Natural stable isotopes ratios (δ¹³C_carb and δ¹⁸O_carb) of carbonates archived in the geological record are routinely used to reconstruct local and global paleo temperatures and the secular evolution of the biogeochemical carbon cycle. The state-of-the-art technique, employed since the mid 20th century, to measure these isotopic ratios starts with field sampling followed by several steps of physical and chemical laboratory preparation including: (i) microdrilling and/or sawing and crushing, (ii) CO₂ release by wet acid digestion, (iii) gas equilibration, purification and transfer, before (iv) gas phase IRMS measurements. While these steps are time and resource consuming, they provide accurate measurements of δ¹³C_carb, δ¹⁸O_carb and carbonate contents. This study presents a new protocol involving a compact and modernized laser calcination system that decreases drastically the analyses time by reducing the number of preparations steps together with offering the possibility of performing spatially resolved analysis at the mm scale. This new method is based on the use of a fiber coupled laser diode device emitting 30 W in the near infrared at 880 nm. The energy provided by the laser source induces the decomposition of calcium carbonate into lime and carbon dioxide. In this work, the CO₂ was collected in sample tubes under a controlled atmosphere for offline analysis, however additional developments should permit online analysis in the near future.

We analyzed 9 different types of carbonate minerals encompassing a range of isotopic compositions VPDB between +3.3 and − 18.2‰ and between −1.7 and − 14.6‰ for δ¹³C_carb and δ¹⁸O_carb, respectively. A comparison of isotopic results was performed for carbonate zones analyzed both by classic methods (micro-drilling followed by acid digestion) and laser calcination. This isotopic cross-calibration exercise shows a direct positive co-variation between both methods with a correlation coefficient of 0.99 and a regression slope of 1 within uncertainties for the δ¹³C_carb values. The δ¹⁸O_carb values also compared well with a correlation coefficient of 0.96, suggesting a constant gas-solid phase isotopic equilibrium between carbon dioxide and lime. The reproducibility of our laser calcination method performed on replicate analyses of dolomite, siderite and malachite shows a 1σ standard deviation of 0.31 and 0.77 for δ¹³C_carb and δ¹⁸O_carb, respectively. These reproducibilities are within the observed isotopic natural inhomogeneity of samples (up to 1.3 and 0.57‰ for the δ¹³C_carb and δ¹⁸O_carb, respectively) as assessed by microdrilling and acid digestion.

Based on the suit of samples analyzed in this study, we demonstrate that (i) fiber coupled laser diode calcination enables accurate and reproducible C and O isotopic characterization of natural carbonates, (ii) physical effects during calcination do not introduce any isotopic fractionation for C and is accompanied by a constant isotopic offset for O over a range of isotopic compositions and mineral matrices. These findings pave the way for a new range of possibilities for carbonate δ¹³C and δ¹⁸O measurements directly in the field using rapid, portable, and easy to manipulate laser preparation devices paired with CRDS/IRIS optical-mass spectrometers.

自然稳定的同位素比率（δ ¹³ C ^_{碳水化合物}和δ ¹⁸ ö_{碳水化合物}）的地质记录归档碳酸酯的常规地用于重建局部和全局古温度和生物地球化学碳循环的世俗进化。自20世纪中叶以来，用于测量这些同位素比的最先进技术始于现场采样，随后是物理和化学实验室准备工作的几个步骤，包括：（i）微钻孔和/或锯切和粉碎，（ ii）CO ₂在（iv）气相IRMS测量之前，通过湿酸消化释放（iii）气体平衡，纯化和转移。虽然这些步骤是耗费时间和资源，它们提供了δ的精确测量¹³ Ç_{碳水化合物}，δ ¹⁸ ö_{碳水化合物}和碳酸盐含量。这项研究提出了一种新的方案，其中涉及紧凑且现代化的激光煅烧系统，该方案通过减少制备步骤的数量而大大减少了分析时间，并提供了进行毫米级空间分辨分析的可能性。这种新方法基于使用光纤耦合激光二极管器件，该器件在880 nm的近红外波段发射30 W功率。激光源提供的能量促使碳酸钙分解为石灰和二氧化碳。在这项工作中，将CO ₂收集在受控气氛下的样品管中以进行离线分析，但是，更多的发展应允许在不久的将来进行在线分析。

我们分析了9种不同类型的碳酸酯的矿物质包括一系列同位素组成VPDB的3.3之间- 18.2‰之间-1.7和- 14.6‰，δ ¹³ C ^_{碳水化合物}和δ ¹⁸ ö_{碳水化合物}，分别。对碳酸盐岩地区的同位素结果进行了比较，这些碳酸盐岩地区均通过经典方法（微钻孔，然后进行酸消解）和激光煅烧进行了分析。这种同位素交叉校准锻炼示出了具有0.99的相关系数为1的不确定性内的回归斜率为δ两种方法之间的直接正共变¹³ Ç_{碳水化合物}值。该δ ¹⁸ Ø_{碳水化合物}该值也很好地与0.96的相关系数进行了比较，表明二氧化碳和石灰之间的气固相同位素平衡恒定。上白云石，菱铁矿和孔雀石显示0.31的1σ标准偏差和0.77的复制分析为δ执行我们的激光煅烧方法的再现¹³ Ç_{碳水化合物}和δ ¹⁸ ö_{碳水化合物}，分别。这些再现性是样品的观察到的同位素自然不均匀性内（高达1.3和0.57‰的δ ¹³ C ^_{碳水化合物}和δ ¹⁸ ö_{碳水化合物}，分别地）通过钻削和酸消化评估的。

根据本研究中分析的样品，我们证明（i）光纤耦合激光二极管煅烧能够对天然碳酸盐进行准确且可重现的C和O同位素表征，（ii）煅烧过程中的物理影响不会对C引入任何同位素分馏并伴随着一系列同位素组成和矿物基质中O的恒定同位素偏移。这些发现铺路碳酸δ一个新的可能性范围¹³ C和δ ^18个使用快速，方便携带，并且容易操纵与CRDS配对激光制备装置在现场直接测量ø/ IRIS光学质谱仪。