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

Abstract

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.