Elemental composition, environment of deposition of the lower Carboniferous Emma Fiord formation oil shale in Arctic Canada

Abstract

The sedimentary succession of 51-m consisting of a thin coal seam (1 m) and oil shale with a marlstone and carbonate-mudstone matrix of the Lower Carboniferous (Viséan) Emma Fiord Formation located on the Grinnell Peninsula, Devon Island, Arctic Canada was examined. The techniques used include reflected light microscopy, and instrumental neutron activation analysis (INAA) for elemental concentration, and inductively coupled plasma emission spectrometry (ICPES) for boron concentration.The coal and oil shale was deposited in a lacustrine, freshwater environment. Due to the climatic variation, two types of oil shale were developed based on the amount of precipitation. One with carbonate-mudstone matrix, with high calcite (75%) and low TOC (1.14–1.87%) content. The other a marlstone-dominated matrix with high aluminosilicate (64%) and TOC (16.4–53.6%) content.Oil shale from Emma Fiord experienced a slow rate of sedimentation and terrestrial flux as determined using Th/K/ Na/K, ratios Mn/Ca ratio to Ca respectively, and compared to the oil shale of Carboniferous age deposited in a lacustrine environment with a regular rate of recharge/discharge. The redox conditions for the Emma Fiord oil shale indicate anoxic to dysoxic conditions based on the variation of Cr and V + Ni.Thorium and U systematics indicate that U is more concentrated in oil shale with marlstone matrix and is associated with clay minerals and organic matter (OM), similar to the Carboniferous oil shale from the Big Marsh. The authigenic U is associated with TOC content and is higher for oil shale with the marlstone matrix.The variation of U with TOC indicates both paleo-productivity and preservation and is higher for oil shale with the marlstone matrix.The concentration of rare earth elements (REEs) is 95% due to the presence of light rare earth elements (LREEs) in both oil shale with marlstone and carbonate-mudstone matrices.The REES were normalized to the post-Archean average shale (PAAS). The high volatile bituminous coal at the base of the oil shale sections displays a flat, featureless pattern. The oil shale with a carbonate matrix decreases slightly from light rare earth elements (LREEs) to heavy rare earth elements (HREES). In contrast, the REEs concentration for oil shale with the marlstone matrix decreases more sharply from the LREEs (La-Eu) to HREEs (Tb-Lu). It displays a weak negative Eu anomaly typical of the upper continental crust.