Carbonate U-Pb dating by (LA-ICP-MS) Laser Aablation Inductively Coupled Plasma Mass Spectrometry 

U-Pb dating by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is an advanced method for dating carbonate minerals, providing crucial information on the timing of diagenesis, hydrocarbon migration and the geological history of subsurface reservoir bearing carbonate. This technique is particularly beneficial in deeply buried reservoirs, where the presence of multiple generation of primary and diagenetic carbonates allows the tracing of complete fluid-rock interactions and reservoir history across its geological evolution. 

Fig. 1. The figure illustrates a comprehensive approach to dating geological events and diagenesis using relative, absolute, and indirect dating methods. The top right of the figure demonstrates a CT scan of a core section highlighting the importance of sample context. The left diagram presents a paragenesis of diagenetic events, establishing a timeline of geological processes without specific ages throught cross-cutting relationship. The middle diagram features a Tera-Wasserburg plot, providing precise U-Pb ages (e.g., 150 ± 16 Ma) for a specific diagenetic stages (blocky calcite), representing absolute dating. The right diagram shows temperature evolution models based on fluid inclusion temperatures (e.g., 72°C and 150°C) with the thermal history of the host reservoir, representing an indirect dating approch. The integration of these dating techniques provides a comprehensive and robust chronological framework for interpreting complex diagenetic and petro-physical evolution.

U-Pb dating – theory and method principle

U-Pb dating relies on the analysis of uranium (U-238) and lead (Pb-206, Pb-207, Pb-208) isotopes present in carbonate minerals (Figure 2). In the LA-ICP-MS method, a laser ablates small samples of carbonate (100um), which are then ionized and analysed by mass spectrometry. This allows for the precise measurement of various uranium and lead isotopic ratios, thereby determining the age of carbonate formation with the Tera Wasserburg method. A Tera-Wasserburg graph plots the isotopic ratios of 207Pb/206Pb and 238U/206Pb. The intersection of the isochrone with the Concordia line (red) indicates the age of carbonate precipitation (or recrystallisation). For example, on the figure 4 and 5, calcite blockage preserves an age of 60 Ma, and dolomite shows 327 Ma, reflecting here their crystallization age.

Figure 2. The figure illustrates the U-Pb dating process in carbonate minerals. Uranium, primarily known as uranyl ion (UO2^2+), substitutes for calcium in carbonate structures. It has two key isotopes: U-235 and U-238, which decay into lead isotopes Pb-207 and Pb-206, respectively. Thorium-232, another contributor, decays into Pb-208. The diagram highlights that carbonate minerals are significantly enriched in lead (Pb) compared to mineralising waters, by a factor of 10-100. By measuring the ratios of lead isotopes (Pb-206, Pb-207, Pb-208) to non-radiogenic Pb-204, geologists can date the mineral formation. This enrichment and the substitution mechanism ensure accurate U-Pb dating, providing insights into the mineral’s age.
Figure 4. LA-ICPMS U-Pb dating of saddle dolomite crystal.  The figure presents a Tera-Wasserburg plot and accompanying micrographs of saddle dolomite rich in petroleum fluid inclusions. The Tera-Wasserburg plot shows the age of carbonate precipitation at 327.4 ± 15 Ma. The top right micrograph displays a thin section under cross-polarised light, revealing the detailed structure of saddle dolomite. The inset shows a UV light image highlighting the luminescent properties of oil inclusions in dolomite. The bottom right image is a composite image (Z stacking) highlighting the distribution of fluid inclusions density within various dolomite crystal.  
Figure 3. Integrated petrographic imaging to in-situ U-Pb dating of carbonate minerals. This figure illustrates various imaging and analytical techniques used during in-situ U-Pb dating of carbonate minerals. The thin section (NPL) shows a photomicrograph under non-polarised light, revealing the general structure, texture, and diagenetic fabrics of the carbonate sample. The cross-polarised photomicrograph enhances better visibility of mineral textures and structures. Cathodoluminescence imaging captures the luminescent properties of the carbonate minerals, allowing to reveal zoning patterns and growth history of various diagenetic cements. The mapping of elemental composition indicates the distribution of uranium concentration within the sample, with colour coding to show varying levels. The mass spectrometry analysis includes symbols for uranium (U) and thorium (Th) isotopes and lead (Pb) isotopes, representing the measurement of signal intensities for various isotopes of interest for U-Pb system. These techniques collectively provide comprehensive data for in-situ geochronological determination of carbonate minerals in reservoir studies. 

