Sci. Rep. Kanazawa Univ.
Vol.51, p.1-13, 2007

1

Status and application of !-spectrometric 230Th/234U dating offossil corals in Ryukyus, Japan and the Philippines
Miyuki INAGAKI1, a, Keiichi SASAKI2 and Akio OMURA1
1 Department of Earth Sciences, Faculty of Science, Kanazawa University.
Kakuma−machi, Kanazawa 920−1192, Japan
2 Department of Cultural Properties and Heritage, Kanazawa Gakuin University.
Sue−machi, Kanazawa 920−1392, Japan
Abstract : High-precision !-spectrometric 230Th/234U dating was achieved by recent improvements of measurement system and chemical procedures and enabled criticalevaluation of age reliability. We review the status and application of !-spectrometric230

Th/234U dating of Pleistocene and Holocene corals to reconstruct past sea levelchanges and tectonic movements in Ryukyus, southwestern Japan and the Philippines
in the western rim of circum-Pacific island arcs. The highest terrace in Kikai Island wasformed during MIS 5c not MIS 5e that previously reported. Coral reef sediments deposited not only during MIS 5e but also during glacial periods, e.g. MIS 6 and 2, havebeen found in the Ryukyus. Coral reef sediments formed during MIS 2 were found at
ca. 120 m below present sea level off Irabu Island located at 25°
N. In addition, it was
clear that three terraces developed during MIS 5e, 5c and 5a at Pamilacan Island on thePhilippines.

1. Introduction
The 230Th/234U method of dating has been developed in the 1950s by using !spectrometry (e.g. Barnes et al., 1956) and has been advanced by the introduction of themass spectrometric techniques, such as Thermal Ionization Mass Spectrometry (TIMS ; e.
g. Edwards et al., 1987) and Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS ; e.g. Stirling et al., 2001). These mass spectrometric methods are
powerful alternatives to the classical method of counting alpha decay to measure U-series
radionuclides. The TIMS and MC-ICPMS 230Th/234U methods have succeeded to reduce
both statistical errors of ages and sizes of samples for dating. These advantages have contributed to establish detailed sea level change during the last glacial cycle from fossil reefs(e.g. Chappell et al., 1996 ; Gallup et al., 1994) and to date terrestrial climate records inspeleothems containing small amounts of uranium (e.g. Winograd et al., 1992 ; Wang etal., 2001). TIMS dating, however, has scarcely been used in Japan because of legal restrictions. Therefore, Omura et al. (1995a) developed high-resolution !-spectrometric 230Th/234U
dating techniques that maximizes the potential of the traditional counting method. Here we
present the status of the !-spectrometric 230Th/234U dating of fossil corals and its application
for studies of coral reefs and reef terraces.

2

Miyuki INAGAKI, Keiichi SASAKI and Akio OMURA

Fossil coral reefs are important as paleo-sea level indicators to unravel histories of sea
level changes and tectonic movements during the late Quaternary particularly in the western Pacific Rim. Rates and patterns of tectonic uplifts have been deduced from elevation ofreef terraces of Marine Isotope Stage (MIS) 5e in the Ryukyu and Daito Islands, southwestern Japan (e.g. Ota and Omura, 1992) and Huon Peninsula, Papua New Guinea (e.g.
Chappell and Shackleton, 1986). However, the age of the MIS 5e terraces had been confirmed by the 230Th/234U dating only in five islands, Kikai, Hateruma, Yonaguni, and Kitaand Minami-Daito Islands until the mid 1990s in Japan (Fig. 1 ; Ota and Omura, 1992 andreferences therein), because it is difficult to collect unaltered fossil corals for dating. Further, the Philippines had been left as a blank area of age data of coral reef terraces until the
1990s in the western rim of circum-Pacific island arcs. Recently, there have been a numberof studies on !-spectrometric 230Th/234U ages of reef terraces from Ryukyu Islands, Taiwan,
and the Philippines (e.g. Yamada et al., 2003 ; Yamaguchi et al., 2004 ; Omura et al.,2004). In addition, former 230Th/234U ages from Kikai Island were re-dated using highresolution !-spectrometric 230Th/234U dating. We thus summarize recent studies in Kikai Island of central Ryukyus and the Philippines, and further mention important findings from asubmerged reef western off Irabu Island, southern Ryukyus of Japan (Fig. 1).

