Early Pleistocene origin of reefs around Lanai, Hawaii Jody M. Webster a, ⁎, David A. Clague b , Iain D.E. Faichney c , Paul D. Fullagar d , James R. Hein e , James G. Moore e , Charles K. Paull b a School of Geosciences, The University of Sydney, NSW 2006, Australia b Monterey Bay Aquarium Research Institute, Moss Landing, California, USA c School of Earth and Environmental Sciences, James Cook University, Townsville, Qld 4811, Australia d Department of Geological Sciences, University of North Carolina, NC, USA e U.S. Geological Survey, Menlo Park, CA, USA abstract article info Article history: Received 21 February 2009 Received in revised form 11 December 2009 Accepted 14 December 2009 Available online 15 January 2010 Editor: M.L. Delaney Keywords: Hawaii Lanai early Pleistocene Sr isotope stratigraphy coral reef evolution 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 87 Sr/ 86 Sr 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 87 Sr/ 86 Sr isotopic measurements on corals, coralline algae, echinoids, and bulk sediments, although lacking the precision (∼ ± 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 ∼ 1.3–0.5 Ma and are therefore about 0.5–0.8 Ma older than the corresponding reefs around the flanks 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 (∼ 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. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The origin of the deep, submerged terraces around the Hawaiian Island of Lanai is poorly understood, largely because of the lack of chronologic data. This lack of age data has contributed to controver- sies concerning the vertical motions of the southeastern Hawaiian Islands, the interpretation of subaerial coral-conglomerate deposits on Lanai and Molokai, and coral reef evolution in these islands (e.g., Stearns, 1966; Moore and Moore, 1988; Felton et al., 2000; Rubin et al., 2000; McMurtry et al., 2004; Webster et al., 2007a for a summary). Currently, little is known about the deep Lanai terraces. For example, based on prior work, it was uncertain if they are coral reefs, when they started growing, and whether the factors that influenced their initiation, growth and demise are similar to those affecting their Hawaii counterparts. Bathymetry, submersible and remotely operated vehicle (ROV) observations, and sedimentary and radiometric data now exist for a series of 12 well-developed submerged reefs preserved at water depths between 150 and 1400 m around the Island of Hawaii (Moore and Fornari, 1984; Szabo and Moore, 1986; Moore and Campbell, 1987; Moore et al., 1990b; Ludwig et al., 1991; Jones, 1995; Webster et al., 2009; Clague et al., in preparation)(Fig. 1). These reefs grew and drowned in response to rapid subsidence (2–3 m/ka; Moore and Campbell, 1987; Ludwig et al., 1991; Moore et al., 1996) associated with the continued accumulation of volcanic material on the Hawaiian Ridge and 100 ka cycles of eustatic sea-level fluctuations over the past 0.5 Ma. Recent observations and numerical reef modeling (summarized in Webster et al., 2007b; Webster et al., 2009) show that the Hawaii reefs initiate growth during stable sea- level highstands and continue growth (albeit episodically) through- out the regression, before final drowning during the major deglacia- tions. In at least one documented case (Webster et al., 2004), this drowning occurred during the early part of the last major deglacia- tion, because of abrupt eustatic sea-level rise associated with global meltwater pulse events. On the basis of their structure and morphology, the Lanai terraces have been interpreted to be submerged reefs (Campbell, 1986; Moore and Campbell, 1987; Grigg et al., 2002; Webster et al., 2007a). Campbell (1986) and Moore and Campbell (1987) used the depths of the Lanai terraces, adjusted for tilting along the Hawaiian Ridge (see Earth and Planetary Science Letters 290 (2010) 331–339 ⁎ Corresponding author. Tel.: + 61 2 9036 6538; fax: + 61 2 9351 0184. E-mail address: jody.webster@sydney.edu.au (J.M. Webster). 0012-821X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2009.12.029 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl