streams. The lower part (Rasau Member) still shows a typical point bar sandstone sedimentary structures sequence. In the south and eastern part of the basin the Sawahtambang Formation lies directly over the Brani Formation with a transitional sequence (Kulampi Member of the Brani Formation). The Sawahtambang Formation also shows a few coal Seams on the upper part (Poro Member).The whole sequence, about 2600 m thick, is conformably (with local erosional surface) overlain by the marine globigerina clay-mark of the Ombilin Formation (Lower Miocene), which is in turn unconformably overlain by the Quaternary tuffs of the Ranau Formation.The Paleogene cycle of sedimentation represents the initial terrestrial phase of the Tertiary sequence. It was presumably deposited in an intermontane basin, developed in the beginning of the Tertiary, when the pre-Tertiary landmass was blockfaulted into grabens. This graben-like basin was filled from all sides by alluvial fans, while several lakes existed in the middle. As the topographic relief decreased, the basin became an alluvial valley with meandering rivers and later on braided river systems, before it was folded and uplifted in Lower Miocene Time.The Ombilin basin may serve as a sedimentation model for the Lower Tertiary of Sumatra.