Provenance of Paleogene to Early Miocene deep-water sedimentary rocks in Sabah, northern Borneo and implications for the Proto-South China Sea subduction

The Sabah province of northern Borneo records a long-lived achieve of deep marine turbidite deposition ranging in age from the Mesozoic to the Early Miocene. Whilst the Mesozoic is poorly preserved, the Paleogene to Early Miocene deep water deposits form a relatively complete succession that was deposited along the southern margin of the Proto-South China Sea (PSCS). This comprises 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 reveal the changing provenance sources associated with the evolution of the PSCS across key stratigraphies and can be used to reconstruct its subduction history. Most analysed formations contain abundant ultra-stable heavy minerals and Mesozoic zircons which indicate multi-recycling from southern sources. However, 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. The thickest and most extensively exposed deep water sequence, the Crocker Formation in western Sabah, was deposited by two different drainage systems. The lower part of the Crocker Formation has a provenance similar to the Rajang Group in Sarawak and is interpreted as a more distal equivalent sourced by multi-recycling of Borneo and Malay Peninsula sources with some input from the Cagayan/PSCS arc. In contrast, the upper Crocker Formation has a provenance similar to the Nyalau Formation in Sarawak and is interpreted as its deeper marine continuation, sourced by sediments from the Sunda Shelf-Malay Peninsula transported in a drainage system which by-passed SW Borneo. The detrital mineralogy of parts of the Labang and Kulapis Formations suggest an extension of this Nyalau-Upper Crocker depositional system into eastern Sabah. In the Early Miocene the Palawan microcontinental fragment collided with the Cagayan Arc and finally closed the PSCS. The forearc was uplifted and mélanges preserved across eastern Sabah document this collision. The uplifted forearc was most likely the source of sediments in the Lower Miocene Temburong Formation in western Sabah, which marks the end of deep marine deposition in Sabah.