Applicability of Diffuse Spectral Reflectance for Clay Mineral Identification in Sedimentary Sequences

Yvette A. Vlack¹, Joseph D. Ortiz¹, Brandon B. Curry², John T. Haynes³, Nancy K. Grant⁴, and Ernest H. Carlson^1
1Geology, Kent State University, Kent, OH
²Illinois State Geologic Survey, Champaign, IL
³Geology and Environmental Sciences, James Madison University, Harrisonburg, VA
⁴Public Adminstration and Urban Studies, University of Akron, Akron, OH

The versatility of diffuse spectral reflectance (DSR) was investigated as a complementary methodology to XRD and XRF when studying clay minerals in stratigraphic sequences. The Analytical Spectral Device (ASD) Labspec Pro FR UV/VIS/NIR spectrometer provides an innovative nondestructive methodology that is cost effective, portable, quick and easy to use with samples in the lab or field. To test the applicability of the method, we evaluated two data sets: (1) sediment from core MNK3, from a slack water Pleistocene lake near St. Louis. Stratigraphic changes in clay mineralogy occur down core, (2) and the Ordovician Millbrig K-bentonite (samples from AL, GA, KY, TN, and VA), an altered tephra in which the changes occur laterally in a single horizon. DSR spectral data is validated against XRD, ICP-MS, and XRF data. To support interpretation of the DSR data, we have employed the Labspec Pro FR to generate a spectral library, which includes four primary clays and clay mixtures, readily available for use as a research reference tool. The aim is to close the gap that currently exists for an expanded spectral library of clay mixtures and explore the DSR variability of clay mixtures. Clay mineral standards used were obtained from the Clay Mineral Repository, and only those clay mixtures that are most prevalent in sedimentary sequences were studied. PCA (Principal Component Analysis) is used to correlate the spectral data of the library with the two MNK3 and Millbrig samples. DSR has already demonstrated its ability to verify clay mineral content variability in both data sets in agreement with XRD data and supported by elemental trends based on XRF and ICM-AES.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas