234U/238U ratios and230Th ages for Hateruma Atoll corals: implications for coral diagenesis and seawater234U/238U ratios

doi:10.1016/0012-821X(93)90213-S

Earth and Planetary Science Letters

Volume 115, Issues 1–4, March 1993, Pages 65-73

https://doi.org/10.1016/0012-821X(93)90213-S Get rights and content

Abstract

Published results for corals that are more than ca. 50 ka old from, for example, Barbados and Vanuata, often yield initial (²³⁴U/²³⁸U) activity ratios that are significantly greater than 1.144 (±0.004), the value for modern seawater. This study reports results for corals from Hateruma Atoll, Japan, and investigates the effects of diagenesis on the initial (²³⁴U/²³⁸U) ratios of the corals. Hateruma consists of over 95% reef material of less than 500 ka in age. Because groundwaters associated with recent carbonates tend not to have elevated (²³⁴U/²³⁸U) ratios, the scope for increasing the (²³⁴U/²³⁸U) ratios of Hateruma corals through groundwater interaction should be minimal.

The corals examined range from those which show no petrographic or X-ray evidence for diagenetic alteration and are ‘pristine’ to those containing secondary cements of either aragonite or high- or low-Mg calcite. These various phases have been mechanically separated and analysed. In agreement with previous assertions the analyses of these separates demonstrates that the presence of calcite should be a cause for rejection of coral samples. It is also shown that aragonite cement can form later than coral death and may bias estimates of age and initial (²³⁴U/²³⁸U) ratios. Of the six ‘pristine’ corals, three have anomalous (²³⁰Th/²³⁸U) ratios requiring U loss and/or²³⁰Th addition. The remaining fifteen of the eighteen total analyses reported here yield ages from 1.6 ka to 260 ka. No evidence for an increase in (²³⁴U/²³⁸U) ratios in past seawater from this period has been found: the best estimates for (²³⁴U/²³⁸U) ratios are close to the current seawater value.

References (22)

BloomA.L. et al.
Quaternary sea level fluctuations on a tectonic coast: New²³⁰Th/²³⁴U dates from the Huon Peninsula, New Guinea
Quat. Res.
(1974)
ChenJ.H. et al.
²³⁸U,²³⁴U and²³²Th in seawater
Earth Planet. Sci. Lett.
(1986)
HamelinB. et al.
²³⁴U/²³⁸U mass spectrometry of corals: How accurate is the UTh age of the last interglacial period?
Earth Planet. Sci. Lett.
(1991)
BannerJ.L. et al.
Uranium-series evidence on diagenesis and hydrology in Pleistocene carbonates of Barbados, West Indies
Earth Planet. Sci. Lett.
(1991)
BannerJ.L. et al.
²³⁴U²³⁸U²³⁰Th²³²Th systematics in saline groundwaters from central Missouri
Earth Planet. Sci. Lett.
(1990)
CohenA.S. et al.
High precision Uranium, thorium and radium isotope ratio measurement by high-dynamic range thermal ionisation mass spectrometry
Int. J. Mass Spectrom. Ion Processes
(1992)
BenderM.L. et al.
Uranium-series dating of the Pleistocene reef tracts of Barbados, West Indies
Geol. Soc. Am. Bull.
(1979)
MuhsD.R. et al.
Age estimates and uplift rates for Late Pleistocene marine terraces: Southern Oregon portion of the Cascadia Forearc
J. Geophys. Res.
(1990)
EdwardsR.L.
High precision thorium-230 ages of corals and the timing of sea level fluctuation in the late Quaternary
BardE. et al.
UTh ages obtained by mass spectrometry in corals from Barbados: sea level during the past 130,000 years
Nature
(1990)

BardE. et al.

Calibration of the¹⁴C timescale over the past 30,000 years using mass spectrometric UTh ages from Barbados corals

Nature

(1990)

Cited by (97)

