Emergent Marine Terraces in Cebu Island, Philippines and Their Implications for Relative Sea Level Changes in the Late Quaternary

The remarkable preservation and extensive distribution of emergent marine terraces in the Philippines allow us to study relative sea level changes and tectonic processes during the Late Quaternary. While higher uplift rates and possible prehistoric coseismic events are recorded by emergent coral reefs facing subduction zones, the central Philippine islands are reported to reflect vertical tectonic stability as they are distant from trenches. To constrain the coastal tectonics of the central Philippine region, we studied emergent sea level indicators along the coasts of northern Cebu Island in Tabuelan, San Remigio, and Bogo City. Upper steps of marine terraces were interpreted from IFSAR-derived DEMs, in which at least two and seven steps were identified along the west (Tabuelan) and east (Bogo) coasts, respectively. In Tabuelan, two extensive terrace steps (TPT) were interpreted with TPT1 at 5-13 m above mean sea level (amsl) and TPT2 at 27-44 m amsl. Five to possibly seven terrace steps (BPT) were delineated in Bogo City with elevations from lowest (BPT1) to highest (BPT7) at BPT1: 4-6 m, BPT2: 12-18 m, BPT3: 27-33 m, BPT4: 39-46 m, BPT5: 59-71 m, BPT6: 80-92 m, and BPT7: 103-108 m amsl. These upper terraces are inferred to be Late Pleistocene in age based on an initial MIS 5e age reported for a 5-m-high terrace in Mactan Island. At some sites, even lower and narrower terrace surfaces were observed, consisting of cemented coral rubble that surround eroded and attached corals. These lower carbonate steps, with elevations ranging from 1 to 3 m amsl, further provide clues on relative sea level changes and long-term tectonic deformation across Cebu Island.