301-4 Developing Two Illite-Rich Sedimentary Rocks as Reference Materials for K-Ar Laser Ablation Dating

Session: Geochronology (Posters)

Poster Booth No.: 145

Presenting Author:

Cynthia Bermúdez

Authors:

Bermúdez, Cynthia¹, Solé, Jesus², Pi, Teresa³

(1) Instituto de Geologia, Ciudad de Mexico, Mexico, (2) Instituto de Geologia, LANGEM, Ciudad de Mexico, Mexico, (3) Instituto de Geologia, LANGEM, Mxico City, Mexico,

Abstract:

Establishing a reproducible and widely applicable standard is an important step for applying laser ablation K-Ar dating in clay materials. In this study, we evaluate two distinct illite- sedimentary rocks from Mexico, a bentonite and a mudstone, as potential reference materials for this technique. Both samples were selected based on mineralogical homogeneity, availability, and consistency of previously measured conventional K-Ar ages. Clay-size fractions (<2 µm) were prepared as oriented mounts and analyzed via laser ablation using 100 µm craters and a multipoint isochron approach. Potassium was quantified by laser-induced breakdown spectroscopy (LIBS), and argon by noble gas mass spectrometry under ultra-high vacuum. Preliminary results show highly reproducible Ω values in both materials, with linear isochrons (r² > 0.999) and consistent age determinations within error margins. Differences in ablation behavior and textural properties are discussed, with suggestions for sample preparation protocols. Mineralogical characterization by X-ray diffraction suggests minor differences in smectite content and crystallinity that may influence ablation efficacy. Our findings suggest that both materials may be used as reference standards, each with specific characteristics: mudstone offers high crystallinity and structural consistency, while bentonite presents ideal textural consolidation and minimal detrital contamination. These results support the creation of multi-material reference systems for K-Ar laser ablation of illite and open the door to standardized protocols in clay geochronology.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4691

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