Mapping and U[sbnd]Th dating of the world's deepest blue hole (South China Sea): Implications for its timing, possible volcanogenic origin, and Pleistocene eolianites in the Xisha Islands
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The Sansha Yongle Blue Hole (SYBH) is the deepest (301.19 m) blue hole known in the world and is a water-filled karst opening in the intertidal reef flats of the eastern Yongle Atoll, Xisha Islands, South China Sea. It is differentiated from the surrounding environment by its deep blue colour as observed when viewed from above. The SYBH exhibits extremely rare karst networks and speleothems and differs from the blue holes of the Bahamas and Bermuda, indicating a different development process. Here, we present the morphology and UTh ages of the SYBH, which document the evolution of the coastal cave over time. Morphology and lithostratigraphy indicate that the hole resulted from dissolution via ascending acidic water/gas followed by subsequent collapse. The adjacent volcanoes surrounding the eastern Yongle Atoll are the most likely source of these ascending fluids. UTh ages of the cemented carbonate sand underlying the entrance constrain an upper limit of the opening time of the SYBH to be up to 111.7 ± 9.5 kyr BP. Deeply submerged speleothems at −116 m determine the lower collapse time of the SYBH to be 29.16 ± 0.17 kyr BP. The SYBH probably formed due to the upward release of volcanogenic acid water/gas through low-lying unconsolidated carbonate sediments, followed by buoyant collapses due to a 40-m fall in the sea level during 31–29 kyr BP. As the sea level rose to −15 m in the early Holocene, corals grew in the cave opening since 8.58 kyr BP and surrounded the entrance for the SYBH.
Holocene sea levels at the Gulf of Aqaba, northern Red Sea
2022, Quaternary Science Reviews
A new relative sea level (RSL) curve is presented for the Holocene Gulf of Aqaba, northern Red Sea. The curve is based on U–Th ages of corals retrieved from leveled fossil reefs comprising the Tur Yam Terrace at the shore of the city of Elat, Israel and the Aqaba reef terraces, Jordan, located respectively east and west of the northern tip of the gulf. Both terrace tops are submerged under high tide and subaerial at low tide. The fossil corals are in growth position between two beachrock units. The corals comprise 100% aragonite, show pristine textures with no secondary aragonite cements and yield initial ²³⁴U/²³⁸U activity ratios of 1.146 ± 0.004, similar to the values of live corals and modern Gulf of Aqaba (GoA) waters. Sixteen U–Th ages of corals from the Tur Yam Terrace span the time interval of 6.8 to 5.5 ka, and are ordered along the growth direction of the terrace. Detailed mapping of the terrace, the distribution of corals’ genera and the order of their ages on the terrace, suggest that the exposed terrace was the back reef/lagoon zone, a very close to shore environment of a fringing reef. Identification of this reef zone was based on a detailed ecological study that we conducted on the Nature Reserve Reef (NRR), a modern fringing reef located several hundred meters to the south. A morpho-tectonic analysis of the Elat shore indicates that the Tur Yam Terrace lies on top of the footwall of the active Elat Fault and has remained at its original level, with negligible vertical shift. Thus, it appears that during the time interval of formation of the Tur Yam corals, sea level at GoA reached a maximum stand that was 1–2 m above the modern elevation. A similar figure is shown by Mid-Holocene corals from the Aqaba fossil reefs and shore indicators from the Red Sea. The relative sea level (RSL) curve deduced from the Gulf of Aqaba corals and from the Red Sea indicators resembles those of precisely-dated stable reefs off west and east Australia and a few other well dated reefs in the Indo-Pacific. This similarity calls for coeval response of the Indo-Pacific oceans to ice melting during the early to mid- Holocene, and a similar pattern of decline to the present level during the late Holocene. Such a coeval rise of distant parts of the Indo-Pacific oceans is consistent with dominance of melt waters releases over the oceans with minor effects of all other “sea level drivers".
Late Quaternary sporadic development of Desmophyllum dianthus deep-coral populations in the southern Labrador Sea with specific attention to their 14C- and 230Th-dating
2020, Marine Chemistry
About 70 fossil and live-collected specimens of Desmophyllum dianthus were collected from steep rocky surfaces and time-averaged assemblages at their base (“coral graveyards”) in the southern Labrador Sea at depths ranging from ~1700 m (Orphan Knoll) to ~2200 m (Flemish Cap). Aside from stable isotope and mineralogical analysis, U-series and ¹⁴C age determinations were performed on the samples. Fossil corals from the coral graveyards display two principal age clusters corresponding respectively to the Holocene and Marine Isotope Stage (MIS) 5c intervals. Three samples lay outside these clusters, at ~13.5 ka (Bølling-Allerød), ~ 64 ka (MIS 3) and at ~181 ka (MIS 7a). The clusters are thought to record intervals with both i) high food availability, either through pelagic primary production in the overlying water column or more effectively in relation with particulate and dissolved organic carbon transport via an active Western Boundary Undercurrent (WBUC), and ii) high carbonate micrite advection by this current from more open North Atlantic coccolithophorid production areas, maintaining an aragonite saturation horizon (now at 2300 m) slightly deeper than the coral habitat (~ 2200 m). Attempts at estimating ventilation ages from ²³⁰Th vs ¹⁴C age offsets in Holocene samples failed. This is due to uncertainties about the initial ¹⁴C-apparent age of coral skeletons and to their high initial excesses in ²³⁰Th. This initial excess relates mostly to the scavenging of ²³⁰Th produced by the dissolved marine U by the coral-feeding organic