Comparison of the geochemistry of lacustrine oil shales of Mississippian age from Nova Scotia and New Brunswick, Canada

The bulk elemental concentration of selected Albert Formation oil shale deposits of Mississippian age from New Brunswick was analyzed using ICP-MS and Prompt Gamma. Results compared to that of the Big Marsh oil shale of similar age from Nova Scotia. Reflected white and fluorescence light was used to determine the characteristic organic matter, and RockEval analyses were used to determine the hydrocarbon potential of oil shale. Both Albert and Big Marsh oil shales were deposited in lacustrine environments, based on geological and sedimentological evidence. The Big Marsh oil shale has low and stable B content (28-54 ppm), which stays almost constant and with the range for freshwater with depth. By contrast, the oil shales from the Albert Formation from New Brunswick have high and were for Albert oil shale. The Big Marsh deposit, in contrast, had stable discharge and recharge with higher aluminosilicate input and limited or no carbonate content. The rate of sedimentation, as determined by Na/K and Th/K ratios indicates that the Albert oil shales deposited at a slower rate as compared to the Big Marsh oil shales. The lower Th/U ratio for Albert oil shale as compared to the Big Marsh is likely due to lower input of weathered and recycled sedimentary terrestrial flux, and allochthonous U content, into the lacustrine setting during their deposition. Albert oil shales deposited in oxic-dysoxic conditions based on their Cr and V/Cr ratio, suggesting a well-oxygenated and uniform, warm temperature upper water level. Variation of Ca/Sr versus Ca/Mn ratios for the Albert oil shale, indicates low Mn/Ca and relatively high Sr/Ca ratio for most of the samples, due to low terrigenous influx and warmer water, which is supported by the mineralogy of the oil shales, which contain low quartz and clay minerals. The presence of higher authigenic U and Mn/Ca ratio for Albert oil shale indicates low terrestrial flux and, therefore Th as compared to Big Marsh oil shales. The Rare Earth element (REEs) content is higher for the Big Marsh oil shales owning to a higher input of aluminosilicate than the Albert oil shale as supported by variation of Y and La and that of Hydrogen index (HI) and Heavy Rare earth (HREEs). The Albert oil shale displays a positive Eu anomaly, typical of a high carbonate environment. By contrast, Big Marsh, which shows a negative Eu anomaly, which is typical of upper continental crust.