- Email: [email protected]
ESR dating of corals
Quaternary Science Reviews, Vol. 7, pp. 465-470, 1988. Printed in Great Britain. All rights reserved.
0277-3791/88 $0.00 + .50 Copyright© 1988 Pergamon Press plc
ESR DATING OF CORALS Ulrich R a d t k e * and Rainer GriJnt
* Geographisches Institut, Universitiit D~seldorf, Universitiitsstrasse, D-4000 Diisseldorf, F.R.G. t Department of Geology, McMaster University, Hamilton, Ontario L8S 4M1, Canada
The ages of 24 coral samples from Barbados and the New Hebrides were determined simultaneously by ESR and another independent dating method (a- and MS-U-series and 14C). All parameters for ESR dating were determined, without crosscalibration, with another dating method (including thermal stability and effective c~-efficiency). The results show a relatively good concordance. Furthermore, a systematic ESR dating study on the reef tracts of Barbados (83 samples) revealed satisfactory agreement between ESR and U-series data whereas previously published He/U data seemed to show open system behaviour. The thermal stability of the ESR signal at g = 2.0007 (_+0.0002) estimated to be in the range of 500 ka does not seem to have an apparent influence on the ESR results.
INTRODUCTION Coral growth is dependent on various parameters such as water temperature, salinity and purity. Optimal conditions for reef-building occurs between about 30°N and 30°S in water depths down to 50 m, although some other species are able to live in more northern latitudes and at greater depths. Absolute dating of corals is of interest for paleoclimatic and paleosea-level investigations (see, for example, Bloom et al., 1974; Harmon et al., 1981, 1983; Radtke, 1987). The first applications of ESR dating on corals were carried out on sites in Southern Japan (Ikeya and Ohmura, 1983; Ikeya, 1983; Koba et al., 1985) followed by studies on Haitian corals (Skinner, 1985, 1986). This paper presents the dating results of 24 coral samples each of which were dated by ESR and at least one other independent dating method (U-series, 14C). Additionally, the results of a systematic ESR dating study on the reef tracts of Barbados are summarized (for details see Radtke et al., 1988). The U-series and taC-results from the New Hebrides were kindly provided by A.L. Bloom and are published elsewhere (Bloom et al., 1978; Jouannic et al., 1980; Edwards et al., 1987b). The U-series results on the corals from Barbados were determined following the McMaster routine analysis (see, for example, Gascoyne et al., 1978). ESR DATING The details of ESR dating are described elsewhere (see, for example, Ikeya, 1978; Hennig and Grtin, 1983; Griin, 1985a, 1988). An ESR age is determined from the relationship: t
AD =
/ D(t) dt
0
#Present address: Subdepartment of Quaternary Research, University of Cambridge, Free School Lane, Cambridge CB2 3RS, U.K.
where the accumulated dose (AD) is the total radiation dose that the sample acquired since the time of its formation. The dose rate D is generated by the radioactive elements U, Th, and K in the sample (internal dose rate) and its surroundings (external dose rate) plus cosmic rays.
Determination of Accumulated Dose A D The AD is determined via ESR spectroscopy by the additive dose method (see, for example, Aitken, 1985): aliquots of the sample are irradiated stepwise with defined ~- or [3-doses and the extrapolation towards zero ESR-intensity allows the determination of AD (see Fig. 2). All samples were taken from corals which were still in their living position; apparent recrystallization zones were avoided. The following species were collected:
Acropora palmata, Acropora cervicornis, Montastrea annularis, Montastrea cavernosa, Siderastrea siderea, Diploria strigosa, Stephanocoenia michelini, Platygyra lamellina, Leptoria phrygia, Oulophyllia crispa, Porites lutea, Acropora humilis, and Montipora sp. Samples were ground and 7-9 aliquots of a sieve fraction of 200-100 ~m were successively irradiated with defined "V- and f3-doses (25, 50, 75, 100, 125, 150, 175, and 200 Gy). In case the AD was above 200 Gy, the sample was reirradiated up to 1000 Gy. The ESR spectra were recorded with a Bruker 200 tt ESR spectrometer at a frequency of about 9.5 GHz and a magnetic field strength of about 340 mT. The microwave power was 4 mW, the modulation amplitude 0.1 mTpp, and the scan time in the range of 1 mT min- i. Figure 1 shows an ESR spectrum typical of that observed on all samples. It is different from that reported by Skinner (1985, 1986) who observed a spectrum similar to that which is common for aragonitic mollusc shells (Radtke et al., 1985). As can be seen in Fig. 1, two ESR peaks (at g = 2.0007 and g = 2.0036) show enhancement upon artificial radiation, whereas
465
466
U. Radtke and R. Griin
: "';
/
I
I
2.01
f
2.005
2.0
'
'
'
'
I
g-Value
FIG. 1. ESR spectrum of a Pleistocene coral: solid line = non-irradiated; dotted line = irradiated. .,,,.
A.'recent coral
g,
"f
B: B-To j
,,e
•
o~
-;'o
o
J
/
I S
ADL/N 5o
ioor-dos tffyj
-100 -50 '
I
.-ADLod I:~ULI N
0
bo ioo r-'dos {Gyl
-~ I
FIG. 2. ESR signal growth upon artificial ~-irradiation. ADLIN: AD estimated through linear extrapolation (solid line); ADLoG: AD estimated by logarithmic extrapolation (dotted line).
the signal at g = 2.0058 is nearly insensitive to ~/irradiation; however, this line is not present in recent samples and cannot be generated by artificial ~/- or 13irradiation in recent samples. The ADs derived from the peak at g = 2.0036 were invariably smaller than the ADs from g = 2.0007, which is probably due to the lower thermal stability of the former peak. Therefore, the signal at g = 2.0007 was used for our investigation. ADs based on this peak show no change on grinding or light exposure. The thermal stability of this peak was estimated by isothermal annealing at three temperatures (220, 160, and 120°C) using an Arrhenius plot
(Hennig and Griin, 1983) giving a mean-life in the range of 500 ka at the present average annual temperature of 26°C on Barbados (the signal at g = 2.0036 has a mean life in the range of 100 ka at 26°C). Such mean life determinations have, however, very large uncertainties (they may be three times smaller or larger; see Debenham, 1983; Griin, 1985b). The samples were routinely checked for recrystallization from aragonite to calcite by X R D analysis. All but 2 samples (of 91) showed saturation effects which can occur even at low artificial ~/-doses (see Fig. 2). Therefore, a logarithmic extrapolation [plotting
467
ESR Dating of Corals
-In(1 - I//max) VS. 7-dose (Apers et al., 1981)] was used for AD determination. /max w a s determined iteratively.
