History of sedimentary infilling and faulting in Subic Bay, Philippines revealed in high-resolution seismic reflection profiles |
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Authors: | Ma. Edweena Joan A. Cabato Kelvin S. Rodolfo Fernando P. Siringan |
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Affiliation: | aNational Institute of Geological Sciences, University of the Philippines, Diliman QC 1101, Philippines;bDepartment of Earth and Environmental Sciences (M/C 186), University of Illinois at Chicago, 845 W Taylor Street, Chicago, IL 60607-7059, USA |
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Abstract: | Subic Bay sediments and faults identified in seismic-reflection profiles were dated using sea-level curves. The oldest sedimentary packages are marine sediments subaerially exposed and eroded 20 ka. Fluvio-marine to wholly marine sediments were deposited during the ensuing transgression, and prograding units were deposited during stillstands or minor sea-level falls. Faults within the bay have three age ranges. The oldest set cuts through the pre-δ18O Stage 2 rock units, >18 ka; a second disrupts 10.2–11.3 ka sediments; and the youngest, which cut the uppermost sedimentary package, show that movements occurred about every 2 ky, most recently about 3 ka. Northwest–southeast faults that parallel onshore structures associated with Paleogene emplacement of the Zambales Ophiolite Complex to the west and north likely represent rejuvenated tectonism. The northern coastline and north–south-trending axial bay islands appear related to a lineament that dissects Mt Pinatubo farther northeast. A breach in the caldera of Mt Natib is the most likely source of a presumed pyroclastic deposit in the eastern bay that is associated with sediments about 11.3–18 ka, indicating that a Natib eruption occurred much more recently than previously documented for this volcano. |
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