Figure 1. (A) Map showing the location of Ryukyu Islands, Taiwan and the Philippine Islands. (B, C)
Enlarged map of Ryukyu Islands and the Philippine Islands, respectively.

2. Accuracy and precision of the !-spectrometric 230Th/234U method
The !-spectrometric method counts the numbers of alpha particles emitted from U
and Th isotopes in contrast with the mass spectrometry, which measures the abundance of
U-series radionuclides remained. Because the half-lives of 238U, 234U and 230Th are long, it isessential for reducing age errors that the radioactivity of these nuclides is measured by !spectrometry for prolonged periods. The high-resolution !-spectrometric 230Th/234U dating
has been achieved by using both enlarged sample weights (up to 10 g) and prolonged
counting time by the !-spectrometry (Omura et al., 1995a). Such measurements have been

Status and application of !-spectrometric 230Th/234U dating of fossil corals

3

reached by improvements in energy resolution and counting efficiency of the detectors.
Age errors are less than 3% in 2"range for MIS 5e corals using the recent !-counting system (e.g. Omura et al., 1995a ; Inagaki and Omura, 2006). Solitary corals can also be
dated with the same precision by using at least 2 g of samples.
Further, it has been possible to apply high-resolution !-spectrometric 230Th/234U
method to Holocene corals with age errors less than 4% (Sasaki et al., 1998 ; Ota et al.,2000). The accuracy of !-spectrometric 230Th/234U ages of Holocene corals was confirmed
by comparing with calibrated Accelerator Mass Spectrometric (AMS) 14C ages of the same
samples (Sasaki et al., 1994). Fossil corals dredged from the continental shelf off southern
Queensland, Australia, were dated to be from 11.25 to 6.36 ka by the 230Th/234U method(Sasaki et al., 1994). These ages are consistent with cal. AMS14C ages calibrated by using awell-established reservoir age of 450±35 yr (Gillespie and Polach, 1979). Thus, thismethod can be used as an effective alternative to 14C because it does not require any correction for the reservoir effects and calibration for calendar ages.
To obtain reliable 230Th/234U ages, it is essential that coral samples satisfy the prerequisite conditions ; samples should initially be free of non-radiogenic 230Th and have beenpreserved as a closed system for U and Th isotopes. After calculation of 230Th/234U ages,
their reliability was evaluated using the five-step screening method with the following criteria (Omura et al., 1995a, 2004 ; Sasaki et al., 2006) : (1) samples have no evidence of
re-crystallization of coral skeleton and/or cementation with secondary calcite or aragonite,(2) skeletal textures have not undergone changes through their diagenetic history, (3) the
sample should not contain 232Th, indicating free of initial and secondary contaminated 230Th,(4) the uranium concentration should be the same as those in the present-day counterparts,
ranging from 2 to 4 ppm, except for Acropora corals, which incorporate 3-4.5 ppm of U in
their skeletons, (5) the initial 234U/238U activity ratio should be within 1.13-1.16 in medianvalues, or should be consistent with that of the modern corals, 1.1466±0.0014 in 2"ranges.
Figure 2 shows a direct comparison of the high-resolution !-spectrometric 230Th/234U ages
with the TIMS ages of the same coral specimen. Only ages satisfying these criteria (solid
circles) are consistent with each other (Omura et al., 1995b). This supports the accuracy ofthis method even with larger errors than those of the TIMS and the validity of the five-stepscreening method.
3. Application to coral reef studies in Kikai Island
Kikai Island is characterized by the highest uplift rate, ~1.8 m/ky, in the Ryukyu Islands (e.g. Ota and Omura, 1992). The main part of the island has three major Pleistocene
terraces. The island is encircled with Holocene raised coral reef, which forms four steps ofmarine terraces (Sugihara et al., 2003, and references therein). The elevation of the highest
point in Kikai Island is 214 m on the topographic map (Fig. 3).
Many U-series dates of coral limestone in Kikai Island have been reported since the

4

Miyuki INAGAKI, Keiichi SASAKI and Akio OMURA

Figure 2. Comparison between !-spectrometric 230Th/234U and TIMS 230Th/234U dates of the same samples
collected from Huon Peninsula, Papua New Guinea (Omura et al., 1995b).
Solid and open circles represent reliable and less reliable dates based on the five step screening
method.