matter carried along the WBUC trajectory. In addition, discrete diagenetic U-fluxes can be documented in fossil samples. They are well illustrated in specimens from MIS 5c age, which depict variable excesses in ²³⁴U vs ²³⁸U, but similar ²³⁰Th/²³⁸U activity ratios, pointing to a recent but fractionating redistribution of uranium in the samples. These are also documented by the development of FeMn coatings of specimens exposed at the sea floor, due to the winnowing of embedding slope sediments, with the mid- to late Holocene intensified WBUC. Such diagenetic processes are to be notably taken into consideration for the dating of pre-Holocene samples. Thus, both the initial isotopic properties of corals from this WBUC-influenced, mid-continental slope, and subsequent diagenetic effects impact their calculated ages, and blur estimates of “ventilation ages” based on their ¹⁴C vs ²³⁰Th-ages offsets.
Geochemical proxies in marine biogenic carbonates: New developments and applications to global change
2020, Chemical Geology
Improved constraints on open-system processes in fossil reef corals by combined Th/U, Pa/U and Ra/Th dating: A case study from Aqaba, Jordan
2019, Geochimica et Cosmochimica Acta
Citation Excerpt :
In general, altered 230Th/U ages coincide with increased (234U/238U) activity ratios compared to modern seawater values (Edwards et al., 1987; Hamelin et al., 1991; Bard et al., 1993; Henderson et al., 1993; Gallup et al., 1994) suggesting that the processes affecting the (234U/238U) activity ratios of the corals also affect their (230Th/238U) activity ratios (throughout this study, activity ratios are presented in parentheses). Mobilization of U and Th isotopes is thought to be the result of different processes, such as secondary aragonite precipitation resulting in U addition (Bar-Matthews et al., 1993; Henderson et al., 1993; Lazar et al., 2004), leaching leading to U loss (e.g., Tomiak et al., 2016) or aragonite-to-calcite recrystallization, which is usually accompanied by U loss. Other processes include detrital contamination particularly adding Th isotopes as well as recoil processes resulting in daughter mobilization (Gallup et al., 1994; Henderson and Slowey, 2000; Thompson et al., 2003; Villemant and Feuillet, 2003).
Here we present ²³⁰Th/U, ²³¹Pa/U as well as ²²⁶Ra/²³⁰Th isotope ratios from five fossil reef corals of Last Interglacial origin from the Gulf of Aqaba, Northern Red Sea. The results show clear evidence for open-system behaviour with strongly elevated δ²³⁴U values and U concentrations indicating post-depositional U addition. The combined application of all isotope systems enables us to better constrain the nature and timing of the open-system processes than only based on the ²³⁰Th/U data.
Quantitative modelling of the diagenetic processes allowed us to reproduce the trends in the isotope ratios. Two of the five corals were probably affected by two separate phases of U addition with different δ²³⁴U values. The trends observed for two other corals can be explained by U addition followed by U loss. The fifth coral shows signs of both U gain and loss at the same time in the more recent past. The timing of the diagenetic processes is remarkably similar for the five corals and can be constrained to approx. 1 and 6 thousand years (ka) and 100 and 102 ka after coral growth, respectively.
Based on the modelling results, we suggest that conventional ²³¹Pa/²³⁰Th ages provide the best estimate for the true age of four of the five corals, which range from 109.1 to 114.1 ka. This implies a late Last Interglacial time of deposition. For the fifth coral, the most reliable age estimate is the conventional ²³⁰Th/U age of one of the subsamples (117.3 ka), based on a concordia diagram for all subsamples.
The timing of the modelled open-system processes suggests that the early event of U addition was associated with interaction of the corals with ²³⁴U-enriched seawater or saline groundwater. The later open-system event can be described as U redistribution within the coral reef, since some corals apparently lost U while others gained U. The timing of the second event is broadly consistent with the Bølling-Allerød interstadial, which was probably characterised by enhanced wetness in this typically hyper-arid region.
Influence of glacial meltwater on global seawater δ234U
2018, Geochimica et Cosmochimica Acta
We present the first published uranium-series measurements from modern Greenland Ice Sheet (GrIS) runoff and proximal seawater, and investigate the influence of glacial melt on global seawater δ²³⁴U over glacial-interglacial (g-ig) timescales. Climate reconstructions based on closed-system uranium-thorium (U/Th) dating of fossil corals assume U chemistry of seawater has remained stable over time despite notable fluctuations in major elemental compositions, concentrations, and isotopic compositions of global seawater on g-ig timescales. Deglacial processes increase weathering, significantly increasing U-series concentrations and changing the δ²³⁴U of glacial meltwater. Analyses of glacial discharge from GrIS outlet glaciers indicate that meltwater runoff has elevated U concentrations and differing ²²²Rn concentrations and δ²³⁴U compositions, likely due to variations in subglacial residence time. Locations with high δ²³⁴U have the potential to increase proximal seawater δ²³⁴U. To better understand the impact of bulk glacial melt on global seawater δ²³⁴U over time, we use a simple box model to scale these processes to periods of extreme deglaciation. We account for U fluxes from the GrIS, Antarctica, and large Northern Hemisphere Continental Ice Sheets, and assess sensitivity by varying melt volumes, duration and U flux input rates based on modern subglacial water U concentrations and compositions. All scenarios support the hypothesis that global seawater δ²³⁴U has varied by more than 1‰ through time as a function of predictable perturbations in continental U fluxes during g-ig periods.