Determination of Dose Rate D The dose rate was derived from the analysis, by INAA or a-spectrometry, of U in the <100 Ixm sieve fraction of each sample and using the conversion factors from Nambi and Aitken (1986). The 232Th and K-concentrations in the samples were negligible. Skinner (1986) reports that Rn-loss in corals is also negligible• Figure 3 (top) shows that the U-concentration is not dependent on the age of the samples• This supports the results of Swart and Hubbard (1982), i.e. U is accumulated at the time of, or shortly after, the death of the coral organism. The effective c~-efficiency was determined with a 24tAm a-source on five samples yielding a value of 0.06 + 0.01 which was used in all age calculations. This value might still contain some uncertainty, since Lyons (1987) found that the effective a-efficiency of the Udecay chains might be 20-30% higher than the value determined by a monoenergetic a-source (of 4.1 MeV). U-series disequilibria were taken into account by use of formulas given by GriJn et al. (1987). Cosmic dose rates were determined using the graphs of Prescott and Stephan (1982). A peculiarity in ESR dating of corals is that the coral stock is more or less an infinite medium for gamma-rays. Since the U-distribution in corals is rather homogeneous, U-series disequilibria have to also be taken into account in calculating the natural 7-dose. Additionally, in situ gamma dose measurements were carried out on Barbados. In case the measured "y-dose rate was larger than the internal 7-dose rate at the estimated age of the sample (which might be due to additional irradiation by
soils etc.), this difference was added to the cosmic dose rate. For the samples from the New Hebrides, no in situ ~-measurements were carried out and the burial depths were not available; therefore, a cosmic dose rate of 180 ~Gy/year was assumed in all cases. Ages were calculated using the computer program ESR-DATA. RESULTS
Figure 4 and Table 1 shows the U-series and ESR results• The analytical data of U-series and 1 4 C a r e given elsewhere (Edwards et al., 1987b; Bloom et al., 1978; Radtke et at., 1987)• The listed internal dose rates are mean values over time. There is relatively good agreement, although the ESR data have the tendency to be slightly older than the U-series ages. The laboratory uncertainty of an ESR result on corals is mainly due to the uncertainty in AD determination, which is in the range of 10 to 20%; however, this is only an estimate since we do not yet have a mathematical treatment available to calculate the confidence interval of a single AD determination• Therefore, we prefer to compare the mean ages (with standard deviation) of repeated analyses. Table 2 and Fig. 5 compares the ESR data from Barbados (for details see Radtke et al., 1987) with Useries and U/He results published earlier (Mesolella et al., 1969; Bender et al., 1979). The geological units in Table 2 are arranged approximately according to their geomorphological sequence• The mean ages in Fig. 5 were calculated from the mean ages of repeated analyses on the geological unit; in the case of single age data, the error bars for ESR were assumed to be 10%; the errors for the U-series dates were taken from the original publication; and for He/U, from Fig. 9 in Bender et al. (1979). DISCUSSION
0 0 a
The study of Radtke et al. (1988) shows that recrystallization seems to have only a limited effect on the ESR results: samples with aragonite concentrations down to 60% did not show a trend towards younger ages compared to samples with concentrations of 95-100%. Samples with aragonite concentrations as low as 20% showed a severe underestimation of AD.
0
3
0 00,
oo~O
0 0 ~ 0o0°°°o o
2
°°o°
o o
•
o
1 0 100 -
CORAL o
o
o
"~.
~ 400.
o
,/ I"
•
•
•
~m 300. t~ 200.
/
•
I."
100. 0t
o
zi~o
~bo
6bo
Esh-,,go'tka;
FIG. 3. U-concentration (top) and aragonite contents (below) vs ESR ages of corals from Barbados.
o
lbo 2oo 3bo ~oo O-series age{kal
FIG. 4. Mean ESR vs mean U-series ages (for data see Table 1). Dotted lines give a 20% uncertainty interval.
468
U. Radtke and R. Griin TABLE 1. Age results on corals from the New Hebrides and Barbados which were investigated by at least two methods Ages (years)
Sample no.
U (ppm)
AD (Gy)
Int. D (~Gy/year)
Ext. D 0,Gy/year)
ESR
a-Th/U
New Hebrides E.AD.2 M.G.3 M.G.4 S.AC. 1 S.D.2 E.L.3 E.T.2 S.D. 1
2.95 2.76 2.58 2.37 3.58 2.43 2.09 3.44
4.2 41.9 42.6 3.2 32.1 102.0 79.1 32.7
336.8 523.7 474.2 266.4 594.3 625.9 515.3 579.4
180 180 180 180 180 180 180 180
8170 59,700 65,200 7200 41,600 127,000 114,000 43,200
6800 55,000 57,000 5700 37,000 141,000 141,000 38,000
Barbados B-4a B -5a B-7a B-59a B-64-I
2.80 2.95 3.33 3.30 2.00
63.9 88.5 103.9 114.8 67.8
586.8 670.2 806.2 797.8 459.1
250 280 150 250 250
76,600 93,300 109,400 109,000 95,800
B-64-Illa
2.11
360.3
783.2
120
399,000
B-64-V B-64-VII B-65-IIa B-65-IIIa B-65-IIic B-65-IVa/2 B-65-IVb/1 B-65-IVb/2 B-65-IVb/3 B-66
1.67 2.25 2.10 1.91 2.12 3.38 2.73 3.08 2.89 3.50
754.3 1065.4 75.0 382.0 n.d. n.d. 193.2 151.9 180.3 176.0
684.0 923.8 540.4 734.3 --816.2 834.2 835.3 962.0
250 250 50 50 --210 210 210 210
808,000 908,000 127,000 487,000 --188,000 145,000 172,000 150,000
66,700 70,300 72,900 100,000 66,500 83,700 220,000 >350,000 >350,000 >350,000 130,000 >350,000 >350,000 97,700 106,900 106,200 147,600 127,000
MS-Th/U -----125,000 129,900 --
6350 5940
m
h
m
B
m
m
m
m
m
.
m
m
m
n.d. = not determined due to large scattering of data points. TABLE 2. Average age results on the reef tracts on Barbados Age (ka) Geologic unit Worthing (W) Ventnor (V) Rendezvous Hill (R) Kendal Hill (K) Durants (D) Kingsland/Aberdare (K/A) Adam's Castle (A) Thorpe (T) Rowans (Ro) Husbands (Hu) Kent (Ke) Lodge (L) St. David (S) Cottage Vale (C) Second High Cliff (SH) Hill View (H)
ESR ~ 92 110 136 228 223 222 286 321 310 380 433 477 625 585 425 405
Th/U 2
4- 15 (16) 4- 15 (8) 4- 15 (13) + 12 (2) ± 17 (3) 4- 27 (4) _+ 28 (2) ± 27 (3) (1) ± 36 (2) (1) (1) (1) (1) (1) ± 36 (2)
82 105 126 221 207 235 >180 220 >350
± ± ± ± ± ±
Corr. He/U 3
2 4 2 65 14 33
(4) (4) (10) (4) (3) (7) (4) ± 25 (1) (1)
180 110 207 235 215 300 320 327 360 283 490 450 515
± 10 (3) (1) ± 15 (3) ± 34 (4) ± 6 (2) ± 8 (4) (1) ± 15 (3) (1) ± 46 (3) (1) ± 10 (2) ± 5 (2)
(1) = data from Radtke et al. (1988). (2) = data from Mesolella et al. (1969), Bender et al. (1979) and Fairbanks (1977). Letters in brackets: abbreviations used in Fig. 5. Numbers in brackets: numbers of analyses used for averaging and standard deviation.