1970s (e.g. Konishi et al., 1974). Previous dates, however, were not so precise that reliabilities of ages could not be strictly evaluated based on the five-step screening criteria.
Here, we introduce chronologic studies in Kikai Island within the past decade since the reliability and accuracy were improved.
3.1. Dating of solitary corals
Recent studies for the Ryukyu Group composed of Pleistocene coral reef sediments
focus to distinguish each lithofacies, e.g. coral, rhodolith, detrital, and CycloclypeusOperculina limestone, as coeval components of coral reef complex and to regard one reef
complex as one stratigraphic unit based on the modern biofacies and lithofacies around
Ryukyu Islands (e.g. Iryu et al., 1992,1998 ; Tsuji, 1993). This approach permits to interpret sedimentary succession associated with sea level change. However, it was difficult toStatus and application of !-spectrometric 230Th/234U dating of fossil corals

5

Figure 3. Topographic map of Kikai Island and distribution of dated Late Pleistocene coral reef sediments.
Number in boxes means marine isotope stage. Data were derived from Omura et al . (2000),
Sasaki et al . (2004), Inagaki et al . (2005) and Inagaki and Omura (2006).

distinguish units containing detrital limestone because the depositional depth of this facies
has wide range.
Since improvements of measurement system enable to date using small amount ofsample, solitary corals can be dated accurately. The age obtained from autochthonous solitary corals indicate the depositional age of the host sediment. Thus, we can certainly distinguish units of reef complex based on high-resolution ages separately from unclear depositional depth.
Detrital limestone is extensively distributed on southwestern part of the lowest Pleistocene terrace. Omura (1983) reported that the detrital limestone was fore-reef sediments
deposited during MIS 5a based on the U-series dating of solitary corals collected from thelimestone. Inagaki et al . (2005) provided new U-series ages from solitary corals collectedfrom detrital limestone at several sites on the terrace and concluded that the detrital limestone was deposited from 93 to 56 ka, corresponding to MIS 5b to 3 (Fig. 3). The detrital

6

Miyuki INAGAKI, Keiichi SASAKI and Akio OMURA

limestone was the prograded insular shelf sediments from MIS 5b to 3.
3.2. The highest Pleistocene terrace
Previous work concluded that the highest terrace and the coral limestone distributedon the cliff between the highest and middle terraces were formed during MIS 5e and 5c, respectively (e.g. Omura, 1988). However, these results were based only on dating and were
not supported by litho- and bio-facies data.
Recent studies combining dating and litho- and biofacies observation show new information of the terrace age. Coral limestone collected from bindstone at ca. 195 m in elevation was dated as 104-97 ka, corresponding to MIS 5c (Fig. 3). This bindstone consists ofan assemblage of Porites sp., Favia speciosa, Cyphastrea sp., Goniastrea sp., Acropora
palifera (encrusting) and other hermatypic corals, indicating depositional depths of 5 − 15m (Sugihara et al., 1999 ; Sagawa et al., 2001). The age correlated with MIS 5e was obtained from only one Porites sample, which is difficult to use as a depth indicator. These
facts suggest that the highest terrace in Kikai Island was formed during MIS 5c not 5e (Inagaki and Omura, 2006). We presume that the relative sea level position during MIS 5e wassituated at a higher position not just above the top of the island based on the litho- and biofacies. The uplift rate of Kikai Island since MIS 5e was re-calculated to be 2.1-2.3 m/ky using the new terrace age of MIS 5c (Inagaki and Omura, 2006). A coral limestone dated as
MIS 6 was also found on the highest Pleistocene terrace. Exposure of MIS 5e or 6 corals is
possibly due to erosional effect during MIS 5c transgression (Inagaki and Omura, 2006).
3.3. The lowest Pleistocene terrace
Chronological studies of coral limestone on the lowest Pleistocene terrace have indicated that the coral limestone was deposited at 65-50 ka, corresponding to MIS 3 (Omura,1988). Konishi (1967) called the youngest Pleistocene coral limestone in Kikai Island as
Araki Limestone, which was dated about 45-35 ka (Konishi, 1967 ; Konishi et al., 1974 ;Omura, 1988).
During the same period, nine reef terraces were developed in Huon Peninsula (Omura
et al., 1995b ; Chappell et al., 1996). To clarify the differences between Kikai and Huon
reefs in the MIS 3, detailed stratigraphy was done using high-resolution !-spectrometric230
Th/234U dating. Newly obtained ages demonstrated offlapping sequence of five reef complexes, ages of which are ~66, ~64, ~62, ~55, and ~52 (Omura et al., 2000 ; Sasaki et al.,2004). Coral limestone deposited at ~46 and ~41 ka also distributed on the lowest Pleistocene terrace (Inagaki et al., 2005). Four of these ages, ~62, ~52, ~46 and ~41 ka, can becorrelated with the Huon terraces (Fig. 4). It was suggested that the reefs in Kikai were developed in response to the millennial scale climatic change (Sasaki et al., 2004). No Pleistocene carbonate sediments, younger than about 41 ka, are exposed on the surface of Kikai
Island (Inagaki et al., 2005).