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Abstract

References (22)

Quaternary sea level fluctuations on a tectonic coast: New²³⁰Th/²³⁴U dates from the Huon Peninsula, New Guinea

Quat. Res.

²³⁸U,²³⁴U and²³²Th in seawater

Earth Planet. Sci. Lett.

²³⁴U/²³⁸U mass spectrometry of corals: How accurate is the UTh age of the last interglacial period?

Earth Planet. Sci. Lett.

Uranium-series evidence on diagenesis and hydrology in Pleistocene carbonates of Barbados, West Indies

Earth Planet. Sci. Lett.

²³⁴U²³⁸U²³⁰Th²³²Th systematics in saline groundwaters from central Missouri

Earth Planet. Sci. Lett.

High precision Uranium, thorium and radium isotope ratio measurement by high-dynamic range thermal ionisation mass spectrometry

Int. J. Mass Spectrom. Ion Processes

Uranium-series dating of the Pleistocene reef tracts of Barbados, West Indies

Geol. Soc. Am. Bull.

Age estimates and uplift rates for Late Pleistocene marine terraces: Southern Oregon portion of the Cascadia Forearc

J. Geophys. Res.

High precision thorium-230 ages of corals and the timing of sea level fluctuation in the late Quaternary

UTh ages obtained by mass spectrometry in corals from Barbados: sea level during the past 130,000 years

Nature

Calibration of the¹⁴C timescale over the past 30,000 years using mass spectrometric UTh ages from Barbados corals

Nature

Cited by (97)

Mapping and U[sbnd]Th dating of the world's deepest blue hole (South China Sea): Implications for its timing, possible volcanogenic origin, and Pleistocene eolianites in the Xisha Islands

Holocene sea levels at the Gulf of Aqaba, northern Red Sea

Late Quaternary sporadic development of Desmophyllum dianthus deep-coral populations in the southern Labrador Sea with specific attention to their <sup>14</sup>C- and <sup>230</sup>Th-dating

Geochemical proxies in marine biogenic carbonates: New developments and applications to global change

Improved constraints on open-system processes in fossil reef corals by combined Th/U, Pa/U and Ra/Th dating: A case study from Aqaba, Jordan

Influence of glacial meltwater on global seawater δ<sup>234</sup>U

234U/238U ratios and230Th ages for Hateruma Atoll corals: implications for coral diagenesis and seawater234U/238U ratios

Abstract

Quat. Res.

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Int. J. Mass Spectrom. Ion Processes

Uranium-series dating of the Pleistocene reef tracts of Barbados, West Indies

Geol. Soc. Am. Bull.

Age estimates and uplift rates for Late Pleistocene marine terraces: Southern Oregon portion of the Cascadia Forearc

J. Geophys. Res.

High precision thorium-230 ages of corals and the timing of sea level fluctuation in the late Quaternary

UTh ages obtained by mass spectrometry in corals from Barbados: sea level during the past 130,000 years

Nature

Calibration of the14C timescale over the past 30,000 years using mass spectrometric UTh ages from Barbados corals

Nature

²³⁴U/²³⁸U ratios and²³⁰Th ages for Hateruma Atoll corals: implications for coral diagenesis and seawater²³⁴U/²³⁸U ratios

Calibration of the¹⁴C timescale over the past 30,000 years using mass spectrometric UTh ages from Barbados corals