Revisiting the Imperial Formation – palaeoenvironmental reconstruction and potential hydrocarbon playTuesday, November 19, 2019 - 9:40am to 10:00am Theatre Three
The Late Devonian Imperial Formation overlies the carbonates and shales of the Horn River Group, which have been the target of conventional and unconventional oil and gas exploration and development in the Northwest Territories (NWT) for approximately 100 years. The Imperial Formation, however, has to date been comparatively understudied, with the latest research on the formation conducted by the Northwest Territories Geoscience Office – now the Northwest Territories Geological Survey (NTGS) for the Peel Project from 2004 to 2007.
The Imperial Formation comprises predominantly clastic marine deposits, with up to several decametre thick shale and sandstone packages. Previous studies have divided the Imperial Formation into two parts: a lower sand-rich interval, and an upper shale-rich interval. The sand-rich interval was interpreted to represent a lower shoreface to basin-floor sedimentary succession with westward dipping clinoforms, and a terrestrial sediment source to the east or northeast; and the shale-rich interval as slope to basin-floor sediments. The terrestrial deposits related to the Imperial Formation deposition are not preserved. In previous projects, the Imperial Formation was only studied in the Peel areas of the NWT.
The Energy Group of the NTGS conducted a one-week scoping study in 2019 to examine five Imperial Formation outcrops: Carcajou River South, Imperial River, Mountain River, Powell Creek, and Gayna Gorge. Carcajou River South, the southernmost outcrop, is in the Central Mackenzie Valley area of the NWT and has not been studied previously. Here, the Imperial Formation comprises intercalated shales and tabular and weakly channelized sandstones. Current and wave ripples, decorated with cm-scale bioturbation, are common and indicate oxygenated shallow marine environments. Carbonate-rich debrites and tempestites suggest the presence of a carbonate shelf or platform that periodically contributed sediment to the clastic depositional system. At Imperial River, the sand-rich middle member of the Imperial Formation comprises an upward shallowing succession, with turbidites common in the lower part of the outcrop. Upward there is an increasing prevalence of current, wave, and interference ripples, bioturbation, and hummocky cross-stratification. Terrestrial vascular plant detritus in the form of mm to dm size coaly fragments is common. This shallowing upward trend was also observed during previous studies, and was interpreted as the result of a prograding shelf and shifting sediment flux. At Powell Creek, tabular sandstones were previously interpreted as a deep-water turbidite fan. During the 2019 study, the sandy part of the outcrop was divided into two units similar to that observed at Imperial River and in contrast to previous studies, indicating that shallow-water environments stretched further westward than previously recognized. At Mountain River and Gayna Gorge, the observed portions of the Imperial Formation comprise only deep-water turbidite facies.
The results of the 2019 field season combined with previously obtained permeability and porosity data of the sandstones in the Imperial Formation highlight the need to devise a multi-year research program to research the Imperial Formation as a potential hydrocarbon source and reservoir.