APPLICATION OF PXRF TO A CHEMOSTRATIGRAPHIC FRAMEWORK FOR THE QUATERNARY OF SOUTHERN ONTARIO

In glacial basins stratigraphic correlation is commonly limited to lithostratigraphic methods. Correlation can be significantly improved through the use of geophysical and geochemical properties. Widespread subsurface geophysical data is often limited, and application of chemostratigraphic techniques is under-utilized. A chronostratigraphic framework is being developed for southern Ontario using portable X-ray fluorescence spectrometry (pXRF) in trace element mode, which is optimized for elemental concentrations that are expected to be <1%. Sixteen elements are commonly detected (As, Ba, Ca, Cr, Cu, Fe, K, Mn, Ni, Pb, Rb, Sr, Ti, V, Zn, Zr). Analytical protocols have been developed to maximize instrument stability, and to obtain precise and accurate data. A grain size fraction of <63 microns is used to minimize nugget effect and a dwell time of 60 seconds is used for each of the Low, Main and High filters. Internationally recognized, certified reference materials (CRM’s), which span the range of element concentrations, are analyzed with the unknown samples to monitor precision, and allow for post-analysis data correction with respect to accuracy. This protocol was developed through the analyses of over 10,000 samples obtained from multiple glacial basins across Canada, and verified against traditional laboratory methods (fusion, four acid, aqua regia digestions) using >500 samples. The comparison with laboratory chemistry has supported the suitability of pXRF spectrometry for regional baseline studies where more complete elemental analysis my not be required or where cost is a factor. For subsurface samples, obtaining adequate sample material from core is sometimes a challenge. To address this uncertainty in the minimum sample required a study was completed on samples ranging from 1 to 20 mm in thickness, in order to establish calibration equations. Results from all studies have demonstrated the ability of chemical analyses obtained from pXRF spectrometry to identify stratigraphic units, refine sedimentological interpretations, and correlate within glacial basins. The addition of geochemical analyses has refined paleogeographic interpretations, provenance studies and will support more realistic 3-D geological models with increased confidence in stratigraphic correlations.