Evolution of Paleogene to Early Miocene deep-water provenance sources in Sabah, northern Borneo reveals changing Proto-South China Sea paleogeography

Most of Sabah in northern Borneo is covered with Paleogene to Lower Miocene deep marine turbidite sequences that were deposited along the southern side of the Proto-South China Sea (PSCS). They include the Sapulut and Trusmadi formations of central-south Sabah, the Labang and Kulapis formations of eastern Sabah, the Kudat Formation of NW Sabah and the Crocker Formation of western Sabah. Sandstone petrography, heavy mineral analysis and detrital zircon U-Pb geochronology reveals changing sources associated with the evolution of the PSCS. Volcanic lithic fragments in some Labang Formation samples and Middle Eocene zircons in a lower Crocker Formation sample, as well as unstable heavy minerals such as apatite and epidote indicate input from contemporaneous volcanism, likely derived from the PSCS subduction arc to the north. By contrast, abundant ultra-stable heavy minerals and Mesozoic zircons indicate multi-recycling from southern sources. Changes in provenance are seen across key stratigraphies. The lower part of the Crocker Formation has similar provenance as the Rajang Group in Sarawak and is interpreted as a more distal equivalent. While the upper Crocker Formation has a similar provenance as the Nyalau Formation in Sarawak and is interpreted as its deeper marine continuation. Parts of the Labang and Kulapis formations suggest an extension of this depositional system into eastern Sabah. In the Early Miocene the Palawan microcontinental fragment collided with the Cagayan Arc, resulting in uplift of a forearc high and formation of mélanges in eastern Sabah. The uplifted forearc was most likely the provenance source for the Temburong Formation in western Sabah. • Turbidites in Sabah show a mix of multi-recycled and fresh volcanic sources. • Middle Eocene zircons show volcanic activity related to Proto-South China Sea (PSCS) subduction. • PSCS subduction initiated at least in the E. to M. Eocene and continued until the E. Miocene. • Unstable heavy minerals indicate input from contemporaneous active arc volcanism. • Drainage shifts were related to tectonic evolution of PSCS and uplift phases in Borneo.