Effects of oxygen plasma ashing treatment on carbonate clumped isotopes

Abstract

Rationale For clumped isotope analysis (Δ47), hydrocarbon and organic molecules present an important contaminant that cannot always be removed by CO2 purification through a Porapak‐Q trap. Low‐temperature oxygen plasma ashing (OPA) is a quick and easy approach for treatment; however, the impact of this treatment on the original carbonate clumped isotope values has never been fully studied. Methods We tested the isotopic impact of OPA using three natural samples with a large range of initial Δ47 values. Crushed and sieved (125 μm mesh) samples were placed into a Henniker Plasma HPT‐100 plasma system and treated at a flow rate of 46 mL/min and a power of 100 W at a vacuum of 0.2 mbar for 10, 20, 30 and 60 min before clumped isotope analysis using two MAT 253 isotope ratio mass spectrometers modified to measure masses 44–49. Results OPA treatment for 30 min or more on calcite powder samples has the potential to alter the clumped isotopic composition of the samples beyond analytical error. A systematic positive offset is observed in all samples. The magnitude of this alteration translates to a temperature offset from known values ranging from 4°C to 13°C. We postulate that the observed positive offset in Δ47 occurs because the bonds within lighter isotopologues are preferentially broken by plasma treatment, leading to an artificial increase in the ‘clumping’ value of the sample. Conclusions We recommend that any laboratory performing OPA treatments should reduce the runs to 10–20 min or carry out successive runs of 10 min followed by sample stirring, as this procedure showed no alteration in the initial Δ47 values. Our results validate the use of OPA for clumped isotope applications and will allow future research to use clumped isotopes for challenging samples such as oil‐stained carbonates, bituminous shales or host rocks with very high organic carbon content.

InterCarb: A Community Effort to Improve Interlaboratory Standardization of the Carbonate Clumped Isotope Thermometer Using Carbonate Standards

“…Carbonate clumped isotope (Δ 47 ) thermometry is the most developed branch of the rapidly evolving field of clumped isotope geochemistry. Given the broad range of applications in Earth Sciences (e.g., Affek & Eiler, 2006; Dale et al., 2014; Eagle et al., 2010; Ferry et al., 2011; Ghosh, Adkins, et al., 2006; Ghosh, Garzione, & Eiler, 2006; Grauel et al., 2013; Guo & Eiler, 2007; Huntington et al., 2011; Mangenot et al., 2018; Passey & Henkes, 2012; Veillard et al., 2019) and the improvement of analytical methods including automation (Adlan et al., 2020; Bernasconi et al., 2018, 2013; Defliese & Lohmann, 2015; Dennis et al., 2011; Fiebig et al., 2019; Ghosh, Adkins, et al., 2006; He et al., 2012; Hu et al., 2014; Huntington et al., 2009; Meckler et al., 2014; Müller, Fernandez, et al., 2017; Passey et al., 2010; Petersen et al., 2016, 2019; Schmid & Bernasconi, 2010), the last 5–10 years have seen an increasing number of laboratories implementing this technique. The great potential of this thermometer can only be fully exploited if precision and accuracy are sufficient to resolve differences of a few degrees in formation temperatures.…”

Origin and distribution of calcite cements in a folded fluvial succession: The Puig‐reig anticline (south‐eastern Pyrenees)

“…Measurements were carried out in the Qatar Stable Isotope Laboratory at Imperial College London using a fully automated system, Imperial Batch Extraction (IBEX), and following the method of Adlan et al . (2020). Around 4 mg aliquots of calcite powders for each sample were individually dropped into 105% phosphoric acid at 90°C and reacted for 10 min on an automated IBEX device.…”

“…Clumped isotope thermometry was applied to four samples of calcite cements to calculate the temperatures and d 18 O values of the fluids from which these calcite cements precipitated. Measurements were carried out in the Qatar Stable Isotope Laboratory at Imperial College London using a fully automated system, Imperial Batch Extraction (IBEX), and following the method of Adlan et al (2020). Around 4 mg aliquots of calcite powders for each sample were individually dropped into 105% phosphoric acid at 90°C and reacted for 10 min on an automated IBEX device.…”

Changing surface ocean circulation caused the local demise of echinoid Scaphechinus mirabilis in Taiwan during the Pleistocene–Holocene transition

“…Both living and fossil specimens were rinsed and ultrasonicated in water and dried overnight before being ground into powder. The carbonate powder was subjected to oxygen plasma ashing 40 to remove organic matter, which may interfere with the measurement. The measurement followed the methodology outlined in Adlan et al 40 .…”

“…The carbonate powder was subjected to oxygen plasma ashing 40 to remove organic matter, which may interfere with the measurement. The measurement followed the methodology outlined in Adlan et al 40 . Briefly, samples of calcite powder (~ 4 mg) were reacted with 105% orthophosphoric acid at 90 °C for 10 min to generate carbon dioxide (CO 2 ) gas.…”