Status and application of !-spectrometric 230Th/234U dating of fossil corals

7

Figure 4. Relative sea level curve from uplifted coral reed terraces in Huon Peninsula, Papua New
Guinea (HP) (Lambeck et al., 2002) and ages obtained from the lowest Pleistocene terrace in
Kikai Island.
Number and age of terraces are taken from Chappell et al . (1996). White and black boxes
mean the age of detrital limestone and coral limestone, respectively (Omura et al., 2002 ;Sasaki et al., 2004 ; Inagaki et al., 2005).

3.4. Holocene reef terraces
Recent studies of Holocene reefs in Kikai Island refined the timing and magnitude of
uplift events and the growth pattern of the raised reef. Sugihara et al . (2003) found that acoral species, Pocillopora verrucosa, has a peak abundance at a depth of 1.5 m and is a reliable sea level indicator in the Ryukyu area. They reconstructed relative paleo-mean sea
levels at 10.8-11.1, 8.5-8.9, 5.0-5.3, 4.0-4.3 and 1.9-2.5 m based on the distribution of P.
verrucosa. These data combined with cal. 14C and !-spectrometric 230Th/234U ages show thatthe four terraces were formed in response to repeated uplift events at 6.3, 4.1, 3.1 and 1.4
ka. Noteworthy from these results is that precisely defined magnitudes and timings basedon the calendar ages of uplift events also support the time predictable model, i.e., idea of
regularity in large earthquake recurrence (Shimazaki and Nakata, 1980). The welldeveloped raised fringing reef along the northeastern coast was investigated by drilling fivecores through the Holocene section and by dating corals with !-spectrometric 230Th/234U
method (Ota et al., 2000). The Holocene reef, which is underlain by unconsolidated PlioPleistocene mudstone, is composed of two lithologic units with a total thickness of 25.8 m

8Miyuki INAGAKI, Keiichi SASAKI and Akio OMURA

and a basal age of 9.56±0.15 ka. The upper limestone “reef” unit, which consists of atypically-zoned coral reef community, overlies a lower mixed-carbonate “bank” unit, amixture of terrestrial grains derived from the basal mudstone and limestone and Holocene
bioclastics. This growth pattern can be classified as a catch-up reef and is important to understand the development of Holocene reef terraces.
4. Coral reef terraces in the Philippine Islands
Coral reef terraces and emerged tidal notches are well developed along certain coastal
stretches of the Philippines. However, the implications of uplifted marine terraces on theregional tectonic movements have not been fully understood until recently due to the lackof age control. Since a collaborative work between Japan and the Philippines on the chronology of Late Pleistocene and Holocene coral reefs started in 1998, MIS 5e coral reef terraces have been found in Palawan (western Philippines), Cebu, Bohol and Panglao Islands(central Philippines) at 2 to >14 m, except for the case of up to 27 m in Pamilacan Island,neighboring Panglao and Bohol Islands (Fig. 1, Table 1 ; Omura et al., 2004 ; Ringor etTable 1. Elevation of the MIS 5e sea levels in the western rim of the circum-Pacific island arcs and in
tectonically stable areas in the Pacific.