What minerals can be dated by LA-ICPMS and at what spatial resolution ?

At H-Expertise Service, we provide advanced analytical services using state-of-the-art equipment to deliver precise U-Pb dating for a variety of carbonate minerals, including calcite, dolomite, siderite,  commonly found in petroleum reservoirs. Our micro-sampling techniques enable the dating of small samples (around 100 micrometers), which is essential when the mineral of interest is very fine, such as intragranular cement in sandstone or zoned minerals. The laser ablation micro-sampling allows for the progressive erosion of the sample surface with depths around 25 micrometers, enabling detailed analysis on thin sections (30 micrometers) or wafers (100 micrometers). Additionally, we can work directly on rock samples mounted in resin or on thick/thin sections, providing flexibility and convenience for your specific sample preparation needs.

Figure 5. LA-ICPMS U-Pb dating of blocky calcite in tectonics veins. The figure presents a Tera-Wasserburg plot and accompanying micrographs of blocky calcite in tectonic veins. The Tera-Wasserburg plot shows the age of calcite precipitation at 59.83 ± 0.59 Ma. The bottom left image is a thin section under cross-polarised light, revealing the detailed structure of blocky calcite within the tectonic veins. The middle left micrograph displays the arrangement of all analytical spots on a thin section (here n=36), highlighting a closer view of the sampled areas. The top left image shows 3D view of ablation spots realised for ablation quality control. These images and data collectively illustrate how isotopic and imaging techniques can be used to determine the geological history of reservoirs and timing of diagenetic events.
Figure 6. The figure showcases various stages and techniques in the process of laser ablation for U-Pb dating of carbonate grains (data acquisition and interpretation). The top left image shows a thin section under a microscope. The middle top image displays a detailed view of ablation spots on a calcite spar thin section, and the top right image highlights the precise placement of multiple ablation spots on a rudist shell sample. The bottom left image presents a 3D depth profile of an ablation crater, demonstrating the precision and depth achieved. The bottom right image, under cathodoluminescence, shows the detailed zoning of the ablated cements, indicating areas targeted for analysis (post-ablation image). These images together represent the meticulous approach taken to ensure accurate and detailed U-Pb dating results.

Our cutting-edge technologies

To ensure precise and reliable results, we use the best equipment available on the market.

  • The Keyence VHX-7000N Digital Microscope is a state-of-the-art instrument designed for high-resolution imaging and analysis. It offers exceptional clarity and depth of field, which is crucial for detailed examination of geological samples. The microscope’s multi-angle observation capability allows for comprehensive analysis of sample surfaces, revealing intricate details of mineral structures and textures. The VHX-7000N also includes a 3D measurement function, enabling precise quantification of surface topography and micro-features, which is critical for accurate observation of ablation profiles.
  • The ThermoFischer ELEMENT XR Mass Spectrometer is a high-resolution sector field inductively coupled plasma mass spectrometer (SF-ICP-MS), designed for precise analysis of isotopic ratios. It offers high sensitivity, capable of detecting trace elements at very low concentrations, which is essential for precise U-Pb dating. The sector field technology allows for excellent mass resolution, reducing interferences and providing accurate isotopic measurements. The ICP source ensures complete ionization of the sample, improving accuracy and reliability. The ELEMENT XR also features a wide dynamic range and exceptional stability, providing consistent precision over extended periods, crucial for high-quality isotopic analysis.
  • Our ESI 193 nm Excimer Laser Ablation System is a high-precision laser designed for detailed analysis of solid samples. Its 193 nm wavelength provides high-energy photons effective at breaking chemical bonds in carbonate minerals, resulting in clean and efficient ablation. The laser can focus to very small spot sizes, allowing precise targeting within a sample. Controlled depth profiling with typical ablation depths around 25 micrometers enables detailed analysis of thin sections and wafers. The excimer laser produces minimal heat during ablation, reducing thermal damage and preserving sample integrity. Automated sample handling allows for precise and repeatable positioning and ablation. These advanced technologies enable H-Expertise Service to provide reliable, accurate U-Pb dating services tailored to geological and petroleum reservoir studies.
Figure 7. Advanced equipment used for in-situ carbonate U-Pb dating and imaging. See text for detail on the equipment.

