Late Quaternary uplift across northwest Luzon Island, Philippines constrained from emergent coral reef terraces

Abstract

Emergent coral reef terraces in northwest Luzon Island, Philippines are studied to understand relative sea level (RSL) changes and uplift along the Manila Trench forearc region during the Late Quaternary. Coral reef sequences in Currimao, Badoc, and Badoc Island were mapped and were described based on geomorphological characteristics, elevation patterns, and ages. The lower emergent coral reef terraces, which are dated Holocene, are subdivided into three to possibly four terrace steps (TI–TIV in ascending order) with the highest terrace (TIII–TIV) rising up to ~7–9 m amsl. The well‐preserved staircase morphology and meter‐scale terrace risers possibly imply episodes of abrupt RSL changes that resulted from coseismic uplift during the mid‐Holocene. Around 6.8 kyr BP, ~3 m of rapid uplift (possibly coseismic) is inferred to account for the vertical separation of TI (6.2 kyr BP at 3.5 m amsl) and TII (6.8 kyr BP at 6.6 m amsl) in Currimao site. A subsequent episode of RSL fall occurred at 6 kyr BP, based on dated coral samples, and has emerged the lowest terraces in the study sites. New geomorphic and radiometric data suggest that the mid‐Holocene sea level highstand in northwest Luzon occurred at around 7–6 kyr BP. From the elevation and thorium‐230 age of dated terrace surfaces, we estimated Holocene uplift rates from 0.17 ± 0.12 to 0.82 ± 0.15 mm/yr across the three study sites. The estimated uplift rates of northwest Luzon are relatively lower than the uplift rates reported in similar tectonically active regions of the west Pacific such as Papua New Guinea, Taiwan, New Zealand, and Japan. The geomorphological characteristics and age of emergent coral reef terraces reported in this study offer insights on the preservation of long‐term deformation along the northwest Luzon coastal plain that is bordered by a subduction zone and upper‐plate faults. © 2018 John Wiley & Sons, Ltd.

A standardized database of Last Interglacial (MIS 5e) sea-level indicators in Southeast Asia

“…Most of the studies on LIG sea-level indicators in Southeast Asia aim to estimate long-term uplift rates and constrain vertical land movements using uplifted coral reef terraces (e.g., Chappell and Veeh, 1978;Merritts et al, 1998;Major et al, 2013;Pedoja et al, 2018). Some studies discuss LIG sea levels alongside tectonic uplift derived from these raised coral terraces (e.g., Omura et al, 2004;Ringor et al, 2004;Bard et al, 1996).…”

“…In Semau Island, we extracted two RSL data points from the coral reef terraces studied by Merritts et al (1998) and Jouannic et al (1988). In Cape Oeloimi, situated on the southeast coast of the island, a reef terrace dated MIS 5e is reported by Jouannic et al (1988), while in Aikalui Point, located on the north coast of the island, a low emergent reef is dated MIS 5a by Merritts et al (1998). The point represents a paleo-RSL at 8.4 ± 1.3 m (WALIS RSL ID 3615) and is dated to MIS 5e.…”

“…The rocky coastlines of the Philippines are mostly fringed by coral reef terraces. The sea-level indicators in the Philippines (coral reef terraces and tidal notches) were generally examined to constrain Holocene paleo-sea level (e.g., Shen et al, 2010) and derive tectonic uplift rates (e.g., Ramos and Tsutsumi, 2010;Maxwell et al, 2018). Three studies report on the elevations of LIG sea-level indicators and provide coral ages (Omura et al, 2004;Ringor et al, 2004;Maxwell et al, 2018).…”

A standardized database of Last interglacial (MIS 5e) sea-level indicators in Southeast Asia

“…The sea-level indicators in the Philippines (coral reef terraces and tidal notches) were generally examined to constrain Holocene paleo sea level (e.g., Shen et al, 2010) and derive tectonic uplift rates (e.g., Ramos and Tsutsumi, 2010;Maxwell et al, 2018). Three studies report on the elevations of LIG sea-level indicators and provide coral ages (Omura et al, 2004;Ringor et al, 2004;Maxwell et al, 2018). Geomorphic mapping of the raised coral reef terraces in west Luzon by Maemoku and Paladio (1992) lacks radiometric age constraints and was not included in the WALIS database.…”

“…In Ilocos Norte, northwest Luzon, Maxwell et al (2018) recognized Late Pleistocene coral reef terraces. At one particular site, in Currimao, four coral samples yielded less reliable ages (108-198 ka, WALIS U-Series ID 2049, 2050, 2051, 2052 not being precise, these ages provide evidence for an MIS5e terrace in Currimao, Ilocos Norte (Maxwell et al, 2018). For this site, we inserted one RSL data point, with RSL calculated at 30.2±5.5 m (WALIS RSL ID 1339).…”