Status and application of !-spectrometric 230Th/234U dating of fossil corals

9al., 2004). Elevations of these MIS 5e terraces are lower than those in other circum-Pacificisland arcs, such as the Ryukyus and Huon Peninsula (e.g. Ota and Omura, 1992 ; Chappell and Shackleton, 1986), and are rather similar to those in the stable area, such as Hawaii and western Australia (e.g. Stiring et al., 1998 ; Szabo et al., 1994) (see Table 1).
These vertical stabilities in western and central Philippenes can be observed in Holocene
reef terraces and emerged tidal notches. Maeda et al . (2004) investigated these sea level indicators in Ilocos, Palawan and Samar coupled with 14C and 230Th/234U dating to estimate local and regional tectonic uplifts (Fig. 1). Paleo-mean sea levels in Holocene are less than
2.9 m in Palawan and Samar in contrast with those of up to 6.7 m in Ilocos. The oldest age
is ~8.2 ka in the 230Th/234U method in Ilocos. Such an old age of Holocene corals above thepresent sea level can only be found in highly uplifted area, such as in Kikai (8.1 ka ; Sumi,
1999MS) and Taiwan (8.6 ka ; Yamaguchi et al., 2004). In addition to these regional
trends, differential local uplift and tilting have been revealed to be influenced by localized
tectonic activities (Maeda et al., 2004 ; Omura et al., 2004 ; Ringor et al., 2004).
Further, Ringor et al . (2004) demonstrated three successive coral reef terraces of MIS
5e, 5c and 5a developed at 20-27 m, 9-13 m, and 3-6 m, respectively, in Pamilacan Island,and succeeded to estimate paleo-sea levels during MIS 5c and 5a to be 9-11 m and 6-9 m
below present, respectively, assuming constant uplift rate of 0.18-0.21 m/kyr since MIS 5e.
These paleo-sea levels are consistent with uplift-corrected reef data from Haiti, Barbadosand Huon Peninsula (Chappell and Shackleton, 1986 ; Dodge et al., 1983 ; Gallup et al.,1994) as well as with submerged reefs from the tectonically stable Florida margin (Ludwig
et al., 1996).
5. Submerged reef off Irabu Island
Fossil reefs of the Last Glacial Maximum (LGM) period were reported only from thetropical region, such as Barbados and Tahiti (e.g. Fairbanks, 1989 ; Camoin et al., 2001).
Sasaki et al . (2006) reported the LGM coral reef from western off Irabu Island in the subtropical region of western Pacific (Fig. 1). High-resolution seismic reflection profiles delineated the distribution of mounded-shaped reflection beneath the insular shelf off Irabu
Island, the Southern Ryukyus of Japan (Obata and Tsuji, 1992). A sediment core throughone of these structures was recovered from seafloor at -118.2 m by offshore drilling by theTechnology Research Center, Japan National Oil Corporation (presently Technology andResearch Center, Japan Oil, Gas and Metals National Corporation). Lithology and the coralfauna in the core indicate that the mounded structure was composed of coral-algal boundstone, suggesting a 5-m thick coral reef. High-resolution !-spectrometric 230Th/234U dating
coupled with cal. AMS14C ages of corals indicates reliable ages ranging from 30.47±0.98 to
22.18±0.63 ka. This proves that such a submerged reef was formed during the lowstandstage of MISs 3 to 2 at 25°
N.

