Early-to-Late Holocene Emerged Fossil Corals along the Negros Trench Forearc, Philippines

Corals have been used as proxies of relative sea-level (RSL) change and key inputs in refining glacial isostatic adjustment (GIA) models globally. Along subduction zones, interseismic, coseismic, and postseismic processes act as local drivers of relative sea-level changes, which can also be used to elucidate past tectonic deformation. In this study, we present new radiometric (Th-230) ages of marine-limiting sea-level proxies (i.e., emerged fossil coral reefs) along the coasts of Southwest Panay Peninsula and Nogas Island facing the Negros Trench forearc. Real-time kinematic (RTK) GNSS and drone surveys were conducted to determine the elevations relative to the tide datum and the extent of the emerged fossil coral reefs. In the Southwest Panay Peninsula, emerged fossil coral reefs were observed at 4.20 m and 3.967–4.647 m above mean low low water (amllw), with Th-230 ages of 12.44 kya and 8.65–8.82 kya BP, respectively. About 15 km from the trench forearc, Mid-Holocene emerged fossil coral reefs dated 6.37–7.55 kya BP with elevations 1.596–2.810 m amllw. Late Holocene emerged fossil coral reefs were dated 4.33–1.48 kya BP with elevations 1.256–2.280 m amllw. On the western side of Nogas Island facing the trench forearc, emerged fossil coral reef platforms dated 1.08–1.66 kya BP with elevations 1.446–1.960 m amllw. The calculated RSL of these marine-limiting sea-level indicators is generally higher compared to the ICE-6G C and ICE-7G NA sea-level curve models and other coral proxies in Southeast Asia and Palawan that have relatively low tectonic deformation activities. In this study, we highlight the spatiotemporal variability of RSL coral proxies in local scales along the trench forearc. These initial results further imply active tectonic deformation induced along the Negros Trench since the Holocene.    Keywords: fossil coral reefs, relative sea level, Holocene, Negros Trench forearc, Southwest Panay Peninsula, Nogas Island, Philippines