Ichnological Expressions of Low Oxygen Settings: An Ichnological Analysis of the Canol Formation, Northwest Territories, Canada

Abstract

The Canol Formation, part of the Horn River Group in the Northwest Territories, primarily consists of black shales deposited during the Middle to Late Devonian. The formation is considered to represent distal basin fill accumulated in an anoxic to euxinic depositional setting, owing to the shale’s organic-rich character, pyrite content, and lack of obvious biogenic reworking. The sediment transport processes resulting in the deposition of these shales have yet to be identified. This study aims to identify depositional processes and paleo-redox fluctuations within the Canol Formation via comprehensive ichnological analyses and some integration with geochemical paleo-redox proxies. Detailed petrographic ichnological analyses are carried out on thin sections taken from several cored Canol Formation intervals (MGM Shell East Mackay I-78, Husky Little Bear N-09 and H-64, and ConocoPhillips Mirror Lake N-20 and Loon Creek O-06) and outcrop localities (Mountain River, Carcajou River, Dodo Canyon, Powell Creek, and Rumbly Creek). Biogenic-sedimentary structures (i.e. ichnofossils) have been identified throughout the Canol intervals. Identified ichnofossils are grouped into a morphological classification scheme based on characteristics such as orientation, structure fill and fill organization, and burrow linings. Six morphologically separate ichnofossils have been documented. Three morphotypes are classified as vertical burrows, and include relatively small sinuous vertical traces, inclined-to-vertical unlined meniscate-backfilled traces, and fugichnia. Three morphotypes display horizontal orientations, and include tubular lined traces with organized fill, tubular unlined traces with homogenized fill, and relatively small sinuous horizontal burrows. Bioturbation intensities range from unburrowed to heavily bioturbated, with sinuous vertical traces being the most commonly documented. Integration of geochemical data collected for paleo-redox analyses, such as molybdenum enrichment to indicate euxinic deposition, will help to define a link between the ichnological textural features and basin-wide depositional conditions. The data collected from this study will result in the identification of small-scale physio-chemical fluctuations within the basin during deposition of the Canol shales. This will ultimately lead to a deeper understanding of the large-scale geochemical and sequence stratigraphic trends occurring throughout the formation.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019