10

Miyuki INAGAKI, Keiichi SASAKI and Akio OMURA

Acknowledgements
We thank Dr. Cherry Ringor of the National Institute for Materials Science for criticalreading of the first draft and improving English.
References
Barnes, J. W., Lang, E. J. and Potratz, H. A. (1956) Ratio of ionium to uranium in coral limestone. Science, 142, 175-176.
Camoin, G. F., Ebren, P., Eisenhauer, A., Bard, E. and Faure, G. (2001) A 300,000-yr coral reef recordof the sea level changes, Mururoa atoll (Tuamotu archipelago, French Polynesia). Palaeogeography
Palaeoclimatology Palaeoecology, 175, 325-342.
Chappell, J. and Shackleton, N. J. (1986) Oxygen isotopes and sea level. Nature, 324, 137-140.
Chappell, J., Omura, A., Esat, T., McCulloch, M., Pandolfi, J., Ota, Y. and Pillans, B. (1996) Reconciliation of late Quaternary sea levels derived from coral terraces at Huon Peninsula with deep sea oxygen isotope records. Earth and Planetary Science Letters, 141, 227-236.
Dodge, R. E., Fairbanks, R. G., Benninger, L. K. and Maurrasse, F. (1983). Pleistocene sea levels fromraised coral reefs of Haiti. Science, 219, 1423-1425.
Edwards, R. L., Chen, J. H., Ku, T. L., Wasserburg, G. J. (1987) Precise timing of the last interglacial
period from mass spectrometric determination of Thorium-230 in corals. Science, 236, 1547-1553.
Fairbanks, R. G. (1989) A 17,000-year glacio-eustatic sea level record : influence of glacial melting
rates on the Younger Dryas event and deep-ocean circulation. Nature, 342, 637-642.
Gallup, C.D., Edwards, R.L. and Johnson, R.G. (1994). The timing of high sea levels over the past
200,000 years. Science, 263, 796-800.
Gillespie, R. and Polach, H. A. (1979) The suitability of marine shells for radiocarbon dating of Australian prehistory. Proceedings of 9th International Conference Radiocarbon Dating. (Eds.) R. Berger& H. E. Suess : 402-421, University of California Press.
Inagaki, M. and Omura, A. (2006) U-series age of the highest marine terrace of the Upper Pleistocene on
Kikai Island, central Ryukyus, Japan. The Quaternary Research (Daiyonki-Kenkyu) , 45, 41-48.
Inagaki, M., Omura, A., Yagi, H. and Kato, M. (2005) U-series ages of carbonate sediments underlying
the lowest marine terrace of the Upper Pleistocene in Kikai Island, central Ryukyus, Japan. The
Quaternary Research (Daiyonki-Kenkyu) , 44, 93-106 (in Japanese with English abstract).
Iryu, Y., Nakamori, T. and Yamada, T. (1992) A unit of lithostratigraphic classification of the Ryukyu
Group, Pleistocene reef complex deposits. Journal of the Sedimentological Society of Japan, 36, 5766.
Iryu, Y., Nakamori, T. and Yamada, T. (1998) Pleistocene reef complex deposits in the Central Ryukyus,
South-western Japan. In Camoin, G. and Davis, P.J. (eds.), Reef and Carbonate Platforms in the Pacific and Indian Oceans. 197-213, Special Publications of the International Association of Sedimentologists, 25, Blackwell Sci. Ltd., Oxford.
Konishi, K. (1967) Rate of vertical displacement and dating of reefy limestones in the marginal facies of
the Pacific Ocean −Application by natural alpha-radioactive nuclides in biogenic carbonate rocks up
to 150,000 years old-. The Quaternary Research (Daiyonki-Kenkyu) , 6, 207-223 (in Japanese with

