Rocks always remember: Sedimentology and ichnology of the Upper Albian Sikanni Formation in the Liard Basin, NWT, Canada

Abstract

Situated within a critical freshwater basin and a major unconventional hydrocarbon resource, the understudied Liard Basin in the Northwest Territories has become a focus for baseline geological research to support groundwater quality monitoring and resource management in Acho Dene Koe (Fort Liard). This study characterizes the facies and ichnofacies of the Upper Albian Sikanni Formation based on 333 metres of continuous outcrop along Mbehcholah (Petitot River). Six distinct facies were identified, representing a clastic medial shelf environment. Vertical facies associations illustrate various tempestite expressions, such as hummocky cross-stratification and quasi-planar lamination, within a storm wave-dominated system influenced in part by geostrophic combined flows. Sixteen ichnogenera were identified for the first time in the Sikanni Formation, representing predominantly deposit-feeding and dwelling ethologies and expressing a distal Cruziana to Zoophycos ichnofacies. Ichnological and sedimentological evidence reveals a temporal shift from relatively stressed to increasingly stable paleoenvironmental conditions in the northern Mowry Sea. Lower strata are characterized by low bioturbation intensity, abundant storm structures, low ichnodiversity, and a dominance of large and robust Zoophycos, suggesting an oxygen-restricted, high-stress setting. Toward the top of the section, ichnodiversity increases, storm structures become less common, and Zoophycos is observed alongside a broader range of trace fossils and ethologies. These changes reflect a transition to more oxygenated, low-energy, and ecologically stable conditions with reduced competition for resources over time. Additionally, well-defined simple parasequences were identified and compared to Sikanni outcrops in BC from Jowett et al. (2007), demonstrating fourth- and fifth-order Milankovitch cyclicity in the northern Liard Basin consistent with other strata of the Western Interior Seaway. The extent of deltaic influence on distal Sikanni outcrops was evaluated using both physical and biological models, with both indicating no deltaic influence in this locality. This is corroborated by the limited scale of associated fluvial channels that would have fed the Sikanni Delta in northeastern BC. Finally, sandstone units near the confluence of the Liard and Mbehcholah rivers were reassessed and are more likely part of the Sikanni Formation than the Scatter Formation based on lithostratigraphic correlation. These findings refine the depositional history of the Sikanni and Sully formations and offer new insights into their paleoenvironmental and paleoecological evolution in the northern Liard Basin.