A s s h o w n in Fig. 3 it s h o u l d b e p o s s i b l e to c o l l e c t n o n r e c r y s t a l l i z e d s a m p l e s u p to at l e a s t 1 M a . T h e o l d e s t s a m p l e s o f this s t u d y ( s e e T a b l e 1: B - 6 4 - V a n d B - 6 4 V I I ) still h a d a r a g o n i t e c o n c e n t r a t i o n s o f 1 0 0 % a n d 6 0 % . H o w e v e r , w h e t h e r this f i n d i n g c a n s t a n d a d e t a i l e d i n v e s t i g a t i o n is q u e s t i o n a b l e since this rec r y s t a l l i z a t i o n p r o c e s s is a c c o m p a n i e d by U - m i g r a t i o n ( K a u f m a n , 1986). T h e r e f o r e , s a m p l e s w i t h a r a g o n i t e concentrations of lower than 95% must be avoided.
T h e a n n e a l i n g s t u d y y i e l d e d a v a l u e f o r t h e m e a n life "r o f a b o u t 500 k a f o r t h e p r e s e n t a v e r a g e a n n u a l temperature on Barbados (26°C). T h e m e a n life c o n t r o l s t h e A D a c c o r d i n g to ( D e b u y s t e t a l . , 1984): A D = D "r [1 - e x p ( - t / - r ) ] i.e. w h e n a s s u m i n g -r = 500 k a t h e n at 100 k a an E S R a g e w o u l d b e a n u n d e r e s t i m a t i o n o f 1 0 % (10 k a ) ; at
469
ESR Dating of Corals
.... i¸¸ 400 300
Xt'::
200 100
0'" 0
100
2O0
30o
~oo 0
Th/U uge[ko]
100
200
300
~oo
500
He/U uge[ko]
FIG. 5. Left: average ESR ages (from Radtke et al., 1988) vs average U-series ages (from Mesolella et al., 1969; Bender et al., 1979) on the geological units on Barbados (see Table 2). Right: average ESR ages vs average He/U-ages (from Bender et al., 1979) on the reef tracts on Barbados. For abbreviations see Table 2.
250 ka about 20% (50 ka); and at 500 ka about 37% (184 ka). In case the steady state level (for an infinite number of traps) is well below saturation level, the maximum age observable is the mean life of the particular center (otherwise the maximum age is lower than "r). The oldest calculated ages were around 800 to 900 ka. Coral reef growth on Barbados is indeed supposed to have started in this age range (700 ka: Mesolella et al., 1969). Additionally, all comparisons with other dating methods show no trend of ESR underestimations. Therefore, the estimated low stability does not seem to have any impact on the calculated ages. Whether this is due to the overall uncertainty of the mean life evaluation method (as mentioned above) or the general validity of those plots is uncertain. The comparison of ESR with U-series data (Table 2 and Figs 4 and 5) shows a satisfactory concordance except for the Thorpe (T) terrace whose ESR age suggests a formation during stage 9 whereas the Useries result indicates stage 7 age. The ESR ages seem to have a slight tendency towards older ages. However, this does not necessarily mean that the U-series analysis yielded the correct age: e.g. sample B5-a was collected from the Worthington (W) terrace which is supposed to be 82 ka old (Barbados I or stage 5a). ESR gives an age which is about 11 ka too old, whereas the U-series result is about 12 ka too young. There is no geological evidence which either supports the ESR or U-series data of the Thorpe terrace. The average ESR ages of the stage 5 terraces increase in the correct stratigraphic order (Worthing: 92 + 15 ka; Ventnor: 110 + 15 ka; Rendezvous Hill: 136 + 15 ka) and show a fair agreement with previous U-series results (Mesolella et al., 1969; Fairbanks, 1977; Bender et al., 1979) of 82 + 2 ka, 105 + 4 ka, and 126 + 2 ka, respectively. New high precision Useries dates obtained by mass spectroscopy yielded ages of 87,700 ___ 200, 112,000 + 200, and 125,000 + 2600
for the respective geological units (Edwards et al., 1987a). When comparing the ESR results of the older units with He/U-data, nearly all ESR ages are older than the estimated He/U-data. Generally, this finding supports the suspicions that the He/U-method is very sensitive to open system behaviour. However, it must be mentioned that most of the older geological units (>400 ka) are represented by one ESR or U/He date, only. Some ESR ages are certainly totally contradictory to the geological context, e.g. the Second High Cliff (SH) is older than the Lodge (L), Kent (Ke), St. Davids (S), and Cottage Vale (C) terraces; the ESR data suggest just the opposite. Similar inversions can be seen in the U/He-data set. This demonstrates nicely the risk in drawing any stratigraphical conclusions from single age results or a small data set (see also Schwarcz and Grtin, 1987). Additional investigations have to be carried out in the future for a better understanding of ESR dating of older corals (>400 ka). The repeated analyses yielded standard deviations of about 10-15% for samples of oxygen isotope stages 5 and 7. With this precision it is certainly possible to distinguish the oxygen isotope stages of the last four interglaciations (up to stage 11). However, at the moment it does not seem possible to make fine adjustments such as determining substages within stages 5 or 7. CONCLUSIONS This ESR dating study on corals from the New Hebrides and Barbados showed reasonable consensus with independently determined U-series and ~4C ages. This shows clearly the applicability of this method for studies on paleoclimate and Quaternary stratigraphy. The present data set does not allow us to draw any conclusions about the upper dating range and precision on older Pleistocene samples (older than stage 11).
470
U. Radtke and R. Griin
H o w e v e r , t h e few d a t a w h i c h a r e a v a i l a b l e in this r a n g e s e e m to h o l d g r e a t p o t e n t i a l for E S R d a t i n g o f c o r a l s , e s p e c i a l l y b e y o n d t h e limits o f U - s e r i e s d a t i n g .
ACKNOWLEDGEMENTS The authors wish to express their sincere gratitude to A.L. Bloom, Ithaca, for providing samples from the New Hebrides along with the age results; O. Katzenberger, K61n, for determining the a-efficiency; and N. Cesar, Hamilton, for U-series analysis. We thank H.P. Schwarcz, Hamilton, for his valuable comments on the manuscript. W.C. Dullo kindly determined the species of the corals from Barbados. Financial support was provided by the Wissenschaftsministerium of NRW, F.R.G., and NSERC grants to H.P. Schwarcz and D.C. Ford.
