DIAGENETIC HISTORY OF CARBONATES IN EAST SABAH

During Oligocene – Miocene, there is a major tectonic deformation which cause a
widespread of uplift followed by carbonate sedimentation (Gomantong Limestone
Formation) when the depositional environment changed from deep to shallow marine.
These onshore Gomantong Limestone formations are often isolated and only been
exposed due to plantation development and quarrying activities, which lacks in
detailed study done onto the carbonate in that area, particularly the diagenetic features.
Therefore, this study will focus on the diagenesis of Gomantong Limestone Formation
through comprehensive petrography analysis for evaluation of the fossils, mineral
structures, microfacies, cement stratigraphy and diagenetic features which is then
followed by scanning electron microscopy (SEM) analysis and X-Ray Diffraction
(XRD) analysis. The findings show that microfacies of Gomantong Limestone
formations range from wackestone to boundstone, which is dominated by benthic
foraminifera (Lepidocyclina sp. and Miogypsisna sp.) that deposited in open shelf to
shallow marine environment. Gomantong Limestone formations had mostly
undergone micritization, cementations and mechanical fracturing in shallow marine to
shallow burial diagenetic environment. However, intense cementation occurred during
the diagenesis of Gomantong Limestone results in poor potential of reservoir quality.