Status and application of !-spectrometric 230Th/234U dating of fossil corals

11

English abstract).
Konishi, K., Omura, A. and Nakamichi, O. (1974) Radiometric coral ages and sea level records from thelate Quaternary reef complexes of the Ryukyu Island. Proceedings of the Second International
Coral Reef Symposium, 2, 595-613.
Lambeck, K., Esat, T.E. and Potter, K. (2002) Links between climate and sea levels for the past three
million years. Nature, 419, 199-206.
Ludwig, K. R., Muhs,D. R., Simmons, K. R., Halley, R. B. and Shinn, E. A. (1996) Sea-level records at~80 ka from tectonically stable platforms : Florida and Bermuda. Geology, 24, 211-214.
Maeda, Y., Siringan, F., Omura, A., Berdin, R., Hosono, Y., Atsumi, S. and Nakamura, T. (2004) Higher-than-present Holocene mean sea levels in Ilocos, Palawan and Samar, Philippines. Quaternary International , 115-116, 15-26.
Obata, M. and Tsuji, Y. (1992) Quaternary geohistory inferred by seismic stratigraphy of a carbonate
province in an active margin, off Miyako Island, south Ryukyus, Japan. Carbonates and Evaporites,
7, 150-65.
Omura, A. (1983) Uranium-series ages of some solitary corals from the Riukiu Limestone on the KikaiJima, Ryukyu Islands. Transactions and Proceedings of the Palaeontological Society of Japan,
New Series, no. 130, 117-122.
Omura, A. (1988) Geologic history of the Kikai Island, Central Ryukyus, Japan : Summary of uraniumseries dating of fossil corals from the Riukiu Limestone. Memoirs of the Geological Society of Japan, 29, 253-268 (in Japanese with English abstract).
Omura, A., Ise, A., Sasaki, K, Shinsaka, T. and Hasebe, Y. (1995a) Resolution and reliability of the !spectrometric 230Th/234U method for age determination. The Quaternary Research (DaiyonkiKenkyu) , 34, 195-207 (in Japanese with English abstract).
Omura, A., Chappell, J., Bloom, A.L., McCulloch, M., Esat, T., Pillans, B., Ota, Y., Sasaki, K., Nakamori, T., Matsuda, S. and Kawada, Y. (1995b) Re-evaluation of !-spectrometric 230Th/234U ages for
Late Pleistocene coral reef terraces of Huon Peninsula, Papua New Guinea. Journal of Geography(Chigaku-Zasshi) , 104, 758-776 (in Japanese with English abstract).
Omura, A., Sasaki, K., Terao, D. and Murakami, K. (2000) A chronological and sedimentary study on
the Pleistocene Series in Kikai Island, central Ryukyus, southwestern Japan. The Quaternary Research (Daiyonki-Kenkyu) , 39, 55-68 (in Japanese with English abstract).
Omura, A., Maeda, Y., Kawana, T., Siringan, F. P. and Berdin, R. D. (2004) U-series dates of Pleistocene corals and their implications to the paleo-sea levels and the vertical displacement in the Central
Philippines. Quaternary International , 115-116, 3-13.
Ota, Y. and Omura, A. (1992) Contrasting styles and rates of tectonic uplift of coral reef terraces in the
Ryukyu and Daito Islands, Southwestern Japan. Quaternary International , 15/16, 17-29.
Ota, Y., Sasaki, K., Omura, A. and Nozawa, K. (2000) Holocene sea level and tectonic history related to
the formation of coral terraces at Kikai Island, Northern Ryukyu Islands. The Quaternary Research(Daiyonki-Kenkyu) , 39, 81-95 (in Japanese with English abstract).
Ringor, C. L., Omura, A. and Maeda, Y. (2004) Last interglacial sea level changes deduced from coral
reef terraces in Southwest Bohol, Central Philippines. The Quaternary Research (Daiyonki-Kenkyu),