Toward our grain-by-grain dating protocol for studying cuttings samples

In petroleum geoscience, cutting samples are small rock fragments brought to the surface during drilling. These samples are crucial for identifying subsurface lithology, stratigraphic correlation, reservoir characterisation, and providing geochemical insights such as U-Pb dating and fluid inclusion analysis, which aid in understanding the geological history and potential hydrocarbon zones in not well explored area. At H-Expertise Service, our approach to dating carbonate grains in cutting samples involves a novel in-house methodology designed to maximise accuracy and reliability. Initially, all cutting samples undergo LA-ICPMS screening in a non-collection mode to ensure they contain sufficient uranium and minimal common lead. Only samples passing this screening proceed to further analysis. We then perform detailed analysis on small spots (4-10 per grain) using our Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICPMS), allowing for precise erosion of the sample surface and providing detailed data for each individual grain. For samples where multiple grains are dated (10-15 grains), we employ a statistical approach using weighted means to obtain robust age estimations, ensuring enhanced reliability and precision of the age data. This aids in the accurate targeting of petrographic phases for dating complex mixing of cutting samples and replace them in chronological framework (stratigraphic correlation, diagenetic fabrics/pattern etc).

Figure 8. Dating individual carbonate grains within carbonate cutting samples using laser ablation U-Pb dating methods. The upper left images show various grains from the cutting samples. The top right image displays a polished thin section of rock cuttings impregnated in blue resin, prepared for analysis. The bottom right shows a Tera-Wasserburg diagrams, which plot the isotopic data used to determine the age of each individual carbonate grain. These diagrams illustrate the robust methodology and statistical approach employed to achieve precise and reliable age estimations for each individual grain.

Enhance reservoir characterisation by coupling U-Pb dating with different mineral geothermometers

Combine U-Pb carbonate dating with fluid inclusion studies and clumped isotope geothermometry for a comprehensive understanding of your reservoirs geological and thermal history. Fluid inclusion analysis can correlate hydrocarbon migration with pressure and temperature changes, while U-Pb dating provides a quantitative chronological framework for these events. This integrated approach enhances the understanding of fluid-rock interactions, reservoir thermal evolution, and fluid history reconstruction. U-Pb dating helps establish the chronology of diagenetic changes, date fluid inclusion entrapments, and better constrain geological processes such as thermo-chemical sulfate reduction and H2S formation. It also accurately dates fluid migration events, natural rock fracturing, and fault activities, providing valuable insights for reservoir management and optimisation.

Comprehensive U-Pb analytical services offered by H-Expertise Service

Figure 9. Comprehensive U-Pb Carbonate Dating Workflow at H-Expertise Services. The workflow diagram illustrates the comprehensive process of U-Pb carbonate dating. The process begins with Sample Preparation, involving thick section preparation and mineral characterization through observations such as cathodoluminescence, microscopy, and trace element maps. Samples then undergo Screening using the LA-ICP-MS system to ensure favourable U-Pb ratios. It is important to note that approximately 50% of samples contain sufficient uranium and minimal common lead to be precisely dated, though this rate of success cannot be guaranteed. In the Strategy phase, samples are evaluated for uranium content, determining the next steps. If favourable ratios are found, they proceed to the Analysis phase for U-Pb analysis, assessing carbonate age. The Results phase includes age calculation and raster age calculation (for age mapping), providing interpretable or non-interpretable ages. Finally, the Synthesis & Interpretations phase compiles the data into a comprehensive session report, delivering detailed insights and interpretations.

Turnaround time

We understand the importance of timely results. Our typical analysis turnaround time is approximately 2-6 weeks, ensuring you receive detailed and precise data without undue delay.

Contact us

Please contact our specialist, Xavier Mangenot, at xavier.mangenot@h-expertise-services.com, to discuss your operational needs, pricing, and to design a customised analytical strategy in geochemistry. Let us assist you in achieving your research and industry objectives with our comprehensive and reliable U-Pb dating services.

Recent case studies and geological projects

Curious about the impact of our U-Pb analytical services? For concrete examples of recent case studies and geological projects we have worked on, please visit our case study section. Explore how our expertise has provided valuable insights and enhanced reservoir characterisation for our clients. ….read more here