The presentation describes some fundamental issues in geology with exciting implications for plate tectonics, basin development and stratigraphic framework for the deposition of petroleum systems elements. Stratigraphy in Sarawak basin is dominated by thick and irregularly distributed siliciclastic deposits with two periods of reefal limestone growth.

Fieldwork was conducted and samples were collected for analysis in SW and NE of Sarawak. The presentation shares the insight from the work focussing on the Oligocene and Early Miocene intervals. In the Palaeogene of southern Sarawak, ‘basement’ is not basement. The transition into oil and gas bearing “Cycle I” interval (late Eocene-Oligocene) was a highly dynamic period that has been overlooked as it has only been seen in short sections in a handful of wells, and outcrops were misidentified. A review of original data and some new fieldwork has changed our over-simplistic, passive view of the rarely drilled Palaeogene across the entire Sarawak region.

In the NE of Sarawak, the early Miocene intervals were investigated. Outcrop and stratigraphic data contradict the popular plate models that have Early Miocene subduction under NW Borneo. The outcrops are of thick aggrading delta-plain sediments identified as Meligan Formation. Equivalent intervals offshore are termed ‘Stage III’, consisting of bathyal turbidites that were called ‘basement’ in earlier publications. The depositional direction was inferred to have been from SE to NW, however this does not match the outcrops. The observations and findings from the recent work points towards a need for new regional geology concept.

Combining the new insights of Palaeogene through Early Miocene tectonism, stratigraphy and general geology over the NW Borneo area gives us a new alternative view of the under-explored strata. We believe that it is in such mis-understood sedimentary systems that the next generation of oil and gas plays will occur.