The oldest sediments in eastern Sabah are the Crocker and Kulapis Formations, of Eocene to Oligocene age. The Crocker Formation is a thick succession of generally proximal turbidites deposited in an accretionary wedge. The Kulapis is a clastic unit interpreted as lower bathyal to abyssal deposits. To the east the Kulapis interfingers with the clastic Labang Formation deposited in a large SW-NE trending basin developed partly due to loading by sediment eroded from the accretionary wedge to the north. The Labang Formation was deposited in environments ranging from shallow to deep marine. The upper Oligocene-lower Miocene Gomantong Limestone occurs as isolated outcrops in central eastern Sabah and was deposited in a range of shallow marine environments. The opening of the Sulu Sea to the east in Early Miocene times resulted in deposition of extensive melange deposits; these chaotic deposits are composed of blocks of the underlying sediments set in a scaly clay matrix.

Sabah-mapWeb (1)


Overlying the melanges are the clastic-dominated Tanjong and Sandakan Formations of Miocene age. Our work suggests these formations were deposited on an extensive shallow shelf, with sediment input from the palaeo-Kinabatangan River to the southwest rather than a series of isolated subcircular sub-basins as previously described. The Tanjong Formation is made up of wave-dominated deltaic sediments, while the Sandakan Formation was deposited in a large bay head delta. The apparent isolated nature of these formations results from bounding faults, mostly trending NNE and WNW, that may represent reactivated basement trends associated with the subduction to the northwest. To the southeast, large areas of the Dent Peninsula are made up of the Tabernak Formation; a volcaniclastic unit, and the Mio-Pliocene Ganduman and Sebahat Formations. These two formations contain thick open marine mudstones and tidally-influenced deltaic sediments. The succeeding Plio-Pleistocene Togopi Formation is a highly fossiliferous shallow marine limestone. Late Paleogene/early Neogene volcanic arc activity was contemporaneous with deposition of sediments in the Central Sabah Basin (Labang Formation of Late Oligocene/lowermost Miocene age). The location of this basin between the accretionary prism  and the volcanic arc suggests a forearc basin setting. The Labang sedimentary rocks are characterised by mass flow sedimentary facies formed in a deep water environment and they underlie the melange units with uncertain contacts. The ‘circular basins’ (Malabau Sesui, Luis and Selimpopon Basins) contain a thick succession of continental and marine clastics approaching 10 km in thickness and were the subject of a PhD thesis by Allagu Balaguru.