Discriminant Function Analysis of Spectral Gamma Data as a Tool for Regional Stratigraphic Correlation of Pleistocene Deposits
Abstract
The protection of groundwater resources is a growing environmental concern in North America. A key requirement in glacial terrains is an understanding of the subsurface distribution and lithologic characteristics of thick, regionally extensive Pleistocene till deposits, as they are a dominant control on regional groundwater flow and contaminant migration. Regional correlation is often problematic when based on lithologic or textural characteristics alone. This paper presents the results of one of the first studies that has utilized borehole and outcrop spectral gamma measurements as tool for regional correlation of tills. A hand-held Exploranium GPX-21 gamma spectrometer and 2SNA-1000 spectral sonde were used to obtain more than 400 measurements on Pleistocene tills and deltaic deposits in the Greater Toronto Area. To quantify separation of each unit, a discriminant function was applied to classify the data. Successful classification of greater than 75% of the stratigraphic units was achieved using this method. Crossplots and three-component plots show that the most sedimentary units have a unique spectral gamma signature. Clay-rich glaciolacustrine strata (e.g. Sunnybrook diamict, Thorncliffe and Scarborough clays) are characterized by more abundant Th, K and U when compared to sandy deltaic units and subglacial tills (e.g. Newmarket and Halton Tills). The element ratios for each unit show a regional consistency, except for the Halton Till, which has a variable spectral signature that reflects the composition of underlying deposits. This association reflects the sub-glacial reworking and incorporation of pre-existing deposits into the till during ice readvance. The results show that many Pleistocene units have unique spectral gamma signatures and that gamma is a useful attribute for regional stratigraphic studies in southern Ontario.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSM.H41D..06C
- Keywords:
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- 0932 Radioactivity methods;
- 1827 Glaciology (1863);
- 1829 Groundwater hydrology