More information can be found in the abstracts reprinted below, from:

1. Excerpted from: Nature, vol. 408, p. 657-681 (2000).
2. Reprinted from:Geol. Soc. Abs. Prog., vol. 29 (5), p. 61 (1997).
3. Reprinted from: Trans. Amer. Geophys. U, vol. 76, p. 307 (1995).

FOSSILIFEROUS LANA'I DEPOSITS FORMED BY MULTIPLE EVENTS RATHER THAN A SINGLE GIANT TSUNAMI.

K H Rubin, CH Fletcher III and CE Sherman (Dept. of Geology and Geophysics, University of Hawaii, Honolulu, HI 96822; 808-956-8973, e-mail a reprint request for this paper: krubin@soest.hawaii.edu)

Giant tsunamis, generated by submarine landslides in the Hawaiian Islands, have been thought to be responsible for the deposition of chaotic gravels high on the southern coastal slopes of the islands of Lana'i and Moloka'i, Hawaii. Here we investigate this hypothesis, using uranium-thorium dating of the Hulopoe gravel (on Lana'i) and a study of stratigraphic relationships, such as facies changes and hiatuses, within the deposit. The Hulopoe gravel contains corals of two age groups, representing marine isotope stages 5e and 7 (,135,000 and 240,000 years ago, respectively), with signifcant geographical and stratigraphic ordering. We show that the Hulopoe gravel was formed by multiple depositional events, separated by considerable periods of time, thus invalidating the main premise of the `giant wave' hypothesis. Instead, the gravels were probably deposited during interglacial periods (when sea level was relatively high) by typical Hawaiian shoreline processes such as seasonal wave patterns, storm events and possibly `normal' tsunamis, and reached their present height by uplift of Lana'i.

WHAT DO AGES OF CORAL CLASTS IN HIGH-ENERGY SEDIMENTARY DEPOSITS TELL US ABOUT THE AGE OF THE DEPOSIT: AN EXAMPLE FROM LANAI, HAWAI'I

K H Rubin and CH Fletcher III (Dept. of Geology and Geophysics, University of Hawaii, Honolulu, HI 96822; 808-956-8973, e-mail: krubin@soest.hawaii.edu)

Reliable age-determinations for high-energy sedimentary deposits aretypically very difficult to obtain because such deposits often lack simple stratigraphy, primary (in-place) marker biota, and competent cementation. Typically, age determinations are made on clasts in these deposits with the hope that they will shed some light on the age of the deposit. We will discuss the reliability of, and potential conclusions to be drawn from, ²³⁰Th-²³⁴U-²³⁸U dating of aragonitic coral clasts from such a deposit on the island of Lanai. Issues related to the reliability of age assignments made in this manner can be grouped into (a) those associated with the determination of clast ages themselves and (b) the temporal and spatial relationship of the individual clasts to the deposit as a whole. There are many examples in the literature of the reliable application of the ²³⁰Th-²³⁴U-²³⁸U dating technique to age determinations of in-place reef deposits from their contained aragonitic corals. This is because the intial (zero-age) isotopic composition is easily constrained, the systematics allow for internal and external checks on system closure, and the isotopes of interest can be analyzed to very high precision using mass spectrometric analysis. The relationship of clast age to deposit age is more complicated, since the age of the clasts at the time of incorporation into the deposit, as well as potential post-depositional re-working within the deposit itself are hard to constrain. For this reason, a statiscal approach utilizing large numbers of clasts from a single outcrop probably provides a more reliable (but still not absolute) assesment of deposit age. Our results generally confirm the Pleistocene age of the Lanai deposit (as determined by previous workers), but indicate an older mean age and suggest that the age may increase in an upslope direction

Ages of Emerged Coral Deposits in Kapihua Gulch, Lanai, Hawaiian Islands and Speculation About Their Environment of Deposition, .

K H Rubin, C.E. Sherman and CH Fletcher III (Dept. of Geology and Geophysics, University of Hawaii, Honolulu, HI 96822; 808-956-8973, e-mail: krubin@soest.hawaii.edu)

Emerged deposits of fossil coral are widespread in the Hawaiian Islands and have been interpreted as reflecting both paleo-shorelines and deposits of large sea waves (depending on the locality). Both of these scenarios should cause predictable age relationships within a given deposit and between neighboring deposits, reflecting in some way the global sea level history for the Pacific Ocean, vertical movements of the Hawaiian Islands, and the analogous modern depositional environments. We are actively working on the chronology of one such deposit, the so-called Hulopoe Gravel (Moore and Moore, Science v226 p1312, 1994), as expressed and exposed at Kapihua Gulch, on the southern shore of the island of Lanai.

Ages are being determined using the ²³⁰Th-²³⁴U-²³⁸U technique, using the HAS-TIMS instrument at the University of Hawaii. So far, ages have been measured on 4 samples of aragonitic CaCO₃ (all with <3% calcite). 3 of these samples come from within Kapihua Gulch (at 20m, 42m and 62m above sea level) and one comes from a 10m terrace in nearby Kapihua Bay. Preliminary results indicate that this part of the Hulopoe Gravel is 173 ka to 230 ka, aging upslope through the deposit. These ages are in contrast to those reported by Moore and Moore (GSA special paper 229, p101, 1988) for a different occurrence of the Hulopoe Gravel at 115-120m in Kawaiu Gulch, Lanai (105 ka) and at 155m in Kaluakapo Crater, Lanai (134 ka). It seems evident, based on this preliminary evidence, that the Hulopoe Gravel is actually a number of similar deposits of different ages in different locations. It is still unclear from the present data whether these deposits were created in high-energy xshoreline locales or by catastrophic events, but it is clear that a single catastrophic event for the deposition of the Hulopoe Gravel as a whole is not consistent with the observed semi-regular distributions of ages in the "unit".

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