Spatial variability of initial 230Th/232Th in modern Porites from the inshore region of the Great Barrier Reef

Investigating fossil hydrothermal systems by means of fluid inclusions and stable isotopes in banded travertine: an example from Castelnuovo dell’Abate (southern Tuscany, Italy)

“…Samples (about 0.01 g powders) were completely dissolved using ultra-pure double-distilled concentrated HNO 3 mixed with a 229 Th-233 U spike. Hydrogen peroxide was added to the samples after digestion to remove any possible organic matter, and a new anion-exchange column chemistry procedure (modified after Edwards et al 1987;Zhao et al 2001;Clark et al 2012) was used to purify U and Th. Unlike the procedure commonly used in the past, in this modified procedure, U and Th are eluted together using ~3 ml of a 1 % HNO 3 + 0.03 % HF mixture.…”

Reef cores as records of Holocene water temperatures of the southern Great Barrier Reef: Geochemical analysis of traditional (Porites) and non-traditional (Acropora) reef building corals

“…This dating mechanism for coral aragonite is based on the fractionation of U from Th in seawater, which has a 230 Th/ 238 U ratio approximately 10 5 times lower than observed within igneous rocks [Edwards et al, 1987]. Uranium is slightly soluble and predominately exists as uranyl tricarbonate in seawater [Saito and Miyauchi, 1982] at pH > 8 [Djogić et al, 1986]; thus carbonate precipitation in a marine environment will incorporate trace amounts of U, but almost no Th (insoluble) [Clark et al, 2012;Zhao et al, 2009].…”

“…This low content requires strict analytical procedures including the separation of laboratory equipment used for handling and storage of young and old carbonate material [Edwards et al, 1987;Shen et al, 2012;Zhao et al, 2009]. Young coral material also requires a correction for non-radiogenic, initial/detrital 230 Th [Yu et al, 2006;Yu et al, 2012;Zhao et al, 2009], which may be derived from aeolian dust inputs; surface water signatures containing both dissolved and particulate Th; upwelled seawater from the deep sea, carbonate sands derived from coral reef weathering or terrestrial riverine runoff in coastal regions [Clark et al, 2012;Moran et al, 2002;Shen et al, 2008;Yu et al, 2006]. This initial 230 Th correction is where most of the dating error is introduced [Yu et al, 2012;Zhao et al, 2009], with a 20% uncertainty estimated for non-radiogenic Th corrections in massive Porites colonies collected from the South China Sea [Yu et al, 2006].…”

High-precision U–Th dating of storm-transported coral blocks on Frankland Islands, northern Great Barrier Reef, Australia

“…Eisenhauer et al, 1993), the large associated uncertainty makes the age uncertainty of the corrected 230 Th age for young corals too large to be meaningful (see Zhao et al, 2009b). As site-specific or region-specific initial 230 Th/ 232 Th values for non-radiogenic 230 Th correction are more appropriate than the bulk-Earth value in coral 230 Th age calculation (Clark et al, 2012), a site-specific mean 230 Th/ 232 Th in the study area is needed to improve the accuracy and precision of 230 Th ages. Moreover, for most inshore reef corals,…”

“…Approximately 0.15-0.35g (most ~0.15g) of each sub-sample was spiked with a 229 Th-233 U mixed tracer and dissolved in double-distilled nitric acid following the procedures described in Clark et al (2012). After complete digestion, 5 drops of 30% H 2 O 2 were added, and the sample beakers were tightly capped and placed on a hot-plate at 90˚C overnight to allow for complete decomposition of residual organic matters and homogenization of tracer-sample mixed solution.…”