Abstract

The Gething Formation in the Kahntah River–Ring/Border region of northeastern British Columbia is a variably thick, heterolithic succession of facies deposited in continental and marginal-marine depositional settings. This unit was deposited on the southwestern flank of the Keg River Highlands in the northern Western Canada Foreland Basin (approximately 58°N, 120°W). Although Gething Formation sandstone bodies are exploration targets further south, it is not considered to be a primary exploration target in the study area due largely to its complex and laterally discontinuous nature. However, in the study interval several of the lithofacies possess good reservoir properties, and the overlaying Wilrich Shale provides a potential stratigraphic seal. Hydrocarbon sources are available in both the Wilrich Shale and the Triassic Montney Formation into which the Gething Formation incises. An understanding of the overall palaeogeography and lithofacies distribution of the Gething Formation in the study area is necessary for efficiently exploiting these hydrocarbon resources and will facilitate characterization of other Gething Formation reservoirs that may flank the Keg River Highland to the east and west.

Subsurface mapping in the area of Ring and Kahntah River gas fields shows that the Gething Formation in the study area occurs within three sinuous incised valleys that debouch southward into a large structural basin. In their northernmost (upstream) reaches, Gething Formation strata are dominated by unbioturbated, high-angle cross-bedded and current-ripple laminated upper-fine-grained sandstones, rich in organic detritus (primarily coal flakes). These are interpreted as fluvial channel and bayhead delta deposits.

Lithofacies deposited in continental settings grade southwards into bioturbated, low- and high-angle cross-bedded, lower to upper-fine-grained sandstones with thin, bioturbated siltstone and mudstone intervals. Rhythmic bedding, mud flasers and mud/sand couplets characterize these lithofacies. The trace fossils Planolites, Skolithos, Cylindrichnus, Arenicolites, Teichichnus, and fugichnia are common. These strata are interpreted to represent brackish-water bay deposits. South of this, the Gething Formation is dominated by interstratified, sporadically bioturbated sand, silt and mud, sedimentologically similar to the aforementioned brackish channel deposits, but with more diverse and robust ichnofauna (the previous assemblage as well as large Thalassinoides, rare Helminthopsis and Phycosiphon). These deposits are ascribed to tidal channels in a larger, more marine bay.