CGRG Bibliography of Canadian Geomorphology
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Author : Francus P. ; Abbott, M.; and Bradley, R.S.
Date : 2000.
Title : Deciphering an annually resolved climate signal invarved sediments using image analysis.
Publication : 8th International Paleolimnology Symposium, August 20 to August 24, 2000. Queen's University, Kingston, Ontario
Issue :
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Abstract
Varved sediments are valuable paleoclimatic records, because data retrievedfrom such laminated sequences can be temporally constrained. Varvesthemselves contain climatic information, but up to now, varve thickness wasthe only available climatic indicator. Imaging techniques allow the retrieval of additional data. Individualvarve color and thickness measured on digital pictures of freshly cut corescan be linked to sediment properties (Petterson et al., 1999). X-raydensitometry images retrieved from hardened sediment slabs can also be processed to infer rapid downcore relativedensity variations. Petrographic and backscattered electron microscope micrographs ofthin-sections provide multivariate quantified data for each varve. Micrographs are processed to produce black and white images, where whitepixels represent the clay-rich sedimentary matrixand black pixels represent particles in the matrix: silt- or sand-sized,terrigenous or authigenic particles, diatoms or organic debris.Measurements of the size, shape, orientation and packing of the particles forming the varves areobtained. Data obtained on each single varve of the uppermost sections ofthe cores are compared with on-site present-day meteorological andhydrological data. At Sawtooth lake, Arctic Canada (79û 20' N, 83û 51' W), we found a strong correlation between snowmelt intensity and themedian grain-size measured for each annual lamination for the last 33years. Lamination thickness does not correlate with mean summer temperatureover the same period. Coarse subannual sandy layers due to summer rain events aretracked by the 90th percentile of the grain-size of each lamina. This comparison is necessary for the quantification of the climatic control onsediment fluxes to the lake and for the construction of a model linking sediment to climate.
Bibliography of Canadian Geomorphology