Tertiary stratigraphy and basin evolution, southern Sabah (Malaysian Borneo)

Abstract

New mapping and dating of strata in the southern part of the Central Sabah Basin in northern Borneo has made it possible to revise the lithostratigraphy and chronostratigraphy of the area. The recognition in the field of an Early Miocene regional unconformity, which may be equivalent to the Deep Regional Unconformity recognised offshore, has allowed the development of a stratigraphic framework of groups and formations, which correspond to stages in the sedimentary basin development of the area. Below the Early Miocene unconformity lies ophiolitic basement, which is overlain by an accretionary complex of Eocene age and a late Paleogene deep water succession which formed in a fore-arc basin. The late Paleogene deposits underwent syn-depositional deformation, including the development of extensive melanges, all of which can be demonstrated to lie below the unconformity in this area. Some localised limestone deposition occurred during a period of uplift and erosion in the Early Miocene, following which there was an influx of clastic sediments deposited in delta and pro-deltaic environments in the Middle Miocene. These deltaic to shallow marine deposits are now recognised as forming two coarsening-upward successions, mapped as the Tanjong and Kapilit Formations. The total thickness of these two formations in the Central Sabah Basin amounts to 6000 m, only half of the previous estimates, although the total stratigraphic thickness of Cenozoic clastic strata in Sabah may be more than 20,000 m.