REFERENCES Aitken, M.J. (1985). Thermoluminescence dating. Academic Press, London, 359 pp. Bender, M.L., Fairbanks, R.G., Taylor, F.W., Matthews, R.K., Goddard, J.G. and Broecker, W.S. (1979). Uranium-series dating of the Pleistocene reef tracts of Barbados, West Indies. Geological Society of America, Bulletin, 90,577-594. Bloom, A.L., Broecker, W.S., Chappel, J.M.A., Matthews, R.K. and Mesolella, K.J. (1974). Quaternary sea level fluctuations on a tectonic coast: New 23ffFh/234U dates from the Huon Peninsula, New Guinea. Quaternary Research, 4, 185-205. Bloom, A.L., Jouannic, C. and Taylor, F.W, (1978). Preliminary radiometric ages from the uplifted Quaternary coral reefs of Efate. Appendix to: Ash, R.P., Carney, J.N. and Macfarlane, A. Geology of Elate and offshore islands, New Hebrides Geological Survey Regional Report, pp. 47-49. Debenham, N.J. (1983). Reliability of thermoluminescence dating of stalagmitic calcite. Nature, 304, 154-156. Debuyst, R., Dejehet, F., Griin, R., Apers, D. and DeCanniere, P. (1984). Possibility of ESR dating without determination of annual dose. Journal of Radioanalytical Nuclear Chemistry, Letters, 86, 399-410. Edwards, R.L., Chen, J.H., Ku, T.L. and Wasserburg, G.J. (1987a). Precise timing of the last interglacial period from mass spectrometric determination of thorium-230 in corals. Science, 236, 1547-1553. Edwards, R.L., Chen, J.H. and Wasserburg, G.J. (1987b). 23Su234U- 23°Th- 232Thsystematics and the precise measurement of time over the past 500,000 years. Earth and Planetary Science Letters, 81, 175-192. Fairbanks, R.G. (1977). Geochemistry of marine skeletal carbonate for use in paleoenvironmental reconstructions. PhD Thesis, Brown University, Providence, R.I., 193 pp. Gascoyne, M., Schwarcz, H.P. and Ford, D.C. (1978). Uranium series dating and stable isotope studies of speleothems: Part I: Theory and techniques. British Cave Research Association, Transactions, 5, 91-111. Griin, R. (1985a). Beitr~ige zur ESR-Datierung. SonderverOffentlichungen des Geologischen lnstituts der Universitfit zu KOln, 59, 1-157. Griin, R. (1985b). ESR dating without determination of annual dose: A first application on dating mollusc shells. In: Ikeya, M. and Miki, T. (eds), ESR Dating and Dosimetry, pp. 115-123. IONICS, Tokyo. Griin, R. (1988). Electron spin resonance (ESR) dating. In: Rutter, N. and Brigham-Grette, J. (eds), Applied Aspects of Quaternary Geochronology, (in press).
Grtin, R., Schwarcz, H.P. and Zymela, S. (1987). ESR dating of tooth enamel. Canadian Journal of Earth Sciences, 24, (in press). Harmon, R.S., Land, L.S., Mitterer, R.M., Garrett, P., Schwarcz, H.P. and Larson, G.J. (1981). Bermuda sea level during the last interglacial. Nature, 289, 481-483. Harmon, R.S., Mitterer, R.M., Kriausakul, N., Land, L.S., Schwarcz, H.P., Garrett, P., Larson. G.J., Vacher, H.L. and Rowe, M. (1983). U-series and amino-acid racemization geochronology of Bermuda: Implications for eustatic sea-level fluctuation over the past 250,000 years. Palaeogeography, Palaeoclimatology, Palaeoecology, 44, 41-70. Hennig, G.J. and Griin, R. (1983). ESR dating in Quaternary Geology. Quaternary Science Reviews, 2, 157-238. lkeya, M. (1978). Electron spin resonance as a method of dating. Archaeometry, 20, 147-158. Ikeya, M. (1983). A trip to interdisciplinary world: Electron spin resonance (ESR) dating in archaeology and geology. Geological News, 19A, 26-30. Ikeya, M. and Ohmura, K. (1983). Comparison of ESR ages of corals from marine terraces with 14C and 23°Th/234U ages. Earth and Planetary Science Letters, 65, 34-38. Jouannic, C., Taylor, F.W., Bloom, A.L. and Bernat, M. (1980). Late Quaternary uplift history from emerged reef terraces on Santo and Malekula Islands, Central New Hebrides Island Arc. UN ESCAP, CCOP/SOPAC Technical Bulletin, 3, 91-108. Kaufman, A. (1986). The distribution of 23°Th/234U ages in corals and the number of last interglacial high-sea stands. Quaternary Research, 25, 55-62. Koba, M., Ikeya, M., Miki, T. and Nakata, T. (1985). ESR ages of the Pleistocene coral reef limestones in the Ryukyu islands, Japan. In: Ikeya, M. and Miki, T. (eds), ESR Dating and Dosimetry, pp. 93-104. IONICS, Tokyo. Lyons, R.G. (1987). Alpha/gamma response of calcite speleothems as determined by nuclear accelerator techniques. Presentation held on: Fifth Specialist Seminar on TL and ESR Dating, 6-10 July 1987, Cambridge (Abstract 30). Mesolella, K.J., Matthews, R.K., Broecker, W.S. and Thurber, D.L. (1969). The astronomical theory of climatic change: Barbados data. Journal of Geology, 77,250-274. Nambi, K.S.V. and Aitken, M.J. (1986). Annual dose conversion factors for TL and ESR dating. Archaeometry, 28,202-205. Prescott, J.R. and Stephan, L.G. (1982). The contribution of cosmic radiation to the environmental dose for thermoluminescence dating - - latitude, altitude and depth dependencies. PACT, 6, 17-25. Radtke, U., Mangini, A. and Hausmann, R. (1987). Paleosea-level and discrimination of the last and the penultimate interglacial of fossiliferous deposits by absolute dating methods (Th/U, ESR) and geomorphological investigations: Illustrated from marine terraces in Chile. Berliner Geographische Studien, 25, 313-342. Radtke, U., Mangini, A. and Griin, R. (1985). ESR dating of fossil marine shells. Nuclear Tracks, 10, 879-884. Radtke, U., Griin, R. and Schwarcz, H.P. (1988). New results from ESR dating of Pleistocene coral reef tracts of Barbados (W.I.). Quaternary Research, 29, 197-215. Schwarcz, H.P. and Grtin, R. (1987). Comment on: Sarnthein, M., Stremme, H.E. and Mangini, A, "The Holstein Interglaciation: Time-Stratigraphic Position and Correlation to Stable-Isotope Stratigraphy of Deep-Sea Sediments". Quaternary Research, 27, (in press). Skinner, A.F. (1985). Comparison of ESR and 23f~Fh/234Uages in fossil aragonitic corals. In: Ikeya, M. and Miki, T. (eds), ESR Dating and Dosimetry, pp. 135-138. ION1CS, Tokyo. Skinner, A.F. (1986). Dating shells and corals by using the ESR signal in aragonite. Symposium on Archaeometry '84, Washington, D.C., 14-18 May 1984, Proceedings, pp. 477-480. Swart, P.K. and Hubbard, J.A.E.B. (1982). Uranium in skieractinian coral skeletons. Coral Reefs, 1, 13-19.
