Relative sea-level changes and reef development in the northern Coral Triangle during the late Quaternary

The Philippines, situated at the apex of the Coral Triangle, is fringed by both modern and fossil coral reefs that preserve valuable records of Quaternary relative sea-level changes and tectonic deformation. This study presents a new interpretation of the formation of the Late Pleistocene coral reef terraces at Cape Bolinao in western Luzon, offering insights into sea-level history, reef development, and tectonic uplift within the northern Coral Triangle. Integrating high-resolution morphological analysis, new geochronological data, and reef stratigraphic numerical models, we delineate nine distinct reef terraces. The lowest terrace (∼4 m above mean sea level) dates to the mid-Holocene, while reef simulations replicating present-day terrace morphology constrain the highest terrace (∼155 m amsl) to Marine Isotope Stage (MIS) 5e, indicating a long-term uplift rate of 1.17 ± 0.03 mm/yr for Cape Bolinao. We propose a morpho-chronologic framework wherein a Late Pleistocene table reef developed on a gently sloping substrate and was progressively uplifted, leading to successive fringing reef terraces. This high uplift, coupled with observed tilting and deformation patterns, provides compelling evidence that subduction of the Scarborough Seamount Chain beneath Luzon Island exerts a primary control on localized forearc deformation along the Manila Subduction Zone. This work offers a key dataset for understanding Quaternary CRT development in the northern Coral Triangle and sheds light on how subduction-related processes have shaped the region's sea-level and coral reef records.