Clumped isotope analyses (Δ47) – A new geothermometer for carbonate 

Stable isotope analyses (δ13C, δ18O, Sr) and non-conventional analyses (clumped isotopes) on carbonates have become increasingly important in various domain of geosciences. These techniques provide valuable insights into geochemical processes and formation conditions (temperature, fluid composition) of various primary (syn-depostional) and diagenetic carbonates found in subsurface reservoirs. H-ES can offer significant assistance to clients by using these isotopic measurements on carbonates as part of its analytical services toolbox.  

Carbonate reservoirs exhibit petrographic complexity due to diagenetic processes such as cement precipitation and recrystallization. Measuring the formation temperatures of these processes is crucial for understanding the diagenetic and thermal history of the reservoir and better evaluating reservoir properties. This knowledge enhances petroleum exploration, better understands the petroleum system, and correlates temperatures with other geochemical characteristics, such as U-Pb dating or fluid inclusion studies. 

Clumped isotope thermometry relies on the tendency of heavier isotopes (e.g., 13C and 18O) to bond, or “clump,” together more frequently at lower temperatures. The degree of clumping is thermodynamically controlled and thus can be used to calculate the formation temperature of the mineral (Figure 1). Clumped isotope analyses on carbonates have gained interest due to their ability to provide precise information on geochemical processes and formation temperatures of carbonates. Unlike oxygen isotopes, clumped isotopes are solely sensitive to the absolute temperature of carbonate formation and are not influenced by the isotopic variation of the mineralizing water (δ18O). This allows for more accurate and direct estimations of paleotemperatures in various geological contexts (e.g., diagenesis, paleoclimatology, petroleum reservoir analysis).  

Carbonate reservoirs exhibit petrographic complexity due to diagenetic processes such as cement precipitation and recrystallization. Measuring the formation temperatures of these processes is crucial for understanding the diagenetic and thermal history of the reservoir and better evaluating reservoir properties. This knowledge enhances petroleum exploration, better understands the petroleum system, and correlates temperatures with other geochemical characteristics, such as U-Pb dating or fluid inclusion studies.

Figure 1. Clumped isotope  – theoretical principles. This figure illustrates how crystallisation temperature affects the formation of clumped and non-clumped isotopologue​ within calcium carbonate. Cold water, representing low crystallisation temperature, results in more abundant clumped isotopologues within the carbonate structure, here measure on CO2 resulting from acid digestion of the carbonate. Conversely, hot water, representing high crystallisation temperature, leads to fewer clumping​. In the diagrams, blue circles represent Ca2+ ions, black molecule non-clumped CO2​, and yellow molecule clumped CO2​.

What minerals can be analysed ? What is the precision on temperature?  

Clumped isotope analysis can be applied to various carbonate minerals, which are common in geological formations. These include calcite (CaCO3), dolomite (CaMg(CO3)2), aragonite (CaCO3) and siderite (FeCO3). The precision of clumped isotope analysis depends on several factors, including the quality of the sample, the instrument used, the absence of mixing and the analytical protocol. Modern clumped isotope analysis using state-of-the-art mass spectrometers can achieve a precision of around ±0.002‰ (20ppm) for Δ47 measurements. High-quality sample preparation and multiple replicates are essential to ensure accurate results. Typically, three replicates of 5 mg each are analysed to achieve an optimal precision. The precision in temperature estimation derived from Δ47 values is around ±2/3°C (ranging 20°-30°C) for well-prepared samples at low temperature and up to ±5-10°C at higher temperature (ranging 100-200°C). This high level of precision allows for detailed reconstructions of diagenetic conditions (shallow, deep, hydrothermla etc). 


Figure 2. This figure illustrates the relationship between clumped isotope composition (Δ47) and temperature in carbonate minerals, demonstrating its application for determining formation temperatures. The left panel shows values plotted against temperature for various carbonate minerals, with different symbols and error bars indicating precision. The provided equation offers a calibration curve for temperature estimation. The right panel features a carbonate rock sample with a colour map showing the temperature gradient from 15°C to 300°C, corresponding to the crystallisation temperature of various petrographic domains and minerals constituting the bulk rock. The bottom section includes chemical representations of clumped isotope formation, highlighting their temperature dependence

How D47 can help in characterising diagenetic history and paragenetic sequence of subsurface reservoirs.

