Determination of KGa-1b and SHCa-1 Δ′17O and δ18O via Laser Fluorination of Lithium Fluoride Clay Pellets

Rationale

Stable oxygen isotope measurements in silicate clays, such as smectite and kaolinite, provide crucial information for understanding Earth's climate history and environmental changes. Despite a growing interest in the oxygen isotope analysis of silicate clays and clay-rich sediments, there lacks a consensus on the preparation and standardization of clay mineral samples. To improve the accuracy and interlaboratory comparisons of clay isotope measurements, especially those involving laser fluorination techniques, newly established kaolinite and smectite oxygen isotope standards are much needed.

Methods

We employed conventional nickel bomb fluorination combined with dual-inlet isotope ratio mass spectrometry to establish precise δ¹⁸O and Δ′¹⁷O values for leached clay reference materials KGa-1b and SHCa-1, a kaolinite and a hectorite/smectite, respectively. We further measured leached KGa-1b and SHCa-1 pressed into pellets with a lithium fluoride as a binding agent for the laser fluorination method, allowing us to test the reproducibility between methods and utilize a standard laser chamber drift correction scheme.

Results

The laser fluorination technique yielded highly precise and reproducible δ¹⁸O and Δ′¹⁷O measurements for the KGa-1b and SHCa-1, aligning with bomb values of δ¹⁸O. This confirms the method's reliability and comparability to conventional isotope measurement techniques while also stressing the importance of proper sample preparation and laser chamber drift corrections.

Conclusions

This study demonstrates that laser fluorination is an effective method for accurately measuring the stable oxygen isotope composition of silicate clays or clay-rich sediments when corrected with known silicate clay standards. These methods offer a valuable methodology for future research and applications that will significantly improve our understanding of past climate and environmental conditions.