Submerged Shorelines on O'ahu, Hawai'i: Archive of Episodic Transgression During the Deglaciation?

• Published in: Journal of coastal research 1995-01, p.141-152
• Main Authors: Fletcher, Charles H., Sherman, Clark E.
• Format: Article
• Language: English
• Subjects: Bards; Coral reefs; Geology; Ice sheets; Part B: Holocene and Late Pleistocene Eustasy and Climate; Reefs; Sea level; Sea level rise; Shorelines; Terraces; Transgression
• ISSN: 0749-0208; 1551-5036

The shallow submerged slopes of O'ahu are characterized by a stepped topography consisting of broad, sand-covered shelves, separated by eroded paleoreef fronts that bear complexes of notches indicating periods of slow sea-level rise. Previous workers have described the location and depth of numerous submerged shoreline features but were unable to propose a history that agreed with present models of sea-level movements over the last interglacial cycle. Using correlations to the Barbados and Huon Peninsula record of reef accretion, we identify a deep shoreline complex, at a depth of ∼90 m, produced by the relatively slow rate of sea-level rise at the start of the deglaciation ∼14–16 ka. This unnamed shoreline was preserved by a rapid acceleration of sea level related to the partial collapse of the European Ice Sheet that produced melt-water pulse IA. The shallower Penguin Bank shoreline complex (pbsc), at a depth range of -49 to -67 m, was produced during a period of reduced ice-sheet melting and slow sea-level rise during the Younger Dryas cold epoch (∼11 to 13 ka). The pbsc was drowned and preserved by the sudden acceleration of sea level known as melt-water pulse IB. We also identify the Kaneohe shoreline complex (ksc) at a depth range of -24 to -34 m as the product of slow sea-level rise in the period ∼8 to 9 ka, preserved by the sudden acceleration of sea level related to the breakout of the Agassiz/Ojibway glacial-lake complex. This effectively produced an additional melt-water pulse (IC?) that was not identified in the Barbados reef accretion record. Using a correlation to the marine oxygen isotope record of Shackleton we propose an age of 79–110 ka for the ksc paleoreef and an age of 50–64 ka for the pbsc paleoreef. Continued work on this problem includes coring and dating of the ∼90 m shoreline, the pbsc, and the ksc to more fully establish the influence of antecedent reef complexes on bathymetric features and to understand the relationship between reef accretion histories and sea-level movements over the last interglacial cycle.