Quantifying Multi-Source Sediment Supply in a Tropical Foreland Basin (Oligocene-Miocene Nyalau Formation, Borneo)

Abstract

Petrographic, mineralogical and geochemical analyses and 803 published detrital zircon U–Pb ages are here integrated to provide the first quantitative provenance analysis of the Oligocene-Miocene Nyalau Formation in the Sarawak Basin foreland basin, northwest Borneo. Statistical unmixing reveals that simple two-source models are insufficient: three distinct sources contributed sediment—the Malay-Thai Peninsula (58%), the Rajang fold-thrust belt (31%) and a previously unrecognised component (11%) characterised by syn-depositional Oligocene-Miocene volcanic zircons and Neoproterozoic populations absent from the other two established sources. This third source represents contemporaneous magmatic input plus recycled cratonic material from unexposed Bornean basement. Long-distance axial drainage from the Malay-Thai Peninsula dominated over proximal orogenic input from the Rajang fold-thrust belt. Compositional variations record coupled tectonic-climatic controls: quartz-rich intervals with high ZTR indices reflect extensive recycling coupled with prolonged weathering, whereas lithic-rich intervals indicate enhanced transverse input plausibly modulated by relative sea-level and monsoonal discharge variability. This quantitative three-source framework demonstrates that statistical provenance unmixing can reveal cryptic sediment contributors missed by binary mixing models, providing critical insights into tropical foreland basin evolution during major Oligocene-Miocene geodynamic reorganisation.