Philippine Journal of Science
152 (6B): 2303-2314, December 2023
ISSN 0031 – 7683
Date Received: 14 Jul 2023

Benham Bank: a Thick Carbonate Bank
on the Philippine Rise, West Pacific

Denise Faye S. Janer*, Fernando P. Siringan, and Cesar L. Villanoy

Marine Science Institute, University of the Philippines Diliman,
Quezon City, National Capital Region 1101 Philippines

*Corresponding author: dsjaner@msi.upd.edu.ph

[Part 1, Part 2]
Janer DF et al. 2023. Benham Bank: a Thick Carbonate Bank on the
Philippine Rise, West Pacific. Philipp J Sci 152(6B): 2303–2314.
https://doi.org/10.56899/152.6B.04

 

ABSTRACT

Little is known about Benham Bank, a guyot with a highly diverse coral reef ecosystem expanse. The Benham Bank is one of several seamounts in the Philippine Rise, a ~ 48-Myr ocean island basalt complex. Recently acquired high-resolution continuous seismic profiles and existing multi- beam bathymetry reveal its internal architecture, overall morphology, and history. Benham Bank is capped by at least 1300–1600-m-thick limestone that grew on top of the former Benham volcanic island, whose development varied with the lateral and vertical tectonic motions of Benham Bank in geologic time. The former Benham volcanic island underwent subsidence of at least 2400 m due to thermal cooling since its formation around 40 Myr ago. Intense denudation may have also significantly reduced the height of the Benham volcano, so that by about 5 Myr after it became inactive, the initial Benham atoll had already formed. The 1600-m minimum thickness of the carbonate sequence may have been attained about 4 Mya during the Pliocene. A warm relatively stable climate and higher sea levels during this period may have caused progradation and complete fill-up of the lagoon. Further westward migration of the Benham Bank towards the Philippine Trench positioned the bank at the crest of the topographic forebulge and led to its emergence. During this period of emergence, karstification may have reduced the carbonate cap of the Benham Bank. The present submergence of Benham Bank associated with its incipient subduction along the Philippine Trench provides vertical space for continued reef growth.