0277-3791/88 $0.00 + .50 Copyright© 1988 Pergamon Press plc
ESR DATING OF CORALS Ulrich R a d t k e * and Rainer GriJnt
* Geographisches Institut, Universitiit D~seldorf, Universitiitsstrasse, D-4000 Diisseldorf, F.R.G. t Department of Geology, McMaster University, Hamilton, Ontario L8S 4M1, Canada
The ages of 24 coral samples from Barbados and the New Hebrides were determined simultaneously by ESR and another independent dating method (a- and MS-U-series and 14C). All parameters for ESR dating were determined, without crosscalibration, with another dating method (including thermal stability and effective c~-efficiency). The results show a relatively good concordance. Furthermore, a systematic ESR dating study on the reef tracts of Barbados (83 samples) revealed satisfactory agreement between ESR and U-series data whereas previously published He/U data seemed to show open system behaviour. The thermal stability of the ESR signal at g = 2.0007 (_+0.0002) estimated to be in the range of 500 ka does not seem to have an apparent influence on the ESR results.
INTRODUCTION Coral growth is dependent on various parameters such as water temperature, salinity and purity. Optimal conditions for reef-building occurs between about 30°N and 30°S in water depths down to 50 m, although some other species are able to live in more northern latitudes and at greater depths. Absolute dating of corals is of interest for paleoclimatic and paleosea-level investigations (see, for example, Bloom et al., 1974; Harmon et al., 1981, 1983; Radtke, 1987). The first applications of ESR dating on corals were carried out on sites in Southern Japan (Ikeya and Ohmura, 1983; Ikeya, 1983; Koba et al., 1985) followed by studies on Haitian corals (Skinner, 1985, 1986). This paper presents the dating results of 24 coral samples each of which were dated by ESR and at least one other independent dating method (U-series, 14C). Additionally, the results of a systematic ESR dating study on the reef tracts of Barbados are summarized (for details see Radtke et al., 1988). The U-series and taC-results from the New Hebrides were kindly provided by A.L. Bloom and are published elsewhere (Bloom et al., 1978; Jouannic et al., 1980; Edwards et al., 1987b). The U-series results on the corals from Barbados were determined following the McMaster routine analysis (see, for example, Gascoyne et al., 1978). ESR DATING The details of ESR dating are described elsewhere (see, for example, Ikeya, 1978; Hennig and Grtin, 1983; Griin, 1985a, 1988). An ESR age is determined from the relationship: t
AD =
/ D(t) dt
0
#Present address: Subdepartment of Quaternary Research, University of Cambridge, Free School Lane, Cambridge CB2 3RS, U.K.
where the accumulated dose (AD) is the total radiation dose that the sample acquired since the time of its formation. The dose rate D is generated by the radioactive elements U, Th, and K in the sample (internal dose rate) and its surroundings (external dose rate) plus cosmic rays.
Determination of Accumulated Dose A D The AD is determined via ESR spectroscopy by the additive dose method (see, for example, Aitken, 1985): aliquots of the sample are irradiated stepwise with defined ~- or [3-doses and the extrapolation towards zero ESR-intensity allows the determination of AD (see Fig. 2). All samples were taken from corals which were still in their living position; apparent recrystallization zones were avoided. The following species were collected:
Acropora palmata, Acropora cervicornis, Montastrea annularis, Montastrea cavernosa, Siderastrea siderea, Diploria strigosa, Stephanocoenia michelini, Platygyra lamellina, Leptoria phrygia, Oulophyllia crispa, Porites lutea, Acropora humilis, and Montipora sp. Samples were ground and 7-9 aliquots of a sieve fraction of 200-100 ~m were successively irradiated with defined "V- and f3-doses (25, 50, 75, 100, 125, 150, 175, and 200 Gy). In case the AD was above 200 Gy, the sample was reirradiated up to 1000 Gy. The ESR spectra were recorded with a Bruker 200 tt ESR spectrometer at a frequency of about 9.5 GHz and a magnetic field strength of about 340 mT. The microwave power was 4 mW, the modulation amplitude 0.1 mTpp, and the scan time in the range of 1 mT min- i. Figure 1 shows an ESR spectrum typical of that observed on all samples. It is different from that reported by Skinner (1985, 1986) who observed a spectrum similar to that which is common for aragonitic mollusc shells (Radtke et al., 1985). As can be seen in Fig. 1, two ESR peaks (at g = 2.0007 and g = 2.0036) show enhancement upon artificial radiation, whereas
465
466
U. Radtke and R. Griin
: "';
/
I
I
2.01
f
2.005
2.0
'
'
'
'
I
g-Value
FIG. 1. ESR spectrum of a Pleistocene coral: solid line = non-irradiated; dotted line = irradiated. .,,,.
A.'recent coral
g,
"f
B: B-To j
,,e
•
o~
-;'o
o
J
/
I S
ADL/N 5o
ioor-dos tffyj
-100 -50 '
I
.-ADLod I:~ULI N
0
bo ioo r-'dos {Gyl
-~ I
FIG. 2. ESR signal growth upon artificial ~-irradiation. ADLIN: AD estimated through linear extrapolation (solid line); ADLoG: AD estimated by logarithmic extrapolation (dotted line).
the signal at g = 2.0058 is nearly insensitive to ~/irradiation; however, this line is not present in recent samples and cannot be generated by artificial ~/- or 13irradiation in recent samples. The ADs derived from the peak at g = 2.0036 were invariably smaller than the ADs from g = 2.0007, which is probably due to the lower thermal stability of the former peak. Therefore, the signal at g = 2.0007 was used for our investigation. ADs based on this peak show no change on grinding or light exposure. The thermal stability of this peak was estimated by isothermal annealing at three temperatures (220, 160, and 120°C) using an Arrhenius plot
(Hennig and Griin, 1983) giving a mean-life in the range of 500 ka at the present average annual temperature of 26°C on Barbados (the signal at g = 2.0036 has a mean life in the range of 100 ka at 26°C). Such mean life determinations have, however, very large uncertainties (they may be three times smaller or larger; see Debenham, 1983; Griin, 1985b). The samples were routinely checked for recrystallization from aragonite to calcite by X R D analysis. All but 2 samples (of 91) showed saturation effects which can occur even at low artificial ~/-doses (see Fig. 2). Therefore, a logarithmic extrapolation [plotting
467
ESR Dating of Corals
-In(1 - I//max) VS. 7-dose (Apers et al., 1981)] was used for AD determination. /max w a s determined iteratively.
