Provenance of Neogene sedimentary rocks of Sabah, northern Borneo
Simon Suggate – Completed PhD
This study focuses on Neogene sedimentary rocks of the Kudat, Tanjong, Sandakan, and Bongaya Formations of Sabah, northern Borneo. The post-TCU (Top Crocker Unconformity) Neogene sedimentary rocks were deposited in fluvio-deltaic to shallow marine environments, after the Early Miocene Sabah Orogeny. This event uplifted, deformed and exposed pre-Neogene rocks.
This project has 5 major aims:
- To determine the types of sediment eroded into the Neogene basins of Sabah,
- To determine the timing and rates of sediment deposition.
- To determine the likely sediment source areas.
- To assess the relationships of the Neogene sediments, the older Paleogene sediments, and the volcanic rocks of the Dent/Semporna Peninsula.
- To develop paleogeographic maps for the north Borneo region for the Miocene.
At the start of this study very little was known about the compositional and textural maturity, heavy minerals, zircon ages, provenance and sources of the Neogene sediments of Sabah. Previous work provided good insights into the stratigraphy of Sabah. Work by van Hattum (2005) and van Hattum et al. (2006) has given a good understanding of the provenance of Paleogene sandstones of Sabah.
Results and Conclusions
- The majority of Neogene sandstones are compositionally and texturally mature, have a quartzose recycled orogenic source, and ultrastable heavy mineral assemblages dominated by zircon, tourmaline and rutile.
- An exception is the oldest member of the Kudat Formation, which is compositionally and texturally immature, has a mixed and dissected arc provenance, with heavy mineral assemblages dominated by euhedral and subhedral zircons and garnets.
- Petrographic data, garnet analyses and U-Pb geochronological studies of the sandstones indicate multiple sediment sources.
- LA-ICPMS U-Pb ages from detrital zircons reveal a spread of ages from Proterozoic to Early Miocene, with the majority being Mesozoic. The most significant clusters of ages are Cretaceous, Jurassic and Permo-Triassic.
- A new garnet compositional database is presented, compiled from the literature, to help identify the provenance of detrital garnets.
- The Rajang and Crocker Groups were the principal sources throughout the Neogene for the Tanjong and Sandakan Formations in eastern Sabah, to the offshore basins in western Sabah, and contributed to the Kudat Formation of northern Sabah.
- Sediments were derived from recycled pre-Neogene sedimentary rocks which were ultimately derived from the Schwaner Mountains and Tin Belt Granites, with some input from northern Borneo ophiolitic basement, and Cenozoic volcanic rocks.
- In contrast, during the Early Miocene, granites and metamorphic rocks of the Palawan Microcontinental Block contributed significant amounts of sediment to the oldest member of the Kudat Formation.
- The absence of volcanic material in the Miocene sediments indicates that the Lower Miocene Cagayan Volcanic Arc and the Middle to Upper Miocene Dent/Semporna Volcanic Arc were not sources of sediment.