Comparison of clumped isotope signatures of dolomite cements to fluid inclusion thermometry in the temperature range of 73–176 °C

Abstract

Widespread application of the novel clumped isotope paleothermometer (Δ 47) using dolomite samples from shallow crustal settings has been hindered by a lack of adequate constraints on clumped isotope systematics in dolomites that formed at temperatures greater than 50 ºC.

Carbonate clumped isotope analyses with the long‐integration dual‐inlet (LIDI) workflow: scratching at the lower sample weight boundaries

“…The average external reproducibility of ±0.023 ‰ for our raw standard measurements is excellent and in the range reported for conventional DI measurements of large samples at constant beam (e.g. SD = ±0.018–0.059 ‰; SD = ±0.010–0.024 ‰; average SD = ±0.016 ‰). Conventional DI measurements use large amounts of sample material to obtain enough CO 2 to fill the sample bellow of the mass spectrometer and during sample gas integration the valve between the bellow and source remains open (V15 in Fig.…”

“…A value of ±0.013 ‰ at the 95% CL is equal to a ± 4 °C precision of our Δ 47 temperature proxy (using our Δ 47 ‐1/T calibration). The precision of small aliquot LIDI measurements is the same as for conventional DI measurements, but can be achieved with a factor of 40 or higher less sample material.…”

“…These scans are essential to determine and correct for the m/z 44 dependent backgrounds that are responsible for non-linearity effects in the clumped isotope signal. [29] The raw files of the background scans can be dragged into Easotope, and the software uses them to automatically apply a pressure-sensitive baseline (PBL) correction on the raw intensities of each sample or standard aliquot according to Meckler et al [25] and Müller et al [26] Easotope then uses the PBL corrected beam intensities to calculate the bulk and clumped isotope composition (Δ 47 raw (PBL)) of the sample gases following the mathematical principles described in Huntington et al [32] All data have been processed using the parameters from Brand et al [33] for the 17 O abundance correction, as recently recommended. [34] The next step consists of using the accepted Δ 47 values of the four ETH standards to convert the raw Δ 47 values of the samples with an empirical transfer function (ETF) into the absolute reference frame (ARF).…”

“…Relatively large sample sizes are needed because the sample bellow of the mass spectrometer must be filled with enough gas (50–200 μmol) for the long ion counting times needed to obtain internal standard errors (SE) of less than ±0.01 ‰ at constant signal intensity. Moreover, samples are typically measured several times because the external reproducibility of individual replicates is of the order of ±0.02–0.03 ‰ …”

“…Moreover, samples are typically measured several times because the external reproducibility of individual replicates is of the order of ±0.02-0.03 ‰. [16][17][18][19] In 2010, Schmid and Bernasconi [20] demonstrated the feasibility of an alternative approach, the analysis of the Δ 47 of carbonates with an automated Kiel IV carbonate device connected to a MAT 253 isotope ratio mass spectrometer. The Kiel IV automatically digests small carbonate samples of 100-200 μg (depending on the performance of the mass spectrometer, e.g.…”