Determination of Dose Rate D The dose rate was derived from the analysis, by INAA or a-spectrometry, of U in the <100 Ixm sieve fraction of each sample and using the conversion factors from Nambi and Aitken (1986). The 232Th and K-concentrations in the samples were negligible. Skinner (1986) reports that Rn-loss in corals is also negligible• Figure 3 (top) shows that the U-concentration is not dependent on the age of the samples• This supports the results of Swart and Hubbard (1982), i.e. U is accumulated at the time of, or shortly after, the death of the coral organism. The effective c~-efficiency was determined with a 24tAm a-source on five samples yielding a value of 0.06 + 0.01 which was used in all age calculations. This value might still contain some uncertainty, since Lyons (1987) found that the effective a-efficiency of the Udecay chains might be 20-30% higher than the value determined by a monoenergetic a-source (of 4.1 MeV). U-series disequilibria were taken into account by use of formulas given by GriJn et al. (1987). Cosmic dose rates were determined using the graphs of Prescott and Stephan (1982). A peculiarity in ESR dating of corals is that the coral stock is more or less an infinite medium for gamma-rays. Since the U-distribution in corals is rather homogeneous, U-series disequilibria have to also be taken into account in calculating the natural 7-dose. Additionally, in situ gamma dose measurements were carried out on Barbados. In case the measured "y-dose rate was larger than the internal 7-dose rate at the estimated age of the sample (which might be due to additional irradiation by
soils etc.), this difference was added to the cosmic dose rate. For the samples from the New Hebrides, no in situ ~-measurements were carried out and the burial depths were not available; therefore, a cosmic dose rate of 180 ~Gy/year was assumed in all cases. Ages were calculated using the computer program ESR-DATA. RESULTS
Figure 4 and Table 1 shows the U-series and ESR results• The analytical data of U-series and 1 4 C a r e given elsewhere (Edwards et al., 1987b; Bloom et al., 1978; Radtke et at., 1987)• The listed internal dose rates are mean values over time. There is relatively good agreement, although the ESR data have the tendency to be slightly older than the U-series ages. The laboratory uncertainty of an ESR result on corals is mainly due to the uncertainty in AD determination, which is in the range of 10 to 20%; however, this is only an estimate since we do not yet have a mathematical treatment available to calculate the confidence interval of a single AD determination• Therefore, we prefer to compare the mean ages (with standard deviation) of repeated analyses. Table 2 and Fig. 5 compares the ESR data from Barbados (for details see Radtke et al., 1987) with Useries and U/He results published earlier (Mesolella et al., 1969; Bender et al., 1979). The geological units in Table 2 are arranged approximately according to their geomorphological sequence• The mean ages in Fig. 5 were calculated from the mean ages of repeated analyses on the geological unit; in the case of single age data, the error bars for ESR were assumed to be 10%; the errors for the U-series dates were taken from the original publication; and for He/U, from Fig. 9 in Bender et al. (1979). DISCUSSION
0 0 a
The study of Radtke et al. (1988) shows that recrystallization seems to have only a limited effect on the ESR results: samples with aragonite concentrations down to 60% did not show a trend towards younger ages compared to samples with concentrations of 95-100%. Samples with aragonite concentrations as low as 20% showed a severe underestimation of AD.
0
3
0 00,
oo~O
0 0 ~ 0o0°°°o o
2
°°o°
o o
•
o
1 0 100 -
CORAL o
o
o
"~.
~ 400.
o
,/ I"
•
•
•
~m 300. t~ 200.
/
•
I."
100. 0t
o
zi~o
~bo
6bo
Esh-,,go'tka;
FIG. 3. U-concentration (top) and aragonite contents (below) vs ESR ages of corals from Barbados.
o
lbo 2oo 3bo ~oo O-series age{kal
FIG. 4. Mean ESR vs mean U-series ages (for data see Table 1). Dotted lines give a 20% uncertainty interval.
468
U. Radtke and R. Griin TABLE 1. Age results on corals from the New Hebrides and Barbados which were investigated by at least two methods Ages (years)
Sample no.
U (ppm)
AD (Gy)
Int. D (~Gy/year)
Ext. D 0,Gy/year)
ESR
a-Th/U
New Hebrides E.AD.2 M.G.3 M.G.4 S.AC. 1 S.D.2 E.L.3 E.T.2 S.D. 1
2.95 2.76 2.58 2.37 3.58 2.43 2.09 3.44
4.2 41.9 42.6 3.2 32.1 102.0 79.1 32.7
336.8 523.7 474.2 266.4 594.3 625.9 515.3 579.4
180 180 180 180 180 180 180 180
8170 59,700 65,200 7200 41,600 127,000 114,000 43,200
6800 55,000 57,000 5700 37,000 141,000 141,000 38,000
Barbados B-4a B -5a B-7a B-59a B-64-I
2.80 2.95 3.33 3.30 2.00
63.9 88.5 103.9 114.8 67.8
586.8 670.2 806.2 797.8 459.1
250 280 150 250 250
76,600 93,300 109,400 109,000 95,800
B-64-Illa
2.11
360.3
783.2
120
399,000
B-64-V B-64-VII B-65-IIa B-65-IIIa B-65-IIic B-65-IVa/2 B-65-IVb/1 B-65-IVb/2 B-65-IVb/3 B-66
1.67 2.25 2.10 1.91 2.12 3.38 2.73 3.08 2.89 3.50
754.3 1065.4 75.0 382.0 n.d. n.d. 193.2 151.9 180.3 176.0
684.0 923.8 540.4 734.3 --816.2 834.2 835.3 962.0
250 250 50 50 --210 210 210 210
808,000 908,000 127,000 487,000 --188,000 145,000 172,000 150,000
66,700 70,300 72,900 100,000 66,500 83,700 220,000 >350,000 >350,000 >350,000 130,000 >350,000 >350,000 97,700 106,900 106,200 147,600 127,000
MS-Th/U -----125,000 129,900 --
6350 5940
m
h
m
B
m
m
m
m
m
.
m
m
m
n.d. = not determined due to large scattering of data points. TABLE 2. Average age results on the reef tracts on Barbados Age (ka) Geologic unit Worthing (W) Ventnor (V) Rendezvous Hill (R) Kendal Hill (K) Durants (D) Kingsland/Aberdare (K/A) Adam's Castle (A) Thorpe (T) Rowans (Ro) Husbands (Hu) Kent (Ke) Lodge (L) St. David (S) Cottage Vale (C) Second High Cliff (SH) Hill View (H)
ESR ~ 92 110 136 228 223 222 286 321 310 380 433 477 625 585 425 405
Th/U 2
4- 15 (16) 4- 15 (8) 4- 15 (13) + 12 (2) ± 17 (3) 4- 27 (4) _+ 28 (2) ± 27 (3) (1) ± 36 (2) (1) (1) (1) (1) (1) ± 36 (2)
82 105 126 221 207 235 >180 220 >350
± ± ± ± ± ±
Corr. He/U 3
2 4 2 65 14 33
(4) (4) (10) (4) (3) (7) (4) ± 25 (1) (1)
180 110 207 235 215 300 320 327 360 283 490 450 515
± 10 (3) (1) ± 15 (3) ± 34 (4) ± 6 (2) ± 8 (4) (1) ± 15 (3) (1) ± 46 (3) (1) ± 10 (2) ± 5 (2)
(1) = data from Radtke et al. (1988). (2) = data from Mesolella et al. (1969), Bender et al. (1979) and Fairbanks (1977). Letters in brackets: abbreviations used in Fig. 5. Numbers in brackets: numbers of analyses used for averaging and standard deviation.
