Higher-than-present Holocene mean sea levels in Ilocos, Palawan and Samar, Philippines

Abstract

Holocene paleo-mean sea levels along the coasts of Ilocos, Palawan, and Samar in the Philippines are established using estimates from emerged tidal notches and coral reef terraces. Age control is provided by 17 14C and 22 230Th/ 234U dates. The notches and terraces, with the oldest dating back to approximately 8.2 ky, have elevations from 0.1 to 6.7 m above the present mean sea level. In each of the study sites, adjacent coastal areas show different paleosea-level histories in both the level and number of relative stillstands due to local faulting. In Ilocos, paleosea levels show greater elevation and number of recorded stillstands due to a significant thrust component along this segment of the Philippine Fault. In Samar, a general increase in the elevation of paleosea level to the east indicates tilting of the island towards the Philippine Fault. Abrupt changes in the elevations of correlative paleosea-level indicators and an overall northeast and southwest tilting, respectively, of northern and southern Palawan suggest the presence of active faults in central Palawan. Discrete double notches suggest two emergent stillstands occurring between 7.3 and 2.4 ky; the lower and higher notches, respectively, correspond to earlier and later stillstand events. Possible across-site variation in the duration and timing of initiation and termination of these stillstands can be due to differences in regional tectonics and crustal response to hydro-isostasy, or an artifact of sampling.