12

Miyuki INAGAKI, Keiichi SASAKI and Akio OMURA

43, 401-416.
Sagawa, N., Nakamori, T. and Iryu, Y. (2001) Pleistocene reef development in the southwest Ryukyu Islands, Japan. Palaeogeography, Palaeoclimatology, Palaeoecology, 175, 303-323.
Sasaki, K., Omura, A., Nakamura, T., Tsuji, Y., Matsuda, H., Honda, N., Davies, P.J. and Marshall, J.F.
(1994) Radiometric dating of submerged corals off southern Queensland, Australia. Summaries of
Researches Using AMS at Nagoya University, 5, 189-196 (in Japanese with English abstract).
Sasaki, K., Omura, A., Ota, Y., Murase, T., Azuma, T., Kobayashi, M. and Ikura, K. (1998) Holocene
regressive coral reef terraces at the northern Shidooke Coast of Kikai Island, Central Ryukyus. The
Quaternary Research (Daiyonki-Kenkyu) , 37, 349-360 (in Japanese with English abstract).
Sasaki, K., Omura, A., Murakami, K., Sagawa, N. and Nakamori, T. (2004) Interstadial coral reef terraces and relative sea-level changes during marine oxygen isotope stages 3-4, Kikai Island central
Ryukyus, Japan. Quaternary International , 120, 51-64.
Sasaki, K., Omura, A., Miwa, T., Tsuji, T., Matsuda, H., Nakamori, T., Iryu, Y., Yamada, T., Sato, Y.,
and Nakagawa, H. (2006) 230Th/234U and 14C dating of a lowstand coral reef beneath the insular shelf
off Irabu Island, Ryukyus, southwestern Japan. Island Arc, 15, 455-467.
Shimazaki, K. and Nakata, T. (1980) Time-predictable model for large earthquakes. Geophysical Research Letters, 7, 279-282.
Stirling, C.H., Esat, T.M., Lambeck, K. and McCulloch, M.T. (1998) Timing and duration of the Last Interglacial : evidence for a restricted interval of widespread coral reef growth. Earth and Planetary
Science Letters, 160, 745-762.
Stirling, C.H., Esat, T.M., Lambeck, K. and McCulloch, M.T., Blake, S.G., Lee, D.-C. and Halliday, A.
N. (2001) Orbital forcing of the marine isotope stage 9 interglacial. Science, 291, 290-293.
Sugihara, K., Iryu, Y. and Nakamori, T. (1999) Coral bleaching, geological ranges, and adaptation tohigh sea surface temperatures. Galaxea, 1, 89-95.
Sugihara, K., Nakamori, T., Iryu, Y., Sasaki, K., and Blanchon, P. (2003) Late Holocene sea-levelchanges and tectonic uplift deduced from raised reef terraces, Kikai-jima, Ryukyu Island, Japan.
Sedimentary Geology, 159, 5-25.
Sumi, K. (1999MS) When was formed the first Holocene coral reef at Kikai Island, Central Ryukyus,
Southwestern Japan. Master thesis, Kanazawa University, 78 p (in Japanese with English abstract).
Szabo, B.J., Ludwig, K.R., Muhs, D.R. and Simmons, K.R. (1994) Thorium-230 ages of corals and duration of the last interglacial sea-level high stand on Oahu, Hawaii. Science, 266, 93-96.
Tsuji, Y. (1993) Tide influences high energy environments and rhodolith-associated carbonate deposition on the outer shelf and slope off the Miyako Islands, southern Ryukyu Island Arc, Japan. Marine
Geology, 113, 225-271.
Wang, Y.J., Cheng, H., Edwards, R.L., An, Z.S., Wu, J.Y., Shen, C.-C., and Dorale, J.A. (2001) A highresolution absolute-dated late Pleistocene monsoon record from Hulu Cave, China. Science, 294,2345-2348
Winograd, I. J., Coplen, T.B., Landwehr, J. M., Riggs, A. C., Ludwig, K. R., Szabo, B. J., Kolesar, P. T.
and Revesz, K. M. (1992) Continuous 500,000-year climate record from vein calcite in Devils Hole,
Nevada. Science, 258, 255-260.

Status and application of !-spectrometric 230Th/234U dating of fossil corals

13

Yamada, S., Matsuda, H. and Omura, A. (2003) New information on uranium-series dates of fossil hermatypic corals of the Ryukyu Group in Ryukyus. Programme and Abstracts of the 33rd Annual
Meeting of the Japan Association for Quaternary Research, 52-53 (in Japanese).
Yamaguchi, M., Ota, Y., Omura, A. and Nakamura, T. (2004) Local marine reservoir effects and climatechanges deduced from !-spectrometric 230Th/234U and AMS14C dates of Holocene fossil corals collected from Taiwan. The Quaternary Research (Daiyonki-Kenkyu) , 43, 181-188 (in Japanese withEnglish abstract).