Calibration of the oxygen and clumped isotope thermometers for (proto-)dolomite based on synthetic and natural carbonates

Abstract

This is a repository copy of Calibration of the oxygen and clumped isotope thermometers for (proto-)dolomite based on synthetic and natural carbonates.

Analytical effects on clumped isotope thermometry: Comparison of a common sample set analyzed using multiple instruments, types of standards, and standardization windows

“…Most standardization techniques also yield results that are statistically identical to the reprocessed Defliese et al data, with all slopes statistically indistinguishable, and only the intercepts significantly different at the 95% level (Figure ). These differences in intercept are of the order of the differences reported for the error on acid digestion with an average offset of 0.022‰ in this dataset, and may reflect slight differences in acid temperature and/or other measurement discrepancies. It should be noted that these discrepancies are detectable only at the 95% confidence level because the reproducibilities of the Perspective IS and UMich 253 instruments are quite high, as evidenced by the low measurement error for each.…”

“…All three of these calibrations are within error of each other, and are generally slightly steeper in slope (but still within error) than the calibration produced solely using data from the UMich . Notably, recently published calibration studies have steeper slopes and smaller intercepts that do not overlap with these calibrations, suggesting that there are probably real differences in the absolute Δ 47 ‐temperature relationships among these carbonates, given that the Perspective IS (which should be immune to issues arising from the non‐linearity correction) shows the same result as the UMich MAT 253 (Figure ). If there is a universal calibration, it is likely that calibration studies encompassing a larger number of samples, measurements, and range of temperatures, such as Petersen et al better capture the true Δ 47 ‐temperature relationship …”

“…The first two published calibrations had almost a 50% difference from each other, and this discrepancy has been referred to as the “two slope” or “steep and shallow slope” problem. Many studies have attempted to address the underlying cause of these discrepancies, investigating factors such as mineralogy, precipitation rate, acid digestion temperature, the use of varying isotopic constants, and the use of natural versus synthetic materials, in addition to other procedural and methodological issues. No single factor has yet been found as the cause of this historical discrepancy in the literature.…”

“…Yet quantifying the impacts of standardization method on resultant Δ 47 values is critical for resolving why there are still discrepancies in Δ 47 ‐temperature calibrations, and for quantifying the magnitude of equilibrium and kinetic isotope effects. There are three end‐member hypotheses for the origin of discrepancies in reported calibrations: (a) there are measurable equilibrium and kinetic isotope effects that give rise to the range of values observed in the literature, (b) inter‐laboratory differences in sample digestion give rise to the variation observed in Δ 47 , and (c) inter‐laboratory differences in Δ 47 measurement and/or standardization give rise to the variation observed in Δ 47 ,…”

Effects of different constants and standards on the reproducibility of carbonate clumped isotope (Δ47) measurements: Insights from a long‐term dataset

“…Since the initial proposal of this proxy, a number of different Δ 47 –T calibrations have been published, leading to reconstructed temperature discrepancies of up to 10–15°C based on the same Δ 47 value . Several hypotheses exist as to the origin of calibration differences, including different gas preparation procedures, different mass spectrometric corrections, and potentially different acid fractionation factors (e.g. 0.069‰ from Guo et al, 0.081‰ from Passey et al, 0.082‰ from Defliese et al, and 0.153‰ from Murray et al at the same temperature of 90°C), or use of temperature calibrations for different carbonate minerals (e.g.…”