A s s h o w n in Fig. 3 it s h o u l d b e p o s s i b l e to c o l l e c t n o n r e c r y s t a l l i z e d s a m p l e s u p to at l e a s t 1 M a . T h e o l d e s t s a m p l e s o f this s t u d y ( s e e T a b l e 1: B - 6 4 - V a n d B - 6 4 V I I ) still h a d a r a g o n i t e c o n c e n t r a t i o n s o f 1 0 0 % a n d 6 0 % . H o w e v e r , w h e t h e r this f i n d i n g c a n s t a n d a d e t a i l e d i n v e s t i g a t i o n is q u e s t i o n a b l e since this rec r y s t a l l i z a t i o n p r o c e s s is a c c o m p a n i e d by U - m i g r a t i o n ( K a u f m a n , 1986). T h e r e f o r e , s a m p l e s w i t h a r a g o n i t e concentrations of lower than 95% must be avoided.
T h e a n n e a l i n g s t u d y y i e l d e d a v a l u e f o r t h e m e a n life "r o f a b o u t 500 k a f o r t h e p r e s e n t a v e r a g e a n n u a l temperature on Barbados (26°C). T h e m e a n life c o n t r o l s t h e A D a c c o r d i n g to ( D e b u y s t e t a l . , 1984): A D = D "r [1 - e x p ( - t / - r ) ] i.e. w h e n a s s u m i n g -r = 500 k a t h e n at 100 k a an E S R a g e w o u l d b e a n u n d e r e s t i m a t i o n o f 1 0 % (10 k a ) ; at
469
ESR Dating of Corals
.... i¸¸ 400 300
Xt'::
200 100
0'" 0
100
2O0
30o
~oo 0
Th/U uge[ko]
100
200
300
~oo
500
He/U uge[ko]
FIG. 5. Left: average ESR ages (from Radtke et al., 1988) vs average U-series ages (from Mesolella et al., 1969; Bender et al., 1979) on the geological units on Barbados (see Table 2). Right: average ESR ages vs average He/U-ages (from Bender et al., 1979) on the reef tracts on Barbados. For abbreviations see Table 2.
250 ka about 20% (50 ka); and at 500 ka about 37% (184 ka). In case the steady state level (for an infinite number of traps) is well below saturation level, the maximum age observable is the mean life of the particular center (otherwise the maximum age is lower than "r). The oldest calculated ages were around 800 to 900 ka. Coral reef growth on Barbados is indeed supposed to have started in this age range (700 ka: Mesolella et al., 1969). Additionally, all comparisons with other dating methods show no trend of ESR underestimations. Therefore, the estimated low stability does not seem to have any impact on the calculated ages. Whether this is due to the overall uncertainty of the mean life evaluation method (as mentioned above) or the general validity of those plots is uncertain. The comparison of ESR with U-series data (Table 2 and Figs 4 and 5) shows a satisfactory concordance except for the Thorpe (T) terrace whose ESR age suggests a formation during stage 9 whereas the Useries result indicates stage 7 age. The ESR ages seem to have a slight tendency towards older ages. However, this does not necessarily mean that the U-series analysis yielded the correct age: e.g. sample B5-a was collected from the Worthington (W) terrace which is supposed to be 82 ka old (Barbados I or stage 5a). ESR gives an age which is about 11 ka too old, whereas the U-series result is about 12 ka too young. There is no geological evidence which either supports the ESR or U-series data of the Thorpe terrace. The average ESR ages of the stage 5 terraces increase in the correct stratigraphic order (Worthing: 92 + 15 ka; Ventnor: 110 + 15 ka; Rendezvous Hill: 136 + 15 ka) and show a fair agreement with previous U-series results (Mesolella et al., 1969; Fairbanks, 1977; Bender et al., 1979) of 82 + 2 ka, 105 + 4 ka, and 126 + 2 ka, respectively. New high precision Useries dates obtained by mass spectroscopy yielded ages of 87,700 ___ 200, 112,000 + 200, and 125,000 + 2600
for the respective geological units (Edwards et al., 1987a). When comparing the ESR results of the older units with He/U-data, nearly all ESR ages are older than the estimated He/U-data. Generally, this finding supports the suspicions that the He/U-method is very sensitive to open system behaviour. However, it must be mentioned that most of the older geological units (>400 ka) are represented by one ESR or U/He date, only. Some ESR ages are certainly totally contradictory to the geological context, e.g. the Second High Cliff (SH) is older than the Lodge (L), Kent (Ke), St. Davids (S), and Cottage Vale (C) terraces; the ESR data suggest just the opposite. Similar inversions can be seen in the U/He-data set. This demonstrates nicely the risk in drawing any stratigraphical conclusions from single age results or a small data set (see also Schwarcz and Grtin, 1987). Additional investigations have to be carried out in the future for a better understanding of ESR dating of older corals (>400 ka). The repeated analyses yielded standard deviations of about 10-15% for samples of oxygen isotope stages 5 and 7. With this precision it is certainly possible to distinguish the oxygen isotope stages of the last four interglaciations (up to stage 11). However, at the moment it does not seem possible to make fine adjustments such as determining substages within stages 5 or 7. CONCLUSIONS This ESR dating study on corals from the New Hebrides and Barbados showed reasonable consensus with independently determined U-series and ~4C ages. This shows clearly the applicability of this method for studies on paleoclimate and Quaternary stratigraphy. The present data set does not allow us to draw any conclusions about the upper dating range and precision on older Pleistocene samples (older than stage 11).
470
U. Radtke and R. Griin
H o w e v e r , t h e few d a t a w h i c h a r e a v a i l a b l e in this r a n g e s e e m to h o l d g r e a t p o t e n t i a l for E S R d a t i n g o f c o r a l s , e s p e c i a l l y b e y o n d t h e limits o f U - s e r i e s d a t i n g .
ACKNOWLEDGEMENTS The authors wish to express their sincere gratitude to A.L. Bloom, Ithaca, for providing samples from the New Hebrides along with the age results; O. Katzenberger, K61n, for determining the a-efficiency; and N. Cesar, Hamilton, for U-series analysis. We thank H.P. Schwarcz, Hamilton, for his valuable comments on the manuscript. W.C. Dullo kindly determined the species of the corals from Barbados. Financial support was provided by the Wissenschaftsministerium of NRW, F.R.G., and NSERC grants to H.P. Schwarcz and D.C. Ford.
