Early Pleistocene origin of reefs around Lanai, Hawaii

A sequence of submerged terraces (L1-L12) offshore Lanai was previously interpreted as reefal, and correlated with a similar series of reef terraces offshore Hawaii island, whose ages are known to be < 500 ka. We present bathymetric, observational, lithologic and 51 Sr-87/Sr-86 isotopic measurements for the submerged Lanai terraces ranging from -300 to -1000 m (L3-L12) that indicate that these terraces are drowned reef systems that grew in shallow coral reef to intermediate and deeper fore-reef slope settings since the early Pleistocene. Age estimates based on Sr-87/Sr-86 isotopic measurements on corals, coralline algae, echinoids, and bulk sediments, although lacking the precision (similar to +/- 0.23 Ma) to distinguish the age-depth relationship and drowning times of individual reefs, indicate that the L12-L3 reefs range in age from similar to 1.3-0.5 Ma and are therefore about 0.5-0.8 Ma older than the corresponding reefs around the Hanks of Hawaii. These new age data, despite their lack of precision and the influence of later-stage submarine diagenesis on some analyzed Corals, clearly revise the previous correlations between the reefs off Lanai and Hawaii. Soon after the end of major shield building (similar to 1.3-1.2 Ma), the Lanai reefs initiated growth and went through a period of rapid subsidence and reef drowning associated with glacial/interglacial cycles similar to that experienced by the Hawaii reefs. However, their early Pleistocene initiation means they experienced a longer, more complex growth history than their Hawaii counterparts. (C) 2009 Elsevier B.V. All rights reserved.