A new depositional and provenance model for the Tanjung Formation, Barito Basin, SE Kalimantan, Indonesia

The Barito Basin in southeast Kalimantan contains a thick, and well exposed Cenozoic sedimentary succession. The Tanjung Formation represents the oldest part of the succession, and was deposited in a largely terrestrial setting followed by a transgression to shallow marine deposition. The formation is well exposed along the eastern margin of the basin, and this has provided a rare opportunity to study and date the earliest stages of basin development. There has been considerable debate over the age of the formation, and most previous interpretations suggest it to be a deltaic succession. The provenance of the Tanjung Formation has never been studied. Palynomorphs and foraminifera of this study have established that the Tanjung Formation was deposited from late Middle Eocene, until the late Early Oligocene. Detailed facies and palaeocurrent analysis suggest the majority of the formation was deposited in a tidally-influenced coastal plain and estuarine setting, and sediment was transported by rivers flowing towards the north. Heavy mineral assemblages and zircon geochronology have identified the Schwaner Complex in west Borneo, the Karimunjawa Arch and the southern continuation of the Meratus Complex currently submerged under the Java Sea, as the main sediment sources of the formation.

► A new depositional and provenance model for the Tanjung Formation.
► Palynology indicates the formation is no older than Middle Eocene.
► It records fluvio-tidal coastal floodplain and estuarine deposition.
► Deposition was from rivers flowing towards the north.
► Sediment sources were the Schwaner and Meratus Complexes, and the Karimunjawa Arch and equivalents.