Depositional environments and sedimentary provenance of the Cenozoic deposits of Natuna Island, Indonesia: Implications for basin evolution in central Sundaland

The Cenozoic depositional history of central Sundaland is well known from subsurface studies of the numerous basins that litter the region, which record an Eocene to Miocene rift–inversion basin evolution. However, as is common with offshore studies, these often lack the 3D spatial observations and sedimentary provenance data required to link depositional environments, sediment pathways, and tectonic events at scale. The benefits of onshore analogue studies for understanding offshore stratigraphy are well recorded and they are of particular importance in the largely submerged area of Sundaland. Here we provide new facies analysis, sedimentary provenance data, and palaeogeographic histories for Eocene to Pleistocene sediments from Natuna Island, off the northwest coast of Borneo. Natuna Island sits atop the Natuna Arch, a structural high that straddles the East and West Natuna basins. This research records a well-preserved source-to-sink package, including an uplifted granitic basement that eroded into conglomerates and quartz-rich sandstones deposited in deltaic and paralic environments with intermittent volcanism throughout the Cenozoic. U-Pb zircon geochronology, heavy minerals, and light minerals record dominantly local sourcing with periodic influx of more diverse sources during the post-rift basin interlinkage phase (e.g., Peninsular Malaysia and West Borneo). Uplift of the Natuna Arch during two basin inversion events since the Eocene has led to the erosion of the granitic basement into a series of sandstones and overlying siltstones that now form the lowlands of the island (the Raharjapura and Pengadah formations, respectively). These onshore sediments correlate directly in both age and sedimentology with Oligocene to Pliocene successions in the West and East Natuna basins that flank the island (e.g., the Gabus, Arang, and Muda formations). These comprehensive onshore studies provide insights into larger drainage patterns and sediment transport pathways along with the linkage of basins and emergence of land at key intervals.