Clumped isotope analysis allows for the determination of absolute formation temperatures of diagenetic phases such as cementation, recrystallisation, and dolomitisation. By distinguishing between different diagenetic phases through their formation temperatures, geologists can map out the sequence of diagenetic events calibrated in absolute temperature. For instance, early-stage low-temperature cementation can be differentiated from later high-temperature hydrothermal events, providing insights into the fluid flow history and thermal evolution of the reservoir. This comprehensive understanding of the diagenetic history and paragenetic sequence is crucial for unravelling the geological processes that have affected the reservoir over time.

Sample size requirements and homogeneity quality control.

For these analyses, 15 mg of powder is needed. Clumped isotope measurements are repeated three times per sample (5 mg/replicate) to ensure optimal precision (approximately 20 ppm, not guaranteed). Please contact us if you have any questions about the feasibility of analysis or the weight of your sample.


Figure 3. This figure outlines the protocol for selecting and preparing carbonate samples for clumped isotope analysis to ensure homogeneity and accuracy. A piece of carbonate rock with a polished surface is prepared to make a thin section (~30 μm thickness). This thin section undergoes cathodoluminescence (CL) and conventional petrographic analysis to examine detailed micro-petrography and diagenetic feature. Homogeneous samples (uniform phase) where a single phase can be sampled without mixing are accepted for analysis, while heterogeneous samples (multiple phases) are rejected. For accepted samples, 15 mg of powder is collected using a macro-Dremel tool.

Comprehensive workflow for clumped isotope analytical services offered by H-Expertise Services

Figure 4. Our clumped isotope workflow. This figure outlines the workflow for clumped isotope analyses. It begins with Sample Evaluation, including petrographic characterisation and phase identification. Next, Powder Sampling is performed using a Dremel tool or micro-drill. The IRMS delta V stage measures δ18O and δ13C using 2 mg samples on a large set of samples at low cost, from which the most interesting samples are selected for more detailled clumped isotope analysis. IRMS Mat 253 conducts clumped isotope analysis on 5 mg samples, requiring three replicates for correct precision. Results involve data interpretation, visualisation, and integration with fluid inclusion analyses where possible. Finally, Synthesis and interpretation integrate geological insights, resulting in a technical report and recommendations of future work.

Integration with U-Pb dating and fluid inclusions

H-ES also offers the coupling of clumped isotope analysis with U-Pb dating and fluid inclusion studies for a more detailed geological interpretation. U-Pb dating provides absolute age constraints on carbonate formation events, while fluid inclusion analysis offers insights into the composition and temperature of the fluids involved in diagenetic processes. By integrating these techniques, geologists can obtain a more complete picture of the timing, temperature, and fluid conditions during diagenesis. This multi-faceted approach enhances the accuracy of reservoir characterisation and improves the understanding of the reservoir’s evolution.

Cost of clumped isotope analysis and delay

To provide accurate pricing and an official quote, please specify the number of samples along with the name and billing address of the paying institution. Note that δ18O/δ13C measurements are included with clumped isotope analyses at no additional cost. Nor­mally, the turnaround time is ­on the order of­ two to four months, de­pend­ing on the number of new samples ­sub­mitted­ and those already on the waiting list.

Sample shipping/transportation

Please use a sturdy box with sufficient protection to avoid damage during transport. We recommend sending samples in plastic tubes (centrifuge type) or glass. Avoid paper, cardboard, or metal packaging, as the powder often sticks to these materials.

Contact us 

At H-Expertise Services, we leverage advanced techniques, state-of-the-art equipment, and the expertise of our geochemist with decades of practical experience to ensure you receive precise and insightful data, deepening your understanding of geological systems.  Partner with us for unmatched expertise and impactful results. Please contact our specialist, Xavier Mangenot, at xavier.mangenot@h-expertise-services.com to discuss your operational needs, pricing, and to design a customized analytical strategy tailored to your requirements.

Recent Case Studies and Geological Projects

Interested in the practical applications of our geochemistry analysis services? For detailed examples of recent case studies and geological projects we have undertaken, please visit our case study section. Discover how our advanced techniques have delivered crucial insights and improved reservoir understanding for our clients. ….read more here