Neogene sedimentary successions in northern and central Sabah: Provenance and tectonic implications

The Paleogene of Sabah is characterized by deepmarine sedimentation on the south side of the Proto-South China Sea (PSCS), which was subducted beneath the Cagayan Arc and North Sabah. With the onset of collision and elimination of the PSCS in the Early Miocene several melanges formed, including the Kuamut Formation. Zircons from this formation indicate magmatism associated with the PSCS subduction continued after c. 21Ma. The Temburong Formation in western Sabah indicates a continuation of magmatism until c. 19.6Ma. Deep water turbidite deposition and melange formation ended, marked by the Top Crocker Unconformity (TCU). The enigmatic Tajau Member of the Kudat Formation, likely deposited during and shortly after collision, suggests a northern, Palawan, source based on immature mineral assemblages and detrital zircon spectra. The post-TCU 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. Sandstones are compositionally mature, have a mainly quartzose recycled orogenic source, and ultra-stable heavy mineral assemblages dominated by zircon, tourmaline and rutile (ZTR). The lower Neogene formations (Tanjong, Kalabakan) have substantial amounts of chrome spinel, while upper Neogene formations (Sandakan, Bongaya, Umas Umas) are almost devoid of chrome spinel and have higher contents of ZTR. This suggests a major unconformity between two Neogene sedimentation cycles. The Sikuati Member of the Kudat Formation has characteristics similar to the Tanjong Formation, suggesting it represents an equivalent to the first sedimentation cycle in north-western Sabah. Based on sandstone petrography, heavy mineral assemblages and detrital zircon ages, sediment sources were recycled Paleogene turbidite sequences with input of chrome spinel from uplifted peridotites for the first sedimentation cycle, and recycled Paleogene turbidite sequences and older Neogene fluvio-deltaic formations for the sedimentation cycle 2.