REFERENCES Aitken, M.J. (1985). Thermoluminescence dating. Academic Press, London, 359 pp. Bender, M.L., Fairbanks, R.G., Taylor, F.W., Matthews, R.K., Goddard, J.G. and Broecker, W.S. (1979). Uranium-series dating of the Pleistocene reef tracts of Barbados, West Indies. Geological Society of America, Bulletin, 90,577-594. Bloom, A.L., Broecker, W.S., Chappel, J.M.A., Matthews, R.K. and Mesolella, K.J. (1974). Quaternary sea level fluctuations on a tectonic coast: New 23ffFh/234U dates from the Huon Peninsula, New Guinea. Quaternary Research, 4, 185-205. Bloom, A.L., Jouannic, C. and Taylor, F.W, (1978). Preliminary radiometric ages from the uplifted Quaternary coral reefs of Efate. Appendix to: Ash, R.P., Carney, J.N. and Macfarlane, A. Geology of Elate and offshore islands, New Hebrides Geological Survey Regional Report, pp. 47-49. Debenham, N.J. (1983). Reliability of thermoluminescence dating of stalagmitic calcite. Nature, 304, 154-156. Debuyst, R., Dejehet, F., Griin, R., Apers, D. and DeCanniere, P. (1984). Possibility of ESR dating without determination of annual dose. Journal of Radioanalytical Nuclear Chemistry, Letters, 86, 399-410. Edwards, R.L., Chen, J.H., Ku, T.L. and Wasserburg, G.J. (1987a). Precise timing of the last interglacial period from mass spectrometric determination of thorium-230 in corals. Science, 236, 1547-1553. Edwards, R.L., Chen, J.H. and Wasserburg, G.J. (1987b). 23Su234U- 23°Th- 232Thsystematics and the precise measurement of time over the past 500,000 years. Earth and Planetary Science Letters, 81, 175-192. Fairbanks, R.G. (1977). Geochemistry of marine skeletal carbonate for use in paleoenvironmental reconstructions. PhD Thesis, Brown University, Providence, R.I., 193 pp. Gascoyne, M., Schwarcz, H.P. and Ford, D.C. (1978). Uranium series dating and stable isotope studies of speleothems: Part I: Theory and techniques. British Cave Research Association, Transactions, 5, 91-111. Griin, R. (1985a). Beitr~ige zur ESR-Datierung. SonderverOffentlichungen des Geologischen lnstituts der Universitfit zu KOln, 59, 1-157. Griin, R. (1985b). ESR dating without determination of annual dose: A first application on dating mollusc shells. In: Ikeya, M. and Miki, T. (eds), ESR Dating and Dosimetry, pp. 115-123. IONICS, Tokyo. Griin, R. (1988). Electron spin resonance (ESR) dating. In: Rutter, N. and Brigham-Grette, J. (eds), Applied Aspects of Quaternary Geochronology, (in press).
Grtin, R., Schwarcz, H.P. and Zymela, S. (1987). ESR dating of tooth enamel. Canadian Journal of Earth Sciences, 24, (in press). Harmon, R.S., Land, L.S., Mitterer, R.M., Garrett, P., Schwarcz, H.P. and Larson, G.J. (1981). Bermuda sea level during the last interglacial. Nature, 289, 481-483. Harmon, R.S., Mitterer, R.M., Kriausakul, N., Land, L.S., Schwarcz, H.P., Garrett, P., Larson. G.J., Vacher, H.L. and Rowe, M. (1983). U-series and amino-acid racemization geochronology of Bermuda: Implications for eustatic sea-level fluctuation over the past 250,000 years. Palaeogeography, Palaeoclimatology, Palaeoecology, 44, 41-70. Hennig, G.J. and Griin, R. (1983). ESR dating in Quaternary Geology. Quaternary Science Reviews, 2, 157-238. lkeya, M. (1978). Electron spin resonance as a method of dating. Archaeometry, 20, 147-158. Ikeya, M. (1983). A trip to interdisciplinary world: Electron spin resonance (ESR) dating in archaeology and geology. Geological News, 19A, 26-30. Ikeya, M. and Ohmura, K. (1983). Comparison of ESR ages of corals from marine terraces with 14C and 23°Th/234U ages. Earth and Planetary Science Letters, 65, 34-38. Jouannic, C., Taylor, F.W., Bloom, A.L. and Bernat, M. (1980). Late Quaternary uplift history from emerged reef terraces on Santo and Malekula Islands, Central New Hebrides Island Arc. UN ESCAP, CCOP/SOPAC Technical Bulletin, 3, 91-108. Kaufman, A. (1986). The distribution of 23°Th/234U ages in corals and the number of last interglacial high-sea stands. Quaternary Research, 25, 55-62. Koba, M., Ikeya, M., Miki, T. and Nakata, T. (1985). ESR ages of the Pleistocene coral reef limestones in the Ryukyu islands, Japan. In: Ikeya, M. and Miki, T. (eds), ESR Dating and Dosimetry, pp. 93-104. IONICS, Tokyo. Lyons, R.G. (1987). Alpha/gamma response of calcite speleothems as determined by nuclear accelerator techniques. Presentation held on: Fifth Specialist Seminar on TL and ESR Dating, 6-10 July 1987, Cambridge (Abstract 30). Mesolella, K.J., Matthews, R.K., Broecker, W.S. and Thurber, D.L. (1969). The astronomical theory of climatic change: Barbados data. Journal of Geology, 77,250-274. Nambi, K.S.V. and Aitken, M.J. (1986). Annual dose conversion factors for TL and ESR dating. Archaeometry, 28,202-205. Prescott, J.R. and Stephan, L.G. (1982). The contribution of cosmic radiation to the environmental dose for thermoluminescence dating - - latitude, altitude and depth dependencies. PACT, 6, 17-25. Radtke, U., Mangini, A. and Hausmann, R. (1987). Paleosea-level and discrimination of the last and the penultimate interglacial of fossiliferous deposits by absolute dating methods (Th/U, ESR) and geomorphological investigations: Illustrated from marine terraces in Chile. Berliner Geographische Studien, 25, 313-342. Radtke, U., Mangini, A. and Griin, R. (1985). ESR dating of fossil marine shells. Nuclear Tracks, 10, 879-884. Radtke, U., Griin, R. and Schwarcz, H.P. (1988). New results from ESR dating of Pleistocene coral reef tracts of Barbados (W.I.). Quaternary Research, 29, 197-215. Schwarcz, H.P. and Grtin, R. (1987). Comment on: Sarnthein, M., Stremme, H.E. and Mangini, A, "The Holstein Interglaciation: Time-Stratigraphic Position and Correlation to Stable-Isotope Stratigraphy of Deep-Sea Sediments". Quaternary Research, 27, (in press). Skinner, A.F. (1985). Comparison of ESR and 23f~Fh/234Uages in fossil aragonitic corals. In: Ikeya, M. and Miki, T. (eds), ESR Dating and Dosimetry, pp. 135-138. ION1CS, Tokyo. Skinner, A.F. (1986). Dating shells and corals by using the ESR signal in aragonite. Symposium on Archaeometry '84, Washington, D.C., 14-18 May 1984, Proceedings, pp. 477-480. Swart, P.K. and Hubbard, J.A.E.B. (1982). Uranium in skieractinian coral skeletons. Coral Reefs, 1, 13-19.