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An examination of the role of sediment surface area in controlling the preservation of organic matter in a paralic environment and its influence on petroleum source rock formation and contaminant adsorption, Howe Sound, British Columbia Adams, Rupert Spencer

Abstract

Howe Sound, a glacial fjord situated between Vancouver and Squamish, British Columbia, is subject to a semi-restricted, estuarine type flow regime that results in easily quantifiable sources for the organic matter present in the sediments. Therefore, it was chosen as an ideal location to examine the effects of sediment surface area on the preservation of organic matter and industrial pollutants in the paralic environment. A variety of surface sediment and core samples were retrieved and analyzed for organic content and surface area, as well as other sediment biomarkers and organic pollutant concentration. The role of sediment surface area as a key factor in the preservation of organic matter in marine sediments was then assessed both on historical and geological time-scales, in terms of its potential for generating petroleum source rocks. Organic carbon content of sediments within the study area ranges from 0.1-11 wt.%; a carbon/total nitrogen ratio (C[sub org]/N) of 6-24 in conjunction with other sediment parameters such as δ¹³ C[sub org] and electron microscopy, confirmed a dominant terrestrial signature for the organic fraction of the sediments collected. Sediment surface area varies between 0.5-22 m²/g depending on sample type, location, depth and grain size distribution. Good correlation between surface area and organic carbon in bulk sediments and size fractionated sediments suggests that organic matter is adsorbed to mineral grain surfaces. Correlation between dioxins, furans and surface area varies from r² = 0.23-0.54 in bulk samples, up to r²=0.99 in size fractionated sediments, suggesting that organochlorine pollutant concentration is also linked to sediment surface area. Mineralogy and elemental composition did not appear to correlate with TOC concentration, but additional factors such as molecular chlorination and sample depth did appear to influence the correlation between organochlorine pollutants and surface area. However, in all cases sediment surface area appeared to be the primary factor that governed the preservation of organic matter and industrial pollutants within the study area.

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