An abrupt backreef infilling in a Holocene reef, Paraoir, Northwestern Luzon, Philippines |
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Authors: | Shou-Yeh Gong Tso-Ren Wu Fernando P Siringan Ke Lin Chuan-Chou Shen |
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Institution: | 1. Department of Geology, National Museum of Natural Science, Taichung, 40419, Taiwan, ROC 2. Institute of Hydrological and Oceanic Sciences, National Central University, Jhongli City, 32001, Taiwan, ROC 3. Marine Science Institute, University of Philippines, 1101, Quezon City, Philippines 4. High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617, Taiwan, ROC
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Abstract: | We describe a sudden backreef infilling at the west coast of Luzon, Philippines, which occurred after 324 ± 12 yr ago (year BP, before 1950 AD). Results of 30 230Th-dated fossil corals from the surface and 5 cores, 17–29.1 m in length, recovered from a Holocene reef at Paraoir show that the reef flat developed in two stages. The reef margin is dated at 10,256 ± 50 (2σ) yr BP at 23.9 m below mean sea level (MSL) and about 6,654 ± 29 yr BP at 3.7 m below MSL with ages increasing with depth. The reef flat was formed with sediments of 818–324 yr BP old, which do not follow an age–depth correlation. The evidence suggests that a backreef moat remained empty throughout the buildup of the reef for about 6 kyr and was filled abruptly with a 26-m-thick succession of rubble and bioclastics by an extreme wave event (EWE) after 324 ± 12 yr BP. Field evidence, historical records, and tsunami simulation suggest the EWE sedimentation was likely caused by a single severe tropical cyclone, although the possibility of tsunami is not ruled out. The Paraoir reef flat was built up in a mode different from previously reported cases of Holocene reefs. |
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