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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 72 (1988)

Issue: 1. (January)

First Page: 8

Last Page: 20

Title: An Early Carboniferous (Visean) Lacustrine Oil Shale in Canadian Arctic Archipelago

Author(s): G. R. Davies (2), W. W. Nassichuk (3)


The Lower Carboniferous (Visean) Emma Fiord Formation in the Canadian Arctic Archipelago is an oil shale of lacustrine origin composed of black carbonaceous shale, siltstone, and marlstone with interbedded sandstone, conglomerate, and oolitic and algal limestones. At Kleybolte Peninsula on Ellesmere Island, the Emma Fiord Formation was deposited on the tectonically active northwestern rim of the Sverdrup basin; it is now thermally overmature and well beyond the dry gas zone of organic maturation (vitrinite reflectance ^approx 5.0). In contrast, the Emma Fiord sequence on Grinnell Peninsula, Devon Island, near the southern edge of the Sverdrup basin, is immature to marginally mature (vitrinite reflectance = 0.26-0.44) and is composed predominantly of liptinite-rich oil sha e. These kerogen-rich rocks contain a high volume of microcrystalline calcite and compositionally are marlstones.

The Emma Fiord lake system probably was a closed basin and may have been thermally and chemically stratified (meromictic). Seasonal or continuous high organic productivity by phytoplankton (and bacteria?) in the epilimnion resulted in accumulation of lipid-rich calcareous sediment below an anoxic hypolimnion.

The Emma Fiord oil shales on Grinnell Peninsula contain both autochthonous and allochthonous organic material. Two types of oil shales are recognized in this sequence: (1) Alginite-rich oil shales with a clay-carbonate matrix in which liptinite content may be as high as 93% of the organic matter. The hydrogen/oxygen index indicates kerogen of intermediate composition between types I and II. These oil shales are hydrogen rich and oxygen poor. (2) Alginite-poor oil shale with a carbonate matrix, relatively hydrogen poor and oxygen rich. The hydrogen/oxygen index indicates kerogen of intermediate composition between types II and III.

The Emma fiord oil shales were deposited in lakes formed immediately prior to or possibly synchronous with the initiation of rifting in the Sverdrup basin. Syntectonic red-bed conglomerates derived from uplifted horst blocks directly overlie the Emma Fiord rocks. A few beds of conglomerate and sandstone in the upper part of the Emma Fiord Formation possibly record the onset of faulting.

The formation closely resembles contemporaneous sequences in northern Alaska, Yukon Territory, Greenland, and Spitsbergen. Clearly, similar tectonic and paleoclimatic factors influenced sedimentation over this area in the Early Carboniferous, with the Sverdrup basin locations lying within 10°-15° of the paleoequator.

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